By David Shaw
Updated 2014/02/17 to include GaA
Updated 2013/06/05 with a worked example in the Old Port
Updated 2013/05/08 to include reference to NASA
Updated 2013/05/05 to include reference to solar airplanes
Updated 2013/06/05 with a worked example in the Old Port
Updated 2013/05/08 to include reference to NASA
Updated 2013/05/05 to include reference to solar airplanes
Updated 2013/04/15 to include hybrid schematic
Updated 2013/10/11 to include Solana solar field
Updated 2013/10/11 to include Solana solar field
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Designing the M/Y Sharina: A Guide to Key Differentiating Factors in Designing Your Trawler describes the development of a specification to build a 55-ft trawler yacht. Includes a spreadsheet application to calculate electrical and HVAC requirements. 240 pg., ISBN-978-0-9694443-1-2.
EPUB format (eBook). DRM-free, meaning it's not tied to Kindle (I have it on my iPhone) and you can lend it to your friends.
USD $9.99 on Amazon. Stock #B0040V4B96
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Hybrids Are Cool
There have been a lot of new developments on the renewable-energy front, so I thought I would take another look at renewable energy for boat propulsion. A few years ago I wrote that powering a trawler with solar energy would require towing a solar-barge larger than the boat. In the meantime, I ignored stories about solar boats because I figured they must all be hybrids of some kind. Hybrids are the cool way to go.
A diesel-electric hybrid with solar. In an emergency it is capable of using the house bank for propulsive power.
But still the headlines persisted 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.
- Houses all over the world are being powered by roof-top solar panels, and selling excess energy back to the grid.
- PlanetSolar is the biggest solar ship in the world.
- Solar Impulse HB-S1A airplane left on a transcontinental flight acorss the USA on May 4.
- New solar cells adjust sensitivity for latitude.
So I thought maybe I was out of the loop too long and should
have another look at this subject. I think there are only two possible renewals
for powered boats:
- Solar
- Hydrogen
Wind is a non-starter because, well, if you want to use wind
power, get a sailboat! Right?
Before I got back up to speed on solar, I did all kinds of
calculations and scenarios before I got myself grounded again. Here's the short
version (which has been getting longer).
According to NASA, the earth's surface receives a maximum of 137 Watts per square meter (W/m2) at noon at the equator when the sun is perpendicular. At other latittudes and sun angles the energy is less.
According to NASA, the earth's surface receives a maximum of 137 Watts per square meter (W/m2) at noon at the equator when the sun is perpendicular. At other latittudes and sun angles the energy is less.
In practice, for an 8-hour summer day, 40 degree latitude,
the sun delivers a total average of 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.
The highest density commercial solar cell I can find has a
capacity of 174 W/m2 or ~16 W/ft2. I don’t know the conditions, but let’s assume
this marketing claim is realistic output even though it doesn't align with the preceding paragraph or the NASA figures. For our 147 kW motor we would need 845 m2 (9,092 ft2)
of panels. At most a 70-ft yacht would have less than 1,000 ft2 of surface
area, so you can see why most boats using solar have hybrid propulsion systems.
New developments promise to change this solar-scape but not enough. The cost of silicon-based photovoltaics (PVs) has dropped enormously, making them very cost-competitive. However, their efficiency of conversion remains very low and doesn't look to increase organically. One way of increasing efficiency is to use external and cumbersome focusing mirrors to concentrate sunlight.
Other technologies offer better promise. Gallium arsenide (GaA) PVs are around twice as efficient as silicon but their high expense has restricted them so far to applications in space. Several new fabrication techniques promise to make GaA cost-competitive with efficiencies as high as 40%. One approach uses a small plastic sphere on each cell to focus more light.
This still doesn't shift the calculus enough. Even at 100% efficiency at the equator noon we need 5.4 m2 to drive one horse. Two hundred horsepower would require just over 1,000 m2 .
New developments promise to change this solar-scape but not enough. The cost of silicon-based photovoltaics (PVs) has dropped enormously, making them very cost-competitive. However, their efficiency of conversion remains very low and doesn't look to increase organically. One way of increasing efficiency is to use external and cumbersome focusing mirrors to concentrate sunlight.
Other technologies offer better promise. Gallium arsenide (GaA) PVs are around twice as efficient as silicon but their high expense has restricted them so far to applications in space. Several new fabrication techniques promise to make GaA cost-competitive with efficiencies as high as 40%. One approach uses a small plastic sphere on each cell to focus more light.
This still doesn't shift the calculus enough. Even at 100% efficiency at the equator noon we need 5.4 m2 to drive one horse. Two hundred horsepower would require just over 1,000 m2 .
-- From Wikipedia
On land, Computerworld reports that Abengoa Solana has flipped the switch on a massive solar field near Phoenix AZ built with federal loan gurantees of $1.45 billion and a 30-year guaranteed contract for the output. The plant covers 3 square miles and generates 280 mW, or 3.347 W/ft2.
Back on the water, 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.
And in the air, 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).
People reading this stuff are seized by the vision and write things like, "This is awesome. Let’s get electric passenger airplanes as soon as possible." Or boats. Or cars.
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. This is why renewable energy needs government subsidies, and why it is a supplement on a boat.
Back on the water, 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.
And in the air, 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).
People reading this stuff are seized by the vision and write things like, "This is awesome. Let’s get electric passenger airplanes as soon as possible." Or boats. Or cars.
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. This is why renewable energy needs government subsidies, and why it is a supplement on a boat.
| 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 |
| Average = 3.40 | |||||||||||
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 trawler only with a solar platform that is sized within the hull's boundary. It doesn't compute.
