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Will the Norwegian hydro reservoirs normalize in 2021?

Eylert Ellefsen
Archived blog post. This blog post has been transferred from our previous blogging platform. Links and images may not work as intended.

The Nordic hydropower situation has been extreme this year. Norway has seen the highest inflow and reservoir levels in a 30-year perspective. By New Year's Day we will see about 13 TWh higher reservoir filling than normal in Norway, and snow/groundwater about 1-2 TWh above normal.

Norwegain reservoir filling for 2020 (blue) compared to the normal and the min/max levels.

Energy Quantified (EQ) has studied the hydropower situation for 2021. We made some production strategy scenarios and focused on the according export-profiles.

Key Findings

  • With normal weather conditions, the substantial reservoir surplus can normalize by the end of week 30 (start of August).
  • Normalizing the reservoirs require close to all-time high production until the end of July.
  • Most likely, we will see a production level that brings Norway to nearly max export levels during Q1-2021.
  • Mild weather will be a threat to utilize export capacity and to equalize the reservoir surplus.

Power balance and production scenarios

In the table below, we see the main parts of the Norwegian power balance, i.e. hydropower, consumption and exchange.

Power balance for Norway.

We saw 160 TWh inflow in 2020 compared to a normal of 135 TWh. Given normal conditions, we expect hydropower for 2021 to equalize today's 13 TWh reservoir surplus. But not necessarily wholly, as this might take 1-2 years.

For 2021, we see about 10 TWh production above the normal. To avoid a 2020-like situation during the summer in 2021, we expect high generation during Q1-2021.

EQ calculated the net exchange for 2021 to be about 11 TWh under normal circumstances. However, these years far from ordinary. We expect around 20 TWh exports for 2020, and for 2021 a rough estimate would be 20-25 TWh.

We have made four production scenarios until week 30 (see below). We focus on different production strategies until week 30 by normal weather conditions, and finally, make some comments about the weather- and inflow uncertainty.

Four alternative production scenarios.

The production scenarios 1 and 2 represent upscaled normal profile until week 30, while scenarios 3 and 4 represent a stronger Q1-profile, and return to normal level after week 11 and 19.

Scenario 3 (Max prod Q1) seems to be unrealistic (127%, +4900 MW).

So our main scenario is the Base which ends the increased production by week 19 (111% of normal, +3200 MW).

In scenarios 2, 3 and 4, the total production until end week 30 is 86 TWh, which is 8 TWh above the normal (111%). In comparison, the 2020-production for the same period was 79 TWh, only 1 TWh higher than normal. The 2020-production was partly limited by reduced export capacity and low consumption during Q1.

Production scenarios 1-4.

Scenarios for reservoir filling and net exchange

For the reservoir filling, you can see that no scenario comes out below the normal, not even scenario 3 (Max prod Q1) as the production normalizes after week 11.

From week 30, we have followed the normal curve for all scenarios. The focus has been the needed Q1-production to achieve a reasonable reservoir filling after the spring inflow period (week 30). 

The conclusion is that, given normal weather conditions, the reservoir levels in Norway will be normalized by about 11% (+8 TWh) more production until week 30. EQ believes that the production during Q1 will be even stronger as scenario 3 and 4 suggest. From these scenarios, the producers are better prepared to take care of more precipitation than normal - if that happens.

Effect of production scenarios on reservoir filling in 2021.

The exchange chart shows that the net exchange for scenario 3 (Max prod Q1) is close to the net exchange capacity (based on 95% of the raw REMIT-reported capacity numbers). The Base scenario (4) has a difference of 1000 - 1500 MW to the capacity limitation.

In a mild scenario, the Q1-consumption is about 1000-1500 MW below the normal. Meaning that the production, according to the Base scenario, can be maintained even when it's mild. However, with the Max prod Q1-scenario the production level has to reduced due to exchange limitations.

Inflows will increase too in a mild scenario. So then the production has to be increased. An upscaled production, like in scenarios 1 and 2, will equalize the reservoir curve, leaving close to 80% filling after the main melting period (week 30).

Net export scenarios for Norway.

Inflow and reservoir scenarios until week 30

The chart of accumulated inflows week 1-30 based on 30 years of climatic scenarios from the SMHI HYPE models, shows that the 5%-95% variation band is about the range 67-102 TWh. The normal is 86 TWh. 102 - 86 = 16 TWh above the normal in the 95%-scenario. Will this mean filled reservoirs by the end week 30?

Scenario 2 and 4 means 80% reservoir filling, +16 TWh = 18.5%, which means that a Base production scenario will not lead to filled reservoirs.

In reality, the reservoir's capacity can not be utilized so efficiently as we anticipate in such a simplified calculation. However, the conclusion is still that by scenario 2, a production of 111% of normal it is possible to avoid major water spillage, whatever hydrological scenario.

30 climate weathers, sorted from lowest to highest inflow, plotted versus the normal and 2020-inflow.

See the simulated reservoir filling below. It's using each of the 30 climatic inflow years with the production scenario 2.

The probability for spillage (>95% filling) is about 10% (3 out 30 years) by the fixed Scenario 2 production profile (111% of normal for the first 30 weeks).

111% of normal is, however, a much higher production level than seen before. It represents 87 TWh, the highest level for the period 2015 - 2020 is 85 TWh (which was during a very cold in January).

Simulated reservoir filling using 30 climatic inflow years (1990-2019).

Final words

EQ has revealed that there would be challenges maintaining such a high production until end week 30 that can avoid water spillages.

A mild winter will be a threat to maintaining the needed production level.

Exchange capacity may also this be a limitation for the production volume.

All the selected production scenarios show that most of today's hydrological surplus of 13-14 TWh can be equalized by normal inflows and weather conditions. But then the production for weeks 1-30 has to be close to an all-time high.

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