Michelle Grattan, University of CanberraAnthony Albanese will promise a Labor government would deliver a discount to cut the cost of electric cars and install community batteries, in modest initiatives costing $400 million over several years.
The announcement, to be made Wednesday, comes as Labor debates its platform at a “virtual” national conference involving some 400 participants.
At present only 0.7% of cars sold in Australia are electric – considerably under the global average of 4.2%. There are only about 20,000 electric cars registered in Australia.
Labor’s policy would cut taxes on non-luxury vehicles – the luxury threshold is $77,565 in 2020-21 – exempting them from tariffs and fringe benefits tax.
The Electric Vehicle Council has estimated a $50,000 model would be more than $2000 cheaper if the import tariff was removed. These tariffs are not on all the imported vehicles – there are exclusions where Australia has free trade agreements.
If a $50,000 vehicle was provided through employment, exempting it from the fringe benefits tax would save the employer (or employee, depending on how the FBT was arranged) up to $9000 annually, Labor says.
The opposition at the last election had a policy to promote electric cars, with a target of 50% per cent of new car sales being electric vehicles by 2030.
This came under heavy attack from the government, which cast it as a “war on the weekend”.
The government recently released a discussion paper on electric cars, and flagged it would trial models for the COMCAR fleet which transports politicians.
In a statement on the initiatives, Albanese and energy spokesman Chris Bowen said electric vehicles remain too expensive for most people, although a majority of Australians say they would consider buying one. There are no electric cars available in Australia for less than $40,000.
“By reducing upfront costs, Labor’s electric car discount will encourage uptake, cutting fuel and transport costs for households and reducing emissions at the same time,” Albanese and Bowen said.
The discount would begin on July 1 2022 and cost $200 million over three years.
The community batteries would help households who have solar panels but do not have their own battery storage, which is expensive.
Australia has one in five households with solar, but only one in 60 households has battery storage, which gives the capacity to draw overnight on the solar energy produced during the day.
Labor would spend $200 million over four years to install 400 community batteries across the country. This would assist up to 100,000 households.
Albanese and Bowen said the measure would cut power bills, reduce demands on the grid at peak times and lower emissions.
“Households that can’t install solar (like apartments and renters) can participate by drawing from excess energy stored in community batteries.”
A community battery is about the size of 4WD vehicle and provides about 500kWH of storage that can support up to 250 local households.
The exponential growth in solar PV and associated problems has attracted media and political attention.
In 2018, federal Energy Minister Angus Taylor warned his state counterparts lives were at risk from substandard solar panel installations. An audit of the Clean Energy Regulator by the Australian National Audit Office found there were potentially tens of thousands of badly installed and even unsafe rooftop systems. The regulator had inspected just 1.2% of rooftop installations.
It’s a nationwide problem
State and territory regulators are responsible for electrical safety. Only Victoria mandates an inspection of each installed system.
Components such as DC isolators and inverters, rather than the actual panels, are the cause of most solar-related fires. A DC isolator is a manually operated switch next to a solar panel array that shuts off DC current between the array and the inverter. It was intended as an extra safety mechanism, but the switches have caused more problems than they have solved – particularly when not installed correctly or when poor-quality components are used.
Solar is cheaper in Australia but poorly regulated
A recent report rated Australia as one of the cheapest per kilowatt for solar PV, but it questioned our safety standards. Most solar systems sold in Australia use DC voltages that can pose a serious fire risk.
Unfortunately, Australia has been slow to adopt safer solar regulations. In contrast, the United States has had safety standards preventing the installation of conventional DC solar systems since as early as 2014.
It’s more difficult for lower-voltage, microinverter-based systems (requiring no DC isolator switch) to catch fire, but it’s not impossible.
An amendment to the DC isolator standard (AS/NZS 5033:2014) to improve product datasheets and ensure isolators can withstand the harsh Australian climate took effect on June 28 2019. By then, over 2 million systems had been installed on Australian rooftops.
