## December 23, 2013

### Solar power per square kilometer

please note: this is just a 'quick & dirty' reply to an interesting question on Twitter, the usual more in-depth stories about renewables can be found here : http://ezrdevelop.blogspot.com)

@went 55 shared, @RF_HFC was skeptical and so I found the source of this map and shared the pdf document and its main underlying thesis : (on page 25, map on page 26)

Robin Fransman (@RF_HFC) replied in Dutch: "250 GWh per square kilometer is way to high"

So I looked it up, and indeed this value is at best a theoretical value, but I couldn't really understand the assumptions made by the author Nadine May.
Although she referred to thermal solar energy potential, the solar yield for photovoltaics in the Sahara desert is between 1800 kWh/per 1kW installed capacity based on silicon panels, and 2100 kWh/ per 1 kW thin film panels. (according to PVGIS optimized slope and several locations probed) . Concerning 'land use' of solar plants it's not possible to just make calculations of efficiency per m2, but it is important to leave some space between rows of racks where the panels are attached to, because otherwise the shade will affect the solar yield. So per ha (=10000 square meter) the power production capacity is +-300 kWpeak for thin film panels and +-500 kWpeak for silicon based panels.

A practical problem which obviously is somehow ignored by the scientific community:
>>2.  At home: 1 kWp ≈ 1000 Wp ≈ 5 m2 (at 20%)
At large:: 1 GWp (Giga Watt peak) ≈ 5 km2<<
At 'home level' it's correct (but no obligation to purchase panels with highest efficiency = often with highest price per kW) , but for utility scale it isn't.

So in reality it's
1 ha= 500 kW,
10 ha = 5 MW,
100 ha =1 sq km = 50 MW
5 sq km = 250 MW
(Also taking into account frames & space between 2  panels)
practical exception: If you install panels on a mountain slope of +-30°

but on the other hand it isn't really important how much land is used to produce solar power, since there  is lots of wasteland available. Especially when the use of the vast spaces of the Sahara desert is intended. In the end not the efficiency per square meter, kilometer or mile is important , but the price per installed kW, MW and GW is ! So no need to impress the public by small numbers of land needed.

Although the use of thermal solar energy by CSP is perhaps better to store the energy for the time after the sunset, it's by now cheaper (and less complicated) to use PV panels.

Concerning 'land use' of CSP I found this
http://en.wikipedia.org/wiki/Solar_power_in_Utah