Ready ! - Aim ! - ...

Skippy

As you guys know, I am currently playing with my 3 - 110 watt panels. . right now, I can only run my aqarium pump 3/4 of the day, since the batteries are not the best, and when the sun is shinning, I can run the pump as well as a 100 watt edison bulb. . . . I need new batteries - (600 - 700 $) new inverter ( 600 -700 $) and upgrade the wiring a bit. . . and it "might" be enough to run my fridge. . if I run my washing machine, I can't keep the fridge going. . .

Now, if I wanted to be able to reliably run my fridge, as well as my washing machine - say - twice a week, what would you guys reccommend ? I cannot quote the actual power usage of the washing machine, (its an old top loading maytag) but have listed on the forums the usage of my fridge. . . what really has me thinking, is that I have found out, you can get a 70 volt panel, and feed it into a battery charger that drops it down to the correct voltage of your batteries. . . so I could get 4 - 70 volt - 300 watt panels (as an example) and drop it down to 24 (or whatever) Volts - charging . . . which means, that in the future, if they lower the bar on grid intertie systems, I might be able to add an intertie inverter and plug into the house (its an idea. .)

So now, before I go and spend the money on the 12 V inverter and batteries, I thought I would ask you guys what you would do, as an example - cost wise . . .

Goal : to run fridge 24-7, with washing machine 2-3 x's a week.
funds : like everyone else - limited - cheaper the better, but want quality - and want it to work.
Voltage : undecided - heard 36 V is hard to get a hold of 24 -48 ?
existing parts: #4 gauge wire to the top of a hydro pole and a midnite battery monitor which can monitor different voltages. - not much that does not have to be bought new. . .

What do you guys think ? Ready, just trying to aim - no where near ready to fire

Cariboocoot

Re: Ready ! - Aim ! - ...

Refrigerators and washing machines are big power users. They have heavy start-up demands which require a substantial inverter, and significant Watt hour consumption which needs a sizable battery bank. Batteries require recharging, and the more battery the more panel you need to recharge it.

Best compromise on system Voltage is 24: it's less current per Watt delivered than 12 and no issues with finding fuses/breakers/switches that can take the Voltage (48 Volt systems run upwards of 60 Volts so this becomes a problem).

Without any actual consumption numbers/target you're guessing, and you'd better guess right or else the system either doesn't work or costs to much. Heck, it can do both for that matter.

Think of it like this: a washing machine usually has its own 20 Amp outlet. A refrigerator could share that most of the time. If you're prepared to do load shifting, you need "one outlet's worth" of capacity: 1800 Watts. If you want to play it safe, double this to 3500-4000 Watt inverter. That will run most everything you through at it.

The Watt hours is another matter. A refrigerator can consume 1000 to 2000 Watt hours per day. The washing machine ... how long does it run? And while it runs its consumption will go up and down.

I have to go put a roof on today (or at least start it) but tomorrow I will load up the washer and run some numbers through my UPM meter and see what we're dealing with. It ain't gonna be pretty.

westbranch

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As a suggestion I would go to the Midnite site and run the numbers of those panels through the Classic string sizing tool and see just which model works for you, because you are going to need a GOOD MPPT CC to go with panels like those... there are 3 models, a 150, 200 & 250 volt max input ...

http://www.midnitesolar.com/sizingTool/displaySizing.php

hth

NorthGuy

Re: Ready ! - Aim ! - ...

Skippy wrote: »

Now, if I wanted to be able to reliably run my fridge, as well as my washing machine - say - twice a week, what would you guys reccommend ? I cannot quote the actual power usage of the washing machine, (its an old top loading maytag) but have listed on the forums the usage of my fridge. . .

