I’ve been reading the walden effect blog, and a comment thread there led me down some interesting avenues that I’d like to share.

When they blogged that a power outage stopped the fan in their furnace from working, I immediately thought that it would be neat if there were fans driven by the heat of the furnace, e.g. by a stirling engine. Some googling later, and we have a stirling-driven fan.

By the by, the thread turned to photovoltaic solar power, and I did some calculations based on numbers I could find. Basis for the discussion was a Northern Industrial solar panel, with a rated power of 15W, costing about US$100.

On the fast facts page of the solarbuzz website, I found the following info. A solar system of 1 kW peak power will annually deliver;

• 1600 kWh in a sunny climate
• 750 kWh in a cloudy climate

(As an aside, 1 kWh is 1000 J·s⁻¹ · 3600 s = 3.6 MJ)

So a small appartment (definitely cloudy climate, say 2100 kWh annually) would need an installation with 3 kW peak power to be self-sufficient in electricity. Extrapolated from the same website such a system would cost around €19000. The total cost for an installation with the cheap solar panels I estimate at €23000. Assuming an electricity cost of €0.25/kWh, this installation would save €525 in electricity bills per year. Clearly this is not a cost-effective investment at this time.