What is security of fuel supply?
An energy source is defined as secure on this site if electricity generators can be sure of obtaining enough of the relevant fuel to maintain an adequate electricity supply.
Countries that rely on fuel that must be constantly imported to power their electricity supply expose themselves to potential energy security issues, including fluctuating international market prices and disruptions to fuel supplies caused by geopolitical disturbances.
Every energy source has strengths and weaknesses, such as its inherent limitations on security of supply, which could contribute to the likelihood of an energy gap, when supply falls short of demand, and might cause interruptions to the electricity supply. Reducing dependence on constant imports of fuel to generate electricity can help to mitigate security of supply issues. This could include using renewable sources such as wind and marine, which don't depend on imported fuels, alongside fuels that come from a range of suppliers and can be stored.
For example, the uranium nuclear fuel used in the UK is imported. But uranium has a high energy density: a given amount of uranium can be used to generate more electricity than an equivalent amount of a fossil fuel. That makes uranium relatively easy to import and store. Plus it can be imported from several countries.
A large proportion of coal and gas also has to be imported, so an over-reliance on these fuels would threaten the security of the UK's fuel supply. But the UK still has some domestic reserves of coal and gas, which aids fuel supply security, although the potential to harness them has limits.
There will always be sun, wind and tides in the UK, so any generation from these can help the UK's fuel security.
The UK Government favours a diverse mix of generating technologies where the strengths of one energy source compensate for another's weaknesses.
What does it mean for the UK?
Each of the different energy sources has its security of supply constraints and possible solutions, all with important impacts for the UK.
The Energy Sources
The UK is one of the windiest countries in Europe and it obviously doesn't need to import wind. But wind is intermittent so backup generating technologies are required that can be powered up at short notice.
The UK doesn't have to import solar energy, so in that respect it is secure. But obviously it doesn't work at night or in cloudy weather.
As an indigenous energy source hydro is highly secure, but the number of sites where large-scale hydro can be sited in the UK is limited, so it will only ever make a small contribution to the energy mix.
Marine energy could help improve the overall security of the UK's energy mix by relplacing imported fossil fuels. However, wave and tidal technologies are subject to intermittency.
All the uranium the UK uses for nuclear fuel is imported, but it can be sourced from a number of suppliers. The energy density of uranium is very high, which means it can easily be stockpiled to guard against short-term security of supply issues.
The UK imported 45% of the natural gas it used in 2009 and, as North Sea reserves dwindle, that is predicted to rise to 69% by 2019. Importing from a variety of countries and using a diverse mix of generating technologies can help to mitigate this.
The UK imported 79% of the coal used for electricity generation in 2009, and the majority of that came from one source. The UK is diversifying its energy mix with other energy sources to be less reliant on coal for electricity.
In 2009 the UK imported around 67% of the oil used for generating electricity and indigenous North Sea reserves are diminishing. But oil-fired power stations are used only to meet peak demand and they will be phased out by 2015.