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Solar Load Calculator

When sizing a solar PV system, doing an electrical load evaluation is a critical preliminary step. This is because the number of solar panels you need is determined by 1) how much electricity your lifestyle demands now and 2) how much additional capacity for future appliances you want to allow.

A load evaluation is especially important for off-grid solar installations because battery storage is involved. Your solar batteries will degrade faster if they aren't being given enough energy to store (and batteries are usually the most expensive part of the off-grid PV system).

Using Our Solar Load Calculator

List your appliances and their power consumption in the calculator below. It's important to include every appliance in every room of your home, and light bulbs too (you may find it's easiest to add up all your light bulbs' wattages on paper first and include them as one item in the calculator). If it's on a switch or plugged into an outlet, list it.

Most appliances list the instantaneous Watts they draw somewhere on them - often on the back near where the power cord comes out. But since Watts are the instantaneous draw, it's important to include the hours per day and days per week each appliance is run in order to get the energy the appliance uses in Watt-hours.

When you submit the calculation form, the results will be emailed to the Real Goods Tech Desk and to the email address you provide.

calculatorIf you can't find Watts listed on an appliance, you can either use a Kill-a-Watt device, or apply the formula: Watts = Volts x Amps


light bulbThe easiest way to reduce the cost of a solar PV system is to reduce the load it needs to satisfy. Replacing your light bulbs with LEDs and replacing appliances with non-electric appliances is a great place to start.


warningBe sure to list ALL your appliances, no matter how small. If it's on a switch or plugged into an outlet, list it.

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