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How Pumping Rivers Could Heat Thousands of Homes

The UK wants heat pumps to help meet its renewables targets.
The River Thames. Image: Shutterstock/Philip Bird

Think sustainable energy and you probably think of a wind turbine on a hill, or maybe a solar panel on a roof. You probably wouldn't picture a heat pump. You probably don't know what one looks like, because you've probably never seen one.

Heat pumps in general have been used in the US, Japan, and some European countries, but they've never really taken off in the UK. That's something the government hopes to change. It published a map of England that shows how rivers and estuaries could used to supply water-source heat pumps and heat domestic buildings in some of the areas with the greatest demand.

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The attraction is obvious: It's a low-carbon alternative to the conventional gas or electric heating systems used in British homes, and the country is committed to getting 15 percent of its energy from renewable sources by 2020. According to the Department of Energy and Climate Change (DECC), which put out the map, most gas consumed in the UK is used for heating. It's cold over here, after all.

Water source heat pumps work by taking latent heat from the sun that's naturally stored in the water and boosting it so it's enough to heat a building or provide hot water. An eco-friendly development in South London already uses the technology to heat its apartments, and earlier this year an 18th century mansion started using a pump system powered by the sea to replace its previous reliance on thousands of litres of oil a day.

"We want to give power to communities to take control of how they produce the energy they use and encourage action by local authorities, private developers and groups to establish their place in the UK's energy market," a DECC spokesperson said. "We also support the development of a clean, renewable energy industry that will make us less dependent on imported fossil fuels."

Jonathan Busby, a renewables expert at the British Geological Survey who isn't involved with the project, told me that the UK's late interest in heat pumps is probably down to oil prices as well as increasing concern over carbon emissions. "Mainly that delay was caused by the fact, of course, that we had cheap North Sea gas," he said.

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The UK's resources are of course running lower now, and the country is keen to reduce its dependence on imports (though it hasn't exactly been pushing the envelope in renewables yet).

The new map shows how much potential heat is up for grabs and is aimed at developers who might use it for large-scale initiatives; it's overlaid on a map of heat demand to show that some of the cities with the highest requirements, like London, could use their natural resources. "A water source heat pump can be installed in any water source but if the flow rates are not sufficiently high, the amount of heat supplied could be an issue," said DECC.

In London, the map shows a fast-flowing stretch of the River Thames capable of producing over 10,000 GWh of heat a year. That's a significant chunk of the city's total demand, which the mayor's office calculates as 66,000 GWh/year. The official announcement said each heat pump on the identified waterways could provide heat and hot water for 400-500 homes.

Not everyone would be able to make use of heat pumps using the rivers however, as they do have their limitations. Busby pointed out that it's difficult to transport heat, so it depends how close you are to the source. And heat pumps do use some electricity to run, but the DECC office said they're still a very efficient source, as according to the Renewable Energy Directive any heat pump has to produce 2.9 units of energy for each unit of electricity it uses.

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The biggest barrier is perhaps the infrastructure on the other end, in the buildings you want to heat. The problem is that many British buildings have pretty old heating systems that just aren't appropriate for heat pumps.

"You need a well-insulated building so your heat loss is at a minimum and also, because the heat coming out of a ground source heat pump is at a lower temperature than you'd have, let's say, from a fossil fuel boiler, you tend to have what's called a low-impact heating system," said Busby. That includes things like underfloor heating and oversized radiators, which can easily be included in new-builds but make retrofitting more costly.

To really cut back on fossil fuel heating systems, different technologies will need to be adopted where they're most appropriate.

The government is encouraging efforts with its Non-domestic Renewable Heat Incentive, which offers a financial incentive for businesses and organisations looking to invest in heat pumps as well as other renewables like biomass equipment and solar thermal collectors.

Busby reckons the industry is now watching and waiting to see if renewables tariffs are set at the right price to attract investment. "If it doesn't, the government may have to think again," he said, and pointed out that changes in regulations could also spur further change.

DECC said its next move is to develop project exemplars to prove the reliability and cost-effectiveness of the river-powered pumps, and that it will release a more detailed version of the map later this year.