Commissioning extra power stations to deal with spikes in electricity demand is becoming increasingly costly, and today’s power utilities are considering decentralised systems, where customers may also double up as suppliers. Energy storage and smart metering all play a part in distributed generation, also known as grid integration. Here, we canvas the views of the experts.
In November 2016, Ofgem, government regulator for the electricity and downstream natural gas markets in the UK, awarded National Grid and UK Power Networks NIC £9.5 million in funding towards the formation of a Distribution System Operator in the South East region. The trial will connect more renewable energy storage, and could potentially expand to 59 other locations with potential savings of up to £412 million for UK consumers by 2050.
The aim is to reduce the need to build additional electricity generation infrastructure, and to save consumers in the South East up to £1 million by 2020 and £29 million by 2050. Distributed generation around London’s metropolitan area has increased greatly over the past five years.
In August 2017, Ofgem published its decision on Future Arrangements for the Electricity System Operator (ESO) in Response to a January 2017 Consultation on SO Separation, when the Department for Business, Energy and Industrial Strategy (BEIS), Ofgem and National Grid issued a joint statement setting out their aspiration for the future of the ESO and how it might be delivered. The ESO will be physically separated from other parts of National Grid’s business.
“It is not so much a problem of centralised versus distributed power generation but more an issue of variable load and generation you get on distributed networks,” argues Steven Stapleton, consultancy services manager at S&C Electric Europe.
Well known problems
“These problems have been well documented for 15 to 20 years now, including thermal rating of equipment, transformers and cables through bi-directional power flows on the system. Voltage regulation is vitally important, whether it is a generator or external equipment such as a capacitor. Reactive compensation provides reactive power to support voltage, but also leads to issues of harmonics on the system.
“If you want to connect a renewable generator source, it has to take into account the requirements imposed by the network operator. There are many energy storage options, the main one today being battery storage, but other options in the past have included compressed air, flywheels and capacitors.”
According to Stapleton, current regulations do not allow distribution network operators to own and operate battery storage as an asset because this can distort the market, but this is something that is currently being investigated. There is a National Grid Code review looking into the classification of storage. Standards include the GB Distribution Code and the European Standards and Network Codes.
In November 2017, Stapleton chaired the IET Distributed Generation 2017 Professional Development Course at Glasgow’s University of Strathclyde. The training course provides engineers with a solid understanding of both the technical and applied issues relating to distributed generation. He delivered a presentation on the application of IEC60909 and G74, including a short introduction into the standards and an example of using power system software
Stapleton says: “IEC standards relating to short circuit analysis basically tell you how you should model for short circuit analysis and studies to look at the fault level in a system. During the course, we went through an example of building a model for a network and generator, and how to apply the standards.”
Flexible approach
Dr Alastair Martin is founder and chief strategy officer of Flexitricity, a demand response aggregator created in 2004 after formulating the core concepts of aggregated load management and flexible generation. Before founding Flexitricity, he worked on energy efficiency and renewable energy at Scottish Water.
Martin recalls: “We were working on a high-efficiency fossil fuel plant at the time of our launch, at which time I learnt about the sacrifice in efficiency that you have to make if you want flexibility, and vice versa. That is when I saw that the industrial and commercial customer base is where required flexibility resided.
“We have a control room in Edinburgh running demand response on a total capacity of about 300MW, all of which is owned by third parties that do not operate from within the energy industry other than as users.”
All the flexible load and distributed generation that Flexitricity works with belongs to other users and they have built it for their own purposes. If it involves a combined heat and power (CHP) plant, its primary purpose is to supply heat to customers, while the purpose of a standby generator is to protect a process, for example in a hospital.
Martin adds: “Some of them will have generators such as CHP, some are consumers such as cold storage facilities or chemical manufacturers, and some are critical sites that need their own standby generating capability. The ratio is about 50:25:25 for each type of customer and our job is to find them extra income.
“There is also a small-scale dispatchable hydro generating facility for dams and reservoirs. A hydro operator will want to maximise the total megawatt hours output in the same way as a CHP operator would. We find flexibility and monetise that flexibility for the operators.
“We are not currently aiming to work in domestic power generation although at some point it will become important. Domestic demand response today is limited because people do not have big thermal loads such as air conditioning on the electricity network, and their heating is mostly gas supplied, and electric cars are still some time away from mass deployment.”
Moving towards distributed assets
Since 2015 Centrica has reshaped its power generation portfolio in line with a wider trend towards decentralised and flexible energy sources. In June 2017, it sold the last of its large centralised Combined Cycle Gas Turbine (CCGT) plants at Humber and Langage. This transaction supports the shift to more distributed assets – Centrica has converted some sites to peaking plants and has a number of projects underway to build new gas-fired rapid response generation sites.
Mark Hedges, head of power asset optimisation at Centrica, has witnessed major changes in the energy industry in the past few years. He says: “The low carbon generation that has come on recently is intermittent and not dispatchable exactly when needed.
“There is centralised generation in wind farms into the transmission and distribution network, but what that means is that larger power stations are running less frequently. The duty is no longer 24/7 but for shorter periods of time during cold periods over the winter, and therefore generating efficiency is no longer the key driver, so the type of power plant that provides short-term power is different to continuous duty plants.
“There are lots of sites around the country – such as hospitals, data centres and water treatment works, for example – that have back-up generators for resilience reasons. We do not need to build large centralised generating plants if we can connect customer assets that are already there.”
Operating distributed assets
Hedges contends that it is now possible to operate these distributed assets collectively via the internet, which previously was difficult to do until a decade or two ago. Now operators can send signals to these assets though the cloud and instruct numerous small generators to fire up to provide as much power as a large centralised generator.
He adds: “When you have sites that are difficult to get to, you can now install a mobile SIM-card based solution to access the internet. The owners of back-up generators in hospitals and data centres can run their assets during peak power consumption times and reduce their energy bills or make additional revenues from assets that were not previously earning revenues.
“We are also putting in battery storage, both on the grid and behind the meter at customer sites where solar photovoltaic equipment has been installed. In addition we have many examples of hydro generation or pumped storage as we call it, the biggest one of which is Dinorwig Power Station in Snowdonia, North Wales.”
Dinorwig pumps water up to a higher reservoir overnight and then lets the water go through turbine at peak times during the day as and when needed. Another traditional energy storage method, in the form of flywheels, is costly to install according to Hedges, and not as flexible as battery or pumped storage. Furthermore, a spinning flywheel loses energy over time, unlike battery or pumped storage.”
On the gas side of things, Centrica is currently building a new gas plant on land next to its existing Brigg power station, for a project that forms part of a £180 million investment programme into four new flexible power generation and storage facilities. Rated at 50MW, it will produce enough power to meet the needs of around 50,000 homes. Construction is expected to take around 15 months. Ian Griffiths, Brigg generation manager says: “The site team has been working hard on the demolition of redundant equipment, including four chimneys and old fuel oil tanks where the new plant will be built.”
Centrica also claims that the construction of a new battery storage facility at the site of its former Roosecote power station will be one of the largest in the world. The facility helps keep the local distribution network stable by either absorbing power from the system (charging the batteries) or supplying it to the grid (discharging the batteries). Once complete, it will be capable of responding to fluctuations in demand in under a second, holding enough power to meet the needs of around 50,000 homes.
