Are lightweight foldable solar panels possible? One research team is trying to find out

These, only lighter. Image: Getty.

The energy-generating potential of solar panels – and a key limitation on their use – is a result of what they’re made of. Panels made of silicon are declining in price such that in some locations they can provide electricity that costs about the same as power from fossil fuels like coal and natural gas. But silicon solar panels are also bulky, rigid and brittle, so they can’t be used just anywhere.

In many parts of the world that don’t have regular electricity, solar panels could provide reading light after dark and energy to pump drinking water, help power small household or village-based businesses or even serve emergency shelters and refugee encampments. But the mechanical fragility, heaviness and transportation difficulties of silicon solar panels suggest that silicon may not be ideal.

Building on others’ work, my research group is working to develop flexible solar panels, which would be as efficient as a silicon panel, but would be thin, lightweight and bendable. This sort of device, which we call a “solar tarp,” could be spread out to the size of a room and generate electricity from the sun, and it could be balled up to be the size of a grapefruit and stuffed in a backpack as many as 1,000 times without breaking. While there has been some effort to make organic solar cells more flexible simply by making them ultra-thin, real durability requires a molecular structure that makes the solar panels stretchable and tough.

A small piece of a prototype solar tarp. Image: University of California, San Diego/creative commons.

Silicon semiconductors

Silicon is derived from sand, which makes it cheap. And the way its atoms pack in a solid material makes it a good semiconductor, meaning its conductivity can be switched on and off using electric fields or light. Because it’s cheap and useful, silicon is the basis for the microchips and circuit boards in computers, mobile phones and basically all other electronics, transmitting electrical signals from one component to another. Silicon is also the key to most solar panels, because it can convert the energy from light into positive and negative charges. These charges flow to the opposite sides of a solar cell and can be used like a battery.

But its chemical properties also mean it can’t be turned into flexible electronics. Silicon doesn’t absorb light very efficiently. Photons might pass right through a silicon panel that’s too thin, so they have to be fairly thick – around 100 micrometers, about the thickness of a dollar bill – so that none of the light goes to waste.

Next-generation semiconductors

But researchers have found other semiconductors that are much better at absorbing light. One group of materials, called “perovskites,” can be used to make solar cells that are almost as efficient as silicon ones, but with light-absorbing layers that are one-thousandth the thickness needed with silicon. As a result, researchers are working on building perovskite solar cells that can power small unmanned aircraft and other devices where reducing weight is a key factor.

The 2000 Nobel Prize in Chemistry was awarded to the researchers who first found they could make another type of ultra-thin semiconductor, called a semiconducting polymer. This type of material is called an “organic semiconductor” because it is based on carbon, and it is called a “polymer” because it consists of long chains of organic molecules. Organic semiconductors are already used commercially, including in the billion-dollar industry of organic light-emitting diode displays, better known as OLED TVs.

Polymer semiconductors aren’t as efficient at converting sunlight to electricity as perovskites or silicon, but they’re much more flexible and potentially extraordinarily durable. Regular polymers – not the semiconducting ones – are found everywhere in daily life; they are the molecules that make up fabric, plastic and paint. Polymer semiconductors hold the potential to combine the electronic properties of materials like silicon with the physical properties of plastic.


The best of both worlds: efficiency and durability

Depending on their structure, plastics have a wide range of properties – including both flexibility, as with a tarp; and rigidity, like the body panels of some automobiles. Semiconducting polymers have rigid molecular structures, and many are composed of iny crystals. These are key to their electronic properties but tend to make them brittle, which is not a desirable attribute for either flexible or rigid items.

My group’s work has been focused on identifying ways to create materials with both good semiconducting properties and the durability plastics are known for – whether flexible or not. This will be key to my idea of a solar tarp or blanket, but could also lead to roofing materials, outdoor floor tiles or perhaps even the surfaces of roads or parking lots.

The ConversationThis work will be key to harnessing the power of sunlight – because, after all, the sunlight that strikes the Earth in a single hour contains more energy than all of humanity uses in a year.

Darren Lipomi, Professor of Nanoengineering, University of California San Diego

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

 
 
 
 

Covid-19 is highlighting cities' unequal access to green space

In the UK, Londoners are most likely to rely on their local park for green space, and have the best access to parks. (Leon Neal/Getty Images)

As coronavirus lockdowns ease, people are flooding back to parks – but not everyone has easy access to green space in their city.

Statistics from Google show that park attendance in countries across the globe has shot up as people have been allowed to move around their cities again.

This is especially true in urban areas, where densely populated neighbourhoods limit the size of private green space – meaning residents have to go to the park to get in touch with nature. Readers from England can use our interactive tool below to find out how much green space people have access to in their area, and how it compares to the rest of the country.

 

Prime Minister Boris Johnson’s announcement Monday that people are allowed to mingle in parks and gardens with groups of up to six people was partially following what people were doing already.

Data from mobile phones show people have been returning to parks across the UK, and also across Europe, as weather improves and lockdown eases.

People have been returning to parks across the world

Stay-at-home requirements were eased in Italy on 4 May, which led to a flood of people returning to parks.

France eased restrictions on 1 May, and the UK eased up slightly on 13 May, allowing people to sit down in public places so long as they remain socially distanced.

Other countries have seen park attendance rise without major easing of lockdown – including Canada, Spain, and the US (although states there have individual rules and some have eased restrictions).

In some countries, people never really stopped going to parks.

Authorities in the Netherlands and Germany were not as strict as other countries about their citizens visiting local parks during lockdown, while Sweden has famously been avoiding placing many restrictions on people’s daily lives.


There is a growing body of evidence to suggest that access to green space has major benefits for public health.

A recent study by researchers at the University of Exeter found that spending time in the garden is linked to similar benefits for health and wellbeing as living in wealthy areas.

People with access to a private garden also had higher psychological wellbeing, and those with an outdoor space such as a yard were more likely to meet physical activity guidelines than those without access to outdoor space. 

Separate UK research has found that living with a regular view of a green space provides health benefits worth £300 per person per year.

Access is not shared equally, however, which has important implications for equality under lockdown, and the spread of disease.

Statistics from the UK show that one in eight households has no garden, making access to parks more important.

There is a geographic inequality here. Londoners, who have the least access to private gardens, are most likely to rely on their local park for green space, and have the best access to parks. 

However the high population in the capital means that on the whole, green space per person is lower – an issue for people living in densely populated cities everywhere.

There is also an occupational inequality.

Those on low pay – including in what are statistically classed as “semi-skilled” and “unskilled” manual occupations, casual workers and those who are unemployed – are almost three times as likely as those in managerial, administrative, professional occupations to be without a garden, meaning they rely more heavily on their local park.

Britain’s parks and fields are also at significant risk of development, according to new research by the Fields in Trust charity, which shows the number of people living further than a 10-minute walk from a public park rising by 5% over the next five years. That loss of green spaces is likely to impact disadvantaged communities the most, the researchers say.

This is borne out by looking at the parts of the country that have private gardens.

The least deprived areas have the largest gardens

Though the relationship is not crystal clear, it shows at the top end: Those living in the least deprived areas have the largest private green space.

Although the risk of catching coronavirus is lower outdoors, spending time in parks among other people is undoubtedly more risky when it comes to transmitting or catching the virus than spending time in your own outdoor space. 

Access to green space is therefore another example – along with the ability to work from home and death rates – of how the burden of the pandemic has not been equally shouldered by all.

Michael Goodier is a data reporter at New Statesman Media Group, and Josh Rayman is a graphics and data visualisation developer at New Statesman Media Group.