Letters / Waste of energy
Reading the latest articles in the Shetland News regarding SSE and SHEAP’s approach to energy generation and utilization on Shetland (www.shetnews.co.uk/news/9559-views-sought-on-local-energy-costs) gave me a distinct feeling of deja vu.
It also gave me a distinct feeling that no-one from either organisation seems to be willing to take note of the need for a major (but actually very small) change in the way that electrical energy is generated up here, with a view to using expensive fossil resources much more efficiently.
The problem as I see it is that energy is being wasted wholesale down at Gremista power station, and for no reason that I can understand, good or bad.
The waste that I’m referring to here is the dumping of the ‘waste’ heat by-product of the electricity-generating process, which currently is thrown straight out into the environment without any apparent effort being made to utilise it more efficiently.
The way I see things is as follows:
- for every megawatt hour of electricity generated at Gremista, between two and three megawatt hours of waste heat are discarded;
- this otherwise wasted heat could very easily be supplied to the SHEAP building, which is situated right next door to Gremista;
- this quantity of waste heat, if harvested efficiently and utilised fully, could (by rough calculation) supply enough free energy to the District Heating System as it stands to run the whole setup several times over FOR FREE. (My rough calculations suggest 47 times over.)
When Gremista Power Station was built in 1953, its probable initial overall efficiency would have been in the region of 33 per cent. Six decades of wear and tear resulting from hard use suggest that its present level of efficiency has probably fallen to about 25 per cent.
This means that, for every three barrels of diesel oil (‘heavy fuel’) consumed by that power station in 1953, one barrel’s worth of the heat energy developed in the generators ended up as electricity at the power station’s output terminals. The other two barrels-worth of the heat developed ended up in the air, or in Lerwick Bay via submerged heat exchangers.
Fast-forwarding to 2014, 61 years on from Gremista’s inauguration, the probable reduction in overall efficiency to 25 per cent (due to wear and tear) means that only one barrel of diesel fuel out of four now ends up as generated electricity. The waste heat energy from burning the other three barrels of diesel go towards the unnecessary job of heating up the surrounding environment.
If Gremista’s output were as high as 60 MW, which on many days in winter it probably will be, the amount of discarded waste heat from the generating process would amount to between 120 and 180 MW – every hour that Gremista’s rate of electrical output remains at 60 MW.
Considering that the generation of one megawatt hour of electricity now gives rise to the dumping of three megawatt hours of waste heat, the creation of a heat exchange link between Gremista power station and the SHEAP building that’s located barely 100 metres away from it (to take advantage of this ‘free’ heat) might be quite a good idea.
If such a link were to be created, instead of SHEAP having to rely on the combustion of burnable rubbish out at Greenhead, or the burning of ‘heavy oil’ on low-refuse days just to keep the District Heating System going, SHEAP could harvest part or all of the estimated 120 to 180 mega watts an HOUR of waste heat that Gremista discards, and then be able to provide the DHS as a completely free service to the good people of Lerwick.
Philip Andrews
Unst
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