Added to issues such as flammable cladding, dodgy electrical cable and other “grey imports” (products not sourced from approved manufacturers) in the building industry, we are now playing a game of catch-up.
Poor-quality solar rooftop components have led to an expanding list of product recalls. The latest Australian Competition and Consumer Commission (ACCC) recall list includes installations managed by industry giants such as Origin and AGL.
One notable recall in 2014 reported a risk of “arcing” and “eventual catastrophic failure, resulting in fire”. It listed no fewer than nine traders operating nationally as having used this failed product. The recall noted that the product supplier, Blueline Solar Pty Ltd, was insolvent.
What should consumers do? The ACCC said:
Owners should immediately shut down the PV system following the standard shutdown procedure.
If a consumer suspects they have one of the affected units, they should have an electrician inspect and replace the DC isolators.
Solar systems do not fall under the National Construction Code unless an ancillary structure is being created. Most systems are simply fixed with rails to an existing roof. If the code covered rooftop solar, this would require private certification and a compliance check on any system, as is the case overseas.
Research has shown consumers’ knowledge of solar systems is poor. Many owners have little idea if their system is working properly, or even at all.
And how would a consumer know what kind of DC isolator is on their roof or how to shut down the system in the event of a fire?
Solar panel systems are a growing incident category for firefighters. Yet even among firefighters there is some confusion on procedures to deal with a fire on live solar panels.
Solar panel fires have yet to make it onto a top 10 list of domestic fire causes (statistically, your Christmas tree lights are a greater risk). But the sheer volume of installations and ageing components in uninspected older systems are increasing the risks.
One Aussie inventor has developed a product PVStop — “a spray-on solution to mitigate solar panel risks by reducing DC output to safe levels to offer homeowners and emergency personnel peace of mind”.
The latest update on Clean Energy Regulator inspections completed to June 30 2020 shows a negligible 0.05% decrease in substandard systems. Roughly one in 30 systems (3.1%) have been deemed unsafe and another 17.9% substandard.
Without adequate solar PV industry standards, tools, inspection regimes, procedures or training, dangerous scenarios may increasingly put lives at risk. The high uptake of solar is very good news for reducing household electricity bills and carbon emissions, but safety issues undermine these positives.
The surge in installations, the introduction of batteries, the ageing of panels and components together with more extreme weather events mean solar panel incidents are likely to continue increasing.
Australia prides itself on being a world leader in household solar but until now we have not fully appreciated the safety risks. Fire authorities would do well to update fire safety guides that omit specific information on solar. And system owners should ensure they understand the risks and shut-down procedures.
With the cost of energy generated from wind and solar now less than coal, the share of Australia’s electricity coming from renewables has reached 23%. The federal government projects the share will reach 50% by 2030.
It is at this point that integrating renewables into the energy system becomes more costly.
We can add wind and solar farms at little extra cost when their share is low and other sources – such as coal and gas generators now – can compensate for their variability. At a certain point, however, there comes a need to invest in supporting infrastructure to ensure supply from mostly renewable generation can meet demand.
But by 2030, even with these extra costs, adding new variable renewable generation (solar and wind) to as high as a 90% share of the grid will still be cheaper than non-renewable options, according to new estimates from the CSIRO and Australian Energy Market Operator.
Calculating energy costs
International research, including from the International Renewable Energy Agency, suggests solar and wind power are now the cheapest new sources of electricity in most parts of the world.
Our estimates, made for the third annual “GenCost” report (short for generation cost), confirm this is also now the case in Australia.
We compare the cost of new-build coal, gas, solar photovoltaics (both small and large scale), solar-thermal, wind and a number of speculative options (such as nuclear).
What we’ve been able to more accurately estimate in the new report is the cost of integrating more and more renewable energy into the energy system, as coal and gas generators are retired.
The two key extra integration costs are energy storage and more transmission lines.
For any system dominated by renewables, storing energy is essential.