It may be cheaper to buy newer energy efficient model of washing mashine and/or fridge rather than build up solar capacity to run old ones. I bought a new fridge which is twice as big as my old one (which was 30 year old) and uses less than half the power of the old one. Replacing old washer with new frontloader also saves power.

vtmaps

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NorthGuy wrote: »

I bought a new fridge which is twice as big as my old one (which was 30 year old) and uses less than half the power of the old one. Replacing old washer with new frontloader also saves power.

You're quite correct about new fridges being much more efficient than the old ones. I'm not so sure that new front loading washers use less electric energy than the old top loaders. Most of the energy savings with a front loader are based on the fact that they use less hot water, and may extract more water (= less time in drier) during the spin cycle. I don't think your batteries will notice much difference between the old and new washer.

--vtMaps

waynefromnscanada

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Re front load washer electricity use. My smaller 3 year old Sears front loader is quite easy on power compared to the old top loader. It runs on an inverter controlled 3 ph motor. During wash or rinse action, depending on the size of wash load it has to deal with, the Kill-a-Watt shows between 50 and 150 watts. Only during the spin cycle does it go higher, up to about 450 watts. AND!! The start surge is totally non existent! When it starts in ANY mode, the consumption starts out around 25 watts, then slowly ramps up to whatever the dull load will be for that part of the cycle.
Point of interest: This washer is not direct drive, rather belt driven from the rather small PM Inverter motor. The drive ratio is roughly 20 revolutions of the motor for every one revolution of the drum. In the highest spin speed, the drum easily exceeds 1000 RPM. That means the motor would be ticking along at over 20,000 RPM! Good thing it's a ball bearing motor. No wonder it sounds like a jet engine spooling up for takeoff when it goes into spin mode. On the other hand, in wash mode, it idles along at roughly 400 RPM.
One of these days, out of curiosity, I'm going to try it on the PureSine 300, which states surge as 600 volts. Just not sure how long it can take the spin cycle.

Skippy

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Cariboocoot wrote: »

Refrigerators and washing machines are big power users....
If you're prepared to do load shifting..... you need "one outlet's worth" of capacity: 1800 Watts.
The Watt hours is another matter. A refrigerator can consume 1000 per day.
The washing machine ... how long does it run? And while it runs its consumption will go up and down.

I don't see a problem with load shifting, as the washing machine only runs when I turn it on - rather than the fridge, that comes on automatically. . . so an inverter that would be big enough to run the washing machine surge would be needed, if it can cover that, it can cover the fridge....
Since I tested the fridge on the k.o.w meter, I know it uses roughly .70 - .75 kilowatts per day . . don't think I need a new fridge. . . will have to look into a new washer though. . .
My washer only runs for about 1/2 an hour. . . since the water pump I have fills the tub in a minute. . . take away the fill time, and there is not much "run" time. .

O.k., so in a "dream" world, I would be able to stay with a 12 V system, buy the new inverter and larger batteries - for the larger loads - to get me going right now - and charge them with my exsiting panels - making sure not to discharge the batteries too much . . . then after that, I would just be able to buy the new mpp charger, with the new panels and add to it . . the newer panels would be a much higher voltage, so they would need thinner wire to install . . . . but that is in a "dream world" . . .

Just thinking out loud, there are lots of options, not ready to fire yet. . .

Skippy

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Cariboocoot wrote: »

I will load up the washer and run some numbers through my UPM meter and see what we're dealing with. It ain't gonna be pretty.

Thank you. I have a friend who has one of those jet engine washing machines, I will get him to do a large load - hooked up with the k.o.w meter, and see what he comes up with as well . . .

Cariboocoot

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There will be a small delay. After I finally found the meter this morning I also found the (original) batteries were dead. Since this is 100 Mile there's no chance of buying a couple LR44's on Sunday. Oh well, Monday can be wash day too.

NorthGuy

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I tried to measure the washer and I only could do the max, which is about 350W when it's spinning. Everything else varies with cycles, and there are so many of them, and my wife wants to try them all. All this is extremely hard to quantify. I will need to do that some day. The toploader was 330Wh/cycle. Toploader used to produce way more noise and vibrations.

