Research Highlights

Energy Use Patterns in Off-Grid Houses – Case Study #4: Gulf Islands, BC

House Description

Originally a 1 1/2 storey 4.6 x 7.6 m (15 x 25 ft.) float home, in 1980, this was converted into a house on a crawlspace foundation. A 7.3 x 6.7 m (24 x 22 ft.) single storey addition on an open crawlspace was built on the SW side of the original structure. A 3.7 x 7.3 m (12 x 24 ft.) greenhouse was built onto the SE face of the addition. An unheated porch area buffers the NW side of the house. The site has good solar access and is well protected to the N and NW by trees. It was chosen for the wind/water/PV potential. An airtight cookstove provides cooking, space and water heat (5 cords wood/year), with a drain down solar DHW system used in the summer. Two adults live in the house.

Thermal Envelope Summary
AC/H@50 Pa: n/a, as float home section fragile
Walls: float home, RSI 2.1 (R12) addition, RSI 3.5 (R20),
Ceilings: float home RSI 2.1 addition, RSI 4.9 (R20)
Floors: float home: RSI 3.5 (R20)
Windows: float home, single plexiglass; addition, thermopane
Doors: solid wood

System Description

The power is supplied by a 280 W output PV array (8-35 W panels); a 400 W Aerofoil 3 wind generator; and a seasonal 150 W microhydro system (runs November through May, 24 hr/day) from a source 0.4 km from house. A small generator is used for seasonal backup. Energy is stored in a bank of 12 salvaged forklift batteries, wired to produce 12 VDC (1,200 Ah). A Trace 1512 modified sine wave inverter produces 120 VAC. There is a combination of 12 VDC and 1,200 VAC wiring. The system cost approximately $7,000 CAD.

System Performance

The load on the system includes AC lights, water pump, washing machine, microwave, a computer, an answering machine, two cordless phones, a mini stereo, TV/VCR, and small kitchen appliances as well as power tools in the workshop. The total possible daily load is approximately 18 MJ (5 kWh), while the actual load is estimated to be 11 MJ (3 kWh). Propane fuels the fridge and a cooktop. There is a propane-fired hot water tank in the house, but it is not hooked up. Approximately 400 L of propane are purchased annually. The genset runs regularly September through November during the shift from solar and wind to microhydro.

The actual electrical use in this house is about 4,000 MJ (1,100 kWh) annually. This figure does not include the non-electric appliances used in the house. When the kWh equivalent of the propane appliances is included in the actual energy use for this house, the figure is approximately 19,300 MJ (5,370 kWh). The average annual lighting and appliance use for this vintage house in British Columbia is 26,470 MJ (7,350 kWh). There is a difference of 7,140 MJ (1, 980 kWh), a reduction of 27%. These figures do not include space or water heating.

Notes From Homeowner @ System Operation:

The wind generator needs to be shifted from its current position, as the trees have grown up around it. A load dump shunts power to other functions when the batteries are full. In the spring, a heating coil is run under seedbeds in the greenhouse, and in the summer a heavy-duty ceramic resistor is used (water could be heated with this extra load in the summer). Heavy-duty wire from the microhydro to the house reduces the power loss.

Homeowners’ reasons for going off-grid:

One person in this household has lived off-grid for 20 years, as a conscious lifestyle choice. The other member moved into this off-grid house eight years ago.

Homeowners’ observations on living off-grid and energy use patterns: