There are many metrics by which to assess PV inverters. Performance indices – such as energy density, maximum power point tracking (MPPT) count, or efficiency, are among the more popular numbers on spec sheets. In its non-financial report, Germany-based inverter giant SMA demonstrates how the company has worked with stakeholders to identify different parameters that serve as new targets its product engineers are supposed to strive for. What stands behind these targets is the aspiration to be more sustainable, not just compared to fossil fuels.
“The supply of renewable energy leaves an impact like other industries. This impact starts with raw material sourcing practices right to end-of-life treatment and recycling,” argues Matthias Schaepers, corporate sustainability manager at SMA. ”It is not just about generating renewable energy but also ensuring that everything that happens before and after power generation is sustainable.”
To achieve this, SMA committed to raising the proportion of recyclable materials in its inverters to 90%, lowering the amount of CO2 produced during inverter production by 25%, and omitting 15% of nonpreferable materials, among several other goals it set itself to achieve by 2025. The approach SMA is using to achieve these goals is to scrutinize at product and company level and devise performance indices for sustainability. If SMA wants to improve on material intensity in its products, for example, it will not do so by introducing a new lighter material composition, which can be more toxic or harder to recycle. “We are looking at it holistically. In the end, we want to say that we have improved our overall sustainability,” explains Schaepers.
This holistic approach requires SMA to quantify and report on many aspects of its production, from energy consumption to the impact of its car fleet, and this reporting goes far beyond SMA’s factory gates. Each step within the value chain of an inverter must be considered. That means reporting begins with an assessment of the origin of the raw materials that are being used. Mining companies can be assessed for particularly harmful practices, like the release of toxic wastewater into rivers.
Furthermore, a PV inverter includes a range of subcomponents, many of which are not produced in-house. IGBT and MOSFET semiconductors, but also circuit boards, capacitors, fans, and screws, are usually supplied by third parties. As a final step, recycling processes are considered. A recycling assessment addresses whether procedures are economically feasible. It includes an evaluation of waste materials to determine whether they can be recycled or are toxic.
Therefore, accurate reporting is not just dependent on the reporting practice of an individual inverter manufacturer, but the same reporting methodology must be applied to the entire value chain. The Global Reporting Initiative (GRI) has been working since 1997 to establish a universal reporting standard. Only if all the companies in the value chain report according to the same methodology, is it possible to devise a reliable quantification of a product’s sustainability. The GRI claims to have filed nearly 15,000 organizations with 37,000 GRI reports. Infineon, Texas Instruments, and Cree are among the well-established suppliers of IGBTs and MOSFETs used in PV inverters that have joined the initiative.
Additionally, there is the GaBi databank which provides life-cycle assessment numbers for the bill of materials of a broad range of products. To date, the databank counts 15,000 entries. There are also generic entries for components that their manufacturers have not classified, but a mean value had been determined. An inverter manufacturer can now access such a database and obtain the relevant data points for the full component list. The data can be fed into purpose-built software, which will eventually produce a product-specific sustainability report.
On the company level, there is another index. Since 2018, SMA has tasked Ecovadis, a prominent corporate social responsibility (CSR) auditing organization, with vetting its supply chain. Ecovadis has vetted more than 65.000 companies from 200 industries for labor and human rights, environmental, ethical, and sustainable procurement performances. The organization gives scores from 0-100%, with 100% being virtually unattainable. Ecovadis says that scores from 45% demonstrate proactive and comprehensive CSR management. In its sustainability targets for 2025, SMA formulated that it seeks to improve the average rating of its supply chain according to Ecovadis to 55% – a 7% increase from today’s value.
Schaepers adds that despite all this effort, accurate reporting across the supply chain is still challenging. Nonetheless, the attempts result in a reasonably good approximation of the sustainability of a particular inverter. More importantly, the process gives a good overview of the specific hotspots which have to be addressed to improve sustainability performance.
“If we take a look at our CO2 footprint, we can see that SMA is only responsible for about 5% of the CO2 emissions connected to its inverter production,” explains Schaepers. This is because SMA mainly sources its energy from renewable and regional sources. An impressive 40% of the electricity used in its production comes from on-site PV; the remainder is grid-sourced renewables. Most emissions come from producers of individual components or the mining of the raw materials, according to Schaepers. Hence, to lower CO2 emissions of its products, SMA reviews its supply chain and works with its suppliers to perform better on that metric.
