Tuesday, July 27, 2021
HomeNewsRun a hospital on batteries in a power cut? Think again, greens

Run a hospital on batteries in a power cut? Think again, greens

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EIGHTEEN months ago, I was on my way to a meeting of the Global Warming Policy Foundation trustees when, as I approached Cambridge station, a tall man stepped forward and offered me a thin newspaper.

‘Socialist Worker returns to the streets,’ I said.

‘No, I am from Extinction Rebellion,’ he replied.

‘You are the ones that are convinced the energy transition will need to be done by 2025. How will the emergency wards in Addenbrooke’s Hospital be protected?’

‘With batteries, without a doubt.’

That provoked me. I looked up the details of the then largest battery, installed by Elon Musk outside Adelaide in Australia, with a 100MW/138MWh power/energy capability at a cost of A$90million or approximately £45million. I mentally transplanted it to Addenbrooke’s Hospital, and having got the facilities data, established that on a single discharge from 80 per cent capacity to 20 per cent capacity (these being the limits that protect the battery for a long lifetime) the emergency wards of the hospital could continue for 24 hours. The whole hospital could continue for about eight hours.

A present, the hospital protects its power supply for those emergency wards with the use of two diesel generators, with a combined rating of 3MVA, costing £250,000. The ratio of the capital costs to protect the wards is 180:1. No sensible engineer would opt for the more expensive option when the ratio is so high.

The back-up in practice is used to cover hiccups in the electricity supply or the occasional local brown-out. In extremis, one could imagine a severe storm that might take down the electricity transmission lines for a week in the East of England. This presents no problem for the diesel generators, as long as there is fuel available, either on site or capable of delivery. For the battery option the situation is much worse: in the absence of electricity to recharge the battery, six more batteries are needed. The ratio of the capital cost for guaranteeing a week rises to 1300:1.

It is unfortunate that I have not seen the man from Extinction Rebellion again, and indeed I have only just been back to London after an absence of 16 months. I would want to put him right, and seek a better and more practical alternative, and, on the basis of progress on decarbonisation over the last 30 years, to suggest that a five-year target is plain bad prognostication.

There is a lesson for us all: the disparity in costs between diesel generators and battery banks applies not only to hospital back-up, but to all the other applications where batteries are proposed for energy storage.  Not even the City of London could afford batteries to keep themselves going during the prolonged absence of wind and sunshine.

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Michael Kelly
Michael Kelly is Emeritus Prince Philip Professor of Technology, University of Cambridge and trustee of the Global Warming Policy Foundation.>/a>

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