Curious Kids: how do solar panels work?



Installing solar panels on a roof.
Shutterstock/lalanta71

Andrew Blakers, Australian National University


How do solar panels work? – Nathan, age 5, Melbourne, Australia.



The Sun produces a lot of energy called solar energy. Australia gets 20,000 times more energy from the Sun each day than we do from oil, gas and coal. This solar energy will continue for as long as the Sun lives, which is another 5 billion years.

Solar panels are made of solar cells, which is the part that turns the solar energy in sunlight into electricity.

Solar cells make electricity directly from sunlight. It is the most trusted energy technology ever made, which is why it is used on satellites in space and in remote places on Earth where it is hard to fix problems.




Read more:
Curious Kids: how does electricity work?


How do solar cells work?

Solar cells are made using silicon atoms. An atom is basically a building block – just like a Lego brick but so tiny you’d need a special machine to see them.

Because the silicon atoms are so small you need trillions and trillions of them for a solar cell.

To make the solar cell you need a wafer layer of silicon, about the same size as a dinner plate but much much thinner – only about three times the thickness of a strand of your hair.

This silicon layer is changed in a special way using hot temperatures of up to 1,000℃. Then, a sheet of metal is put onto the back of the layer and a metal mesh with holes in it, like a net, is put on the front. It is this mesh side of the layer that will face the Sun.

When 60 solar cells are made they are fixed together behind a layer of glass to make a solar panel.

On this roof you can see one solar hot water collector (top left) and 42 solar electricity panels, each of which is made of 60 solar cells combined behind a protective glass.
Shutterstock

If your house has a solar power system, it will probably have 10 to 50 solar panels attached to your roof. Millions of solar panels are used to make a large solar farm out in the countryside.

Each silicon atom contains extremely tiny and lightweight things called electrons. These electrons each carry a small electric charge.

Each tiny silicon atom has a nucleus at the centre made up of 14 teeny-tiny protons and 14 teeny-tiny neutrons. And 14 teeny-tiny electrons go around the nucleus. It doesn’t really look exactly like this diagram but you get the idea.
Shutterstock

When sunlight falls on a solar panel it can hit one of the electrons in a silicon atom and knock it free.

These electrons can move around but because of the special way the cell is made they can only go one way, up towards the side that faces the Sun. They can’t go the other way.

So whenever the Sun is shining on the solar cell it causes many electrons to flow upwards but not downwards, and this creates the electric current needed to power things in our homes such as lights, the television and other electrical items.

If the sunlight is bright, then lots of electrons get hit and so lots of electric current can flow. If it is cloudy, then fewer electrons get hit and the current will be cut by three quarters or more.

At night, the solar panel produces no electric power and we need to rely on batteries or other sources of electricity to keep the lights on.

How are solar cells being used?

Solar cells are the cheapest way to make electricity – cheaper than new coal or nuclear power stations. This is why solar cells are being installed around the world about five times faster than coal power stations and 20 times faster than nuclear power stations.

In Australia, nearly all new power stations are either solar power stations or wind farms. Solar and wind electricity can be used to run electric cars in place of polluting petrol cars. Solar and wind electricity can also heat and cool your house and can be used in industry in place of coal and natural gas.

Windmills and solar panels can produce electricity.
Shutterstock

Solar and wind are helping lessen the amount of greenhouse gases which damage our Earth. They are cheap, and they continue to get even cheaper and the more we use it the quicker we can stop using energy that can hurt the Earth (like coal, oil and gas).

What’s more, silicon is the second most common atom in the world (after oxygen). In fact, sand and rocks are made of mostly silicon and oxygen. So, we could never run out of silicon to make more solar cells.




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Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.auThe Conversation

Andrew Blakers, Professor of Engineering, Australian National University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

We can make roof tiles with built-in solar cells – now the challenge is to make them cheaper



This, except printed directly onto your roof tiles.
Cole Eaton Photography/Shutterstock

Md Abdul Alim, Western Sydney University; Ataur Rahman, Western Sydney University, and Zhong Tao, Western Sydney University

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.

The solar roof tile.

Australia’s greenhouse emissions continue to rise, making it harder to meet its commitments under the Paris agreement.

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.

Here in Australia, buildings account for only about 20% of energy consumption, meaning that the overall emissions reductions on offer from improved efficiency are smaller.

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.




Read more:
New solar cells offer you the chance to print out solar panels and stick them on your roof


Taking Australia’s temperature

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.




Read more:
Are solar panels a middle-class purchase? This survey says yes


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.

Challenges ahead

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.




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There’s a looming waste crisis from Australia’s solar energy boom


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.


