Is photovoltaic technology worth the trouble?

Joel Fairstein
November 08, 2012 | 3 Comments

Given the 2012 ITC ruling against China for its massive government support of its photovoltaic manufacturers, no clear consensus has emerged as to the effect this will have on our solar industry at large. However, it's certain the continuing drama will tittilate policy hacks for a long time to come while distracting us from our overall energy strategy.

Let's take stock of where we are now with photovoltaic technology. With smart-phone elegance and as a plug-in replacement for coal, photovoltaic panels have game in the popular mindset. In the United States, solar energy equates with photovoltaic technology despite other parts of the world having quietly embraced solar thermal solutions and energy conservation as more cost-effective. What's up with this?

Photovoltaic efficiency is limited by physics to around 25% for single-junction materials (everything on the consumer market) and 50% for multi-junction materials (concentrating photovoltaics) with a reduction of approximately 1/3 of the efficiency after adding AC converters and wiring. Currently, 13% system efficiency is considered acceptable in consumer systems. That 13% is when the sun is facing the solar panels directly on a clear day, so in real world terms, solar yield is in the low single digit range. These incidentals are usually lost in policy discussions.

In earlier days, energy policy was a grass-roots movement. Self-sufficiency geeks cobbled their own solutions and had fun doing it while lowering the energy bill. A ton of literature was produced in the '70s and '80s detailing these home-brewed energy strategies, many of which work and make perfect sense. Very few of these solutions resulted in consumer products, however, which limited their mainstream acceptance. This situation could change if we again focused our resources on frugal innovation.

Since Bell Labs invented the photovoltaic chip in the 1960s, can you think of a single renewable energy solution from Big Science that has gone mainstream? While we are waiting to be saved by monolithic plug-in solutions to our energy needs, we could embark on a national campaign to reduce energy consumption and encourage innovation at the grass-roots level.

So, we’ll continue following the fate of our beloved solar photovoltaics, but that shouldn’t stop us from reshaping our overall energy future.

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3 Comments

John Nistler
November 8, 2012

Joel, to calculate LCOE you have to know your equivalent hours at peak power or the amount of kWh you produce with your overall system. DC ratings have no real bearing since different systems will vary in their overall power production based on a lot of factors. I assume since you are talking about grid transmissions then you are referencing solar farms? Overall grid transmission of 100 to 150 miles is under 1.5% in general, independent of the power source in the USA. Elsewhere it is higher, so which country are we referring to? Solar used at location is impacted more by potential shading then transmission losses. An overall system needs to be designed to account for potential shading throughout the year. Thus string layout and connection come into effect in figuring out overall performance. So how about clarifying what you mean by system efficiency, because apparently we are discussing two different things. Its like people assuming that a nuclear plant runs 24 hours a day, 365 days a year constantly instead of understanding that a nuclear power plant runs at an 80% availability rate so that proper maintenance and pile control is in place. Solar does not produce power when the sun does not shine, thus if you use a closed loop fuel cell system such as ours the average round trip cycle efficiency of power in / power out is on norm 80%. But this varies depending on current requirements. High current has less efficient storage cycles. Then there is the aspect of optical enhancement for roof top or full polar tracking systems. Here efficiencies are different. This is not a focusing but non-imaging optical approach. A balance of economics, good engineering and physics is maintained and more power is produced (kWh). 32% efficient single junction solar cell cited at AFORE2012, Nov. 26-29, Jeju, Korea. Lead researcher is from Alfa University, Seoul, Korea.

Joel Fairstein
November 8, 2012

John, thanks for the comments. Can you cite a source for 32% cells? My understanding has been that SI bandgap was too narrow for that efficiency. System efficiency does degrade substantially from cell and module efficiencies, due to wiring and inverter losses, not to mention transmission losses when traveling the grid. It is relevant to this discussion, because one cannot generate power without connecting to either a load or to the grid. AC peak power is not a consistent indication of off-axis panel performance and therefore total performance. I agree that efficiency is not the best yardstick, but I only bring it up to clear some misconceptions and exaggerations. Levelized cost is a better standard, albeit subject to interest rates, wage levels, and balance-of-system raw materials cost.

John Nistler
November 8, 2012

Lots of mis-information here. First, single junction silicon based solar cells have been demonstrated now at 32%. Presently commercial solar cells are under 25%. System efficiency does not degrade. If you are referring to loss in theoretical power production based on fixed installations, that is a different discussion. Using the term 13% system efficiency is incorrect. It would be better to talk about equivalent hours at AC peak power. This allows comparison between different systems.