Thread for discussing money saved with OpenHAB

NL: 2023-05-21 12-13 CEST: -7.6 ct/kWh (plus - AFAIK - 21% VAT; source: epexspot)

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NL: 2023-05-28 14-15 CEST: -40 ct/kWh (plus VAT, source: epexspot)

You already know the prices of tomorrow? :crazy_face:

I hope dynamic energy tariffs for pivate costumers will become more common in the future. So that someone without own pv system can profit from this.

I mean in germany we are talking about lots of founded pv systems, BEV and “intelligent” wallboxes, smart grid ready heat pumps and in many cases the potential fizzles out.
So I also hope load management in private households finds more popularity.

I’m not sure whether negative prices for energy are a good sign, but let’s not get into politics - BTT:

Tibber doesn’t seem to be able to handle negative prices for energy: neither the App nor the API have the prices for tomorrow. Prices for tomorrow were published by epexspot at 14:30 CEST …

Prices at EPEX (Leipziger Strombörse) are fixed every day ~13:00 for the next day.
You can obtain them from various sources, e.g. sends them via mail once a day.

It’s actually quite interesting that the EU has made this a mandatory thing to offer some years ago already but Germany failed to enforce this into national law. Now they do, government very recently (6 weeks?) agreed on a new law that by 2025 any power company has to offer a dynamic tariff.
Let’s hope that makes it to the market.

So do I. Well, then again to be fair as I wrote some posts up I’m selling a system to provide this :rofl:
Just won the German industry award for that by the way.
The dynamic tariff integration was right what convinced the jury most.


But how will that work. As far as I remember smartmeters are to be rolled out until 2032 ?

It’s the usual lobbying game with every contender trying to avoid moving as much as possible.
But the law does not enforce how this is to be implemented, just that, it’s up to the companies
(the famous “free market” and “technology openness” our 3-Pünktchen-Partei keeps asking for).

There’s several options. You can bring your own smart meter like aWATTar does with Discovergy meters or add your own device to read a (non-smart) digital meter like Tibber does with their “Pulse”. I’ve implemented both of them in my system so it is already available to customers to benefit from this today. And I’m sure there will be more ways by the time it applies.

… and even with a Ferraris meter you can take part in the game: Tibber bills monthly according to standard load profile (Standardlastprofil) and hourly energy rates - other energy providers might jump on the waggon.

From the discussion I assume you are in Germany?

Okay, here are my numbers that I promised @timo12357 to share.

Month kWh Market avg Our avg Diff Diff % Ref 1, EUR Ref 2, EUR Actual EUR Diff to ref 1 Diff to ref 2
2022-08 518 32,4 22,5 -9,9 -31 % 204 119 25 -178 -93
2022-09 625 26,6 18,6 -8 -30 % 202 119 43 -160 -76
2022-10 873 14,1 8,9 -5,2 -37 % 152 81 84 -68 3
2022-11 1034 24,2 20,2 -4 -17 % 305 213 112 -193 -101
2022-12 1503 27,1 24,2 -2,9 -11 % 496 369 179 -317 -191
2023-01 1369 8,9 6,9 -2 -22 % 152 100 175 23 76
2023-02 1570 8,82 6,02 -2,8 -32 % 173 100 188 15 88
2023-03 1723 8,16 5,76 -2,4 -29 % 177 106 214 37 108
2023-04 975 6,66 4,66 -2 -30 % 82 49 125 42 76
2023-05 890 3,28 2,18 -1,1 -34 % 73 49 109 36 60
-762 -51

So this is all about optimizing the electricity usage with the same solution that Timo uses. It’s documented here, if somebody has not found the thread earlier: Control a water heater and ground source heat pump based on cheap hours of spot priced electricity - #13 by masipila

Explanation of the table above.

