Research Highlights

Energy Use Patterns in Off-Grid Houses – Case Study #3 : Gulf Islands, BC

House Description

A two-storey 7.6 x 15.2 m (25 x 50 ft.) house with walkout basement. The family of four moved in 1997. A 7-sided two-storey passive solar greenhouse wrapped around the SE corner is the main source of space heating. A vacuum tube collector and tank with integral heat coil supply most of the hot water. A combination wood furnace with water coil and cookstove built around a massive central chimney heat the house and the water (3 cords wood/yr) when there isn’t enough solar gain. The high mass construction includes a 100 mm concrete slab on the lower floor and 50 mm concrete overpour on the main floor. The lower walls and north facing stairwell are built of stone with an interior insulated stud wall. The remaining walls are standard 2x6 framing.

Thermal Envelope Summary
AC/H@50 Pa: n/a, as one window and a door were not in place
Walls: lower stone walls w/vermiculite, RSI 2.4 – 3.2 (R14- 18), upper walls 2x6 framing, RSI 3.5 (R20),
Ceilings: RSI 3.5 (R20)
Windows: thermopanes in wood frames
Doors: solid wood

System Description

The power is supplied by a 620 W output PV array (8-60 W and 4-35 W panels); a 1,000 W Whisperlite wind generator and a 25 W microhydro system which runs seasonally (November through May) from a pond overflow. A 3.5k W gas generator acts as backup. Energy is stored in a bank of 6, P23 golf cart batteries, wired to produce 12 VDC (1,250 Ah). A Brutus pure sine inverter/charger is used to produce 120 VAC. The lights in this house are all 12 VDC fixtures, as is the fridge. The remainder of the wiring is for 120 VAC appliances. The system cost $10,000 CAD to install.

System Performance

The load on the system includes 12 VDC lighting and fridge, 120 VAC water pump, built-in vacuum, an energy efficient front-loading washing machine, microwave, two computers (one PC and one laptop), a fax machine, a stereo, a TV, an air cleaner (Bionaire type) and several small kitchen appliances as well as music equipment in the studio. The total possible daily load on the system is approximately 38 MJ (11 kWh), while the actual load is estimated to be 20 MJ (6 kWh). Propane fuels the cooktop and oven. Approximately 250 L of propane is purchased annually. The genset, which is housed in a small shed to the north of the house, is run once a week for one to four hours (approx. 4.5 L gas @ 4 hrs). Clothes washing, vacuuming, flour grinding or other high-load activities are done when the generator is on.

The actual electrical use in this house is about 7,380 MJ (2,050 kWh) annually. When the kWh equivalent of the propane appliances is included in the actual energy use for this house, the figure is approximately 17,560 MJ (4,880 kWh). The average annual lighting and appliance use for this vintage house in British Columbia is 24,500 MJ (6,810 kWh). There is a difference of 6,940 MJ (1,930 kWh), a reduction of 28%. These figures do not include space or water heating.

Notes From Homeowner @ System Operation:

The installation of the PV on the roof has turned out to be awkward for maintenance. Another two 75 W panels are to be installed within the coming year.

Homeowners’ reasons for going off-grid:

Homeowners wanted to live on this remote island, it was never an option to have a generator “plunking away". There was a long-standing desire to live off-grid “as if we were on grid”. The result is an interesting juxtaposition of low-tech and high-tech solutions (passive solar and wood space and water heating with PV/wind/microhydro system; low-tech microhydro system built specifically for the site; modified 12 V fridge on timer).

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