Nothing beats a challenging issue for encouraging creative solutions. Aiming to live in an off-grid home with regards to electricity is a stretch goal that we set because anything else seems so “been there, done that”. How do we know it’s a stretch goal? Basically, we suspect the fact that it’s not common practice in an urban setting and the way people raise their eyebrows when we mention the idea are clues to challenging times ahead. Still, where’s the fun is just whacking a few solar panels on the roof and still being tied to the electricity grid?
With that objective set in the project philosophy, David suggested we first consider our electricity consumption. How much do we actually need for cooking, lighting, heating in winter, cooling in summer, etc? There will also be the demand imposed by our Nissan LEAF. A full charge will take 15 kW from whatever electrical supply system we end up with. Having a limited supply of a resource (ie similar to a farm house operating solely on tank water) means watching consumption far more closely than someone tied to an apparently inexhaustible supply.
Essential to make good use of passive design elements
Minimising electricity consumption starts with maximising passive design options in the house. No matter what we do about electricity supply in the final design, ensuring we do all we can to take advantage of naturally available energy sources will put us in a good position. Getting as much natural light into the house during daylight hours reduces the need for powered lighting. Excellent insulation helps to limit the need for extra heating and cooling. Providing good ventilation should limit the need for artificial, powered cooling in summer.
Explore alternatives when electrically powered devices are required
At this stage of the design, we are keeping our minds open to emerging technologies that might meet the need of a household that required an ultra-low electricity demand to provide a service. An example would be heating. In the middle of a cold Melbourne winter, there could still be the need for some warm air top-up to keep the occupants comfortable. Good passive design should delay the time when something extra, like underfloor heating, is needed to keep the internal temperature within a comfortable range. After that, the heating would just cut in and out to hold the house in the desired range, relying on insulation to limit the energy loss.
But where does the energy come from to gently heat the floor? David came across an idea that is being tested overseas – seasonal thermal energy storage (STES). It’s basically making hay while the sun shines. One way of doing this is to use solar collectors to heat a large volume of water that is stored underground (insulated). During summer, the temperature builds up to 80 degrees C or so. Some designs have this water storage available for hot water in the house. Others have it purely available for the winter months when it can be used as the energy source for underfloor heating. The bulk temperature in the tank gradually falls over winter but then is warmed up again during the following months. It is attractive to think that the summer sun would be heating our home during winter.
Scandinavian Homes are running a detailed trial of this technology in a house in Ireland. The website contains some reports on their systems and information about the trial results.
No decisions yet on whether or not we will go this way. However, this shows there are lots of ideas floating around, probably just outside the mainstream technologies.