As renewable energy use rises, electricity grids face an increasingly challenging task to balance generation sources and load demands. Within a decade or so many regions are aiming to source 20% or more of their energy from renewables, leaving utilities and grid system operators in a race to ensure the reliable, stable and responsive control of grid voltage.
Many wind farms currently rely on capacitor banks to store electricity in order to respond to grid demand, meaning response time is very slow, often struggling to reach 200 millisecond (ms). Now that many utility end users are pressing for the introduction of a global standard for grid code compliance, reducing required response time to at least 60ms by around 2013, pressure on system operators is greater than ever.
The Rockwell revolution?
In the UK, Rockwell Automation has designed a system with a reaction time of just 10 milliseconds, well below the proposed 2013 standard. The system runs all hardware and control units off an industrial version of office EtherNet/IP, bypassing the need for a capacitor bank. A key advantage is that EtherNet/IP is standard, and no special hardware or software needs to be built into the switch to allow for communication.
“Because we use ‘Standard Ethernet’ we are able to take advantage of all the capability available now and in the future to create architectures and control traffic on EtherNet/IP,” says Adrian Fowler, Business Development Manager for Alternate Energies at Rockwell.
When the grid demands peak power, the Rockwell Wind Farm Controller can send power request messages to a wind turbine to supply the required power in less than 10ms. Since it can communicate with all wind turbines instantaneously, the system can also decide which wind turbines are best suited to the wind directions, enabling a much more dynamic solution. Moreover, the system can improve the dynamic response of the wind turbine, offering manufacturers the possibility of using the wind turbine generator itself to control reactive power, thus managing power factor and grid bus voltage control without the need for additional capacitor and inductor banks.
By removing or reducing the need for additional voltage-control equipment, the Rockwell technology may help to edge the price per MW of wind energy closer to the price of traditional energy, making wind more competitive and appealing.
“It makes a huge difference to many wind farms, as it can mean a €20m+ investment in capacitor banks in order to meet [even] the 140ms reaction-time requirements of many utility end users,” says Fowler.
Rise of the ultracapacitor
Given the emergence of such potentially game-changing technology, the future for capacitor-based wind park management solutions might seem precarious. However, a new breed of ‘ultracapacitors’ may ensure that the technology remains competitive for some time yet.
In 2009, US-based ultracapacitor company Ioxus launched its first Electric Double Layer Capacitors (EDLCs) and power modules offering more capacitance and greater power densities than competitors. Using a unique prismatic design for more practical use of space, Ioxus ultracapacitors are capable of more than a million recharge cycles, helping to reduce power expenditures and lengthen the life of other energy sources.
“Ultracapacitors provide high power instantly, achieving hundreds of thousands of complete discharges throughout a wide temperature range,” says Harvey Wilkinson Vice President of Business Development at Ioxus.
Ioxus ultracapacitors offer improved energy storage solutions for grid ancillary services such as frequency regulation, spinning reserve, and peak shaving. Hybrid battery energy storage systems with ultracapacitors achieve superior performance and last significantly longer than battery-only solutions because the ultracapacitors absorb the fast discharges and recharges, allowing battery systems to supply the longer-term energy required.
“Battery energy storage systems are now starting to be deployed in volume for ancillary services and renewable integration, particularly for island grid applications,” says Chad Hall, Chief Operating Officer at Ioxus.
“Ultracapacitors are now used in wind turbines for emergency pitch control. In the near future, [they] will also be used in larger storage systems for renewable ramp management and grid stability,” he adds.
Future of wind park management
Historically, grid codes were designed for generators installed within power stations, not 100km out at sea. In view of this, turbine manufacturers have sometimes found grid code compliance a difficult task. Against a background of increasing investment in renewable energies, country grid codes are expected to become even more demanding in future years and there is talk of a common European grid code. In view of this, there is a danger that developments could be postponed as operators seek reassurance over specific requirements that they will need to meet.
However, the new approaches to wind park management outlined above raise the exciting possibility of vastly improved grid response times, and it is perhaps possible that anxieties over future regulations will reduce as the new innovations become more widely adopted.