balancing charge, discharge of battery bank, + multiple solar panels

edro · March 2014

Here I am on the Solar Beginners Corner reading Solar 101, Batteries 101, etc. and I'm still confused. I read a very interesting page referenced on this forum (http://www.smartgauge.co.uk/batt_con.html ) about balancing batteries in parallel but there's gotta be more to it. What if the batteries are not charged the same or if they are of differing amp/hr rating?

Please let me present a theoretical solar energy system and maybe someone can give me more links, even products that would help solve issues that I think need to be solved -- or tell me that I'm making it more complicated than is needed.

Let's say there are 3 solar panels -- there could be 6, 12, whatever, but there are more than 2, so let's say 3. I'll make the panels all the same. Let's say they are 100 watt each. (but one could be more in the shade than another!)

Let's say there are 3 batteries. For jollies let's make the batteries all different than the others, one is 125 ah, another 100 ah, and something else, maybe a 75 ah, or SLI instead of AGM, or an older battery that might not charge up as well, anything, but the point is they are all different.

Okay. The basic plan is to connect the solar panels in parallel into an MPPT charging the bank of 3 batteries.

I gather that I need a combiner for the panels with breakers. Is that correct? Or do I use multiple MPPT controllers?

Is there an equivalent of a combiner for batteries? Do I need to use battery isolators? I've seen an isolator for 2 batteries but how would I apply that to 3 or 4 batteries?

Sorry for so many questions. It just seems to me that batteries each need their own charging amperage based on their level of discharge and ah rating. Or am I just making this complicated. I'm hoping for a mostly maintenance-free system.

Oh - before I forget - there is an inverter in there, of course. How do I "feed" the inverter from the batteries when the batteries may be different? I understand that I connect the inverter to the batteries, not to the "load" of the mppt -- is that correct? (My understanding of the MPPT is that the "load" terminals cannot handle the draw amperage of a large inverter.)

In reality I plan to get 2 of the same battery initially. But if I need to add a 3rd, or later a 4th, then I may run into the situation where the batteries are different.

If it is at all possible I'd really love to see a diagram of this including the 3 solar panels, the 3 batteries, the MPPT or MPPT's, the battery isolators if needed, and any combiners if they fit in. Am I asking too much? If so just send me a paypal invoice -- well, let me check with my wife on that first. Give me a picture of your solar energy system setup and I'll use my feeble Visio talents to make up the diagram of what I see.

Thank you.
Ed

WillBkool · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

The short answer is don't try to mix batteries like that. The uneven charge/discharge rate will kill them pretty quick. There are people who claim to mix and match batteries, but in general, it just won't work properly. You can use 3 panels together, either in series or parallel. If in series, you wouldn't need breakers, but it would be a good idea to have a way to disconnect them. If in parallel, then you would definitely want to use breakers in case one panel shorted out. It would depend on the amperage of the MPPT controller and what the panels put out if you needed more than one. Most MPPT controllers, except the very smallest ones, can handle 3 panels either in series or parallel.

vtmaps · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

Welcome to the forum,

Do NOT mix and match batteries. If fact, once you commission a new battery bank, you shouldn't even add more of the same batteries to it (unless you do it very soon after commissioning).

Actually, you shouldn't even add new batteries to a new battery bank! Explanation: Best design practice for a battery bank that cycles frequently is single string of identical batteries in series. Short discussion here.

If you cannot achieve your storage goals with a single string of the batteries of your choice, then you need to choose bigger batteries. Another option to grow capacity is raise system voltage... a single string of batteries at 48 volts stores twice the energy of a single string of the same batteries at 24 volts.

Power systems do not scale very well. When you design a system you need some hard numbers on your loads, and then you can calculate the requirements for battery, solar panels, etc. It's sort of like buying a truck... What is the load? Then we can talk about whether you need a half ton, or a one ton truck. You can't convert one truck to the other if your loads change.

So, if your electrical loads change after you build your solar power system... Oh Truck! That's a common issue on this forum... sometimes it requires a whole new system. One thing is absolutely certain: Do not deal with system expansion by adding batteries to an established system.

--vtMaps

edro · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

Do NOT mix and match batteries.

LOUD AND CLEAR! Thank you for that. That does make a lot of sense to me. I better have my calculations right before building as you clearly suggest--the calculations being a topic for another thread. (I'm probably not real knowledgeable on forum etiquette but I think if I change the content discussion of a topic, that's called hijacking, isn't it? Or did I just do that by asking that question on this thread! Oh, my!)

How about adding solar panels? I read how solar panels do not have the issue of needing matched resistance wiring paths--but do they need to be the same wattage?

Power systems do not scale very well. It's sort of like buying a truck...

Ya know -- I hadn't thought of that. The truck example is good; it makes this point clear although one probably could improve, within some limits, the load capacity of a truck... but it is still a very good example that helped me to understand this.

If I discovered that I need more capacity there's really nothing I can do. Got it. Calculations better be correct. Got it.

I read the article about how that wire lengths should be balanced between parallel paths/connections. I hadn't thought of that either. Got it.

The thread, ("Series rule of thumb"), was compelling however I based my 12 volt parallel battery bank plans partly because I already had a good 2,000 watt inverter that uses 12 volts.

Now...
Somewhere on the internet (I'm not one to believe everything they read) I saw a diagram where someone was using multiple MPPT's to charge their batteries. I can't seem to find that diagram again. I was wondering, though, if using multiple MPPT's and multiple battery isolators could somehow prevent unbalanced charging. This idea is really above my understanding... I just thought I'd throw that out there and see if anyone has done anything like that.

Thank you vtmaps, WillBkool, for your comments. I got it. It's difficult to find a partner to help me build this system. My wife is very supportive but she isn't interested in hearing or discussing the technical details. Without a forum like this I'd be pretty isolated.

Ed

vtmaps · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

edro wrote: »

Somewhere on the internet (I'm not one to believe everything they read) I saw a diagram where someone was using multiple MPPT's to charge their batteries. I can't seem to find that diagram again.

It is quite common to have multiple charge controllers connected to one battery bank.

This happens to folks who paint themselves into a 12 volt corner, and then want to expand. for example, consider an MPPT controller that can handle 1000 watts of panels on a 12 volt system. That same controller can handle 2000 watts if it is used with a 24 volt system. If you stick with 12 volts you would need 2 controllers to expand beyond 1000 watts.

Multiple controllers are also used by folks that have a mixture of different panels. Some mismatched panels cannot be run on one controller, you may need one controller for each type of mismatched panel.

Multiple controllers are also used by folks that have partially shaded arrays or arrays with different orientations, each array having its own controller.

Although one battery bank may be charged by many controllers, one solar array may NOT be connected to more than one controller.

edro wrote: »

I was wondering, though, if using multiple MPPT's and multiple battery isolators could somehow prevent unbalanced charging.

Sure. Each controller is connected to one array and one battery bank. Basically you would have multiple 12 volt systems. You would need to have another inverter for each system. You might as well do it right and build a 24 or 48 volt system.... AFTER you figure your loads and design the system on paper.

--vtMaps

edro · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

You might as well do it right and build a 24 or 48 volt system....

Ouch.

