Interesting, I assume there is some fundamental calculation that takes the radius of the greenhouse and chimney height in order to estimate the energy output.
I think the general idea here is that there's a lot of thermal energy that does not get used in a cost-effective way. IIRC the majority of 'efficiency' wrt energy hitting a panel comes out as heat, and here it's a question of if that heat can cost effectively be stored/used.
> "there's a lot of thermal energy that does not get used in a cost-effective way"
Reminds me of a discussion in the comments on Terence Eden's blog[1], where a commenter argues that photovoltaic panels on home roofs are not the best idea, and solar-thermal panels are better; an edited summary:
"solar thermal, 4 square meters of roof space will generate 1500kWh per year; to achieve the same with PhotoVoltaics [PV] you would need 16 square meters. Solar thermal would roughly address water heating for showers for a family of 4 for using 4msq of panels. If that doesnt represent a useful amount of energy from a small amount of roof space I don't know what does! And with a lower environmental cost, lower CO2 emission, than PV for that energy."
i.e. it's sad that government subsidies are making PV cheaper than solar-thermal, even though it makes worse use of roof space, with worse CO2 profile.
