Easing the pane: The development of light weight and flexible solar cells could kindle a resurgence in the BIPV space as design possibilities expand | Photo: Researchgate

Emerging building integrated tech can shine new light on India’s solar energy sector

Advances in technology are bringing flexible, light weight solar panels closer to scalability. Will India’s fledgling BIPV sector be able to capitalise? 

In 2019, away from mainstream attention, Mumbai’s cityscape was undergoing a small but significant upgrade. One of India’s largest data centres, CtrlS Datacenters Ltd, began replacing the entire façade of its Mumbai facility with solar panels. By mid-2020, the four walls of the data centre were covered with a total of 5,000 sqft of panels. The resulting 1MW capacity system, used to run the centre, is estimated to provide CO2 reductions equivalent to 7,000 trees.

Buildings currently account for almost a third of India’s total energy consumption. But with nearly 70% of the buildings that will stand in India in 2030 yet to be built – at 700–900 million sqm each year in new developments – the deep energy footprint of the country’s buildings needs urgent addressal.

In response, zero-energy building technologies are steadily gaining traction. Building Integrated Photovoltaics (BIPV), as was used in Mumbai’s CtrlS building, is among the more popular approaches to making zero-energy buildings. But while the BIPV concept has been expected to take off in the country for some years now, there has been little progress in real terms.

Rooftop’s issues, BIPV’s loss

To promote solar power in India, the Ministry of Power started an initiative – Jawaharlal Nehru National Solar Mission – in 2010. The mission has been revised twice and, at present, boasts a target of 100 GW of solar PV by 2022. It was also fixed that out of 100 GW, rooftop PV should produce 40 GW by 2022.

However, rooftop installations in India fell to a four-year low in the first half of 2020. According to data from renewable energy consultant Bridge to India, only 473MW of new rooftop systems were installed between January and June against 1,534MW in the same period a year ago. A report by consulting firm Mercom Capital Group, further revealed that rooftop installations incurred a 35% drop year-over-year.

India’s rooftop solar industry was particularly hard hit by the supply shocks due to last year’s lockdown and the import duties imposed on Chinese solar imports. In addition, uncertainty regarding the net-metering for rooftop installations and fears regarding the viability of rooftop metering for power distribution companies has further throttled India’s BIPV market. But while regulatory issues continue to threaten growth of the space, conventional solar technology itself has been a major bottleneck for developments.

Conventional silicon crystalline cells ill-suited to BIPV

With excellent stability, low generation cost of electricity and high efficiencies of above 20%, crystalline silicon solar is dominating the PV market. However, the carbon footprint generated by traditional solar technology has become a cause for concern.

In the manufacturing of traditional solar panels, metallurgical-grade silicon is purified into polysilicon, which creates silicon tetrachloride. While recycling tetrachloride to extract silicon needs less energy, the reprocessing equipment required is quite expensive, and produces potentially toxic by-products.

Since BIPV designs have weight limitations, standard crystalline silicon solar panels, which weigh 20-30kg each on average, are ill-suited for vertical integration on walls. In addition to being heavy, conventional panels are also rigid and delicate, which make them especially cumbersome to work with as a construction material.

As a result, there is a lot of interest in alternative photovoltaic materials. A few promising new materials include organic photovoltaics and perovskite solar cells.

Organic solar cell (OSC): A cleaner technology

Like traditional solar cell technology, OSCs convert the sun’s energy into electricity. They are made up of multiple layers, one of which is the acceptor layer. When an OSC is exposed to sunlight, an electron is released from the layer of organic molecules. The acceptor layer’s job is to pass that electron onto the electrode. This leads to a build-up charge, which generates electricity.

The most common material used for acceptors in OSC is fullerene – a molecule composed of 60 carbon atoms joined together in a tight molecular structure. However, the efficiency with fullerene acceptor is limited to 10%, prompting many researchers to look for non-fullerene alternatives.

