Solar Panels and Energy Storage
Article 7 of 7
Solar Panels and Energy Storage
Find out about batteries that can store energy generated by solar panels, including what’s on offer and whether you should get one.
We tell you all you need to know about home-energy batteries, including which households can benefit from investing in energy storage, what types of battery are available, and how much they cost.
Whether you’re wondering what the difference is between Ikea, Solax and Tesla storage systems, or just want to know more about energy storage, we’ll help you to find out more.
What is a home battery?
An energy-storage system, also called a battery, lets you capture electricity so you can use it at another time. For example, you can store the electricity your solar panels generate during the day, and use it at night.
Big brands including Samsung and Tesla have begun selling home-energy storage systems. Energy companies including EDF Energy and Eon are also currently selling solar panel and storage packages.
Ovo will begin trialling batteries with customers in autumn 2018. It will use its VCharge platform to buy energy cheaply when demand is low, store it until the household needs it, or discharge it back into the grid when electricity demand is high. Customers involved in the trial will receive £100 off their energy bill after three months.
This relatively new technology may be worth considering if you generate your own energy at home but could use more of it – or plan to start doing so.
Read on to find out about different energy-storage products, how much they cost, and the pros and cons of batteries. Or jump straight to our table of the latest home batteries.
Is energy storage right for my home?
If you have solar PV panels, or are planning to install them, then using home batteries to store electricity you’ve generated will help you to maximise the amount of renewable energy you use. In fact, 60% of people who have, or would consider, a home battery told us the reason was so they could use more of the electricity generated by their solar panels.*
Home-energy storage will also reduce the energy you use from the grid, and cut your electricity bill. If your home is off-grid, it can help to reduce your use of fossil fuel back-up generators.
In the near future, time-of-use tariffs will let you store up electricity while it’s cheap (overnight, for example) so you can use it during peak times. A few energy companies have launched these already.
Home-energy storage will cost you upwards of £2,000, so you’ll need to make sure your investment is worthwhile.
If you’re at home during the day and already use a large proportion of the electricity you generate, or divert surplus electricity to heat your water (for example), then a battery may not be right for you.
This is because home-energy storage will cost you more than £2,000, so you’ll need to make sure it's a worthwhile investment.
If you’re looking to save money by installing energy storage, like the 22% of Which? members who are interested in home batteries*, read on for our first impressions of energy-storage systems available now.
Before you think about storing electricity, make sure your home is as energy-efficient as possible.
Can I save money with a battery?
Which? members we spoke to typically paid either less than £3,000 (25%) or between £4,000 and £7,000 (41%) for a battery storage system (excluding the cost of solar PV, where relevant). Quoted prices in the table below range from £2,500 to £5,900.
Installing a home-energy storage system is a long-term investment to help cut your energy bills, although this may not be your motivation.
Whether a battery will save you money will depend on:
- the cost of installation
- the type of system installed (DC or AC, chemistry of the battery, connections)
- how it’s used (including the effectiveness of the control algorithm)
- the price of electricity (and how it changes during the lifetime of your system)
- the battery’s lifetime.
Several systems come with a 10-year warranty. They require little maintenance, so the main cost is the initial installation. If you install it with solar PV (which can last 25 years or more), you should factor in the cost of replacing the battery.
While the cost of a battery is high, it'll take a long time for the battery to pay for itself. But if battery prices drop in future (as with solar panel prices), and energy prices increase, then payback times would improve.
Some storage companies offer financial benefits – for example, payments or reduced tariffs for providing services to the grid (eg letting spare electricity from the grid be stored in your battery). If you have an electric vehicle, being able to store cheap electricity to charge it could help to cut your costs.
We haven’t yet tested home-energy storage systems to be able to calculate how much they could cost or save you.
If you get the Feed-in Tariff (FIT), part of it is based on the amount of electricity you generate and export to the gird. At present this is estimated at 50% of what you generate, and your payments will continue to be based on this even if you store electricity.
After the smart meter roll-out, the government may base export payments on actual meter readings.
Financing energy storage
A small proportion of Which? members we spoke to have paid more than £8,000 for their home battery, although a quarter of them paid less than £3,000. However, it’s still a significant investment.
Most (86%) of the people who installed solar panels paid for them upfront using savings; this is also an option for storage. If you don’t have the cash to do this, you may want to consider a loan. However, remember you’ll have to pay interest on money you borrow, so make sure that gains made from storage would outweigh this.
If you live in Scotland, the government offers interest-free loans to homeowners to fund energy-saving improvements, including energy storage. You can borrow up to £6,000, which you must repay within 10 years. See Energy Saving Trust Home Energy Scotland to find out more.
As a relatively new technology, there is a limited, but growing, range of products. Capacity of new lithium-ion batteries ranges from around 1kWh to 8kWh; a 4kWh system would store enough energy to boil your kettle 37 times, according to the Energy Saving Trust.
If you want a larger capacity, some firms offer ‘stackable’ systems which combine more than one battery.
These range from the size of a small computer to the size of a washing machine. Greater capacity means a bigger and heavier battery. Small systems can be wall-mounted, while larger ones sit on the floor.
