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== Summary ==There have been a lot of new developments on the renewable-energy front, and yet solar energy is not a good candidate for boat propulsion. A few years ago powering a trawler boat with solar energy would require towing a solar-barge larger than the boat, and in 2013 2016 not much has changed.

* Solar Impulse HB-S1A airplane left on a transcontinental flight acorss the USA on May 42013.

There are only two possible renewals for powered boats:

* [[FuelCell|Hydrogen]]

Wind is a non-starter for propulsive power because, well, if you want to use wind power, get a sailboat! Right? [[WindEnergy|Wind energy]], like solar is useful for supplementary power; or, for supporting a minimal lifestyle on a sailboat. [[#top|Top]] == Solar Facts ==

According to NASA, the earth's surface receives a maximum of [http://www.grc.nasa.gov/WWW/k-12/Numbers/Math/Mathematical_Thinking/sun12.htm 137 Watts per square meter ] (W/m2m²) at noon at the equator when the sun is perpendicular. At other latittudes latitudes and sun angles the energy is less.

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/m2m²]. 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 m² averaged over 8 hours (0.768 kWh).

Now, metric horsepower, widely used in the auto industry, is defined as 0UPDATE: In 2015 solar panel company SolarCity announced [http://www.73549875 kilowatt (kW)solarcity. Assuming we need 200 horsepower (hp) to drive a 70-ft boat, this is ~147kW. At 96 Wcom/m2 this equals 1,531 m2 (16,472 ft2) of newsroom/press/solarcity-unveils-world%E2%80%99s-most-efficient-rooftop-solar-panel acreage [1 m2 = 10-be-made-america commercial cells that are 22.76 ft25% efficient]. And this is just for propulsion during daylight hours. There is no extra for storage in a battery for night operations.

The highest density commercial solar cell has a capacity of 174W/m2 or ~16W/ft2. Assume this is feasible outputNow, even though we only receive 137 W/m2 at metric horsepower, widely used in the equator and 96 W/m2 at 40 degrees latitudeauto industry, is defined as 0. For our 147-73549875 kilowatt (kW motor ). Assuming we would need 845 m2 200 horsepower (9,092 ft2hp) of panels. At most to drive a 70-ft yacht would have less than boat, this is ~147kW. At 96 W/m² this equals 1,000 531 m² (16,472 ft2 ) of surface area, so you can see why most boats using solar have hybrid diesel-electric panel acreage [1 m² = 10.76 ft²]. And this is just for propulsion systemsduring daylight hours. There is no extra for storage in a battery for night operations.

The huge carbon-fibre catamaran PlanetSolar MS Tûranor highest density commercial solar cell has 537 m2 (5,780 ft2) a capacity of 38,000 photovoltaic panels with an 18.8% yield. These are mounted on deck and on large fold-out wings [http:174W/m² or ~16W/wwwft².planetsolar.orgAssume this is feasible output, even though we only receive 137 W/]m² at the equator and 96 W/m2 at 40 degrees latitude. The panels feed six blocks of lithiumFor our 147-ion batterieskW motor we would need 845 m² (9, like those used in the Boeing Dreamliner092 ft²) of panels. The reported maximum daily yield during one 24At most a 70-hour period was 661 kWh. According to the logsft yacht would have less than 1, recharging each day typically took until noon. Build cost was 000 ft² of the order of USD $16 millionsurface area, so you can see why most boats using solar have hybrid diesel-electric propulsion systems.

[[#top|Top]] == Solar at a Cost == The huge carbon-fibre catamaran PlanetSolar MS Tûranor has 537 m² (5,780 ft²) of 38,000 photovoltaic panels with an 18.8% yield. These are mounted on deck and on large fold-out wings [http://www.planetsolar.org/]. The panels feed six blocks of lithium-ion batteries, like those used in the Boeing Dreamliner. The reported maximum daily yield during one 24-hour period was 661 kWh. According to the logs, recharging each day typically took until noon. Build cost was of the order of USD $16 million. The Solar Impulse HB-S1A airplane can carry only the pilot. Using high-technology materials it weighs 3,527 lbs and has a gigantic wing span of 208 ft -- as much as an Airbus A340 or a Boeing 747. It has four 10-hp electric motors driving propellers. These are powered by 11,628 monocrystallane solar cells spread across every available surface. "With 200m² of photovoltaic cells and a 12 % total efficiency of the propulsion chain, the plane’s motors achieve an average power of 8 HP or 6kW," according to the design team. So if we had 100% efficiency the plane would have 67 hp average available. Build cost is reported to be 90 million Euros (USD $118 million).

[[#top|Top]]  == Worked Example ==  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. Assume a solar field 10x3 m (30 m²). This would yield an average of 16.8 kW/day. In comparison 200 hp is why renewable energy needs government subsidies, and why it equivalen to 150 kW. {| class="wikitable"|+ Montreal - Incident Solar Energy on Horizontal Surface (kWh/m²/day)|-! Jan !! Feb !! Mar !! Apr !! May !! Jun !! Jul !! Aug !! Sept !! Oct !! Nov !! Dec|-| 1.58 || 2.48 || 3.58 || 4.44 || 5.05 || 5.63 || 5.54 || 4.88 || 3.71 || 2.31 || 1.44 || 1.23|-|colspan="12"|Average = 3.40|-|colspan="12"|http://solarelectricityhandbook.com/solar-irradiance.html|} The reality (do the math yourself) is that even with solar panels at 100% solar-conversion efficiency it isn't feasible -- for practical purposes -- to fully power a supplement on trawler only with a solar platform that is sized within the hull's boundary. It doesn't compute. Solar is best as a supplemental charging system for the boat's batteries. == Links ==  [http://arstechnica.com/science/2015/08/the-solar-sunflower-harnessing-the-power-of-5000-suns/ Solar Sunflower]