How Much Power Will You Need from Your Solar Electric System?

Pointers on sizing a photovoltaic system to collect and use solar power in your off-the-grid home. Excerpted from the Gaiam Real Goods Solar Living Sourcebook.

NOTE: This information applies to off-grid homes. If your home is tied to the power grid, see note below.

There’s no such thing as “one size fits all” when it comes to energy systems. Everyone’s needs, expectations, budget, site, and climate are individual. The design of your power system, in order to function reliably, must be take these individual factors into account.

First you need to know what makes your house, site and lifestyle unique, including your household electrical demands. Start by completing a system sizing worksheet. This is usually followed by a phone call and a customized system quote.

Keep in mind — the primary principle for off-grid systems is: Conserve, conserve, conserve! As a rule of thumb, it will cost about $3 to $4 worth of equipment for every watt-hour per day you must supply. Trim your wattage to the bone! Don’t use incandescent light bulbs or older standard refrigerators.

You are in the best position to make lifestyle decisions that affect your power usage: How late do you stay up at night? Are you religious about always turning the light off when leaving a room? Are you running a home business, or is the house empty five days a week? Do you hammer on your computer for twelve hours a day? Does your pet iguana absolutely require his rock heater twenty-four hours a day? Figure out your watt-hour usage, and assess where you can trim it.

Once you've estimated your power usage and output requirements for your system, note that to assemble a safe, reliable energy system, you'll need to know a little about related topics including batteries, safety equipment, controls and monitors.



Not off the grid?

If your home is on the power grid, your existing utility company will cover whatever power needs your solar electric system doesn’t. So you don't need to account beforehand for every watt-hour of power you'll need. Your up-front considerations will include how much you want to spend and how many kilowatt-hours of utility power you’d like to displace on an average day.

For direct-intertie systems without batteries, you’ll invest about $2,000 for every kilowatt-hour per day your solar system delivers. For battery-based systems that can provide limited emergency back-up power, you'll invest about $3,500 for every kilowatt-hour per day. These are very general ballpark figures for initial system costs. Remember, state and other rebates can reduce these costs by up to 50%.

 

 

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