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Will tomorrow's solar panels generate electricity from rain?

Posted by Alex Barrett on 24 January 2017 at 10:15 am

There are potential sources of energy all around us. Any natural system contains energy and in theory we can tap into that energy to generate electricity or work. Something that we don’t currently harness is rain. Unfortunately rainfall doesn’t generate a sufficient volume of water to power gutter-mounted hydroelectric systems. Even in the heaviest rain storms there isn’t sufficient flow to generate a useful amount of electricity. However there might be another way to get power from raindrops.


Salty rainwater provides positive ions

Researchers at the Ocean University of China and the Yunnan Normal University are working on a method which can generate current from the small electrical charge in slightly salty rainwater.

All water contains some dissolved salts, even bodies of freshwater, and the rain that feeds them. Salts are made up of ions. These are atoms which have a net positive or negative charge. This is due to an imbalance between the number of positively charged protons in the atom, and the number of negatively charged electrons. An atom with too few electrons will have an overall positive charge, while one with too many will be negative. Salts such as sodium, calcium, and ammonium, which are quite common in rainwater, all contain positive ions. So how do we convert that charge into electricity?

To get electricity we need to make a current flow through a conductive material such as a wire. This requires a voltage, a difference in electrical potential between one point and another. The positive charge of our rainwater ions is very small, but it can be enough to create that potential difference.

Graphene Electrode

The researchers have developed an electron enriched graphene electrode. This is a thin layer of graphene, which has additional electrons to ensure that it has a strong negative charge. When raindrops hit the device the positive ions accumulate on the graphene layer. This creates a new, adjacent, layer with a positive charge. Taken together the two layers form what is called a pseudo-capacitor. The difference in charge between the positively charged ion layer and the negatively charged graphene layer provides our voltage. The proof of concept experiments have shown this potential difference to be in the order to hundreds of microvolts, which is enough to generate an electric current.

All-weather solar cells

This device is intended to augment solar photovoltaic cells. Solar panels are great during sunny periods. But tend to be less productive on cloudy and rainy days. By manufacturing solar panels with this graphene layer we can get energy come rain or shine. During sunny periods the panel will function normally, to generate electricity through the photovoltaic effect. When rain falls it will interact with the graphene coating. This may not produce as much power as on a sunny day, but it is better than nothing.

This technology is still in the development phase. So don’t expect to be able to get one any time soon. But research is ongoing to make this a viable power generation tool.  The researchers state that “All-weather solar cells are promising in solving the energy crisis”. It will take a lot more work before the efficiency of the system can match that of current photovoltaics, but this is definitely a step in the right direction.

References

  1. Science Alert
  2. Tech Times
  3. Digital Trends
  4. The original study at the journal Angewandte Chemie

Image credit Paul Wilkinson via flickr

 

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