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jdemaris
12-31-2006 12:17:38
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Re: 12v DC to 115v AC for boiler pump in reply to JoeBob/IN, 12-31-2006 11:32:17
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There are many ways to do it. I run the electric hot-air blower on my wood-furnace with solar - and it draws a lot more current than a water-circulator does. When it's gets good and cold outside, my blower draws 3 amps at 120V for 15-20 hours a day. You need to figure what the most current use in one day is for your setup. You then have to figure how much electricity - producing sun is available on an average winter day. In my area - four hours is used as an average - but we actually get less. If you get four hours - you then have to have enough solar-panel wattage to produce the power you need in that four hours - actually about 20% more. That 20% takes into account inverter loss, battery storage loss, etc. You also have to size your battery bank to be capable of running with no sun for X amount of time. Since you have grid backup - seems 20 hours of battery storage is a good goal. If, for example, your circulator draws 1 amp at 120 VAC, and runs 6 hours a day - it then uses 720 watt-hours. Add 20% to that for loss, i.e. you have 864 watt-hours. You need approx. a minimum of 200 watts in solar panels. A good buy on solar panels comes to around 4.50 per watt - so two 100 watt panels will cost you around $900 if you buy right. And, the Federal government will give you a tax credit for part of it. For batteries - to have 844 watt-hours of storage - take a battery and mulitply its AH rating times its voltage. For example, a Trojan golf-cart deep-cycle battery is 6 volts and 225 AH - i.e. 1350 watt-hours. You need 12 volts for an inverter, therefore you hook two of the Trojan 6 volt batteries in series - and get 12 volts but the watt-hour storage stays the same. Series connections do not change watt-hours - only parallel connections do. These are just examples. I don't know how much reserve you want, how much sun you get, etc. In answer to an automatic system - there are inverters made just for that purpose. When the batteries reach a state of low-charge, the inverter automatically switches over to grid-power - or an automatic-starting fuel-driven generator if you want. Cheapest automatic inverter I know of on the market is a Trace/Xantrex DR series. It is cheaper than most because it's a modified-wave inverter - and today - any house hooked on solar to feed back to the grid (grid-tie) requires a full-wave inverter - and they are much more expensive. Just priced an inverter for my house if I want to go to grid-tie and it's list price is $5500. You can buy a Trace DR 2000 watt inverter - with a 12 volt input and 120 VAC - with built in battery charger, automatic changeover to grid, etc. - for around $400-$600 but you have to shop around. If you don't want automatic changeover, you can buy all kinds of $100 inverters that will do the job of voltage-conversion - but the changeover will be up to you.
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