BIT Studio

June 20, 2014

Emergency Power

Filed under: Solar — webmaster @ 8:11 am

 Canadians can expect only 3 or 4 hours of usable solar power sunlight per day and a realistic expectation of what a solar system can actually accomplish is critical. An oversight in my previous calculations made my original plan unfeasible. I had not fully taken into account the overhead required to convert 12V DC power to 110V AC.  A 1000 watt DC to AC inverter requires approximately one amp per hour to operate, and in a closed solar system this creates an additional load expense of 24 amps per day. The inverter overhead, not including appliances, would require an additional 150 watts (watts=amps x volts, plus rainy day variables) of solar panels.

It was not unusual 10 years ago to pay $10/watt for an installed solar-to-grid system. For example, a 2 kilowatt rooftop solar system would have cost $20,000. The cost is much less now and solar panels for under $1/watt can be found. A system that includes a charge controller and inverter can be purchased for under $4/watt, and depending on the interface (batteries versus grid), a complete $5/watt system is possible.

The cost of a system to power a mini-fridge and mini-freezer (and emergency furnace power when needed) would be at least $2,500 plus installation plus rooftop real estate. In Ontario, we have the luxury of paying less that 20 cents per kilowatt hour for our electricity. If it was just about cold beer and ice cream, the return-on-investment would be well over 20 years, which is prohibitive even by European standards. But the purpose of the system is to have a back-up in place for a grid power failure, and for that the ROI figures become much more forgiving.

The solar component of this project has been reduced to a 150 watt trickle charger (1m x 1m solar array) that maintains two deep-cycle, sealed, 100Ah batteries. The day-to-day responsibility of the batteries has been reduced to lighting the laundry room with two 0.2 amp LED lights. In case of a power failure, running a 1200 watt gas powered generator for one hour per day provides sufficient battery energy to power a furnace and fridge throughout the day, as well as a hot water tank and freezer for one hour per day while the generator is running. For communication and entertainment, phones and iPads would be chargeable anytime.

The emergency power back-up system will cost less than half of the original project and depending on the duration and severity of the next blackout (and your skill with a sharpened pencil), the project ROI could be as little as three or four days. The system could be easily expanded in the future to include more solar panels as the battery infrastructure will already be in place.


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