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= Renewable Solar Power =

== Summary ==

But still the headlines persist about the miracle of renewable wind and solar energy:

* Holographic foil that is twice as efficient as typical photovoltaic (PV) solar cells, using light selection, deflection, and concentration. The Dresden-based company Apollon GmbH & Co claims this has 28% efficiency compared to a typical 17%.

* Modern silicon and indium-tin-oxide-based solar cells are approaching the theoretical limit of 33.7% efficiency but a research team at Princeton has used nanotechnology to create a mesh that increases efficiency over organic solar cells nearly threefold.

* Solar

Wind is a non-starter for propulsive power because, well, if you want to use wind power, get a sailboat! Right?

In practice, for an 8-hour summer day, 40 degree latitude, the sun delivers an average [http://zebu.uoregon.edu/1998/ph162/l4.html 600 W/m²]. Currently the best commercial solar panels are ~16% efficient. At an efficiency of ~16% on a perfect sun day this is a yield of 96 W/m² averaged over 8 hours (0.768 kWh).

Now, metric horsepower, widely used in the auto industry, is defined as 0.73549875 kilowatt (kW). Assuming we need 200 horsepower (hp) to drive a 70-ft boat, this is ~147kW. At 96 W/m² this equals 1,531 m² (16,472 ft2) of panel acreage [1 m² = 10.76 ft²]. And this is just for propulsion during daylight hours. There is no extra for storage in a battery for night operations.

Let’s cut to the chase with a real worked example. Assume a boat moored in Montreal’s Old Port at 45.5 degrees N and 73.35 degrees W. The sun’s azimuth angle varies between 20 and 68 degrees from winter to summer. Assume 365 perfectly sunny days and solar panels that are horizontal on the boat deck and do not track the sun’s azimuth and east-to-west travel. The average available energy over a year is 3.40 kW/m²/day. At 16% solar-panel conversion efficiency, this is only 0.56 kW/m²/day.

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