What kind of solar power system do I need to power my cottage?
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What kind of solar power system will I need to power my cottage?

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What size of solar power system would meet the requirements of three 60-watt bulbs, a 5″ TV, a vacuum cleaner, hairdryer, recharger for a cellphone, and a composting toilet, and allow for other small appliances or power tools, such as a circular saw? (We have a propane fridge and oven.)
–Kevin Beattie, Gananoque, Ont.

“Solar power systems are sized according to load and use,” explains Jean Harding, manager of the Perry Sound office of Sun Volts Unlimited. Load is the total electricity draw of all your appliances used at the same time. Use is case specific: Are you a neat freak who vacuums daily? Do you watch TV with the lights blazing or do you prefer reading by lantern light?

Before you buy, you’ll need to calculate your usage in detail. Multiplying the wattage draw of each item by an accurate estimate of daily use. You also have to keep in mind that appliances with motors, such as power tools and refrigerators, have what’s known as surge – the additional draw that comes when the motor first starts up. A typical circular saw will use 750 watts when running, but the surge can be twice as high.

“If all the items you listed were on at the same time, they could draw over 5600 watts,” estimates Rob McMonagle, president of Prometheus Energy in Concord, Ont. “However, with a little load management – use the vacuum, hair dryer or circular saw one at a time – the draw could be kept below 1500 watts.” (We factored your composting toilet in at 3 watts an hour; however if it has a heater and a fan, it could burn up to 500 watts in an hour.)

Charge your cell phone before you go to the cottage and use the charger sparingly. Another method of lowering energy consumption would be to replace the 60-watt bulbs with 15-watt compact fluorescents, suggests McMonagle. “This reduces the consumption by over 500 watt-hours a day and would save almost $1000 in system costs.”

Based on your specifications it looks as if you’ll need at least a pair of 60cm by 120cm 75-watt solar panels (Sun Volts Unlimited suggests four 64-watt panels); six to eight batteries (to store the energy from the panels); a 1500-watt inverter (which converts the DC energy from the batteries to the AC of your cottage wiring); and all the necessary wiring and hardware. Both Sun Volts and Prometheus Energy have packages meeting these requirements for about $6000 installed.