Use the table below to compare the latest battery prices, capacities and key features.
|Energy storage systems round-up|
|Product||Price (excl. installation)||Size (cm)||Weight (kg)||Capacity||Warranty||Key features||Availability|
Enphase AC Battery
|£1,699||39 x 33 x 22||25||1.2kWh||10 years||Enphase Enlighten software shows you energy production and consumption.||Available via UK installers.|
LG Chem Resu
|£5,545+||44 x 43 x 10||33||3.3kWh||Up to 10 years||Can be wall or floor-mounted.||Via Eon surveyors.|
|Moixa Smart Battery (AC)||£2,950 - £3,450 (including installation)||51 x 35 x 25||40 or 49||2kWh or 3kWh||10 years (extendable for Gridshare members)||Moixa will pay £50 per year to trade excess power stored in your battery using web-connected GridShare.||Available direct from Moixa.|
|£5,550+||122 x 89 x 22||135||4.2kWh and 6kWh||5-10 years||Batteries are re-used from Nissan electric vehicles. Home energy management app tracks energy storage and consumption.||Available from Nissan.|
(all excl VAT)
|97 x 100 x 25 (smallest model)||129kg (4kWh) to 179kg (8kWh)||4kWh and 8kWh||10 years||Online portal monitor performance charging, discharging, solar generation and energy usage.||Available from Powervault, UK installers and distributors.|
Samsung SDI All-in-one
|£5,500||100 x 27 x 68||95||3.6kWh||5 years||Monitoring system detects errors and lets you control the battery remotely. Accessible online and mobile.||Available in the UK.|
SolaX Battery System
|£1,920+||33 x 45 x 11||26 or 44||3.3 kWh or 6.5kWh||10 years||The Solax portal lets you monitor your system remotely and decide which items to power.||Available via UK installers.|
|£6,200||74 x 111 x 14||125||13.5kWh||10 years||The Tesla App allows you to monitor your system.||Available direct from Tesla.|
Varta Pulse 3 and 6
|£3,729+ (exlc VAT)||60 x 69 x 19||45 and 65||3.3kWh and 6.5kWh||10 years||Varta's Storage App lets you monitor and control your system remotely.||Available via UK installers..|
Bear in mind that usable capacity is usually less than stated capacity. This is because batteries tend to lose some energy in charging and discharging, and most aren’t designed to be fully discharged on a regular basis.
The products in the table above are designed to work with the grid. If you’re off-grid, speak with an installer directly to get an appropriate system for your situation.
Before you install a home-energy storage system
Consider whether you’re generating enough electricity that you don't use to make it worth adding energy storage to an existing solar panel system.
If you’re looking to protect yourself against power cuts with a home battery, as 6% of Which? members with solar panels who own or would consider a battery system told us they are, not all systems are suitable.
Get quotes from several installers on cost of installation and estimated savings. Ask them to explain their calculations to you and question anything you’re not sure about.
Check that your installer is signed up to the Renewable Energy Consumer Code (RECC), which now covers storage. This means they’re signed up to a high standard of conduct, including providing good information about your installation. You also have access to RECC’s complaints process if something goes wrong.
Battery installation systems
There are two types of battery installation: DC and AC systems.
DC battery systems
A DC system is connected directly to the generation source (eg solar panels), before the electricity generation meter. You won’t need another inverter, which is more efficient, but charging and discharging is less efficient, so could affect your FIT (this isn’t usually recommended if you’re retrofitting a battery to an existing PV system).
DC systems can’t be charged from the grid, according to the Energy Saving Trust.
AC battery systems
These are connected after the electricity generation meter. So you’ll need an AC-to-DC power unit to convert the electricity you generate into AC you can use in your home (and then back again to store it in your battery).
AC systems are more expensive than DC systems, according to the Energy Saving Trust. But an AC system won’t affect your FITs payments, as the generation meter can register the total system output.
Battery installation tips
If you’re installing a storage system, you should notify your local Distribution Network Operator – check with the Energy Networks Association if you’re not sure who it is. You may also need to inform your local council.
Beware of pressure selling. Check our solar panels buying advice for things to look out for, including rapidly reducing quotes and lack of detailed information. RECC received one complaint a week about battery storage in 2017.
Home-energy storage: pros and cons
- Helps you use more of the electricity you generate.
- Some firms pay you for allowing your battery to be used to store excess grid electricity.
- Could enable you to take advantage of cheap-rate electricity.
- Require little maintenance: ‘Fit and forget’, said one owner.
- Currently pricey, so payback time may be long.
- A DC system could reduce your FIT payments.
- Likely to need replacing during the lifetime of a solar PV system.
- If retro-fitted to existing solar PV, you may need a new inverter.
- Batteries added to existing solar PV systems are subject to 20% VAT. Batteries installed at the same time as solar panels are subject to 5% VAT.
We asked solar-panel experts and owners for their top tips. Find out how to make the most of your solar panels.
*Online survey of 1,562 Which? members who have solar PV and have or would consider a home-battery system, May 2018.