Solar is the future of the global energy mix. More solar capacity was added to the US grid in 2024 than from any other single energy source in the past two decades.
Over in China, the world’s leading consumer of solar, installed capacity rose 45.2 per cent year-on-year.
Yet the rise of this renewable energy has its own environmental costs. They are critical components of a greener economy, but as the industry grows, we must make sure that solar manufacturing itself sticks to sustainable principles.
The main sustainability issue with solar is that the panels need many energy-intensive minerals and chemicals.
Each panel contains a panoply of mined elements, pushing up the ecological footprint of renewable energy: tellurium, silver, zinc, and silicon. The panels also contain petrochemicals.
Renewable biobased resources can underpin a new generation of solar panels that balance energy efficiency, cost, and environment.
Power-hungry silicon
To see how biomaterials can improve the sustainability of the new energy landscape, we have to understand the components and materials inside a typical solar panel.
Solar cells are an important component of the solar module. When they are exposed to light, they absorb energy.
The solar cells turn this energy into negatively charged particles, which make up the electric current that enters the grid and power your homes.
More than 98 per cent of solar panels on the market today contain solar cells made from crystalline polysilicon. This silicon-based solar tech is so popular because it is highly efficient at turning light into energy.
However, the silicon solar cell has major downsides in terms of sustainability. Environmental impact assessments of solar power typically show that the cells of a panel are among its most energy-hungry components.
This is largely down to how energy-intensive the mining, processing, and purifying of silicon is. Coal power is prominent in the global polysilicon manufacturing industry, which is overwhelmingly dominated by China.
Silicon alternatives: organic solar cells
Concerns about the ecological footprint of silicon are driving researchers to develop a new generation of solar cells.
Cue organic solar cells, which dispense with silicon and use carbon-based materials instead.
Organic solar cells appeal for different reasons. One is a reduced environmental footprint from the absence of silicon.
Another is that carbon-based materials are much cheaper raw materials than silicon.
These materials also have unique physical properties. Silicon leans towards heavy, rigid, and bulky products. Carbon-based materials can be rendered into flexible, thin sheets.
This means organic solar cells could form the basis of new types of panels, ones that are easily transported, and fitted onto various surfaces, including windows and even apparel.
Biobased organic solar cells
The word ‘organic’ conjures associations with natural and renewable materials. This is not the case for organic solar cells. Despite the name, they are made today from oil-based plastics (plastics are carbon-based, just like biological materials are).
Biobased components of organic solar cells are however coming into development.
Researchers at Sweden’s Linköping University and KTH Royal Institute of Technology have now shown that wood can be used to enhance performance in ordinary organic solar cells.
The wood-based material the researchers have come up with goes into the middle of the solar cell, the part that is sandwiched between two electrodes. This is known as the electron transport layer.
The material they have used is known as kraft lignin which is made from ordinary wood pulp.
The role of kraft lignin in the solar cell is to make the device more stable – in other words, its ability to perform reliably over time – something that can make organic cells more commercially viable.
Organic solar cells may not match dominant silicon cells for efficiency in energy conversion. However, the marginal difference in efficiency between the types doesn’t matter in many applications.
Lower efficiencies are good enough for solar panels integrated into textiles, vehicles and buildings – lower-energy applications where ramping up efficiency at the cost of the environment is difficult to justify.
Red onions trump petrochemicals
Apart from energy-intensive minerals, there are also fossil-based plastics found inside typical solar cells – both in organic and polysilicon solar technologies.
Within a typical solar panel, solar cells are sandwiched between two layers called ‘encapsulants’. These are two protective layers that keep pollution, moisture, and dirt out of the energy-generating cells.
Unfortunately, these protective layers often rely on fossil polymers, like polyolefin or ethylene-vinyl acetate (EVA).
Researchers at the University of Turku, Finland found that cheap biobased materials can be used to replace these oil-based coatings.
The researchers applied red onion dye to a biomaterial called nanocellulose. Nanocellulose is a broken-down version of cellulose, which is found everywhere in the biological world, particularly in plants. Astonishingly, the biobased dye outperformed a commercial PET-based UV filter.
