Secrets of Ultra-Low-Cost
Photovoltaics
Photovoltaics
By William H. Mook, Jr., CEO The Mök Companies Crystalline silicon is the stuff of the computer revolution. Silicon is behind every advance in consumer electronics. Silicon is also the magic material that is at the heart of solar panels. Sunlight illuminates a silicon crystal made just so and electricity is the result. Simple. But even though silicon wafers are simple, they’re also costly. A square inch of silicon crystal costs $1.00 and while that may not seem like much when making $200 processors, $1.00 per square inch is very costly when harvesting sunlight in a solar panel. That’s because a square inch of sunlight falling on a square inch of wafer produces no more than 117 milliwatts of power. This adds up to $8.60 per watt and even in a sunny area that adds up to $0.40 per kWh – which is why that out of the more than 10 million megawatts of power generated by humanity in 2006 less than 2,000 megawatts was in the form of solar panels. The Mök Companies have pioneered a series of innovations that dramatically change the economics of solar panels and move them from being a specialty item in the energy business to being the mainstream energy source of the 21st century. The Mök Companies achieve this by concentrating sunlight to a very tiny point and covering only that point with silicon. Increase the energy levels falling on the silicon by 1,000x and the cost of silicon drops by a factor of 1,000x. The trick is to keep the balance of system costs low at the same time silicon costs fall. In this way Mök achieves system costs 1/100th that of conventional solar panels and costs of energy less than half a cent per kilowatt-hour. In fact costs are so low, Mök sells commodities, not equipment. That because this cost is lower than the cost of fuel which means Mök solar panels can make commodities like synfuel, hydrogen fuel, and fresh water competitively with more traditional systems. What are the secrets of keeping balance of systems costs low? To answer that question requires we understand what balance of systems costs are; 1. Optics 2. Thermal Control 3. Tracking The optics focuses sunlight on a solar cell. Mök uses an array of 4,608 lenses each 1 square inch in area on a 4’ x 8’ panel that illuminate a photovoltaic dot only ½ square mm in area. The lenses are made of water held in an optical shape by two precisely molded sheets of clear PET plastic that are then ultrasonically welded together like a water filled bubble wrap plastic and the entire sheet is back-filled with expanded polystyrene (EPS) foam for rigidity. In this way a square yard of lens collector area costs only a few pennies and focuses sunlight onto only 1 square inch of silicon material costing only $1.00 – but that $1.00 worth of silicon produces the same output as a $1,296 square yard of conventional solar panels. When light is focused brightly onto a silicon cell it gets hot. Controlling heat is a problem. The first problem is parasitic heating. When electricity moves through a resistance heat is produced. By focusing a lot of light in a small space, a lot of current is generated generating a lot of heat. 15 years ago experts thought focusing light on photocells was impractical because of this sort of heating. But, Mök reduces this source of heating two ways, the first is to increase the voltage of the cell, the second way, is to reduce the cell resistance. In this way, intensities of up to 2,000x solar can be maintained. Another source of heat comes from the fact that only certain colors are efficiently used by the solar cell itself. To eliminate this source of heating Mök places a special mirror on the face of each of its photocells that reflect away the ineffective light and let only the effective light pass through to power the cell. Even with these two tricks, there is still a lot of heat, so another technique is to immerse the cell in a water bath rather than mount it on a copper block. Mök uses water as the lensing material to lower optical costs. By causing the light to focus inside the lens itself, the photo material is immersed in a water bath and cooled from both sides. Finally, the back of the cell is structured with tiny triangular channels and treated so bubbles are formed at the peak of the channel. As they expand they move to the wider section of the channel and push water ahead of it creating a pumping action. In this way, without any moving parts (Except the bubbles) hundreds of watts per square inch are dumped into the lens medium and cooled over the area of the lens. Having handled the optics and cooling costs the cleverest trick Mök engineers came up with was to get rid of the need for tracking. In optics there are limits in what a lens can do, the same way that there are limits in thermodynamics. One optical limitation is called entendue’ This limit says that the more a lens concentrates sunlight the narrower its field of view. That is, to get 1,200x solar concentration requires a field of view only a few degrees wide. That means the lens has to move to track the sun as it moves through the sky to keep the sun image in focus. This means in turn that panels must be stiff enough to stay aligned as they move and are blown about by the wind. This all adds significant costs for tracking. Mök engineers solved this last cost problem too by noticing that a fish-eye lens focuses the entire sky into an image plane. In that image plane the sun shows up as a tiny dot that moves across the plane. By creating an array of dot-like conical mirrors – over 400,000 of them – precisely formed in a sheet of plastic – each solar image is redirected to a common focal point through a separate lens element. The main lens gets reused 400,000 times by 400,000 separate optical systems, each of which follow the entendue’ limit, but together the array tracks the sun without any moving parts, and only each lens need be rigid, while a collection of lenses can be quite flexible and still work. |
USOAL
United States Oil from Coal
United States Oil from Coal
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