Just 5 years ago, the photovoltaics industry was in energy deficit, consuming 75% more energy to manufacture and install photovoltaic panels than it produced. To silence sceptics, installed panels must ultimately pay back the energy used to create them.
Michael Dale, postdoctoral fellow, and Sally Benson, director of Stanford University's Global Climate and Energy Project (GCEP) have found the industry is making positive strides.
According to their new paper on the energy balance of the the global photovoltaic industry, 2012 was a turning point, where the PV industry "likely" became a net electricity provider. The research suggests that with continued technological advances, the industry is poised to pay off its energy debt as early as 2015, and no later than 2020, due to "declining energy inputs, more durable panels and more efficient conversion of sunlight into electricity."
Dale developed new tools to assess the industry's progress and, in a recent news piece commented, "Despite its fantastically fast growth rate, PV is producing, or is just about to start producing, a net energy benefit to society."
The paper developed a number of unique data sets: a calculation of distribution of global capacity factor for PV deployment; meta-analysis of energy consumption in PV system manufacture and deployment; and documentation of the reduction in energetic costs of PV system production.
In order to analyse the data, a model analogous to financial learning curves was used to track the energetic costs associated with PV system manufacture, Dale tells pv magazine. The fit between model and data is not perfect, and therefore the researchers have not pinned the date at which the industry became a net producer with certainty. Nevertheless, he said they found that in 75% of the cases studied, the PV industry became a net producer before 2012.
Much of the improvement seen in global performance is due to the declining energy required in the manufacture and installation of PV systems. Thinner silicon wafers and less highly refined materials are now used to make cells, in addition, recent improvements in the manufacturing processes mean less material is wasted.
Benson is eager to see how further developments in technology will impact global energy consumption, and is excited about the role Stanford's GCEP could play in the grand challenge of building a global energy future with much lower greenhouse emissions.
"If we can continue to drive down the energy inputs, we will derive greater benefits from PV," said Benson. "Developing new technologies with lower energy requirements will allow us to grow the industry at a faster rate."
If solar industry growth rates continue, by 2020 around 10% of the world's electricity could be produced by PV systems. At current energy payback rates, production and installation of new modules would consume 9% of global electricity. However, if the energy intensity of PV systems continues along with the current downward trend, by 2020 less than 2% of global electricity will be needed to sustain growth of the sector.
Energy payback time could also be reduced if PV installations proliferate in locations with high quality solar resources, such as the deserts in south west United States and the Middle East.
Dale makes the point that currently "Germany makes up about 40 percent of the installed market, but sunshine in Germany isn't that great, from a system perspective, it may be better to deploy PV systems where there is more sunshine."
The study also highlights the on-going necessity of research into PV modules with lower energy costs to manufacture and the importance of development of thin film technologies, with the potential to increase efficiency. Without special attention to reducing energy inputs, the energy demands of the solar sector may not be reduced to as low as 2%.
The study's data covers silicon-based technologies alongside modules utilising cadmium telluride (CdTE) and copper indium gallium diselenide (CIGS) as semiconductors. At present, these comprise 99% of installed panels. Continued reduction of the energetic costs of producing modules may be accomplished in the future by switching to technologies with lower energy costs than silicon.
The report compared the breakdown of financial costs and energy requirements at each stage in the production process. Around a third of the total financial cost is absorbed by installation, together with the components outside solar cells such as wiring and inverters, and soft costs such as permitting.
In terms of energy, only 13% of the total is required for this stage. In a crystalline silicon system, around half the total energy cost is required just for the extraction of silica, purification, crystallization and manufacture of the PV wafers. The research points out that the industry is focused primarily on cost reduction.
Edited by Becky Beetz.
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