Since we're on the well, the amount of water we use is directly proportional to the amount of power used by the pump. So if you're on the well, this is a thing to consider too.

Photowhit

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Skippy wrote: »

. . . then after that, I would just be able to buy the new mpp charger, with the new panels and add to it . . the newer panels would be a much higher voltage, so they would need thinner wire to install . . . .

If this is the reason for buying the 70V-300watt panels, please understand that you can run panels in series to get the same effect. A 300watt panel will be quite difficult to move around and install. I just finished installing 200-230 watt panels and they were no piece of cake, I really should have had some help (I'm just stubburn and wiling to work slowly)

Skippy

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NorthGuy wrote: »

I tried to measure the washer and I only could do the max, which is about 350W when it's spinning. Everything else varies with cycles, and there are so many of them, and my wife wants to try them all. All this is extremely hard to quantify. I will need to do that some day. The toploader was 330Wh/cycle.

Can you plug in the k.o.w meter, run a full load from start to finish, and let us know what it says - total kwh used ? Make the wife happy as well, and try a few different settings . . see if it makes any difference in consumption. . . If the max draw is only 350 watts, that would not be a very big inverter to meet that start up surge / load . .

Skippy

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Photowhit wrote: »

If this is the reason for buying the 70V-300watt panels, please understand that you can run panels in series to get the same effect. A 300watt panel will be quite difficult to move around and install. I just finished installing 200-230 watt panels and they were no piece of cake, I really should have had some help (I'm just stubburn and wiling to work slowly)

Good thing to keep in mind, these are large panels to handle. The main reason I am leaning towards this type of panel, is they are listed at 1 $ a watt, and the higher voltage for lighter wire runs. .

I am still thinking about this, I can see that as summer time approaches, and I get more power from my panels, I am going to WANT to do something with them. . . I am just trying to figure that out . . If I stay with the 12 V system, and just get a mpp charger that drops the voltage to 12 V, I can keep the little bit of a start that I have made, and get the inverter that I had planned to.... if I change the voltage, then my existing set up is scrap.

What would be the limit for a 12 V system ? I think I read somewhere that it would max out at 1 outlets worth ? 2,000 watts or so ?

inetdog

Re: Ready ! - Aim ! - ...

Skippy wrote: »

What would be the limit for a 12 V system ? I think I read somewhere that it would max out at 1 outlets worth ? 2,000 watts or so ?

Hooboy! That is a question that you will see a lot of answers to. Here are some of the considerations raised:

1. The size wire needed to run a 2000 watt inverter off a 12 volt battery is expensive and difficult to work with. When you figure in the need for surge current, and the fact that the inverter will try to draw more current as the voltage drops, it gets a lot worse. A 12 volt inverter at high power will also be less efficient.
2. Getting enough AH capacity for your needs from a 12 volt system will either require paralleling batteries (not the greatest idea) or will limit you to battery types that are available in 2, 4 or 6 volt units to allow you to build the AH capacity you need from a series string.
3. Same wire size argument as 1 from the CC to the batteries, just not as bad.
4. Some conservative designers will tell you that the limit for a 12 volt system should be a 300 watt inverter!
5. If you have existing or planned 12 volt DC loads that cannot be replaced by 24 or 48 volt loads or AC loads, then the balance tilts back toward 12 volts.
6. Do not try to save money now by going to 12 volts if it is likely that you will regret it later. Do you plan to eventually expand the system? A lot of people do not expect to expand but find that circumstances and lifestyle drive them to anyway.

NorthGuy

Re: Ready ! - Aim ! - ...

Skippy wrote: »

Can you plug in the k.o.w meter, run a full load from start to finish, and let us know what it says - total kwh used ? Make the wife happy as well, and try a few different settings . . see if it makes any difference in consumption. . . If the max draw is only 350 watts, that would not be a very big inverter to meet that start up surge / load . .