  • The first two columns are obvious, it’s the month and our consumption in kWh on that month
  • The third column is the monthly average price in Finland.
  • The fourth column is showing what our actual average has been on that month compared to the market average. In other words, we have been consuming most of our electricity during hours that are cheaper that the monthly average.
  • The consumption factor is the difference between the market avg and our actual avg. For example, in 2022-08 market avg was 32,4 c/kWh and our actual avg was 22,5 c/kWh so the “consumption factor” was -9.9 c/kWh.

Then to the original question “how much money have you saved”. It of course depends on where do you compare to, so I calculated a couple of scenarios.

Reference cost 1 has the following assumptions:

  • I would have a dynamic tariff / spot price contract with 0,38 c/kWh margin (this is the cheapest margin that I was able to find today when I quick compared the dealers)
  • I would not have any scheduling for the consumption so our monthly average would be 20% above the market average because most of the consumption would happen during the day when the spot prices are usually above the monthly average.
  • I have no idea if this 20% is the correct factor for this since I’ve never had a spot price contract without doing schedule optimization.

Reference cost 2 has the following assumptions:

  • I would have a dynamic tariff / spot price contract with 0,38 c/kWh margin
  • Our consumption is optimized to the cheapest hours like it has been since last summer

Our actual cost is with the Väre Välkky contract type

  • With this contract type I share the price risk with the dealer so that our price is 14,8 c/kWh +/- consumption factor
  • In other words, if we consume electricity during an hour where the spot price is below the monthly market average, we get discount for the whole month’s consumption. If we consume electricity during an hour where the spot price is above the monthly average, our price / kWh for the whole month increases.
  • Väre was the only company having this contract type last summer but now also Helen has this same contract type (Helen Fiksusähkö) and Fortum has it (Fortum Duo)

So how much have we saved… Compared to reference cost 1, our cumulative saving so far is 762 EUR. Compared to reference cost 2, we are still on the saving side by 51 EUR.

Now that the prices are back to normalish, we will most probably end up losing against reference cost 2 in the 24 month contract period that we have, but I consider that as the price of the “insurance” that we decided to take last summer when the hell broke loose in the energy market. When the 24 month contract ends in a year from now, we will for sure go to a pure spot price contract and continue the schedule optimization.

Edit: I forgot to mention that we got an electric vehicle in 2023-02 so the consumption went up.
Edit 2: Table formatting
Edit 3: Fixed copy-paste error from May 2023


Another aspect to this cost savings is the durability of our ground source heat pump. Our heat pump is a traditional on/off compressor pump. In other words, it’s not a modern inverter pump where the pump is able to adjust its speed, our heat pump is either ON or it’s OFF.

Based on the discussions on heat pump forums, some people are saying that the compressors of on/off pumps will last about 100 000 compressor starts before they break down. Between 2020-01-29 and 2022-05-20 our compressor had a massive 22 808 compressor starts, which is 28 compressor starts per day!

The pump had been running on full automation. The biggest contributor to this massive number of compressor starts turned out to be a water pump that circulates domestic hot water so that when you open the tap, you’ll get hot water immediately. The pump had been running 24/7 for 2,5 years and the circulation was causing the low sensor of the domestic hot water tank to fall below the lower threshold every 45 minutes or so. When I realized this, I immediately bought a mechanical timer that started to cut the power from the circulation pump so that it was only circulating the water when we need hot water. This helped a lot, but I then later automated this to openHab-controlled relay so that I was able to automate it more elegantly.