Probably 20 or 25 years ago I purchased a Tripp Lite Powerverter APS2012 (2,000 watt), current price about $600. I once used it to run sump pumps to prevent basement flooding which seemed to happen simultaneously as the power went out. I fixed the basement flooding problem with better grading but kept the inverter. Being on a fixed income and one who hates to waste anything I feel compelled to use the inverter. (cry me a river) But doing things right is also important to me.

My system is targeted to two functions: running a 110 volt 8 amp well pump enough to provide drinking/bathing water for the family, and operating a few AA/AAA battery chargers so that we can have basic lighting (flashlights, lanterns) as needed. We can heat & cook with either propane or wood (kero for heat as a backup). I'm probably naive about this but I can't think of anything else I really need electricity for. We've lost power on several occasions and sometimes for many days. It's not a big deal at least for the experiences that I've had so far.

AFTER you figure your loads and design the system on paper.

Using the battery bank calculator I estimate that I'll need (3) of either the 100 or 125 ah batteries. I've had more difficulty calculating how many solar panels. I originally calculated that I need (1.6) 100 watt panels, (rounded up to 2 panels, of course) but when I went to calculate it again I came up with 2.something 100 watt panels. The first time I did the calculations I didn't take inefficiencies into consideration.

I'm pretty sure that getting (qty 3) 100 watt panels and (3) 100 ah AGM batteries I can support my well pump and a couple of small AA/AAA chargers. (and a charger for my ham radio) But I do plan to verify my calculations before I start.

Again, you've helped me a lot. I really want to keep this system simple. already having the inverter and wanting it simple, I still feel like a 12 volt system would be best for me even if not a 24 or 48 volt system. I don't mind the heavier gauge wiring necessary. I didn't even know they made 48 volt inverters until today! I see 'em now! But that would add another $600 to my system...I can't tell if that would be worth it or not. That would be another calculation. But maybe you're right. As it is, I'll be taking money out of my IRA (not that big in the first place) in order to build this system, panels, batteries, MPPT, combiner... Okay, cry me a river (again). Now I've gone from rambling to complaining.

Your comments & thoughts are appreciated. Thank you.

Ed

vtmaps · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

edro wrote: »

We can heat & cook with either propane or wood (kero for heat as a backup).

Are you sure you can cook with propane when there is no AC power? Most (not all) propane ovens use a glowbar which is a substantial AC load.

edro wrote: »

My system is targeted to two functions: running a 110 volt 8 amp well pump enough to provide drinking/bathing water for the family, and operating a few AA/AAA battery chargers so that we can have basic lighting (flashlights, lanterns) as needed.

It might be more cost effective to run a generator for the pump and to recharge your flashlights.

btw, you didn't mention refrigeration as something you want to keep running during a grid outage.

--vtMaps

BB. · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

Can you give us an idea of how much power you need (Watts, and Watt*Hours or kWH per day)? We then can run through the math pretty quickly to size a system.

Also, Amp*Hours is not enough... I can guess you are talking about 12 volt battery system--But sometimes folks confuse Amps*Hours on their 120 Volt AC side of the system and don't realize that the Amp*Hour of a 12 volt battery bank is 10x as large.

For example... Run a 100 watt light 120 VAC bulb for 8 hours a day:

100 watts * 8 hours = 800 WH per day
800 WH * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days of storage * 1/0.50 max discharge = 314 AH @ 12 volt battery bank

Just to give you some feeling for the size of an off grid power system:

1,000 WH per day (1 kWH per day/30 kWH per month) = LED/CFL lighting, radio, laptop computer, small water pump, cell phone charger
3,300 WH per day (3.3 kWH per day/100 kWH/month) = Above + Refrigerator, well pump, clothes washing machine, TV--Near normal electrical life for very efficient home and minimum of standard electric loads
10 kWH per day (300 kWH/month)= Above + gas/propane central heat, more appliances, "efficient" modern home
33 kWH per day (1,000 kWH/month)= Average North American home without any conservation measures
100 kWH per day (3,000 kWH/month)= Full A/C and electric heating, hot water, in Hot/extreme temperature climate

The first two systems are good candidates for an "off grid" lifestyle. With something like a $10,000 to $30,000 or so out of pocket installation cost (very rough numbers).

The third system can be done, but takes a fair amount of money for an off grid system and is expensive to maintain. If you have utility power, look at Grid Tied (solar panels+GT inverter) plus a backup AC generator--Usually makes much more economic sense unless you simply do not have reliable utility power available (miles away from nearest utility pole).

In general, when you take a 20 year service life and all the installation+maintenance costs (new batteries every 5-10 years, new AC inverter+Charge controllers every 10+ years, etc.), the cost of off grid power is around $1-$2+ per kWH--Or about 10x the cost of utility power.

That is why conservation is so important... When living off grid--You cannot afford to waste any power at all.

-Bill

WillBkool · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

One thing that's big on this forum,as you can tell from above, is to measure your loads with either a kill a watt meter or a current clamp style meter on things that are hard wired. Then from that, you can calculate what size battery bank that you will need, and from there calculate the amount of solar panel wattage that you will need to keep the batteries charged. It's usually cheaper to buy a generator and gas than to buy solar as was said above. Of course, I was able to obtain some free batteries, so I took the off-grid plunge too.

edro · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

I'm working on it. I'll post again probably next week when I have some solid data.

Ed

edro · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

Purpose: Provide 200 gallons of water per day using a shallow well pump:
Based on depth of water (55 feet) and horsepower of motor (.5) estimate 10-12 GPM probable.
If used continuously 200 gallons could be obtained in less than 20 minutes.
Pump motor uses maximum 9.5 amps.
9.5 amps for 20 minutes would be 1.9ah (let's round that to 2ah)
Does that mean that I only need a single 2ah battery???

There are other things that I need but they are small, I think, in comparison to the pump motor:
(1 of these) PowerEx MH-C9000 AA/AAA charger analyzer 12V 2.0A
(1 of these) Maha MH-C204FA Intelligent AA/AAA Rapid Charger 12VDC 500mA
(3 of these) ham radio chargers: AC 100V 0.5A
I will need to charge four other 12V AGM batteries (smaller, 35ah each) for use elsewhere (to power communications).
Two are operational using about 12ah per day and 2 are redundant so I'll only be topping off the second pair.
(1 of these) NOCO Genius G3500 6V/12V 3.5 Amp Smart Battery Charger and Maintainer 110-120 VAC, 1200mA RMS Max, 85% Approx. efficiency, 60W Max

Notes:
I had planned on getting 2 or 3 group 31 AGM deep cycle 100ah batteries for this solar energy project. After my novice calculations above that sounds like way too much for my needs.

I was also planning on getting 3 solar panels, 100 watts each and a 30 amp MPPT.

The inverter I already have: Tripp Lite APS2012 PowerVerter® APS 2000W Inverter, specifications:
"2000 watts continuous, 3000 watts OverPower™ and 4000 watts DoubleBoost™ inverter output. Rated over 90% efficient."
"Supplies up to 2000 watts of continuous 120V AC power from any 12V battery or automotive DC source. OverPower TM inverter output feature temporarily provides up to 150% of the continuous output for 1-60 minutes, and DoubleBoost TM inverter output feature delivers up to 200% of the continuous output for up to 10 seconds..."

Your thoughts are greatly appreciated. I have no one else to discuss all this with me and I don't like making decisions in the dark.
Thank you,
Ed

Pump & motor specifications:

Motor: Goulds M05421 Series 1/2 Hp Motor 115V, 1 Phase, 60 Hz
Brand Goulds Pumps
Model Number M05421
Type 2 Wire Submersible Pump Motor
HP 0.5
Phase 1
Volts 115
Wire Qty. 2 Wire
Amps 7.4
Full Load Watts 845
Thrust Rating 700
Service Factor 1.6
Locked Rotor Amps 36.4
Winding Resistance 1.3-1.8
Full Load Efficiency % 49
Service Factor Efficiency % 61
Full Load Power Factor % 99
Service Factor Power Factor % 99
KVA Code K
Length (in) 11
Service Factor Watts 1088
Amps 9.5
Red Jacket Number 50C201

Wet end
Brand Goulds
Model 10GS05
Flow Range GPM 3 – 16
Horse-power Range ½ – 5
Best Efficiency GPM 10

vtmaps · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

edro wrote: »

Purpose:
9.5 amps for 20 minutes would be 1.9ah (let's round that to 2ah)
Does that mean that I only need a single 2ah battery???

You are confusing AC amps with DC amps. Use watts and watthours to go back and forth.

Thus 9.5 amps at 120 volts is 1140 watts. Over 20 minutes, that 1140 watt draw will consume 1/3 hour X 1140 watts = 380 watthours.

If your battery is 12 volts, the current it will have to supply is 1140 watts ÷ 12 volts = 95 amps. Over 20 minutes that would be 31.67 amphours (from a 12 volt battery).

If you follow that, then the next step is to realize that the inverter is not 100% efficient, so you draw MORE than 1140 watts (more than 95 amps) from your battery.

The next step is to learn about Peukert's law. This means that the capacity of a battery goes down as the load goes up. For example, suppose you have 2 golf cart batteries in series to make 12 volts. They have 220 amphour capacity. That capacity is based on drawing 132 watts (11 amps DC) from the battery. If you try to draw over 1140 (probably 1300) watts from the battery, it will have a severely reduced capacity.

edro wrote: »

Pump motor uses maximum 9.5 amps.

The pump may draw 9.5 amps AC once it is up to speed, but its maximum current is 36.4 amps. That's what Locked Rotor Amps are for that pump. What this means is that your inverter must have a much higher rating than the 1140 watts you expect to draw from it.

--vtMaps

edro · March 2014

Re: watts and watthours, Locked Rotor Amps

Use watts and watthours to go back and forth.

Yes, of course. That makes sense. All the calculations you gave make sense and they help a lot.

Locked Rotor Amps

I didn't even see that in the motor specs and never heard of "Locked Rotor Amps" before.

Would a starting capacitor resolve this? If so, do you have any sizing recommendations? (and where to obtain one?)

Thank you.

And sorry about the shout out font. I just picked a size of font randomly and went with it.

Ed

edro · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

Okay.
So I got that the Goulds motor has a Locked Rotor Amps specification of 36.4 amps for a 120v motor. That's 4368 watts.

My inverter says this:
"2000 watts continuous, 3000 watts OverPower and 4000 watts DoubleBoost inverter output"

The 4000 watt output is for up to 10 seconds. But that still exceeds the 4368 watts of the LRA for the motor.

Am I hosed here? I already have both the inverter and the pump motor.

Ed

edro · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

Hey vtMaps... I made a mistake. I thought that I understood the calculations but I'm having trouble with this:

The next step is to learn about Peukert's law. This means that the capacity of a battery goes down as the load goes up. For example, suppose you have 2 golf cart batteries in series to make 12 volts. They have 220 amphour capacity. That capacity is based on drawing 132 watts (11 amps DC) from the battery. If you try to draw over 1140 (probably 1300) watts from the battery, it will have a severely reduced capacity.

I found a Peukert Number Battery Life Calculator online. Here are the results for a typical group 31 AGM 100ah battery:

Attachment not found.

I'm at a loss to understand how this applies to the 12 volt draw (amps) necessary to power the inverter (90% efficient) to make the 4000 watts of 120v power for the seconds needed to start up the motor.

The last part of the quote, (can I quote it again?) baffles me:

They have 220 amphour capacity. That capacity is based on drawing 132 watts (11 amps DC) from the battery. If you try to draw over 1140 (probably 1300) watts from the battery, it will have a severely reduced capacity.

Why is that capacity based on drawing 132 watts from the battery?

The "bottom line" question that I'd like to know (and know how it was calculated) is how many group 31 batteries would I need to power the well pump motor for 20 minutes given all the specs that I've been able to find so far?

Note that the inverter has a 20amp breaker built in on the 120 volt AC side. I'm willing to try to start the pump to see if the 4000 watt AC "DoubleBoost" output can start the pump.

I don't like cutting things this close. If I absolutely have to buy a bigger inverter then I will--eventually. I'm also going to see if I can get a smaller well pump if it can still meet my needs. But I'll also research if there's any way to deal with the Locked Rotor Amps start up draw on the inverter.

Thank you.

Ed

vtmaps · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

edro wrote: »

Hey vtMaps... I made a mistake. I thought that I understood the calculations but I'm having trouble with this:
<snip>
Why is that capacity based on drawing 132 watts from the battery?

If you have a 12 volt battery rated at 220 ah, that rating (unless specified otherwise) is based on drawing the battery down over 20 hours. So a 220 ah battery can provide 11 amps for 20 hours (11 amps x 20 hours =220ah). If you are drawing 11 amps from a 12 volt battery, you are drawing 132 watts (11 amps X 12 volts = 132 watts). If you try to draw 1300 watts from that battery, I doubt that it will last 20 minutes.

edro wrote: »

My inverter says this:
"2000 watts continuous, 3000 watts OverPower and 4000 watts DoubleBoost inverter output"

The 4000 watt output is for up to 10 seconds. But that still exceeds the 4368 watts of the LRA for the motor.

Am I hosed here? I already have both the inverter and the pump motor.

No, you are not necessarily hosed. Try the inverter and see what happens. There is often enough resistance in the line to the pump to limit the current and get a somewhat "softer" start. If you do try it and it doesn't work, don't blame the inverter... it may be the battery and cables that limit the inverter's capacity. That is often a problem at 12 volts. Your battery and cables need to handle 400 amps if that inverter is going to put out 4000 watts. I'm not saying it won't work, but you need to give it a fair trial... no jumper cables... you need big short cables and a big battery for your test.

--vtMaps

BB. · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

There are also well pumps that have internal VFDs (variable frequency drives) that have virtually no surge current--Very nice for off grid power systems (Grundfos Flex series is one--Not cheap).

And there is a choice between "two wire" and "three wire" pumps (external motor start capacitor at well head). The three wire motors have lower starting surge current vs 2 wire motors.

And you can get a three phase motor and pair it with a VFD directly. Another solution that can be cheaper and give you low surge current (and reduce pump RPM to your needed flow rates instead of running pump "flat out" all the time).

