By Kris De Decker, originally published by Low-Tech Magazine
Picture: Jonathan Potts.
Solar photovoltaic (PV) systems generate "free" electricity from sunlight, but manufacturing them is an energy-intensive process.
It’s generally assumed that it only takes a few years before solar panels have generated as much energy as it took to make them, resulting in very low greenhouse gas emissions compared to conventional grid electricity.
However, the studies upon which this assumption is based are written by a handful of researchers who arguably have a positive bias towards solar PV. A more critical analysis shows that the cumulative energy and CO2 balance of the industry is negative, meaning that solar PV has actually increased energy use and greenhouse gas emissions instead of lowering them.
This doesn’t mean that the technology is useless. It’s just that our approach is wrong. By carefully selecting the location of the manufacturing and the installation of solar panels, the potential of solar power could be huge. We have to rethink the way we use and produce solar energy systems on a global scale.
There’s nothing but good news about solar energy these days. The average global price of PV panels has plummeted by more than 75% since 2008, and this trend is expected to continue in the coming years, though at a lower rate. [1-2] According to the 2015 solar outlook by investment bank Deutsche Bank, solar systems will be at grid parity in up to 80% of the global market by the end of 2017, meaning that PV electricity will be cost-effective compared to electricity from the grid. [3-4]
Lower costs have spurred an increase in solar PV installments. According to the Renewables 2014 Global Status Report, a record of more than 39 gigawatt (GW) of solar PV capacity was added in 2013, which brings total (peak) capacity worldwide to 139 GW at the end of 2013. While this is not even enough to generate 1% of global electricity demand, the growth is impressive. Almost half of all PV capacity in operation today was added in the past two years (2012-2013). [5] In 2014, an estimated 45 GW was added, bringing the total to 184 GW. [6] [4].
Solar PV total global capacity, 2004-2013. Source: Renewables 2014 Global Status Report.
Meanwhile, solar cells are becoming more energy efficient, and the same goes for the technology used to manufacture them. For example, the polysilicon content in solar cells — the most energy-intensive component — has come down to 5.5-6.0 grams per watt peak (g/wp), a number that will further decrease to 4.5-5.0 g/wp in 2017. [2] Both trends have a positive effect on the sustainability of solar PV systems. According to the latest life cycle analyses, which measure the environmental impact of solar panels from production to decommission, greenhouse gas emissions have come down to around 30 grams of CO2-equivalents per kilwatt-hour of electricity generated (gCO2e/kWh), compared to 40-50 grams of CO2-equivalents ten years ago. [7-11] [12]
According to these numbers, electricity generated by photovoltaic systems is 15 times less carbon-intensive than electricity generated by a natural gas plant (450 gCO2e/kWh), and at least 30 times less carbon-intensive than electricity generated by a coal plant (+1,000 gCO2e/kWh). The most-cited energy payback times (EPBT) for solar PV systems are between one and two years. It seems that photovoltaic power, around since the 1970s, is finally ready to take over the role of fossil fuels.
Manufacturing has Moved to China
Unfortunately, a critical review of the PV solar industry paints a very different picture. Many commenters attribute the plummeting cost of solar PV to more efficient manufacturing processes and scale economies. However, if we look at the graph below, we see that the decline in costs accelerates sharply from 2009 onwards. This acceleration has nothing to do with more efficient manufacturing processes or a technological breakthrough. Instead, it’s the consequence of moving almost the entire PV manufacturing industry from western countries to Asian countries, where labour and energy are cheaper and where environmental restrictions are more loose.
Less than 10 years ago, almost all solar panels were produced in Europe, Japan, and the USA. In 2013, Asia accounted for 87% of global production (up from 85% in 2012), with China producing 67% of the world total (62% in 2012). Europe’s share continued to fall, to 9% in 2013 (11% in 2012), while Japan’s share remained at 5% and the US share was only 2.6%. [5]
Compared to Europe, Japan and the USA, the electric grid in China is about twice as carbon-intensive and about 50% less energy efficient. [13-15] Because the manufacture of solar PV cells relies heavily on the use of electricity (for more than 95%) [16], this means that in spite of the lower prices and the increasing efficiency, the production of solar cells has become more energy-intensive, resulting in longer energy payback times and higher greenhouse gas emissions. The geographical shift in manufacturing has made almost all life cycle analyses of solar PV panels obsolete, because they are based on a scenario of domestic manufacturing, either in Europe or in the United States.
