Creating the ultimate hybrid system by mixing solar energy and hydroelectricity

Bernard Prouvost

Compared to its traditional solar counterparts, floating photovoltaic (FPV) allows standard solar panels to be installed on dead water spaces to maximize utility of resources, addressing potential conflicts in areas such as food vs. fuel on land use.

Solar energy has become much more accessible and affordable, making it extremely competitive to oil and gas. Prices have dropped significantly in previous years, allowing consumers to see a greater return on investment for solar energy. This opens up doors for individuals, private businesses and public utilities alike to seek long-term solar options. Unlike more popular choices, like rooftop and ground mounted solar, floating PV is quickly catching on as a third alternative to traditional solar especially amongst resource intensive industries.

Compared to its traditional solar counterparts, floating photovoltaic (FPV) allows standard solar panels to be installed on dead water spaces to maximize utility of resources. Valuable resources like land can then be solely used and dedicated to their industry i.e. for agricultural use in the case of “Food vs. Fuel”.

FPVs are now being combined with existing hydropower dams to create powerful energy generating hybrid systems, which will create a new renewable energy market to generate more energy, answer peak loads demand, increase economical benefits and also solve environmental issues. With the help of FPVs, mutually exclusive renewable energy sources, solar and hydropower, can now be combined into a more powerful source of synergy.

Floating solar as a third alternative

Floating solar is the latest green-tech and real alternative solar option that has been catching on worldwide. Currently there is more than 100 MWp of floating solar power installed globally, and is expected to climb to 5000 MWp by the end of 2017. Japan was the first country to adopt the solution because of its ability to conserve precious land and water. Now, FPVs have been implemented all over the globe in countries including: South Korea, China, UK, France, Brazil, Singapore, Malaysia, Italy and the United States.

Installation of FPVs can serve self-consumption by private or public entities, but has been especially valuable for energy and water intensive industries such as water treatment plants and reclamation facilities, wineries, and dairy farms that cannot afford to waste resources. Electricity generated by FPVs can also be fed back into the grid and sold to local electric utilities. The technology allows standard solar panels to be placed on top of man-made bodies of water such as industrial water ponds, quarry/mine lakes, irrigation reservoirs, retention ponds, drinking water surfaces, water treatment sites, aquaculture farms, desalinization reservoirs, canals and dams.

Installation is quick, simple and requires no heavy tools. The assembly of the floating structure happens offshore where the five main components are put together to create a floating island. The main float, which supports the 60 or 72 PV module, are attached to the secondary float, which maintains the buoyancy of the entire floating system, and are connected like Lego pieces with the connection pin. The modular floats are then lined up in rows where the secondary floats also provides the appropriate amount of spacing between each PV panel and also doubles as maintenance alleys. After assembly offshore, the floating structure is then pushed out and anchored to the side of the banks or onto the bottom of the body of water.

The anchors are the most important part of the installation process, so it is especially important to take into account all environmental impacts and hazards the floating structure may incur. Therefore, each anchoring system is adapted to each individual site with consideration to wind speed, water variation and ground soil composition to determine where to install the anchors. Then environmental hazards like wind, snow and rain are also taken into account for long-term durability. The design of the structure must prioritize the impact of wind variation as wind speeds test the structure’s integrity the most. With consideration to these factors, the anchors are able to withstand the worst-case scenarios and provide a long lasting solution.

Floating PV systems are cabled in the same way as ground mounted systems, except that the junction boxes (NEMA 4 X minimum) mounted on the floating arrays are connected to on-shore inverters using either a flexible marine DC cable or normal DC cable protected in an adapted waterproof and sealed floating conduit. The main electrical equipment is located on the embankment for easy and safe maintenance at all time.

Overall, floating solar creates a new use for the surface area of commercial and industrial bodies of water. In addition to the direct benefits, floating solar systems bring an array of environmental benefits. By covering a significant surface area on a body of water, the system conserves water by reducing evaporation and preserves existing ecosystems. It also improves water quality, while the shading of the panels reduces algal bloom. Lastly, it limits erosion of reservoir embankments by reducing wave action.

Thanks to the natural cooling effect of the water, PV panels operate much more efficiently and produce more power than traditional ground-mounted systems, thus providing enormous environmental, economic and social benefits. With a vast amount of untapped water resources, it is important to explore areas where floating solar can be used to double the amount of energy generated. So by taking advantage of the versatility floating solar provides and combining it with hydroelectric dams, entering this new marketplace optimizes power storage solutions as the cheapest way to store power using only renewables. 

Challenges hydroelectric dams are currently facing

According to the Renewable Energy Policy Network for the 21st Century, by the end of 2015, renewable capacity supplied an estimated 23.7% of global electricity, with hydropower generating about 16.6% of the world’s total electricity and 70% of all renewable electricity. Similar to solar power, the cost of hydropower is relatively low, making it a competitive source of renewable electricity. Although hydropower continues to provide the majority of renewable power capacity and generation–1064 GW as of 2015–the industry faces many challenges.

