* a registered trademark of Phototherm, Inc.
Dr. Alvin M. Marks
Advanced Research Development, Inc.
359R Main Street
ATHOL, Massachusetts 01331
United States of America
A most profound change in the electric utility industry could be wrought by a commercially available, low-cost, efficient source of electric power from the sun.
Examples of such forthcoming solar energy conversion technologies are the LEPCON* and LUMELOID* systems, which are the trademarks of Phototherm, Inc. of Amherst, New Hampshire, a public corporation (OTC), dedicated to the research, development, manufacture and marketing of these products.
Glass panels and plastic sheets of LEPCON* and LUMELOID* respectively convert sunlight to electric power with an efficiency of 70 to 80%, at a cost of $ 0.01 to $ 0.02 per kwhr. The investment in I square meter of a LEPCON* glass panel is about $ 250.00. It produces 500 W of electric power in bright sunlight. The investment then is $ 0.50/W, spread over a life expected to exceed 25 years.
The investment in LUMELOID*, a thin, continuously cast polymer film, including electrodes, and lamination to a supporting sheet is about $ 5/sq m. The investment cost will be $ 0.01/w, spread over an expected life of 6 to 12 months in strong sunlight.
LEPCON* panels are particularly applicable to large-scale solar/electric power farms. They may be sited to produce an average of 400 w/sq m or 400 Mw/sq km during the daytime, for example, in New Mexico, Nevada and similar regions where clouds seldom obscure the sun. An area 200 km x 200 km will produce 16 million Mw at $ 0.01 /kwhr during the daytime hours. Two-thirds of this energy must be stored for use during the dark hours. Electric energy storage technologies are known, and are being developed, which would serve this requirement. This would be enough to supply the electric grid for the entire U.S..
(* a registered trademark of Phototherm, Inc.)
Alternatively, LUMELOID Sheets will be utilized by many consumers of electric power to produce their own electric power. Such sheets may be installed on roofs or building sides, and connected through an electric storage device and an AC/DC inverter to directly provide electric power for all domestic needs at a few cents per kwhr. Excess electric power may be fed into the grid and charged to the local electric company, which will provide standby power to the consumer. The existing electric power grid will be essential, however, for industry and urban use, particularly in those areas where the sunlight is frequently obscured by clouds.
The economic implications
To totally convert the electric utility industry to solar electric power farms using LEPCON* panels will require an investment of trillions of dollars over many years. The economic and health benefits to the nation will be enormous:
1. Lower energy costs
2. Elimination of nuclear hazards
3. Elimination of the need to burn coal or oil fuel, thus diminishing air pollution, and preventing a disastrous Greenhouse Effect.
4. Decreased dependence on foreign oil imports, with consequent improvement in our balance of trade and reduction of the federal deficit.
5. A substantial increase in useful employment on a vast long-term project, which will enable a cutback in the funding of the wasteful military industrial complex.
6. If the electric utility industry becomes involved, as it must, then it can benefit from the large profits to be made in this huge endeavour. To start, it must provide the funds for the R & D, manufacturing facilities and the installation of the LEPCON* and LUMELOID* technologies.
Figure 1 shows a conventional metal-insulator-metal (MIM) tunnel diode, in which two dissimilar metals are separated by a small gap of about 30 Angstroms. Electrons can pass easily in one direction but not in reverse. Each metal has a different work function or natural electric barrier surrounding the metal. An electron moves readily in a metal, as though it were in empty space, but it bounces off a wall of the metal due to the potential barrier at the wall.
Figure 2 shows a potential diagram for an MIM diode.
Figure 3 illustrates a quantum property of electrons known as "tunnelling". As an electron approaches a barrier with a small insulating gap, and an electric potential difference across it, it is either transmitted or reflected across the gap without loss of energy. In an MIM diode the electron can move more readily in one direction than in the other.
Figure 4 shows a submicron rectenna element of an array in a LEPCON* panel. This element is also known as an "antenna-well diode".
The light photon has an electric field with its direction at right angles to the light ray direction. The photon energy is totally absorbed by an electron in a metal strip. The photon transfers its energy without loss to the electron as kinetic energy in the mostly empty space in the metal. The electron moves parallel to the electric vector of the light, to the right or to the left. If the electron moves to the right, it bounces off the high-potential barrier at the wall, and the moves to the left. So all the electrons eventually approach the tunnel diode on the left, where the electron is either transmitted or reflected without energy loss, as shown in Figure 3; all electrons being eventually transmitted through the tunnel diode without energy loss. However, a potential difference across the diode will convert the kinetic energy to electric energy which will just equal the photon energy. Thus the light photon energy is converted to electric energy without loss.
This differs from the conventional photovoltaic device, which requires that the electron move parallel to the light beam into a semiconductor layer, which it can only do after losing energy, and so the photovoltaic devices are fundamentally flawed.
