Textile solar cell research often attracts great public interest. As solar cells are one of the most climate, environmental and cost-friendly way for renewable energy production, they are often expected to bring similar benefits to all applications of energy technology. However, it is not quite that simple. Let us answer a few important questions, so that it is clear what the results of the Sun-Powered Textiles project mean in practice and what they do not.
How do you make these textile solar cells and how do they work?
We laminate commercially available solar cells between two fabrics, hiding the solar cells from view. You can read more about this solution and its benefits in this other article. We will explain the technical solutions in more detail in our research publications that will be published later.
What kind of solar cells do you use and why?
The cells we use are small rigid cells made of monocrystalline silicon and larger flexible cells made of amorphous silicon. The rigid crystalline silicon cells have higher efficiency and are especially suitable for outdoor use. On the other hand, the flexible amorphous silicon cells work better than the crystalline silicon cells in weak light, such as indoors. Being thinner and flexible, they can therefore be installed, for example, on a jacket with a larger surface area without the jacket being uncomfortable to wear.
Can your textile solar cells withstand washing?
Yes, they can. Our research is still on, but the preliminary results are good. The cells are laminated between two fabrics with a waterproof thermoplastic plastic film on both sides. This prevents water from penetrating into the cell. In addition, the fabrics protect the cells from mechanical stress in the washing machine. In the tests, the small rigid cells endured 50 washes in a washing machine with a 40 °C program. The results with flexible cells are also promising.
Can you charge a smartphone with a solar cell jacket like this?
In principle, yes, but not in practice. Smartphones consume so much energy in conventional use that producing it with solar cells integrated in a jacket makes virtually no sense. It would take a larger area of cells to fully charge your phone's battery over one day than you could comfortably fit in a jacket.
What, then, can these textile solar cells be used for?
For example, they could be used to charge electronic sensors embedded in clothes. Sensors that measure the state of the environment (e.g. temperature, humidity, altitude) or the user (e.g. steps counter) are increasingly being integrated into wearable electronics. The energy consumption of such sensors is so low that even a relatively small solar cell is enough to generate all the power they need, even indoors. Thanks to the solar cell, such a sensor could thus be energy self-sufficient, i.e., it would never have to be charged externally.
What good would the energy self-sufficiency of such sensors do?
Consumer products may be easier to use when the device works without having to worry about charging it. In professional use, a sensor connected to clothing that works without the need for charging can improve occupational safety. In textiles, the operating costs of an energy self-sufficient sensor may be significantly lower than for a sensor whose batteries need to be replaced regularly. This is concerning wireless sensors; in particular, ones that are used in situations when it is not possible or profitable to connect the sensor to the mains using wires.
What would be an example of such an application?
The purpose of our research was not to develop the actual smart textile products, but to examine whether our idea for energy production works, how the fabric covering solar cells should be designed so that the cells hidden under them work well enough, and how the cells should be connected to the fabric so that they can withstand machine washing. The aim is to demonstrate the functionality, durability, and suitability of the solar cell-textile component for industrial manufacturing. The aim is that based on our results, you can develop any products and services that combine textiles with energy-self-sufficient electronics.
Do the solar cells connected to a jacket affect how comfortable the jacket is to wear?
By physically examining and bending the fabric, the presence of solar cells is noticeable, but the cells are located at points where they do not impede the natural movement of the back to ensure an ergonomic fit. In addition, the sensor to which the solar cell provides power, as well as all conductors, are laminated inside the fabric. No wires come out because there is no need for it: you never need to externally charge the sensor when there is a solar cell inside.
Will solar cells connected to textiles reduce greenhouse emissions or the other environmental impacts of energy production?
No. From the point of view of reducing greenhouse gas emissions, it would be best to charge wearable electronics with mains power produced with renewable energy, such as solar power. In simple terms, a solar cell installed in the jacket always causes greater environmental damage than if the same solar cell were permanently installed outdoors, where it can be directed and tilted at an optimal angle for solar energy collection. When installed in a jacket the solar cell produces significantly less energy during its life cycle than the one installed outdoors, which increases all its environmental impacts per amount of energy produced. This is because the environmental impact of solar cells arises almost exclusively from their manufacture and not from use. In other words, the environmental impact of solar cells is directly related to how much light they see, and convert to electricity, during their whole life cycle, which in turn depends greatly on where and how they are used.
The aim of our research was not to reduce greenhouse gas emissions from energy production, but to enable energy-self-sufficient textile electronics.
Well, will the solar cells connected to textiles then reduce the environmental impact of textiles?
No. From the textile product's point of view, adding more materials to it increases its environmental impact. This also applies to adding electronics and solar cells to textiles. However, it is essential to remember that textile electronics bring new useful features to the textile product. Environmental impacts should therefore be compared with an alternative way of producing the same feature or function. In addition, the designer of a textile electronics product should consider whether the added feature is useful enough to justify accepting the environmental damage it brings. This consideration must always be carried out on a case-by-case basis.
What other ways would be to implement the same function, i.e. to make textile electronics energy self-sufficient?
The energy needed for wearable electronics could be produced instead of solar cells, for example by a piezoelectric, electromagnetic, or triboelectric generator, or by a thermoelectric generator from the heat produced by the user. Even sweat salts can be used to charge a battery. The weakness of all these technologies is that they produce significantly less energy than solar cells in the conditions and ways in which textile products are normally used, so that a larger device is needed to produce the same amount of energy. Making a larger device consumes more materials and energy, increasing the environmental impact. The weakness of solar cells, on the other hand, is that they do not produce energy in the dark. On the other hand, only a small part of all textile products are used in the dark. It may still be that there are some specific cases where one of these alternative technologies would be a more environmentally friendly way of implementing energy-self-sufficient textile electronics than solar cells. Again, this would need to be studied on a case-by-case basis.
Did you take recycling or other sustainable development principles into account?
Yes. We considered it important that the solar cell textiles are easy to recycle. Therefore, the textiles we designed consist of a single material, instead of using mixed materials. In addition, it is possible that solar cells laminated in fabrics can be disassembled by heating and mechanical removal, which is tremendously easier than if the solar cells had been knitted or woven deep into the fabric. In the best-case scenario, solar cells removed from the fabrics during recycling could be available to be used in manufacturing new products. However, further research would be needed to confirm this.