Lastly, as vtMaps and others here have mentioned, sometimes you can run a large surge well pump motor on "smaller gauge" wiring to reduce the maximum surge. Sometimes, this is enough to keep the inverter from tripping/resetting other AC appliances sharing the inverter/etc. when the pump starts.

Some of this stuff is a choice between the school of hard knocks (you buy and test on your own), learning from others who have a working combination, and/or designing a conservative system (a bit more costly) and it "just runs" (usually).

-Bill

edro · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

I got a reply from the well pump motor guy that I've dealt with before here in the states. He told me about a submersible pump with a controller, load reactor, pump--all together costing over $1,000. (The total amount was actually over $1,600.) I found a 36 volt inverter that will operate the pump that I already have for less than $1,000 and it would power a whole lot more than just the well pump motor.

One thing I'm learning on this forum (one of many things I'm still learning about here) is about voltage... specifically how inverters that operate on 12 volts are not as good as ones operating on 24 volts, 36 volts even better, and 48 volts still better. That seems to go for your solar panel hookup. Running them all in parallel giving 12-20 volts isn't as good as running them in series (or series+parallel) to yield higher voltages. I'm not sure that I understand why that is...I'm sure that I don't know why that is... But it is clear that I've been myopic and stuck on everything being on 12 volts. It just seemed simpler to me. If my understand of this is flawed then please set me straight.

So now I'm rethinking everything. And I feel stuck. I already have the inverter (12 volt) and two 100 watt solar panels which came with a 12 volt MPPT. I hate to waste anything. But I guess I need to back up and rethink how I'm going to run this pump.

I still plan to at least try the inverter that I have with the pump motor that I have but I don't like that the inverter maximum intermittent output is the same as the pump motor LRA requirement. It's too close for me even if it ends up working. Water is life or death--this has to work reliably.

But I don't even have the batteries yet so I can't test this. I have a pair of old 70ah AGM electric wheelchair batteries, (I'm disabled and when they replaced my wheelchair batteries recently I ask to keep the old ones). But I don't think the two will be enough for the inverter to yield the 4000 watts (AC, 115 volt) necessary to run the pump motor.

One of the things that I was hoping to find out here is how many 100ah batteries I would need to purchase in order to operate my submersible well pump motor for 20 minutes a day, and then how many solar panels would I need to charge up the batteries for the next day. My requirements seem simple enough to me but working out the plan to make it happen is proving to be a real challenge to me so far. But I'm not giving up.

Any replies to this would be very much appreciated. I need help and, to be frank, I have no one here that can help me.

Ed

BB. · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

edro wrote: »

One thing I'm learning on this forum (one of many things I'm still learning about here) is about voltage... specifically how inverters that operate on 12 volts are not as good as ones operating on 24 volts, 36 volts even better, and 48 volts still better. That seems to go for your solar panel hookup. Running them all in parallel giving 12-20 volts isn't as good as running them in series (or series+parallel) to yield higher voltages. I'm not sure that I understand why that is...I'm sure that I don't know why that is... But it is clear that I've been myopic and stuck on everything being on 12 volts. It just seemed simpler to me. If my understand of this is flawed then please set me straight.

It is just the higher the power you want to support (and/or the farther you want to send the power), the higher voltage you (generally) need to use.

Roughly, it works out that around 1,200 watts or so is about the maximum 12 volt DC input inverter you would want to power (some folks have done OK on 12 volt battery bank up to a 2,000 watt, good quality, AC inverter).

For example, just looking at the maximum current such an inverter will draw at 12 volts:

1,200 Watts * 1/0.85 inverter eff * 1/10.5 volts inverter cutoff = 134.5 Amps @ 12 VDC draw

And many inverters can supply upwards of 2x their rating for starting surges (2x 134.5 amps). You need very heavy/short cabling to support that large amount of current, as well as a relatively large battery (or battery bank).

Go to 24 volts, then 2x larger (maximum) AC inverter. Go to 48 volts, another 2x larger AC inverter...

Note that 32 and 36 volt devices/DC power systems used to be more popular--But has pretty much faded away from mainstream solar/off grid battery power systems. To support a 36 volt battery bank, your selection of solar charge converters and AC inverters is more limited (36 volt AC inverters are getting quite rare), and many charge controllers need to be configured to operate on a 36 volt battery bank (sometimes a computer interface option). I would suggest you avoid building out a 36 volt system unless you have a supply of replacement parts (like a 36 volt AC inverter). You may end up designing yourself into a box.

Note that if you have two 12 volt batteries... And put them in parallel for 12 volts or in series for 24 volts, it does not change the amount of power or energy they are capable of... It just changes the diameter of the copper wire you need to support that power (power = Voltage * Current, 2x the voltage, then 1/2 the current).

Similar for solar panels--Series or parallel connections is really only based on the voltage needs of your system. Put two "12 volt" (really Vmp~17.5 volts or so) in parallel to charge a 12 volt bank. Or put them in series to charge a 24 volt battery bank.

So now I'm rethinking everything. And I feel stuck. I already have the inverter (12 volt) and two 100 watt solar panels which came with a 12 volt MPPT. I hate to waste anything. But I guess I need to back up and rethink how I'm going to run this pump.

It is very difficult to do full solar off grid power "cheaply" and reliably. If you need to to that--Then you need to not fall in love with any of your hardware/solutions. You need to do paper designs/configurations to see what will work best for you.

If you had to do an off grid system "cheaply" with an existing (relatively) large well pump... A gasoline genset and a large cistern may be a better solution. Use the genset to run the well pump once or a few times a week, then use a small DC (or AC) water pump to pressurize your home plumbing from the tank. You can get away with a pretty small battery bank and solar array if you avoid the whole well pump issue.

Otherwise, you are back to looking for a well pump designed for off grid use... There are some very nice ones that will only draw 300-600+ watts maximum (surge included). And are much more "off grid" (but not wallet) friendly. You do have to make some tradeoffs where you will put your money (more money in pump, less in solar; save money on pump, use genset+fuel+cistern and a small solar system for surface pumping/lights/etc.).

I still plan to at least try the inverter that I have with the pump motor that I have but I don't like that the inverter maximum intermittent output is the same as the pump motor LRA requirement. It's too close for me even if it ends up working. Water is life or death--this has to work reliably.

This is going to be a tough thing to test unless you are already setup for this at your home. You virtually need to build out your Battery Bank and AC inverter system, plus wire/plumb up the pump. If it does not work, what then? There are some things that can be done to help (smaller gauge wire limits starting surges to a degree, changing starting capacitor, or a VFD variable frequency drive for the well pump motor--if proper pump motor type/wiring etc.).

Is there anybody near you that has the experience that can help (or a well contractor/electrician that has some successful installs)?

But I don't even have the batteries yet so I can't test this. I have a pair of old 70ah AGM electric wheelchair batteries, (I'm disabled and when they replaced my wheelchair batteries recently I ask to keep the old ones). But I don't think the two will be enough for the inverter to yield the 4000 watts (AC, 115 volt) necessary to run the pump motor.

Probably not--The batteries are probably near the end of their life anyway--And if they have not been kept on charge since they have been replaced, they probably are dead now.

