Green and greener

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In Berlin, climate protection is taught in school, as stipulated in Germany’s Energy Transition Act. The act states that school projects should raise awareness and understanding of this topic. This makes it all the more surprising that the Berlin Senate is now passing up a great opportunity to introduce students to applied climate protection: The Senate Department for Urban Development and Housing recently announced that it had received a parliamentary inquiry from the Greens regarding the Department’s decision not to install PV or solar thermal systems in new school buildings.

On the one hand, the authorities argued that solar systems were not economical –an absurd assertion. More absurd, however, is that the senate cited climate protection as the reason for its rejection. The administration argued that, since the state of Berlin exclusively purchased green electricity for its properties, schools would be supplied with 100% of their energy from renewable sources even without generating their own electricity. This, the government claimed, would be even better than producing solar power on-site.

However, green electricity purchased is usually only green on paper: Some green electricity certificates, for example, trade domestically produced German electricity from lignite-fired plants for hydropower and hydroelectric power produced in Norway, a simple relabeling of coal power without any physical change.

Positive energy balance

Above all, however, the authority’s reasoning is based on a preconceived notion which many people who deal with PV have already been confronted with: the idea that so much energy is consumed in the manufacture of PV plants that at best their contribution to climate protection and the transition to clean energy is modest and at worst, counterproductive.

Although such positions are often based on ignorance, economic interest, or political agenda, the underlying questions are more than justified: How green are PV systems, really? How much energy goes into their production? How much CO2 is released in the process, and how much do they avoid by displacing fossil fuels? In view of the anticipated worldwide spread of solar power, PV’s energy demand and carbon footprint are of major importance for global climate protection.

One thing is clear: Blanket statements are impossible to make, because the product landscape is simply too diverse to put every system in the same basket. For instance, thin film panels perform much better in this respect than crystalline modules because their production requires less energy. However, this benefit comes at the expense of the environmental impact of some of the materials used.

Production location also plays a major role in the carbon footprint, explains Andreas Neuhaus, head of module technology at the Fraunhofer Institute for Solar Energy Systems (ISE). “Due to the high proportion of coal in the electricity mix, production in China causes more emissions than production in Europe,” says Neuhaus. This is the case if the carbon emissions of a PV plant are calculated on the basis of the country’s electricity mix. But some manufacturers generate their own solar power for manufacturing or tap hydropower, to produce modules in an environmentally friendly way even in a country with numerous coal-fired power plants. Taking such conditions into account when assessing the carbon footprint is a virtually impossible task.

The design of the modules also influences energy consumption. “Aluminum frames consume a lot of energy, for instance – laminates are better,” says the Fraunhofer researcher. Glass-glass modules on the other hand have the benefit of a longer service life and less degradation, but this also comes at the cost of higher energy requirements for production. And then there are efficiency and the installation site, important factors when calculating the climate benefit. “It’s complicated,” Neuhaus says.

Progress in production

One thing an international group of experts did not shy away from, however, was collecting energy and emissions data for individual product categories on behalf of the International Energy Agency’s Photovoltaic Power Systems program (IEA PVPS).

In its 2015 study, one of the authors’ conclusions was that energy payback time for monocrystalline rooftop systems with a yield of just under 1,000 kilowatt hours per kilowatt peak was an average of 2.4 years. They considered the entire cycle, including upstream processes such as silicon production and going all the way through to component disposal at end of life. The report accounted for inverters, mounting racks, and cables and modules. According to the IEA PVPS experts, the generation of one kilowatt hour of electricity in such a plant equates to an average emission of some 80 grams of CO2 equivalent. By far, the largest proportion of this is attributable to the modules. Yet these figures are just a single data point, and they are already five years old. “The big challenge is keeping the carbon footprints up to date and adequately reflecting the production situation in East Asia,” explains Rolf Frischknecht, one of the authors of the IEA PVPS study and head of Swiss company Treeze, which prepares life cycle analyses. The report does not take the latest efficiency improvements in manufacturing processes into account either. In addition to improvements in sawing wafers, the industry has made major progress in the production of solar grade polysilicon using the Siemens process, a very energy-intensive procedure.

Wacker Chemie, one of the world’s leading manufacturers of solar silicon, is convinced that potential in this area has not yet been exhausted. The company has set itself a goal of reducing its energy requirements by a further 10% to 15% over the next few years. Karl Hesse, Vice President of Process Development at Wacker Polysilicon, sees several approaches to this. “Here’s an example: The Siemens process involves several high-temperature steps, such as the deposition of gaseous trichlorosilane at around 1,000 degrees Celsius, which forms high-purity polycrystalline silicon. The thermal losses that occur during this process… have already been reduced considerably through numerous measures.”

