Hydropower plays an important role in the energy transition. It is a renewable energy source and contributes to reducing global emissions. In Switzerland, hydro provides nearly 60% of domestic electricity generation. According to Swiss government statistics, Switzerland is the fourth largest hydropower producer in Europe, behind Norway, Austria and Iceland.
Hydropower also plays a huge role in helping to balance the grid, by compensating for fluctuations in solar photovoltaic (PV) and wind energy generation, through pumped storage. Electricity is used to pump water into reservoirs at a higher altitude during periods of low energy demand. When demand is at its strongest, the water is piped through turbines situated at lower altitudes to produce electricity.
Environmental cost of large hydro plants
Some significant disadvantages are part and parcel of dealing with this age-old renewable energy. Large hydro projects are expensive to build with prohibitive capital costs. Another crucial drawback is the environmental cost of these large installations. According to Scienceinsights.org, most hydroelectric reservoirs require vastly more land per unit of energy produced than any other major electricity source. We all have seen TV reports of flooded land and villages when big dams were built. Most of the world’s hydroelectric capacity comes from these reservoir-based dams. Flooding an area of land can destroy both communities and terrestrial ecosystems. Scienceinsights reports that Brazil’s Balbina Dam inundated over 2 300 square kilometres of Amazon rainforest to produce a relatively modest amount of electricity.
The other environmental cost is to marine life – especially fish. Dams built on rivers stop fish from migrating. Salmon moving upstream to spawn in freshwater streams are prevented from doing so by dams – even if some of these have built-in passages to alleviate the problem. Dams can also affect water temperatures and cause fluctuations in water flow, both of which affect marine life.
What is small and micro hydro?
Pundits call small hydro systems “run-of-the-river”, and such installations generally do not involve a massive amount of energy storage. According to this paper from this supplier of equipment to small hydro facilities, run-of-the-river hydro systems use turbines that can operate on wide flow ranges generating energy on high or low river flows, whatever is in the watercourse at the time. However, some of the larger run-of -the-river hydro projects do operate with a river dam and can store a small amount of energy.
According to the Energy Education website, systems are classified as micro, mini or small depending on the amount of power they can generate at any given moment. Micro systems generate under 100 kilowatts (kW) of electricity while mini ones go up to 1 megawatt (MW), with small hydro systems reaching 50 MW.
But the classification of hydro projects does vary between different countries. Pierre Maruzewski is the Chair of IEC TC 4, the technical committee which develops standards for hydro turbines. He is also a hydro expert at France’s state-owned electricity company EDF. He has a different view of what constitutes a small turbine.
“In France, EDF classifies hydro systems as small if they generate 7 MW, and pico ones, 20 kW. In China or the US, hydro power plants are so much bigger that for them, 50 MW is small, but we don’t build hydro plants on the same scale,” he explains.
One of the advantages of micro systems is their cost. According to Energypedia, they can cost as little as USD 1000 and up to USD 20 000 to install, depending on the size, the location and the energy required.
Micro systems can power individual homes and even small communities. Their impact on the environment is negligible compared to the larger hydro systems. The only prerequisite is to have a river flowing nearby. However, seasonal variations need to be taken into account. River flows can drop during hot summers and generate less electricity. And permission must generally be sought from local authorities and environmental agencies before installation, which can take time.
Competing with solar PV for energy access in emerging countries
Market research company Coherent Market Insights estimates the global small hydropower market will be worth USD 300 billion in 2026. The same company expects it to grow to 3,77 billion by 2033, showing a compound annual growth rate (CAGR) of 3,5%. This includes micro systems, which it estimates will lead the market with a 61,1% revenue share of the market in 2026, due to “their compact design and scalability.”
