Research Highlights

Energy Use Patterns in Off-Grid Houses – Case Study #7: Southern Manitoba

House Description

House #6 and House #7 are located on the same farm, which has seven offgrid houses, five of which are permanently occupied. All the systems on the farm are small, but very efficient.

House #7 is a 15 x 4.9 m (60 x 16 ft.) one-storey house with a sleeping loft, built on a pole foundation in 1980. The house has been occupied by one person for several years. The house has good solar access and some protection to the north. An Enterprise cookstove provides cooking, space and water heat (3 cords wood/year). The original part of the house (a 6-sided structure of approximately 28 m2 /300 sq. ft.) is 2x4 framing. The newer “wing” additions to the west (4.9 x 3.7 m/16 x 12 ft.) and the east (3.7 x 3.7 m/12 x 12 ft.) are 2x6 framing. A 4.9 x 1.2 m (16 x 4 ft.) greenhouse on the west addition helps to keep the living space comfortable, with a site-built venting system operated by a temperature sensor and a small 12 VDC motor. There is a cold room with the same operating system as House #6.

Thermal Envelope Summary
AC/H@50 Pa: 5.63
Walls: Original, RSI 2.1 (R12);
Additions, RSI 3.5 (R20)
Ceilings: RSI 3.5 (R20)
Floors: RSI 3.5 (R20)
Windows: double pane/combination
Doors: solid wood

System Description

The power is supplied by a 100 W output PV array (2-50 W panels). Energy is stored in 2, 6 V RV batteries, wired to produce 12 VDC (100 Ah). All lighting is 12 V, several of which are site-built fixtures which use 3 W automotive bulbs. A 150 W Powerstar modified sine wave inverter produces 120 VAC for a few small appliances. The system cost approximately $1,500 CAD.

System Performance

The load on the system includes 12 VDC lights, small motors to operate the venting systems in the greenhouse and cold room, as well as a fan for a food dryer in the greenhouse, a water pump and a stereo. Small appliances run off the inverter: blender, shaver, glue gun and soldering iron as does a 22 W fluorescent fixture in the “summer kitchen” (screened-in area where food is processed during harvest season). An electric lawnmower is charged off this system during the summer. A 10 Ah motorcycle battery in the summer kitchen powers the washing machine. The total possible daily load is approximately 2 MJ (0.5 kWh), while the actual load is estimated to be 0.7 MJ (0.2 kWh).

The actual electrical use in this house is about 260 MJ (70 kWh) annually. The average annual lighting and appliance use for this vintage house in Manitoba is 20,850 MJ (5,790 kWh). There is a difference of 20, 580 MJ (5,720 kWh), a 99% reduction. These figures do not include cooking, space or water heating.

Notes From Homeowner @ System Operation:

The system is designed to carry the house through several short days of poor solar gain during the winter months, resulting in too much power for the rest of the year. The largest load on the system is the water pump, which runs for two hours a day, using 30 W. Water is taken from this container and used in the house (heated on the cookstove) or in the garden. The summer watering needs of the garden are the largest draw on the system, matched well with the availability power from the sun. Sauna replaces showering or bathing.

Homeowner’s reasons for going off-grid:

Homeowner chose to off-grid, simplified living because of political and environmental convictions. The homeowner is one of the original co-operants on the farm, established in the late 1970s. This system was originally on a manual tracker, but there was not enough difference in power generation to warrant the effort to move the array.

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