Research Highlights

Energy Use Patterns in Off-Grid Houses – Case Study #2: Gulf Islands, BC

House Description

A 17.7 x 7.3 m (58 x 24 ft.) bungalow on an open crawlspace with a 5.5 x 7.3 m (18 x 24 ft.) second storey addition. The house was built in 1960 and barged to its new island site in 1981 as a retirement home for a couple. The primary axis is N-S, with view windows to the west. A wood stove and a cookstove (9 cords softwood/yr) heat the house.

Thermal Envelope Summary

AC/H@50 Pa: 17.28 Walls: 2x4 framing w/RSI 2.1 (R12) (+/- 25% crawlspace RSI 1.4/R8) Ceilings: RSI 2.1 (R12) Windows: single pane, sashless sliders, thermopane patio doors and one upper window Doors: solid wood with storm door

System Description

The power is supplied by a 200 W output PV array (4-50 W panels) which was installed in 1994. A 5 kW diesel generator is used as backup. Energy is stored in a bank of 10, Canadian National “Performer” batteries, wired to produce 12 VDC (1200 Ah). A Trace DR2401 Inverter/ Charger is used to produce 120 VAC. The original power system to this house was the 12 VDC diesel genset with propane and kerosene for refrigeration, cooking and some lighting. The genset was kept to backup the PV system. The original wiring in the house was for the 12 V genset system. After the PV was installed, wiring for new AC loads was added. The cost of the system (with the genset system) was $7,000 CAD.

System Performance

The load on the system includes lighting, water pump, vacuum, washing, machine dishwasher microwave, computer, two small TVs (AC/DC) and several small appliances, as well as an air compressor, table saw and radial arm saw in the workshop. The total possible daily load on the system is approximately 14 MJ (4 kWh), while the actual load is estimated to be 7 MJ (2 kWh). Propane is the energy source for the refrigerator and range (one pilot kept on, light pilot when oven is in use), and a much-used barbeque. There is a propane clothes dryer in the house, but it is not hooked up. Approximately 870 L of propane is purchased annually. The running of the genset, which is housed in a small shed to the east of the house, has been logged since 1996. In four years, the homeowners have only required the genset to run for 540 hours, which averages to less than 1/2 hr/day. However, the typical usage pattern is periodic equalization of the batteries, which means the genset is often not used for months at a time, depending on the season.

The actual electrical use in this house is about 2,700 MJ (750 kWh) annually. When the kWh equivalent of the propane appliances is included in the actual energy use for this house, the figure is approximately 23,300 MJ (6,470 kWh). The average annual lighting and appliance use for this vintage house in British Columbia (1981) is 21,450 MJ (5,960 kWh), with water heating adding another 22,900 MJ (6,360 kWh). It is estimated that wood heat accounts for 25% of cooking and water heating. Allowing for a corresponding reduction in baseloads, the total average annual baseload is 33,270 MJ (9,240 kWh). There is a difference of 9,970 MJ (2,770 kWh), for a 30% reduction. These figures do not include space heating.

Notes From Homeowner @ System Operation:

Two “sunpipes” were installed in the kitchen (which is on the east face of the house) to increase the daylighting potential in the afternoon/evening. Initially, the cooking was done on the woodstove and in a large microwave. However, the owners found that the microwave was noisy and the inverter didn’t supply enough power to the microwave. A propane range was installed and the microwave use reduced. The battery bank is typically charged before noon on clear days, and the homeowners switch over to using just the available PV when this happens.

Homeowners’ reasons for going off-grid:

This is a retirement home. The homeowners had bought the diesel genset as the affordable, convenient option. Their son gave them the PV system. The homeowners enjoy the quiet operation of the PV system and the reduced fuel costs associated with using renewable energy.

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