Primary demand of direct electrolysis and solar/wind with integrated battery systems

[mabijkerk]

Following a discussion in https://github.com/quintel/etsource/pull/2876.

Direct electrolysis The model allows direct electrolysis of solar PV and direct electrolysis of wind. These technologies consist of two nodes, an electrolyser and a producer of renewable electricity. The electrolyser input capacity does not necessarily match the output capacity of the producer. If electricity production in a given hour exceeds hydrogen consumption capacity, the excess is curtailed.

The question is whether 1) the produced hydrogen should be registered as primary hydrogen demand, or whether 2) the original renewable electricity production should be registered as primary electricity demand.

In the first case, the renewable electricity production is effectively out of scope of the model; the direct electrolysis technology is presented as a black box and the curtailment is hidden as well. In the second case, the renewable electricity production is in scope; the hydrogen is a conversion step and the curtailment is explicit as well.

Solar/wind with integrated battery systems The model allows installing solar PV or wind in combination with a battery system. These technologies consist of multiple nodes, among which a node that represents the connection to the grid. If the electricity production exceeds the grid connection capacity, the electricity is stored in the battery. If the battery is full, the excess production is curtailed. Once the electricity production drops below the grid connection capacity, the battery starts to release its stored electricity to the grid.

The question is whether 1) the supplied electricity to the grid should be registered as primary electricity demand, or whether 2) the original renewable electricity production should be registered as primary electricity demand.

In the first case, the curtailment, roundtrip efficiency losses and storage decay losses are out of scope of the model; the whole system is presented as a black box. In the second case, all flows are presented as explicit conversion steps in the model.

Overall question The overall question is where to place the 'primary demand' boundary for such systems. @AlexanderWirtz could you weigh in on this?

[AlexanderWirtz]

Interesting questions. I will give an answer tp the second first, because it looks easier.

Solar / wind with integrated battery systems As far as I understand the definition of primary electricity production (I find demand confusing in this context, although I understand that this primary production shows up in the primary demand mekko as primary electricity demand), what you count is what is effectively delivered to the grid.

Let's consider storage and associated losses later and focus on curtailment I understand curtailment is an important thing to know and report by the ETM. It is, however, in essence an calculation/estimate of something that was never produced. It's not like one can throw electricity away, after all. So in my understanding, primary production should exclude curtailment, always. I do knot know how best to model this, but I assume one can calculate the amount of curtailed power and subtract it from something like 'gross primary production' to get 'actual primary production' and report curtailed power separately. Or is this where primary production and primary demand should be used instead of 'gross' and 'actual'? This calculation would have to be well documented / consistently applied throughout the ETM.

Now, whether or not primary production should include the lost in a dedicated/inetgrated battery (of course it includes the energy delivered by the battery), my first guess would be: yes. The energy was actually produced and delivered to the battery, after all. It should be counted as 'storage or conversion losses' of course and be reported as such (separately) in the Mekko.

Is there also a case where power is curtailed because the battery does not have enough capacity, @mabijkerk? That is more like the Direct electrolysis case below.

Direct electrolysis Now, if we apply the same logic to the dedicated electrolysis, then we should agree that all electricity delivered to the electrolyser is primary production. The curtailed power never existed and should not be counted as having actually been produced. Of course, I agree that we want to be able to quantify how much was curtailed and when. So this would mean the primary production is solar and wind electricity excluding curtailed PJ. This would make the hydrogen production a conversions step like grid connected P2G. It would also make it easier to compare ETM results to those of other models. During the Metastudie we noticed that we kept having to correct for the fact that the dedicated hydrogen production was actually produced from offshore wind.

Does this help or make things harder, @mabijkerk?

[mabijkerk]

Thanks for your contribution @AlexanderWirtz!

There has already been some discussion on this topic in issue #2172. It seems like it would be best to have a very clear definition and accounting of curtailment and primary demand for curtailment. I propose to plan a session at some point to tackle this.