Efficient batteries to bridge the gap between energy supply and demand
The in-depth analysis by Luca Longo
Producing energy from the sun , tides, wind or even agricultural waste is beautiful and very green, but what happens when it is night, there is no tide, the wind does not blow or it is not harvest season?
Another problem: surely, the most useful form of energy we have is electricity: we can use it to move, illuminate, heat, cook and operate all the electrical or electronic devices that surround us. But electricity is not readily available in nature: we have to produce it on purpose from other forms of energy. Furthermore, if when we generate it we do not find a way to use it immediately, we lose it forever.
Since we can't stay in the dark – let alone we can afford to stay ten minutes without updating our social profiles – we need to find a way to have energy just when we need it. For this reason, all the plants for the production of renewable energy that exist today are connected to a storage system or to an electricity grid. When the sun shines or the wind blows, isolated plants collect energy that is not being used at that moment and store it for when it is needed.
The plants connected to the electricity grid, on the other hand, limit themselves to transmitting the excess energy to the grid itself (there will also be someone around somewhere who will need it) and then go and take it from there when it is needed by us.
Those who manage the networks (often as large as countries or continents) do the same thing. Usually the excess electrical energy is stored as hydraulic energy: the current that advances is used to take water from the sea or some low-altitude lake and pump it into a high-altitude lake. However, when energy is needed, the water is brought back down by making it fall along a penstock to a turbine that generates new electricity. If there is a peak in the demand for energy and there is no way to find it within the grid, then it is bought from abroad or, at worst, thermoelectric plants that burn fossil fuels to produce energy are put into operation. electric.
For this reason, being able to accumulate and store electricity serves to improve the efficiency in the use of renewable and fossil resources, to balance the discontinuity of sources with the variability of industrial and civil energy demand and also to improve stability, flexibility. and reliability of distribution grids. Batteries, therefore, are a fundamental tool for accessing energy, but they allow a more intelligent use of resources with a lower environmental impact and therefore a reduction in CO2 emissions.
Batteries can have extremely different sizes, each one is suitable for a certain use. They range from the clock battery to that of phones and notebooks to the accumulators connected to the photovoltaic system of the house up to those used by large infrastructures coupled with power plants.
But the types of battery also vary according to use, the so-called average storage time: from the battery of our smartphone (it must last at least a day or we are lost!), Up to those of large systems, which must compensate for variations in supply and demand of energy between day and night. The older ones have to manage the fluctuations of entire seasons.
If we think about it, the main limitations of all mobile devices, from smartphones to electric cars, are due to the weight, the cost of production (and disposal) and the low capacity of the battery that powers them. The same problem arises for larger systems – from electric cars to large plants – if we delude ourselves to solve the problem simply by building bigger batteries.
For this, new solutions are being sought all over the world. And even in Italy cutting-edge research is being conducted: for example electrolysers – which exploit excess electricity to produce hydrogen from water in an electrolytic cell and then make it work in reverse when you want to regain electricity by consuming stored hydrogen. .
Eni is also developing the flow battery: it is an electrochemical cell connected to two tanks containing two different electrolytes dissolved in solution. In the cell, the electrolytes come into contact through a special semi-permeable barrier where a redox reaction takes place. This transforms the chemical energy stored in the two fluids into electrical energy that can be taken out of the cell and used. Conversely, when we have a renewable source at hand – for example a photovoltaic system on a beautiful sunny day – the electricity produced by the system goes into the electrochemical cell and is used to make the same redox reaction take place, but in reverse. Thus the two fluids can return to store chemical energy ready for use when needed.
Flow battery technology is among the most promising both for the current level of development (industrial installations already exist), but also for its potential (research is constantly evolving). Furthermore, it gives the possibility to easily separate the power component (the cell size) from the energy storage component (the volume of the tanks).
This decoupling allows to eliminate the self-discharge phenomenon (you know when you take a battery that you had recharged some time ago and – even if you have never used it – you find it already at zero?) And offers the possibility of building customized batteries for the desired power and storage needs.
Finally, at the end of their life, flow batteries can be recycled much more simply than other types of batteries: the electrolytes – which make up the majority of the system – can be recovered and purified, and the rest of the system is made up of metal alloys, plastics and commercial electronics; also separable and recoverable.
Until the studies on flow batteries do not lead to industrial plants, the development of renewables will not be able to unfold in all its potential: therefore, full speed ahead with research on batteries.
(Extended version of an article published on eni.com)
This is a machine translation from Italian language of a post published on Start Magazine at the URL https://www.startmag.it/energia/batterie-efficienti-per-colmare-il-gap-fra-offerta-e-domanda-di-energia/ on Sat, 12 Jun 2021 05:39:19 +0000.