RE: Vanadium and wind energy23 Jan 2020 14:46
Ophidian, as usual you are 100% correct - energy is measured in Joules and in a VRFB it is stored as chemical energy.
The problem is that many in the media do not use the term energy precisely - power and energy are often conflated or confused but even if you get that right you have to be careful about confusing electrical energy with heat energy. Whilst both are measured in Joules they are different forms of energy and electrical energy is better than heat energy not through any subjective personal opinion but because electrical energy is more ordered than heat energy.
It is a bit of a quick recap over 200 years or so of thermodynamics but the difference is measured by a concept called entropy - ordered systems have low entropy (perfectly ordered is entropy zero) whilst disordered systems have high entropy. A fully closed system will always show an overall increase in entropy, i.e. become more disordered, as time passes. Thus the chemicals in your body shuffle the atoms amongst themselves so as to increases your overall entropy, time passes and heat is generated.
Why all this discussion about heat and electricity ? Because to generate highly ordered electrical energy from lowly ordered heat you are restricted by the laws of thermodynamics and you have to build a heat engine with hot input at temp Th and a cold reservoir at Tc - at the end thermodynamics shows you cannot do any better than the Carnot efficiency which is (Th-Tc)/Th [all temperatures expressed as absolute temperatures in Kelvin (not degrees Kelvin, you at the back again ! don't get me started !]
So imagine a power station that boils water to make steam at 100 deg C (373 Kelvin) - you run this through a turbine to where you cool it back down to, say 20 deg C (293 K) - this gives an efficiency of (373-293)/373 = 21.5% pretty bad. You can get the steam to operate at a higher temperature if you run it under higher pressures but even then efficiencies of 40% are about as good as you can get from such a process.
Why all this talk about power stations and efficiency ? Because the media regularly talk about the difficulty of replacing X MWh of oil/gas/coal with renewables - the thing is renewables such as wind or PV give you electricity directly, whilst fossil fuels can only give you heat. Thus to displace X MWh of thermal PRIMARY ENERGY you only need X times 0.4 PV or wind ENERGY.
The distinction between primary (heat) energy and electrical energy is almost always missed in the media but it is crucial.
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