The combination of solar power and water is in use around the world, with various solar arrays placed on lakes to provide renewable energy from the sun. However, a project in Portugal has found a new way to integrate solar energy and hydropower. The premise: expand the generation capacity of hydropower facilities by adding floating solar panels that are integrated with the existing hydro plant, eliminating the need for expensive dam reconstruction.
The Alto Rabagão dam in Montalegre (Figure 1), in northern Portugal near the border with Spain, is the site of the world’s first hydro-solar power station, or “hydro-plus-PV” project. The water near the dam is outfitted with 840 floating solar panels, or floating photovoltaic (FPV), covering about 2,500 square meters. The project came online late in 2016 but was not dedicated until July 2017. The system is a 220-kWp power plant equipped with a Hydrelio FPV system developed by Ciel & Terre International, a French company specializing in floating solar projects. The dam is managed by Energias de Portugal (EDP Group), which expects the project to generate 332 MWh annually.
Paulo Pinto de Almeida, EDP’s CEO and the project’s manager, told Portuguese media that the integrated solar-hydro project “has all the ingredients to succeed.” EDP envisions the system being used in many locations, including Brazil, where EDP has operations under EDP in Brazil, a 51%-owned subsidiary. More than 70% of Brazil’s power generation comes from hydropower plants, and the Brazilian government has forecast power demand will triple by 2050.
The Portuguese government says about 60% of Portugal’s power annually comes from renewable sources, though there have been short periods of much-greater renewable output, including in May 2016, when all of the country’s electricity came from renewable sources for a four-day period. The largest hydroelectric plant is the 630-MW Alto Lindoso dam, and the country has about 100 small hydro projects, with a generation capacity of 256 MW. By comparison, hydropower accounts for 6.5% of U.S. power generation, according to the U.S. Energy Information Administration.
Alto Rabagão is the first project where floating solar panels work in tandem with the dam’s hydroelectric rotors. It differs from other hydro-solar projects, in which power generated from floating solar panels is not integrated with hydropower. Other projects in the same vein are being considered: India’s government-run National Hydroelectric Power Corp. (NHPC) is working on a 600-MW PV project at its 1,960-MW Koyna hydroelectric plant (four dams) in the Satara district of Maharashtra. That FPV would be combined with pumped hydro storage.
The Alto Rabagão dam opened in 1964, and its standalone generation capacity is 68 MW without the solar panels. The water near the dam is about 200 feet deep. The project has additional benefits for the area; the panels partly shield the water, slowing evaporation and algae growth. The panels also reduce wave action in the reservoir, which lessens erosion on the shore.
EDP, which operates the pumped-storage hydroelectric power plant at the dam, wanted to ensure that the FPV would not interfere with any of the existing operations at the site, where the power plant sits on top of the 308-feet-tall dam wall. EDP considered the possibility of an emergency drawdown of the reservoir’s water and had the floating solar array moored at a depth of more than 60 meters, or about 200 feet.
EDP said the solar generation at the dam will help at times of increased demand for power in the region, such as late afternoon or early evening when people arrive home from work. Ciel & Terre said it developed its Hydrelio system for installation in a variety of bodies of water, from larger reservoirs to lakes, or for use in irrigation canals or remediation or tailing ponds.
The company first tested its system at a pilot project in France in 2011, and today it says it has more than 75 FPV systems in place in 16 countries. The company also has started construction on what will be the world’s largest floating solar plant, a 70-MW installation in China’s Anhui province for China Energy Conservation and Environmental Protection Group, a renewable energy project developer in China. The installation is scheduled to be finished in 2017, using 194,000 PV modules divided among 13 floating arrays.
Japan was the first country to bring FPV online in 2013, but the renewable energy option has since been implemented in several countries. The world’s largest FPV farm came online in June of this year in China, a 40-MW system on a lake near Huainan. The world’s now-second-largest project came online in 2016; the 6.3-MW Thames Water solar farm sits on the Queen Elizabeth II reservoir outside London, near Heathrow Airport.
FPV systems are cabled the same way as ground-mounted PV systems, except that the junction boxes on the floating arrays are connected to onshore inverters via a flexible marine direct current (DC) cable or normal DC cable, which is protected in a waterproof, sealed, floating conduit. The main electrical equipment is located onshore. Floating PV panels usually operate more efficiently, and can produce more power, than ground-mounted solar arrays due to the natural cooling effect of the surrounding water.
—Darrell Proctor and Sonal Patel, POWER associate editors.