My k.o.w. died after I used it outside for a week. I'm going to get a new one. If you're only interested in Max, I can do that with the Fluke, although it only measures current, not power. Will do next time my wife does the washing.

westbranch

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I am switching to 24 volt, after having a 12v system for ~ 7 years. The big push came from building a new place at the lake that would have cost me in the thousands to wire in 12v due to distances involved. Too much line loss.

I opted for wiring in 110V AC, simple , cheap, components readily available in town, and parts always stocked. And if you need an electrician they can be found or you can do it. For the DC part slightly smaller wire size can be used and the amperage is cut iin half and less worries about running you inverter at full throttle, less wear and tear and tears when it fails...

The ONLY person that knew how the 12V system worked and its weak points is ME...with the 24V system its only the RE part that is dependent on ME to keep it going.

hth

Skippy

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inetdog wrote: »

Hooboy! That is a question that you will see a lot of answers to. Here are some of the considerations raised:

1. The size wire needed to run a 2000 watt inverter off a 12 volt battery is expensive and difficult to work with. When you figure in the need for surge current, and the fact that the inverter will try to draw more current as the voltage drops, it gets a lot worse. A 12 volt inverter at high power will also be less efficient.
2. Getting enough AH capacity for your needs from a 12 volt system will either require paralleling batteries (not the greatest idea) or will limit you to battery types that are available in 2, 4 or 6 volt units to allow you to build the AH capacity you need from a series string.
3. Same wire size argument as 1 from the CC to the batteries, just not as bad.
4. Some conservative designers will tell you that the limit for a 12 volt system should be a 300 watt inverter!
5. If you have existing or planned 12 volt DC loads that cannot be replaced by 24 or 48 volt loads or AC loads, then the balance tilts back toward 12 volts.
6. Do not try to save money now by going to 12 volts if it is likely that you will regret it later. Do you plan to eventually expand the system? A lot of people do not expect to expand but find that circumstances and lifestyle drive them to anyway.

This is what it comes right down too, once I get the fridge running, and being able to do my laundry, what ELSE am I going to want to do. . . especially # 6, since you can't expand, and have to buy new - again. . . Thanks for the info, I will have to digest this. . 24 Volts is sounding better and better. .

Photowhit

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Skippy wrote: »

Good thing to keep in mind, these are large panels to handle. The main reason I am leaning towards this type of panel, is they are listed at 1 $ a watt, and the higher voltage for lighter wire runs. .

I think you missed my point, so you get 2 - 200watt panels that have a VMP of 30 Volts and run them in series, now you have 400 watts at a VMP of 60 for your long run on skinny wires... I understand your in Canada, but suspect you can find the 200 watt size panels in the same neighborhood.

Skippy wrote: »

I am still thinking about this, I can see that as summer time approaches, and I get more power from my panels, I am going to WANT to do something with them. . . I am just trying to figure that out . . If I stay with the 12 V system, and just get a mpp charger that drops the voltage to 12 V, I can keep the little bit of a start that I have made, and get the inverter that I had planned to.... if I change the voltage, then my existing set up is scrap.

If you do decide to go with a mppt type charge controller, I'm now going to say there is NOT any better choice than the Midnite Classic, particularly since they have anounce that they will have a shunt based battery module that will allow the charge controller to properly charge your battery while you are running loads! I think this is a feature we've been looking for and basically stops the hunt for any other charge controller!

Your 12V panels will likely have some value locally. I've been surprised at the value of 12 volt nominal panels, seems lots of people want the low voltage for small projects. I'd say stick them on Craigslist at $1 to $1.10 a watt.

Skippy wrote: »

What would be the limit for a 12 V system ? I think I read somewhere that it would max out at 1 outlets worth ? 2,000 watts or so ?

