Solar Batteries – A Homeowner’s Guide

Please note: This page was last updated in July 2017

 
Comparing solar power batteriesDid you know that in just one hour the sun radiates more energy than the whole world uses in a year? That’s an unlimited supply of free energy that we could be taking advantage of.

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While solar panels have opened up the way forward in terms of using the sun’s energy practically, the ongoing struggle has been to find a way to store it for times when the sun isn’t around. Effective solar batteries are the solution; they could completely transform the way use energy and give us independence from the National Grid and from paying energy suppliers, but progress in this area has been slow.

But there is hope on the horizon, if you’ll pardon the pun. Solar technology has made huge strides in recent years and a growing number of manufacturers are producing better quality and more affordable solar batteries that, in time, may make the dream of free energy a reality.

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At Solar Guide, we have found the best solar storage batteries currently on the market today, and have broken down the most important metrics. When looking to purchase your solar battery, you’ll want to know how long the warranties are, what they weight, how big they are etc. In the table below we break these metrics down plus many more.

Supplier Capacity Technology Cycles Warrantied Warranty Weight Operating Temperature Dimensions (mm) Mounting Cost
Tesla Powerwall 2.0 Tesla Powerwall 2.0 13.5 kWh Lithium-ion Unlimited 10 years 264.4 lb / 120 kg -20°C to 50°C 1150 x 755 x 155 Floor / wall / interior / exterior £5,400
LG Chem Resu 6.5 solar battery storage LG Chem Resu 6.5 4.9 kWh Lithium-ion 6,000 10 years 52kg -10°C to 45°C 452 x 654 x 120 Floor / wall / interior / exterior £3,600+
sonnenBatterie Eco Sonnen Batterie Eco 4-16 kWh Lithium-ion 10,000 10 years 53kg (+27kg per additional battery) 5°C to 40°C 660 x 1295 x 356 Indoor £4,500+
Powervault G200 Battery Powervault G200 2 – 6 kWh Lithium-ion 4,000 10 years 100 – 200 kg 0°C to 35°C 500 x 580 x 820 Indoor £2,500+
Enphase Solar Battery review Enphase 1.2 kWh Lithium-ion 7,300 10 years 25 Kg / 55lbs -20°C to 45°C 390 x 352 x 220 Wall mounted indoor £1,000+
Mercedes Solar Battery costs Mercedes 2.3 – 18 kWh Lithium-ion 8,000 10 years 35 – 133kg 6°C to 44°C 470 x 290 x 420/1180 Wall mounted / floor standing £7,000+
Samsung SDI Solar Power Storage Samsung SDI 3.24 kWh Lithium-ion 6,000 5 years 95kg -10°C to 40°C 1000 x 267 x 680 Floor standing £3,500+
*Prices are estimates only and do not include installation costs which can range from £500 to over £2,000.
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How do solar batteries work?

Solar panels are fitted onto a roof or exterior wall where they can be exposed to the most sunlight. Each panel includes solar cells which convert the sun’s energy into DC electricity which is then converted to AC electricity by an inverter. This can then be used to power your home.

Whatever you don’t use is sent back to the National Grid to be redistributed around the country. Your energy supplier will pay you for every kWh of energy you send back (which is deducted from your energy bills) but you will pay a significantly higher price per kWh when you buy it back at a later date.

So you can only use solar energy as and when it is available i.e. when the sun is shining. This means that complete independence from the National Grid isn’t a realistic option, although you can reduce the amount of power you are buying from them.

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By introducing a solar battery into the process you can keep hold of the surplus energy you’ve produced for use at a later date and further reduce your reliance on the National Grid.

Fitting a solar battery to your home

Solar energy systems that can store their own electricity have three main components:

  • Solar panels that absorb and convert the sun’s energy to DC electricity.
  • A battery (or batteries) to store the electricity that is not used straight away for use later on.
  • An inverter that converts DC electricity to AC ready for use in your lights, appliances etc.

As solar technology continues to progress many modern systems also incorporate smart technology such as apps and wifi so you can easily monitor the battery’s charge level and general efficiency.

What are the benefits of using solar batteries?