Persistent droughts have affected hydropower output in many regions, including the Americas and Southeast Asia, while investment and construction for new hydropower dams in more thriving areas have fallen due to heavy environmental impacts. Thus, climate risk and rise of variable renewable power are driving adaptation in the hydropower industry. Responses have included an increased emphasis on co-implementation of hydropower with solar and wind power.

Advantages & benefits of a hybrid hydroelectric and FPV system

Thus, establishing a synergy between hydroelectric dams and floating solar to generate even more energy. The hybridization allows panels to produce solar energy during the day while saving water for hydroelectricity to complete during intermittent times when the sun goes down. When water storage is possible, it also allows high-value hydropower to be produced at peak demand time.

Another great advantage when installing floating solar power on a dam is the benefit of using existing electrical infrastructure, including high voltage grid access and transformation devices. This drastically lowers the overall capex costs and makes projects happen quicker. Since solar and hydropower are smartly hybridized, exporting either solar or hydroelectricity according to the hour of the day, it is not necessary to augment transformation or transport capacity if the maximum peak output of the solar array does not exceed the maximum hydro peak capacity.
Dams seldom reach a full power production ratio over 4,000 hours per year, and often have a much lower ratio, leaving a large opportunity for energy generation to complete the grid output with solar.

Soon, investors in large solar plants will be confronted with a new financial issue where regulation boards will impose them to cope the intermittency problem by installing storage systems, mainly batteries. These storage systems, even if prices are decreasing, remain very expensive. Storing only one hour of peak power raises the capex price of a solar plant by 50% (with consideration to the cost of the solar plant equal to $800MWp, and cost of a 1MWh battery system equal to $400) For a hybrid dam FPV plant, the reservoir is the battery, and so the extra cost of storage is saved.

This completely renewable energy system was just perfected in Portugal at the Alto Rabagão Dam. Located in Montalegre, Portugal, it is the world’s first hybrid FPV and hydroelectric dam power plant system. With a total capacity of 68MWp, the dam adds an additional 220 kWp through the floating PV installation. The installed 840 floating PV panels is expected to generate 332 megawatts per hour in its first year—equivalent to the annual consumption of around 100 homes. This array will be extended as soon as the first results are computed.

The location of the Alto Rabagão dam, built in the 60’s presented new technical challenges due to the water variation and depth. The operator EDP, that operates the pumped-storage hydroelectric power plant on the 94 meters tall wall of the dam wanted confidence that the floating system would not create any possible conflict of use with their asset even in case they have to have an emergency drawdown of the water. Following those conditions, the floating solar array has been designed and was moored at more than 60 meters in depth, while dealing with a water level variation of 30 meters.

After success at the Alto Rabagão Dam, another experiment will start in Brazil, at the Balbina Dam, in Amazonia state, with an initial 5 MW peak capacity. The Balbina Dam currently suffers from drought issues, sedimentation, and high greenhouse gas emissions because of the drowned forest. By adding solar energy, it could easily double the total power of the dam to 250 MWp, by covering less than 1/1000th of the lake surface.

Future projections for floating solar in other hybrid systems

Dams have several purposes: providing electricity of course, regulating the river flow and supplying water for irrigation. Water for irrigation is extremely valuable, because uses are endless, mainly for agriculture, the largest water user at global scale accounting for around 70%. Therefore, future trends are heading towards a higher need of water for this purpose. If power capacity is increased with the addition of a solar plant, then the dam managers will be able to allow more water for irrigation.

Also, any dams equipped with a pumped storage with a double reservoir (PHES) are placed in an even better situation for solar hybrid systems. During the sunny hours, solar electricity can be, without export limitation, used to raise water in the upper reservoir to provide power capacity in the evening or during cloudy periods.  Reservoirs are usually much smaller here in those facilities, however they are still large enough to generate a significant part of the required pumping power.

About Ciel & Terre International
Established in 2006 as a renewable Independent Power Producer (IPP), Ciel & Terre International has been fully devoted to floating solar PV since 2011. The company pioneered the first specific and industrialized system –named Hydrelio® to make solar panels float on water, with criteria such as cost-effectiveness, safety, longevity, resistance to winds and waves, simplicity, drinking water compliance and optimized electrical yield. To date, floating solar projects have been implemented by Ciel & Terre in countries including Japan, Korea, China, UK, France, Brazil, Singapore, Malaysia, Italy, and the United States with demo systems in California and the University of Central Florida. With more than 60 MWp of solar PV power production currently utilizing the Hydrelio® system, Ciel & Terre will expand to 130 MWp of floating solar by the end of 2017.


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Other marine energy and hydropower  •  Photovoltaics (PV)  •  Policy, investment and markets  •  Solar electricity  •  Solar heating and cooling  •  Wave and tidal energy


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