Dr Soumitra Satapathi, associate professor at IIT Roorkee, told CarbonCopy that currently, the development of low bandgap polymers and non-fullerene acceptors is receiving significant research attention. In addition to these, small molecules which are capable of showing singlet fission – a molecular energy multiplication process – significantly improves efficiency and performance of OSCs, he said.

The Council of Scientific and Industrial Research (CSIR)-National Physical Laboratory has undertaken many research and development activities for the advancement of “efficient stable solar cells”.

According to the data, CSIR group has started working on the design and synthesis of donor and acceptor materials for organic solar cells to improve the power conversion efficiencies and lifeline of devices.

Many institutes in India are also working on OSC. Researchers from the Indian Institute of Technology, Kanpur, have developed 12×12 cm2 sub-modules from organic solar PV cells on a paper substrate. It can be used to power flexible electronic devices under an indoor lighting environment.

When it comes to OSCs application in BIPV, OSC as a plastic foil with a surface density of less than 1kgm-2 can be used because it weighs at least 10 times less than crystalline silicon modules. Since the weight of cells is a crucial factor in designing BIPVs, OSCs are a more appropriate match than silicon modules.

According to Dr Karl Leo, professor at Technische Universität Dresden, Germany, “They [OSCs] are addressing very different markets where lightweight and flexibility are the features that are asked for – for example in building integration.” They can be printed and stuck onto buildings, car windows and can also be used for mobile charging.

Despite being limited to some niches, it is interesting to speculate whether OSCs will be able to enter the mainstream PV market. According to Leo, “In the very long term, if organics would reach very high efficiency, they might compete, but this is not very likely in the near and mid-term.”

A study published last year pointed out that OSCs can only compete with crystalline silicon if it reaches the following parameters – “module efficiency around 20%, lifetime of more than 20 years, and cost well below silicon.” Results from laboratories and companies show that of these, OSCs can reach the ‘20-year lifetime’ parameter most easily.

Cost-wise, the study notes that OSCs are more expensive than mainstream crystalline silicon solar technology. The cost difference, however, is not surprising since OSCs are still far from reaching economies of scale unlike silicon PV, which has been commercially available for decades.

Additionally, in comparison to silicon solar technology, OSC’s carbon footprint is less. According to Leo, OSCs can reduce carbon footprint “dramatically, and it has a super-low CO2 emission.”

A study by the German testing institute TÜV Rheinland revealed that organic solar films potentially allow recovery of carbon arising during the entire life cycle (from manufacture to disposal) in just 3 months.

Prior to the Covid-19 pandemic, market trends were also painting a positive picture for OSCs. According to Fortune business insights report, the global organic cells market size was $55.63 million in 2019 and it was projected to grow from $44.9 million in 2020 to $101.29 million in 2027 at a CAGR of 12.30%. However, due to the pandemic, the global organic solar cells market will exhibit a huge decline of -19.2% in 2020, it said.

Perovskite solar cell: A game changer

Perovskite is a rapidly expanding class of solar cells. It consists of a perovskite structured compound, most commonly a hybrid organic-inorganic lead or tin halide-based material, as the light-harvesting active layer. There has been a lot of research going on because of its high efficiency – even higher than silicon in some cases.

At the molecular level, perovskites are crystalline structures. But unlike conventional silicon solar cells, which have rigid structures where atoms are held tightly in place, perovskites are very soft. This allows for greater possible motion at the atomic level without compromises in structural stability. It also allows for much greater efficiency than conventional solar cells. In addition, perovskite structures allow for layered applications, which makes it very flexible.

Lately, perovskite developed by Oxford PV – a start-up set-up by Oxford University – reached a record-breaking efficiency of 29.52% last year. While standard silicon cells have an average conversion rate of just 15-20% and a practical maximum conversion rate of around 26%, perovskite has been independently proven to convert 29.52% of solar energy into electricity.

Perovskite was found viable for PV 10-12 years ago, said Don Scott, business development director at Power Roll, a UK-based flexible solar film developer. Since then, the amount of research and average efficiency has gone up dramatically – from 1-2% to 16-17% – in the labs, he added.

