Defining avoided burdens in a hybrid CSP-PV system

Data and Modelling
1

Hello everyone,
I am conducting a consequential LCA of two energy systems. The baseline system (system A) consists of a CSP plant with thermal storage, while the alternative system (system B) integrates curtailed PV electricity into the CSP, increasing its output.
My main challenge is defining the avoided burden for System B. Since the curtailed PV would otherwise be lost, how should the avoided flow be accounted? Would it be appropiate to consider that the additional electricity generated by System B displaces another marginal energy source?
Thank you very much

2

Hi, I am not sure what you mean by the excess electricity from the curtailed photovoltaic (PV) plant being fed into the concentrated solar power (CSP) plant, increasing its output? Would the PV electricity not rather be fed into the thermal storage? In that case both the PV and the CSP is simply using the same thermal storage, which will have to be dimensioned optimally to the output from both (also considering that if the electricity from the PV is curtailed, then probably also at the same time the electricity from the CSP will in excess, so both will feed into the thermal storage at the same time). But maybe, I have misunderstood your system design?

3

Thank you for the reply,
Yes, exactly, what I mean is that in my System B, the PV is injected onto the thermal storage system to increase its charging capacity compared to System A. But both thermal storage systems remain the same in both systems (their dimensions). What it is obtained with this implementation is an increase in the overall net electricity delivered to the grid by System B compared to the electricity delivered to the grid by System A.

4

Hi again, Mariasun

So your question is simply what electricity source is displaced by the output from the thermal storage? This will always be the marginal supply to the electricity market at the time that the output from the storage is dispatched. Optimally, the thermal storage would dispatch in times of peak demand, so displacing marginal supply of peak electricity in the affected grid.

I am a bit skeptical about the thermal storage system being the same in both systems, since then you only change the capacity utilisation, and since - as I already mentioned - the full storage capacity should be dimensioned to optimally cater for the duration of the excess supply (curtail) periods, which will be largely simultaneous for the two electricity sources.

5

Hello, good afternoon
Thanks for the reply.
Regarding thermal storage: I am considering the same system since generally in CSP plants both tanks are designed to be able to dispatch a certain number of hours the nominal capacity of the power system in charge of delivering electricity to the grid. However, due to the nature of the energy source, this is not always the case. That is why I would like to know if, by being able to inject PV into the storage system, how much extra energy I can deliver to the grid. Hence the marginal supply that would be displaced. Thanks a lot.

6

Hello again Bo,
I’ve been thinking about this topic again and I wanted to raise a new perspective:

  • The main goal of my system, rather than improving the electricity ouput, can also be seen as decreasing the plants’ electricity need during operation. That is, if we have more operating hours, the parasitic consumption when the plant is not working (for instance, to maintain the molten salts warm to avoid freezing), decrease thanks to the injected PV (that provide the plant with more operating hours). For example: On the one hand, system A does not inject PV into the tanks, resulting in tanks designed to operate without sunlight for 6 hours. On the other hand, system B, thanks to the extra load from the PV, is able to work 7 hours a day without sunlight, with the same tank design. Would it be correct to analyse the consequential point of view from the dimensioning of the tanks? For example, if we want to be able to work 7 h per day without sunlight and without injecting PV, following the current state-of-the-art design in CSP plants, we would have to increase the design of the tanks (more salt volume, more steel, etc.). With the new technology (proposing to inject PV), these 7 h are achieved without the need to increase the design of the tanks.

Thank you very much again

7

yes, that makes sense. My main concern was that the PV and the CSP will be largely active at the same time, due to their reliance on the same insolation.