Not all energy sources are equally accessible: solar depends on the weather, wind depends on the landscape, and hydropower requires infrastructure. Against this backdrop, researchers are increasingly turning to processes that occur almost everywhere. Water evaporation is such a process. In the Rambler article, read about how scientists learned to generate electricity this way.
Why does it evaporate?
The thermodynamics of evaporation have been known for a long time: when water changes from liquid to vapor, a significant amount of heat is required – about 2250 joules per gram. This is the energy that water takes from the environment as it evaporates, reducing the surface temperature and creating a temperature difference.
Water evaporates continuously – from rivers, lakes, oceans, soil, plants and even from the surface of the skin – and this happens regardless of the time of day, as long as there is movement of heat and air. Unlike solar panels that depend on sunlight or wind turbines that depend on wind, evaporation can occur almost anywhere with a wet and warm surface. This makes it a potentially sustainable but relatively low-intensity source of energy.
How does a steam generator work?
Modern devices that convert evaporation into electricity are based on thermoelectric generators (TEG). They work on a simple principle: the temperature difference between two surfaces creates a voltage.
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An approach described by researchers from the Chinese University of Hong Kong and the National University of Singapore, has been published in the journal Popular mechanics. It assumes the following construction:
- two heat sinks are placed on both sides of the thermoelectric generator;
- one of them is bonded to a porous polyvinyl alcohol (PVA) gel that is continuously wetted;
- Water evaporates from the gel surface, cooling it;
- the other side remains at ambient temperature.
This temperature gradient between the warm side and the cool side provides the energy to generate electricity without moving mechanical parts. At the laboratory testing stage, such a system is only capable of generating microscopic levels of energy, enough, for example, to power small displays or sensors.
However, scientists have seen the prospect of increasing electricity production. The authors estimate that the potential could increase tenfold when materials and design are optimized.
Advantages and limitations of technology
Favorable:
- Evaporation is a process that occurs everywhere, especially in warm and humid areas that are not affected by direct sunlight or wind.
- There are no moving parts as reported in AZoCleantechSimplify equipment and reduce operating costs.
- May not be suitable only for high power tasks but could be useful for micro devices – sensors, wearables, Internet of Things devices.
Limit:
- The current efficiency of such systems is extremely low – about 0.1% of evaporative energy is converted into electricity, and this is comparable to the early stages of development of other renewable technologies.
- The device requires a constant source of water for evaporation, without which the effect will be lost.
- To become a competitive energy source at scale, significant optimization of materials, design and integration with other sources is required.
Where can such technologies be useful?
The most likely initial applications for evaporative generators are in areas requiring a continuous, albeit small, power supply without the need for batteries or wires:
- Wearable electronics – health monitors, medical sensors, watches can be partially powered by their own humidity or the environment.
- Environmental sensors – monitor soil, climate, air quality in remote locations where batteries are difficult to change.
- Low-power IoT devices need to operate for long periods of time without requiring maintenance.
In the future, there may be more ambitious works using evaporation from large bodies of water or industrial facilities to generate energy. But such projects are still conceptual and require years of technical development.
We have previously written about when we will have unlimited energy.
