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Making the most of passive solar energy

Posted by Tim Pullen on 14 October 2009 at 9:24 am

Using passive solar energy is a matter of design. To put it another way, if you don't design the house to use passive solar energy, it is difficult to use it well. So pretty much the same as any other form of energy then.

What you need is three things; thermal mass (something to absorb the solar heat), a means of getting it around the house and insulation to make sure it doesn’t get out again.

Assuming you have the insulation (if you don’t then you need to deal with that first) you need a means of getting the heat into the house. Solar energy falls most on the south side of the property and large windows (patio doors, conservatory or the like) are a good idea. They will let the heat in, and to some extent amplify it. But generally you don’t want a lot of heat in one spot at one time. And most often you don’t want all the heat when the sun is shining. You want it in the evening when the sun has set.

So you need a means of absorbing the heat which is where the thermal mass comes in. You need something heavy – generally stone, brick or concrete – to absorb and store the heat. The mass needs to be where the heat falls on it, so the floor in front of the patio doors or the wall opposite are the best spots.

While the sun is shining that the whole area will be warmed and the mass will be storing the excess heat. But you will still need to move some of the heat to areas that are not being warmed directly. That generally calls for passive ventilation. A good system will be designed to move air, from the conservatory or the room with the patio doors, to other parts of the house using natural air movement.

Without the thermal mass and the ventilation you will have a hot conservatory when the sun is shining and a cold one when it is not.

In a new build designing the passive solar energy is relatively simple – you may need expert help but it is quite achievable. It can be more tricky in a renovation or refurb. But in essence it needs little more than common sense and a little thought

Photo by the couple next door

The author: Tim Pullen is eco-editor for Homebuilding & Renovating magazine, author of Simply Sustainable Homes and founder of sustainable property consultancy WeatherWorks.

About the author: Tim Pullen is eco-editor for Homebuilding & Renovating magazine, author of Simply Sustainable Homes and founder of sustainable property consultancy WeatherWorks.

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