Research Highlights

Energy Use Patterns in Off-Grid Houses – Case Study #5: Gulf Islands, BC

House Description

A 9.1 x 12.2 m (30 x 40 ft.) 1 1/2 storey house on an open crawlspace was built in 1991, on the high side of a steeply sloping south-facing site with excellent solar access and winter wind protection from tree cover at the top of the mountain. An airtight woodstove provides space heat (3 to 4 cords wood/year, unless winter holiday taken, then 2 cords, primarily arbutus) for the single occupant (and guests).

Thermal Envelope Summary
AC/H@50 Pa: 15.14
Walls: RSI 3.5 (R20)
Ceilings: RSI 3.5 (R20)
Floors: RSI 2 (approx) (R12)
Windows: thermopanes
Doors: solid wood

System Description

The power is supplied by a 360 W output PV array (6-60 W panels) and a seasonal 240 W microhydro system (runs November through May, 24 hr/day) from a source 0.4 km from house. A propane-converted generator is used for seasonal backup. Energy is stored in a bank of 6, 85T13 batteries, wired to produce 12 VDC (1,200 AH). An inverter produces 120 VAC, and the whole house is wired for standard AC lights and appliances. The system cost approximately $15,000 CAD.

System Performance

The load on the system includes 120 VAC lights, water pump, washing machine, vacuum cleaner, a computer, laser printer and modem (heavy use for several hours a day), a cell phone, a stereo, two radios, TV/VCR, and small kitchen appliances. The total possible daily load is approximately 11 MJ (3 kWh), while the actual load is estimated to be 6 MJ (1.6 kWh).

Propane is the energy source for the fridge, range, water heat and generator. Approximately 1,300 L of propane is purchased annually. The genset runs regularly September through November during the shift from solar to microhydro, and sometimes on winter evenings when the homeowner is working late on the computer.

The actual electrical use in this house is about 2,080 MJ (580 kWh) annually. When the kWh equivalent of the propane appliances is included in the actual energy use for this house, the figure is approximately 23,680 MJ (6,580 kWh). The average annual lighting and appliance use for this vintage house in British Columbia is 24,500 MJ (6,810 kWh).Water heating accounts for a further 22,900 MJ (6,360 kWh), for a total of 47,400 MJ (13,170 kWh). There is a difference of 23,720 MJ (6,590 kWh), a reduction of 50%. These figures do not include space heating.

Notes From Homeowner @ System Operation:

A load dump shunts excess power to two heat coils in the bathroom; grow-lights are used during the winter to absorb power as well as grow plants. The generator is also frequently required in the summer for early morning garden watering, as the sun doesn’t hit the PV until mid-morning because of the surrounding trees and the slope of the hillside. Batteries are typically full by 1 p.m., year round. The only limitation is the water pump can’t be run at the same time as the printer or the vacuum cleaner.

The microhydro provides continuous 20A service at the house, over 0.4 km of 110 cable from the end of the driveway, which is stepped down to 12 V for the batteries and then stepped back up again through the inverter for household use. There is a problem with the microhydro system when too much water flows down the hillside, bringing rocks with it which pile over the intake valve. The site is such that the intake valve cannot be set into a more protected area.

Homeowners’ reasons for going off-grid:

The homeowners knew about PV before buying the land. Fell in love with site. Would have cost $1/2 million to bring in- grid connection. Reread Harrowsmith and gathered information from technical manuals for six months before beginning construction. Thought of using propane for lighting as well, but needed to run the computer and didn’t feel comfortable with the generator for hours at a time, so went with the PV/microhydro system.

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