Storage means renewable energy can be saved when it is overproducing relative to demand – for example, in the middle of the day for solar, or during extended windy conditions. Stored energy can then be used when renewables cannot meet demand – such as overcast days or at night for solar.
Among options being considered for large-scale investment in Australia are batteries and pumped hydro energy storage (using excess renewable power to pump water back up to dams to again drive hydroelectric turbines).
Pumped hydro sites can provide storage for hours or days. There are three schemes in Australia: Talbingo and Shoalhaven in New South Wales, and Wivenhoe near Brisbane.
Battery costs have been falling steadily and tend to be most competitive for storage electricity for less than eight hours. South Australia’s big battery (officially known as the Hornsdale Power Reserve) is the most obvious example.
The other key cost to integrate more renewable energy generation into the electricity grid is building more transmission lines. Right now those lines mostly run from coal and gas power stations near coal mines.
But this not where new large-scale renewable generation will be. Solar farms are best placed inland, where there is less cloud cover, and in the mid to northern regions of Australia. Wind farms are generally better located in elevated areas and in the southern regions. We’ll need to build new transmission links to these “renewable energy zones”.
Transmission links between the states in the National Electricity Market (Queensland, New South Wales, Australian Capital Territory, Victoria, Tasmania and South Australia) will need to be improved so they can better support each other if one or more are experiencing low renewable energy output.
So how much extra will it cost for Australia to have a higher share (up to 90%) of electricity from wind and solar (variable renewable energy)? The following graph summarises our findings based on 2030 cost projections.
The cost of generating energy from wind and solar (shown in light blue) is about A$40 per megawatt-hour (MWh). This is is slightly below current average market prices.
A higher share of renewable energy adds storage costs (in black) and transmission costs (grey and dark blue). These integration costs increase from A$4/MWh to A$20/MWh as the variable renewable energy share increases from 50% to 90%.
At 90% renewable energy, the total cost is A$63/MWh. But that’s still cheaper than the cost of new coal and gas-fired electricity generation, which is in the range of A$70 to A$90/MWh (under ideal assumptions of low fuel pricing and no climate policy risk).
The 2020-21 GenCost report is now in the formal consultation period with stakeholders including industry, government, regulators and academia. The final report is due to be published in March 2021.
Australia is the world’s third largest fossil fuels exporter – a fact that generates intense debate as climate change intensifies. While the economy is heavily reliant on coal and gas export revenues, these fuels create substantial greenhouse gas emissions when burned overseas.
Australia doesn’t currently export renewable energy. But an ambitious new solar project is poised to change that.
The proposed Sun Cable project envisions a ten gigawatt capacity solar farm (with about 22 gigawatt-hours of battery storage) laid out across 15,000 hectares near Tennant Creek, in the Northern Territory. Power generated will supply Darwin and be exported to Singapore via a 3,800km cable slung across the seafloor.
Sun Cable, and similar projects in the pipeline, would tap into the country’s vast renewable energy resources. They promise to provide an alternative to the export business of coal, iron ore and gas.
As experts of east-Asian energy developments, we welcome Sun Cable. It could pioneer a renewable energy export industry for Australia, creating new manufacturing industries and construction jobs. Importantly, it could set our economy on a post-fossil fuel trajectory.
To export renewable energy overseas, a high-voltage (HV) direct current (DC) cable would link the Northern Territory to Singapore. Around the world, some HVDC cables already carry power across long distances. One ultra-high-voltage direct current cable connects central China to eastern seaboard cities such as Shanghai. Shorter HVDC grid interconnectors operate in Europe.
The fact that long distance HVDC cable transmission has already proven feasible is a point working in Sun Cable’s favour.
The A$20 billion-plus proposal’s biggest financial hurdle was covering initial capital costs. In November last year, billionaire Australian investors Mike Cannon-Brookes and Andrew “Twiggy” Forrest provided initial funding to the tune of up to A$50 million. Cannon-Brookes said while Sun Cable seemed like a “completely batshit insane project”, it appeared achievable from an engineering perspective.
