1KW Off Grid

ozarkcabin · March 2014

Hi, everyone.

I'm absolutely new to solar so I have almost no (very little) knowledge about starting my setup right.

I'll be running a small 560 watt AC during the hot sunny part of the day in summer, continuous use of a small 80 watt refrigerator, a small energy efficent fan at night, and a few LED lights and other minor things which would use no more than 200 watts combined.

The summer time is what's going to use most of the energy with an AC running. Let's give it an average of 12 hours a day just to make sure I'm not underpowering myself.

I was thinking about the 4 pack of 250 watt Grape panels I seen at home depot. If that would work for summer time, what batteries would you recommend for the system?

Thanks.

waynefromnscanada · March 2014

Re: 1KW Off Grid

Hi "ozarkcabin", welcome to the forum. I'm glad you came here asking questions BEFORE you purchased what you saw at HD.
I'm not fully awake (assuming I may sometimes be at this hour of 4:30AM) so will leave the calculations etc to others, but for now, suffice it to say, you will not have anywhere near the power you need to run your planned loads. AC in particular is a huge load with huge startup surges, and many of those small fridges are real energy hogs compared to new, energy star full sized units. AND you need enough solar to run all your loads, PLUS produce enough power left over to properly recharge your batteries. Major rethink required before you go ahead. Now that I've raised the red flag, I'll leave it for others to give more detailed info on a system that will work for you, and this may require a rethink of your loads as well, depending on how much you're willing to spend.

vtmaps · March 2014

Re: 1KW Off Grid

Welcome to the forum,

Designing a system requires hard numbers. How many kwh per day will you draw from the batteries? Get a kill-a-watt meter and find out exactly what your needs are. The labels on the A/C and the fridge are maximum draws... not representative of the actual draw.

One other thing... duty cycle. Duty cycle is the percent of time the A/C or fridge compressor is running. The duty cycle will increase as the ambient temperature increases.

To design your system, first determine the load, then determine what size battery can handle the load. The rest is the easy part... just buy enough solar panels and electronics to keep the batteries happy.

If your A/C did draw 560 watts continuously for 12 hrs that would be 6.72 kwh. If that were your only load, I would recommend a battery capable of storing 4 times that much energy (25% discharge per day). A battery bank of 560 amphours at 48 volts would suffice. Of course, you have other significant loads, and don't forget that the inverter itself consumes power.

This is looking like a large system, but we're shooting in the dark to design it if we don't have hard numbers to work with. One thing that works in your favor is that some of your loads occur while the sun is shining... that means you can power the A/C for a few hours per day without first storing the energy in your batteries. Of course, you will need enough panels to power the A/C and recharge your batteries at the same time.

Get some real kwh numbers and we will design a system to meet your needs.

--vtMaps

ozarkcabin · March 2014

Re: 1KW Off Grid

Thanks, for the help.8)

48 volts? Does that mean I'll need a 48 volt battery or four 12v wired together?

Don't know the formula to convert watts to kwh, so let's just assume a maximum amount of watts within a budget and then I'll downsize from there if needed.

800 maximum watts (12 hours) on a sunny summer day and 300 maximum watts at night (12 hours).

Thanks.

jcheil · March 2014

Re: 1KW Off Grid

ozarkcabin wrote: »

Thanks, for the help.8)

48 volts? Does that mean I'll need a 48 volt battery or four 12v wired together?

Don't know the formula to convert watts to kwh, so let's just assume a maximum amount of watts within a budget and then I'll downsize from there if needed.

800 maximum watts (12 hours) on a sunny summer day and 300 maximum watts at night (12 hours).

Thanks.

A 48v battery bank would be any number of x-volt batteries connected in series to produce 48v.
99% of the time, you would use 6v batteries, but 2v is the ultimate choice if $ allow it.

