Over eight years the couple, from Twickenham, southwest London, have spent more than £22,000 installing a solar thermal system to heat their water; loft, wall and floor insulation; low-energy LED lights; radiator foils; thermal blinds; and a more energy-efficient boiler.
They also installed dual flush toilets and a water butt to save water.
Energy bills for their two-bedroom Victorian terrace have fallen to nothing in most years.
Gallop, a physicist, uses an energy monitor he bought for £10 but which is now available for free from energy suppliers.
He says the best savings come from low-cost or even free measures. “One of the best ways to save is simply to be more aware of what energy is being used.
“Many people have no idea how much energy different appliances use. Once we found out, it was easy to work out the best ways to cut costs.”
Their biggest saving was made by turning off an electric bath rail, costing £256 a year to run. “It was installed when we redid our bathroom, but we had no idea how much it was costing us,” said Gallop.
Turning off appliances rather than leaving them on standby saves £32 a year. Turning the washing machine down from 40C to 30C cuts another £16 from their bills.
The most expensive purchase was the solar electricity and heating system, which cost £9,350 in 2005, although they received a government grant of £4,250. The grants were aimed at encouraging development of Britain’s renewable energy industry but are no longer available. Instead, anyone producing green energy today can receive payments for each unit of power produced.
The most cost-effective measure was a central heating thermostat. The £35 device, fitted in 2006, saves £105 a year, covering its cost in four months.
Gallop said: “Our main aim has been to reduce the carbon footprint of our house, although the measures have also made it more comfortable.”