New 'concentrator windows' for solar?

Well, research continues apace. Here's an interesting idea for a dye sensitized window that reradiates laterally into cells placed around a window frame. http://www.sciencedaily.com/releases/2008/07/080710142927.htm If is important to think of two things when evaluating new technologies: 1) what is the installed system cost, and 2) is it something people want? Re: cost, the issue really boils down to cell efficiency. In a typical solar roof and field, about 60% of the installed system cost is "balance of system" today. That means, if the solar cells were free, the system would still cost 60% of what it costs today. However, thats for a typical silicon system at ~18% efficiency. Start using lower efficiency systems, even with the same layout, and ... that balance of system cost (connectors, wires, inverters, pedastals, etc) goes UP inversely with the drop in efficiency. Conversely, the approach of CPV or Concentrated PhotoVoltaic is to use complex optical systems to provide high concentration (500x or more) onto very efficient cells (>38%). Here the hope is that the balance of system costs of this complex optical approch will be less than the savings of a typical cell vs the fancy triple junction cell. In the end, the amount of energy delivered per square meter is a (relative) constant, and what differs is the areal efficiency of the system.

Now, to our windows. They provide some nice features: the dyes absorb over a wide range of angles, given the intercepted solar flux, and still transport the power to the edges. But they also still allow some light to be transmitted. So the conversion efficiency is unknown. Then they talk about putting solar cells around the edge of the window. This is not the most efficient from a manufacturing point of view, and electrical connections -- "balance of system" -- costs could be high. Furthermore, since windows are rarely oriented towards the sun, there's a raw loss of intercepted solar flux. So the real question about when these windows would be economic is much more complex than the authors would have you believe.

As to the second question, would consumers really want them? Lets presume that the tint of the window is acceptable, and that the maintenance of these glass panels with 'paint' on them is nominal, and then lets assume that the electrical system is robust as well, with these strangely mounted cells and complex electrical connection to a window, and that installation is similarly easy, only then does it become a question of cost to the builder. Hmm, a lot of preconditions.

The long point of this post is that just because some one releases an item promising a new low cost way to use solar power, the economics of most decisions are in fact not in the cost of the technology. In fact, the dirty little secret of the solar industry is that the most effective way to create utility scale power from the sun is solar thermal techniques, in otherwords use the sun to make steam and power a standard turbine with that. Not only is the conversion efficiency higher, but the steam can be stored until needed relieving some of the day/night problems of solar power.

Often the better use of a technology might in fact not be the sexy comercial that a scientist might hope. For instance, I could see this technology being very helpful with work going on at the University of Deleware on extremely high efficiency solar cells (>60%). The key innovation there is the splitting of light into separate bands that are individually absorbed by optimized cells. This dye approach could provide such splitting and concentrating, if it is highly efficient.