Abstract
New environmental constraints for hydropower improve ecosystems but reduce energy production
and flexibility, creating a dilemma between protecting nature and ensuring a sufficient and reliable
energy supply. Approximately 88% of Norway’s power comes from hydropower, produced by over
1770 plants. We assess how 285 potential new or revised environmental constraints affect
hydropower production and flexibility in the Northern European power system. To do so, we
combine a method for estimating environmental flow releases in bypass reaches and stochastic
power system optimization. Our results show that reductions in hydropower output due to these
constraints are consistent across power system scenarios and two power system models. The
reductions amount to 3 TWh yr−1
(2% of Norway’s production), by our estimates. These
reductions are primarily driven by flow diversions to bypass river sections. Further, we find that
high power prices increase and low prices decrease, reflecting reduced system flexibility. Price
increases typically occur in dry spring periods and are linked to activation of season-dependent
reservoir restrictions in that period, while price decreases result from higher reservoir volumes
entering periods of rain-heavy summer or autumn periods, indirectly linked to restrictions active
earlier in the year. In our simulations, we observe that flexibility losses due to environmental
constraints to some degree are offset by increased flexible operation of unaffected reservoirs and
transmission interconnectors. Finally, our findings suggest that reservoir restrictions may cause
spilling, as higher water levels in regulated reservoirs increase the risk of spilling during wet
summer or autumn periods. This system-level understanding is crucial for regulatory authorities
designing new environmental requirements and revising the terms of hydropower licenses. Our
study contributes to informed discussions for balancing hydropower production with local
environmental benefits and offers a framework for studying similar constraints in other regions,
such as Sweden, North America and European Alpine countries.
and flexibility, creating a dilemma between protecting nature and ensuring a sufficient and reliable
energy supply. Approximately 88% of Norway’s power comes from hydropower, produced by over
1770 plants. We assess how 285 potential new or revised environmental constraints affect
hydropower production and flexibility in the Northern European power system. To do so, we
combine a method for estimating environmental flow releases in bypass reaches and stochastic
power system optimization. Our results show that reductions in hydropower output due to these
constraints are consistent across power system scenarios and two power system models. The
reductions amount to 3 TWh yr−1
(2% of Norway’s production), by our estimates. These
reductions are primarily driven by flow diversions to bypass river sections. Further, we find that
high power prices increase and low prices decrease, reflecting reduced system flexibility. Price
increases typically occur in dry spring periods and are linked to activation of season-dependent
reservoir restrictions in that period, while price decreases result from higher reservoir volumes
entering periods of rain-heavy summer or autumn periods, indirectly linked to restrictions active
earlier in the year. In our simulations, we observe that flexibility losses due to environmental
constraints to some degree are offset by increased flexible operation of unaffected reservoirs and
transmission interconnectors. Finally, our findings suggest that reservoir restrictions may cause
spilling, as higher water levels in regulated reservoirs increase the risk of spilling during wet
summer or autumn periods. This system-level understanding is crucial for regulatory authorities
designing new environmental requirements and revising the terms of hydropower licenses. Our
study contributes to informed discussions for balancing hydropower production with local
environmental benefits and offers a framework for studying similar constraints in other regions,
such as Sweden, North America and European Alpine countries.