What size solar panels do I need?

Written by hazel morgan
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What size solar panels do I need?
Solar panels on a house (Image by Flickr.com, courtesy of Dominic Alves)

Sustainable living advocates supply power to their homes with solar power exclusively, or they supplement their standard electricity supply with solar power components. When you're tied to the grid, you can draw power from the grid, as well as from your solar panels.

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Electrical power is measured in watts (W); 1000W is 1kW, or one kilowatt. Your electricity bill is figured in kWh, or kilowatt-hours: 1000W used for one hour is 1kWh. A 1kW heater left on for an hour uses 1kWh.


Air conditioning and electric heat draw lots of electricity. It would take five 200W solar panels to run a 1kW heater through the hours of daylight.


Determine how much electricity you want to generate from solar. If you skip heating and cooling, 50 per cent could be enough. Arrive at a figure in kilowatt-hours by averaging out your electricity bills from the last year, then divide by two.


If your average was 1200 kWh, half is 600 kWh, or around 20 kWh per day. Assuming you have ten hours of usable daylight per day, you'd have to generate 2kW of power each hour (20 divided by 10 is 2). You need two kilowatts' worth of solar panels.


The temperature, how directly the sun hits the panels and whether there is shade, affect how many watts a solar panel actually produces. You might consider an extra panel to cover energy losses.


For houses, panels that generate 200 and 400W are common. To generate 2kW of electricity, you would wire together five 400W or ten 200W panels.

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