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# Solar Energy: How Much Would It Cost To Use Solar Energy If I Use 790 KWh Usage In My Home From Electrical Energy? (9/15/2011)

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c2builder September 15, 2011 at 11:52 am

You really should be asking a solar company but I think I can give you an approximation. ‘Labor’ will be the big unknown in my calculation.

790kWh in (say) 30 days is an average of 26.3 kWh. The notion of using an average implies that you’re storing the energy into batteries for use at night, handling peak loads, cloudy days etc. The solar industry at my latitude of 38 degrees calculates solar energy accumulation for a single day as being the equivalent of 4.3 hours of direct sunlight. So you’d need panels producing 6.12 kW _if_ everything were 100% efficient downstream (like the batteries and inverter). So let’s add a fudge factor to account for storing and retrieving energy from batteries. Multiply by 1.2 to get 7.3 kW. (I’m guessing at the fudge factor here).

Panels sold on Ebay seem to go for \$ 3 / watt so you’ve got \$ 22000 (7300 x \$ 3) in panels. 20 kWh of deep cycle lead acid batteries cost me about \$ 2500 (for an electric truck). And you need an “inverter”, labor to mount the panels etc. I’ve almost certainly oversimplified here and there.

The good news, in Calif at least, is that a local solar company wrote to say that total rebates and tax breaks amount to 45% of the system cost. Beware, however, that their system cost doesn’t overlook labor etc.

Consider doing an energy ‘audit’ of your home where you identify the essential electrical appliances (eg. refrigerator). You could scale the solar panels to handle these essentials. If the main grid goes down, you’ve at least got your house ‘covered’ in some minimal sense.

I’m doing an energy audit of my house right now and have found some supposedly ‘off’ gadgets are quite power hungry. I bought a killawatt power meter off Ebay for \$ 14 to make the measurements.