The proposal would also bring business to local high-technology companies. Sun Cable has contracted with Sydney firm 5B, to use its “solar array” prefabrication technology to accelerate the building of its solar farm. The firm will pre-assemble solar panels and deliver them to the site in containers, ready for quick assembly.
The Northern Territory government has also shown support, granting Sun Cable “major project” status. This helps clear potential investment and approval barriers.
Similarly, the planned Asian Renewable Energy Hub could have renewable hydrogen generated in Western Australia’s Pilbara region at 15 gigawatts. This would also be exported, and supplied to local industries.
These projects align with the Western Australian government’s ambitious Renewable Hydrogen Strategy. It’s pushing to make clean hydrogen a driver for the state’s export future.
Generating and transmitting power from renewable resources avoids the energy security risks plaguing fossil fuel projects. Renewable projects use manufactured devices such as solar cells, wind turbines and batteries. These all generate energy security (a nation’s access to a sufficient, affordable and consistent energy supply).
Australia controls its own manufacturing activities, and while the sun may not shine brightly every day, its incidence is predictable over time. In contrast, oil, coal and gas supply is limited and heavily subject to geopolitical tensions. Just months ago in the Middle East, attacks on two major Saudi Arabian oil facilities impacted 5% of global oil supply.
Apart from exporting electricity produced on its own solar farm, Sun Cable could profit from letting other projects export electricity to Asia through shared-cost use of its infrastructure.
This would encourage future renewable energy exports, especially to the energy-hungry ASEAN nations (Association of Southeast Asian Nations) – Indonesia, Malaysia, the Philippines, Singapore and Thailand.
However, as with any large scale project, Sun Cable does face challenges.
Other than raising the remaining capital, it must meet interconnection standards and safety requirements to implement the required infrastructure. These will need to be managed as the project evolves.
Also, since the power cable is likely to run along the seabed under Indonesian waters, its installation will call for strategic international negotiations. There has also been speculation from mining interests the connection could present national security risks, as it may be able to send and receive “performance and customer data”. But these concerns cannot be validated currently, as we lack the relevant details.
Fortunately, none of these challenges are insurmountable. And within the decade, Sun Cable could make the export of Australian renewable energy a reality.
In the 1980s, a global race was underway: to find a more efficient way of converting energy from the sun into electricity.
Some 30 years ago, our research team at the University of New South Wales (UNSW) came up with a breakthrough, called the PERC silicon solar cell. The cells have become the most widely deployed electricity generation technology in terms of capacity added globally each year – comfortably exceeding wind, coal, gas, hydro and others.
PERC stands for Passivated Emitter and Rear Cell. By the end of this year, PERC technology will be mitigating about 1% of global greenhouse gas emissions by displacing coal burning. Assuming that its rapid growth continues, it should be reducing greenhouse gas emissions by 5% by the mid-2020s and possibly much more in later years.
The terrible bushfires in Australia this summer, enhanced by the hottest and driest year on record in 2019, underline the need for urgent reductions in greenhouse gas emissions. By far the most effective way is driving coal out of electricity systems through very rapid deployment of solar and wind.
Soon, our Aussie invention will be generating half the world’s solar power. It is a pertinent reminder of Australia’s capacity for finding transformative technical solutions to address climate change. But we need the right government support.
An Aussie invention
Solar cells convert sunlight directly into electricity without moving parts. More efficient solar cells generally produce cheaper electricity because fewer solar cells, glass covers, transport, land and support structures are needed for a given solar power output.
By the early 1980s, the best laboratory cells around the world had reached 17% efficiency. This means that 17% of the sunlight was converted to electricity, and the rest (83%) of the solar energy was lost (as heat).
During the 1980s, our research team at UNSW led by Martin Green and myself created a series of world-record-efficient silicon solar cells. We reported 18% efficiency in 1984, 19% efficiency also in 1984, and the important milestone of 20% efficiency in 1986.
In 1989 our group reported a new solar cell design called “PERC”, with a record efficiency of 22-23%.
