Hydropower plants were often constructed as a supplementary facility to the hydro-technical objects built to protect surrounding land from floods as well as to increase water resources via construction of water storage reservoirs. When comparing to other renewable energy sources water energy has quite low efficiency. According to GUS, Poland's statistical office, the share of energy from renewable sources in Poland is about 12%, with the EU average of 16% in 2015 (Fig. 1). By 2020 it is planned to increase this share to 15% and 20% respectively. In both cases, the most important renewable sources are biofuels (EU 44%, Poland 72%), while hydroelectricity has second place in the EU (14%), in Poland it has a marginal share in the total of renewable energy - only 1.8% in 2015 (Fig.1). Despite the growing share of renewable energy in recent years, neither the number of hydropower plants nor their share in energy production has risen, it has slightly decreased from 2.7% in 2011 to 1.8% in 2015, mainly driven by rising the importance of wind energy (Fig. 1).
The theoretical hydrotechnical potential for Poland is estimated at about 23TW, of which up to 16.5TW belong to the Vistula river and its tributaries, while the Odra river and its tributaries are estimated to be 6TW. The technical capacity, which already includes existing hydro facilities, currently not used or not equipped, is estimated at 12TW/year. The most popular in Poland are small hydropower plants (called also 'small hydro' or in Polish 'MEW'), with capacity not higher than 10 MW. There are only few bigger ones, such as Żarnowiec (680 MW) or Porąbka-Żar (500 MW). Mini hydropower plants, with capacity between 300 kW and 1 MW, are usually dedicated to smaller communities or small businesses.
There are about 750 small hydropower plants in Poland currently, with a majority of about 600 being units of low power (less than 10 MW) with a total energy production from water of 1.8 TWh. This is only a small part of all the facilities that operated in the country in the 1950s, however those units had much less power than it is possible to obtain nowadays using current technologies. This indicates that the potential of the Polish hydropower industry is still not being fully exploited and may be a chance for small and mini hydropower plants. In Poland there are thousands of historic mills, water wheels, inoperative hydropower stations, weirs and other lateral structures in rivers (even 6,000 objects in full use).
As a result of not reaching this full potential, in 2015, a database called RESTOR Hydro was compiled and proposed for Poland. RESTOR Hydro (Renewable Energy Sources Transforming Our Regions) is an European project aiming at increasing renewable energy production from small and mini hydropower plants. Poland is represented in this project by Polish Hydropower Association, founded in 1991.
The database consists of a broad selection of potential small hydropower sites, based on their historical location, considering environmental conditions and flows in watercourses. The database includes such attributes as: estimated average flow, historical purpose, current technical condition, information on environmental restrictions and protection of historic buildings as well as distance from the closest power grid. What is important, the energy capacity of those objects is mostly suitable for small and mini hydropower plants.
When analysing the history of water power usage in Poland, repowering sites, which are currently not in use, could result in generating extra hydroelectric power for local use and hopefully for supplying the electric grid. This, simultaneously, leads to increase in the electricity production from renewable sources, energy independence and grid stability as enhancing energy supply security is an important factor. The creation of local energy sources gives new opportunities to local economy, as well provides financial income and creates jobs opportunities.
From the environmental point of view, small and mini hydropower plants are usually seen to have a relatively low environmental impact when comparing to large hydropower plants, even considered as environmentally sustainable, although this is not fully realistic view. The most significant environmental impact is that hydropower plants change the stream regime. Small and mini hydropower plants are located on medium- and small-sized rivers and streams, usually organised as a cascade system. Densely located facilities results in controlled outflow, influenced low environmental flow under drought conditions, water overheating during heat wave, reduction of oxygen, sediment deposition and accumulation within the plant’s reservoir, as well as can lead to pollution with toxic substances. The result of water storage for the purposes of hydropower production, as well as outflow regulation, constitutes pressure on water ecosystem, like disturbances of the river's biological balance and impoverishment of the aquatic ecosystem. Dams and other constructions drastically impede fish migration by fish passages (migration is a vital function of aquatic organisms). Hydropower plants, at the same time, play an important role in water management systems. Reservoirs increase surface and groundwater retention abilities. Outflow regulation has a positive impact on water erosion and decrease of sediment transportation, which helps to protect river corridor and maintain its stability.
Regardless all positive and negative impacts of small or mini hydropower plants on the environment, from the economic point of view success of water energy production depends on the water stream capacity, thus the structure of river network in Poland, from supply position, does not enhance the energy production as more than 95% of surface water is supplied by precipitation. only small fraction of water is fed to Polish river network from outside of country, mostly by Odra (south) and Bug (east) rivers. As a consequence, the volume of country’s surface waters strongly depends on atmospheric supply and retention from previous seasons. Due to Poland's moderate climate conditions, precipitation varies in time and amount, changing seasonally and yearly. Long-term prediction is difficult as weather extremes can be observed year after year. This situation results in an instability of water resources, which translates directly into the working conditions of hydropower plants. Moreover, climate models show mostly that future condition for atmospheric supply will rather not be stable. Results predict that snow will decrease while rain will change its frequency to more short but intense episodic downfalls. That would rather suggest that even for the same total amount of precipitation there is a high risk of drought occurrence, especially when mean temperature is already increasing.
Mott MacDonald Poland had recently developed several projects in the field of water management and water protection. Especially within the last two years the company has been actively contributing in environmental water programmes dedicated to diagnosing the drought risk and its environmental and social impact. The drought impact in Poland has become more significant over the past two decades. Due to the drought impact on water volume and water temperature, the crisis of surface water resources is visible and noticeable, especially for small hydro plants. The 2015 can be considered as significant as power plants, located in the area of south Poland, were closed due to a lack of water supply and too high water temperature linked to the heatwave of that summer.
Mott MacDonald believes that Poland has an under-used natural potential to produce energy from renewable sources, with water being an important source. Hydropower plants have an impact on the natural environment, yet current technologies allow us to gain potential profits from currently unused hydropower plant sites to achieve sustainable development for both nature and society.