LCA of Solar Panels Manufactured in China
We could find only one study that investigates the manufacturing of solar panels in China, and it’s very recent. In 2014, a team of researchers performed a comparative life cycle analysis between domestic and overseas manufacturing scenarios, taking into account geographic diversity by utilizing localized inventory data for processes and materials. [13] In the domestic manufacturing scenario, silicon PV modules (mono-si with 14% efficiency and multi-si with 13.2% efficiency) are made and installed in Spain. In the overseas manufacturing scenario, the panels are made in China and installed in Spain.
For solar panels manufactured in China, the carbon footprint and the energy payback time are almost doubled
Compared to the domestic manufacturing scenario, the carbon footprint and the energy payback time are almost doubled in the overseas manufacturing scenario. The carbon footprint of the modules made in Spain (which has a cleaner grid than the average in Europe) is 37.3 and 31.8 gCO2e/kWh for mono-si and multi-si, respectively, while the energy payback times are 1.9 and 1.6 years. However, for the modules made in China, the carbon footprint is 72.2 and 69.2 gCO2e/kWh for mono-si and multi-si, respectively, while the energy payback times are 2.4 and 2.3 years. [13]
At least as important as the place of manufacturing is the place of installation. Almost all LCAs — including the one that deals with manufacturing in China — assume a solar insolation of 1,700 kilowatt-hour per square meter per year (kWh/m2/yr), typical of Southern Europe and the southwestern USA. If solar modules manufactured in China are installed in Germany, then the carbon footprint increases to about 120 gCO2e/kWh for both mono- and multi-si — which makes solar PV only 3.75 times less carbon-intensive than natural gas, not 15 times.
Solar insulation in Europe and the USA. Source: SolarGIS.
Solar PV electricity remains less carbon-intensive than conventional grid electricity, even when solar cells are manufactured in China and installed in countries with relatively low solar insolation. This seems to suggest that solar PV remains a good choice no matter where the panels are produced or installed. However, if we take into account the growth of the industry, the energy and carbon balance can quickly turn negative. That’s because at high growth rates, the energy and CO2 savings made by the cumulative installed capacity of solar PV systems can be cancelled out by the energy use and CO2 emissions from the production of new installed capacity. [16] [19-20]
At high growth rates, the energy and CO2 savings made by the cumulative installed capacity of solar PV systems can be cancelled out by the energy use and CO2 emissions from the production of new installed capacity
A life cycle analysis that takes into account the growth rate of solar PV is called a "dynamic" life cycle analysis, as opposed to a "static" LCA, which looks only at an individual solar PV system. The two factors that determine the outcome of a dynamic life cycle analysis are the growth rate on the one hand, and the embodied energy and carbon of the PV system on the other hand. If the growth rate or the embodied energy or carbon increases, so does the "erosion" or "cannibalization" of the energy and CO2 savings made due to the production of newly installed capacity. [16]
For the deployment of solar PV systems to grow while remaining net greenhouse gas mitigators, they must grow at a rate slower than the inverse of their CO2 payback time. [19] For example, if the average energy and CO2 payback times of a solar PV system are four years and the industry grows at a rate of 25%, no net energy is produced and no greenhouse gas emissions are offset. [19] If the growth rate is higher than 25%, the aggregate of solar PV systems actually becomes a net CO2 and energy sink. In this scenario, the industry expands so fast that the energy savings and GHG emissions prevented by solar PV systems are negated to fabricate the next wave of solar PV systems. [20]
Several studies have undertaken a dynamic life cycle analysis of renewable energy technologies. The results — which are valid for the period between 1998 and 2008 — are very sobering for those that have put their hopes on the carbon mitigation potential of solar PV power. A 2009 paper, which takes into accountthe geographical distribution of global solar PV installations, sets the maximum sustainable annual growth rate at 23%, while the actual average annual growth rate of solar PV between 1998 and 2008 was 40%. [16] [21]
This means that the net CO2 balance of solar PV was negative for the period 1998-2008. Solar PV power was growing too fast to be sustainable, and the aggregate of solar panels actually increased GHG emissions and energy use. According to the paper, the net CO2 emissions of the solar PV industry during those 10 years accounted to 800,000 tonnes of CO2. [16] These figures take into account the fact that, as a consequence of a cleaner grid and better manufacturing processes, the production of solar PV panels becomes more energy efficient and less carbon-intensive over time.
