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Old 11-08-12, 11:10 AM   #11
creeky
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Hey Jon,
The advantage of going 24 volt (or 48) is three fold. One. you can use smaller wire. so there's some savings there, though, given the price of everything else it's pretty small.
Two: you can plug more panels into your system. My Morningstar controller is 60 amps max. 60 amps at 12 volts means I can use 800 watts of panels at peak sunshine. After that it "current limits". 60 amps at 24 volts means I can plug in and charge with 1600 watts of solar. and 48 volts (matching my ongrid panels) will mean 3200w. (I have seriously considered just adding another Morningstar controller ... that way I could have 1600 watts charging and a 12v system.)
Three: you can build a bigger battery pack more easily. 16 batteries at 12 volts is a lot of wiring. at 24 you can cut in half the number of wires running to the bus bar from the batteries. On the down side it also means a more expensive inverter, charger.

I don't like hauling gas and running the genny so I've gone a bit overkill on the panels. I just prefer the solar system running my offgrid cottage. Going to 24 or 48 volts will cost me more money in inverters/chargers/batteries. But I'll have a more robust system capable of handling all my current mod cons and adding a fridge.

Note that, depending on how long you've had your batteries. Mine are three years old. If I add new batteries to the pack I have essentially thrown away three years of life span. So when adding batteries, you really need to do them all at once. Kind of a bummer.

Now: real world: The key advantage of 1500 watts into a 12v system (I'll be running 1500 watts as soon as I can find the time to install the two new panels found online at .80/w!) is that my 350 watts of morning power (8 a.m.) becomes 525. By nine I'm getting around 500. That'll become 750. By 11 I should be current limiting right until two or even 3. This will be a good thing!

This is the key thing I've learned this year. People talk about the efficiency of this that and the other thing, but what really dictates your power creation is, gosh, sunshine. If it's even a bit cloudy, as it is here today, sunny with a bit of haze, I'm making 682 watts instead of 800. If I had that other 500 watts installed I'd be current limiting and that would be awesome. My batteries really respond well to the higher watts. At 850 you can watch the battery voltage climb. hitting the target, which, cold adjusted (my batteries are currently about 50 degrees F) is 15.27 to go into "absorption."

To fully charge my batteries I need 2.5 hours at absorption. So getting my early morning and late afternoon power levels up should help me a lot.

Okay. Now to the fridge. If you insulate your fridge: divert the heat from the compressor: Be careful about opening and closing it. You'll get your energy needs down. There are some great posts about this right now.

However, worst case scenario: how to cover that 1kw drain every day.

My solution is to buy a new battery pack and up my solar panel power input. I have to say though, I'm currently (ha ha) running my generator for an hour in the a.m. to give my batteries a head start on charging. During the week of clouds that was Sandy, I too ran my genny two hours a.m. and p.m..

Hope this helps.

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