Hi-i Trout, to answer your question about the cons of an undersea power cable from Shetland to the mainland:
According to my 'source' employed in Scottish Power Glasgow's National Policy dept, the price of physically laying the cable, although astronomical, isn't the real reason why this isn't cost-effective for the National Grid.
It's all about how the Electricity network as a whole works in the UK. In essence, you have 3 steps:
the Electricity generator companies produce electricity and sell it to the National Grid;
the Electricty Businesses (Hydro, etc) buy it from the National Grid;
then the consumer buys it from the Hydro etc.
It's a lot like the city traders in the stock exchange, they bid, buy and sell like crazy to and from the grid desperate for the best possible price.
The relevant factor for Electricity is the dramatic fluctuations in demand. When it's getting dark, everyone in the area puts on their lights. At roughly mealtimes, demand increases hugely as cookers, microwaves & kettles turn on. In the UK the most densely-populated area is the south-east quarter of England. So at any time of the day, and particularly peak times, their usage will be disproprotionately higher than elsewhere.
Now back to the 3 steps. Electricity is produced, it is stored on the National Grid, then it is released on demand.
Most demand is in the south-east, but we are as far north as you can get. The problem is it's very expensive to transport Electricity. Power lines are transformed to high voltage/ low wattage to reduce heat-loss but is still really inefficient. This means that most Electricity companies will prefer to buy electricity from generators as near to their customers as possible, to maximize their profits. There are already generators in the rural highlands of Scotland who really struggle to compete with those further south because those several hundred miles of transportation can make a big difference when you're looking at millions of customers.
If we were producing electricity to join the Grid and we were in Aviemore we'd have a hard enough time being profitable but when you add on the burden of recouping the expense of a massive 200 mile undersea cable it is not financially viable until the Electricity watchdogs set new regulations to favour the more remote renewable energy producers. Hope this helps, and correct me if I'm wrong if anybody knows anything more to add. Ta.
If your source really works for Scottish Power then he/she should be very worried about competence assessments. The 3 steps are a fair description but you went somewhat astray 2 paragraphs later. The south of England is the major demand centre in the UK but it is not disproportionate. At peak time the energy use across the UK does increase but while a percentage increase across 2 different volumes gives different measured rises, the rises are exactly proportionate.
Then the most obvious mistake. Electricity is not stored on the National Grid. It is transmitted across the National Grid. Power for the UK electricity system is generated on demand. Normally the system operator knows roughly what they will need and so can have enough generators running to meet demand. Short-term fluctuations in demand are handled by increasing or decreasing the output of particular individual generators. Think of a car throttle with the increasing/decreasing demand acting as a foot controlling the engines to different outputs.
While most demand is in the south east of England it is not like there is only a couple of 40 watt lightbulbs in Scotland. Scotland is currently a net exporter of power, which means it exports power more often than it imports power. This is changing rapidly and with the imminent closure of only 1 or 2 of several ageing power station, Scotland will soon be a net importer (estimate 2010). Further, the electricity market is deregulated and there is no connection between who you buy your electricity from (be you consumer or supplier) and who generates it. The system operator makes sure that everyone gets what they need and that someone pays for everything that is consumed. So suppliers have no reason or incentive to buy power locally. It would probably harm their profits to do so as they would be reducing their options. Generators in north Scotland are not automatically competing with generators in England. Suppliers might be but since the two are unrelated then this is not relevant.
Power cables do have losses but these are not massive. Losses over a cable between Shetland and mainland Scotland would be no more than around 3%. Even allowing for taking the power to the Central Belt (Scotlandâ€™s demand centre) these might get as high as 5-6%.
Profitability depends on so much more than location. A windfarm, such as the proposed Viking Energy project, will be more profitable than one in Aviemore. This is because a windfarm in Shetland will be about 25% more productive for the same capital outlay (conservative 50% capacity factor per MW in Shetland vs optimistic 40% CF in Aviemore). Even allowing for a full 6% transmission loss, the Shetland windfarm will still be about 17.5% more productive (50%reducedby6%=47%. 7is17.5%of40). So long as the costs of transmission are less than this 17.5% advantage then it is worthwhile.
Without wanting to shift topics, Shetland would not be chosen as a site for a new nuclear power station because in that case the transmission costs would over and above otherwise identical economics for building on the mainland. With wind we get more â€œfuelâ€ at no extra cost. 2MW in Shetland produces the same power over time as 3MW anywhere outside the north highlands and islands.