I usually suggest the upper limit of what is cost effective for a 12 volt system is what a single charge controller can handle, or about 60 amps at 12 volts, or about 1000 watts on a PWM or 900 watts on a MPPT. With the Classic you could go as high as about 1300watts. at that point you would need a 2nd charge controller for a 12 volt system, but a single charge controller, in a 24V system, would be good up to 2000 or about 2500 with the Classic (or other 80 amp charge controllers) If you think/expect your system to be that size, I'd make the system higher voltage as your inverter choice and investment may keep you in a 12V (or lower system) longer than is reasonable. For me it was my investment in a large 24V fork lift battery that made moving to a higher voltage system less cost effective. If I had planned to have a larger place, I would have planned ahead and purchased a 48V system...

...and so it goes...

Cariboocoot

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I have a simpler criterion for the 12/24 choice: unless there is a specific need for 12 VDC (such as mobile application) go with 24. Maybe that's too simple, but it saves a lot of debate.

What I do NOT have are the LR44 batteries my meter requires! Why don't they just make these things run of AAA's?

Rybren

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Skippy,

I don't know where you are located, but if you are in Eastern Ontario, I can point you to some 210W panels for less than $1.00/W.

Photowhit

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The only 2 advantages to a 12 Volt system are inexpensive inverters and 12 volt applications.

...I guess for really small systems small battery banks, but at the point of parallel strings...

MarkP

Re: Ready ! - Aim ! - ...

waynefromnscanada wrote: »

Re front load washer electricity use. My smaller 3 year old Sears front loader is quite easy on power compared to the old top loader. It runs on an inverter controlled 3 ph motor. During wash or rinse action, depending on the size of wash load it has to deal with, the Kill-a-Watt shows between 50 and 150 watts. Only during the spin cycle does it go higher, up to about 450 watts. AND!! The start surge is totally non existent! When it starts in ANY mode, the consumption starts out around 25 watts, then slowly ramps up to whatever the dull load will be for that part of the cycle.
Point of interest: This washer is not direct drive, rather belt driven from the rather small PM Inverter motor. The drive ratio is roughly 20 revolutions of the motor for every one revolution of the drum. In the highest spin speed, the drum easily exceeds 1000 RPM. That means the motor would be ticking along at over 20,000 RPM! Good thing it's a ball bearing motor. No wonder it sounds like a jet engine spooling up for takeoff when it goes into spin mode. On the other hand, in wash mode, it idles along at roughly 400 RPM.
One of these days, out of curiosity, I'm going to try it on the PureSine 300, which states surge as 600 volts. Just not sure how long it can take the spin cycle.

I second this. I have a Bosch front loader that I have run from my SmartUPS 3000 UPS supplied by eight 6-volt wet Costco golf cart batteries. The UPS has a rudimentary load display of five LEDs. When running the washer there aren't even any load LEDs lit until the spin cycle when one lights up. I figure that is 20% of 2,700 watts or around 500 watts. That is too much for the little Honda EU1000i so during spin cycle the UPS tries to switch to battery power. However, as soon as the switch is made the generator is of course able to catch up and the power looks good again, causing the UPS to switch back to genny line (genny) power which falls off again and so on and so forth. It'll sit there switching back and forth about once per second untill I cut the genny power and let the UPS get on with it.

Point being that the new front loaders have no starting surge and not that high peak load. Factor in the water savings which for most off-grid applications translates to energy savings as well and the new washer starts looking pretty good. As for refrigeration I would not even consider trying to run an old reefer. The cost of a panel or two will buy you a new efficient one if you really shop hard. Everything I read seems to indicate that reefers have improved substantially just in the last few years.

About battery bank voltage, I did have a little difficulty finding the right over-current protection and disconnects for my 48 volt system. Most stuff is limited to 32 volts or even 48 volts at the most. Since a 48 volt nominal system actually sees voltage higher than that I wasn't sure what to do. I am not sure that what I did is actually correct. I got a 240 volt fused disconnect for hot tubs and A/C units. DC is harder to interrupt than AC for the simple reason that AC current stops on its own 60 times a second whereas DC will sit there and weld. I guess I'll never know unless I have a short.

