Solar panels and battery storage

The reality of PV solar panels and battery storage
 Battery Storage What everyone seems to be reading about at the moment, is how battery storage will plug the gap from generation to consumption and make us all very rich or at least smug. I hear stories from neighbours with PV who are being targeted by battery storage sales people promising all sorts of claims.

But what does a battery do and how does it behave?

What's the difference between Lead Acid and the becoming cheaper Lithium battery. The difference seems to be efficiency, cost and the availability of energy. My main lesson has been the last bit. If you buy a 6.4 kwh Tesla Power wall with all its hype and nice packaging. You don't actually get 6.4 kwh but more like 75% of this because a battery never truly empties. A lead acid is more like 50% of the capacity is available. On the Power wall the 6.4 kwh actually means 4.7 kwh in available energy. You also loose 7.5% in efficiency in terms of what you put in vs what you get out (Tesla efficiency rating, I will leave that out for now)

Will it pay for itself in a reasonable time frame or should I keep looking at what to do with the excess power in summer when I don't need it for heat or evening electricity and so on. I have a 4kw PV system in the back garden and then I realised I did not understand my daily, monthly and seasonal use of energy or my energy generation characteristics. I then spent a couple of evenings modelling, measuring and understanding what I make in PV energy and how much I need and when do I need it?

The truth of battery storage - facts and figures

  1. A Typical house using the national average of 3800 kWh per year and solar PV system generating 3500 kWh per year.
  2. Price of electricity per kWh is £0.12 pence.
  3. The Energy Saving Trust quotes an average saving of £125.00 per year for a typical home, they also quote £0.145 pence per kWh.
  4. £125.00 divided by £0.145 = 862 kWh used in the home from the generated solar PV system, or a saving of 23% of the 3,800 kWh.
  5. So what else can you save by installing a battery storage?
  6. Look at it this way, if you use 3,800 kWh per year you use on average 10.41 kWh per day, so it's only possible to save 10.41 kWh per day.

From data downloaded from SMA inverters  the following conclusions.

  1. Real PV facts, real figures
  2. 3 KW solar PV generating on south facing roof 3000 kWh per year.
  3. Unit price of electric per kW, £0.13 pence.
  4. Normal PV savings without Battery storage according to the Energy saving trust (EST) is £125.00.
  5. The EST quote £0.145 price per kW so £125 divided by £0.145 is 862 kWh per year.
  6. Battery Storage savings over 300 days @ 5KW (size of battery bank) 1500 kWh @ £0.13p = £195.00.
  7. FIT payment if available 3000 kWh @ 4.3 p = £129.00.
  8. Export payments 3000/2 x 4.86p = £72.90.
  9. The total savings for year 1 = £125.00 + £195.00 + £129.00 + £72.90 = £521.00.
  10. Battery lifespan is ten years or 3,000 cycles.

Important technical details to check

Solar PV systems with battery storage may not be eligible for the FIT's payments if the battery is installed before the generation meter.

One benefit of the Solax inverter charger is in the event of a power cut the inverter can power the home up to a maximum load of 2kW, a manual change over switch is required to isolate the incoming supply and an external earth rod is required to earth the property.

Geographical location

It is important to point out that PV solar panels installed in different locations will give different output figures. However, as these figures were produced in Lincolnshire and this is a central location within the UK, I would use them as an average with greater figures occurring the more southerly your location and lesser figures when your location is more northerly.


There are brilliant battery storage systems on the UK market that are tried and tested around the world. PV solar panels working alongside battery storage devices and even EV charging are an option to consider in addition to the current incentives for solar panels. A good solar installer will be able to advise you on both types of system.

Yes, there are sharks in our industry as with any other, but clear facts will always trump 'bullshit' sales when time is taken to research your options properly. Remember sharks feed off ignorance!

Yes, solar PV and battery storage systems are on the rise and it will remain a viable option for many when bought at the right price from the right installer.


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