This is clearly not sustainable in a world aiming for net zero emissions by 2050, which the IEA estimates will require the share of clean heat technologies from heat pumps, district heating, renewable and hydrogen to more than double to 50% of sales by 2030.
Governments are pursuing different strategies to decarbonise heat. Heat pumps are already in widespread use globally, though met only 5% of residential heat demand in 2019, IEA figures show. Sales figures show that the construction sector is responsible for most heat pump technology purchases, meaning the majority of heat pumps are being installed in new buildings.
For example, in the US, the share of heat pump sales for newly constructed buildings is near 50% for new multi-family buildings. The EU market is expanding quickly, with around 1.3m households purchasing a heat pump in 2018 – France, Italy and Spain are responsible for half of all sales in the bloc.
Hydrogen is not yet used to heat homes and commercial buildings, though countries including the UK, Australia, Japan, Canada, the US, Italy, France and Germany are investigating its feasibility. In Scotland, a project in Fife on the east coast could be the first in the world to see hydrogen used for heating across a whole neighbourhood – hydrogen boilers are being fitted in 300 homes, in a government project due to go live from 2023 and run for four and a half years.
Uses renewable energy electricity to power electrolysers that split water into hydrogen and oxygen. Blue hydrogen is the same, but uses natural gas to power the production process.
The UK has the least energy efficient building stock in Europe. Heating comprises 74% of emissions from its buildings and about 23% of all UK emissions, government data shows. Decarbonising heat therefore poses a huge challenge to the UK, but if successful, it also has the potential to make a big dent in emissions.
In addition to research and development into hydrogen heating such as the Fife project, the UK government is planning to use heat pumps to decarbonise buildings. A detailed policy for heat pumps is yet to be revealed, but the government’s Ten-Point Plan outlined ambitions to accelerate installation of heat pumps from the current rate of around 25,000 a year to 600,000 a year by 2028.
There are pros and cons to both technologies, explains Stephen Richardson, director of the European Regional Network at the World Green Building Council. “The main advantage of hydrogen is that it does not require significant changes to equipment inside the building, using boilers very similar to those that currently burn natural gas and pipes and radiators staying the same,” he says.
Richardson believes this could make it more acceptable to the public compared to heat pumps, which require the installation of a unit outside as well as bigger radiators or underfloor heating, since water in the system will be heated to a lower temperature.
However, hydrogen is only zero carbon if it is produced using renewable energy. This has caused many to question the validity of the UK’s strategy – plants to produce hydrogen from renewable generation such as offshore wind farms and supply chains to distribute it are being planned but do not yet exist.
Heat pumps take heat from the air, ground or water and boost it to a higher temperature using a compressor, and then transfer the heat to the heating system in a building. They work a bit like refrigerators in reverse.
Even the gas industry, which is working on research and development with the government and hydrogen producers, does not foresee significant production of so-called ‘green hydrogen’ till the mid-2040s, according to Stella Matthews, hydrogen development manager for Northern Gas Networks. Until then, ‘blue’ hydrogen produced using natural gas, will be needed, she says.
“We will need to rely on blue hydrogen initially, but as new technologies come forward to produce green hydrogen, eventually it will take over, probably by the mid-2040s. We’re aware that we do need both, because green hydrogen can’t scale up enough in time,” she says.
Leading energy experts recently wrote to the UK government to caution against its focus on hydrogen. “Truly zero emission hydrogen is essential, but it does not yet exist at scale. We cannot expect hydrogen to have an impact on emissions or jobs within the next decade. Developing a hydrogen economy is a long and uncertain path forward, yet climate science shows us we need to act today to reach our net-zero goals,” it states.
Heat pumps can already deploy at scale, making them far more suitable for decarbonising home heating, while the limited amounts of green hydrogen that can be produced in the near-term should be prioritised for industrial uses such as the production of cement and steel, where emissions reductions are far harder, they added.
Heat pumps are also far more efficient than hydrogen heating could be, since they do not suffer losses in the pipes, according to many experts. “I’m deeply sceptical of using hydrogen at scale for heating, it will take a lot longer,” says Jan Rosenow, principal and European programme director of the Regulatory Assistance Project (RAP), a global thinktank on power system strategy.
“You need five times more electricity to generate one unit of heat from hydrogen compared to just feeding electricity directly into a heat pump, so that means five times more renewable energy capacity, land, and raw materials, which makes it far more expensive and much more difficult to achieve very high levels of penetration,” he says.
But the UK gas industry is adamant that it can improve the efficiency of its networks. Existing metal pipes, some of them 100 years old, have been undergoing upgrades to plastic for the past 20 years, in a programme that is due to continue to 2032, says Matthews. “By 2035, 80% of the network will be plastic – the benefit is that the plastic pipes are much more suitable for hydrogen,” she says.
Northern Gas Networks is currently trialling injecting blends of 20% hydrogen with natural gas at a pilot project in Winlaton, near Newcastle, UK. This is permitted under current regulations, but needs government permission to use 100% hydrogen, she says.
“This would be a quick win that allows production companies to scale up quickly," says Matthews. "Hydrogen producers want to generate 5GW by end of the decade, but they want to know where they can put it into the network. We’re not regulated to make that change yet – but once we are, we think that we’ll be inundated by requests from producers of both green and blue hydrogen.”
Whichever heating technology is chosen, buildings will need energy efficiency upgrades. “It’s often an argument that’s applied to heat pumps, but that’s unfair, it’s absolutely needed for hydrogen as well,” says Richardson.
In the end, there will probably be a role for both heat pumps and hydrogen, Richardson believes. “There are some buildings where it’ll be hard to make them more energy efficient, and in those cases a hydrogen boiler might be the best way to get off natural gas,” he says.