Unreliable renewable energy is hitting quality

The quality of British electricity is falling because unreliable renewable generation is becoming an increasingly large component in the power supply, causing more flickering in households and potentially triggering outages.

Because electricity flows constantly, power grids need to maintain a stable current, known as fault level. The problem might not be fixed any time soon as the technology to store electricity, and so balance renewable supply, is in its infancy.

Britain’s power grid is balanced around a frequency of 50Hz. Any major deviation above or below this level hits the quality of electric supplies, causing flickering of light bulbs and, in the worst case, blackouts.

Maintaining a frequency of 50Hz has not been a big challenge in the past as Britain’s electricity was produced by a generation of gas, nuclear, and coal-fired power stations, controlled by a handful of utilities.

But experts warn that the rise of decentralised and unreliable renewable capacity, such as wind, makes it more difficult to maintain a stable frequency, reducing the quality of supplies and potentially collapsing the grid.

The European Network of Transmission System Operators for Electricity (Entsoe) said a subsidy-fuelled boom in renewable capacity across Europe had coincided in a quality drop of the power frequency.

Entsoe also said a clash of low renewables with a major capacity outage such as the power link between France and Britain would pose “a severe risk for the system to collapse”.

“As you put more renewables into the system you will lose flexibility and have more flickering and also increase the threat of frequency outages,” said Andrew Jones, Europe’s managing director for US based S&C Electric, a provider of equipment and services for electric power systems.

“All you need is an interconnector or a big station to go out at the same time as winds drop off and you will have a frequency-based outage,” Jones said.

National Grid, which operates Britain’s power transmission system, has also warned of a drop in electricity quality. “The reduction in fault levels weakens the overall strength of the network which in turn can give rise to quality of supply issues such as large voltage steps, harmonics and flicker,” National Grid said.

A decade ago, Britain had almost no renewable power capacity installed and instead relied on a mix of gas, coal, and nuclear generation.

Today, it receives around 10% of its electricity from renewable sources, and by 2020 Britain’s share of installed renewable capacity is expected to reach 20%.

Falling frequency is caused by a lack in power production, while rising frequency is triggered by a surplus of power.

Dynamic Demand, a renewable energy consultancy, says that a frequency around 48.5Hz would result in local blackouts and a frequency of 52Hz or more would cause power stations to trip and forcefully shut down.

National Grid says the last reportable frequency event occurred in 2008, when an unplanned loss of 1,714mW of power generation capacity cut system frequency to 48.15Hz.

“These events resulted in the system frequency being outside of National Grid’s lower statutory limit of 49.5Hz for nine minutes,” National Grid said.

There had been another frequency anomaly in the mid-1990s.

Data from Entsoe shows that continental Europe has seen a strong rise in renewable capacity in the last 10 years, alongside a sharp rise in the duration and number of frequency events.

To address the problem, most utilities are developing plans to deal with sudden swings in frequency, introducing primary, secondary, and tertiary control measures to balance the grid.

These measures range from small scale but fast (within 30 seconds) production adjustments to full-scale emergency back-up generators being started up within 15 minutes of an event in order to deal with a sudden drop in frequency as a result of changing renewable generation.

National Grid says that developing storage technology would help stabilise the grid. “Energy storage technology could play a significant role in the operation of the transmission networks by improving the utilisation of renewable generation... particularly with regard to inertia and fast frequency response,” the operator said.

The first such storage technologies are now being tested, but industry experts say much more is needed.

In Dec 2012, electric distribution company UK Power Networks was awarded £13.2m (€15.6m) from Britain’s energy regulator Ofgem to install a 6mW power storage device to find ways to improve the economics of electrical energy storage.

“We’d need around 2,000mW of storage capacity installed to show that the economics of power storage work,” said S&C Electric’s Andrew Jones.

He added that much more would be needed to properly balance a grid that has 20% of its installed capacity coming from volatile renewable sources.



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