[matzab]

This is explicitly aimed at producing energy in cold environments (high altitude, polar regions), so it's less of an issue (and not exactly the point). Anyway, they seem to aim at 12% STH efficiency and provide some examples (assuming 65% hydrogen fuel cell efficiency):

Then, powering a Raspberry Pi computing device (PRPi = 4W) for an autonomous measurement device year-round at the > Neumayer III station (70.68°S, 8.27°W, Tavg,y = −15.5 °C) would prospectively require a module area of 0.41 m2, whereas at Paranal observatory (Chile, 24.63°S, 70.40°W, Tavg,y = 0.4 °C) 0.18 m2 would suffice.