22 May 2012 – As South Africa braces itself for a bitterly cold winter this year with high electricity demand, Eskom is doing everything possible to keep the lights on. One of its most effective initiatives in recent times has been the Enerweb developed Virtual Power Station (VPS), introduced in 2007.
Eskom uses the VPS as a means to schedule all its controllable demand side resources and view available customer negaWatts. “This negaWatt generation capacity reduces Eskom’s reliance on meeting reserve margin needs with costly gas turbine generation plant, and avoids load shedding. A total of 854 MW of customer load is certified and available for dispatching through Eskom’s National Control,” Rob Surtees, managing director of Enerweb, says.
A variety of Demand Response (DR) programmes are being catered for within the VPS, including customers with standby generation and ripple control systems, and a number of Eskom’s largest customers in an interruptible load programme. From an operational point of view, the VPS is indistinguishable from physical power stations. When additional load is needed because of an unexpected shortage or an expected peak, the Eskom system operator (SO) can dispatch the VPS as it would an emergency or supplemental generator.
Apart from being the cleanest energy source available to the SO, the VPS can be deployed faster than any physical energy source of similar capacity, and can quickly modify its capacity and energy delivery capability. The effects of supply from the VPS are geographically distributed, thereby reducing network constraints where required. “While currently only Eskom’s large customers are being utilised within the VPS, Eskom is planning to expand its demand response initiatives to include smaller industrial and commercial loads under its now well publicised demand response aggregation pilot programme,” Deborah Blane, demand response manager at Enerweb says.
In this initiative, an initial 500 MW of load has been targeted, with a further 1,100 MW planned to be incorporated by 2013. Residential load can also be incorporated within the VPS, particularly when integrated with smart metering systems. Numerous pilot and small scale projects are being undertaken within municipalities and Eskom.
Other potential participants are customers with standby generation, e.g. backup diesel generators. “While incentives for utilising this type of load would need to be substantially greater than they currently are, these types of programmes have been very successfully deployed internationally e.g. in the UK, USA and France,” Surtees says.
There has been much focus in recent years on the smart grid which achieves distributed control through a network of automated real time load monitors and switches, e.g. smart meters which automatically limit load under certain network conditions. The VPS would in time interface with these systems, thereby adding to the megawatts available for dispatch.
Electricity grid management in general is moving from a traditional load-following approach towards load-shaping strategies in which demand side resources are managed to meet the available generation and the grid’s power delivery capabilities at any given time. With the integration of more renewable and variable generation technologies onto the network, this flexibility becomes critical. Substantial growth in the number of megawatts under VPS control is anticipated over the next few years, with the full potential of the VPS and demand response in general still to be realised. The Virtual Power Station will play a key role in South Africa’s smart grid architecture of the future, enabling Eskom to optimise usage of its electrical network in an environmentally beneficial manner.
VPS key statistics
Since July 2008, the VPS has…
- up to 800 MWs of load available for dispatch.
- managed more than 6,000 customer dispatches with the associated performance reports.
- dispatched a total 203,435 MWs on request from the system operator.
- been used on average every second day to assist with system frequency or demand constraints.
- managed all Eskom VPS customer availability, scheduling, dispatching and the gathering of metering information, event performance measurement, settlements and reporting.