A Home Battery might be helpful to store electricity for later. This can be economic if there is a price differential between when the excess is stored and when the electricity is needed. For example, if solar photovoltaic panels are producing a good surplus of electricity during the day then it may well be economically advantageous to store some of that surplus temporarily and then use that in the evening. Another example may be if you have access to off-peak electricity (such as a Time of Use tariff or Economy 7) then storing cheaper off-peak electricity in the battery for use during the peak times means you are effectively accessing off-peak electricity all day. If the cost savings available doing this are much more than the price of the battery installation then there is an economic case. The environmental case for doing so depends on what the carbon intensity of the power being stored is compared to the carbon intensity of the peak power being avoided. Just as with the economic case, we would need to factor the environmental cost of the battery against these savings to determine if the environmental case is strong.
The graph in the figure above shows the power production on a typical day in early March. This is a split East- and West-facing Solar PV system which actually spreads the power production more during the day. Typical South-facing installations have a much narrower power production time during which much higher powers are produced. The spikes in the power production are because this day was one with sunny intervals: power produced during overcast periods was lower and power produced during times of bright sunlight was higher.
Ideally we would like to use electricity when the sun is shining. So we need to find out when we use electricity and then compare that to when we generate.
In the screenshots above we see that for this typical April day we are importing from the grid about the same amount of electricity as we are exporting to the grid. We import during the night and for the higher consumption periods of the morning and evening.
If a battery had been installed then it would have started charging from about midday and started discharging from about 6:30pm. If the next day had been identical to this one then the battery would have been discharged by around 8am. The round-trip efficiency for a battery is high (depending on battery type and manufacturer and claims are for up to around 90%) so we could retrieve up to around 7.5 kWh if we had stored 8.3 kWh. If the electricity unit cost from the grid were 30p/kWh then this single day could save us £2.25.
A large battery is similar to the battery in a battery electric vehicle and it shares a number of the same advantages and disadvantages related to the battery, ethics and electricity choice. To read more about batteries read section 4 of our electric vehicle reference article. The key question environmentally is whether it is displacing fossil fuels. If the answer to that is yes then it may be well-aligned to the energy transition.
| Pros | Cons |
|---|---|
| If displacing fossil fuel power => reduced fossil fuels | Battery needs critical minerals |
| Compatible with renewable energy (maximises use of self-generated Solar PV) | Emissions as a result of electricity used (especially if overnight off-peak charging) => householder’s choice of electricity matters |
| Can be used as grid attached storage (may help with storage of cheap excess electricity on the grid on sunny and windy days) | Pollution associated with battery material mining, refining and manufacture |
| High round-trip efficiency | Up-front cost |
| Can re-use an old automotive battery (although this is not as common as it should be) | A little degradation in capacity to be expected |
| A few installations may provide power during rare grid outages | Not all dwellings have an easy location for the battery |
Using the model developed for Churches we can see that there is potential for an improvement in overall carbon dioxide emissions (the example without a heat pump at the end of the model article shows that it reduced the number of years to break-even from a greenhouse gas perspective from 7 to 5). The case for a battery becomes strong when we are storing excess renewable electricity for use later. As we move away from gas and oil then we will be needing more electricity throughout the day and night – a battery can help to make sure that the electricity we use, at whatever time, is as low carbon as possible.
Living Laudato Si' 