PV solar panels and battery storage in the UK
The reality of PV solar panels and battery storage in the UK
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.