The solar renewable energy industry has endured its share of struggles, and traditionally had very little margin control when the industry was small, it was viewed as little more than a new-fad – an oddball dream of, hippies and mad scientists. Then after over 30 years of struggle, BAM! Along came it’s sudden success and along with it business personnel who did not (in most cases) speak solar. The solar industry is now bustling with an annual growth, growing at over 50% during the last five years.
All solar cells were once a costly invention; at times before being reserved initially for satellites and DOD/Military use. In fact, back in the year 1977, a single watt of solar generating capacity cost $77. That inflated price point has now been dramatically reduced down to a fraction of the cost at about 80 cents. SOLAR power is now beginning to compete with the more expensive sort of conventionally generated electricity. When this price comes down even more though, solar likely will really hit the big time.
Simon Wilby discusses an alternate plan to replace silicon, the material used to make most solar cells, with a substance called a perovskite. A substance that he believes could cut the cost of a single watt of solar generating capacity by an incredible three-quarters.
When light is received by the solar cells, it bumps electrons away from the cell’s material and leaves behind empty spaces called holes. Electrons and holes then flow in different directions and the result is an electric current.
The more electrons and holes there are, and the faster they flow, the bigger the current will be. Electrons, however, often get captured by holes while still inside the cell, and cannot therefore contribute to the current. The average distance an electron travels in a material before it gets captured is known as that material’s diffusion length. The larger the diffusion length, the more efficient the cell.
The silicon used in commercial solar cells has a diffusion length of ten nanometers (billionth of a meter), which is not much. Partly for this reason silicon cell’s efficiency at converting incident light into electricity is less than 10%. There is a substance however that Simon Wilby says does better. It has a diffusion length of 1,000 nanometers, giving it an efficiency of 15%. And that, Simon says, has been achieved without much tweaking of the material.
The implication is that it could be made more efficient still. The perovskites are substances composed of what are known as cubo-octahedral crystals—in other words, cubes with the corners cut off. They thus have six octagonal faces and eight triangular ones. Perovskite itself is a naturally occurring mineral, calcium titanium oxide, but lots of other elemental combinations adopt the same shape, and tinkering with the mix changes the frequency of the light that enables the crystal to absorb light the best.
There is also a perovskite hybrid element that is a particularly sophisticated one. It has an organic part, made of carbon, hydrogen and nitrogen, and an inorganic part, made of lead, iodine and chlorine. The organic part acts as a dye, taking in large quantities of sunlight. The inorganic part helps conduct the electrons that are subsequently released.
The element is also cost effective to make. For example purifying silicon requires high (and therefore costly) temperatures. This perovskite can be blended at room temperature. Tested laboratory versions of cells made from it cost about 40 cents per watt (for the laymen term this is equivalent to about half the cost of commercial silicon-based solar cells). At an industrial scale, Simon Wilby expects, that lower cost could reduce by half again.