Tandem Cell
The Tandem Cell™ consists of two photo-catalytic cells in series:
the front cell absorbs the high energy ultraviolet and blue light in sunlight,
using nano-crystalline metal oxide thin films to generate electron-hole pairs.
The longer wavelength light in the green to red region passes through the front
cell and is absorbed in a Graetzel Cell producing electrical potential under
nearly all light conditions The two cells are connected electrically and
together provide the potential required to split the water molecules in the
electrolyte. The Cell is fabricated from widely-available and cheap
materials.
The key to the Tandem Cell™ is the performance of the metal oxides in reacting
to the photons of the incident light. We are developing processes to obtain high
efficiency films in a usable form. The metal oxides are expected to be the
limiting feature of Tandem Cell™ efficiency, but we also need to optimise all
other aspects, including the counter-electrodes, the electrolytes and the
mechanical design to maximise light gathering and hydrogen collection. The most
expensive component of the Cells is currently the special glass, on which the
nano-crystalline films are deposited. Cheaper alternatives will be found to
reduce the cost of the Cell. We envisage arrays of Tandem Cells incorporating
optical collection devices optimised for maximum efficiency.
Applications:
Early applications of the Tandem Cell™ will be in vehical refuelling and in supplemental energy for industrial and domestic buildings. Hydrogen generated from sunlight and water in the Tandem Cell™ offers a renewable vehicle fuel with no carbon or carbon dioxide emissions. We envisage local generation of hydrogen from solar energy using Tandem Cell™ arrays on roofs to produce fuel for local journeys. We also foresee a national infrastructure of refuelling stations which would provide for long distance journeys. They would produce hydrogen on a larger scale and transport it by tanker or pipeline as oil and gas is today. We foresee the energy needs of buildings will be provided by a combination of renewable sources. The roof of a building, particularly a large building, provides an area for the generation of hydrogen fuel by Tandem Cells™, which can be stored for use in HVAC and back-up power generation. In addition, in hot climates – eg. California, the Tandem Cell™ will absorb energy, reducing the external heat load on the building and thus reducing the air conditioning requirements. A unique feature of the Tandem Cell™ technology is that it will work in reduced sunlight conditions, when no direct beam radiation is present, although clearly a sunny day in California will produce more.
