Friday, 11 December 2015

Shiny white roof good, solar PV panel bad.

It seems that all this fuss (e.g. the Guardian solar subsidy campaign) over installing solar PV panels is actually bad for the environment. Solar PV panels cause global warming! The best way to prevent global warming is by reflecting sunlight back into space using white and/or reflective surfaces. For example shiny white roofs! If one really wants to save energy, and stop using fossil fuel, the best contraption to put on one's roof is a solar water heater. Wikipedia has two articles on this: Solar radiation management | Reflective surfaces (geoengineering)

Alex Cannara: tell your friend that roof of his does more to damage climate than he gains from energy savings! Remember, the sun delivers 1kW/square meter. PV only converts ~20%. The pic shows what we should all do, as recommended for many years by The Heat Island Group [2], Lawrence Berkeley Labs,the CEC, Steve Chu.

Alex Cannara: your friend's panels aren't better than 20% efficient, no matter how he loves them. That means they radiate ~800 Watts per square meter back into air ... That waste of convection and IR radiation adds directly to local global warming. By the way, solar hot-water is good, because its collectors run at lower temps and transfer most heat to their intended target -- insulated water storage.

Alex Cannara: The fundamental point is that a 100 square meter, poorly-reflective roof/solar installation, generates about 100kW of waste heat/IR while the sun is on it, giving the physical effect of greater GHG concentration that actual. That waste dwarfs whatever savings the design & systems in the home can make, or cause to be saved, at a serving utility.

Solar reflectivity increaseCO2 offset by 100 m²CO2 offset globally
White Roof0.4010 tons (~ 2 cars)
Average Roof0.256.3 tons24 Gt
Cool Pavement0.154 tons20 Gt
Total potential----44 Gt
Value of 44 Gt CO2 at $25/t ~ $1 trillion
100 gallons of gasoline/year => ~ 1 ton CO2
Global CO2 emissions in 2009 ~ 24 Gt
(Akbari, Menon, Rosenfeld[1]. Climatic Change, 2008)

Alex Cannara: just increasing roof reflectivity around the world by 40%, would have the same warming prevention as parking all 700,000,000+ vehicles on Earth for a decade.

  1. Akbari, Menon, Rosenfeld. Climatic Change, 2008, DOI 10.1007/s10584-008-9515-9
  2. The Heat Island Group, Lawrence Berkeley Labs,the CEC, Steve Chu.

3 comments:

  1. This analysis seems to omit the largest benefit of PVs - that their kWh will offset fossil fuel-derived kWhs and their associated CO2 emissions and the lifetime heat absorbed by that CO2 - "If our solar panel is pure black, and 14% efficient, then for each kWh of electric power that comes out, there are 7 kWh of heat that were absorbed and radiated. But each kWh it generates it eliminates the release of 1.4 pounds of CO2, which during its lifetime in the atmosphere will absorb 210,000 kWh of heat. So the energy balance for the solar panel (when it’s connected to the US grid) is about NEGATIVE 209,993 kWh(heat) per kWh(electric) " From http://thinkprogress.org/climate/2009/10/12/204787/superfreakonomics-errors-levitt-caldeira-myhrvold/

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  2. I'll put that to Alex to see what he says, and go over it myself, line by line. Being a US Democrat, Alex has almost certainly read that Think Progress (ha, ha, ha, they're so 'ironic') blog link already.

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