All I seem 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. I was off last week and so decided to look into what this could mean to me if I went over to the storage side. At commercial, gird and such like there are other aspects such as dealing with power interruption, grid shortages, peak power, selling at peak times and such like. For Mr Jones its a mater of economics. 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?
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 Powerwall 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 Powerwall 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)
The results of all of this data crunching when tested against my initial objective which was economics is an estimated saving of £110 per annum (for credibility lets allow another 20% variance and push the saving to £132 pa.) This has to be matched against energy inflation (cost in theory goes up over time) but then balanced against the degradation of the battery over thousands of cycles as it gets older and wears out. Tesla Powerwall (the reason I have chosen the Powerwall for the comparison is that it seems competitively priced) seems to be costing around £2000 to buy plus let’s be generous and allow £500 for installation (one day, plus brackets, some cabling and such like). This presents me with a 19 year pay back. According to the BRE Batteries and Solar Power guidance the expected life is around 10 years ‘but is improving all the time’ The Powerwall would also need to be next to the PV for DC charging before the inverter (or a new trench for the 240ft of cable to and from the house to the inverter). Outside is ok since it has been designed to be inside or outside
Overall and for my situation it’s not quite (quite a bit) there yet. I am though looking to change my heating and hot water system and this may be a better option but as I said earlier, its sunny when I need the least amount of energy! Electric car? But I have no doubt the price is still reducing for storage and I need to look at better energy management in the house. I have a feeling its time will come. But not yet for me!