There are also present many low energy (thermal) electrons in the metal strip which do not take part in this energy conversion except to provide an extra electron for photon-electron interaction; and from another part of the circuit to replace the electrons being transmitted through the diode. In bight sunlight, about one photon-electron energy conversion will occur on the average of every nanosec.
Figure 5 shows a LEPCON* Series-Parallel configuration. Light is resolved into two electric vectors; a first electric vector parallel to the array axis is totally absorbed and converted to electric power; and a second electric vector normal to the array axis is totally transmitted as polarized light. Previous work with polarized light materials and microwave rectannae arrays shows the system to be about 80% efficient. In this system, 40% of the light is then converted to electric power by the antenna array, and 40% is transmitted. The transmitted light may be passed through a second LEPCON* array at right angle to the first, which will convert 80% of the transmitted component to electric power, thus converting a total of 72% of the incident light to electric power.
Figure 6 shows how a single LEPCON* array may be used in combination with a quarter-wave retardation sheet and light-reflecting layer to accomplish the complete conversion of the incident light to electric power at about the same efficiency.
A LUMELOID* sheet is a light/electric power converter. The sheet is a thin (8 micrometers, or .0003") polymeric film. The polymer film is prepared by a method similar to that now employed commercially in the manufacture of polarized film, and using much the same equipment, but with a different chemistry, and with electrodes embedded in the film to gather electric power.
Recent work in the field of photosynthesis in green plants has resulted in the synthetic chemicals which mimic the natural process. In the plant the photosynthetic chemical comprises an antenna which is similar to a long-chain carbon molecule, known as polyacetylene. This is attached to an electron donor acceptor complex, here shown as a large ring and a small ring, respectively known as porphyrin and quinone. The long-chain molecule acts as a conductive antenna, which resolves and converts one-half of the photon energy to electron energy, and transmits the other one-half, as described above for the LEPCON*. The electron energy is stored on the large donor ring, and transmitted by tunneling across a small gap which is the insulating chain of carbon atoms, between the large donor ring and the small acceptor ring. The small acceptor ring is then holding the electron at a greater potential, than at the start. So far this is analogous to the LEPCON*.
Figure 8 shows an energy diagram typical of a Donor-Acceptor Complex, which is analogous to the energy diagram shown in Figure 2 for a LEPCON*.
However, in the green plant, natural photosynthesis uses the electric energy it has stored on the acceptor to drive the chemical synthesis of the carbohydrates and other complex chemicals in the living cell.
Figures 9 to 12 inclusive show the similarities and differences of LUMELOID* compared to natural photosynthesis. The basic difference is that the chemical synthesis step of the natural photosynthesis process is eliminated, and an entire photosynthetic molecule such as is shown in Figure 7 is connected head-to-tail to another such molecule. This is shown in Figure 12, where the long-chain conductor molecules (52) and the donor-acceptor molecular diodes (53), are oriented parallel to each other and connected head-to-tail within the polymer sheet.
Figure 9 shows a cross-section of the polymer sheet parallel to the long axis of the photosynthetic molecule. Electrodes 41 and 42 are shown in Figures 9, 11 and 12, connecting the electric power output to the load 75. The light power input is represented by the photon 2, and the direction of the resolved electric vector is along the X-axis.
Figure 10 is a cross-section through the XOZ plane. The conductive chains are shown as large dots.
The manufacturing process
The manufacturing process resembles the conventional commercial manufacture of polarizing film. In Stage 1, a viscous polymer solution is made with these chemical constituents of polarizing film:
1) Solvent molecules;
2) long-chain polymer molecules;
3) iodine molecules;
4) cross-linking chemicals to tie the chains in a bundle after they are aligned;
5) (OH) groups on the side of the polymer chains to react with the cross-linkers.
In Stage 2, the polymer solution is cast on a moving belt of a non-reactant metal, partially dried to eliminate most of the solvent, and stretch oriented. The result is that the polymer chains are drawn parallel and the cross-linkers hold them that way. The separate iodine molecules now crystallize in the spaces between the parallel chains forming a linear electrical conductor. These react with light photons as described above, only in this case, since polarizers lack molecular diodes and electrodes, the electric power is dissipated internally as heat.
Figure 6 shows the first step in the manufacture of a LUMELOID* film, which is the preparation of the polymer solution similar to that used in the manufacturing process. In this case, however, there is a constituent No. 6 added: the molecular diode. When a molecular diode is exposed to light, its electric charges separate and it acquires a dipole moment; that is, experiences a torque to align it parallel to the direction of the applied electric field.
The final stage in the manufacture of the LUMELOID* is similar to that described for polarizing film, except the additional steps of simultaneously illuminating the film and applying an electric field are utilized in the stretching step, and the electrodes are then subsequently applied.
The following US Patents include extensive bibliographies: 4,445,050 (LEPCON*) and 4,574,161 (LUMELOID*). Additional patents have been filed, which will issue in due course, in the US and foreign countries, which contain additional references.