As we stand on the brink of a radical shift in how we heat our buildings, it’s important to understand the differences between the options being considered – heat pumps and hydrogen being two of them – and their viability as a solution.
On this page, we compare the fundamental differences between the two technologies to show why ground source is superior, safer and more viable and affordable for home heating. The choice is not binary; we also observe how the two approaches could work together to help get the UK to net-zero carbon emissions.
It’s unlikely that zero-carbon hydrogen supplied via a repurposed mains network will be available for the foreseeable future. Hydrogen powered heating is at the trial stage, whereas heat pump technology is ready to be deployed now. This will need policy changes, infrastructure, and investment in the electric grid and in the low-carbon generating technology attached to it, but nowhere near as much as you might think.
WWF worked with experts to explore the potential for hydrogen heating. The research suggests that hydrogen, if available at all, should not be relied upon to heat homes. It is unlikely to be available until the next decade and heating costs to households are expected to be high. WWF recommends that low carbon hydrogen should instead be used in sectors of the economy such as heavy industry, heavy transport and peak power generation.
Green hydrogen is produced through the process of electrolysis, using renewable electricity to split water into oxygen and hydrogen.
Blue hydrogen is produced using Steam Methane Reforming (STR) or Auto Thermal Reforming (ATR), which is extracted from natural gas. The CO2 released as part of the process is captured and stored.
Grey hydrogen is similar to blue hydrogen, where STR OR ATR splits the natural gas into hydrogen and CO2. However, CO2 is not captured – it’s released into the atmosphere.
Pink hydrogen is made via electrolysis, just like green. But it uses nuclear energy as its source of power.
Yellow hydrogen is also made using electrolysis, using only solar power.
What is the efficiency of hydrogen vs. ground source
Efficiency of hydrogen
It has been suggested that using green hydrogen to heat buildings is roughly four times less energy efficient than using heat pumps, which can in fact produce three to four times the amount of energy that it consumes. Although impressive, even this calculation may be modest for ground source.
Gas boilers produce 0.9kWh heat for every 1kWh of energy. Hydrogen heating is by far the least efficient, producing less than 0.6kWh of heat for every kWh of electricity used to make the hydrogen.
Another study suggests that blue hydrogen can be 58% efficient, while ground source heat pumps have been proven to achieve efficiencies of 400%.²
The low efficiency of hydrogen compared to ground source means that a far larger investment in low-carbon electricity generation would be required – put simply this means more solar and wind turbines.
Efficiency of ground source heat pumps
Ground source heat pumps can be 400% efficient, which means they can produce four times the amount of energy they consume from electricity. They do this by using a small amount of electricity to harvest a much larger amount of heat energy locally. The less renewable electricity required, the more likely the fuel costs will be lower for the household. It also means that the electricity production and distribution system has to deliver only a fraction of the energy required.
Efficiency increases even further when individual heat pumps are installed in individual homes and connected to a Shared Ground Array serving the whole street or neighbourhood with ambient-temperature district heat – we call this Networked Heat Pumps.
When sources of waste heat (e.g. data centres, supermarkets, solar, air conditioning) are incorporated, the efficiency of these heat pumps can exceed 600%. The near future of ground source heat pumps could therefore be ten times more efficient at turning renewable electricity into heat energy than using hydrogen.
Cost of hydrogen vs. ground source heat pumps
Hydrogen
When looking at the cost of hydrogen, you must consider all of the costs associated not only with the hydrogen boiler itself, but the investment in the wider network: upgrading the distribution pipework, energy storage and the increased capacity of electricity generation needed compared to ground source heat pumps. This increased capacity will come from sources such as wind turbines, which will also require much more space.
It’s not easy or straightforward to convert the gas network to hydrogen. The production of hydrogen itself creates carbon dioxide as a byproduct, requiring large-scale carbon capture and storage (CCS) technology. CCS has only been demonstrated on a very small scale and will require considerable investment and costs to allow hydrogen to play a major role in the decarbonisation of heat.
There are also hefty costs associated with hydrogen production itself. In cases where hydrogen is extracted from other substances, such as methane, the extra steps involved in extracting the hydrogen would push fuel prices up compared to natural gas.
The case is slightly different for hydrogen produced via electrolysis, which doesn’t create carbon dioxide in the process. The electricity used to power the electrolysis must then be decarbonised via renewable energy generation. The costs for solar and wind power are falling but still need to be accounted for. The low efficiency of hydrogen compared to ground source means that a far larger investment in low-carbon electricity generation would be required.
Ground source
Ground source heat pumps running costs already compete well with mains gas but the installation and infrastructure costs are currently higher. These costs vary depending on factors such as the scale of the installation, available land area and how energy efficient the property is.
Kensa has created an innovative funded offer for developers, housebuilders and social landlords which separates the cost of the heat pump unit from that of the ground array. Kensa Utilities pays for, owns and operates the heat pump infrastructure – the shared ground array, reducing the cost of the installation.
If this underground infrastructure is already provided in a way that mimics the existing gas network, then homeowners could be motivated to replace gas boilers with heat pumps in a phased switchover, subsidised by Government support, paying pay a small annual connection fee. It also means that plumbers could install ground source heat pumps on a neighbourhood scale, without involvement with a ground array, just as they have no involvement in the supply of the gas network.
Ground source heat pumps can also be coupled with smart controls, making use of time-of-use tariffs to shift the heat pump’s consumption to when electricity is cheap and low in carbon. The energy can then be stored, ready to use in line with the household’s usual routine.