“Compared to any material in the history of PV, the curve of perovskite has seen the fastest advancement in efficiency in the shortest amount of time,” he said.

India is also promoting research in perovskite projects. Last year, the Department of Science & Technology (DST) published the list of solar and energy storage research projects, which will be carried out jointly with Israeli researchers. One of the projects is novel electron and hole transport materials for perovskite solar cells by the CSIR-Indian Institute of Chemical Technology.

Perovskite has also performed well in the market. According to market research firm Reports and Data, the global perovskite solar cells market size was $450.1 million in 2020 and is expected to reach a value of $3,926 million by 2028, and register a CAGR of 30.8% during the forecast period.

The report highlighted that further research and development and continuous technological advancements might support growth of the global perovskite solar cell market during the forecast period.

Apart from the positive market trends, perovskite offers many benefits when compared to traditional solar technology. It uses a smaller quantity of material to absorb the equivalent amount of light in comparison to crystalline silicon and the materials required for it are cheap and easy to produce. Additionally, they can be semi-transparent/transparent cells, which makes them suitable for aesthetic business application.

In a significant upgrade to conventional solar technology, perovskite reacts to various different wavelengths of light, which lets them convert more of the sunlight into electricity. Researchers are certain that such characteristics will open up many more applications for solar cells.

However, there are some major bottlenecks related to perovskite. One of them is stability. They are highly sensitive to ambient air and moisture and they break down quickly on exposure. To protect them, they have to be put inside an encapsulation film as soon as they come out from the plant.

The use of toxic lead is another concern that scientists are seeking to resolve.

Will OSC be overshadowed by perovskite?

Considering the increased efficiency and market growth of perovskite, some might wonder whether it would overshadow OSC? Scott is not sure of this, but he emphasised that a lot of research is going on to overcome the challenges of perovskite.

“Perovskite has super-high efficiency, but currently, it contains lead, which is unacceptable for many. Furthermore, there are stability issues,” says Leo.

According to Satapathi, “Perovskite has reached a spectacular efficiency in a very short span of time. As the working principles are quite different, they will be developed at their own pace.”

Potential of emerging BIPV technology in India

India receives sunshine for around 250 up to 300 days per year, which puts it in a good position to harness solar energy to meet the rising electricity demand. The country receives approximately 5,000 trillion kWh solar energy annually.

It has pledged itself to fast and large-scale renewable energy capacity addition. Under the nationally determined contributions (NDCs), India aspires to achieve 40% share of installed power generation capacity from non-fossil fuel sources by 2030.

The country wants to increase its solar capacity to 280 GW by 2030-31 from about 39 GW currently, making it over a third of its overall power requirement. India is chasing a renewable capacity target of 175 GW by 2022 and 450 GW by 2030, from about 93 GW currently, as part of its commitment under the Paris Climate Accord.

With an efficiency of above 20%, crystalline Si solar cells rule the market. However, these cells consume a large amount of energy in the manufacturing process – extremely hot furnaces of around 1,500°C are needed to develop high purity silicon. This increases the payback time.

Compared to conventional solar technology, emerging technologies like OSCs and perovskites are less energy-intensive and owing to their thinness and flexibility they can be manufactured by simply printing the layers of the cell onto a backing such as paper and plastic.

“Emerging thin films usually have lower energy payback time [a few months] than silicon solar cells [2-3 years] considering the cost-effective fabrication process,” said Satapathi. “Therefore, India has huge potential in this technology,” he added.

For developing countries that do not have access to electrical grids and the finance to build one, OSC and perovskite are a great alternative. With low upfront investment and certainly low product shipping costs, they can provide electricity in smaller quantities required for mobile charging, home lighting and in textile industries.

Additionally, if PV solutions require very skilled engineers for installation, it is going to be a problem for people living in rural areas and farmers because of the complications and cost involved, said Scott.

According to him, “For a developing country like India, we need to bring the cost way down and bring ease of use way up. If we are able to do that, we can enable new markets and new applications of emerging thin solar films right at the grassroot level.”

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