Solar plants take much area, so what power does 1km2 with Zn-ZnO cycle produce?
Other metal oxide cycles bring similar performance.
in Andalusia receives 1800GWh/year or mean 0.21GW. The tropics offer more. Some countries have free area and consumers.
Concentrators or solar cells don't catch all the incoming light. I neglect that here, not accurate, but at least the comparison is fair.
The reduction of ZnO to Zn shall be 74% efficient, as on 17 Nov 2022 chemicalforums
This is an estimated target. The few demonstrators achieved half that.
0.15GW Zn make electricity in a battery (which is still research). A zinc-air battery provides 1.45V while Zn->ZnO packs 351kJ/mol=1.82V, so this 80% efficient step leaves 0.12GW electricity
. A power plant takes 8.3km2
to deliver mean 1GW electricity.
The same plant can also distribute ≤0.09GW heat
. Or rather, recycle the high-temperature heat at some process step to provide more Zn. Or use the heat in a combined cycle to make more electricity. 40% of 0.05GW heat provide 0.02GW electricity more and let distribute 0.07GW heat.Zn flexibly produces H2 or electricity
. 0.15GW Zn provide 0.12GW = 27kt/year H2
The plant can also ship Zn to customers
rather than H2
.Zn storage produces electricity on demand
. From day to night, 14h×0.11GW fit in 16kt Zn or 4.4dam3
, a heap 10m tall, 20m wide and 44m long. Even 7 days ×0.15GW need only 73dam3
or 20m×40m×180m. This heap costs only ground area.
========== Compare with engine
Heat storage at moderate temperature prevents a combined cycle, so the engine shall obtain mean 40% = 0.084GW electricity
. It can also distribute 0.13GW heat.
To provide electricity at night
, the plant must store 0.21GW×73%×14h=7.8TJ heat in 26kt melting salt
(300kJ/kg). The salts are cheap if they're little processed ore, like chlorides. Storage for a few days is feasible and demonstrated.
========== Compare with solar cells
The same area costs much more
than concentrators, which are little more than steel sheet.
They convert about 19% of sunlight. 1km2
provides mean 0.040GW electricity
and no heat.Storage does cost
and has a limited capacity, with Li batteries being the present main choice. The same 14×0.11GW from day to night take 7700× Powerpack 2 storing 200kWh each. They weigh 12.5kt too but cost 0.4G€ while a Zn heap is nearly for free. If serving for 20 years, they add 34€/MWh to the stored electricity fraction. A week storage remains too expensive.
========== Compare with solar cells and electrolysis
Demonstrated PEM cells are up to 80% efficient presently, so the output is around 0.032GW = 7.2kt/year H2
Storage and transport are possible but less convenient than with Zn.
In the least inefficient later use of H2
, fuel cells recover ≈62% = 0.020GW electricity
Such a meaningless cascade of losses is just the worst possible combination
among renewables. No idea why everybody concentrates on this.
========== Compare with nuclear and electrolysis
Nuclear electricity is almost twice as expensive as renewables under realistic conditions. EDF get guaranteed 92.50gbp/MWh for the EPR at Hinckley Point while the providers-operators of offshore wind parks got 55gbp/MWh.
Nuclear is an even worse way to hydrogen than solar cells and electrolysis.
More radical processes convert sunlight or sunheat to hydrogen, welcome. I ignore how efficient and proven they are.
Marc Schaefer, aka Enthalpy