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The simplest source of energy to use is household AC current from the power grid. It’s highly reliable and available on demand. Off-grid systems will require considerable effort and engineering to meet similar reliability goals. We use grid power without thinking about the quantities required, or how they compare between situations. An average of 20 kWh/day is enough energy to meet all the energy needs of a small condo. When planning your energy use you need to know which loads will be your major consumers. An important option to consider is the idea of a net zero home that is tied to the electrical grid, but generates power that it can feed in for a net power draw of zero or less, averaged over the year. For the latest recommendations in a Canadian context google “nrcan net zero”.
Useful Approximate Orders of Magnitude
This table is extracted from some of the many you can find searching online, as well as actual product data. The most important lessons from this table are that heating loads can be orders of magnitude larger than everything else. Just about everything you would normally think of possibly running on a small battery will be incidental. Smaller loads that are always on (like a fridge or network equipment) may consume more energy each day than larger loads that run briefly (like a microwave).
| Load or Source | Nominal Voltage [Volts] | Current [Amps] | Power [Watts] | Energy [Watt Hours] |
| Coin Cell | 1.5 | < 0.01 | 0.015 | 0.3 |
| 2 AA Batteries | 3 | < 0.1 | 0.30 | 6.6 |
| Phone | 3.7 | 12 hours life | 0.83 | 10 |
| Phone Charger | 5 | 1 | 5.0 | 120/day |
| LED Desk Lamp | 12 | 0.5 | 6.0 | 144/day |
| Group 27 Battery | 12 | < 5 | 60 | 1200 |
| Fridge or Freezer (cycles compressor on/off) | AC | 40 average | 1000/day | |
| Incandescent Desk Lamp | AC | 100 | ||
| Computer, TV | AC | 100 | ||
| Max Outlet, stove element, kettle, oven, hair dryer, microwave | AC | 1000 – 1500 | ||
| Clothes Dryer, Water Heater | AC | 4500 | ||
| Mini Split Heat Pump | AC | 1000 – 4500 | ||
| Tankless Hot Water Heater | AC | 30000 |
Note that here’s a whole lot of household loads that are around 1500 W, the maximum you want to plug in to a normal household electrical outlet on a standard 15 amp circuit.
Estimating Household Electrical Loads
I took a quick tour through Home Depot, looking at the Energuide labels on some run of the mill appliances, and I would expect you to do as well or better on the energy efficiency of your appliance choices:
- Refrigerators ranged from 327 to 401 kWh / year, so find one that uses less than 1 kWh / day. Freezers were in the same ballpark.
- Dishwashers were around 270 kWh / year.
- Clothes washers ranged from 175 to 428 kWh / year, depending on whether they heated their own water.
- Clothes driers were around 650 kWh / year, and most of that energy goes out the vent.
- Kitchen stoves with ovens were around 600 kWh / year, but at least that heat stays indoors.
Energuide ratings represent average use conditions, a