The basic "numbers" you need to provide for everyone would be as follows:

An AC for example, draws 520w when the compressor is running. However it cycles off and on as needed, so when the compressor is not running it only draws 100w. So if you assume 50% duty cycle for 12 hours, you would be looking at 520watts * .50 * 12 = 3120 watt/hours + 100watts * .50 * 12 = 600 watt/hours = Total: 3720 watt/hours or 3.7kwh. That is a LOT of power to produce from Solar/Batteries.

And as mentioned many times on this forum, you will find that a NEW full sized-18cf energy star fridge will use LESS power then those small 3-4cf "dorm" fridges. My newer model uses about 1.1kwh per day down here in hot Florida. My neighbor's small dorm fridge uses 1.3-1.5 per day.

Either way, you are talking about a LARGE system. As a matter of fact, I run just about what you are talking about myself. You're talking in the $10,000+ price range.

If you get a kill-a-watt meter, you can run your appliances thru it for a few days and it will tell you the exact number of kwn it is consuming. THEN you can have a better idea on how much solar/batteries you need. Since the cost is so high, you really need to narrow it down unless you have money to burn.

Cariboocoot · March 2014

Re: 1KW Off Grid

ozarkcabin wrote: »

I was thinking about the 4 pack of 250 watt Grape panels I seen at home depot. If that would work for summer time, what batteries would you recommend for the system?

Thanks.

I'll just comment on this: you're doing it wrong-way around.
The batteries supply the power, the panels recharge the batteries.
This is because the panels supply power only during the hours of good sun, whereas the power may need to be drawn at any time.
So the first thing you set out to determine is how much battery capacity you need. The second thing is how much panel you need.

A 'small' 560 Watt A/C may run a 50% duty cycle which adds up to 6,720 Watt hours per day. Nothing small about that, and you'd never harvest that much power from 1kW worth of PV in a day.

ozarkcabin · March 2014

Re: 1KW Off Grid

Thanks again.

In my backwards conservative logic, I wasn't counting on the AC running the batteries down at all by only running it when the sun was out. I saw a guy on youtube run a AC without any batteries. He tied directly to the inverter from the solar panels. The batteries will only power a fan, refrigerator, etc at night. I found a cool kenmore 3.1 cubic foot refrigerator/freezer that runs on 30 watts and has enough freezer room for two gallon jugs.

Anyways, I'll get a list of appliances and energy output before going any further. A lot of research to do at this point.

waynefromnscanada · March 2014

Re: 1KW Off Grid

ozarkcabin wrote: »

I saw a guy on youtube run a AC without any batteries. He tied directly to the inverter from the solar panels.

Virtually 100% that video was a hoax. Inverters don't work that way. They have a relatively narrow voltage range, outside of which the inverter shuts down to protect itself.
Uncontrolled PV voltage is all over the place. They need a battery to stabilize the voltage and supply surges and absorb excess from the panels as sun intensity increases and decreases, sometimes minute to minute due to atmospheric conditions.
I don't know why people make these hoax videos, but they do. Perpetual motion machine "inventions" are another favorite for hoax video makers.

vtmaps · March 2014

Re: 1KW Off Grid

ozarkcabin wrote: »

The summer time is what's going to use most of the energy with an AC running. Let's give it an average of 12 hours a day just to make sure I'm not underpowering myself.

ozarkcabin wrote: »

I wasn't counting on the AC running the batteries down at all by only running it when the sun was out.

We often describe a day as having a certain number of full sun equivalent hours. 12 hours of daylight is NOT 12 hours of full sun, and your panels will only put out maximum power for 4-5 hours a day. btw, maximum power will be about 75% of the rated power of the panels because rated power is at 75° and your panels will be much hotter than that.

ozarkcabin wrote: »

I saw a guy on youtube run a AC without any batteries. He tied directly to the inverter from the solar panels.

That is unlikely to work for you. First of all, you need to have a charge controller. Secondly, the charge controller needs a battery. Sometimes if you get the process started with batteries, and then disconnect the batteries, the system will work briefly. Just because someone got it to work long enough to make a video doesn't mean that it will work for you. Sometimes I can drive my car with no hands on the steering wheel... briefly.