  • Backup Power Supply: Even homes which do not rely on solar energy can benefit from the added security of a solar battery. When a power cut strikes a store of this ‘off the grid’ energy could be invaluable to your household.
  • Energy bill savings: By storing energy during times of lower demand you can reduce the amount you need to buy from your energy supplier when energy usage is higher, saving you money on your energy bills.
  • Cuts to Feed-in Tariffs (FIT): Back in 2010, the UK government introduced the Feed-in Tariffs scheme to incentivise homeowners to incorporate solar energy into their power supply. These included:
  • Generation tariff: your energy supplier pays you a set rate for each kWh of electricity you generate.
  • Export tariff: your energy supplier pays you for each unit that you export back to the electricity grid, i.e. the energy you haven’t used.

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When these rates were first introduced they were a rather impressive 44p per kWh. However, this tariff has dramatically reduced over the years and, as of April 2017*, you receive just 4.14p for every unused kWh you return to the National Grid.

So, although the energy supplier will pay you 4.14p for every kWh you send back, if/when you need to buy this energy from a supplier at a later date because your supply isn’t meeting demand, they will charge you a significantly higher price. A battery storage system means you can keep hold of your surplus energy (that cost you nothing to generate) for use later on and avoid paying their higher prices.

*FIT rates are adjusted every 3 months.

What are the problems with solar storage?

    1. Ongoing Maintenance

A solar battery is not a simple ‘install and leave’ unit. It needs regular monitoring and maintenance to keep it working both efficiently and safely. This includes keeping it charged at an optimum level, carrying out regular power ‘boosts’ and gassing as well as ensuring it is stored at a correct temperature and protected from the weather.

    1. Replacements

Solar batteries do not last as long as solar panels. Currently, a high quality solar battery will last for around 10-15 years, but this is dependant on how much you use it and ensuring it is maintained correctly. A battery can cost up to £2,000 (not including installation) so it is a significant expense to consider.

    1. It’s not a complete energy solution (yet)

The ultimate ambition for many is to make complete energy self-sufficiency a reality, without any reliance in the National Grid at all. While technology is certainly moving in the right direction and has made great strides in recent years, a solar battery system is still not a viable option to completely disconnect from the mains supply. Batteries have their faults, shelf-lives and limitations, so until things have progressed it’s necessary to have the option of a backup a backup supply from the National Grid.

Jargon Guide

  • Capacity: This is the ‘usable’ amount of energy in kWh (units) that the battery will store. It’s never a good idea to run a battery down to empty as it will cause damage, so when you are comparing capacities remember to check if the figure given is ‘total’ or ‘usable’.
  • Cycle: The number of cycles refers to the amount of times a battery can be charged and discharged. It will give you an indication of how much ‘life’ a battery has but doesn’t relate to the number of years it’s been operating.
  • Technology / chemistry: Batteries are generally Lead Acid or Lithium Ion. While acid is cheaper it is not as efficient and doesn’t last as long as Lithium Ion.
  • Power output: This is, quite simply, how much power the battery can deliver at one time. The more appliances / lights etc. that you plan to power with the battery the higher this will need to be.

How much do solar batteries cost?

This depends on what storage system you go for. Prices can range from £500 to £8,000 plus the cost of having it fitted. We estimate installation charges to be at least £500 worth of an electrician’s time. You may also have to add the cost of an inverter if retro fitting solar batteries to your existing solar panels, another £1000 or more please. It’s worth noting that there are quite a few system that combine an inverter and battery storage which are referred to as hybrid storage systems.

Do you need solar panels to have a solar battery?

No. If you live in an area affected by regular power cuts then a home battery could be just the system you need to keep the lights on. On average you’ll probably get around 24 hours of backup power but this can be increased by simply installing more batteries. If you’re on an Economy 7 rate a home battery can also save you money by charging when electricity is at it’s cheapest for you to use when it’s not so cheap. Finally, you can even make money by storing energy for the national grid who can discharge it from you in times of need.

Can you add a solar battery to existing solar panels?

Yes and no. Some batteries will only work when installing a new system or one that was specifically designed for it (Tesla) and some systems will retrofit to any system.

Are solar batteries safe?

They are as safe as as any other electrical item in your home. Generally installing a solar battery is not a DIY job and for the most part the public can’t buy solar batteries direct from the manufacturer but rather via an approved installer.

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