Circular waste coatings
Solar cell coatings made from circular materials could be on the horizon thanks to new research.
Scientists from Saudi Arabian, Indian, and Ethiopian universities published in Nature last year on new bio-waste solar cell coatings.
NanoBioCelluSynth (NBCS), and EcoPolyBlend were the names of the two materials they formulated and tested. These are both biobased polymers.
The first, NBCS, is made by breaking down cellulose-rich anaerobic biomass digestate into nanoscale cellulose particles.
Digestate is a huge and largely untapped feedstock. It is a waste byproduct of the biogas industry, which turns biological feedstock into gas energy. Europe alone produces between 118 and 138 million tonnes of the stuff per year.
80 per cent of the NBCS material developed and tested in the study was made from digestate-derived cellulose, a material found in plant cell walls.
Other ingredients in the mix were natural additives (10 per cent), with the remaining share made up of agents, stabilisers, and fillers.
The EPCB material on the other hand is 60 per cent composed of biopolymers and 20 per cent from plant-based cellulose, starch or lignin, all of which are abundant natural materials.
For testing, these materials were applied to the solar cell’s surface. After this, the panel was subject to solar simulators that mimic sunlight as well as ‘outdoor’ weather conditions in an indoor chamber.
The study showed these bio-waste solar coatings are high performing while offering a lower impact – up to a 30 per cent carbon footprint reduction compared to conventional materials.
Environmental multi-tasking
Circular and biobased solar cell coatings can benefit the environment in multiple ways.
Apart from potentially reducing demand for petrochemical coatings from the solar industry, it can also clean up waste created by the anaerobic digestion sector.
Digestate may be biobased but in large quantities in nature, it can cause soil and water pollution.
The problem is that it is expensive for digestate operators to process the digestate to render it harmless.
Upcycling the waste could become more viable if new sources of demand arise from the solar panel industry.
Power from plant pigments
Another emerging type of non-silicon-based solar cell are dye-sensitised solar cells. This uses dyes to convert light into electrical energy.
Like organic solar cells, the dye sensitised cell is a ‘third-gen’ solar technology, which is just starting to get commercialised.
Usually, the dyes used here are synthetic and ruthenium-based. Ruthenium – a metal – has been popular for its efficiency at absorbing light and facilitating charge transfer.
However, ruthenium is relatively scarce and its compounds can be highly toxic. These issue are sparking research into possible alternatives that use more common and natural materials.
The plant world is an obvious place to look. Fruits, plants, and flowers are full of colourful and natural pigments that have the kind of light-absorbing properties developers need for dye-sensitised solar cells.
Many are investigating anthocyanins, a class of natural pigments that are responsible for some of the boldest colours in the plant kingdom.
Scientists have been experimenting with a range of anthocyanins extracted from black rice, red cabbage, mulberries and blueberries for the purpose. Chlorophyll is another natural pigment that scientists believe could be an efficiency-enhancing yet sustainable input for dye sensitised cells.
Biobased supports solar recycling
Recycling is a major roadblock in making solar panels sustainable. Despite solar panels containing highly valuable elements, recovering them is still to costly to be done at scale.
One solution could be to fabricate solar panels with more biobased materials.
The reasoning is that recovering precious metals from solar panels could become more profitable if more of the device could be incinerated at the end of its life.
A panel made from plant-based materials, particularly the substrate layer on which other components are mounted, could be burned to leave only precious metals behind.
This straightforward incineration recovery gets rid of the need for costlier and more complex chemical processes to selectively pick out valuable elements for re-use.
Cutting edge research into biobased additions and enhancements in solar reflect changes in perceptions around clean energy technology.
For years, the focus of renewables policy and the solar industry was simply to maximise solar cell efficiency, drive capacity roll-out, and replace fossil fuels as quickly as possible.
Yet as the industry matures and the environmental impacts of renewables become clearer, attention is now turning to the sustainability aspects of the energy transition itself.
Biobased materials can help keep the ecological impacts of the clean energy transition to a minimum while striking a balance between cost, performance, durability, and environment.