Research Highlights

Energy Use Patterns in Off-Grid Houses – Case Study #6: Southern Manitoba

House Description

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

House #6 is a 4.9 x 6.7 m (16 x 22 ft.) 1 1/2 storey house on a pole foundation built in 1995. Four people occupy the house (two are children). The house has good solar access and some protection to the north and the NW from trees and the screened porch/insulated cold room. An Enterprise cookstove provides cooking, space and water heat (4 cords wood/year). The house was built from recycled wood, the double stud walls allow 200 mm (8 in.) of fiberglass insulation. A solar cooker is also used for baking and slow cooking.

Thermal Envelope Summary
AC/H@50 Pa: 7.22
Walls: RSI 4.9 (R28)
Ceilings: RSI 5.6 (R32)
Floors: RSI 3.5 (R20)
Windows: triple pane, no openers (adjustable vents for fresh air)
Doors: solid wood

System Description

The power is supplied by a 125 W output PV array (6-40 W panels). Energy is stored in 2, 6 V golf cart batteries, wired to produce 12 VDC (220 Ah). All lighting is 12 V, several of which are site-built fixtures which use 3 W automotive bulbs. A 150 W Statpower 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, water pump, two small motors to operate the vents in the cold room, washing machine (not used much), vacuum cleaner (not used much), a cordless phone (fitted with an energy saving feature) and a stereo. Small kitchen appliances run off the inverter: blender, mixer and sewing machine. The total possible daily load is approximately 2 MJ (0.5 kWh), while the actual load is estimated to be 1 MJ (0.3 kWh).

The actual electrical use in this house is about 330 MJ (90 kWh) annually. The average annual lighting and appliance use for this vintage house in Manitoba is 20,450 MJ (5,80 kWh). There is a difference of 20,120 MJ (5, 590 kWh), a reduction of 98%. These figures do not include cooking, space or water heating.

The cold room, a large walk-in cooler/pantry which replaces a fridge, takes up the NW corner of the house. It is completely insulated and isolated from the rest of the house. It is kept at a constant temperature by a sensor that causes an exterior venting system to open when the temperature exceeds 8°C (46°F), allowing cold air in from outside until the temperature drops to 5°C (41°F). An interior venting system opens when the temperature is below 5°C, bringing warmer air from the interior of the house into the cold room. The sensor closes the interior vent when the temperature reads 8°C (46°F). The small 12 VDC motors that operate the venting system run for a few seconds at each opening/ closing sequence, drawing hardly any discernible load.

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 homeowner ran out of power on the original 50 W system once during a 3-week cloudy spell when one of the children was a newborn. The system was boosted with a 20-minute charge from another off-grid source on the farm. The largest load on the system is the water pump, which is the motor out of a windshield wiper assembly. This 12 V motor runs for about 1 hour a day to fill a 225-L (50 gal) container. 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.

Homeowner’s reasons for going off-grid:

Homeowner chose to move from an urban environment to a rural one. The choice to be off-grid came from political and environmental convictions.

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