One of the things that I was hoping to find out here is how many 100ah batteries I would need to purchase in order to operate my submersible well pump motor for 20 minutes a day, and then how many solar panels would I need to charge up the batteries for the next day. My requirements seem simple enough to me but working out the plan to make it happen is proving to be a real challenge to me so far. But I'm not giving up.

If you can get a 2kW AC inverter 24 VDC input to run your pump, then you would need about a 400 AH @ 24 volt battery bank to support that load.

Not that I would suggest you use 100 AH 12 volt batteries, but it would take 8 of them to make such a bank (2x 12 volt batteries in series, 4 parallel strings).

Your better bet would be to use 6 volt ~220 AH "golf cart" batteries (cheap, fairly rugged). Of those, it would be 4x 6 volt batteries in series, 2 parallel stings for 8 total golf cart batteries. This would be the minimum battery configuration I would suggest as having a possibility to support your needs.

Not knowing your total overall power needs.... One way to size the solar array is simply based on the size of the battery bank (a larger battery bank needs a larger solar array). A 24 volt @ 440 AH "golf cart" battery bank would need 5% to 13% rate of charge (if you use the system lightly, you may get away with 5% rate of charge--However, if you can swing it, you would probably be much happier with a 10+% rate of charge):

440 AH * 29 volts charging * 1/0.77 controller+panel derating * 0.05 rate of charge = 829 Watt array minimum
440 AH * 29 volts charging * 1/0.77 controller+panel derating * 0.10 rate of charge = 1,657 Watt array nominal
440 AH * 29 volts charging * 1/0.77 controller+panel derating * 0.13 rate of charge = 2,154 Watt array "cost effective" maximum

Guessing that you are somewhere in the Baltimore Md. area, using PV Watts with a fixed array facing south, tilted to latitude, the amount of sun you get is around:

Month    Solar Radiation (kWh/m 2/day)
1      3.47     
2      4.40     
3      4.79     
4      5.12     
5      5.28     
6      5.70     
7      5.61     
8      5.28     
9      4.95     
10      4.90     
11      3.58     
12      2.85     
Year      4.66

Looks like not a lot of sun there (lots of marine layer/humidity/clouds?). If I drop the bottom three months, that gives us 4.40 hours of sun for February. A "nominal" array of 1,657 Watts would produce (your break even month--may need generator or not depending on weather that your):

1,657 Watt array * 0.52 system efficiency * 4.40 hours of sun = 3,791 Watt*Hours of 120 VAC power per day

For a minimum of ~9 months a year... Deep in winter, you will get less power from solar.

Any replies to this would be very much appreciated. I need help and, to be frank, I have no one here that can help me.

Sorry there is nobody near you that can help. If tell us (roughly) where you are at--perhaps somebody here can give you a suggestion for a local supplier/well pump person/etc. that can help some.

Just be aware--There is no "cheap" offgrid solar power. It is all expensive. And after you install it, you still need to replace the batteries every ~5-8 years, and replace the solar charge controller+AC inverter every ~10+ years.

If you cannot afford to do that--Then you need to rethink your plans.

There are some really nice "slow" well pumps that will run directly from a "smallish" solar array. The pumps are not cheap, but you bypass the entire need for a battery bank (except for bad weather water pumping--if your storage is not large enough).

But it is a balancing act. There are no short cuts and no magic solutions that will make this a cheap installation. Do your planning and go in with your eyes wide open.

We will do our best we can here to help you with understanding your needs and designing a system (or several options)... But don't buy anything more until you do your designs.

-Bill

mike95490 · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

give up the thought of running a 4000w pump off 12v

Lets step back, and look at your water source, depth/lift, pressure/head needed, and gallons needed. Storage volume needed?

There are some DC power solar pumps that can do this

Another option, is an inexpensive gasoline or propane generator, for the time you need to run the pump, and leave the
12V for the lights and toy chargers. You should have a functioning generator anyway, for emergency battery charging in bad weather so you don't flatten your batteries to death.

vtmaps · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

BB. wrote: »

Otherwise, you are back to looking for a well pump designed for off grid use... There are some very nice ones that will only draw 300-600+ watts maximum (surge included). And are much more "off grid" (but not wallet) friendly. You do have to make some tradeoffs where you will put your money

edro, Bill is right on the money.... do some research on pumps and see what it would cost to buy/install a pump designed for off-grid or solar power. It may be less expensive to keep your 12 volt system and spend money on the pump.

For many off-grid folks the water pump is a defining factor in the design of a power system. If you've got a large off grid system, it's usually cheaper to go with a conventional pump (such as yours). Those pumps are widely available and cheaper than the solar friendly pumps. If the conventional pump is the only large draw, then you end up supersizing your entire system for the pump.... that may, or may not be, cost effective. Do a paper design to find out.

How far is your well from your house? How deep is your well?

--vtMaps

edro · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

Wow. Thank you all (Bill, Mike, vtMaps) so much for all the information. I'll try to compile my questions to each of you in this one post.

Questions about Bill's post:

1,200 Watts * 1/0.85 inverter eff * 1/10.5 volts inverter cutoff = 134.5 Amps @ 12 VDC draw

Sorry for being such a noobie.. I guess that the 134.5 Amps @ 12 VDC draw probably indicates several things. First of all my wiring better be able to handle that load, and the batteries, too, need to handle that draw. But I'm sure it also indicates how many batteries of what ah I need to run the pump for 20 minutes a day. Does "134.5 Amps @ 12 VDC" convert in some way to reserve capacity or amp-hours? (There's another note on this below. Maybe this has already been answered there.)

Go to 24 volts, then 2x larger (maximum) AC inverter. Go to 48 volts, another 2x larger AC inverter... ... Similar for solar panels--

Okay. Got that. 24 volts it is. I discovered that the MPPT that I have will do either 12 or 24 volt so maybe I can still use that.

Why wouldn't everyone just use 48 volt if that is the best for wiring and inverter capacity? Or am I oversimplifying again?

It is very difficult to do full solar off grid power "cheaply" and reliably.

I'm not interested in "full" solar if that means powering everything in my home. This is primarily for running a submersible well pump.

But it will have to be completely off grip and it needs to be reliable. As for cheaply, well, I want to do it economically. I don't want to waste anything and I don't need to buy a Cadillac system. No frills for us.

This is going to be a tough thing to test unless you are already setup for this at your home.

Agreed.
As for the battery bank: As soon as I know how many of which kind of battery to get I'll get them. I already have money set aside for this project but it is limited. I want to spend it well.

But just for a test I do have two group 31 wheelchair batteries which are in good condition. They have been in light duty use for a couple of years and have been kept charged even after they were taken out of service. They test out well...I have a good "smart" charger (CTEK Multi US 7002) and I happen to have a SOLAR BA7 battery tester, too.

I will just use the wheelchair batteries for a test of just starting the motor (testing to see in my inverter can deal with the Locked Rotor Amps of the motor). For the test I won't care if it runs for only minutes so long as it will start up.

As for wiring up the pump, I have no trouble with electrical wiring.

As for setting the pump up in a well... I'm planning all this away from the remote site where it will be set up. I suppose that I could rip my own submersible pump out of my own well (it's a 220v) and put the 110v pump for my remote solar application but I'd really rather not do that. I'm disabled and that would require the disruption of our household service and more help than I can muster. What I was thinking was to find a 1/2HP sump pump with similar electrical specs and try it out on that.

