My Conclusions from the Phoenix Energy Sustainability Conference

A summary of what I have learned is that solar energy engineering is in a phase of rapid development. It is profitable business and there is still quite a way to go before plateau performance levels will be reached. Real progress is being made in reducing the costs of photovoltaic collectors. Issues of inverting and cleaning up the power produced and integrating it with the grid appear to me to have been largely solved. Reliability and durability of photovoltaic panels seem to be very satisfactory. Costs of these units appear to be decreasing quite rapidly. Efficiency values are still increasing, but are already at levels that I consider very good. Furthermore, concepts such as combining photovoltaic collection and thermal collection or using concentration with photovoltaic collectors are subjects of current research.

Perhaps it is because of personal bias, but I found that current activities and developments in concentrated solar power production were the most exciting. Really excellent progress has been made in recent years. Stirling engine dishes, parabolic trough collectors and solar towers are currently the main contenders. What was really exciting was that all three, competing, technologies were now being implemented on a really large scale. Just imagine a large four-wheel drive vehicle dwarfed as it drives within long lanes between lines of huge parabolic trough collectors or within arrays of Stirling engine collector dishes. This is already reality. Best of class solar-radiation-to-electricity conversion efficiency now stands at 32%. As a professional engineer and thermodynamicist I know that that is excellent and I believe that 50% is achievable.

The players in this business are very cagey, understandably. It was mentioned that $500M has been put into the development of the Stirling engine that is being used by United Stirling in its solar thermal power dishes. It can be difficult for researchers to obtain actual performance information.

In like vein there are things that I have realized at this conference that I am not writing here because I see so much commercial potential that it would not be sensible to do so.

One thing which I will dare to say, because it is so obvious, is that the situation on Earth has just changed very dramatically. The desert areas of the world have suddenly become some of the most valuable assets on Earth: they are probably more valuable than all oil reserves. Deserts, areas of high direct insolation, can be expected to meet huge energy demands in a cost effective way.

Some relatively short term difficulties referred to at the conference, whereby some current solar thermal plants work much better with wet cooling (requiring lots of water), can be overcome. It was mentioned by one paper presenter that some proposed solar thermal projects in Arizona had sought rights to 20% of all available scarce water in the state. In the future, I believe, all major deserts will no longer be deserts. They will be areas of solar energy collection and will be habitable with adequate water for human and vegetable life amid the collector fields. There are likely to be climatic effects, worldwide, of converting, for example, the Sahara into a non-desert. Once again, resources that are local will be key elements of the global energy mix and will have global environmental impacts.

It has now been technically demonstrated that significant energy storage is possible in conjunction with concentrated solar thermal power production. Proven molten salt technology allows energy storage for periods such as sixteen hours. With such technology, utilities can choose to use the power while it is being generated, or to hold it to meet particular daily load demands. While the type of storage that has been demonstrated does not allow solar thermal power to be considered a constantly available resource, it does allow solar thermal plant to be operated at maximum efficiency on an almost continuous basis for a predictable fraction of the time.

It is likely that developments in the use of phase change materials will allow even greater amounts of storage to be used in conjunction with solar thermal power. It appears to me that at this point in time solar thermal power is well ahead of wind power as regards approaching base load capability.

While in the shorter term solar thermal power is most likely to be used relatively locally, in the longer term it will require carefully planned development of long distance transmission systems. One reason for this, as evidenced by a presentation at the conference, is that solar thermal power is likely to be correlated with load profiles that are not local to the sites of generation. Another very interesting conclusion from the same presentation was that solar power is likely to be moderately well anti-correlated with wind power. This means that when wind power is not available, solar thermal power may be available and vice versa. Therefore when solar thermal power and wind power are part of the overall, wide area, energy mix, availability of power is likely to be enhanced.

What about solar power for individual dwellings? Where individuals and families live in high rise tower-type developments it is likely that power will have to be imported from external sources. Energy use minimization will be increasingly important in such contexts. Solar power collection requires vast surface areas (as found most commonly in vast deserts). For scattered individual dwellings in areas with high rates of insolation, local harnessing of solar power, most likely through the use of photovoltaic panels, is technically possible. Effective individual-dwelling capture and use of solar-generated power will depend on full grid integration and smart metering. Harnessing of solar heating is also possible, although individuals who are not trained in thermodynamics (including many policy makers and politicians) are unlikely to appreciate that harnessing solar energy for low temperature heating is inherently wasteful and inefficient (but, of course, if it makes economic sense do it). Whether solar heating or solar power production are being considered, it is generally desirable to optimize energy use, building insulation and ventilation before making significant investments in harnessing solar renewable energy on a per dwelling basis.

What about the use of solar energy in a country like Ireland where the amount of direct sunshine is relatively low and the average solar elevation is not very favourable? Generally the markets ensure that low hanging fruit is picked first. Right now, power companies are likely to exploit solar energy where it is most abundant and in a form that is most readily harvested. Progress with photovoltaics should make it increasingly attractive to use solar energy capturing surfaces in an unobtrusive way. Indeed, even apart from energy capture, recent developments, when fully rolled-out, will result in the very widespread use of albedo-engineered surfaces. These surfaces will have the look and feel of traditional surfaces, such as roof tiles or pavement materials. They will allow better thermal management of urban heat islands and play a role in energy demand minimization.

Very widespread harnessing of solar energy will, I strongly suspect, affect the albedo (the reflectivity) of the Earth itself, which will have implications for the average global temperature.

Returning from the Energy Sustainability conference I feel uplifted, not because I feel the problems of humanity have been solved, but because there is a lot of exciting engineering going on in an attempt to address the issues.