--vtMaps

solar_dave · March 2014

Re: 1KW Off Grid

Used sparingly in the AZ heat my mini split used an average of about 10kWh a day.

ozarkcabin · March 2014

Re: 1KW Off Grid

Ah, should've known the video was fake when he disabled comments. That way, no one can expose it.

I thought the 2 volt battery posted earlier was a typo that was meant to be 12 volt. After looking around, I found that they do make 2 volt batteries. I saw a surette 2 volt battery with 1700 amp hours that weighs over 200 pounds! I know that watts are watts and amps are amps no matter how you add or divide them up, but would a person get more life out of one big battery instead of bank of smaller ones? Surette had a 10 year warranty on the battery, which is at least twice as long as any other battery I've seen.

Actually, wouldn't a 2 volt battery require 24 of them to get to 48 volts? That would be about half a million dollars and just as many amps. LOL

vtmaps · March 2014

Re: 1KW Off Grid

ozarkcabin wrote: »

After looking around, I found that they do make 2 volt batteries. I saw a surette 2 volt battery with 1700 amp hours that weighs over 200 pounds! I know that watts are watts and amps are amps no matter how you add or divide them up, but would a person get more life out of one big battery instead of bank of smaller ones?

All lead acid batteries are composed of 2 volt cells... a 6 volt battery is 3 cells in series. When you build a battery bank you must put enough cells in series to create the voltage (usually 12, 24, or 48 volts) that your system uses. The optimal design of a battery bank has a single string of battery cells in series. Short discussion here.

Suppose your design goal calls for 500 amphours at 24 volts. Your optimal design would be twelve 500 ah cells in series.

If you used 6 volt, 250 amphour batteries, you would make a string with four batteries in series to make 24 volts at 250 amphours, and then use two of those strings in parallel to make 24 volts at 500 amphours. This is acceptable, but not optimal.

--vtMaps

waynefromnscanada · March 2014

Re: 1KW Off Grid

My Surrette 2 volt batteries are rated just under 1000 ah, forget exactly the ah.
Thing I really liked about Surrette is that their 2 volt L-16 battery is composed of one, single, large 2 volt cell with one single fill/inspection cap. All other L-16 two volt batteries I came across were composed of 3 two volt cells wired in parallel within the one case, and thus have 3 fill/inspection caps per 2 volt battery, basically just a 6 volt battery that's been internally rewired for 2 volts.
You will find some people who don't like Surrettes, but you'll also find a few folks who don't like other brands/makes either.
So far mine have been treating me very well, and my cousins 6 volt L-16 Surrettes have been treating him well in spite of being badly abused. He and his totally non-understanding family have not been able to murder them - - yet.
http://rollsbattery.com/public/specsheets/S-1380.pdf And note, this links to older info and lists SG as 1.280. The new ones now being delivered are being filled with 1.265 electrolyte which is supposed to extend the life of the battery.

jcheil · March 2014

Re: 1KW Off Grid

ozarkcabin wrote: »

I thought the 2 volt battery posted earlier was a typo that was meant to be 12 volt. After looking around, I found that they do make 2 volt batteries. I saw a surette 2 volt battery with 1700 amp hours that weighs over 200 pounds! I know that watts are watts and amps are amps no matter how you add or divide them up, but would a person get more life out of one big battery instead of bank of smaller ones? Surette had a 10 year warranty on the battery, which is at least twice as long as any other battery I've seen.

Actually, wouldn't a 2 volt battery require 24 of them to get to 48 volts? That would be about half a million dollars and just as many amps. LOL

You have found out what a lot of people find out eventually. BATTERIES can be the most expensive part of a solar installation! Back in the day, panels were more expensive than batteries. Now it is the other way around. So people see panels for less 75 cents per watt and go "wow, I am gonna get solar!" - Then when you add the batteries, controller, WIRE (many times large 0000 wire) you say "Wow that's 2-3 times the cost of the panels!"/

As far as 2v vs 12v, etc. Like everyone says, a "perfect world" is ONE STRING of batteries to make the voltage you need that contain the number of amp/watt-hours that you need. Very few of us however have that setup due to the initial cost (as you found out). But, it is pretty much a given that you (end everyone else) will (and have) ruined their first set of batteries. So it is generally a good idea to get a cheaper basic set the first go-a-round. 6v GC2 (golf cart - sams club, etc) are the best bang for the buck even though you end up with multiple strings.

