Could the country’s roads be used as a large-scale sink of demand response? Not now, or with current technology at least. But in its liquid form, bitumen frequency controlled, and by extension other types of load similarly controlled and connected, shows potential for network balancing with increasing levels of variable renewable generation.
The network challenge
A challenge facing grid operators with increasing levels of renewables is to maintain the balance between generation and demand. Renewable energy sources that are connected by power electronic converters reduce inertia of the power system and so changes in frequency become more rapid. Thus, a faster frequency response than hitherto is needed to compensate for this reduction of inertia.
To meet the operational requirements of the UK power system, using partly loaded conventional generators to provide frequency response would be a costly option – an estimated £160 million per year based on the price of frequency response in 2009. Thus cheaper alternatives are necessary.
Dynamic demand to the rescue
New research from Open Energi, National Grid and Cardiff University using liquid bitumen finds that demand side response technology could fit the bill, able to contribute to the grid frequency control in a manner similar to, and, crucially, faster than that provided by traditional peaking power generation.
Field testing was undertaken on 76 bitumen tanks with power ratings from 17kW to 75kW, equipped with a decentralized frequency controller enabling the tanks to alter their power consumption in proportion to the variations of grid frequency. From these data a model of a population of controlled tanks was developed and integrated with a model of the GB power system to investigate case study examples of loss of generation. Results from the field tests showed that full response could be provided in less than 2s, as compared to 5-10s for a thermal generator.
“Case studies showed that, following a loss of generation, the deviations of grid frequency were reduced with immediate load change of tanks. The power taken from frequency-sensitive generators was also decreased,” the researchers found.
The case studies were based on a population of 5,000 tanks providing a load change of 72MW, which is small in the context of the GB power system. However, if scaled up with other types of loads the contribution of reducing the frequency deviations would be considerable, the researchers concluded.
Accelerating demand response in UK
Demand response is an essential component of the future power system, contributing not only to renewables integration but also security of supply, improved market competition and consumer empowerment. However, despite the initial promise the UK market hasn’t developed as it could. In its latest review, the Smart Energy Demand Coalition (SEDC) attribute this to the policy and regulatory choices.
National Grid has taken steps to accelerate demand response. In June the Power Responsive campaign was launched with the aim to deliver the practice at scale as a balancing service by 2020.
“If just 5% of peak demand is met by demand side response solutions, the response would be equivalent to the generation of a new nuclear power station,” says Nikola Gargov, Power Systems Engineer at National Grid.
Demand response a UK priority
In its Future Energy Scenarios (FES) report published in July National Grid estimated that by 2020 small-scale, distributed generation will represent a third of total capacity in the UK. As a result, speed of response to changes in energy supply and demand will be more important than ever.
Demand response could get the boost it needs from the government’s recently launched National Infrastructure Commission (NIC), which will provide analysis of the UK’s long-term infrastructure needs. One of the three challenges the Commission will address initially is how to improve electricity demand and supply balancing. The major driver is the closure of existing older larger generation in order to curb carbon emissions. Demand side management is an obvious option. Others under investigation are changes to existing market frameworks, increased interconnection and new energy storage technologies.