This new, more efficient cell was better than the old ones because we eliminated some defects in the silicon crystal surface, which led to lower electronic losses. The PERC design also enabled us to capture the sunlight more effectively.
In the 1990s, further improvements to laboratory PERC cells were made at UNSW, leading to cells in the 24-25% efficiency range. The global silicon solar cell efficiency record remained at UNSW until recently.
There was a 25-year gap between development of the PERC cell and its rapid commercial adoption, which began in 2013. During this time, many people worked to adapt the PERC design to commercial production.
PERC cells are more efficient than previous commercial cells. Strong incentives for more efficient cells have recently arisen due to the continually falling share of cell costs as a proportion of total solar power system costs (including transport, land and mounting systems).
The big benefits of solar
Currently, solar power constitutes more than 40% of net new electricity generation capacity additions, with fossil, nuclear, wind, hydro and other renewables making up the balance.
Solar is growing faster than the other electricity generation technologies. Over time, as fossil-fuelled power stations are retired, solar (and wind) will dominate electricity production, with consequent large reductions in greenhouse gas emissions.
This year, enough PERC solar modules will be sold to generate 60-70 gigawatts of power. According to projections, PERC will reach three quarters of annual solar module sales in the mid-2020s, enough to match the generation capacity additions from all other technologies combined.
About A$50 billion worth of PERC modules have been sold to date. This is expected to reach several hundred billion Australian dollars later this decade.
With supportive policy, such as facilitating more transmission to bring solar and wind power to the cities, Australia could greatly increase the speed at which wind and solar are deployed, yielding rapid and deep cuts at about zero-net cost.
Such policy would entail stronger and sustained government support for renewables deployment, and research and development of new technologies.
Solar energy is vast, ubiquitous and indefinitely sustainable. Simple calculations show that less than 1% of the world’s land area would be required to provide all of the world’s energy from solar power – much of it on building roofs, in deserts and floating on water bodies.
Solar systems use only very common materials (we could never run out), have minimal need for mining (about 1% of that needed for equivalent fossil or nuclear fuels), have minimal security and military risks (we will never go to war over solar access), cannot have significant accidents (unlike nuclear), and have minimal environmental impact over unlimited time scales.
Australia is making major contributions to mitigating climate change both through rapid deployment of wind and solar and technology development such as our PERC cells. But with better government support, much more can be done – quickly and at low cost.
Despite being such a sunkissed country, Australia is still lagging behind in the race to embrace solar power. While solar panels adorn hundreds of thousands of rooftops throughout the nation, we have not yet seen the logical next step: buildings with solar photovoltaic cells as an integral part of their structure.
Our lab is hoping to change that. We have developed solar roof tiles with solar cells integrated on their surface using a specially customised adhesive. We are now testing how they perform in Australia’s harsh temperatures.
Our preliminary test results suggest that our solar roof tiles can generate 19% more electricity than conventional solar panels. This is because the tiles can absorb heat energy more effectively than solar panels, meaning that the tiles’ surface heats up more slowly in sustained sunshine, allowing the solar cells more time to work at lower temperatures.
Globally, commercial and residential buildings account for about 40% of energy consumption. Other countries are therefore looking hard at reducing their greenhouse emissions by making buildings more energy-efficient. The European Union, for example, has pledged to make all large buildings carbon-neutral by 2050. Both Europe and the United States are working on constructing buildings from materials that can harness solar energy.
That’s not to say that we shouldn’t go for it anyway, especially considering the amount of sunshine available. Yet compared with other nations, Australia is very much in its adolescence when it comes to solar-smart construction materials.
In a recent review in the journal Solar Energy, we identified and discussed the issues that are obstructing the adoption of solar power-generating constructions – known as “building-integrated photovoltaics”, or BIPV – here in Australia.
According to the research we reviewed, much of the fear about adopting these technologies comes down to a simple lack of understanding. Among the factors we identified were: misconceptions about the upfront cost and payback time; lack of knowledge about the technology; anxiety about future changes to buildings’ microclimates; and even propaganda against climate change and renewable energy.
Worldwide, BIPV systems account for just 2.5% of the solar photovoltaic market (and virtually zero in Australia). But this is forecast to rise to 13% globally by 2022.
Developing new BIPV technologies such as solar roof tiles and solar façades would not only cut greenhouse emissions but also open up huge potential for business and the economy.
According to a national survey (see the entry for Australia here), Australian homeowners are still much more comfortable with rooftop solar panels than other systems such as ground-mounted ones.
In our opinion it therefore stands to reason that if we want to boost BIPV systems in Australia, our solar roof tiles are the perfect place to start. Our tiles have a range of advantages, such as low maintenance, attractive look, easy replaceability, and no extra load on the roof compared with conventional roof-mounted solar arrays.
Nevertheless, the major challenges for this technology are the current high cost, poor consumer awareness, and lack of industrial-scale manufacturing process. We made our tiles with the help of a 3D printing facility at Western Sydney University, which can be attached to an existing tile manufacturing machine with minor modifications.
The current installation cost of commercial solar tiles could be as high as A$600 per square metre, including the inverter.
What’s more, we have little information on how the roof tiles will perform in long-term use, and no data on whether solar tiles will have an effect on conditions inside the building. It is possible that the tiles could increase the temperature inside, thus increasing the need for air conditioning.
To answer these questions, we are carrying out a full life-cycle cost analysis of our solar tiles, as well as working on ways to bring down the cost. Our target is to reduce the cost to A$250 per square metre or even less, including the inverter. Prices like that would hopefully give Australian homeowners the power to put solar power into the fabric of their home.
Our research, published recently in the Journal of Cleaner Production, looked at the barriers to managing solar panel waste, and how to improve it.
A potentially toxic problem
Solar panels generally last about 20 years. And lead-acid and lithium-ion batteries, which will be the most common battery storage for solar, last between five and 15 years. Many solar panels have already been retired, but battery waste will start to emerge more significantly in 2025. By 2050 the projected amount of waste from retired solar panels in Australia is over 1,500 kilotonnes (kT).
Solar panels and batteries contain valuable materials such as metals, glass, ruthenium, indium, tellurium, lead and lithium.
Recycling this waste will prevent environmental and human health problems, and save valuable resources for future use.
Australia has a Product Stewardship Act, which aims to establish a system of shared responsibility for those who make, sell and use a product to ensure that product does not end up harming the environment or people at the end of its life.
In 2016, solar photovoltaic (PV) systems were added to a priority list to be considered for a scheme design. This includes an assessment of voluntary, co-regulatory and regulatory pathways to manage the waste streams.
Sustainability Victoria (on behalf of the Victorian state government and with the support of states and territories) is leading a national investigation into a system of shared responsibility for end-of-life solar photovoltaic systems in Australia. Our research project has supported the assessment process.
Industries play a crucial role in the success of any product stewardship scheme. As we move into assessing and testing possible schemes, Australia’s PV sector (and other stakeholders) will have critical input.
A preferred product scope and stewardship approach will be presented to environment ministers. Scheme design and implementation activities are tentatively set to start in 2020.
Businesses in Australia currently have little incentive to innovate and improve the recycling rate. By helping implement circular business models such as lease, refurbishment and product-service systems, we can boost recycling, reduce collection costs and prolong tech lifetimes.
Requiring system manufacturers, importers or distributors to source solar panels and batteries designed for the environment makes both economic and environmental sense. By doing so, recyclers will recover more materials and achieve higher recirculation of recovered resources.
Consumers need to be provided with proper guidance and education for responsible end-of-life management of solar panels and batteries.
And even if China were to suddenly start accepting Australia’s waste – an unlikely proposition – we cannot simply export our problem. As a signatory to the Basel Convention, exporting hazardous materials requires permits.
