The increasing deployment of intermittent renewable energy technologies has led to the need for additional energy storage capacities. Therefore, the governmental facilitation of renewable energy technologies (RETs) should not only focus on the quantity of energy produced (i.e. kWh), but should also include “quality” aspects. These include the alignment between production and the actual electricity demand thanks to storage facilities and flexible production.

This research evaluates the potential of small hydropower (SHP) to contribute towards energy storage and flexible electricity production. The technical potential and the institutional feasibility of small storage and pumped-storage schemes (<10 MW) were analysed in the case of Switzerland. Such schemes can be developed on streams and within infrastructures.

Energy storage with small hydro power

The electricity sector is undergoing significant changes. Firstly, the current liberalisation process is one major institutional change which leads to the unbundling of the previously vertically integrated network. This favours the development of distributed and small scale power production.

Secondly, many governments are aiming to increase the electricity production from RETs. In Switzerland, the energy policy includes a RET target of at least additional 5.4TWh by 2030 compared to 2000 (the production in 2010 was 66.3TWh; see Figure 1). One of the enabling measures towards reaching this target is the facilitation of hydropower, including SHP. In the light of political decisions after the Fukushima accident, such as the phase out of nuclear power in Switzerland, the facilitation of RETs will even further increase, along with additional measures concerning energy efficiency.

Thirdly, at the regional and local level, initiatives such as the “Covenant of Mayors” lead to increasing RET electricity demand from cities. The “Covenant of Mayors” involves over 3’500 local and regional authorities (February 2012) who voluntarily commit to increasing energy efficiency and the use of RETs on their territories. By their commitment, Covenant signatories aim to meet and exceed the EU 20% CO2 reduction objective by 2020. Several Swiss cities joined the covenant.

Finally, ICT developments enable new applications in the electricity sector which may lead to a more decentralised functioning of the electricity grid (e.g., “smart grids”).

These changes lead to significantly more RETs feeding into the grid in a distributed, and, for some sources, in an intermittent way (e.g. wind power and PV). This leads to the need for more storage capacities to operate the electricity grid [1]. These storage capacities can be developed at the large scale level, as well as at the small scale level.

The RETs facilitation should therefore not only consider quantity of electricity production, but, in order to deal with the intermittency, should also include energy storage and flexible production. Therefore, there needs to be adequate facilitation of RETs which can contribute towards this.

Among the institutionally facilitated RETs (e.g., feed-in remuneration in Switzerland), SHP is the only technology that can produce with flexibility and provide energy storage in the case of storage or pumped-storage schemes. Storage and pumped-storage hydropower remains one of the most efficient technologies to “store” electricity with low GHG emissions and a renewable resource. Small scale schemes have a local and regional importance for operating the grid and are complementary to the large scale schemes. In the case of Switzerland, the latter have a national and continental importance in line with the role of electricity hub that this country holds in Europe. Significant potential remains for large pumped-storage schemes and some new plants are currently under construction. In the case of SHP, the potential of storage and pumped-storage schemes had not been evaluated before this research, neither the necessary evolution of the institutional frameworks to facilitate such schemes.

Technical potential

In Switzerland, SHP is defined by an installed capacity of up to 10MW. In 2010, SHP produced 3770GWh and covered 5.7 % of the Swiss electricity production (see Figure 1). Current estimates suggest that SHP could generate an additional 1200GWh by 2030. The Swiss institutional framework for SHP is very complex. SHP is not only affected by cross-sectorial regulation (e.g., within the water and energy sectors, spatial planning), but also has to develop within a multi-level governance framework (i.e., Federal, Cantonal and Communal level). The latest major development was the introduction of the feed-in remuneration (FIR) in 2009. In January 2012, 245 SHP plants were financed through the FIR producing 484 GWh.

SHP plants with storage capacities and, where feasible, pump capacities, can be built on streams and within multipurpose infrastructures such as artificial snow making and irrigation networks (increasingly needed due to climate change). In 2010, there were three pumped-storage SHP plants and 18 storage SHP plants in Switzerland (see Table 3). In this research, installed capacities between 0.3-10MW were considered.

The technical potential was evaluated by looking primarily at existing and already planned reservoirs to reduce environmental opposition and investment costs. The methodology was bottom-up and explorative. The Canton of Valais was chosen as the unit of evaluation as it has still considerable potential for SHP based on the newly FIR projects. Firstly, reservoir options were identified with which storage and pumped-storage SHP schemes could be constructed (see Table 1). Based on the most promising reservoir options, some reference types were defined as shown in Table 2. A brief technical evaluation was conducted for each type, followed by identifying some reference cases which were evaluated in more depth, including some economic evaluation (e.g., estimates on installed capacity, production, costs and required remuneration to enable economically viable projects). 11 reference cases were identified (see Table 2). Some of these reference cases offer the opportunity for further development (i.e., pre-feasibility or feasibility study). Based on the reference cases and the brief evaluation for each reference type, the technical potential for the Canton of Valais was evaluated. The results were extrapolated for the whole country based on different criteria (e.g., geographical and demographical, and based on existing and planned SHP plants) and the rule of proportion. Table 3 shows the results for Switzerland compared to the existing plants. In 2010, SHP accounted for about 6.3% of the hydropower installed capacity. However, for storage schemes SHP accounted for only 1.3 % of the installed capacity and for pumped-storage schemes even less with 0.7%. There is potential to increase these figures.

