In an earlier article we discussed an interesting company called Brightsource which uses mirrors to concentrate the energy of the sun in a technique known as concentrated solar power. Using mirrors to reflect sunlight into a single spot is perhaps the simplest way to harness the energy of the sun. However, most companies that generate solar use solar cells (or photovoltaic cells) otherwise referred to as PV.
Types of Solar Cells
Solar cells, 80% of which are produced from crystalline silicon wafers, convert the energy of light into electricity through a process known as photovoltaics. There are many types of solar cells as seen below:
Of the above cells, the ones categorized as “Emerging PV” show great promise in reducing the cost of solar cells and increasing efficiency.
Solar Cell Efficiency
The ability of a cell to convert the maximum amount of light into electricity is known as the cell’s efficiency. Each of the above cell types has a peak efficiency as seen in the below example:
The above efficiency example corresponds to the previous listing of solar cell types. As you can see, the “Emerging PV” cells such as quantum dot cells and perovskite cells are low on efficiency as they are in the early stages of development. So does this mean that the cell with the highest efficiency is the best? No, the cell with the lowest cost to produce and the highest efficiency is the best from an investor’s perspective.
Currently, average solar cell efficiency is around 15%. This efficiency is sufficient enough such that a typical house can be powered using 350 – 450 square feet of roof space according to varying estimates based on typical usage in a family home.
In some cases the power generated by the standard installations seen in the above picture can even exceed the amount used by the customer. SolarCity (NASDAQ:SCTY) actually has a policy called “net metering” where you can sell excess solar electricity you generate back to the power company. Therefore, for residential applications, average solar cell efficiency is sufficient and focus needs to be placed on lowering the cost of solar panels.
“Emerging PV” Cells
Silicon, while plentiful and efficient, is expensive to manufacture into solar panels. This is why the “Emerging PV” cells hold such great promise. The appeal lies in their potential to be produced easily at a very low cost. An article last week in the MIT Technology Review titled “A Material That Could Make Solar Power Dirt Cheap” highlights the disruptive nature of perovskite cells currently in development.
Another consideration is that of high rise cities such as New York or Hong Kong. How can solar be put to use when there is no sufficient roof space? The answer lies in solar windows. In order for solar windows to be feasible the solar cells need to be transparent. Solar pioneer Michael Gratzel invented “Emerging PV” cells called “dye sensitized solar cells” which won him the 2010 Millennium Technology Grand Prize. Dye-sensitized solar cells have a very distinct advantage; they can be manufactured in any number of colors.
Gratzel’s cells have already achieved an efficiency of 14.1% but most importantly, they can also be made translucent and therefore can be used in solar window applications. Currently this technology is being used in consumer products such as backpacks and iPad covers.
In an upcoming article we’ll look at some exciting companies, both public and private, that are making great strides in the area of “Emerging PV” cells.