A question I often get during my home energy surveys is about my opinion on whether doing [insert potential energy-saving improvement] is worth it. Any question that includes “is it worth it” tends to send my logic-brain into a spin. I have to restrain myself from entering into a philosophical discussion about what “worth” means for the client: does the warm glow of storing your own energy count towards the “worthiness” and how do you put a value on that? What about the value it might add to your house? Or is it simply a financial payback consideration?
All of these machinations are particularly challenging with, say, windows. You would probably never upgrade any window if your only concern was getting a financial return, but that hasn’t stopped most people from replacing their ropey single-glazed casement windows with lovely new double-glazed units. There are of course other reasons for doing things beyond the financial.
The mental equation is a bit more straightforward with home batteries of the type that are usually installed alongside a solar PV system. Batteries are simply bloody expensive, and without beating around the bush, it is unlikely that most people will get a return on their investment in the expected lifespan of the battery – typically 10-15 years. Calculations are notoriously difficult due to the many variables involved (variable-rate tariffs, changes to demand including the possible introduction of EVs and heat pumps), however if you fancy creating a reliable spreadsheet model then fill your boots – I would be interested to see it!
The cop-out answer I tend to give clients is to wait for V2G. V2G – Vehicle to Grid – is the technology that allows your EV or plug-in hybrid to act as a power station, in effect supplying your home with electrical power on demand. At present only a small number of cars offer V2G capability, however that number is set to increase rapidly in the coming years. The other sticking point has been the lack of availability of V2G chargers, however the arrival of the Wallbox Quasar (if you can find one and afford the cost of several thousand pounds) will start the ball rolling for those who live life at the bleeding edge.
A V2G arrangement would perhaps work best with an EV with a large battery. For example, you could keep 20% (say 15-20kWh) of the battery capacity to run the house at expensive peak times, and use a cheap off-peak tariff to charge the EV battery and run the house overnight. This would still leave 80% of the car’s capacity for travelling at the drop of a hat. The exact proportions of the battery given over to home and car use can be adjusted according to household demand and travel needs. In addition, income could be maximised by exporting power to the grid on a generous Smart Export Guarantee tariff, although it is worth bearing in mind that frequent, heavy and rapid discharges will impact the lifespan of the car battery to some extent.
So unless you have money to burn and have carried out all the other sensible upgrades in your home – in which case fill your boots – I would recommend forgoing that home battery and, er, replacing those rotting timber sashes instead…