614 grams/kWh

Even though there is a certain range of energy consumption and carbon emissions involved in production, there are no two ways about it: PV makes a significant contribution to climate protection. After all, solar power replaces power from coal and gas-fired power plants.

This was corroborated with concrete figures in a study issued by Germany’s Federal Environment Agency (UBA) last October. According to the study, every kilowatt hour of solar electricity generated in Germany in 2017 avoided a total of 614 grams of CO2 equivalent. By comparison, onshore wind turbines managed to avoid 667 grams, and biogas plants avoid 355 grams.

The experts anticipate that solar will only push anthracite and gas-fired power plants out of the market due to their ranking in the merit order.

According to the UBA study, PV could reduce the German carbon footprint for 2017 by a total of 24.2 million metric tons of CO2 equivalent (onshore wind energy: 58.7 million metric tons; biogas: 10.5 million metric tons). That corresponds to nearly 3% of total German CO2 emissions in 2017. In their calculations, the UBA considered the carbon emissions generated during module production and system assembly. For PV, they calculate 67 grams per kilowatt hour based on total power generated, slightly less than their colleagues from IEA PVPS for monocrystalline residential rooftop systems.

Regardless of how the calculation actually turns out, differences between manufacturers are comparatively small when compared with solar’s service life. For instance, a rough calculation shows that it takes about 12 months for a module with a relatively small carbon footprint to achieve a positive climate balance. A module that cost 50% more carbon emissions to produce therefore takes six months longer. Based on the service life of 20 to 30 years, the difference is insignificant.

Mandatory, voluntary measures

Even though the carbon footprint of PV stacks up well, there is room for improvement. But how can manufacturers be persuaded to make their systems even more sustainable? A strong lever would be the inclusion of PV in the European Ecodesign Directive. Since the summer of 2018, the Directorate-General for the Internal Market, Industry, Entrepreneurship and SMEs (DG Grow) has been working on a study examining which policy instruments should be used to promote sustainable product development. One instrument is the Ecodesign Directive. If the EU extends the reach of the directive to include PV, then module and inverter manufacturers would have to meet future environmental standards for products sold in Europe.

Recycling cell materials

The EU WEEE currently requires that 85% of all modules sold be collected at the end of their service life and 80% recycled. This specification refers to the weight of the modules – and is therefore relatively easy to comply with, since the glass, aluminum frame, and junction box account for around 90% of a panel’s weight. By contrast, so far, silicon solar cells along with their lead, zinc, tin, and silver components have ended up in waste incineration plants. The reason for this is that the cells are firmly baked into the EVA and backing films, making recycling difficult. “First you have to neatly separate the recyclables before they can be recycled. But this is extremely expensive,” says Ullrich Didszun, a German representative of the recycling organization PV Cycle.

The recycling industry is therefore busy working on processes to simplify the recycling of semiconductor materials. One research group led by the waste disposal company Suez and the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB has developed a process that uses pyrolysis to remove the metals and silicon from the plastics so that the recyclable materials can be recycled. The process is currently being tested in a pilot plant in the city of Knittlingen, Germany. Suez expects to start building an industrial-scale facility towards the end of this year. It will initially have a capacity of 200,000 modules per year.

The work on recycling solutions is not only driven by possible legal requirements, but by a number of other industrial initiatives that develop criteria and voluntary certificates. They also address the concern that hazardous materials should be avoided wherever possible. It is still impossible, however, to say with any authority how much of a positive impact the recycling of semiconductor materials would have on solar’s carbon footprint. “You’d have to compare the costs of recycling silicon, silver, and lead with the cost of producing the new material,” says Frischknecht. “This question can only be answered reliably when large quantities of modules accumulate and when the costs are better understood.”

According to Frischknecht, however, initial estimates show that recovered materials already have a smaller footprint than new materials. According to the Elektro-Altgeräte Register (EAR) foundation, just 367 metric tons of decommissioned solar modules were delivered to public collection points in 2017. But the volume is set to grow sharply. The lnternational Renewable Energy Agency (IRENA) expects nearly 100,000 metric tons of solar scrap to accumulate in Germany by 2025. By 2030, this quantity is expected to grow to around 400,000 metric tons.