3 Responses to “Can someone explain CPV solar power harvesting to me?”

1. JoelKatz says:

   September 23, 2011 at 12:39 am

   It’s pretty simple basically.

   Imagine the amount of light that falls on a sheet of paper. If your solar panel is the size of that sheet of paper, no matter how efficient it is, the most energy it can collect is the amount of light that falls on that sheet of paper. So you want to make your collector as large as possible to catch as much light as possible.

   There are a lot of ways you can convert that light into electricity, but one of the most efficient is photovoltaic cells. These convert light directly into electricity without converting it into heat first. The thing is, they are expensive.

   So CPV takes a photovoltaic cell the size of, say, a piece of paper and puts a lens (or curved mirror) in front of it. This allows the light from a larger area than the size of the cell to fall on the cell.

   Because photovoltaic cells only last 35 years or so and are so expensive to make, the ability to harvest more energy with smaller cells can make the difference between a system that pays for itself and a system that doesn’t.
2. Ecko says:

   September 23, 2011 at 1:21 am

   CPV is for Concentrating Photo Voltaic technology. The suns rays are focused on the semiconductor device, so the light is more intense and there is correspondingly more output. This means the area capturing the sun’s energy is larger than the device converting the sun’s energy, so fewer but potentially more efficient (and more expensive) solar PV cells can be used. In a way it is a trade-off between more expensive cells and cheaper mirrors compared to larger flat panel arrays, so there are many ways to do this.

   The concentrator usually tracks the sun in some way, so the lighting is more or less constant throughout the day, rather than a peaked (cosine) shape of the daily output for a fixed flat panel peaking in the middle of the day. There is full output from early in the morning till late in the afternoon. However diffuse light is likely to be less effective. This is in common with solar thermal tracking systems. It points towards cloudless (and dustless) desert regions. The first link below states the advantages as:
   1) high efficiency
   2) low system cost
   3) low capital investment to facilitate rapid scale-up.

   The second link describes a system with some statistics. The energy from a 13.7m diameter mirror dish focuses on a single cell to produce ~26kW. Five dishes combined produce 180kW (I think this is capacity) so the capacity is 36kW per dish. This system supplies 100 residents in a remote community with integrated diesel generation, and is expected to save 100,000 liters of diesel fuel a year (about $150K).

   This is 147m^2 of capture area, so 147kW/36kW = 24% conversion efficiency with 1kW of sunlight per square meter. Because of sun tracking it might have double the hours per day of full sun equivalent so this equates to 48% equivalent efficiency compared to fixed flat panels (normally about 12%).

   The cost was A$4.5 million in 2008-9, so about $25 per watt of capacity, but this includes land, is in a remote area, includes integration with the existing diesel system etc. Compare this with local domestic flat panel systems of $8-10$ per watt capacity. However the kWh output over a year could be double an equivalent capacity fixed flat panel system.
3. Ray;mond says:

   September 23, 2011 at 2:05 am

   Ecko and Joel (last paragraph) gave good answers. Short falls are a simple system has been made complex = fails more often. Excessive concentrating may destroy the PV on a hot day unless there is a cooling system for the PV. Neil