Energy Use Patterns in Off-Grid Houses: It's All About the Energy Budget, Right?
I grew up on the West Coast of Canada, and I have had the good fortune to spend lots of time in and around the Gulf Islands, the Sunshine Coast, and Tofino. Earlier in March, an article in Huffington Post (Canada) featured the off-grid community of Lasqueti Island – 400 people living with site-generated power. The article was based on a 2012 episode of Global News’ documentary series 16x9 that was included in an article published this year on True Activist.
The documentary focuses on the some of the fringier of the fringe elements on Lasqueti. I had the opportunity to spend some time there back in 2001, doing field research for a project for the Canada Mortgage and Housing Corporation. I’m happy to tell you that a substantial portion of the community who live in homes with all the modern conveniences, who commute from the island to ‘regular’ jobs, who live a lot like the rest of us. Except of course, they live in an obviously magical place full of ferociously independent and inventive people.
For this project, I travelled across the country and interviewed 12 off-grid homeowners. It was the beginning of the overt discussions in the building science world about net zero energy, and so, what I was investigating was the energy use patterns in off-grid households, how they compared to grid-connected households, and what observations we could pull out of them that could influence change.
I interviewed people on Lasqueti and Salt Spring Islands, southeastern Manitoba, New Brunswick, Prince Edward Island, and Nova Scotia. Across the 12 houses, system size and components varied wildly, as did the lifestyles and overall energy use. The reasons for going off-grid were as varied as the households: political, environmental, financial. Here is a link to the Research Highlight published by Canada Mortgage and Housing Corporation.
There were some constants across the 12 houses, the primary one being how attuned all members of all households were to the electricity they were using. It became clear that living in an off-grid house required an energy budget that was no more or less of a burden than a money budget. You need to define a good budget, one that works within your means, and then you need to stick to it.
Patterns of energy use came clear as well, with some modifications to lifestyle patterns that won’t be too unfamiliar with anyone who has lived in a house with a time-of-use fee structure – move the big users to the time when the energy is cheap. If you’re grid-connected, that means the overnight period. If you’re off-grid, that means when you have a glut of energy. If you rely on PV, for example, it means you use electricity during the day so you don’t deplete the battery bank.
The reduction in energy consumed for electrical use in the off-grid houses varied from 20 to 90% of conventional grid-connected houses. The average energy reduction for baseloads was 44%. Pretty impressive.
Although it was not part of the study, I, of course, could not ignore the building envelope and how it was put together. The energy required for space and water heating in the Manitoba houses was radically low – these were some of the best-insulated houses I had seen up until then, but not so great on the air sealing. On the other hand, the houses in the Gulf Islands were horrifically underinsulated. The New Brunswick and Nova Scotian houses were also fairly well insulated, but only the PEI house and one of the Nova Scotian houses met what I would consider to be a decent level for air sealing, around 2.5 ACH @ 50 Pa. Several of the houses clocked in at over 10 ACH @ 50 Pa.
There was a clear disconnect between the mindfulness around the creation of an electrical energy budget and the amount of thought given to an energy budget for space and water heating. While the Manitoban homeowners (5648 HDD18°C/US Climate Zone 7) reported using 3-4 cords of wood a year for both space and water heating, the Nova Scotian houses (3790 HDD18°C/US Climate Zone 5) reported using 4 cords of wood each for space heating alone. Two Gulf Island houses (4002 HDD18°C/US Climate Zone 5/6) also reported 3 cords of wood for space and water heating, but the other two reported 5 and 9 cords. To be fair, the house sizes are different, and the study didn’t take into account what kind of wood was the primary fuel – softwood like that found abundantly on the Gulf Islands doesn’t have as much heat value in it as the hardwood of Manitoba or the Maritimes.
A quick calculation:
Manitoba, space heating only (3/4 of total heating load) = 50 to 66 million Btu
Nova Scotia space heating only = 88 million Btu
Gulf Islands, space heating only (3/4 of total heating load) = 40 to 122 million Btu
(Assumption: hardwood at ± 22 mill Btu a stacked dry cord, softwood at ± 18 mill Btu a stacked dry cord.)
Some of houses on the Gulf Islands and both of the Nova Scotia used as much or more energy for space heating as the Manitoba houses for space and water heating combined. Ironically, the energy use patterns in these ‘alternative houses’ show a fairly clear representation of the impact of thermal envelopes on space heating energy consumption by region in conventional houses across Canada, even though these houses were built in the 1990s or earlier. This isn't the first time I've said it, but you could drop a typical market-value house built for the Manitoba climate in SW British Columbia and heat it with a hair dryer.
*as per ASHRAE 90.1 International Climate Zone
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