I just realised that the “average power” described here [1] if a perfect tool to estimate if my solar installation is big enough to feed a battery. I can get the real electricity usage and generation data from a day/week window and the average available power is telling me if I can power the house from a battery in that window. The graph below shows that in that particular window I generate enough - the average available power is around 0W.
The actual sizing of the battery would come from “Home Consumption Grid Day” that is provided by my inverter. A bi-weekly or monthly average of consumption from grid gives a good picture of usage depending on the season. There is one BUT…. The average “Home Consumption Grid Day” from the graph (below) is 5.28kWh. It’s OK, because the value changes during the day, so the average is lower that the real average of daily usage. The real average should be based on the maximum daily values or values taken 1 minute before midnight. That average would be in the range of 14-15kWh. Any ideas how to generate that value?
As the author of a commercial (but openHAB based) energy management system, I’d like to distract you somewhat from what you’re attempting because it might NOT make a lot of sense. It’s a little bit of the X-Y problem: you’re desperately trying to figure out a number that in the end won’t be the valuable information you currently still think it is.
Assuming you want to maximize savings, first of all, savings will be a longterm run result, they keep accumulating all year long.
What you did for one autumn week will look vastly different for summer or winter week so it should not become the basis for a buying decision (battery size).
Second, as soon as you get major consumers installed in your household (EV, heat pump), these you cannot operate from battery, but their consumption will totally change the picture.
Still you can control them from openHAB and you will want to have a dynamic power tariff and move their consumption into.
Just my $0.02 to make you rethink your focus.
Thank you very much for the comments! In summer I have tons of available energy, in winter it might be a bit short, but I live in a rather warm and very sunny place. Heat pump - I have AC units installed, technically they are heat pumps air to air, used for heating and cooling. I’m not sure why I could not run them from a battery? I picked a battery that will have nominal output power 8 or 10.5 kW. The max input current of inverter will be the limiting factor. EV - not planning in the next X years. I do have dynamic power tariff already - 3 different prices depending on the time of the day and I can move to “follow the market” if needed.
The price of kWh sold by me dropped by 40% recently - I’m pissed of with giving energy “for free”
P.S. I’m fairly sure my battery sizing calcs are OK, I just want to get the number from the OH. I sent a snip from a random time, but I have real usage for the last 18 months, so it’s not that I try to make a guess based on a 2 week window.
It’s rather simple: battery losses 10-15%.
In summer you can run the AC/heat pump directly powered by your roof yield.
In winter where most of heating will be from the grid anyway you will also not want to charge the battery first then run off it. Only direct consumption will avoid losses.