Is there anybody near you (well contractor/electrician...

No. No one that I can afford to pay.

If you can get a 2kW AC inverter 24 VDC input to run your pump, then you would need about a 400 AH @ 24 volt battery bank to support that load.

This is the specific information that I was originally looking for. (before I learned that I have a lot more to learn)

I see how 400 AH @ 24 volt would be a total of eight 100ah batteries. You said that is what is needed to support that load. Load is amperage, yes? But not ah. Yes?
What percentage would they be discharged if used for 20 minutes per day?

...6 volt ~220 AH "golf cart" batteries...

Back to my confusion again. Sorry.
"400 AH @ 24 volt" using 12 volt batteries would be a total of eight 100ah batteries would cost me over $1,500 if I wanted to use AGM technology.
"6 volt ~220 AH "golf cart" batteries...8 total" would cost me just over $700. That's a big price difference between the two options.

I'm guessing that golf cart batteries-which I know nothing about at the moment-won't last me as long as good AGM batteries. I won't be able to get out to the site to change out the batteries easily. So using good, long lasting AGM batteries (3,000 discharges to 80%) really appeals to me even if that spec isn't real-world.

440 AH * 29 volts charging * 1/0.77 controller+panel derating * 0.05 rate of charge = 829 Watt array minimum
440 AH * 29 volts charging * 1/0.77 controller+panel derating * 0.10 rate of charge = 1,657 Watt array nominal
440 AH * 29 volts charging * 1/0.77 controller+panel derating * 0.13 rate of charge = 2,154 Watt array "cost effective" maximum
....

1,657 Watt array * 0.52 system efficiency * 4.40 hours of sun = 3,791 Watt*Hours of 120 VAC power per day

First of all I had not heard the word "derating" before. I looked it up. Second..whew! Sorry to whine and sorry to be such a noob but I don't understand any of this part.

My goal is that I want to be able to pump about 200 gallons of water per day using a shallow well pump, solar panels & batteries. No gasoline because of the limited storage life of gasoline. I won't be able to bring anything to the site for great lengths of time. I estimate that I only need to run the 110 volt, 7-9amp, 1/2HP motor about 20 minutes per day to pump that much water. It has to be mostly autonomous.

After gaining a LOT of education on this website (oops--I guess putting the word "LOT" in all caps is shouting? idk-help?) -- I've learned that I probably need to run this on at least 24 volts instead of 12, that my existing 12 volt inverter is either not enough or barely enough to operate the pump motor, and that I need eight batteries just to handle the current draw (load) for the wattage the pump will need.

(before I forget, the 24 inverters that I've seen provide 220 volts. The pump that we already have is 110 volt. So I still need to figure that out. Maybe I just need to get a different (220v) pump or I need something to convert the 220 to 110 volts - a transformer? How big would that have to be?)

Back to the solar array calculations you sent. Sorry to be so dense headed but running my 110 volt, 7-9amp, 1/2HP motor about 20 minutes per day on eight 100ah batteries -- how many solar panels would I need?? Let's assume I get that 24 volt inverter and get a 220v pump motor. I'm guessing that I'm yet again trying to oversimplify this. I'll need this to work every day throughout every year. Although we do have plans to convert a generator that we have to run on propane--it will only be used only as a last-resort emergency piece of equipment. We can't afford to bring propane supplies out there on a regular basis.

We do have a 600+ gallon cistern and plan to make a second one but not anytime soon. That will take manpower that I can't muster. The 200 gallons per day is an estimate. More or less... Probably less. But we don't want to run out of clean water.

Questions on Mike's post:

give up the thought of running a 4000w pump off 12v

Thanks Mike. Got it! Although I'm still going to try it out since I already have the inverter, a couple of good batteries, and I'm sure I can find a similar pump/motor, I understand now that my existing inverter is not going to make us a reliable system. I've had that inverter for maybe 10 years although it hasn't been in use at all. I don't like to waste anything. Maybe I can sell it.

look at your water source, depth/lift, pressure/head needed, and gallons needed. Storage volume needed?

Source: 55 foot shallow well. Water is usually about 20-30 feet down the well. I have a 20/40 pressure switch but I don't care about high pressure. Just need to fill an above ground 600 gallon cistern. Will only need to put in about 200 gallons per day.

DC power solar pumps

Do you have an example? A link? I don't know what you mean.

Right now we can store 600 gallons of water; we will need 200 gallons per day from it, So:

So if there's no sun for 3 days then we are in trouble, I think, with a system that works on solar alone.

Using batteries can carry us through on the "thin" days without sun. That's what I'm hoping that a solar/battery bank design will do for us. We have a very nice manual hand pump nzpump.com and, if we have battery juice for it, a small 12volt DC pump (like on an RV). But the main thing we need is to get 200 gallons per day from the submersible well pump into the cistern.

Notes to vtMaps:

For many off-grid folks the water pump is a defining factor in the design of a power system.

Yeah. I definitely get that now. You all have been a great help to me!

conventional pump... Those pumps are widely available and cheaper than the solar friendly pumps.

I definitely want to use a conventional pump exactly because they are widely available. If/when we need to replace it--it will be much easier.

supersizing your entire system for the pump...

That's okay with me. Actually I did expect that. I just grossly miscalculated how much I didn't know about power. --an aside--I'm studying for my Technician's Class FCC exam and I'm realizing how bad my memory has become over the years. It /looks/ easy but I can't seem to keep things in my memory long enough.

How far is your well from your house? How deep is your well?

Well is about 50 feet +/- from the house and 50 feet deep.

Thank you all so very much. I look forward to your replies even if they tax my mental capability to understand this. I think that there are still lots of gaps in my understanding (the more you know, the more you realize you don't know) but I think the most confusing for me right now is the solar panel calculation since that involve my location, Solar Radiation (kWh/m 2/day), and probably a whole lot of other factors--I'm afraid to even try thinking about it right now.

Ed

vtmaps · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

edro wrote: »

Why wouldn't everyone just use 48 volt if that is the best for wiring and inverter capacity? Or am I oversimplifying again?

The fewer battery cells you have the better... fewer points of failure and easier maintenance. From that perspective a 2 volt system would be best, but 2 volts is not practical. Therefore the best design will have a single string of cells at the lowest voltage that is practical. What is practical? Depends on your draw... about 1000 watts for a 12 volt system, 2000 watts for a 24 volt system, 4000 watts for a 48 volt system.

example: Suppose your maximum draw is 1000 watts, and you determine that you need about 10,000 watthours of battery storage, and you want to use 6 volt golf cart batteries (which store about 1300 watthours of energy). You would need 8 of them. You could put the eight batteries in a single series string (48 volt system), or have 2 strings of 4 batteries per string (24 volt system), or have 4 strings of 2 batteries per string (12 volt system). A single string (48 volts) is the best design, even though you don't need a 48 volt system to handle the 1000 watt draw.

BUT, if you use 6 volt L-16 batteries (2400 watthours per battery), you could have a single string of 4 batteries (24 volts). This would be better than using the golf cart batteries because you have fewer cells. Fewer, but bigger, cells.

edro wrote: »

I will just use the wheelchair batteries for a test of just starting the motor (testing to see in my inverter can deal with the Locked Rotor Amps of the motor). For the test I won't care if it runs for only minutes so long as it will start up.