Micro systems have huge potential for enabling energy access in developing countries, notably in sub-Saharan Africa, where off-grid systems enable rural communities to be provided with electricity. According to the International Hydropower Association’s 2025 World Hydropower Outlook, Africa more than doubled the previous three years’ development combined, commissioning 4,5 GW of new hydropower capacity in 2024. Hydropower already delivers 20% of total electricity on the continent, the report says, and there is huge scope for further development, with only a small fraction of the over 600 GW of the continent’s potential currently harnessed. The report mentions several large projects including the kick-off of Tanzania’s Julius Nyere project, the Grand Ethiopian Renaissance Dam adding 800 MW with its third and fourth units, as well as Uganda’s 600 MW Karuma and Cameroon’s 420 MW Nachtigal plants being fully commissioned. However, financing these large hydropower projects remains a challenge in Africa, despite the involvement of many private companies.
Micro hydro systems, on the other hand, can help to electrify regions and areas with little or no energy access and at a relatively low-cost, while being more reliable than other renewables. They compete, however, with solar photovoltaic (PV) projects.
Uganda is a case in point. As Winnie Grace Onziru, who is a Senior Standards Officer at the Uganda National Bureau of Standards, explains: “Most of our grid supplied energy comes from hydropower. It therefore made sense to look at small and micro hydro tech for off grid projects as well, and several were set up across the country.”
But, Onziru says, most of the rivers used for these small and micro projects dried up during recent terrible draught episodes in Uganda: “So the government decided to switch to solar PV. The main criticism of solar PV energy, in the beginning, was its lack of energy efficiency: you had to cover one roof with solar panels to get only enough energy for lighting! But technology has vastly improved since then, with thin film developments and other advances, which means solar panels are now the preferred option in Uganda for rural electricity access.”
According to Pierre Maruzewski, small and micro hydro projects show huge growth potential, not only in emerging countries but in Europe as well, France being a typical example. “Of all the hydro projects we have installed in the country, more than half – 237 to be exact – are small hydro installations. And we expect this segment of the market to grow even further in the future. That’s why we set up a specific unit inside EDF to deal with small hydro.
What standards for small hydropower?
IEC TC 4 has set up a working group to standardize small hydraulic turbines. The group is working on the maintenance of IEC 62006 which specifies acceptance tests of small hydroelectric installations. The standard applies to installations containing impulse or reaction turbines with power per unit up to about 15 MW. The same experts are also working on the revision of IEC 61116, which is a guide for the electromechanical equipment of small hydroelectric installations. It applies to power stations which have outputs of less than 5 MW and turbines with diameters of less than 3 metres.
“We work closely with ISO TC/339 which develops standards for the planning and design of small hydro installations. We have formed a joint working group with the TC and they reference our turbine standards and we reference theirs,” Maruzewski explains.
As the pressure to meet our zero emission targets intensifies, small hydro is a low-cost, environmentally friendly, fairly flexible and renewable option that is gaining increasing traction.
Author: Catherine Bischofberger
The International Electrotechnical Commission (IEC) is a global, not-for-profit membership organization that brings together 174 countries and coordinates the work of 30.000 experts globally. IEC International Standards and conformity assessment underpin international trade in electrical and electronic goods. They facilitate electricity access and verify the safety, performance and interoperability of electric and electronic devices and systems, including for example, consumer devices such as mobile phones or refrigerators, office and medical equipment, information technology, electricity generation, and much more.
The views and opinions expressed in this article are the author’s own, and do not necessarily reflect those held by pv magazine.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.
By submitting this form you agree to pv magazine using your data for the purposes of publishing your comment.
Your personal data will only be disclosed or otherwise transmitted to third parties for the purposes of spam filtering or if this is necessary for technical maintenance of the website. Any other transfer to third parties will not take place unless this is justified on the basis of applicable data protection regulations or if pv magazine is legally obliged to do so.
You may revoke this consent at any time with effect for the future, in which case your personal data will be deleted immediately. Otherwise, your data will be deleted if pv magazine has processed your request or the purpose of data storage is fulfilled.
Further information on data privacy can be found in our Data Protection Policy.