PHAM NEWS | DECEMBER/JANUARY 2025 28 Water Heating & Cylinders T


here has been a quiet revolution in the way that the UK’s energy system works which means


that a new breed of hot water cylinders (called smart cylinders) can now pay homeowners whenever excess wind or solar power is being generated on the grid. Smart cylinders present an opportunity to professional installers, as households look to save on their gas bills while preparing themselves for a future world just around the corner, involving smart tariffs, heat pumps, rooftop solar PV and more. Smart cylinders allow consumers to get the best out of their system boiler while being capable of operating with a heat pump in future, should they wish to install one.


Energy transition So why are Smart Cylinders able to pay homeowners today? Over the last 15 years, there has been a radical shift in the UK’s energy


system. In 2010, coal delivered 30% of our electricity, but this year the last coal power plant in Britain stopped operating, the first time the UK has gone without a coal plant in 142 years! This was achieved by ramping up wind generation to record levels alongside modern gas turbines which can flex up and down depending on the weather. Wind and solar produce


zero carbon emissions when generating, while gas produces less than half the CO2 per unit of electricity compared to coal (with many fewer harmful particulates, carcinogens and volatile compounds). Consequently, the grid carbon intensity has more than halved since 2013 and we are now at the point that, from a carbon perspective, it is now greener to use a combi boiler most of the time.


Price comparison The problem we have is the cost of electricity compared to gas on traditional dual fuel and single rate tariffs. Typically, electricity today costs around 24p/kWh, whereas gas costs around 7p/kWh. However, with ever increasing wind generation, there are now frequent instances where electricity becomes free or even ‘negatively priced’. By negatively priced, we mean that the energy company will pay you to use it. This reflects the fact that


last year over £600 million was spent shutting down wind farms when they produced too much power for the grid. Smart cylinders provide an opportunity


Pete Armstrong CEO at Mixergy


Catching the wind – making the most of renewable energy


By connecting to the internet, smart cylinders open up a range of possibilities, from saving on energy bills to supporting the UK’s transition from fossil fuels to low carbon energy sources. Pete Armstrong, CEO of Mixergy, discusses how installing a smart cylinder can reduce gas consumption by over 20%, while also paying the householder to use excess renewable power.


to use this electricity, whilst crediting the customer’s utility bill at the same time. Our range of smart cylinders


does exactly this with a range of smart tariffs available on the market. One example is British Gas’s Mixergy Bolt-On offer, which will pay any British Gas customer with a Mixergy smart cylinder around £40/year to participate in their demand side response (DSR) services. This is where customers are paid to consume power during periods when electricity is cheap. Our smart cylinders provide a similar solution with other offers such as Octopus Agile, Octopus Go and EDF’s GoElectric Overnight, to name a few.


Heating engineers have an essential role to play in helping


households to future-proof their systems


Better connected A smart cylinder is just like any other hot water cylinder, except in the case of a Mixergy system, where a range of sensors are fitted alongside a control unit which connects to the internet. Like conventional hot water cylinders, these can be installed within a vented or unvented hot water system. All of the usual requirements


around G3 apply, such as PRV and T&PR valves alongside an expansion vessel. They can also


be installed as an indirect system with a gas boiler, standalone direct electric or with a heat transfer module, comprising ancillary pump and plate heat exchanger, connected to a heat pump. If the customer has (or is intending in future to get) solar PV, a PV diverter can come factory fitted to provide free hot water whenever there is excess solar to the grid.


Smart tariffs In the case of the Mixergy smart cylinder range, all our system configurations – indirect, direct, with solar, with a heat pump – can pay the customer or earn them discounts from their energy bill, whenever the electricity supplier has excess electricity to use in the back-up immersion or heat pump compressor. A smart cylinder’s software


platform integrates with the available smart tariffs on the market, which send a signal for the system to use excess energy whenever possible. The software in Mixergy’s smart cylinder range can learn the usage pattern to determine when to heat, and by how much, to save energy whilst also timing heating events to coincide with


the lowest prices available on the market. It even integrates with the


Met Office weather forecast for renewable systems, so that the compressor will run during periods in the day when its COP is at its highest or, in the case of a direct electric solar configuration, the tank will heat less in the morning in anticipation of free energy becoming available when the sun comes out.


Installer’s role What does this mean for the future of hot water cylinders? As the journey towards decarbonising homes accelerates, flexible demand becomes an imperative to avoid blackouts, while minimising running costs for the homeowner. Heating engineers have an


essential role to play in helping households to future-proof their systems. Discussing the advantages of a smart cylinder allows them to introduce customers to a system which saves and pays today, while providing a seamless route to the future use of low carbon technologies, such as heat pumps or rooftop solar PV.


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