Unlike electric heat pumps and heat networks, the feasibility of using hydrogen for clean heat needs further testing and development. The practicalities and cost of safely converting or replacing existing networks and appliances to operate with pure hydrogen need to be fully evaluated.
Business, Energy and Industrial Strategy - Energy white paper: Powering our net zero future
Installation & deployment of hydrogen vs. ground source
Hydrogen
Although it has previously been suggested that hydrogen could flow through the existing gas network – this is not generally considered to be a viable option. Vitally, the greatest obstacle is that there is no proven blueprint for this conversion.
A dedicated study into hydrogen and heat decarbonisation suggests it’s unlikely that zero-carbon hydrogen supplied via a repurposed mains network will be available for the foreseeable future. There are a number of reasons to support this: it could be a major delivery risk to incorporate a new infrastructure for an unproven technology on a large scale and it is unclear who will guarantee and accept liabilities for in-building gas pipework switchover.4 The mass deployment of hydrogen relies on numerous issues being solved – if we wait for the technology to be ready but all of these issues cannot be solved, the delay could be detrimental to the planet.
Without further delay in the journey to decarbonisation, we see a great role for green hydrogen in the drive towards a net zero economy. Decarbonising existing hydrogen use has to be top priority followed by certain industrial uses – following an approach such as Michael Leibreich’s clean hydrogen ladder. One potentially important use can function alongside ground source heat pumps: to produce electricity and low-grade heat when the local or national grid is under strain.
Hydrogen-powered fuel cells or CHP generator produce waste heat which could be connected to a Shared Ground Loop Array. This fuel cell can deliver electricity into the grid around, say, 5-10% of the time in rare cases when wind and solar output is low. As well as this, the waste heat that comes out of the fuel cell can be delivered into the ground array, which improves the efficiency of the heat pumps and reduces electrical demand at exactly the time it is needed.
Rather than competing, the two technologies can in fact work together – with hydrogen improving the efficiency of the ground source heat pump system further and vice-versa. Hydrogen is going to be expensive to make; it makes sense to burn the expensive hydrogen during low renewable generation periods and only support the grid when it really needs it.
Ground source
Heat pumps are ready to be deployed now. Compared to gas, they can already reduce carbon emissions by 77% in properties. As we build more and more renewable electricity generation onto the grid, the carbon savings will continuously improve – and there will be no need to revisit the properties in order to reach net-zero carbon.
In Kensa’s view, the key to the mass deployment of ground source heat pumps is the ground array infrastructure. The low-carbon alternative to traditional district heating, Shared Ground Loop Arrays, can be implemented on a street-by-street basis, mimicking the gas network and connecting to heat pumps in individual homes. An ambient temperature circulates around the distribution pipework at -5°C to 20°C, with each heat pump upgrading the heat to the required temperature for heating and hot water.
This will need infrastructure and investment in the electric grid and in the low-carbon generating technology attached to it, but nowhere near as much as you might think. Grid balancing concepts such as local energy storage, grid-storing batteries and ‘load shifting’, which a ground source heat pump can do when coupled with smart controls, will reduce strain on the grid as more and more heat pumps are deployed.
As for the installation training itself, the skills challenge is surmountable and the skills of gas heating installers are certainly transferable to heat pumps. This is particularly true once you separate out the ground array district infrastructure elements from what happens in the house, in the same way as we currently do for gas infrastructure and boiler installation. All in all, both options present a challenge and change to the way we heat our homes, but it’s certainly worth the momentary disruption that is inevitable in the stretch to net zero.
Carbon emissions of hydrogen vs. ground source
Hydrogen
Although hydrogen won’t emit carbon when used by a boiler, the production of hydrogen itself can emit carbon depending on the production method. For example, blue hydrogen relies on Carbon Capture and Storage (CCS) to capture and store the CO2 produced; the production of grey hydrogen involves releasing CO2 into the atmosphere, and pink relies on electrolysis with nuclear energy as the source.
Meanwhile, the method that produces green hydrogen – electrolysis – must be powered by renewable electricity from wind or solar farms rather than electricity produced by burning fossil fuels. The same goes for yellow, which solely relies on solar power. This shows the choice of hydrogen production is crucial, as it will define the amount of carbon emissions produced.
Even if the issues are solved, blue hydrogen is still a fossil fuel. There is a finite supply, meaning it’s a finite non-renewable form of energy. Therefore, only green hydrogen can be considered a truly renewable, low-carbon, sustainable and environmentally-friendly option for an energy transition.
Ground source
When placed in a district scheme with ambient-temperature pipework and waste heat capture, ground source heat pumps can be 600% efficient. High efficiency plays a part in carbon emissions because it means the majority of energy is absorbed locally from the ground, reducing how much energy is coming ‘down the wires’ from the electricity grid. The majority of the energy that comes from the heat pump is harvested locally from the ground.
Consequently, the only form of carbon produced is from electricity generation. However, as electricity continues to decarbonise through the increased generation of renewable energy – from sources such as wind and solar – the energy it does consume will also be renewable.
This is even more possible now through clever innovations such as load shifting. This means that when coupled with smart controls, a ground source heat pump is capable of shifting or moving its energy consumption to times when the electricity grid is cheap and low in carbon thanks to renewable energy generation.
If blue hydrogen remains the gas supply industry's proposed end state, there is a significant risk that repurposing the gas grid using unproven technology at scale could prove less feasible than previously thought [...] This would leave little time to implement alternatives, and in the midst of a climate emergency, we should be leaving little to chance.
Carbon Offsetting – Friend or Foe? Max Fordham, as cited in Hydrogen: A decarbonisation route for heat in buildings
