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Solar panels and energy storage

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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. From which households can benefit from investing in energy storage, to what types of battery are available and how much they cost.

Whether you’re wondering what the difference is between a Ikea, Solax and Tesla storage systems, or if you just want to know more about energy storage, we’ll help you 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. So you can store electricity generated by your solar panels during the day to use at night, for example.

Big brands, including Samsung and Tesla, have begun selling home energy storage systems. Eon currently sells a solar panel and storage package. This relatively new technology may be worth considering if you generate your own energy at home – or plan to start doing so – but could make more use of it.

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 get them, using home batteries to store electricity you’ve generated will help you maximise the amount of renewable energy you use. Home energy storage will also reduce your usage from the grid, and cut your electricity bill. If your home is off-grid, it can help 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.

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), a battery may not be right for you.

This is because home energy storage will cost you upwards of £2,000. So you’ll need to make sure your investment is worthwhile. 

If you’re looking to save money by installing energy storage, like the 66% 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 paid between £3,000 and £9,000 for a battery storage system (excluding the cost of solar PV, where relevant). Quoted prices in the table below start at between £2,500 and £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:

  • Cost of installation
  • Type of system installed (DC or AC, chemistry of the battery, connections)
  • How it’s used (including the effectiveness of the control algorithm)
  • Price of electricity (and how it changes during the lifetime of your system
  • 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, the payback time is likely to be lengthy. But if battery prices drop in future, as with solar panel prices, and energy prices increase, 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).

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.

Energy storage products

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; enough energy to boil your kettle 10 to 70 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, capacity and key features.

Energy storage systems round-up
  Product Price (excl. installation) Size (cm) Weight (kg) Capacity Warranty Key features Availability
 Enphase-AC-Battery Enphase AC Battery £1,887 39 x 33 x 22 25 1.2kWh 10 years Enphase Enlighten software shows you energy production and consumption. Available via UK installers.
  LG Product Eon Storage £4,495+ (to retrofit to existing panels) 45 x 43 x 10 24 2.4kWh (up to 9.8kWh) Up to 10 years Eon Solar Manager app shows what you’re generating, using, earning, storing and saving “in almost real time” Available in selected counties. You don’t have to be an Eon customer.
 Ikea-Solar-Battery-Storage-Table Ikea Solar Battery Storage (Solarcentury) £3,000+ (battery only), £5,000+ (to fit with existing solar panels) 45 x 40 x 12 31 3.3kWh 10 years Online system shows how much electricity produced, used from the grid and battery use. On sale at Ikea.
 Moixa-Smart-Battery Moixa Smart Battery (AC) £4,995+ (including VAT) 50 x 30 x 20 29 or 37 2kWh or 3kWh 10 years Moixa will pay £50 per year to trade excess power stored in your battery using web-connected GridShare. Available direct from Moixa.
 Nissanx Nissan xStorage £4,850+ 122 x 91 x 21 90 4.6kWh 5 years Batteries are re-used from Nissan electric vehicles. Ovo will pay customers a monthly credit to use your battery to balance the grid. You can pre-order from Nissan. Also available via Ovo Energy in the Midlands and south England as Ovo SolarStore.
 Samsung-Energy-Storage-System Samsung Energy Storage System (DC) £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-Table SolaX Battery System £1,750+ 33 x 45 x 11 26 or 44 3.3 kWh or 6kWh 10 years Online monitoring system to be launched imminently. Available via UK installers.
 Tesla-Powerwall-Table Tesla Powerwall £5,900 76 x 115 x 16 125 14kWh 10 years The Tesla App allows you to monitor your system. Available direct from Tesla
  Varta-Pulse Varta Pulse £3,380 upwards 60 x 69 x 19 46 3.3kWh and 6.5kWh 10 years Varta's Storage App lets you monitor and control your system remotely. Available via approved installers from March 2018

Bear in mind that stated capacity is usually less than usable 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 you’re not using 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 8% 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 electricity generated 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 per week about battery storage in 2016.

Home energy storage: pros and cons

Pros:

  • 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.

Cons:

  • 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 is subject to 5% VAT.

We asked solar panel experts and owners for their top solar panel tips. Find out how to make the most of your solar panels.

*Online survey of 933 Which? members who have solar PV and have or would consider a home battery system, June 2017.

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