The lead author thanks Professor Bijan Samali for valued supervision of his research.The Conversation

Md Abdul Alim, Postdoctoral researcher on sustainable development (Energy and Water), Western Sydney University; Ataur Rahman, Associate Professor, Western Sydney University, and Zhong Tao, Professor, Western Sydney University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

There’s a looming waste crisis from Australia’s solar energy boom



Rooftop solar has boomed, but soalr panels only last about 20 years. What happens to the waste?
Flickr, CC BY-SA

Rodney Stewart, Griffith University; Hengky Salim, Griffith University, and Oz Sahin, Griffith University

As Australians seek to control rising energy costs and tackle the damaging impacts of climate change, rooftop solar has boomed.

To manage the variability of rooftop solar – broadly, the “no power at night” problem – we will also see a rapid increase in battery storage.

The question is: what will happen to these panels and batteries once they reach the end of their life?

If not addressed, ageing solar panels and batteries will create a mountain of hazardous waste for Australia over the coming decades.

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).

Mass of end of life solar panels (a) and battery energy storage (b) 2020-2050.
Salim et al. 2019

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.

Product stewardship

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.

Moving towards a circular economy

Federal and state environment ministers recently agreed to update the National Waste Policy to incorporate the principles of a circular economy.

This approach aims to reduce the need for virgin raw materials, extend product life, maintain material quality at the highest level, prioritise reuse, and use renewable energy throughout the process.




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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.

Immature domestic recycling capability

Now that China is no longer accepting waste for recycling, Australia needs to rapidly develop its domestic recycling industry. This will also spur job creation and contribute to the green economy.

Given Australia is struggling to recycle simple waste, such as cardboard and plastics, in a cost-effective way, we need to question our capability to deal with more complex solar PV and battery waste.

Australia currently has little capacity to recycle both 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.

A previous study suggests half of Australia’s scrap metal is exported for overseas processing, which indicates the lack of incentives for domestic recycling.

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.The Conversation

Rodney Stewart, Professor, Griffith School of Engineering, Griffith University; Hengky Salim, PhD Candidate, Griffith University, and Oz Sahin, Senior Research Fellow, Griffith University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

New solar cells offer you the chance to print out solar panels and stick them on your roof


File 20180829 195313 1i0zj6w.jpg?ixlib=rb 1.1
This roof in Newcastle has become the first in Australia to be covered with specially printed solar cells.
University of Newcastle, Author provided

Paul Dastoor, University of Newcastle

Australia’s first commercial installation of printed solar cells, made using specialised semiconducting inks and printed using a conventional reel-to-reel printer, has been installed on a factory roof in Newcastle.

The 200 square metre array was installed in just one day by a team of five people. No other energy solution is as lightweight, as quick to manufacture, or as easy to install on this scale.




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Our research team manufactured the solar modules using standard printing techniques; in fact, the machine that we use typically makes wine labels. Each solar cell consists of several individual layers printed on top of each other, which are then connected in series to form a bank of cells. These cells are then connected in parallel to form a solar module.

Since 1996, we have progressed from making tiny, millimetre-sized solar cells to the first commercial installation. In the latest installation each module is ten metres long and sandwiched between two layers of recyclable plastic.

At the core of the technology are the specialised semiconducting polymer-based inks that we have developed. This group of materials has fundamentally altered our ability to build electronic devices; replacing hard, rigid, glass-like materials such as silicon with flexible inks and paints that can be printed or coated over vast areas at extremely low cost.

As a result, these modules cost less than A$10 per square metre when manufactured at scale. This means it would take only 2-3 years to become cost-competitive with other technologies, even at efficiencies of only 2-3%.

These printed solar modules could conceivably be installed onto any roof or structure using simple adhesive tape and connected to wires using simple press-studs. The new installation at Newcastle is an important milestone on the path towards commercialisation of the technology – we will spend the next six months testing its performance and durability before removing and recycling the materials.

The solar cells can be installed with little more than sticky tape.
University of Newcastle, Author provided

We think this technology has enormous potential. Obviously our technology is still at the trial stage, but our vision is a world in which every building in every city in every country has printed solar cells generating low-cost sustainable energy for everyone. This latest installation has brought the goal of solar roofs, walls and windows a step closer.




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Ultimately, we imagine that these solar cells could even benefit those people who don’t own or have access to roof space. People who live in apartment complexes, for example, could potentially sign up to a plan that lets them pay to access the power generated by cells installed by the building’s owner or body corporate, and need never necessarily “own” the infrastructure outright.

But in a fractured and uncertain energy policy landscape, this new technology is a clear illustration of the value of taking power into one’s own hands.The Conversation

Paul Dastoor, Professor, School of Mathematical and Physical Sciences, University of Newcastle

This article was originally published on The Conversation. Read the original article.

Policy overload: why the ACCC says household solar subsidies should be abolished


Lucy Percival, Grattan Institute

The keenly awaited report on retail electricity prices, released this week by the Australian Competition and Consumer Commission (ACCC), has made some controversial recommendations – not least the call to wind up the scheme that offers incentives for household solar nearly ten years early.

