This site uses cookies. By continuing to use this site you agree to our use of cookies. To find out more, see our Privacy and Cookies policy.
Skip to the content

[IOP] A community website from IOP Publishing

environmentalresearchweb blog

Wiill the lights stay on?

by Dave Elliott

There has been a long and sometimes heated debate over UK grid security issues, with some claiming that the spread of wind power and PV will undermine it.  Ofgem’s 2013 Electricity Capacity Assessment says ‘Wind generation, onshore and offshore, is expected to grow rapidly in the period of analysis and especially after 2015/16, rising from around 9GW of installed capacity now to more than 20GW by 2018/19. Given the variability of wind speeds, we estimate that only 17% of this capacity can be counted as firm (i.e. always available) for security of supply purposes by 2018/19.’

This is in their Reference Scenario. But it goes on to note that, based on a statistical analysis of probabilities, the wind element will be less important, in terms of a ‘Loss of Load Expectation’ measure of security/continuity of supplies, than other supply side changes:  ‘the figures indicate that reasonably small changes in conventional generation availability have a material impact on the risk of supply shortfalls. This is most notable in 2015/16, where the estimated LOLE ranges from 0.2 hours per year in the high availability sensitivity to 16 hours per year in the low availability sensitivity, for the Reference Scenario is 2.9 hours per year.’   

Moreover, Ofgem’s LOLE figures do not take account of the mitigation measures the systems operator is likely to adopt to avoid disconnections, so in practice their LOLE  figures overstate the expected number of hours per year in which supply does not actually meet demand. Ofgem says ‘most of the time, when available supply is not high enough to meet demand, National Grid may implement mitigation actions to solve the problem without disconnecting any customers’ and ‘as a consequence of the mitigation actions available, the total period of disconnections for a customer will be lower than the value of LOLE’. In any case most of these events will be brief: ‘Given the characteristics of the GB system, any shortfall is more likely to take the form of a large number of small events that would not have a direct impact on customers.

Basically, the total time when, statically, over the year, demand and supply won’t match will be very small and episodes will be brief, so this can be easily dealt with. As well as using back-up plants, Network Operators are meant to able to reduce their total system demand by 20% quickly. Of course, restarting some of the 4GW of mothballed gas plants would help! But wind and/or PV are not the main problem, at least not so far.

What about when and if they make a much larger contribution? Ofgem were only looking at a UK mix with 20GW of wind. If it and other renewables take over a larger share then the balancing requirement will get larger. But that doesn’t have to mean more and more  backup capacity, or a lot of energy storage and demand side management.  They could help, but if supergrid links can be made with rest of the EU, local variations and supply and demand can be balanced across a much wider range of locations.

In a key new paper in Renewable Energy journal  (63, pp 467-476),‘Transmission needs across a fully renewable European power system’, Rolando Rodriguez, Sarah Becker, Gorm Andresen, Dominik Heide and Martin Greiner from Aarhus University in Denmark look at the residual load and excess power generation of 30 European countries with a 100% penetration of variable renewable energy sources in order to quantify the benefit of power transmission between countries. They model hourly mismatches between demand and renewable generation from wind and solar PV. For separated countries, they found that balancing, e.g. via back-up plants, is required to cover around 24% of the total annual electricity consumption, but only15% of all countries are networked together with unconstrained inter- connectors. That would require expanding interconnection link capacity over 11 times. But even it could only be doubled, the balancing requirement would still only be 18%.

Of course HVDC supergrid links are expensive and potentially environmentally invasive, but that may be radically altered by new technologies like for example, cheap underground HVDC supergrids:   Or even a switch away from  long distance electricity transmission to gas transmission. The gas grid already handles four time more energy than the electricity grid in the UK, and in effect acts as a buffer store, helping to deal with variable demand: demand for heat varies much more, both daily and over the year, than demand for electricity.

That approach can be expanded with large gas stores (gas is easier to store) and we could switch to green gas, methane from bioenergy sources (e.g. AD biomass) and from wind-to-gas conversion, making use of the excess energy produced from wind at times of low demand. Some of the gas could of course be used to make electricity locally where needed.  Some of the gas can also be exported and imported. So we don’t necessarily need a lot of electricity supergrids. Green gas could provide a cheaper and more flexible balancing option. Gas pipelines are also less invasive than HVDC or AC power grids.  And if the combustion of green gas is combined  with carbon capture and storage, then you get negative carbon emissions.  All in all, sounds like a winner! Pipes not wires!

Heat production, transport and storage is another possible winner –storing energy as heat is even more efficiently than storing it as gas, and although heat transmission is less efficient, it can be sent quite long distances will low losses- the longest example  so far is a 65km heat link from a waste to energy power station to Pargue. So rather than distributing electricity, or for that matter fossil or green gas, to individual domestic consumers for heating, wherever possible, heat could be supplied via district heating (DH) networks, fed from high-efficiency community-scaled green energy fired Combined Heat and Power plants. DH only makes sense in urban and perhaps suburban areas, but biomass and solar-fired DH is now moving ahead across the EU, usually linked to heat stores, and in some cases inter-seasonal heat stores. So that is an extension of the ‘pipe’ rather than ‘wire’ approach, with piped heat as well as piped gas.

Probably though a mixed system would be best, capitalising on the strengths of each. However the best balance between heat, gas and electricity and which will, or should, dominate in future, is unclear. It will be influenced by the location of the sources and the demand. For example, access for pipes may be hard in some locations. Technological change could also tip the balance of advantage between these vectors. The wind to gas route may prove too expensive, whereas the availability of cheap storage of electricity might make electricity more attractive. The debate continues. But one way or another the lights should stay on.


This entry was posted in Renew your energy and tagged , , , , , , . Bookmark the permalink.
View all posts by this author 

Leave a comment

Your e-mail address will not be published.


  • Comments should be relevant to the article and not be used to promote your own work, products or services.
  • Please keep your comments brief (we recommend a maximum of 250 words).
  • We reserve the right to remove excessively long, inappropriate or offensive entries.

Show/hide formatting guidelines

Tag Description Example Output
<a> Hyperlink <a href="">google</a> google
<abbr> Abbreviation <abbr title="World Health Organisation" >WHO</abbr> WHO
<acronym> Acronym <acronym title="as soon as possible">ASAP</acronym> ASAP
<b> Bold <b>Some text</b> Some text
<blockquote> Quoted from another source <blockquote cite="">IOP</blockquote>
<cite> Cite <cite>Diagram 1</cite> Diagram 1
<del> Deleted text From this line<del datetime="2012-12-17"> this text was deleted</del> From this line this text was deleted
<em> Emphasized text In this line<em> this text was emphasised</em> In this line this text was emphasised
<i> Italic <i>Some text</i> Some text
<q> Quotation WWF goal is to build a future <q cite="">
where people live in harmony with nature and animals</q>
WWF goal is to build a future
where people live in harmony with nature and animals
<strike> Strike text <strike>Some text</strike> Some text
<strong> Stronger emphasis of text <strong>Some text</strong> Some text