Between 2009 and 2014, solar PV grew four times too fast to be sustainable
The sustainability of solar PV has further deteriorated since 2008. On the one hand, industry growth rates have accelerated. Solar PV grew on average by 59% per year between 2008 and 2014, compared to an annual growth rate of 40% between 1998 and 2008 . [5] On the other hand, manufacturing has become more carbon-intensive. For its calculations of the CO2 balance in 2008, the study discussed above considers the carbon intensity of production worldwide to be 500 gCO2e/kWh. In 2013, with 87% of the production in Asia, this number had risen to about 950 gCO2e/kWh, which halves the maximum sustainable growth rate to about 12%.
If we also take into account the changes in geographic distribution of solar panels, with an increasing percentage installed in regions with higher solar insolation, the maximum sustainable growth rate increases to about 16%. [23-24] Although more recent research is not available, it’s obvious that the CO2 emissions of the solar PV industry have further increased during the period 2009-2014. If we would consider all solar panels in the world as one large energy generating plant, it would not have generated any net energy or CO2-savings.
The Solution: Rethink the Manufacture and Use of Solar PV
Obviously, the net CO2 balance of solar PV could be improved by limiting the growth of the industry, but that would be undesirable. If we want solar PV to become important, it has to grow fast. Therefore, it’s much more interesting to focus on lowering the embodied energy of solar PV power systems, which automatically results in higher sustainable growth rates. The shorter the energy and CO2 payback times, the faster the industry can grow without becoming a net producer of CO2.
Annual net CO2 balance of the crystalline silicon PV industry at different growth rates for different combinations of countries of production and installation. Source: Briner 2009.
Embodied energy and CO2 will gradually decrease because of technological advances such as higher solar cell efficiencies and more efficient manufacturing techniques, and also as a consequence of the recycling of solar panels, which is not yet a reality. However, what matters most is where solar panels are manufactured, and where they are installed. The location of production and installation is a decisive factor because there are three parameters in a life cycle analysis that are location dependent: the carbon intensity of the electricity used in production, the carbon intensity of the displaced electricity mix at the place of installation, and the solar insolation in the place of installation. [16]
By carefully selecting the locations for production and installation we could improve the sustainability of solar PV power in a spectacular way. For PV modules produced in countries with low-carbon energy grids — such as France, Norway, Canada or Belgium — and installed in countries with high insolation and carbon-intensive grids — such as China, India, the Middle East or Australia — greenhouse gas emissions can be as low as 6-9 gCO2/kWh of generated electricity. [16] [20] [14-15] That’s 13 to 20 times less CO2 per kWh than solar PV cells manufactured in China and installed in Germany. [25]
Sustainable growth rates of 300-460% are possible when PV modules are produced in countries with low-carbon energy grids and installed in countries with high insolation and carbon-intensive grids
This would allow sustainable growth rates of up to 300-460%, far above what’s even necessary. If solar PV would grow on average at a rate of 100% per year, it would take less than 10 years to meet today’s electricity’s demand. If it would grow at the 16% maximum sustainable growth rate we calculated above, meeting today’s electricity demand would take until 2045 — with no net CO2 savings. By that time, according to the forecasts, total global electricity demand will have more than doubled. [26]
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