A new strategy, a new approach to automation

As I explained before, I was very wary of automating my system beyond what the inverter could do natively. As a retired elecronics and software engineer there is too much danger that such an endeavour would become a slippery slope. Well, I now have one foot on that slope!

What prompted this change of heart?

Well, during the last month we had some periods with VERY low Agile prices and it got me thinking about how I use my generated solar power. One way of looking at it is to look at the "opportunity cost" of the solar power generated. The incoming solar power, thanks to the sunk cost of the system, comes in at 0p/kWh. However, I can sell any excess back to Octopus at 15p/kWh. That means that, effectively, any solar that I use is costing me 15p/kWh - inasmuch as I could sell it if I want to.

This way of thinking leads me to consider a different strategy:

What if I were to charge my batteries on a cheap rate at night and, during the day, export most or all of my solar at 15p/kWh?

In principle, I should be able to charge the batteries for less than 15p/kWh, even accounting for losses. I would still be able to use SOME solar as i comes in (the best way to use it in my opinion) but the 15p/kWh earned from export of any surplus should make up for the cost of topping up the batteries at night.

The only other question, then, is how long to use power from the batteries in the evening. Clearly one should do so from 4pm to 7pm, during the peak rate. Then there is a choice: stop at 7pm and preserve battery life by limiting the degree of discharge, or (if DOD is not such a great consideration) continue for longer and use some or all of the remaining charge instead of paying the post-peak price which is still moderately high.

This thinking has led me to think that it would be interesting to implement a higher level of automation.

Watch this space!