As I wrote earlier in this thread: "If you do try it and it doesn't work, don't blame the inverter... it may be the battery and cables that limit the inverter's capacity." I am not too sure that using those small wheelchair batteries would be a fair test of the inverter.

btw, the LRA may not be as bad as you fear... the LRA surge may be brief enough to not cause you a problem. If it's brief enough, it doesn't take much energy... example: when you get a static shock (or touch an electric fence) you may be exposed to 1000's of volts, but the shock is so brief that it does not contain enough energy to kill you. That's why I said you should test your inverter... it may work, and if it can get past the surge, the operating current of your pump is within the 1000 watt recommended limit of a 12 volt system. But once again, I'm not sure those little batteries will give you a fair appraisal of your inverter.

edro wrote: »

I'm guessing that golf cart batteries-which I know nothing about at the moment-won't last me as long as good AGM batteries. I won't be able to get out to the site to change out the batteries easily. So using good, long lasting AGM batteries (3,000 discharges to 80%) really appeals to me even if that spec isn't real-world.

As a generalization, flooded batteries are cheaper and last longer than AGM batteries. But of course, a high quality AGM may outlast a low quality flooded battery. One thing that AGM batteries are particularly good at is supporting high wattage loads. If you need a high draw (high watts), but only for a short time (low watthours), you can get by with a smaller battery bank if you use AGM batteries.

edro wrote: »

First of all I had not heard the word "derating" before. I looked it up. Second..whew! Sorry to whine and sorry to be such a noob but I don't understand any of this part.

A solar panel rated 100 watts will produce 100 watts under ideal conditions. That means clear skies, noontime, panels aimed at sun, and panels at 75° F. With the sun shining on them, the panels are likely to be much hotter than 75° (which reduces their output). Therefore when calculating their output you must derate them. Bill used some empirically derived derating factors in his calculations.

edro wrote: »

(before I forget, the 24 inverters that I've seen provide 220 volts. The pump that we already have is 110 volt. So I still need to figure that out. Maybe I just need to get a different (220v) pump or I need something to convert the 220 to 110 volts - a transformer? How big would that have to be?)

There are plenty of 24 volt inverters that produce 120 volt AC. (I have one) Keep looking.

I didn't address all your questions, but that's all for now....

--vtMaps

mike95490 · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

DC power solar pumps

Do you have an example? A link? I don't know what you mean.

Right now we can store 600 gallons of water; we will need 200 gallons per day from it, So:

So if there's no sun for 3 days then we are in trouble, I think, with a system that works on solar alone.

Using batteries can carry us through on the "thin" days without sun. That's what I'm hoping that a solar/battery bank design will do for us. We have a very nice manual hand pump nzpump.com and, if we have battery juice for it, a small 12volt DC pump (like on an RV). But the main thing we need is to get 200 gallons per day from the submersible well pump into the cistern.

1) here's a link to pumps with internal power management, AC, DC or straight PV inputs.
http://www.solar-electric.com/grsoposuwapu.html Pricey, but the real deal. How do you price out water, or the lack of it?

2) get a larger tank, to be able to store more than 3 days of water. I use a 1,500 gallon tank, with a spare 1,500 on standby. The plumbing leaks really killed me. My slow sand water filter (no electric or chemicals) can only process 10 GPH, so I need the clean water storage, and use a 50W ozonater to keep it pure.

WMH Cheryl · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

The original poster may want to check out www.solarpumps.com
After I did a bunch of research last year when I realized using solar with conventional pumps was insanely expensive
(Not to mention that normal "solar pumps" were also huge bucks), I found this company.
Very affordable pumps if you only need 200 gallons per day.
Best part is no costly batteries needed. Solar panel direct to prewired pump.
I easily installed it by hand and since the panel I used was 22v it actually pumps more then rated since they base it on 17v panels.
There are so many other great things about their pumps and affordable tank water level controller but typing one fingered
On a tablet is killing me.

edro · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

Responding to vtMaps:

...fewer cells... ...fewer points of failure and easier maintenance...

lowest voltage that is practical

That makes sense to me now.

...small wheelchair batteries...

They are large, group 31. My SOLAR battery tester shows them to be between 500 and 600 CCA.

btw, the LRA may not be as bad as you fear... the LRA surge may be brief enough

I hope that will be the case. It snowed here today. I need better weather for me to set up a test with the inverter & 1/2HP motor.

One thing that I'm concerned about is how it will function over time. I don't like that it is so close. I may have found a solution which registered member WMH Cheryl mentioned in their post: solarpumps.com (I'll comment on them later in this post.)

As a generalization, flooded batteries are cheaper and last longer than AGM batteries. But of course, a high quality AGM may outlast a low quality flooded battery.

Really? I thought it was the opposite. Here from the VMAX website:
( www.vmaxtanks.com/servlet/the-template/faq/Page )

VMAX is known to deliver one of the highest numbers of discharge / recharge cycles. Depending on the use and average depth of discharge it can offer an average of:

Number Of Cycles Depth of Discharge
300 100%
600 75%
900 50%
1500 25%
3500+ 10%

Side note: I tried to put this into a table within HTML tags but it didn't work:
[HTML]<TABLE><TR><TD>Number Of Cycles</TD><TD>Depth of Discharge
<TR><TD>300</TD><TD>100%
<TR><TD>600</TD><TD>75%
<TR><TD>900</TD><TD>50%
<TR><TD>1500</TD><TD>25%
<TR><TD>3500+</TD><TD>10%</TD></TR></TABLE>>[/HTML]

I like that 3,500+ discharge/charge cycles stated.

There are plenty of 24 volt inverters that produce 120 volt AC. (I have one) Keep looking.

I will keep looking. Thank you. Can you tell me which 24 volt inverter you have either in post or PM?

Responding to mike95490:

How do you price out water, or the lack of it?

Brilliant! But the solar-electric.com Grundfos states:

"We do not show pricing for Grundfos - please call or email us for pricing or a quote on items or a complete system."

I haven't contacted them yet but I will.

...get a larger tank, to be able to store more than 3 days of water...

Working on it. I'm not as good at the civil engineering side of this but there are some plans being worked on.

Responding to WMH Cheryl:

solarpumps.com -- Absolutely Brilliant! I've already received a reply from them and I am working on how I can incorporate one of their pumps into a system where a bank of solar panels can power one of their pumps, charge a bank of batteries, and having the batteries run an inverter for the other much smaller power needs that we have.

I'm trying to not jump to any conclusions on designing a system based on one of their pumps but I am pretty excited about the prospect. My "boys" (they are all men now), when they were younger, built their own RC planes from scratch using blue foam. When we discovered brushless motors the sky was the limit! (pun intended)

Attachment not found.

Using a Brushless DC motor is, I think, just the thing I have been looking for. Not that all is figured out here. I still have some questions. But I really think that I'm on to something that will work for us.

Thank you one and all! I still would like any comments or suggestions anyone has.

Ed

vtmaps · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

edro wrote: »

I will keep looking. Thank you. Can you tell me which 24 volt inverter you have either in post or PM?

