More Heat Than Light – The Argument For Passive Solar Energy Over PV

Why we are using for passive solar rather than PV for the energy capture component within of our seasonal energy storage project.

The EnergyCrowd passive solar project started with a blank sheet of paper. The aim was to create a domestic renewable energy solution that was economically sustainable - without subsided feed in tariffs. Having a background in high technology initial thoughts turned to a set of solar PV panels as the energy capture part of the project. However if you have read the preceding three articles you will understand why the decision went another way.

The most cost effective domestic energy efficiency technology is one of the simplest – it is called insulation. If you want the largest reduction in your energy bills for the least outlay you should look towards loft insulation, cavity wall insulation, draft exclusion and double-glazing.

Focussing on that last one; double glazing. At seven thirty this morning there was over 500 watts/m² landing on the 1.2 by 2.4 m² window in my room. Just over 300 watts/m² made it through the double gazing into the room itself. The four windows on that side of the house where bringing in a total of 3.2kw of solar energy - and within an hour, with the sun up a little higher, the total was 4.2kw. The arrival of energy efficient glass, that stops heat energy escaping, has turned windows into solar panels.

On the south west side of the house there is a conservatory with an effective area, as far as solar energy capture is concerned, of 12 m² during the autumn. Above this we have built a solar chimney with an area of 8 m². This afternoon there are 550 watts/m², a total of 11kw entering these two structures – both of which have been built using energy efficient double-glazing.

So here we have, depending on which way you look at it, a passive solar energy, of an active insulation, system. We have used simple building technology to turn an entire building into a solar panel. The logic of generating heat rather electricity is that the consumer will not be tempted to buy an energy consuming gadget to take advantage of this ‘free energy.’ In addition forty percent of household energy expenditure goes on heating – for households experiencing fuel poverty the proportion is higher. We believe the green energy approach we have adopted goes to the heart of the domestic energy problem in the UK.

The configuration of the system - designed to capture maximum heat in Autumn months - is aimed at meeting the challenge we set out to address. Seasonal energy storage requires that heat energy is captured as near as possible to the date it will be consumed. We are looking at a store that will have a half-life of around 60 – 80 days and will still have some useful heat in it three months after it is first tapped. Quite a challenge: but not impossible.

Of course the passive solar energy capture part of the system has to tidied up and integrated with the heat storage component. One thing that has become apparent is there is too much ‘build’ and not enough ‘install’ – an important consideration given PV mania has robbed the market of labour. To solve this problem we intend to add a component that is quasi-passive and can be fitted as one unit instead of being built as a chimney. Over the summer I visited a number of manufacturers who have technology that fits this bill – so watch this space.

And not being totally down on PV technology we did find a panel was an ideal way of producing the energy needed to drive the small pump we used for circulating hot water during one of our early trials. As the panel only came to life when the sun shone it also saved a little on control circuitry.

Have a good weekend

Peter Kruger

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