There are now a few systems on the market which homeowners can connect to their immersion heater and use to heat domestic water when there is excess solar-generated energy available. The stored hot water can then be used to meet the hot water demands of the household later in the day. By directing surplus energy to the immersion element, homeowners can utilise up to 100% of all self-generated green energy – even when they are not at home!

To assess the benefits of using surplus electricity from solar PV installations to heat hot water, EUA’s economist Graeme was tasked with ‘crunching the numbers’.

The calculation was rather more complex than my explanation of it, but in brief; taking the average daily hot water energy requirements for each month, and daily solar PV data estimates- based on modelled daily solar generation data- we have been able to estimate the savings that could be made by using surplus electricity to meet hot water demand.

On an average property, the HWA estimate that the homeowner could save between £90 and £240 per annum and meet around 50% of their hot water energy requirements if they were to divert their excess solar energy using the products currently on the market which homeowners can connect to their immersion heater.

Those numbers may not pay for the annual holiday, but when you consider that this equates to a 3- year payback -based upon current average prices of the products required to do this- it becomes a much easier sell to the homeowner.

Whichever way you look at it, it makes sense to use as much of the solar- generated electricity on site as possible, because there is a huge difference between the amount paid to buy electricity from the grid, and the amount they pay homeowners to export it.

John Forster, product manager at Heatrae Sadia, said: “There are over 900,000 homes in the UK with solar PV arrays installed on their roof. But while these consumers should be delighted with the energy they are generating and the associated savings, research has found that the vast majority of these people are actually dissatisfied because, as they are out at work when the energy is being generated, they cannot consume all of the surplus energy and therefore do not see the true benefits.

“Diverting this energy to a hot water cylinder, which may ordinarily be fueled by a boiler, will save significantly on gas bills. The boiler will only supply energy to the cylinder if the water has not achieved the desired temperature. This means literally every day the cylinder will be at least pre-heated. In summer, when there are longer daylight hours, most cylinders will be brought up to full temperature. Installers can offer customers this benefit without needing any new skills or equipment, and the small premium will pay back rapidly.

“Compared to diverting excess PV energy to batteries, which currently are expensive and have limited lifespan, solar PV hot water is the obvious choice.”

How we store energy is crucial to meeting our 2050 decarbonisation targets. We have all heard of the ‘Tesla Powerwall’, or the attempts to create batteries to store electricity to use later. 50% of homes in the UK have a hot water cylinder. This is the perfect way to store energy without having to install a new appliance. The results of the analysis are currently being collated in a more in-depth report which will show how by simply diverting energy from PV panels into a hot water store, households can save money and store energy. This will then be used to showcase to Government how they need look no further than the humble hot water cylinder in their quest to store energy.