How to size an off-grid solar system in Quebec
Sizing an off-grid system does not start with the choice of panels, it starts with an honest survey of what you use. Add up the draw of every appliance, multiply it by the number of hours it runs each day, and you have your daily requirement in watt-hours. A modern refrigerator uses about 1.2 kWh a day, a well pump between 0.3 and 1 kWh, the LED lighting of a cottage rarely more than 0.3 kWh.
The second step is to apply the reality of our latitude. In Quebec City, a well-oriented installation produces about 4.2 kWh per kilowatt-peak installed in June, but only 1.8 kWh in December. It is that winter trough that sets the size of the array, not the annual average. Sizing on the average leads without fail to a generator running all through January.
Third step: storage. Plan on two days of autonomy if you have a backup generator, three if you do not. For a consumption of 8 kWh a day, that means 16 to 24 kWh of usable battery. In LiFePO4 at 90% depth of discharge, count on 18 to 27 kWh nominal.
Finally, choose the inverter for peak power and not for daily consumption. Starting a submersible pump can call for 4000 W for two seconds while the house averages 600 W. The inverter has to absorb that peak without tripping, otherwise you end up in the dark every time the pump starts.
If the exercise feels abstract, call us at 418-809-9738 with your electricity bills or your list of appliances. We run this calculation every week and we would rather run it before the sale than after the installation.
