Impacts of variable renewable generation on thermal power plant operating regimes
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Date
27/06/2016Author
Bruce, Robert Alasdair Wilson
Metadata
Abstract
The integration of variable renewable energy sources (VRE) is likely to cause fundamental
and structural changes to the operation of future power systems. In the United Kingdom (UK),
large amounts of price-insensitive and variable-output wind generation is expected to be deployed
to contribute towards renewable energy and carbon dioxide (CO2) emission targets.
Wind generation, with near-zero marginal costs, limited predictability, and a limited ability to
provide upward dispatch, displaces price-setting thermal power plants, with higher marginal
costs, changing flexibility and reserve requirements. New-build, commercial-scale, and low-carbon
generation capacity, such as CO2 capture and storage (CCS) and nuclear, may impact
power system flexibility and ramping capabilities. Low-carbon generation portfolios with
price-sensitive thermal power plants and energy storage are therefore likely to be required to
manage increased levels of variability and uncertainty at operational timescales.
This work builds on a high-resolution wind reanalysis dataset of UK wind sites. The locations
of existing and proposed wind farms are used to produce plausible and internally consistent
wind deployment scenarios that represent the spatial distribution of future UK wind capacity.
Temporally consistent electricity demand data is used to characterise and assess demand-wind
variability and net demand ramp events. A unit commitment and economic dispatch (UCED)
model is developed to evaluate the likely operating regimes of thermal power plants and CCS-equipped
units across a range of future UK wind scenarios. Security constraints for reserve and
power plant operating constraints, such as power output limits, ramp rates, minimum up/down
times, and start-up times, ensure the operational feasibility of dispatch schedules. The load factors,
time spent at different loads, and the ramping and start-up requirements of thermal power
plants are assessed. CO2 duration curves are developed to assess the impacts of increasing wind
capacity on the distribution of CO2 emissions. A sensitivity analysis investigates the impacts
of part-load efficiency losses, ramp rates, minimum up/down times, and start-up/shut-down
costs on power plant operating regimes and flexibility requirements. The interactions between
a portfolio of energy storage units and flexible CO2 capture units are then explored.
This multi-disciplinary research presents a temporally-explicit and detailed assessment of operational
flexibility requirements at full 8760 hour resolution, highlighting the non-linear impacts
of increasing wind capacity. The methodological framework presented here uses high spatial-and
temporal-resolution wind data but is expected to provide useful insights for other VREbased
power systems to mitigate the implications of inadequate flexibility.