The report recommends that the small-scale renewable energy scheme (SRES) should be abolished by 2021. It also calls on state governments to fund solar feed-in tariffs through their budgets, rather than through consumers’ energy bills.




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The ACCC has concluded that offering subsidies for household solar was a well-intentioned but ultimately misguided policy. Solar schemes were too generous, unfairly disadvantaged lower-income households, and failed to adjust to the changing economics of household solar.

The lesson for policy-makers is that good policy must keep costs down as Australia navigates the transition to a low-emissions economy in the future. Failure to do this risks losing the support of consumers and voters.

Runaway rebates

Rooftop solar schemes were much more popular than anticipated. This might sound like the sign of a good policy. But in reality it was more like designing a car with an accelerator but no brakes.

Generous feed-in tariffs and falling small-scale solar installation costs encouraged more households to install solar than were initially expected. Premium feed-in tariffs were well above what generators were paid for their electricity production. Historically solar feed-in tariffs paid households were between 16c and 60c per kilowatt-hour, while wholesale prices were less than 5c per kWh.

At the same time, installation costs for solar panels fell from around A$18,000 for a 1.5kW system in 2007, to around A$5,000 for a 3kW system today. The SRES subsidy for solar installations was not linked to the actual installation cost or the cost above the break-even price. So the SRES became relatively more generous as installation costs fell.

As solar penetration increased, and network costs rose to cover this, it became increasingly attractive for households to install solar panels. In Queensland, the initial cost forecast for the solar bonus scheme was A$15 million. Actual payments were more than 20 times that in 2014-15, at A$319 million. And the environmental benefits weren’t big enough to justify that cost, as other policies have reduced emissions at a lower cost. The large-scale renewable energy target reduced emissions for A$32 per tonne, while household solar panels reduced emissions at a cost of more than A$175 per tonne.

In most states, premium feed-in tariffs and rooftop solar subsidies are funded through higher bills for all consumers. Everyone pays the costs, yet only those with panels receive the benefits. That means the costs fall disproportionately on lower-income households and those who rent rather than own their home.

The ACCC report recommends the SRES be wound up nearly 10 years ahead of schedule, because the subsidies are no longer financially justifiable. This would maintain the support for current solar installations but remove subsidies for new solar installations from 2021.

The report also recommends removing the direct costs of feed-in tariffs from electricity bills. Instead, state governments should directly cover the costs of premium feed-in tariffs. The Queensland government has already made this move.

Of course, governments still have to find the money from elsewhere in their revenues, which means taxpayers are still footing the bill. But the new arrangement would at least remove the current unfair burden on households without solar.

Fixing the mistakes

How can governments avoid making similar policy mistakes in the future? The ACCC’s recommendations, together with the proposed National Energy Guarantee (NEG), provide a solid foundation for Australia’s future energy policy.

First, the future is hard to predict, so good policy adapts to change. The NEG provides a flexible framework to direct energy policy towards a low-emission, high-reliability, low-cost future. Reviewing and adjusting the emissions target along the way will enable Australia’s energy policy to respond to new technologies and shifting cost structures, while maintaining consistency with economy-wide targets.

Second, it is hard to pick winners, so good policy creates clear market signals. The NEG provides the energy industry with clear expectations, but is technology-agnostic and minimises government intervention. This encourages the market to find the most cost-effective way to reduce emissions and ensure reliability.




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The ACCC report also recommends simplifying retail electricity offers, which would make it easier for consumers to find a good deal, and in turn making the market more competitive.

The ConversationPoliticians have an opportunity to draw a line in the sand on narrow, technology-specific policies such the SRES. An integrated energy and climate policy should focus on good design, and then step back and let the market pick the winners.

Lucy Percival, Associate, Grattan Institute

This article was originally published on The Conversation. Read the original article.

Are solar panels a middle-class purchase? This survey says yes


File 20180606 137288 19a5k4i.jpg?ixlib=rb 1.1
The latest research suggests that in Australia, rooftop solar photovoltaics are more likely to be adopted by middle-class households.
Author provided

Adam McHugh, Murdoch University

The rate of growth in residential rooftop solar photovoltaics (PV) in Australia since 2008 has been nothing short of breathtaking.

Our new research suggests that the households most likely to join in the solar spree are those that are affluent enough to afford the upfront investment, but not so wealthy that they don’t worry about their future power bills.

Australia now has the highest penetration of residential rooftop PV of any country in the world, with the technology having been installed on one in five freestanding or semi-detached homes. In the market-leading states of Queensland and South Australia this ratio is about one in three, and Western Australia is not far behind, with one in four having PV.

