Retrofitting batteries on existing PV systems

The ending of the UK government’s main renewable energy support scheme in April 2019 might, in most circumstances, be expected to provide a serious blow to the UK’s renewable energy hopes. Except that it could also be just what is needed to provide battery storage systems with the necessary boost to its own hitherto flagging prospects. The feed-in tariff (FiT) subsidy started in April 2010 with a view to providing a cushion to the otherwise erratic price swings of solar power. Now with government subsidies on new residential PV systems about to be removed entirely, users are scrabbling about for ways in which to maximise the benefits of solar PV in order to make the most of their investment. And the solution could well be retrofitted battery storage.

Traditional PV plant designs made it hard to integrate battery storage as a retrofit option. However, a number of companies are coming up with cost effective technological solutions. Solar PV battery storage has been a long time coming. Earlier attempts at entering the market though often foundered on the high price brackets, lack of demand and the support provided by FiT. But the time could well be ripe for battery storage that has been steadily developing, to step up to the plate and flourish.

Waxman Energy, part of the Waxman Group and one of the UK's largest distributors of PV modules, inverters, battery storage and mounting systems, says that the benefits of retrofit PV battery storage are substantial, even for those consumers that currently benefit from the UK’s FiT support scheme. “Users who have already got solar PV installed will undoubtedly be getting a better FiT rate than newcomers, so battery storage means that they can get more for their money by saving on bills while still earning favourable financial instalments for the energy they generate,” it says.

In sunny Australia, meanwhile, retrofitting battery storage to an existing solar PV system is already seen as a serious option, as opposed to installing an entirely new solar plus battery storage system. As with the UK, a number of states in Australia (led by New South Wales) have either removed or are re-examining their solar FiT schemes. As a consequence, Australia’s solar and battery industry comparison service, Solar Choice Pty Ltd, now expects the number of Australian homes that will install battery storage in the coming years to rise significantly with many opting to retrofit batteries onto a pre-existing system.

A number of well known listed products including: LG Chem RESU batteries, Enphase’s modular AC Battery units, GCL Poly E-Kwebe battery bank, Tesla Powerwall 2 and Ampetus Super Lithium batteries all provide retrofit options. But there are pitfalls to consider when choosing this route. Solar Choice points out that (in Australia, at least) if a consumer is in receipt of a state-mandated feed-in tariff programme, “it may not be worth your while to install batteries.”

Depending on when the system was installed, and whether a feed-in tariff is in place, the amount of power generated might also be significantly more, or less, than is required by the household. And this will have to be taken into account when deciding whether to opt for battery storage and what size. An additional consideration is back-up power. This is because only certain battery storage systems allow access to battery power when the grid is down.

Essentially, there are two ways to install batteries on an existing solar system. The first is to replace the existing inverter with a hybrid inverter. This ‘one-box’ solution covers both batteries and PV. The second option is to install an additional inverter. This ‘two-box’ solution is an ‘all-in-one’ battery product that has its own in-built inverter to handle the batteries separately.

While the solar power outlook may be good in the cloudless skies of Australia, in generally overcast UK and the rest of northern Europe hopes are pinned on falling battery storage costs accompanied by a rise in their efficiency. Tesla’s Powerwall, for example, enables people to consume rather than export their solar electricity. And this, says Waxman Energy, makes financial sense. “The solar industry is changing and soon battery storage will be a necessity for all PV customers,” it says. “Gone are the days of having to time electrical appliances to sync with hours of optimum PV generation. Retrofitting PV battery storage means that users can use the energy they have generated at times when it suits them. Solar PV battery storage systems have interactive user interfaces that monitor and track performance and use. This means users can keep tabs on how much energy they are saving, using and feeding back to the grid (if any). This will help them to understand where all their energy goes and make energy efficiency improvements if necessary,” the company continues.