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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?
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It got a bit silly and I had to make informed guesses on some of it. Using a plug-in monitor I went through my electrical use appliance by appliance and then looked at when I use it. I did find that a washing machine being off and off in the wall there is a 4 Watt difference. My smoke detectors use a lot of energy and i need to look at more efficient ones. My single heaviest energy use is the Sunday lunch in the ovens. I don’t produce enough energy at any time of the year for this meal!
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)
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I then modeled my energy generation and matched it to my consumption pattern to see what the match was like. I generate a lot in summer when I least need it (not rocket science) and simple moving of more appliances to the daytime use through the use of time clocks or delayed start would sort out better match. Energy generation on the left and energy need on the right
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The comparison. How much energy am I making and when through the PV and matching against how much is available for storage, what can the battery hold or should I say release vs how much energy do I need in winter and summer nights
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!
Image may be NSFW.
Clik here to view.
Image may be NSFW.Clik here to view.
