For years, energy storage has been seen as a novelty or the preserve of people living off-grid. Now technological developments and the growth of domestic renewable energy have made this an area with big growth potential.
Storage also ties in very well to the idea of the ‘smart home’. Many smart storage systems allow you to keep track of your energy use online and charge the batteries with low rate electricity from the grid if you’re on a tariff that is cheaper at certain times of day, such as Economy 7.
Storage may also lead to households playing a role in smart energy management at grid level. This might mean allowing their energy storage device, including hot water cylinders, to be used to store excess electricity – in return for preferential rates.
All interesting stuff - but is now the time to invest in energy storage, and what needs to be considered?
If you have a renewable electricity generation system in your house, such as solar PV, then you will inevitably generate more electricity than you need at times of high supply and low demand, with any surplus being exported.
At the moment, you will be paid money in recognition of this but, for most people, you get paid according to how much electricity you generate and are assumed to use at home, not exactly how much you actually export. This is called deeming, and for most people is set at 50 per cent of total generation. So, if you can store some of that surplus electricity and use it at another time when you need it, you will still get paid the same for your export but will spend less on electricity bills for your import.
However, things could be set to change. With the roll out of smart meters, it’s possible that export payments will be changed from deemed to metered. If this is what is decided, this may affect everyone with PV and particularly those who have also put in batteries or diverters connected to a hot water cylinder. Definitely a detail to keep an eye on if you’re considering storage in this context.
Storing energy as heat is another option for use with renewables – and with the major energy demand in homes coming from heating and hot water, possibly a sensible one. The cheapest way to do this is to expand the use of your hot water cylinder by connecting a renewable system to it.
If you’re looking for something more space-efficient than a thermal store and more high-tech than a diverter, innovations like that from Scottish company Sunamp may prove just the job. Its heat battery charges from renewables, whether heat or electricity, and also from the grid. It uses what are known as ‘phase change materials’ (actually, just special salts) to capture and release energy from different sources, and provides instant hot water at mains pressure.
Unfortunately, batteries are not cheap at the moment, and neither are more complex options for connecting and controlling inputs to thermal stores. Prices are expected to come down significantly over the next few years, so to get involved in storage now rather than waiting to take the plunge, a number of factors ought to stack up.
Whether the sums add up depends, as often in home energy issues, on how much you use, and when you use it. The size of the renewable energy system you're going to be storing the excess generated from is also key.
If you have an existing small solar PV system, with little excess to go into a battery or other storage options, it's not likely to make financial or practical sense. New build homes integrating small PV systems into their designs are also unlikely to benefit.
On the other hand, if you install a good number of panels onto your roof and there's generally no-one around during the day using the electricity generated, storage may be something to consider.
Ian Cuthbert, Energy Saving Trust's Programme Manager – Sustainable Energy Supply Chain said: “Having a big solar PV system, installed around 2010 when the Feed-in Tariff was highest, may mean it’s more financially viable to invest in storage, whereas for others it may mean a dip into savings. It’s always important to weigh up the costs and the benefits given your particular circumstances. But if you’re earning big money from the Feed-in Tariff then it might make sense to use some of that income to invest in greater self-sufficiency.”
It is worth noting that for many people, the decision to fit energy storage is not purely a financial one. The idea of becoming less dependent on grid electricity suppliers, whilst at the same time reducing their carbon footprint is very attractive to people who wish to make a contribution to local and global sustainability.
The following are the most common types of energy storage options, for both heat and electricity.
There's a misconception – and potentially a misselling – that every battery system will give you back-up power in the case of a power cut. Some systems can be installed to give some basic power for essential items for a period, but they don’t all do this, and it’s unlikely any will give you a full domestic supply for the full length of any power cut. Speak to your installer about what back-up power their proposed system will offer, if any. If your priority is just to reduce the amount of grid electricity used by the house, you may feel that the extra expense of a grid back-up system is not worth it.
Electricity batteries are not massively complicated, but the circuitry and controls can be quite sophisticated. They can be sensitive, and timing and degree of charging need to be optimised from the start to preserve the life of the battery. Without this care, it could quickly diminish. This isn’t the case with heat batteries and thermal stores. One consequence of this is that you may end up charging the battery from the mains during a period where there's not much sun though if the system is well designed then this should not happen very frequently. In addition some battery systems have a 'winter mode' to prevent this.
After that, if you've not been put off, and you think storage may be an option for you and your home – what next? It's time to think about the product you want, and finding an installer to put it in.
An increasing number of renewables installers now offer storage. Ian says: “You should contact installers for more information, and ask about the products that are out there. As ever, if combining with a renewables system we recommend that you only use renewables installers that are MCS-certified and battery installers who are approved by the battery manufacturer. But you should be aware that the storage system and its installation are not themselves covered by MCS certification.”
It is important to talk to your potential installers to make sure you get an energy storage system that is right for you. Ian suggests you should ask for justification for every decision your installer makes. A few questions to get you started: