Solar batteries & storage

A huge step towards energy independence, solar batteries let you store up power for when you really need it.

Adding battery storage minimises your reliance on the grid, and reduces the money you put in your energy supplier’s pocket. But what should you look out for when choosing a system? Below we list the questions you need to ask before making a decision.

The 6 ‘Watts?’ of Solar Storage

1. What’s the ‘useable’ capacity?

Capacity is the amount of energy in kWh (units) that a battery can store. Batteries should never be drained completely. However, some are misleadingly sold quoting ‘total’ capacity. Check what’s being stated. ‘Useable capacity’ is the figure you need to know. Though Tesla Powerwall 2 is 14kWh, it’s sold as 13.5kWh, it’s useable capacity. It will never fully discharge to prevent damage to the battery cells.

2. What are ‘cycles’?

A cycle is one complete discharge and one complete charge. In reality it doesn’t happen like that. A battery may only discharge 25%, then recharge 25%. This would be 1/4 of a cycle. So you need to know how many cycles a battery is warrantied for. Only then can you work out how many kWhs (units of electric) your battery will deliver over its warrantied lifetime.

3. What’s the battery chemistry?

There are two main types available:

  • Lead Acid
  • Lithium

Lead Acid is very cheap to install but it’s inefficient and won’t last for long. Though the price of Lithium (ion or iron phosphate) is higher, it’s much better value. It’ll last far longer and deliver more kWhs (units) during its lifetime.

4. What’s Charge/Discharge power?

Some battery storage systems only deliver 800w (watts) of power. No good if you want a cup of tea (your kettle needs 2000 watts).  Likewise, if you’re generating 4kW but the battery can only take on 3kW then 1kW will be heading to the grid, wasting your precious free energy.

So it’s essential that you check the power output before you buy, otherwise you may find yourself drawing a lot of energy from the grid even though you have energy in your battery.

5. What’s the price per kWh?

As you’ll see from the table below, there are many storage solutions at varying prices.  Checking the price/kWh of storage capacity is fair and accurate way to compare different systems. What’s the right number of kWh for your property? That depends on you. The more kWhs you have, the more you can reduce your bills and take advantage of ‘Time of Use’ tariffs that are starting to emerge on the energy supply market. These allow charging on cheap rate and selling back to the grid at higher rate periods. The greater the storage, the more you can sell.

6. What about power cuts?

Most systems are designed just for storage. However, some offer back-up capability to provide power when there’s a powercut. Two things to consider.

First: to prevent damage to your battery or appliances some of your circuits may need to be rewired.

Second: you’ll need a larger storage capacity to keep some power in reserve. If backup is essential, let us know and we’ll design some bespoke solutions for you to choose from.

At Naked, we ask these questions for our customers every day.

Compare Solar Batteries

Use the table below to compare some of the battery systems available on the market. Prices are a guide only. They should be very close, but check with us for latest info. Remember to add VAT. Currently, installing a battery with a Solar PV system attracts 5%VAT, retro fitting a battery attracts 20% VAT.

Solar PV Battery Storage systemCharge/Discharge in kWStorage capacity (kWh)Useable capacity (kWh)Cycles warrantiedInstallation price£/kWh of storage capacityProduct warrantyBattery chemistry
Tesla Powerwall 2 with Backup*5.013.513.5Unlimited£7450£55110 yearsLithium
SolaX Hybrid X1 Triplepower 12.6kWh3.6812.611.346000£5501£4855 YearsLithium
Sonnen 9.43 - 12.5kWh3.312.512.510000£8060£64410 yearsLithium
Solax Hybrid X1 Triplepower 6.3kWh3.06.35.676000£3838£6775 yearsLithium
SolarEdge LG Chem RESU 1059.89.3Unlimited£6100£65510 YearsLithium
Powervault 3 - 12.3kWh3.3/5.512.312.36000£8090£65710 yearsLithium
Solis/Pylon 7.2kWh3.07.25.766000£4007£69510 yearsLithium
Powervault 3 -
8.2kWh
3.3/5.58.28.26000£6360£77510 yearsLithium
Sonnen 9.43 - 7.5kWh3.37.57.510000£6330£84410 yearsLithium
Nissan X Storage 6kWh4.86.05.43652£7598£140710 yearsLithium

* Tesla Powerwall 2 comes with Backup as standard.  This will give you cover during a powercut allowing your solar and your battery to continue operating when the grid goes down.

powerwall-and-backup-gateway-2-crop

TESLA

The Powerwall has transformed Solar for good. And now, all Powerwalls come with Backup meaning you’ll have electricity even in a powercut.

solax-lg-battery-storage

SOLAX

At last, a battery to rival the Powerwall. Supported by a strong UK service team too.

sonnenbatterie_8_2_small

SONNEN

European contender with excellent efficiency & performance.

resu10h_diagonal_1000x1000

LG CHEM

Popular choice of battery from South Korean company LG Chem.

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