Published on June 26th, 2016 | by Susan Kraemer4
In Our Climate-Changed Future, How Will Solar Perform?
June 26th, 2016 by Susan Kraemer
The solar panels manufactured today will need to power a climate-changed world over the next 25 to 50 years. They will need to be engineered to continue to operate in a climate that will gradually become more extreme.
Many regions will hold more moisture in the air, while others will become drier and warmer, climate scientists predict. So solar panels will need to be engineered to withstand rising temperature and increased humidity over the typical module lifetime.
Image by Kevin Poh via Wikipedia under Creative Commons License
Regions with the fastest growing electricity demand, like the rapidly growing megacities of Southeast Asia and Indonesia are hot and humid now — and will only get hotter and more humid as climate changes. And regions with the best solar insolation like the Middle East, North Africa, Australia, and the US Southwest are predicted to become even more extremely hot and dry in a climate-changed future.
So, are any companies or researchers in the solar industry preparing for this climate changed world?
“This is a interesting topic,” said David Williams, an advisor to the International PV Quality Assurance Task Force (PVQAT).
PVQAT is working with NREL towards setting international standards that would allow owners and operators to quickly assess modules for quality and ability to withstand stress over time.
“My initial thought is that very little research is active on the topic. My assumption is that is would be especially challenging since the error bar of the technical impact of temperature degradation will have large uncertainty. However, it is also true that the temperature will likely be higher on the high irradiance periods and have a more profound impact than 1 degree rise would suggest.”
India’s present day climate has provided a real-world test case for solar performance in a climate-changed future. In 2013, Bloomberg New Energy Finance surveyed several solar plants in operation in India, and found First Solar’s CdTe (Cadmium telluride) panels outperformed silicon panels in that hot and humid climate.
Solar for hotter and more humid climates
First Solar is already preparing for the hotter and more humid climate of the future. Thailand makes a good real-world laboratory, with high temperatures and extreme humidity. First Solar’s CdTe panels have shown superior resistance in real world testing there to both heat and humidity.
According to First Solar senior director of product management, Lou Trippel, the performance comparison between First Solar’s CdTe modules with crystalline silicon in Thailand has shown their panels beating conventional silicon technology by 7% greater specific annual energy yield in kilowatt-hours per kilowatt.
First Solar’s CdTe panels delivered 1,620 kWh a year per kilowatt installed, versus 1,509 kWh with crystalline silicon in the simulation.
Trippel said that the well-known superior performance of thin film in higher temperatures was only part of the reason for the better results.
Just due to the better response in higher temperatures, First Solar’s CdTe panels generated more than 1.4% more annual energy (more kilowatt-hours per kilowatt installed) than the silicon panels in the hotter temperature.
Image by Kurt Bauschardt via Flickr under Creative Commons License
However, humidity itself also creates actual alterations in the solar spectrum.
It turns out that CdTe modules are inherently less sensitive to reductions in wavelengths due to high humidity than silicon. First Solar was able to demonstrate a more than 5% better response to these humidity-caused solar spectrum changes.
As a result, they actually produce up to 6% more annual energy in the extremely humid conditions.
Climate resilience must be designed-in at the manufacturing level
The in-house testing procedures at First Solar are adapted from the aerospace industry — they test modules to failure.
Trippel has said that, “One-time certification is a good start, but falls short of demonstrating the continuously sustained quality and durability of ongoing module production delivered in volume to customer sites.”
By reducing risk, PVQAT standards are intended to increase the confidence of buyers and project owners and operators, as well as provide consistent standards for those developing modules, designing incentive programs, and making investment decisions.
That said, the real world is where the rubber will hit the road, and it is possible that individual modules may perform worse in real world conditions. Once in the field, First Solar faces the same cost/benefit questions of any solar project.
“I think that once one is in the built environment it is very hard to identify where the trouble spots are in a way that’s economic,” Williams said.
For example, with 2 panels out — even if that causes another 20 panels to be performing less than optimally — you’re still only losing 1% or less of overall output.
But to find them, you would have to open up the combiner boxes and check voltage and current from each string, and look for modules that are performing poorly or performing not like the others, and then within those go to each string and then either run an IV curve test or go module by module in that string and narrow it down to which ones are under performing and look for that module or string, it could be 10 or 20 modules. That is very time-consuming.
Christmas tree lights
First Solar not only has the most utility-scale solar under development but also runs the largest operations and maintenance (O&M) service globally. They monitor down to the combiner box level.
“Because of the way that solar modules are electrically connected, if one module in a string has a problem, generally it will affect the whole string anyway,” said a spokesman for their global O&M division. “It’s like the old Christmas tree lights where if one of the bulbs has burnt out, the whole strand won’t work.”
“We think string monitoring has no real benefit for the utility scale solar plants we operate in the US: We know it doesn’t. You’re going to spend more time and money trying to fix the problems with the monitoring versus the benefit you would receive detecting string failures.”
It is possible to detect problems at the string level, but the cost/benefit analysis doesn’t indicate that it’s worth monitoring every module. The cost of the hardware and infrastructure that would be necessary would not pay back in improved performance.
“I think it’s uncommon to do that level of granular monitoring because if two panels are underperforming — even though they are bringing those two strings slightly down, and so now you’ve got 30–50 sub optimally performing modules — then that one megawatt converter block may still only be underperforming by a fraction of one percent,” said Williams.
Regional climate variability makes a big difference.
While the physics of photovoltaic generation is well understood in the lab, operations in the field are affected by so many more climate forces in addition to module quality.
Over a year, you can draw all kinds of understanding of which arrays perform better than others. But in the transient state, it’s almost impossible, according to Williams.
For example, consider being in a particularly volatile climate where in very hot summer weather thunderstorms come through regularly, dropping temperatures drastically in a short time, and thus raising output, but also bringing clouds, lowering output. There are so many variables other than module quality to contend with in real-world performance.
“As for designing for hot and humid conditions; interestingly, UL doesn’t require damp heat but IEC does,” said Williams. “Fortunately, IEC is required everywhere else in the world outside the USA. However, there has been quite a bit of research determining what would lab test will actually reflect conditions in the field. So, it is timely especially as the volatility of weather will likely create more hot, humid, and windy sites.”
Another thing to consider will be that insurance premiums may also rise, Williams concluded.
“I think that the climate change story may also include more frequent and violent storms which could mean higher insurance premiums to buy capacity in addition to more frequent time ‘above design conditions.’ “