Sean said:
Yves, if you are embarking on an attached battery project in the expectation of saving a pile of money please do the maths before you commence - you won't save money (but you'll enjoy the project)
If you want to make productive use of the surplus PV generation I would suggest that a far simpler method would be load diversion to water heating, or any resistive space heater - there are numerous products that will do this very simply and (unlike a battery bank) will have a positive RoI.
If you want provide your home with energy during an incoming grid failure, buy a generator and fit a changeover switch.
I know that the math is the tricky part.
I already have an electric boiler that I can switch on in case I need, however that will not take the entire production.
The basic situation was that initially we had what was called a backwards turning meter and a yearly utility invoice. So basically nothing was required in addition to the basic solar array. The excess production would make the meter turn backwards and you could reuptake the saldo in the winter. All was fine.
My yearly consumption was ca. 7000 kWh and my yearly solar production was also around 7000 kWh. So over the last 5 years I only had to pay for an extra draw of may 100 kWh in total (due to less sun).
The electricity price is roughly around 0.25 per kWh with all the taxes and what not included. So basically I would have to pay 1750 for my electricity.
Then all started to change. They first implemented a 900 tax in solar panels.
Now they are going to implement digital meters. In essence these don't turn backward, but meter the amount of electricity injected into the grid.
They are still very quiet about how they are going to charge us, but you can bet this will not be in our favor. I think we will get 1/3 of the naked electricity price, which is roughly something like 800 out of that 1750.
I know that I have a yearly reserve for the winter of ca. 2250 kWh. 800/7000 is ca. 11,5 eurocents per kWh. 1/3 of that would be roughly 4 eurocents.
So for the 2250 extra produced electricity I would only get 90 !!!.
So the deficit would be :
To pay :
- 900 tax
- 2250 X 0,25 = 562,5 for my winter use.
Total : +- 1462 to produce my own electricity.
This is not withstand that they above is assuming that in summer I will be using up my complete need of electricity from my solar array.
To make this more practical : I use about 20 kWh a day (24 hours) on average. Of course more is using during the nights and the mornings.
The production on a sunny day is ca. 40-45 kWh that is mostly produced between 10 and 17 h. Of that 40-45 kWh I can at best use 10 kWh. The rest goes to the grid and is basically lost to me....hence the need for batteries, which will reduce my deficit to the above, otherwise it will be even bigger.
Pure ripoff.
Then there is more : if I use batteries, I could charge them in the winter when the tarifs are lower and use the cheaper electricity in the evening. It's hard to make exact calculations about this, but the numbers run up pretty fast.
Its a normal 3phase system that. (230v) That will give you 400v between the phases.
