Virtual Power Plant
Six generating sites and a refinery, dispatched as one.
A virtual power plant is usually sold as a software layer over other people's assets. This one was built the other way round: from the control system of a conventional plant outward, with the steam turbine as the machine that absorbs what the renewables do not deliver.
What is in it
| Asset | Rating |
|---|---|
| CHP plant, petroleum coke, coal and gas fired | 61 MW electrical, 300 Gcal/h thermal |
| Photovoltaic plant on the refinery site | 9 MW |
| Photovoltaic plant | 0.999 MW |
| Photovoltaic plant | 0.979 MW |
| Photovoltaic plant | 0.972 MW |
| Photovoltaic plant | 0.972 MW |
| Photovoltaic plant | 0.972 MW |
| Micro-hydro plant | 0.269 MW |
The dominant consumer is the refinery itself at 28.6 MW, with eight smaller industrial consumers behind the same connection.
Three zones of control
Inside the fence
The CHP plant supplies the refinery with steam at 35, 16 and 6 bar and with electricity, and takes refinery gas back as fuel. This is the loop with the shortest time constants and the one the plant controls directly.
The site
The refinery and the 9 MW photovoltaic plant on its territory. Solar output moves on cloud cover; the steam turbine moves to match it, because the refinery's demand does not care where the electricity came from.
The national grid
Remote photovoltaic plants and the micro-hydro, dispatched together with the CHP plant against a schedule, with the balance settled at the connection point.
What the control system does
Output from each remote site is telemetered to the CHP plant's control system. The combined position of the group is compared with the schedule, and the steam turbine's load target is adjusted so the group as a whole meets it. The turbine is the only machine in the set whose output can be commanded rather than merely forecast, which is what makes the arrangement work.
Reporting to the transmission system operator goes over IEC 60870-5-101 and to the market operator over IEC 60870-5-104.
What this is not
It is not a trading platform and it is not an aggregator's portfolio. It is a balancing group whose assets happen to belong to one owner, controlled from one DCS, with a thermal machine doing the regulating. That is a narrower thing than the term usually implies, and it is what was actually built.
Related
The islanding behaviour of the same plant is under Island Mode Operation. The fuel and efficiency calculations behind the dispatch decisions are under Plant Performance.