Home Solar Batteries - Oversold Expectations? : Part 1- The Spark
Background
If you're reading this you probably already share my interest in installing a home battery storage solution to reduce reliance on the grid and are looking for commentary from independent information sources. The primary driver may be to take a major step towards energy independence, to reduce your carbon footprint, reduce the money you hand over to line your energy supplier’s pocket, or even a combination of the three, but a question has come to mind related to the accuracy of information we're currently being told - so should we trust it or look elsewhere?
There's little doubt that Installing a domestic battery solution to use in conjunction with a new or existing solar PV installation provides a huge step towards energy independence by providing the ability to store up power for when you really need it, which often means when solar generation is low or non-existent, but I'm becoming increasingly aware of many claims made by both battery manufacturers and installer networks which seem to border on being incredulous.
You may remember an entry made in mid 2017 which questioned Tesla's decision to uprate storage capacity when the second version of their Powerwall domestic battery (pictured right) was released, so the question of matching capacity to requirement has obviously been revolving around the dark, dusty & cobwebbed shelves at the back of my mind for some time.
Over the intervening months there have been numerous new product offerings brought to market by a plethora of new entrants to the storage sector and I, like many others, have come across much mention as to what capacity an average household would need, along with typical 'payback' calculations. Some manufacturer & supplier websites even offer tools to size installations & provide guides to potential savings, many of which start simple 'rule-of-thumb' logical sanity-check alarm bells ringing on both input & output grounds which raise a number of really basic questions.
Question - Supply
Surely you can't base solution sizing or investment calculations on diverting all (or even the majority) of the power being generated by a solar array to batteries for later use because of variables such as the battery solution's charge constraints.
Also, what's the idea behind selling storage capacity to supplement existing solar installations which equates to somewhere between 4 & 8 days of average summertime energy imports.
Even worse, what's the value of basing the logic to calculate savings on average monthly generation (probably using data from sources such as PVGIS as a basis) Surely such data sources would only act to artificially smooth the self generation supply to a point where every day in a particular month is equal, no peaks, no troughs, just equal, so nothing like what any of us experience on our systems then!
Question - Demand
Okay, so there's a very large question over the calculation behind battery charging, but there's an equally relevant one concerning the ability for a battery solution to meet demand, especially so when there's a range of offerings from a few hundred watts, which is only enough to cover a typical baseload, through to systems capable of supplying up to 10kW for short periods.
Setting a requirement for power output based on our own home would likely result in a figure lower than most others would expect due to having already addressed many of the higher load sources to match the daytime generation capabilities of an existing array, for example we mainly use a 1kW kettle yet still well over half of our annual energy imports are destined to be consumed in that & various other kitchen appliances. Just considering baseload with a reasonable expectation of an additional 1kW load equates to around 3x the output of some solutions which raises serious questions related to potential energy savings and the related payback period for the battery investment.
The Spark - Are Expectations being Oversold?
Being already interested in installing a battery system and having done some initial calculations, I had a brief 'conversation' with a representative of a battery supplier late last Autumn which included a particularly heavy sell on the monetary advantages of their offering. Of course, as was the case in the early days of solar PV sales patter, the normally adopted assumptions related to loading energy price inflation was employed, fully supported by references to carefully chosen sources, but I was astonished to see what other variables had been employed to establish potential savings for what they considered to be a 'typical' UK household, especially so as I've been aware of the officially published statistics for quite a few years, it's not as if they're really hard to come across if you just take a few minutes to look. The decision was made there & then to look deeper into the claims being made by this company & potentially every other too through modelling realistic supply & demand profiles and applying them to published battery solution specifications.
This is the first in a series looking at domestic Batteries
Now Available - Part 2 - Modelling Performance
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