The storage scheme potential lies mainly with SHP on streams. Storage schemes can hold back their production while intermittent RET plants cover the demand. The pumped-storage scheme potential is held in various infrastructures and lakes. The aim is to add value to infrastructures by using them for multiple purposes. During the period when water is stored but not used for its final purpose (e.g., snow, irrigation), it can be used within closed systems for pumped-storage.

The storage and pumped-storage SHP potential is even more important if installed capacities below 300 kW per project are considered. Should it become technically possible to automatize completely micro hydropower plants between 20-100 kW, then such plants could also play a role within decentralised electricity services. This offers a field for further research.

The potential must be compared to large storage and pumped-storage hydropower. For example, should the whole pumped-storage SHP potential be constructed, it would only equal the size of the second biggest existing pumped-storage plant in Switzerland. Furthermore, if large pumped-storage schemes presently under construction are considered (e.g., Linthal 2015, Nant de Drance) which are designed with capacities around or above 900 MW, then the debate leads to whether to build storage and pumped-storage SHP schemes at all or of whether to add another large scale project. However, small and large scale plants are not in competition, but complementary. Large scale schemes are built with an international perspective of operation (e.g., European super grid), whereas small scale schemes should be built with a regional perspective and so-called “smart grid” developments. Energy storage and flexible production will be required at the regional level to integrate important amounts of distributed and intermittent electricity production.

Institutional feasibility

The institutional feasibility was studied mainly by looking at the possible remuneration instruments (e.g., financial incentives). The administrative procedures remain the same as for SHP in general. More research is needed on dynamic residual flow to allow more flexible production, as well as on the environmental aspects. For the latter recommendations developed for large hydropower can be adapted and applied. The methodology was qualitative through 19 semi-structured expert interviews and a survey send to all SHP operators which received the FIR in 2010 (190 responses).

For the remuneration instruments, one must differentiate between storage and pumped-storage schemes. The latter can only be part of RET policies if the pumping energy comes from RETs. Otherwise they have to be operated as traditional pumped-storage schemes or differentiate between the production coming from natural inflows (i.e. renewable) and pumped water (i.e. not renewable).

The economic estimates of the reference cases show that in the case of storage SHP with existing or planned plants, the additional production costs to include the storage facilities are of a few € cents/kWh. In the case of the pumped-storage schemes, the spread between the pumping and turbining would have to be 0.10 – 0.15 €/kWh to cover the additional costs linked to the pumped-storage facilities.

It was not the scope of the research to compare the different instruments below, but to identify and develop the most promising remuneration instruments which would facilitate the economically viable implementation of storage and pumped-storage SHP. Except for the Czech Republic and Portugal, SHP producing peak electricity is not yet considered within the institutional frameworks facilitating RETs [4, 5]. In Switzerland, storage and pumped-storage SHP schemes can sell their electricity on the sport market or within current ancillary services markets. However, for the former the price difference between peak and off-peak is too low (except in certain cases and if several SHP plants are regrouped to a virtual plant), and for the latter the remuneration for tertiary control reaches only about half of the current FIR. Table 4 shows the identified new and adapted remuneration instruments.


The technical potential of storage and pumped-storage SHP in Switzerland is important as shown in Table 3. The technical potential of storage schemes lies mainly with plants on streams. With the introduction of the FIR, the number of such plants will continue to increase and thus offer opportunities for storage applications as well. The technical potential for pumped-storage schemes is found mainly within existing and planned infrastructures (e.g., artificial snow making, irrigation) and lakes. The technical potential is important enough to develop some policy recommendations concerning further shaping of the institutional framework in order to enable economically viable storage and pumped-storage SHP schemes.

The institutional feasibility depends mainly on the introduction of adequate remuneration instruments which should be included within the institutional framework facilitating RETs. The RET facilitation should not only focus to increase the quantity of renewable electricity production, but focus also on flexible production thanks to storage capacities. Storage and pumped-storage SHP schemes fulfil this requirement.

Nicolas Crettanand, Candidate, MSc Civil Engineer EPFL, Chair of Management of Network Industries (MIR) and Energy Center (CEN), Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 5, 1015 Lausanne, Switzerland. Email:

The author thanks EOS Holding (Switzerland) and the Energy Center at EPFL for the funding of the PhD research.

This article is an updated version of a paper presented at the International Conference HYDRO 2011 in Prague in October 2011.


Table 1
Table 2
Table 3
Table 4