BB.

Re: Ready ! - Aim ! - ...

I asked UL Inspectors that question once (I was working with lots of AC/DC/Computer power in a job) and asked if the fuse/switch ratings were 32, 48 volts or 120 volts Maximum or Nominal or whatever--He kind of grunted and passed my design. :roll:

This was back several decades ago when the NEC did DC power systems very badly. And the "Phone" company specs (and labs) were the final word in telephony equipment certifications.

-Bill

inetdog

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MarkP wrote: »

I got a 240 volt fused disconnect for hot tubs and A/C units. DC is harder to interrupt than AC for the simple reason that AC current stops on its own 60 times a second whereas DC will sit there and weld. I guess I'll never know unless I have a short.

The disconnect itself is probably OK as long as you do not try to open it under load. The contacts may not have any arc suppression at all, which could surprise you in a bad way when you open it.
The fused part is great as long as you can find DC-rated fuses to put into the fuse holders. Same problem with even a high voltage AC fuse. An AC fuse will have minimal arc suppression ability and may actually contribute to keeping the arc alive.

Midnite solar offers a range of circuit breakers rated for up to, I believe, 160 volts DC, but they are polarity sensitive. Run the DC current through them the wrong way and try to open them a few times under load and you can end up with a breaker whose contacts are welded in the CLOSED position. Read about it in their blog.

MarkP

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inetdog wrote: »

The disconnect itself is probably OK as long as you do not try to open it under load. The contacts may not have any arc suppression at all, which could surprise you in a bad way when you open it.
The fused part is great as long as you can find DC-rated fuses to put into the fuse holders. Same problem with even a high voltage AC fuse. An AC fuse will have minimal arc suppression ability and may actually contribute to keeping the arc alive.

Midnite solar offers a range of circuit breakers rated for up to, I believe, 160 volts DC, but they are polarity sensitive. Run the DC current through them the wrong way and try to open them a few times under load and you can end up with a breaker whose contacts are welded in the CLOSED position. Read about it in their blog.

The fuses I am using seem to be rated for 250 volts ac and 125 volts dc. The thing I like about the fuses is that their interrupting rating is many times that of a circuit breaker. Yeah, I don't know about the ability of the disconnect to cut active current. Frankly I don't see that I'll ever need it to, short of some freakish short circuit that is still welding away as I desperately try to pull the disconnect. Would have blown the fuses by then. I can't say that the disconnect really looks like it is designed to cut current. It is just a plastic handle with a piece of copper riveted in that you jam between two contacts. Affordable though. The disconnect is $10 and the fuses are $5.

Photowhit

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inetdog wrote: »

Midnite solar offers a range of circuit breakers rated for up to, I believe, 160 volts DC, but they are polarity sensitive. Run the DC current through them the wrong way and try to open them a few times under load and you can end up with a breaker whose contacts are welded in the CLOSED position. Read about it in their blog.

Actually only their Din rail breakers are directional, They have DC breakers rated up to 600 volts (and perhaps 1000V the new standard or coming standard, or at least the European standard for gridtied systems, this may be a figment of my imagination as I see nothing above 600V on their web site) Up to 300V in panel mount versions, with no polarity issues. I understand they are working on changing the Din rail breakerss as I type!

Photowhit

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inetdog wrote: »

Did you mean to say circuit breakers? That is what I was talking about.

Sorry didn't get enough sleep last night, I changed it. Yes, breakers are available up to 600 volts. Up to 300 volts in panel mount with out worries about polarity.

Thanks, Fizzy

Skippy

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Cariboocoot wrote: »

I have a simpler criterion for the 12/24 choice: unless there is a specific need for 12 VDC (such as mobile application) go with 24. Maybe that's too simple, but it saves a lot of debate.

