Study reveals potential of hydropower dams topped with floating solar

Study reveals potential of hyd...
The first floating photovoltaic park on the dam of the River Rabagão, Portugal
The first floating photovoltaic park on the dam of the River Rabagão, Portugal
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The first floating photovoltaic park on the dam of the River Rabagão, Portugal
The first floating photovoltaic park on the dam of the River Rabagão, Portugal
Hydropower plants could be complemented by floating solar power systems
Hydropower plants could be complemented by floating solar power systems

Hydropower plants that leverage the force of falling water to generate electricity are already an important part of the global energy mix, but a new study suggests they may have much more to offer. Scientists have carried out an analysis of the energy potential of combining these facilities with floating solar panels, calculating these hybrid plants could meet a “significant” portion of the world’s current electricity needs.

The analysis was carried out by scientists at the US Department of Energy’s National Renewable Energy Laboratory (NREL), who looked at the freshwater hydropower reservoirs currently installed across the world and their potential to accommodate floating solar photovoltaic panels on the water’s surface. These systems could be retrofitted to allow solar power to be generated during the day, while the hydropower systems store up water and energy for use during peak demand periods.

As it stands, this kind of hybrid floating solar/hydropower system has been installed in only one location, as a pilot project in the dam of Portugal’s River Rabagão. It is made up of 840 solar panels covering 2,500 square meters (27,000 sq ft) and has an estimated energy production capacity of 300 MWh. Energy provider EDP is planning to expand on this pilot project with an 11,000-panel floating photovoltaic system at the Alqueva hydro power plant, one of the largest energy storage facilities in Portugal.

According to the new analysis from the NREL, this is very much just scraping the surface of what these systems could offer. The team estimates that there are almost 380,000 other hydropower reservoirs around the world that could be fitted with these floating photovoltaic systems.

Hydropower plants could be complemented by floating solar power systems
Hydropower plants could be complemented by floating solar power systems

These would hook up to existing substations used by the hydro plants and could produce up to 7.6 TW of power annually, or up to 10,600 TWh each year, not including the energy coming from the hydropower facilities already in place. This is a monumental figure, considering that electricity demand for the entire globe was just over 22,300 TWh in 2018, the researchers say.

The study is much more a way to highlight the potential of this almost non-existent energy solution than a roadmap to implementing it. The researchers say further work would be needed to assess the sites, as some may be dry at certain times of the year or there may be other factors that may make them unsuitable for floating photovoltaics, but even as a ball-park figure the finding is promising.

“This is really optimistic,” says Nathan Lee, lead author of the paper. “This does not represent what could be economically feasible or what the markets could actually support. Rather, it is an upper-bound estimate of feasible resources that considers waterbody constraints and generation system performance.”

The research was published in the journal Renewable Energy.

Source: National Renewable Energy Laboratory

As the graphics hint, wind generators would be a good fit too; presumably the utilities own some of the land surrounding a dam, and these are often wide open spaces for good wind velocity.
This is a fantastic idea, assuming that the ecosystem within the reservoir isn't adversely affected. The problem of dry times seems less important to me - wouldn't the 'rafts' just sit on the dry banks and continue to give power until the water filled again? If the topology of the flooded valley was an issue, could the rafts be strung together so that they hung over the water at low times? Given the amount of wide open surface that reservoirs have, this has to be a great choice to maximise the output from something that may have cost a great deal in terms of displaced homes and real estate.
These rafts could be used to replenish reservoirs with downstream water in dry times. That way,the dams could continue to supply power,although at a reduced rate. There are already power storage systems that use excess power to pump water to elevated reservoirs to supply peak power demands.
Not mentioned in this short article is the reduced evaporation from reservoirs which is a big issue for reservoirs in arid climates such as the US Southwest. Also notable is the cooling effect on the PV panels which provides a marked increase in power production. NREL has been pursuing this for some time:
In Brazil, a floating unit with 11,000 m² has been in operation since 2019, in the Sobradinho dam reservoir.
Nelson Hyde Chick
The solar arrays would also reduce evaporation of the Dam's water.
Another consideration is that these would also reduce valuable water evaporation.
Aside from providing electric solar power, and perhaps lessening the evaporation of precious water as well, could these floating units be retrofitted, with small windmills to make more electrical power? I think that there is a type of ocean buoy, used to provide electric power for deep sea research depots, with that feature already. If mounting heavy electric generators into the small windmills, would not work in this instance, the mini-windmills could empower lightweight air pumps, to force air through a network of hoses, to a collectively-shared big turbine outside of the dam reservoir, to propel a big heavy generator there.
i believe solar panels would also cool the water in the reservoir...might be good for fish!
I like the idea of floating PV rafts, during the heat of the day the reservoir water may mediate the PV efficiency reduction, and as said in many posts, even reduce evaporation over one portion of the reservoir. But during the night they are useless and the dam must provide for demand. Are engineers considering limited refill of the reservoir during high PV production?

I know that caliber of pumping requires huge capital outlay. Most dams are built while bypass channels carry the water - could those bypass channels be retrofitted and used as part of the refill process? These types of "mechanical" batteries are brilliant, but would they be practical? At least the rafts are and the increased MW production during the heat of the day would be welcome.

Fascinating article. Good writing Nick.