The explosion in rooftop PV uptake since 2008.
Derived from Clean Energy Regulator data. Click image to enlarge.

While PV panels give households more control over their electricity bills, and each new installation helps reduce greenhouse gas emissions, the market’s rapid expansion has posed significant challenges for the management of the electricity system as a whole.




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Unlike other industries where goods can be warehoused or stockpiled to manage fluctuations in supply and demand, electricity is not yet readily storable. Storage options such as batteries are now commercially available, but haven’t yet reached widespread use. This means that a system operator is required to keep the grid balanced in real time, ideally with just the right amount of capacity and backup to manage shocks in supply or demand.

Securing the right amount of generation capacity for the electricity grid relies on long-term planning, informed by accurate supply and demand forecasts. Too much investment means excessive prices or assets lying idle (or both). Too little means longer, deeper or more frequent blackouts.

But as solar panels spread rapidly through the suburbs, the job of forecasting supply and demand is getting much harder.

This is because the commercial history of residential rooftop PV has been too short, and the pace of change too fast, for a clear uptake trend to be established. Previous attempts to predict the market’s continuing growth have thus entailed a lot of guesswork.

Why do people buy solar panels?

One way to improve our understanding is to talk to consumers directly about their purchasing intentions and decisions. The trick is to find out what prompts householders to take that final step from considering investing in solar panels, to actually buying them.

This was the approach we took with our research, published today in the international journal, Renewable and Sustainable Energy Reviews. We analysed data from a survey of more than 8,000 Queensland households in 2014 and 2015, part of a survey series commissioned by an industry group now known as Energy Queensland.

Comparison of motivational factors between surveyed PV intenders and adopters.
Bondio, Shahnazari & McHugh (2018). Click image to enlarge.

We found that the decision to go solar was driven largely by housholds’ concerns over rising electricity bills and the influence that economic life events have over perceptions of affordability.

But the households that tended to adopt PV were also those that were affluent enough not to be put off by the relatively large upfront cost.

This combination of having access to funds, while at the same time being concerned about future electricity prices, appears to be a broadly middle-class trait.

While the upfront cost of PV can deter lower-income households, this can be overcome by receiving an offer that is too good to refuse, or if concerns about ongoing electricity bills are acute – particularly in the case of retirees.

Electricity price uncertainty is a particular concern for retirees, who typically have a lower income. We found that retirees were more likely than non-retirees to invest in solar panels, all else being equal. Retirees, like many people who invest in solar power, seem to view buying solar panels as being like entering into a long-term contract for electricity supply, in that it provides price certainty over the life of the PV system.

We also found that while the idea of self-sufficiency was important for developing an intention to buy solar panels, this motivation later fell away among households that went ahead and bought them. This could be because householders who buy solar panels, but find themselves still relying significantly on the grid, may conclude that self-sufficiency isn’t achievable after all.

About one-third of those who said they intended to buy solar panels cited environmental concerns as a reason for their interest. Yet this factor did not significantly increase the odds of them going on to adopt the technology. This suggests that when it comes to the crunch, household finances are often the crucial determining factor.




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WA bathes in sunshine but the poorest households lack solar panels – that needs to change


We also found the chances of adopting solar panels were highest for homes with three or four bedrooms. Smaller homes may face practical limitations regarding roof space, whereas homes with five bedrooms or more are likely to be more valuable, suggesting that these householders may sit above a wealth threshold beyond which they are unconcerned about electricity bills.

But perhaps our most important finding is that analysis of household survey data can be useful to forecasters. Knowing who is adopting rooftop PV – and why – should enable better predictions to be made about the technology’s continuing expansion, including the crucial question of when the market might reach its saturation point.


The ConversationThe research paper can be downloaded here for free until August 1, 2018.

Adam McHugh, Honorary Research Associate, Murdoch University

This article was originally published on The Conversation. Read the original article.

Semitransparent solar cells: a window to the future?


File 20180215 124886 1cij0t2.jpg?ixlib=rb 1.1
Looking through semitransparent cells – one day these could be big enough to make windows.
UNSW, Author provided

Matthew Wright, UNSW and Mushfika Baishakhi Upama, UNSW

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.




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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.

Semitransparent solar cells convert some sunlight into electricity, while also allowing some light to pass through.
Author provided

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.

What next?

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.




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Solar power alone won’t solve energy or climate needs


If science can solve these issues, the large-scale deployment of solar-powered windows could help to bolster the amount of electricity being produced by renewable technologies.

The ConversationSo while solar windows are not yet in full view, we are getting close enough to glimpse them.

Matthew Wright, Postdoctoral Researcher in Photovoltaic Engineering, UNSW and Mushfika Baishakhi Upama, PhD student [Photovoltaics & Renewable Energy Engineering], UNSW

This article was originally published on The Conversation. Read the original article.