Solar Greenhouse Heat Sink

The Greenhouse provides gardeners in a cool climate such as that in the UK the opportunity to grow a wider range of fruits and vegetables and also to extend the growing season. To maximise the benefits of a greenhouse some form of heating is required to guarantee a frost-free winter, and warm nighttime temperatures.

Greenhouse heater powered by mains electricity

In this article we will look at how solar power can be used to keep a greenhouse warm in an environmentally friendly manner as an alternative to the expensive to run paraffin, oil, and electric heaters designed for greenhouse heating.

Greenhouse Heatsink

During the first series of BBC2’s It’s Not Easy Being Green, Dick Strawbridge put together an elegantgreenhouse heating system using a 10 Watt PV Solar Panel, a 12V battery, a small fan, some PVCwaste pipe, and 1 cubic metre of crushed glass.

Dick Strawbridge and a Solar Panel used to power PC fan in a greenhouse heatsink system

The aim of the greenhouse heatsink is to keep the greenhouse warm at night, and also to keep the greenhouse from getting too hot in the day.

Making a Greenhouse Heatsink System

Pea gravel can be used in a greenhouse heat sink

A hole – the bigger the better, but ideally 1 metre wide and deep – is well insulated (using polystyrene and foil) and filled with anything through which air can pass which stores heat. Dick Strawbridge used crushed glass, however pea gravel (available from builders’ merchants and pictured above) can be used instead as can small pieces of metal, small recycled filled bottles of water, fire bricks, etc.
Note that any material which feels cold to the touch will work well as a heatsink/heat store.

12V PC fan used to power greenhouse heatsink system

The solar panel charges the battery which in turn drives a small recycled PC cooling fan (shown above) 24 hours per day. The fan sucks air in from the top (apex) of the greenhouse where the air is hottest and pumps it through the 38mm standard PVC waste pipe into the base of the heatsink hole. The hot air then rises through the heatsink warming the heatsink material and cooling the air which emerges through a vent (e.g. an old chimney pot or waste pipe) and into the greenhouse.

Greenhouse heatsink system plans

At nighttime the now cool air at the top of the greenhouse is pushed through the now warm heatsink heating up the air and cooling down the heatsink material. This warm air then passes through the vent into the greenhouse where it helps to keep up the temperature.

More Information

For more information about putting together a solar powered greenhouse heatsink system, take a look at our new article Greenhouse Heatsink Connection Diagram. There we look at how you go about choosing the solar panel, battery, and fan, and how to connect everything together for a safe, efficient, and reliable system.