The inverter housing is an example used by Schaepers to demonstrate this. At SMA, the casing is made of an aluminum alloy, which the sustainability expert says is relatively easy to recycle. But because global demand for aluminum is so high, the amount of secondary resource metals on global commodity exchanges is limited. Public databases, such as those available under GRI standards, state that the average share of secondary materials in aluminum in Germany is at around 40-50%. With the help of stringent reporting throughout the entire value chain, SMA seeks to improve on its use of secondary aluminum to reach a level considerably better than the German industry average by 2025.
Schaepers says that SMA has improved the material intensity of its inverter products. This is especially true of SMA central inverters, which today only require about 50% of the materials that were needed just a few years ago, for the same capacity. “We can clearly see that we have managed to improve on this metric over the last years,” Schaepers says. “Also, we integrate all necessary functions into our inverters, so that there is no need for resource-intense additional devices.”
Material intensity has another positive effect. “We measure energy use as a function of produced inverter capacity. Over the last five years, we have managed to improve on this metric by a more than half. We used to be at 6.7 kWh of used energy for each kilowatt of produced inverters. Today we have reduced that figure down to 2.8 kWh. And in contrast to some of our competitors, we include all energy used at the company site in this metric, not only the energy used in the production line,” says Schaepers.
This achievement is possible in part because SMA’s inverter production line has become more efficient in terms of energy use. But to a more substantial degree, it’s also because the inverters themselves have achieved an increasingly higher energy density.
Round and round
At SMA, the topic of resource consumption is addressed via three categories. One is nonpreferable materials. These are toxic materials that cannot be recycled or are mined at high social and ecological costs. Lead, cobalt, and tungsten are examples of such materials. Schaepers explains that there are also preferable materials, which mostly refers to secondary resources, meaning those that come from recycling. While omitting all nonpreferable materials at once is either technically or financially not feasible, SMA has committed to lowering the use of nonpreferable materials, while increasing the use of many recycled materials.
As the company seeks to increase the use of secondary materials, SMA has also put design for recycling higher on its priority list. This requires a close partnership with electrical waste disposal companies, Schaepers says. It is not always the materials that are used which cause problems, but often also the way they are assembled. Gluing parts together, for example, often prevents recyclability. This is why SMA strives to avoid gluing to assemble the inverter components and instead opts for screwing or push-fit connections.
Greener green deal
In a report titled “Raw materials demand for wind and solar PV technologies in the transition towards a decarbonized energy system,” the JRC estimated the raw material demand for going carbon-neutral in Europe. The report finds that demand for structural materials like concrete, steel, and aluminum could rise by a factor of eight in 2030 and a whopping 30 by 2050. In 2018, the PV industry consumed 67.9 t/MW of steel, 8.6 t /MW of plastic, 46.4 t/MW of glass, 7.5 t/MW of aluminum, and 4.6 t/MW of copper. There are some supply-chain risks associated with this demand, the JRC concluded in its report. Shortages can also occur in various rare earth metals and materials commonly used in electrical components.
As the EU prepares to go carbon-neutral by 2050, the bloc has started to observe these sustainability metrics more closely. As a part of its Work Plan 2016 to 2019, the European Commission is working on establishing an eco-design guideline and eco-label directive, as a part of its green public procurement guidelines.
The Commission’s Joint Research Center (JRC) has held four stakeholder meetings with representatives from electronic waste disposal companies, NGOs, PV component makers (including SMA), and research institutes. Following this, the JRC will publish a preparatory study this year, which will inform further legislative action to make solar more sustainable.
One popular metric is the Energy Return on Energy Invested (EROI). The figure describes how long it takes for a PV plant to amortize its production-related energy consumption. Research by Raugei et al. from 2017 suggests that PV systems in Switzerland achieve a value of seven to 10, depending on various parameters. This value translates into one to two years of field operations before it is energetically positive. This accounts for entire PV systems, but the research did not break down the specific impacts of components.
There is also new research elaborating on solar’s sustainability credentials. SMA has examined lifecycle assessments of inverters. The data was used by research institute Fraunhofer IBP, which made a life-cycle assessment for entire solar plants. In so doing, the researchers sought out the environmental impacts throughout the entire life cycles of PV plants, covering component production, installation, and even decommissioning. The final results are to be published at some point this year. This rigorous approach to making comprehensive assessments will be essential in enabling a sustainable energy transition and informing future product design.