Should we add a storage battery to our solar?

With the cost of solar electrical generation systems getting lower in price, there may still be a financial case for households to invest in the hope of recouping their outlay through savings on energy bills. The addition of a storage system — essentially a battery — also means that energy generated in the daytime can be reserved for the night-time when there is no sunlight to shine on the panels — maximising the use of the energy generated.

Our interest in installing a battery at our new (to us) property, stemmed from the realisation that not only did the existing solar panels not belong to us (and, therefore, we were not able to claim any monies for the energy they generate) but, also, they did not generate enough power to run, for example, a kettle so we had to draw energy from the grid to make up the deficit. After boiling said kettle, the energy subsequently produced by the panels would then feed into the grid and be lost to us.

A little bit of research online led us to understand that it is possible to buy a battery that can be ‘retro-fitted’ to a house that already has a system of panels. Having checked with the agents for the company who owns the panels, we discovered that they would have no problem with us getting a battery fitted (they didn’t quite use the words ‘couldn’t care less’ but it was pretty close!). This was based on the fact that they received subsidies based on how much was generated, rather than how much was fed into the grid. They also received a feed-in tariff which was calculated as fifty percent of what was generated as there was no way of knowing how much was actually fed in (they were fitted pre-Smart meters).

Further investigation reassured us that, when switching on the (much-fabled and unfairly maligned) kettle, providing we had some charge in the battery, the storage system would join the solar panels in supplying enough energy to run it. So, if our understanding was right, not only would we be able to reserve energy generated by the solar cells for use during cloudy periods or night-time, we could also run the higher powered devices that the panels couldn’t cover on their own.

Since carrying out this research we have also discovered that, since January 2020, energy companies are now required to pay a Smart Export Guarantee of ‘more than zero’ pence per unit but that we would not be eligible for it as there is already a contract for the old government subsidies at our household.

So to the often problematic task of finding suitable companies to provide quotes. None of our local friends or family have solar panels so had no one to recommend and,as the electrical storage technology is relatively new, we were wary of start-up firms that might not be reliable as yet. Luckily, we discovered an online company called SolarGuide (www.solarguide.co.uk) who will put you in touch with three companies in your area. The Solarguide route proved successful as we were soon receiving emails from firms eager to sort us out a quote and site-visits to our home were quickly arranged. Similarly, choosing the company to do the work was relatively straightforward: NPES Solar sent fitters, rather than a sales rep, who were able to discuss some of the pros and cons of the connections and physical installation required — much better than finding out about it later — and then explain how, with the addition of more panels on our south-ish facing extension, we would qualify for a lower rate of VAT than buying the battery alone (5% rather than 15%). They demonstrated a clear desire to get us the best system for our needs and provided solutions to problems that the other companies struggled to explain to us.

From left: six of the new panels, over the extension (four more on the other side); the new panels complement the original; the storage battery, tucked away in an outhouse.

Adding more panels made a lot of sense from the point of view of generating more electricity — potentially useful if we were to buy an electric car in future. We were further reassured that the capacity of our battery could, over time, be increased at a fairly small price. It was an easy decision to take the offer of ten new solar panels and a Solax storage system, supplied and fitted for about £7900 — the battery alone would have cost about half that amount but we reckoned that the extra energy generated by more solar cells would help pay for the higher initial cost of the system in years to come.

Installation took place in November (not the best time of year for the sunshine we needed) and, as we approach May, it seems a good time to check progress. There’s an app that monitors the battery and, while it isn’t the most easily understood app I have ever used (it especially struggles with displaying the amount generated by our two sets of panels), it provides a decent guide to two things: how much electrical energy we have consumed from the grid and how much our panels have fed back in.

Shown as blue bars: left, the energy we have consumed from the grid in the first four months of 2020; right, the energy our panels have fed back to the grid in the same period

Fortunately, we’ve had a pleasant late winter/early spring, with plenty of sunlight (it doesn’t have to be warm, just sunny) and our consumption has dropped accordingly. Over the same period, the amount our panels are feeding back to the grid has increased April has been a particularly good month for generating.

Here, the blue bars denote the energy consumed from the grid (left) and the energy fed in to the grid (right) in April

Conclusions are difficult to draw, with only five full months passing since the installation but there are a few positives to take:

• as one might expect, our energy consumption has dropped rapidly from winter into spring — we should expect even higher levels and longer periods of sunshine in summer time and we probably haven’t seen the best of our system yet;
• there are still short periods of time in which the power we are drawing (eg putting on the, now infamous, kettle) is greater than the power our system can provide — particularly at night time — and this means we are still consuming some energy from the grid but it is much reduced;
• a substantial amount of energy is still being fed into the grid, showing that we are generating a surplus that, in future, could be used for running more electrical devices — an electric car charger being one - and might also benefit from increasing our battery storage at some point;
• the energy we’ve drawn from the grid has dropped dramatically: over March and April 2020 we consumed 144 kWh compared with 281 units in 2019. A back of an envelope (literally) calculation suggests that if this level of saving is a reasonable average for the year, it would lead to savings, over 25 years, of around £3700 at current energy prices — enough to cover the cost of our battery or a little over half of our total expenditure- this is not allowing for future hikes in electricity tariffs;
• if we were able to apply for the new Smart Export Guarantee — some energy providers are paying in excess of 5p per unit fed back to the grid- we would more than likely receive the other half of our investment back, over 20–25 years (sadly, we are unable due to the contract for government-funded feed in tariffs on the original panels)
• since our installation in late November, our energy consumption from the grid has been 1031 units and we have fed 508 units to the grid so, assuming performance increases over the summer months, we may generate more energy than we consume over the year — would this make us carbon-neutral for electricity — particularly as we buy our energy from Ecotricity??

My hypothesis is that, with the development of more efficient and cheaper solar generation systems and complementary battery storage systems, there may still be a financial case for households to invest. I would tentatively suggest that, over time, it is very possible that enough savings will be made on our energy bills to cover most of the outlay — although this is dependent on factors including the annual increase in costs of electrical energy and the ability of the systems to maintain current levels of performance.

Based on our limited experience so far, I am confident that we will recoup the outlay on a battery storage system. Similarly, I would be pretty certain that we will be fully compensated for our investment in new panels and battery through savings on energy bills—it definitely would if were able to take advantage of the smart export guarantee. If this incentive appeals to you and like us, have a desire to contribute to an increase in use of renewable energy sources and reduction in your reliance on fossil fuels then… what are you waiting for?!?