#engineering #energy
Of All the energy that we receive from the sun every day barely 1% of it is used by the pants. This energy is captured in the form of edible food as well as biomass. When we talk about biofuels most of the discussion is centered around ethanol. How can we convert the energy stored in edible food to usable fuels. Ethanol works but it suffers from two major disadvantages
1. Ethanol production must compete with food for human consumption. Are we going to eat sugars or turn it into fuel?
2. It captures a very small portion of energy while disregarding all the waste biomass that is available for free.
There have been attempts at extracting energy from waste biomass by converting it into ethanol in what is known as 2g ethanol but the process has been rather complicated and the results have been only average. On the otherhand using biomass for direct combustion has produced better energy conversion but its only been useful for large power plants. Transportation which consumes vast amounts of energy is still reliant on liquid/gaseous fuels that are getting more expensive by the day.
What could be used as a feedstock?
How can we effectively increase agricultural area to sustain our needs?
On our planet vast portion of lands have been deemed uncultivable for food stocks.
Bamboo is a very hardy plant and has the potential to grow in difficult conditions. One solution would be to cultivate bamboo or some other simillar grass on land that is incapable supporting food grains. But any kind of cultivation requires use of water, labour & other inputs like fertilizers and pesticides.
Can we produce on such a large scale so as to replace fossil fuels?
The same problem is faced by algae based fuel options. There are simply not enough resources to produce these products on scale. It seems like Biofuels will remain only a niche industry supplementing fossil fuels but never doing enough to replace them. Likewise Sustainable aviation fuels are biobased but it's unlikely that they'll ever be able to compete with or even complement drilled oil and gas.
The fact remains even though Earth produces trillions of tonnes of biomas it is too diffuse to be converted into useful fuels.
So what should be done?
What is needed is a different approach. Instead of using chemical fuels ,if we could use heat directly as a source of energy then we may be on to something. Recently Finland has showcased it's sand battery that can store 100 Mwh of energy at 600c in 100 tonne sand. This is energy storage at scale.
https://www.downtoearth.org.in/energy/dirt-cheap-backup-why-finland-s-installation-of-the-world-s-1st-sand-battery-may-be-a-game-changer-87804
The solution is so cheap that it can be used not just to power electrical appliances but also mechanical ones like automobiles. As of now the sand battery is using heat exchangers to boil water and turn steam turbines. But it can be used to directly run Stirling engines to produce mechanical output. The total amount of stored energy/energy density could be increased by raising the temperatures at which it operates. Instead of 600c it could easily be 800 or 900.
Furthermore losses are minimum because the sand is stored in an insulated container. That can hold the heat for weeks or months.
One way to charge the battery is through excess electricity generated by renewable or non renewable sources. Other idea could be to heat the sand block with solar concentrator lenses. We get 1kw/m2 of energy from sunlight. In sunny areas a solar concentrator lens can melt rocks in a matter of seconds. They are >90% efficient. Almost if of the i/p energy can be concentrated to a spot. Compare this with coal fired plants that are 40-60% efficient & solar panels that are are barely chugging along at 20.
While storing energy as heat is a much better option than than biofuels its success depends upon whether the associated technologies like lenses and Stirling engines can be produced at scale.
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