I have decided that I will not be staying with 12 V.. . That being said, while talking with the forklift repair guy at work, he mentioned that the big difference in voltages is more staying power. . . lasts longer - a 12 V forklift would last 4 hours, and a 48 V would last 8 . . . so would it be far off the mark if I said that a 48 Volt system just to run a fridge would be overkill ?

So here is the plan :
Going with a 24 V system. . .

1. Purchase 1 more panel, to match the 3 that I have already. . . What numbers do I have to match ? VMP ? Isc ?
2. Get the new panel installed with the old ones. (thats the big one ! ) split the 4 panels into 2 sets of 24 V.
3. Purchase a small 24 V charge controller and 2 kw - 24 V inverter. (charge controller just big enough to handle the existing panels)
4. Wire my existing batteries - 4 at 12 into 2 & 2 at 24 V.
5. Once I have the juice flowing, I can go out a pick up the appropriate deep cycle batteries. (leaning toward 650 amp hour @ 24 V) so that would be 2 - 12 V - 650 A/H ? wired together ?)
6. After that, its a matter of purchasing another larger 24 V charge controller, and enough panels to keep the batteries charged, since you can NEVER have enough solar panels. .:p

So, If I were to run the fridge all day, everyday, and want to run the washing machine (info in the washing machine thread) - once or twice a week, I am guessing the 650 A/H battery would do, - keeping in mind, I fully intend to purchase 1,000 watts or so of panels to add to this system, so hopefully battery capacity will be kept topped up. . . and I can use any extra power while the sun is shinning, and not have to worry about the batteries dropping to far down in the winter. . .

That's the start of my "plan" . . any ideas ? . . . not ready to fire yet, since I am not really familiar with 24 V systems, but workin on it Thanks guys !

waynefromnscanada

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Skippy wrote: »

I have decided that I will not be staying with 12 V.. . That being said, while talking with the forklift repair guy at work, he mentioned that the big difference in voltages is more staying power. . . lasts longer - a 12 V forklift would last 4 hours, and a 48 V would last 8 . . . so would it be far off the mark if I said that a 48 Volt system just to run a fridge would be overkill ?

There's much more to it than that. Obviously your "fork lift guy" doesn't understand watt hours, or the relationship between voltage and amp hours, OR he's deliberately misleading you.
Yes, on an identical wattage load, a 500 AH 48 volt battery will run that load twice as long as a 1000 AH 12 volt battery, but we're talking two different KWH storage capacities.
500X48= 24 KWH
1000X12= 12 KWH, which is half the power.
BUT, on the other hand, if you have three battery banks, one 12 volt, one 24 volt and one 48 volts, and they all have a storage capacity of for example, 20 KWH, they will all run an identical wattage load, for the same number of hours. There ARE good reasons for using one voltage over another depending on the situation, but the time one or another will run a fridge is not one of them.
First you need to know, not guess, what your daily total KWH loads will be, then use that info to determine the KWH storage capacity of battery bank you will need, then you figure out what you need in solar panels to charge those batteries. Then, depending on what KWH battery bank required for your situation, you can decide which voltage would be a better fit for your situation.

Skippy

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waynefromnscanada wrote: »

First you need to know, not guess, what your daily total KWH loads will be . .

The minimum would be running the fridge all day every day , with a couple of loads of laundry thrown in every week . . all I have is the k.a.w. meter to judge what I use. . .

NorthGuy

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Skippy wrote: »

1. Purchase 1 more panel, to match the 3 that I have already. . . What numbers do I have to match ? VMP ? Isc ?

If you're going to use them in 2x2 configuration, you need to match both Vmp and Imp. It may be a good idea to see if temperature coefficients are simiplar.

If you wire them all in one string, you only need to match Imp. However, this will require an MPPT controller, which you probably need anyway if you're planning to expand.

If you're going to buy 1000W more of panels, it's a good idea to match everything as close as possible. This will give you a flexibility in the future.