Solar Batteries – A Homeowner’s Guide
Solar batteries became mainstream news when Tesla launched their Powerwall in 2015. Tesla put many of us in the picture as to how home energy storage could benefit us all, especially those of us who have solar panels. Tesla’s firm grasp on brand building and what makes a product desirable has placed the Powerwall at the top of many homeowner’s “want list”, there’s already a 6 month waiting list. There’s no doubting the quality product that Tesla has produced but if product aesthetics aren’t that important when considering energy storage then there’s quite a few options out there.
There are four common ways to store the electricity you generate from solar panels:
1. Lead Acid Batteries
Solar batteries have been around for some time, pre-Tesla and the advancement in solid state batteries, lead-acid batteries have been the go to technology to store solar energy. Developed way back in the 1860’s, lead-acid batteries are used in all walks of life and account for 40-45% of the batteries sold worldwide*. It’s the kind of battery you’ll find in your car.
There are some downsides to lead acid batteries; they have a relatively short lifespan, maintenance requirements, they’re inefficient compared to newer technologies and their toxic material makeup is bad for the planet. That’s not to say the technology is defunct, the UK’s latest competitor to the Tesla Powerwall utilises this technology.
2. Solid State Batteries
These are the type of rechargeable batteries you’ll find in your laptop. Usually lithium-ion (Li-ion) or nickel cadmium (Ni-Cd). They can be three to four times more efficient than lead-acid batteries and can store lots of energy in a small space. It is the advancement in this technology that has made it viable for companies like Tesla to produce long range electric vehicles and the coveted Powerwall.
3. Thermal storage
You can store the energy you produce as heat, which is where thermal storage comes into play. Essentially you’ll be using the energy you produce to run an immersion heater in a hot water cylinder. The downside is you can’t convert it back to electricity. If you heat the water and don’t use it then it’s kind of a waste.
4. Store power from The National Grid
Thanks to the UK’s export tariff the default option for most of us in the UK who have solar panels is to sell our unused energy to the national grid. On paper this sounds like a good deal, however it is estimated that you end up buying back 50% of what you exported but at a much higher price. Being able to store your unused energy and use it when you need it starts to make sense very quickly.
How do solar batteries work?
As it stands if you don’t use the electricity generated by your solar panels it will end up in the national grid so a battery to store that energy sounds like a pretty good idea (after all it was free energy). A solar or home battery works in the same way as any other rechargeable battery, you charge it up and you use the energy to power whatever it is you need to power. Various low-tech options have been around for decades but they’ve really only become a viable option for the masses in recent years. This is thanks to a massive leap forward in how efficient we can make them coupled with a sizable cost reduction, smart monitoring and a reduction in their physical size.
Behind the glossy casings that some of the market leaders have designed to tempt us lie a common set of key components. Obviously there’s the battery which is made up of either lead acid or lithium-ion cells. These are charged via your solar panels and the stored energy is released by a battery management system which also monitors the battery health. Some batteries also have an integrated inverter which will convert DC electricity to AC so you can use it in your home. Given that most technology is smart these days solar batteries are no different and most have apps and wi-fi capabilities so you can monitor and tweak your battery via your smart phone/tablet/laptop or all three simultaneously.
How much do solar batteries cost?
This depends on what storage system you go for. Prices can range from £500 to £8000 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 back-up 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 buy 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.
How long will a solar battery last for?
This will depend on what system you buy, however they all have one thing in common, their expected lifespan is shorter than your solar panels. It’s likely you’ll be replacing the batteries within 10 to 15 years. If pounds and pence are the only driving factors for you then solar batteries, as the technology currently stands in 2016, is most likely not at break even point just yet. However, if securing you home against power outages and reducing your reliance on fossil fuels are good enough reasons then compare the best solar battery systems available now (or soon):
Compare Solar Batteries
|Supplier||Storage Capacity||Technology||Cycle Rate||Warranty||Weight||Operating Temperature||Dimensions (mm)||Mounting||Cost|
|Tesla Powerwall 2||7 kWh||Lithium-ion||Daily||10 years||120kg||-20°C to 50°C / -4°F to 122°F||1150 x 755 x 155||Wall/Floor||£5,400|
|Powervault||2-4 kWh||Lead-Acid||Daily||5 years||172-250kg||0°C to 30°C / 32°F to 86°F||450 x 580 x 750||Floor||£2-4,000|
|Mercedes Benz||5-10 kWh||Lithium-ion||Daily||7 years||TBC||5°C to 45°C / 41°F to 113°F||TBC||Wall||£TBC|
|JuiceBox 8.6||8.6 kWh||Lithium-ion||Daily||10 years||127 kg||-20°C to 50°C / 14°F to 122°F||1093 x 559 x 432||Wall||£TBC|
|Enphase AC Battery||1.2 kWh**||Lithium-ion||Daily||10 years||25 Kg||-20°C to 45°C / -4°F to 113°F||390 x 325 x 220||Wall||£680|
|Maslow||2-3 kWh||Lithium-ion||Daily||5 years||28 Kg||TBC||490 x 308 x 150||Wall||£TBC|
|Sonnen Eco||2-16 kWh||Lithium-ion||Daily||10 years||140 Kg||5°C to 35°C / 41°F to 95°F||650 x 130 x 54||Floor||£7,000 +|
|Bosch BPT-S5||4.4 – 13.2 kWh||Lithium-ion||Daily||TBC||TBC||-10°C to 40°C / 14°F to 104°F||TBC||Floor||£TBC|
* Source: en.wikipedia.org/wiki/Lead%E2%80%93acid_battery
** The Enphase AC batteries are modular hence the small size – you need to stack them to store more power.
Prices are estimates only and do not include installation costs which can range from £500 to over £2,000.