Providing electricity through photovoltaic and thermovoltaic cells is becoming more popular as these technologies have come down in cost and reliance on other sources of electric power is increasingly disfavored for environmental and strategic reasons. However, providing a general use tile with electrical components that is easy to install and electrically connectable to other tiles without external wiring has been elusive.
The conversion of electromagnetic radiation from thermal sources to electricity is known as thermophotovoltaic (“TPV”) power generation. While the overall thermal-to-electric conversion (“TEC”) efficiency of TPV systems has typically been lower than hoped for, recent developments in materials and techniques have changed the situation dramatically. Several rare earth oxides, for example, have been shown to alter spectral distributions in their emission spectra, leading to a more efficient TPV operation. For example, GaAs, GaSb, InGaAs are used in thermoelectric applications.
Photovoltaics refer to cells that convert sunlight directly into electrical energy. The electricity is direct current and can be used that way, converted to alternating current through the use of an inverter, or stored for later use in a battery. Conceptually, in its simplest form, a photovoltaic device is a solar-powered battery whose only consumable is light. Because sunlight is universally available, photovoltaic devices have many advantages over traditional power sources. Photovoltaic systems are modular and their electrical power output can be engineered for virtually any application. Moreover, incremental power additions are easily accommodated in photovoltaic systems, unlike more conventional approaches such as fossil or nuclear fuel, which require multi-megawatt plants to be economically feasible.
Although photovoltaic (PV) cells come in a variety of forms, the most common structure is a semiconductor material into which a large-area diode, or p-n junction, has been formed. In terms of basic function, electrical current is taken from the device through a contact structure on the front that allows the sunlight to enter the solar cell and a contact on the back that completes the circuit.
The original and still the most common semi-conducting material used in PV cells is single crystal silicon. Single crystal silicon cells are generally the most efficient type of PV cells, converting up to 23% of incoming solar energy into electricity. These cells are also very durable and have proven their long life in many space related applications. The main problem with single crystal silicon cells is their production costs. Growing large crystals of silicon and then cutting them into thin (0.1-0.3 mm) wafers is slow and expensive. For this reason, researchers have developed several alternatives to single crystal silicon cells, with hopes of reducing manufacturing costs.
Alternatives to single crystal silicon cells include poly-crystalline silicon cells, a variety of “thin film” PV cells, and concentrating collectors. Poly-crystalline silicon cells are less expensive to manufacture because they do not require the growth of large crystals. Unfortunately they are less efficient than single crystal cells (15-17%). “Thin films” (0.001-0.002 mm thick) of “amorphous” or uncrystallized silicon are another PV cell alternative. These thin films are inexpensive, and may be easily deposited on materials such as glass and metal, thus lending themselves to mass production. Amorphous silicon thin film PV cells are widely used in commercial electronics, powering watches and calculators. The problem with these cells is that they are not very efficient (12% in the lab, 7% for commercial cells), and they degrade with time, losing up to 50% of their efficiency with exposure to sunlight.
Thin film PV cells made from other materials have also been developed in an attempt to overcome the inefficiency and degradation of amorphous silicon thin films, while retaining low production costs. Gallium arsenide (GaAs), copper indium diselenide (CuInSe2), cadmium telluride (CdTe) and titanium dioxide (TiO2) have all been used as thin film PV cells, with various efficiencies and production costs. Titanium dioxide thin films, just recently developed, are very interesting because they are transparent and can be used as windows.
In terms of artistic and practical applications (e.g. improved nighttime visibility), electroluminescent materials have become popular novelties. Electroluminescent materials, such as phosphor, emit light when a current is passed through it. Commercially available phosphor-based electroluminescent materials use, for example, zinc sulphide doped with manganese (ZnS:Mn) as amber-glowing phosphor. Making different-color luminescing material for artistic effect is a matter of blending elements that will electroluminesce with red, green, blue (or a combination of these to make light of many different colors). For example, strontium sulphide doped with copper, denoted ‘SrS:Cu’ can be “tuned” by controlling the proportions of five-neighbored and six-neighbored copper by adding the elements sodium and yttrium to the material, tipping light emission toward the greens.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.