Such Stuff as Dreams are Made On

It is normal to want to live in harmony with nature and the unrelenting negative news about climate and CO2 and energy speaks to this. Exciting examples of how things are being done create expectations about how the system should change but also create exasperation about how slow progress is. But the use of flagship projects should be managed with care – these are often in the news because they are the exception, not the norm.

 Gravity Sucks

A while ago, there was a widely-shared video of a huge truck carrying quarried rocks – the electric truck was painted green (of course) and to much adulation was reported to “never need charging”.   Factually correct because the specific circumstance is that the quarry is high on a hillside and its destination (a cement factory) is in the valley. The truck uses regenerative braking to charge its 600kw batteries, and the charge is sufficient to get it back up to the quarry. Magic. The nuance is of course that it carries load down and comes back up empty; thus the losses in generating and storing electricity are compensated for by the additional kinetic energy provided by gravity on the way down – the unladen truck weights 45 tons and carries 65 tons of material – so is 110 tons on the way down and 45 on the way back up.

In many ways this is not too different to counter-weight systems like funicular tramways or building elevators – only here instead of a mechanical transfer with friction losses and a “top-up” of input energy, there is an electro-chemical transfer (with associated losses but net gains).  The laws of thermodynamics still hold.

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