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Off Grid Energy Independence
Posted on July 28, 2009 by  & 

Sea buoys adopt energy harvesting

In 1851 Charles Babbage of London, inventor of the computer, published a paper about putting lights on buoys. It would be another 20 years before technological advances could make lighted buoys a reality. His design for a computer - mechanical of course - was only made a few years ago and, to the delight of all concerned, this programmable device consisting of a huge number of cogs, actually worked.

Small buoys need energy harvesting

A minority of buoys at sea have energy harvesting and that usually means the largest, most mission critical buoys having solar power and occasionally small wind turbines. In particular, the smaller buoys have little or no illumination or at least none that is based on energy harvesting for long life and reliability. That has been because of cost.
Requirements are various. For example, in 2007, the US Navy put out an invitation to tender to "Devise a means for energy harvesting for a 3-inch diameter buoy free floating on the ocean surface. The buoy must also contain an antenna on the upper portion and electronics for the modem. Therefore the energy harvesting should occupy no more than 20 inches in length. The buoy should produce enough energy so that more than 4 milliwatts of power will be available for use at any one instance. Energy will be stored using a rechargeable battery. The battery should be able to store at least 60 joules." It noted that such wireless sensors could be powered by "solar, vibration, thermal and radioisotope."
In 2008, Yoseph Bar Cohen wrote that he had investigated the type of electroactive polymer known as dielectric elastomers and "they had shown considerable promise for a variety of actuator applications and may be well suited for harvesting energy from environmental sources such as ocean waves or water currents. The high energy density and conversion efficiency of dielectric elastomers can allow for very simple and robust "direct drive" generators. Preliminary energy harvesting generators based on dielectric elastomers have been tested." He used a generator attached to a rotating waterwheel via a crankshaft to produce 35 mJ per revolution in a laboratory test with an actual water flow.
A generator that harvests the energy of ocean waves for purposes of supplying power to ocean buoys (such as navigation buoys) was tested at sea for two weeks and he reported, "This buoy-mounted generator uses a proof-mass to provide the mechanical forces that stretch and contract the dielectric elastomer generator. The generator operated successfully during the sea trials. Wave conditions were very small during this test. Although the device did not produce large amounts of power, it did produce net power output with waves as small as 10 cm peak-to-peak wave height. Both the waterwheel and buoy-mounted generators will be scaled up to produce larger amounts of power. The use of significantly larger amounts of dielectric elastomer material to produce generator modules with outputs in the kilowatt range is being investigated for application to ocean wave power systems."
In 2009, the percentage of buoys with energy harvesting for lighting is set to increase with an economical retrofit, recently announced by Electroluminate of Hampshire in the UK. This permits ac electroluminescent lighting tape to be fitted to enhance visibility of even the smallest buoys. It can also be retrofitted on buoys with full lighting systems to act as an enhancement and backup.
Energy Harvesting Journal has just visited the company. In the example that we photographed below, the retrofitted lighting strips are the thin vertical stripes on the upper part of the buoy and they glow a strong red but any color is possible.
Photo by IDTechEx

Electroluminate buoy lighting strips

The Electroluminate product is fully ruggedized and weatherproof and the company also makes illuminating rope and advertising displays that give animated effects by switching on and off blocks of color in sequence, to a chosen artwork design. All these are candidates for energy harvesting and the buoys could employ many feasible types of harvesting such as tidal, wave and wind energy. However, the Electroluminate stripes now being retrofitted to buoys by a manufacturer of the buoys themselves is powered by a modest photovoltaic panel. Later, we shall probably have most buoys illuminating in their entirety. See

Very low power

Ac electroluminescence acel consumes very little power. It is manufactured by printing eight or more layers and the power supplies can also be made for a modest cost, so battery driven indoor displays and lighting over small areas can now be sold for as little as one dollar each in millions. Ac electroluminescence is provided in thin flexible form on polyester film. It is printed reel to reel on webs up to 1.5 meters and sometimes more. Typically it requires about 140 volts at about 400 Hz and the light emitting layers are zinc sulphide variously doped with combinations of copper, iron and silver to give chosen colors. Shelf life is decades but life in use is limited. It varies from 1.5 years to 20 years depending on duty cycle, power and construction. For example, acel light emitting decals that illuminate inside the doors of the new BMWs are guaranteed for 15 years by supplier Schreiner Electric because they are on only when the door is open. There is no catastrophic failure mode with acel. Light intensity may reduce by 50% at what may be called the end of life. Clearly there will be a market for these flexible displays and lighting to be supplied with integral energy harvesting because they are starting to be seen on consumer packaged goods and in many other locations where electronics has not been used before.

Larger buoys

Energy harvesting for conventional marine lighting around Japan is illustrated below. For more info see here
Left: Illuminated buoy in the Akashi Strait, where tidal rips flow fast. The buoy is equipped with a tidal power generator that supplies several dozen watts.
Right: The Mizunokoshima lighthouse uses a combination of wave and solar power. The waves generate about 2,500 W, the sun about 4,400 W.
Source Omori Hiroyuki and Kono Toshihiko
Japan's Maritime Safety Agency has been researching and developing renewable energy since the early 1950s. Offshore sea routes need markers like lighthouses, radio beacons and illuminated buoys to guide maritime transportation. The markers are often placed on isolated islands and reefs, so an independent source of electricity is needed for each one.
There are approximately 5,500 sea route markers off the Japanese coast. By 2004, about 3,000 of them (54%) used renewable energy. The Agency is now progressing towards a figure of around 80%.
In Japan, the biggest source of renewable energy is solar panels, which require little maintenance. The second most important source is wave turbines, which convert the vertical motion of ocean waves and swells into air pressure that turns electric turbine generators. The first wave turbine began operating in 1965, for an illuminated buoy in Osaka Bay. In 2002, the Agency first installed a number of buoys illuminated by electricity from tidal-power turbines. The problem with these renewable energy systems is that the weather affects output. The combination of solar and wave power ensures a more stable supply of electricity. In the summer, the sun is strong and the ocean is calm, so most of the power comes from the sun. Wave energy is used mainly during the winter, when it is cloudy and the sea is rough.
At the other extreme, in Italy, tiny buoys in marinas interrogate RFID tags on arriving leisure boats to ensure that the boat is moored in the correct place. As the owner ties up, the buoy senses this and speaks promotional messages concerning local restaurants etc. Energy harvesting is needed here as well.
Top image source: Wavegen

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Posted on: July 28, 2009

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