On 14 August, just a few days before the heat pump installation works started, I hopped on a train to Edinburgh to attend a free talk titled Unlocking Home Efficiency: The Value of Multiple Technologies.
This was part of the week-long Green Home Festival, held in the Charlotte Square Gardens now vacated by the Book Festival that had outgrown the space. This new kid on the block was a much smaller affair, with a single marquee taking up a corner of the Square, with a heat pump demonstration van parked next to it. I had no idea of this festival’s existence until I received a promo email (from one of the heat pump installers I got quotes from), but apparently this was its third year and the biggest to date.
The talk was delivered by Alex Butcher from a company called Warmur (which has now merged with The Heating Hub). You can download the presentation slide deck from the Festival website, but it may be a bit tricky to decipher without actually listening to the talk.
The key theme of the talk was how you could combine an electric vehicle and an air-source heat pump for central heating solar panels, battery storage and a smart tariff to save money.
Beating the spark gap
There’s a lot of misinformation about the heat pump technology circulating around in the UK, but one negative that is true is that electricity is expensive – much more expensive than gas. The difference between the price of 1 kWh of electricity and that of 1 kWh or gas is often called the spark gap, and there is a huge difference in the size of this gap between different countries. The spark gap exists largely as a result of policy decisions, and the UK, in fact, has the biggest spark gap in Europe. This means that, if you use 1 kWh of electricity, you have to pay four times more than what you pay for 1 kWh of gas.
This, however, is not a complete deal breaker. Why? Because a heat pump is much more efficient than a gas boiler. When a gas boiler burns 1 kWh of gas, it is unable to convert all 1 kWh to heat. At best, it’s efficiency is around 90%. A heat pump works by drawing heat from the environment and compressing it, which is more efficient than generating heat from combustion, and is capable of achieving an efficiency of 350% (or even higher). This efficiency difference goes a long way to filling the spark gap.
Solar, battery and smart tariff
But you can draw out more savings if you have solar panels and a battery. This part of the story was already familiar to me – I had already lived with these technologies for over a year and knew how much you could save by generating your own power during the day, saving power for use in the evening, and exporting to earn money.
Another thing you can do to lower your bills is to switch to a smart tariff. Many energy companies offer tariffs tailored for EVs, heat pumps and solar panels with storage. They are all variable-rate, time-of-use tariffs, which give you cheaper electricity when the demand is low, so by charging the battery from the grid during the cheap-rate hours, and using the stored power from the battery during higher-rate hours, you can save a lot of money.
Fabric Fifth
The last part of the talk was on the idea of “fabric fifth“.
In discussions around heat pumps, you often hear the phrase “fabric first”, which means that, because heat pumps are low-temperature heating systems, they don’t work well in leaky British houses, and that, therefore, you need to improve the thermal performance of the building fabric by upgrading insulation. “Fabric fifth”, proposed by Octopus Energy’s Nigel Banks in his LinkedIn post, is a counterargument to this approach and proposes a different order of priority:
- ASHPs ASAP: replace fossil fuel heating with an air source heat pump to decarbonise your home as soon as possible
- Get Smart: get a smart meter and a smart tariff to lower bills
- Measure & get comfy: understand how much energy you are using and take simple, low cost steps to improve comfort (such as draught proofing and loft & cavity wall insulation) while reducing energy use
- Solar & Storage: fit solar panels and battery
- Fabric Fifth: carry out deep retrofit to improve the fabric of the building
Alex had an alternative “fabric fifth” proposal:
- Measure & get comfy
- ASHPs when you’re ready
- Get Smart
- Solar [& Storage]
- Fabric Fifth
To be honest, I was not really the target audience as I was well on my way on the decarbonisation journey, albeit following a different “fabric fifth”, starting with draught proofing and some insulation, followed by solar and storage, then a smart tariff and now – finally – an ASHP. Still, the talk confirmed many of the things I was thinking and I felt reassured.
If you are thinking about starting the decarbonisation journey, Alex’s company Warmur offers a free online tool to help.