Take DEA CHP assumptions for c_b and c_v, not old PyPSA ones #19
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The old PyPSA values for c_b and c_v assume an extraction plant (like the DEA coal CHP). However, if you look in DEA assumptions at "09b Wood Pellets Medium" (used for solid biomass CHP) and "Gas turbine simple cycle (large)" (used for gas CHP) they are not extraction plants but back pressure plants. The back pressure coefficient in DEA c_b is simply c_b = name plate electricity efficiency / name plate heat efficiency both measured when both heat and electricity are produced at maximum. For the extraction plants, the efficiency is measured in condensation mode, i.e. no heat production. With the old assumptions, the solid biomass CHP was under-producing heat for a given fuel input.
lisazeyen
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Dec 7, 2020
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I fully agree. Maybe one thing to keep in mind, we had a discussion in issue #7 about how comparable the efficiencies are between gas and biomass CHPs. The plants do have different input/output temperatures (50/100^Celsius and 40/80^Celsius) which do depend on whether the plant is usually connected to the distribution or the transmission system what we don't take account for in PyPSA-Eur-Sec.
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After reading the notes and the emails exchange I fully agree. The code is cleaner and we save the constraints on the feasible space for CHP operation. |
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This PR stops the script replacing the DEA values for the back pressure coefficient c_b and the c_v value with the old PyPSA values.
The old PyPSA values for c_b and c_v assume an extraction plant (like the DEA coal CHP) which has flexible production of heat and electricity within the feasibility diagram of Figure 4 in the Synergies paper.
However, if you look in DEA assumptions at "09b Wood Pellets Medium" (used for solid biomass CHP) and "Gas turbine simple cycle (large)" (used for gas CHP) they are not extraction plants but back pressure plants.
The back pressure coefficient in DEA c_b is simply:
c_b = name plate electricity efficiency / name plate heat efficiency
both measured when both heat and electricity are produced at maximum.
For the extraction plants, the efficiency is measured in condensation mode, i.e. no heat production.
With the old assumptions, the solid biomass CHP was under-producing heat for a given fuel input.
In our simulation results the plants produce along the back pressure line anyway for 99.5% of the time, so we don't need the full feasibility space.
I've correct the implementation in the PyPSA-Eur-Sec code too, see:
PyPSA/pypsa-eur-sec@098281b
The CHPs are now implemented as single links with heat output proportional to electricity output.