[Q:] need help to evaluate the pricetag for contents of fueltank/battery filled with "chunks" of energy at different prices

Hi there,

I need to get my head around a thing and how to do this with NR:

  • let's assume I have a fuel-tank / a battery that is able to store/provide a certain amount of energy (kWh) between full (100%) and empty (10%) of its total capacity.
  • before I start to draw power from that tank/battery, I want to know the value/cost for each kWh currently stored/ that will be consumed (if I choose to start drawing from that tank/battery at this time)
  • the tank/battery however is filled at different times with different amounts of energy, which also has a different price-tag/cost associated with it. Hence the combined/total value of all the Energy chunks of the mixture inside that tank/battery is not constant.

In addition, this is what I know of the parameters:

  • net/usable capacity in kWh of the tank/battery between 10% and 100% -> 30kWh
  • when charging, I know the Power (W) that is charged, at any given time (actually I am storing these values in an influxDB, too)
  • when charging, I know the cost per kWh at a certain time for each source of energy going into the tank/battery
  • in my installation I am able to distinguish between loads of different types (heatpumps, EVs, Home, tank/Battery) at any given time.

At home, I have quite a large solar array, a home battery, and 2 heatpumps, as well as 2 electric vehicles.
I do have separate tariffs for my home and the heatpumps/EVs, where the latter tariff is a fixed price and the tariff for home is a dynamic price (tibber) with different hourly rates across the day.
For energy from my solar array, when fed into the grid, I also get a fixed price per kWh, hence when feeding solar energy into the battery, I lose that money (but still saving money overall as the external tariffs will always be more expensive than the money earned from feed-in, even if inefficiency of the energy conversion via the battery is considered).
In general, the tariff for heatpumps/EVs is substantially lower than the tariff for my home.
Because of the nature of the physical installation

  • available solar energy will be directly consumed by active loads at that time
  • any excess solar energy will be stored in the battery until a target SoC is reached
  • any excess solar energy after that will be fed-in to the grid
  • when the battery gets charged from the grid, the tariff for home-use (tibber dynamic prices) will be applied.

Use case:
Because of the price differences in my tariffs I want to decide when it is commercially more feasible to exempt certain loads from being fed by energy from the tank/battery.
Hence I need to have the price-tag of energy stored in my tank/battery at any given time in order to make that decision.
A decision based on SoC and (dynamic) price for charging, which some other people use, is only good for the decision when to charge the tank/battery (lowest price strategy, even with or w/o energy forecasting) and I am planning to combine the two strategies.

This is a large subject and there are many topics similar. Search results for 'tibber energy order:latest' - Node-RED Forum

It may be better to break the subject into sections, and ask the questions separately.

As to calculating stored battery, i may be easier to keep an average of the price, then when you store from tibber recalculate the average.

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Thank you for your message.
Tibber itself and dynamic pricing via node-red is not the problem here...I mentioned it - as an extra information in parathesis - because of the nature of dynamic prices in general.

Yes, I gathered as much, but no clue on how to do that. hence my post.

...right you are...I see that now....will try and do that.

You need to keep a record of the KWH in the battery and the average unit price of that.

Then when you charge calculate the KWH you added and the price.

You can then when you charge.

battery 10 KWH at 2 price unit(average) = 20
charged 10 KWH at 1 price unit = 10

new average

30 / 20 KWH = 1.5 new average for 20 KWH stored.

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