Anyway, here are the stats for the compressor starts, average number of heating hours per day and average number of domestic hot water heating per day. Unfortunately I don’t have data for the last couple of days of March and the almost whole month of April this year because I forgot to enable logging when I plugged the USB stick back to the heat pump :frowning:

Month Compressor starts Starts / day Heating / day (h) DHW / day (h) COP / heating COP / DHW
2022-08 24 0,8 0 0:37 n/a 3,3
2022-09 67 2,3 2:12 0:37 5,5 3,3
2022-10 76 2,5 4:54 0:42 5,3 3,3
2022-11 55 1,8 5:57 0:49 5,4 3,5
2022-12 68 2,2 8:45 1:01 5,4 3,6
2023-01 63 2,1 8:14 0:51 5,3 3,5
2023-02 53 1,9 8:30 0:39 5,3 3,5
2023-03 n/a 1,6 6:44 0:45 5,4 3,5
2023-04 n/a
2023-05 38 1,2 0:46 0:43 5,5 3,1

The number of compressor starts is now on very low numbers so I hope my compressor will have many years ahead. For most of the winter I was able to heat the house at one or max two heating periods when the prices were at lowest on that day. Only on the coldest days had we use three heating periods per day so that the house doesn’t cool too much between the heating periods. This concept of dividing the day to 1-N heating periods is thoroughly discussed between myself and @mstormi in the thread of my solution, the link is in the previous comment above.


My energy bill for May just came, April numbers for reference:

Spot April May
consumption [kWh] 854 613,06
basic fee [€/mth] 4,35 4,9
price [c/kWh] 5,7305 3,2804
margin [c/kWh] 0,22 0,25
Total 55,17 € 26,54 €
Local energy company
basic fee [€/mth] 2,5 2,5
price [c/kWh] 13,18 13,18
Total 115,06 € 83,30 €
Savings [€] 59,89 € 56,76 €
Savings [%] 52 % 68 %
Average spot price [c/kWh] 6,661 3,3
Savings [c/kWh] 0,9305 0,0196
Savings [€] 7,95 € 0,12 €
Savings [%] 14 % 1 %

I was still able to get 1% below average spot price despite the very low spot prices in May. Total savings so far about 116,65 € compared to local energy company prices since taking Control a water heater and ground source heat pump based on cheap hours of spot priced electricity - #13 by masipila in use.

Cost - Cost(standard load profile):

April 2023: -4.01 EUR*
May 2023: -3.37 EUR
June 2023: -0.72 EUR (so far)

*cf. Thread for discussing money saved with OpenHAB - #8 by Ap15e

I think the monthly Tibber fee (3.99 EUR/month in Germany) is based on the average savings that an average household (without PV/EV) can achieve by shifting consumption to cheap hours. :slight_smile:

Now that we’re on the summer months and we don’t need to heat the houses, the heating of domestic hot water plays a huge role here. As we discussed separately before, you only have 180 l capacity and when it is being consumed, you pretty much need to heat more of it regardless of the spot prices because otherwise you will risk running out of hot water and the WAF factor will suffer.

Our house has 180 + 300 liters of hot water so we can easily schedule the heating to the cheapest hours and for the 300 liter tank, we can even skip entire days if needed (unless we use the bathtub).

Because we can schedule the heating of domestic hot water, our May was 34% (-1.1 c/kWh) below the average market price (you were 1% below). In June, the monthly average on June 1-6 is 1.54 c/kWh. We are at 0.94 c/kWh average so far i.e. 0.6 c/kWh below average, or 39% below.

AT, DE-LU: 2023-07-02 14-15 CEST: -50 ct/kWh (plus VAT)

NL: 2023-07-02 13-15 CEST: -50 ct/kWh (plus VAT)

Negative spot market prices appear to be capped at -50 ct/kWh(?).

Epex spot price limits: -500 €/MWh and +3000 €/MWh (source:

-50 c/kWh is a lot, I just wish we would have those prices here in Finland.
Meanwhile my electricity bill for June came in:
Consumption: 498,31 kWh
Price: 4,89 c/kWh
Cost: 29,25 € including tax 24%, margin 0,25c/kWh and monthly fee 4,9€
Average spot price in June: 5,37 c/kWh
Savings: 9,04% below spot average
Savings: 50,2% below local energy company fixed price

We currently have diswasher, washing machine and ground source heat pump under spot price optimisation.

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