And "cost wise", if you do the math based on the watt-hour rating of the batteries (amp-hours X volts) and life-span/warranty, you will find that regardless of the voltage, size and warranty they all generally end up being close in price. There have been discussions here about paying $5,000 for a bank that has a life of 10 years or $1,000 for a bank that has a life of 2 years. In the end (not counting inflation), you end up paying the same.

Going with GC2's, saves you some $ up front, protects that investment since you will likely murder your first set and the way technology is going, IMO I am hoping that in the next few years there will be better/cheaper battery technology coming out when I need to replace my GC2 bank in 3-4 years.

TorontoTim · March 2014

Re: 1KW Off Grid

Just to put it out there and confirm the concept in simple terms (I'm a simple guy and new to all of this myself) - am I right in my understanding that:

4 x 428ah Surrette S-550 6v batteries strung together as a 24v 428ah bank gives me a total of 10,272 watt hours to draw down from, and you don't want to go past 50% so 5,126 watt hours / the number of days standby you'd like.

Assuming 3 days - 5,126 / 3 = 1,712 watt hours per day?

So a 100w light bulb could operate for 17 hours a day at that capacity.

Have I got this right?

jcheil · March 2014

Re: 1KW Off Grid

TorontoTim wrote: »

Just to put it out there and confirm the concept in simple terms (I'm a simple guy and new to all of this myself) - am I right in my understanding that:

4 x 428ah Surrette S-550 6v batteries strung together as a 24v 428ah bank gives me a total of 10,272 watt hours to draw down from, and you don't want to go past 50% so 5,126 watt hours / the number of days standby you'd like.

Assuming 3 days - 5,126 / 3 = 1,712 watt hours per day?

So a 100w light bulb could operate for 17 hours a day at that capacity.

Have I got this right?

If it were a DC bulb drawing 100watts, yes, but due to the efficency rating of the inverter, it would be slightly less, plus the idle draw of the inverter which for many are around 20watts/hour (thus consuming 480 of those watt-hours) so you would only have 1,232 less the amount lost due to the dc-ac conversion (not sure on that amount) to run the light bulb.

TorontoTim · March 2014

Re: 1KW Off Grid

Fair enough - the inverter consumption is a real kicker. Will definitely have to look at that when considering components.

vtmaps · March 2014

Re: 1KW Off Grid

TorontoTim wrote: »

Fair enough - the inverter consumption is a real kicker. Will definitely have to look at that when considering components.

Some folks have two inverters. A small inverter (few hundred watts) that is always on for lights, computer, fans, etc. A large inverter that is turned on for a few hours per week for laundry, power tools, vacuum, water pumping, etc. To make this work, its best to have a separate electrical panel with breakers and dedicated outlets for the large loads.

The two inverter scheme probably won't work if you have an AC fridge that needs a large inverter, because the fridge needs to run many times per day. There are beginning to be available 'inverter fridges' that do not have large start-up surges. Another option is to use a DC fridge which doesn't need any inverter.

The energy savings of a two inverter system can be considerable. My Outback inverter has a no load draw (sometimes called 'tare' load) of 20 watts. That is 480 watthours per day just to be turned on. That's as much as my DC fridge uses. And that's a better number than most other brands of large inverters.

Even on systems that need large inverters all the time, a two inverter system may make sense. If you have occasional very large loads that need a 6 kw inverter, you may be better off stacking two 3 kw inverters in parallel. Whenever the loads are manageable with just one of the two stacked inverters, the other will be in standby mode.

--vtMaps

1KW Off Grid

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