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.

SSL and Energy Star

On June 2, EPA released a revised Energy Star (TM) requirement for residential light fixtures, with immediate effectivity. This standard allows LEDs to be used in residential light fixtures with an Energy Star label. Great right?

Well, not so fast. DOE has been working with the Solid State Lighting (SSL) community since 2000 to advance the SSL industry. In the process, legislation was passed authorizing DOE to work with an industry group, the Next Generation Lighting Initiative Association (NGLIA), to develop programs to assist SSL technology development and deployment. From this collaboration have come programs that ensure better measurements of the light quality 'on task', funding for developments of technology, workshops and conferences on the issues associated with integrating this technology into the existing value chain for lighting, etc. DOE also developed, in long concert with the industry, an Energy Star Criteria, released in September 2007 for effectivity in September 2008. Note, this was developed over the course of a couple of years, was intended to promote real energy savings, and built on the standards and test methods developed with industry. In contrast, the EPA "technical ammendment" was developed in relative secrecy with little outside input and uses unproven test methods.

So why is this important? In the 1980s the first compact flourescent bulbs hit the market. Unfortunately, these products suffered from a variety of problems which we all probably remember. The colors were often too harsh, some complained of flicker, light generated by the devices was often less bright or less useful that similarly-rated incandescent bulbs, etc. These problems had the effect of slowing down the adoption of CFL bulbs, increasing energy consumption, and slowing the change of the industry. In the end, if the product doesn't provide satisfactory results to consumers, it will not be adopted.

Energy Star (TM) is not only an efficiency label, but also a de-facto quality label. Products carrying this rating are assumed by consumers to at a minimum meet the expectations for performance of traditional products. However, in the case of LEDs, there are significant issues related to the nature of the light generated in order to make that light useful. If you were to take an emitter (light engine) and test its light output vs. energy input, you could have an erroneous representation of the actual useful light generated. This is because light emits from the top of the chip, and from the sides, and the radiation pattern may not be well used by the fixture into which the light engine is installed.

Unfortunately, the EPA only chose to measure the efficiency of the light engine. DOE's CALIBER program which performs calibrated measurements of LED lighting products has shown repeatably that this is insufficient for determining useful light and thus useful efficiency. If you had to replace a fixture with two LED fixtures to get the same amount of light, it would halve the efficiency. Furthermore, other characteristics of the light have not been considered or are very loosely specified. For instance, 'color temperature' or the apparent color of the white light is acceptable up to a rating of 6500 deg-K. This is a very harsh bluish color, familiar if you have one of those early LED flashlights, and, per the CFL experience, totally unacceptable to consumers. By comparison the warm yellowish light of a 100W bulb is about 2800 deg-K.

By contrast, DOE's Energy Star criteria include a wide variety of quality metrics including actual light on tast, acceptable color temperature ranges, and efficiency metrics that improve over time. This last is especially important because LEDs are getting better every year, and fixture design is improving rapidly as well. While the standards are more explicit, they are not onerous, and should serve to provide at least a minimum qulaity level to product bearing the Energy Star label. Furthermore, with the one-year run-up to the standard release, manufacturers have time to bring their products into compliance and have them tested at a certified lab.

So why is EPA doing this? It isn't clear, but one problem with the Energy Star program all along has been the dual ownership of the program between EPA and DOE. DOE would seem to be the better stakeholder since its interest are in energy conservation, even though the pollution impact is also important. This could be, then, a classic 'turf war' between the two departments. Ultimately, programs mean money and power for a Department.

The Solid State Lighting Industry Trade Association (SSLITA), under the auspices of the Optoelectronics Industry Development Association (OIDA) filed a grievance with the EPA Office fo Inspector General, claiming that the duplication of effort side-stepped protocol and wasted government resources.

CFl recycling

This is a key development from the Times. One of the major selling points of new types of photonic lighting (LED, OLED) has been that the current standard of high efficiency bulb, the Compact FLorescent bulb has mercury in it. Recycling rates are pitiful which means many are broken in trash cans or put in landfills. Comprehensive recycling programs have not been available, so recycling rates have been about 2%. This should raise the rate significantly, but also raise the awareness of mercury in the units and possibly raise awareness of the dangers of an in-home breakage. Considering the stir about mercury in vaccines, this could counter-intuitively have a positive effect of comparably efficient replacements promissing "NO Mercury!" I suspect that's why the major manufacturers of CFLs have not introduced their own lifecycle programs, and have discounted the mercury danger.

I'll admit that the amount of mercury is minute, but in some situations, say a baby's nursery, the concentration could be significant. Of course, there's a lot more mercury in an old-style thermometer, and people probably didn't know how to dispose of them either. Still, this is fundamentally a marketing game, and LEDs and OLEDs do not 'break' and do not emit toxic substances when mishandled (unless you actually ate one anyway.)