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Hydropower for energy storage and balancing renewables

Hydropower with reservoirs is the only form of large-scale renewable energy storage in wide commercial use today. Pumped storage hydropower plants (PSP) are designed to lift water to a reservoir at higher elevation when the electricity demand is low or when prices are low, and turbine water to produce electricity when the demand is high and/or prices are high. PSP are often designed with a relative high capacity to operate in turbine or pumping mode only for some hours each. They often use artificial reservoirs with limited capacity of storing water. Environmental impacts of hydropower and pumped storage plants are related to impacts of flooding land to create a reservoir, the barrier effect disturbing the connectivity in the river and impacts on the flow regime and related ecosystem downstream from the dam.

Many European countries are increasing the proportion of wind and solar power generation in their electricity supply. This increases the need for energy storage to compensate for the difference between production and consumption, known as balance power. Hydropower with reservoirs is the only form of renewable energy storage in wide commercial use today.

Existing Norwegian hydropower reservoirs have considerable storage capacity that can be exploited for balancing services within the current regulations regarding highest (HRWL) and lowest (LRWL) regulated water levels.

The balance power capacity of Norwegian hydroelectric power stations can be increased by installing larger turbines and generators in some power stations, and by installing (reversible) pump turbines to pump water between two reservoirs. It will be necessary to build new tunnels in parallel to existing ones as well as new power stations in association with existing facilities.

The balance power capacity of hydroelectric power stations depends on how much power can be supplied during periods of shortage and how much power can be absorbed in periods of overproduction. Power can be absorbed if a power station can pump water up to a higher reservoir. In many power stations the capacity of the downstream reservoir will limit the amount of power which can be generated. Pumping at times of the day when the power demand is lowest (e.g. at night) will reduce the capacity restriction effect of the downstream reservoir. Such pumping will also increase the capacity of the upstream reservoir and the periods of power generation can be extended by pumping water back during the part of the day in which the power demand is lowest, to be used at the time when the demand is highest.

Implications for the operational schemes of the affected reservoirs when balancing wind power from the North Sea area are analysed. Based on time series of stage and live storage volume of the upper and lower reservoirs, balancing power on daily basis was simulated on top of the current operation of three existing power plants (Figure 1). The objectives were to compare the current patterns of water level fluctuations to the simulated patterns (season, frequency, rate of change) and to analyse which factors determine how much power can actually be balanced compared to how much is required to be balanced (turbine capacity, free reservoir volumes).This analysis is based on the results from a preliminary case study on large-scale balancing services from Norwegian hydropower (Solvang, Harby & Killingtveit 2012), showing the technical potential to develop 20,000 MW of new hydro where about 10,000 MW includes pumping.

The social acceptance of using Norwegian hydropower reservoirs for large-scale balancing services for Europe are analysed according to how these are expressed by key Norwegian stakeholders. Does this use of Norwegian hydropower have legitimacy, what are the drivers supporting this idea, what are the barriers, and what approaches are necessary to overcome important barriers, are the questions that is addressed. The analysis draws on an analysis of interviews with 22 informants, representing four interest groups, as well as the public authorities concerned. These interests include; energy companies, environmental NGOs, recreational NGOs, as well as the host communities. The interviews performed with the stakeholders focused on the how the idea of Norway as a provider of large-scale balancing services was considered by the different stakeholders in general, and not in relation to concrete projects. 

The issue of social acceptance may be understood in several ways. In this report we have chosen to use a broad interpretation which includes environmental and economic aspects, questions of involvement, as well as reflections on the current national framework’s ability to take key stakeholder considerations into account. The question of social acceptance is therefore treated as a question of societal acceptance.

The main drivers and barriers for large-scale exploitation of Norwegian hydropower for balancing services for Europe as expressed by the informants are presented according to each stakeholder group.

The timeframe in the current study is set to 2030 and beyond. At the same time it is necessary to pinpoint that the timeframe relevant for several of the key stakeholders is somewhat different. When reflecting upon the question of potential concerning the stakeholders' interests it is important to take into consideration that the question of time should be divided in to short, middle and a long term perspective. On the one hand the NGOs for example address the question of potential by directly referring to the political targets (2020 and 2050). On the other hand the companies (except Statnett who has 2030 as their timeframe) reflect upon the current political uncertainties – both nationally and internationally speaking – concerning political support for further investments in the national and international grid development, as well as for instance the unpredictability related to what is perceived as a time consuming concession process.

This article corresponds to the introduction of the report from a pilot study by Solvang et al (2015) that can be downloaded here on the "Download additional documents" section on the right. 

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