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I am a relative newbie to off-grid systems. Our utility (in Arizona) just pulled the plug on true net-metering, and I am maxed out on my current grid-tie inverters, which are about break-even for my use. . I am considering an off-grid system primarily to charge my electric car on a daily basis. I already have 4 panels, which are 235 W output, rated at 30V and about 8A. The car uses about 5 KWH a day. Was considering about 11 KWH of batteries, 6V, wired for a 24 V system. Also would wire the panels 2 in series, 2 in parallel for 60V and 16A of output. Any comments or recommendations on this proposal?
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Very bad idea. Anything you take off the grid is going to cost you 5 to 10 times more the rest of your life than what that mean ole nasty power company will charge you.
Your 11 Kwh battery is going to last about 2 years discharging it that deeply each day. 2 years is for a high end battery, not cheap ones from wally world. Just in battery cost alone a decent 11 Kwh battery will cost you $2400. Assuming you use 5 Kwh of that battery per day will yield you 730 days x 5 Kwh = 3650 Kwh. So just in battery cost alone you would be paying $2400 / 3650 Kwh = 65 cents per Kwh. Then in two year you will have to replace the batteries at even higher cost. Assuming your provider is APS they only charge you roughly 12-cents per Kwh.
Now why on earth would you want to pay 65-cents per Kwh or 540% more than you have to?Last edited by Sunking; 02-08-2016, 12:37 AM.MSEE, PE -
Yup. Batteries aren't cheap enough yet. Give it a couple years.
And by then you'll probably be considering a much higher voltage battery system.Comment
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You are way better off with a grid tied system even if the utility is not allowing net metering anymore. If you charge your car during the day when the sun is out, you are still charging for free - even if the rest of the time you are not getting as good a deal with the utility as you would with net metering.
Get 4 more and do a basic (1800 watt) grid tie system, then charge your car via the convenience charger (1440 watts) while the sun is out. Or if you are feeling adventurous, get an SMA 5.0-US inverter and charge your car off the secure power output - again while the sun is out and providing close to full power.I already have 4 panels, which are 235 W output, rated at 30V and about 8A. The car uses about 5 KWH a day. Was considering about 11 KWH of batteries, 6V, wired for a 24 V system. Also would wire the panels 2 in series, 2 in parallel for 60V and 16A of output. Any comments or recommendations on this proposal?
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I have access to this battery system for about $500. It was retired from an off grid house. I already own the panels. I really wasn't asking so much about the economic value as I was about the logistics of the wiring.Comment
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Logistically you will need a lot more panel wattage to cover that 5kWh usage for your car.
And to get the most out of any solar panel system greater than 200 watts you should use an MPPT charge controller which will get you closer to 98% of the panel wattage instead of only 67% using a PWM CC.Comment
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If you want 5kwhr a day from retired batteries, 20kwhr (rated) of batteries is a better starting place, since you are going to be seeing reduced capacity from day one. For 20kwhr you'd want to target about 1.5 to 2kw of solar. And as mentioned you really want an MPPT.Comment
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You paid $500 for boat anchors? I sure hope money means nothing to you, because you just lost $500 for scrap lead. You must really want to pay a lot for electricity, like 10 times more than that mean old power company would charge you.
Kind of like walking into a bar and offering to buy open bottles of beer with whatever the customer left over in the bottom of the bottle. Sure there is a little beer left in along with spit.Last edited by Sunking; 02-08-2016, 06:20 PM.MSEE, PEComment
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