Even if we build domestic recycling capability for solar panels and batteries, it will be underused while landfills remain available as a low-cost disposal option.
It’s promising that South Australia and the ACT have banned certain e-waste categories from entering landfill, while Victoria will implement an all-encompassing e-waste landfill ban from July 1 2019. This means any end-of-life electrical or electronic device that requires an electromagnetic current to operate must be recycled.
Creating a circular economy for solar and battery waste will need a strong commitment from policymakers and industry. Ideally, we need to prioritise reuse and refurbishment before recycling.
If we combine sensible policies with proactive business strategy and education to promote recycling rates, we can have a reliable and truly sustainable source of renewable energy in this country.
The authors would like to acknowledge the contribution of Michael Dudley from Sustainability Victoria to this article.
Can you see a window as you are reading this article?
Windows have been ubiquitous in society for centuries, filling our homes and workplaces with natural light. But what if they could also generate electricity? What if your humble window could help charge your phone, or boil your kettle?
With between 5 billion and 7 billion square metres of glass surface in the United States alone, solar windows would offer a great way to harness the Sun’s energy. Our research represents a step toward this goal, by showing how to make solar panels that still let through enough light to function as a window.
The economics of renewable energy are becoming increasingly favourable. In Australia, and many other parts of the world, silicon solar cells already dominate the rooftop market.
Rooftop solar power offers an increasingly cheap and efficient way to generate electricity.
But while great for roofs, these silicon modules are opaque and bulky. To design a solar cell suitable for windows, we have to think outside the box.
When we put a solar panel on a roof, we want it to absorb as much sunlight as possible, so that it can generate the maximum amount of power. For a window, there is inevitably a trade-off between absorbing light to turn into electricity, and transmitting light so we can still see through the window.
When thinking about a cell that could be fitted to a window, one of the key parameters is known as the average visible transmittance (AVT). This is the percentage of visible light (as opposed to other wavelengths, like infrared or ultraviolet) hitting the window that travels through it and emerges on the other side.
Of course we don’t want the solar window to absorb so much light that we can longer see out of it. Nor do we want it to let so much light through that it hardly generates any solar power. So scientists have been trying to find a happy medium between high electrical efficiency and a high AVT.
A matter of voltage
An AVT of 25% is generally considered a benchmark for solar windows. But letting a quarter of the light travel through the solar cell makes it hard to generate a lot of current, which is why the efficiency of semitransparent cells has so far been low.
But note that electrical power depends on two factors: current and voltage. In our recent research, we decided to focus on upping the voltage. We carefully selected new organic absorber materials that have been shown to produce high voltage in non-transparent cells.
When placed in a semitransparent solar cell, the voltage was also high, as it was not significantly lowered by the large amount of transmitted light. And so, although the current was lowered, compared to opaque cells, the higher voltage allowed us to achieve a higher efficiency than previous semitransparent cells.
Having got this far, the key question is: what would windows look like if they were made of our new semitransparent cells?
Do you see what I see?
If your friend is wearing a red shirt, when you view them through a window, their shirt should appear red. That seems obvious, as it will definitely be the case for a glass window.
But because semitransparent solar cells absorb some of the light we see in the visible spectrum, we need to think more carefully about this colour-rendering property. We can measure how well the cell can accurately present an image by calculating what’s called the colour rendering index, or CRI. Our investigation showed that changing the thickness of the absorbing layer can not only affect the electrical power the cell can produce, but also changes its ability to depict colours accurately.
A different prospective approach, which can lead to excellent CRIs, is to replace the organic absorber material with one that absorbs energy from the sun outside the visible range. This means the cell will appear as normal glass to the human eye, as the solar conversion is happening in the infrared range.
However, this places limitations on the efficiency the cells can achieve as it severely limits the amount of power from the sun that can be converted to electricity.
So far we have created our cells only at a small, prototype scale. There are still several hurdles in the way before we can make large, efficient solar windows. In particular, the transparent electrodes used to collect charge from these cells can be brittle and contain rare elements, such as indium.