What is it? Created by Tom Seppings, a full-time farmer and part-time engineer, the Solaplug is a small device that can be fitted to an old hot-water cylinder to enable it to connect to a solar thermal heating system.

How does it work? The brass head (on which the patent is still pending) allows two smaller heating coils to be inserted into an existing hot-water cylinder. In this way, the solar panel can be connected without disturbing any of the plumbing in the house.

How green is it? Seppings claims the Solaplug can cut heating bills by 15%-20% and reduce annual CO2 emissions by 400kg — the equivalent of flying 1,905 miles. That said, the product is manufactured in China.

How easy is it to install? The plug is designed to allow a solar hot-water heating system to be installed with minimal disruption. An experienced DIYer may be happy to change the immersion heater and connections; otherwise, hire a plumber.

How much does it cost? £239, including postage and packing.

How much could it save? Up to 50% of hot-water requirements in a year — and it is up to 30% cheaper than installing a solar system from scratch.

Where can I get one? Call 01502 716810 or visit solaplug.co.uk.

- I think the “white meter”, or day and night meter, is much overlooked as a less expensive way to reduce the cost of energy. These meters tend to offer a high rate from 6am to 11pm and a lower rate between 11pm and 6am from Monday to Friday, and at weekends. Energy can thus be saved by operating washing machines and dishwashers off peak. My neighbours continue to heat their hot water using a central-heating boiler throughout the year, which is wasteful, as the boiler needs to start and stop many times. Also, energy is used to run the pump.

Mike Hillas, Wiltshire

Do you have any green tips? Or have you used a product featured in this column? Tell us at greenhouse@sunday-times.co.uk

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