The impact of variable renewable electricity on full load hours and efficiency of fossil-fired power plants

Abstract

Variable renewable electricity (VRE) production, consisting of wind power and photovoltaics (PV), has been increasing between 1990-2014 in EU member states. In the latest 10 years, wind power increased more than fivefold from 1.8% in 2004 to 7.9% in 2014 and PV from 0.02% to 2.9%. The share of VRE is not evenly spread over the EU member states. Higher VRE penetration will have a greater effect on a country’s power system, as the characteristics of the weather can affect up to 70% of daytime solar capacity due to passing clouds, and 100% of wind capacity on calm days. Currently, renewable electricity variability is generally handled by conventional power plants being cycled to operating at part load level or forced to shut-down. Operating at part load level, or even shutting down completely, leads to a decrease in yearly full load hours of these fossil-fired power plants. Additionally, the conventional power plant base load units are designed to run at constant power to achieve maximum energy efficiency. They tend to have limited operational flexibility and operating at part load levels and increased start-ups of these power plants requires extra fuel consumption, resulting in a lower energy efficiency. In this research, the effect of VRE on the average full load hours and energy efficiency of fossil-fired power plants in the EU from 1990-2014 was determined. EU member states were aggregated into three VRE penetration groups. By aggregating EU member states, the effect of VRE penetration was found by only analysing three groups, instead of 28 individual member countries. Additionally, aggregating the countries increases reliability when comparing the three VRE penetration groups and rules out coincidences in individual countries. With production data from Eurostat and capacity data from the WEPP Database from Platts, the fossil-fired full load hours and energy efficiency for coal and gas-fired power plants were calculated for each year between 1990-2014, for each VRE penetration group. Only within the high and medium VRE penetration group an effect of VRE on fossil full load hours was found. Fossil full load hours were found to decrease by 861 from 3,205 in 2010 to 2,344 in 2014 in VRE-high, while the VRE penetration increased from 17% to 25%, and decreased by 892 from 4,156 in 2010 to 3,264 in 2014 in VRE-medium, while the VRE penetration increased from 5% to 13%. The energy efficiency was found to be very strongly dependent on average year of commission. Only in VRE-high an effect of VRE on energy efficiency was found: the increased VRE penetration from 17% to 25% most likely caused a decrease in coal efficiency from 40% to 38% and a decrease in gas efficiency from 54% to 52% between 2010-2014.