My Outback inverter (vfx3524) is in my signature.
http://www.solar-electric.com/oupooffgrand.html
http://www.solar-electric.com/exsiwain.html
http://www.solar-electric.com/samlex-sa-series-pure-sine-wave-inverters.html
http://www.solar-electric.com/samlex-pst-series-pure-sine-wave-inverters.html

edro wrote: »

As a generalization, flooded batteries are cheaper and last longer than AGM batteries. But of course, a high quality AGM may outlast a low quality flooded battery.

Really? I thought it was the opposite. Here from the VMAX website:

I stand by my statement. Read about the cycle life of high quality flooded batteries.

As you can see at the VMAX site, the shallower the discharge, the more cycles.

Note: if you buy a VMAX bank and discharge it 50% you get 900 cycles. If you buy twice the size bank (twice the money) you would get 1500 cycles. Do the math... which is a better deal? Why would you spend twice as much to get less than twice as many cycles?

--vtMaps

BB. · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

Some quick comments:

edro wrote: »

They are large, group 31. My SOLAR battery tester shows them to be between 500 and 600 CCA.

Cold Cranking Amps is not really relavent to deep cycle batteries---That is more towards cranking a vehicle motor with a near fully charged battery on a cold winter day.

The better approximation of useful current from a deep cycle battery (flooded cell) over the life/state of charge/etc.) of a battery is better given by (all numbers are based on C/20 Hour Rating of battery bank--closer to how folks generally use batteries for off grid use--5 hours a night loads for two nights, then 50% maximum discharge--I.e., 25% per night discharge for ~5 hours or 20 Hour rate):

C/20 = recommended "average load" (efficient, lots of excess capacity to start a well pump or refrigerator motor)
C/8 = Max continuous discharge rate (for 4+ hours)
C/5 = Max short term continuous discharge rate
C/2.5 = Max surge current (seconds to minutes)

For AGM, you can have much higher discharge rates--But for various reasons, I would try to stick with the above table of discharging--Overall, it usually works well unless you have some special needs (like a large pump that runs a few minutes every hour where an AGM can supply high current and there is not much average power needed--I.e., small AGM bank vs larger Flooded Cell bank to supply the high surge currents).

I hope that will be the case. It snowed here today. I need better weather for me to set up a test with the inverter & 1/2HP motor.

You are really looking at upwards of 5x running current (worst case) as surge... And it is not unusual for a 1/2 horse pump to take 700-1,000 Watts (or VA) to run.

One thing that I'm concerned about is how it will function over time. I don't like that it is so close. I may have found a solution which registered member WMH Cheryl mentioned in their post: solarpumps.com (I'll comment on them later in this post.)

That is why I suggest the above table (C/20 to C/2.5)--It is conservative, but your batteries should work well over their lifetime until they die (falling storage capacity, failed open/shorted cells, etc.).

Really? I thought it was the opposite. Here from the VMAX website:
( www.vmaxtanks.com/servlet/the-template/faq/Page )
VMAX is known to deliver one of the highest numbers of discharge / recharge cycles. Depending on the use and average depth of discharge it can offer an average of:

Number Of Cycles Depth of Discharge
300 100%
600 75%
900 50%
1500 25%
3500+ 10%

Side note: I tried to put this into a table within HTML tags but it didn't work:

Most batteries should not be drained below ~20% state of charge... If the cells are "out of balance" and normal variability in mfg. of lead acid batteries... It is possible for most of the cells to be at 20% SOC, and have one or two cells at 0% SOC--Almost all rechargeable battery chemistries will die an early death if a cell is "reversed charged" (i.e, below 0% SOC)... So, suggest you avoid that (and the 300 cycle life is probably impossible to achieve in real life).

The VBS is setup to take VBS tags (square bracket [tags])--You can flip between "Raw" and "WYSIWYG" mode (A/A button upper left of edit window).

The software will sometimes allow you to copy and past tables directly into the edit window.

Brilliant! But the solar-electric.com Grundfos states:

"We do not show pricing for Grundfos - please call or email us for pricing or a quote on items or a complete system."

There are "FLEX" models--Very nice AC input pumps (fixed voltage). Low surge current and long lasting.

Then there are the "SQ-FLEX" models (that NAWS usually sells--As I understand--Us moderators are volunteers here, we don't work for NAWS).. They take AC or DC from ~60 VDC to 240 VAC (battery, solar panels, AC genset, AC utility). Really nice, but even more expensive.

-Bill

WMH Cheryl · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

Personally I would just get one of their PV panels or use one you already have instead of trying to incorporate into a larger system. Their pumps are designed to have the PV panel directly above well and pre-wired pump just plugs in. If you use a panel you already own, they will sell you the plug to splice into your panel's wires for a few bucks. I didn't even bother with a fancy pole mount, just tied the panel to a pipe panel fence that I had to put up to keep the horses away. Even with less than optimal sun orientation, it could provide 400+ gallons per day to one of my storage tanks.

BB. · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

I agree with Cheryl,

If you can get enough water into a cistern with a solar panel + pump application (no batteries, no AC inverters, possibly some sort of transfer switch/backup power setup for poor weather pumping)--It would be a good way to go.

If you are going to have an off grid power system anyway that is reasonably close to the well, a low surge in well AC pump is not bad either.

-Bill

edro · March 2014

Re: balancing charge, discharge of battery bank, + multiple solar panels

First I want to thank you all for helping me with your comments and for being patient with me.

There are some things that you have indeed made clear.

Personally I would just get one of their PV panels or use one you already have instead of trying to incorporate into a larger system.

I would agree except that I can't go out there to switch to a backup power source. I'm seeing two options maybe with some variations.

Plan 'A':

Attachment not found.

The advantage to plan 'A' is that I can use my existing 12v inverter to run my smaller power needs. The only purchases would be 2 more solar panels, the pump, and probably only a couple of batteries would suffice for what I need.

The disadvantage to plan 'A' is that if I don't get enough sunlight to keep up with the water demand then I don't have any sort of backup. Plan 'A' looks like a bust to me unless there are some variations to correct the disadvantage.

Plan 'B':

Attachment not found.

I really like plan 'B' because it appears to be the most autonomous. Water and accessory power are both available anytime.

The disadvantages are more cost because I'm sure I'll need more batteries and I don't have a 24v DC to 110v AC inverter. All that, along with the pump and a couple more solar panels would be a lot more expensive.

I'm still trying to figure out just how many batteries I would need to get 200 gallons of water per day. With information that I'm getting from the solar pump guy, (Bill), I might be able to finally get all the facts together to figure it out.

Sorry for all the attachments. I tried several times to get the graphic a little larger but failed to do so. And I can't seem to manually delete the unused attachments. I did read that unused attachments would be deleted in a hour so maybe I'm okay.

Well, that's all I have for today. I'd appreciate your comments. My wife is ill with the flu and she is usually the caregiver around here so not only am I trying to care for her but I'm also caring for those that she usually cares for. I even did the dishes today which, for me, who can't stand on his feet for very long, well, it wasn't easy. I guess I'm whining again.

Ed

balancing charge, discharge of battery bank, + multiple solar panels

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