Efficiency comparison

[gar]

110615-0815 EDT

From today's SME (Society of Manufacturing Engineers) daily briefing.

DOE Offers Nearly $2 Billion In Loan Guarantees For Two Solar Projects.
Dow Jones Newswires (6/15, Sweet) reports that the Department of Energy announced Tuesday that it has offered almost $2 billion in conditional loan guarantees for solar power projects being developed in California by NextEra Energy Inc. and Abengoa S.A. Abengoa was offered a $1.2 billion loan guarantee to help build its 250-megawatt Mojave solar-thermal power project in San Bernardino County that is expected to be finished and generating electricity by December 2013. The agency also offered NextEra a $681.6 million loan guarantee to build the 250-megawatt Genesis solar-thermal power project on federal land in Riverside, which is expected to be operational by November 2013. Both companies have signed power purchase agreements with PG&E Corp.'s utility.

What is the efficiency comparison of a solar-voltaic vs a solar-thermal-electrical system for equal areas of solar collectors?

Separate question --- for equal life cycle cost what is the ratio of cost per KWH of solar-voltaic to solar-thermal-electrical?

A somewhat useful site:

http://en.wikipedia.org/wiki/Solar_thermal_energy

Under Power Tower Design there is one reference to a 50 megawatt system that outputs 300,000 megawatt-hours per year. This is about 6 KWH/year per watt of rating. Photovoltaic in our area are supposed to be about 1.1 KWH/year.

Other references in this article appear to be about 3 KWH/year per watt rating.


Some other sites found in looking for quantitative data, but no data. Little value, but of some interest from a general perspective.

http://solardat.uoregon.edu/SolarRadiationBasics.html
http://zebu.uoregon.edu/1998/ph162/l4.html
http://en.wikipedia.org/wiki/Sunlight
http://en.wikipedia.org/wiki/Solar_constant

DOE sites that should have had data were total useless. Just generalities.

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[K8MHZ]

6 kWh per watt?

Given that there are only 8,760 hours in a year and half of them are at night, I am extremely skeptical.

The only way to get more than 4380 watt hours per year per watt is to increase the time the cell is producing beyond that of sunrise or sunset.

Expanding the useable spectrum into the infra-red range would be one way. After the sun sets IR radiation is still present.

Combining a solar thermal system in the same module as a PV cell presents a problem, as the PV cells lose output capability when they get hot.

A researcher in Missouri, I believe, came up with the idea of using nano antennas to build a cell that captures the entire range of solar energy. The claim is 95 percent efficiency, or about 950 watts per square meter. The problem they have is that the electricity that comes out is not DC. It is AC and dependent upon the frequency of the light that produced it. This makes for an infinite amount of frequencies all mixed up. Rectifying that mess is what has eluded them so far.

Once that little issue is resolved, the good news is that the process they developed for making the cells is very inexpensive. Such a breakthrough just might turn the tide for solar energy.

 

[gar]

110615-1157 EDT

K8MHZ:

The major problem is that it is undefined how the wattage rating of the system was defined.

But one can expect a much greater production from a utility scale solar-thermal-electric system than from a photovoltaic system covering the same land area. At least until photovoltaic becomes much more efficient. Is it a lower cost approach? Mentioned somewhere in the references is a possible thermal to electric efficiency of 40% from a high differential temperature system. This is similar to a typical modern steam power plant. The solar collection is from the entire spectrum down into long infrared, and the mirrors are sun tracking. Also allows for thermal storage of the collected energy over a one day period. The same thermal to electric part of the system could be fed energy from some other thermal source during non-daylight hours.

The significant question is whether thermal or photovoltaic provides a lower cost to the consumer.

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[Electric-Light]

6 kWh per watt?

Given that there are only 8,760 hours in a year and half of them are at night, I am extremely skeptical.

The only way to get more than 4380 watt hours per year per watt is to increase the time the cell is producing beyond that of sunrise or sunset.

Expanding the useable spectrum into the infra-red range would be one way. After the sun sets IR radiation is still present.

Combining a solar thermal system in the same module as a PV cell presents a problem, as the PV cells lose output capability when they get hot.

It is AC and dependent upon the frequency of the light that produced it. This makes for an infinite amount of frequencies all mixed up

What frequency range are we talking about?

Automotive alternator is rectified and voltage regulated, but the ripple frequency is directly proportional to engine speed.

The newer inverter type generators are similar. The 60Hz output is synthesized in the inverter, but the alternator frequency is determined by engine speed.

 

[jaggedben]

Another thing that needs to be mentioned is that solar thermal generating systems generally require direct insolation, whereas PV can produce at significant percentages of its rated power on cloudy or foggy days. Whereas solar thermal is more productive than PV in (desert) areas with lots of direct sun, PV will out compete thermal in other places, perhaps most places.

for equal life cycle cost what is the ratio of cost per KWH of solar-voltaic to solar-thermal-electrical

The way you have worded it, this question is hard to make sense of. ("Equal life cycle cost" per what? Per watt? And is this meaningful if they're not equal in reality?)

The better way to ask the question is "what is the levelized cost of electricity for PV vs. ST?" LCOE is the cost per kWh with all life-cycle costs included.

The answer is that, in really sunny places, ST has been cheaper but PV has been catching up. Both are still more expensive than gas or coal (if you don't include pollution as an externality).

 

[jaggedben]

6 kWh per watt?
Given that there are only 8,760 hours in a year and half of them are at night, I am extremely skeptical.

The system being referred to is a 'power tower.' These systems are often touted for their potential ability to store thermal energy and continue to produce after sunset. The thermal carrier (usually molten salt is mentioned in this context) is heated during the day and continues to retain enough thermal energy to power the generator for some time after the sun goes down. Hours, if you believe the hype. Whether this is realistic or just wishful engineering I don't have the knowledge to talk about.

 

[gar]

110619-1756 EDT

jaggedben:

Per KWH. That is what the customer buys. So of the various alternatives was is going to provide the lowest cost per KWH to the customer? This is going to vary from one part of our country to another, and throughout the world? To a large extent in the final analysis it probably needs to be determined without continued government support.

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