How We Heat our Experimental Off-Grid Solar Home 0

Sunshine through south windows  help heat our home

Sunshine through south windows help heat our home

When I tell people that we live in an off-grid solar home I’m often asked if that keeps our home warm enough.  But the solar panels do not heat our home – they only provide electricity.  This is a common misconception.

We do use solar heating, but it’s of a different sort.  It’s called passive solar design and our south facing windows are one of our primary heat sources.  The sun shining full into the room during the winter, when the sun is low in the sky, provides enough heat that we don’t need any other heating source at the same time.  Brick facing on one of the walls, a section of tile flooring and the general mass of the house is warmed up by the sun during the day and holds the heat for the evening after the sun has gone down.

However, the days are short and the nights very long in the middle of a Saskatchewan winter, so we also have an efficient wood stove, with catalytic converter,  as another renewable energy source.  Emissions are minimal and heating is 76% efficient due to the catalytic converter in the wood stove.  We also have a backup radiant propane heater.  It will keep the house at a minimum set temperature when other heat sources are not available.

Most of our south wall is windows

Most of our south wall is windows

Heating the house has been quite economical.  For example, the total cost of propane for 2006 was approximately $700,which includes the annual tank rental of $96.  This is about $58 per month – a very reasonable cost for heating a 1000 square foot home, especially since the propane also heats the water and provides the cooking fuel.  A typical monthly bill for natural gas for a house of comparable size is around $1200 per year, and this does not normally include the cook stove which is usually electric.

An interesting side note is that over the eight months from April to November, when the propane is being used almost exclusively for water heating and cooking, the cost is about $30 per month, (including the cost of the tank rental).  The four winter months average about $90 per month.  This shows that an on demand water heater and cooking with propane is quite efficient.  Incidentally, the 20 lb. tanks used for the barbecue were filled at the same time as the large tank so are included in our overall propane costs.

The south side of our home

The south side of our home

We have also had the opportunity to observe the impact of thermal mass on the passive solar design of the house.  When the house was still under construction during the early part of the winter, it would become so hot on sunny days in November and December that we would open doors or windows to keep the house comfortable.  Inside temperatures topped 26° C, with no contribution from the woodstove or backup heater.   Once the house was completed, the inside temperature was generally 20 – 24° C under similar conditions.  This shows the contribution of solar thermal mass to even out the temperature in the home.  The overall mass of gyproc, hardwood and brick facing absorbed some of the heat from the sun, imparting less heat to the air during the day.  The heat stored in the walls and floors was radiated into the air after sundown.  This effect, combined with the construction methods of the house, resulted in fairly stable inside temperatures even when there was no heat source used in the house.

Passive Solar Performance

Passive Solar Performance

The roof overhang keeps the sun out in summer

The roof overhang keeps the sun out in summer

There is no doubt that passive solar design is the most cost effective way to help heat a home in the winter and moderate the temperatures in the summer.  It costs essentially the same amount to build a passive solar home as it does to build a non passive solar home, but the energy savings can be as high as 70%.  The main reason that passive design is not extensively used is that most people don’t know about it.

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