Energy developers have begun to pepper hydropower dams with solar panels, and some interesting twists are already beginning to bubble up in that area. In Germany, the company Vattenfall is adding pumped hydro energy storage to the mix. And, if a team of US researchers has their way, rafts of floating solar panels will enable Brazil to avoid building new hydropower dams.
Energy Storage + Hydropower + Solar Panels, Too
If you’re wondering why solar panels need to piggyback on hydropower dams when so much other land is available, that’s a good question. Part of the answer is that so much land is not necessarily available, due to conflicts with farming, valuable habitat, and other uses. Other limiting factors include access to transmission lines, electricity markets, and transportation infrastructure.
These issues are generally not in play where existing hydropower dams and other water infrastructure are concerned. Solar panels can be installed on the built infrastructure, or floated onto the water surface. Hydropower dams also come with built-in roads, transmission infrastructure, and access to markets.
Vattenfall Finds “Free” Land For More Solar Power
For those of you new to the topic, pumped storage is a gravity-based system. It involves pumping water from a lower reservoir to a higher one when excess power is available. When demand rises, the stored water is released to run turbines.
For all the talk about the latest high tech battery technology, pumped storage is still the only large scale, long duration energy storage platform available today.
In the US, for example, pumped hydro still accounts for more than 95% of the nation’s large scale energy storage capacity.
Vattenfall comes into the picture because it operates eight pumped hydro energy storage facilities in Germany. A couple of years ago the firm was casting about for opportunities to expand its generating portfolio, and solar panels provided the answer.
The company launched its “PV@hydro” project with the goal of installing 5 megawatts in energy storage capacity at its pumped storage dams in Germany, taking advantage of available space on the grounds and on the roofs of various buildings on the sites.
By 2018, the PV@hydro project was taking shape with plans for new solar panels at the company’s Geesthacht pumped energy storage plant near Hamburg, and the potential for solar development at pumped storage dams in Wendefurth, Hohenwarte, and Markersbach.
In the latest news on that score, Vattenfall is already reaching beyond the initial 5-megawatt goal. Last week the company announced plans for 11,000 solar panels at the Markersbach totaling 4.6 megawatts. The Geesthacht facility will get an additional 2.4 megawatts.
Re-Powering Hydropower With Floating Solar Panels
Hydropower produces zero-emission electricity, but at a high cost to the riparian habitat. The case against building new hydropower dams also has to do with the finite lifespan of dam infrastructure. That can includes a tendency to underperform after a number of years, as the reservoir fills with sediment and loses water-holding capacity.
Deploying solar panels that float on the water surface could provide a way to boost performance without expanding existing dams or building new ones, while also avoiding land use conflicts.
That’s where the new US research comes in. A team from Michigan State University took a look at the push for building new hydropower dams in the Amazon and came up with the idea that the same thing could be accomplished, with far less environmental harm, by constructing large scale arrays of floating solar panels on existing reservoirs.
Their new study, “Floating PV system as an alternative pathway to the amazon dam underproduction,” argues that “large-scale deployment could potentially be one of the promising solutions for offsetting dams’ underproduction.”
The researchers toted up the electricity production of Amazon dams and calculated how much capacity in floating solar arrays would be required to make up for underperformance. They also factored in environmental and social concerns.
“The results indicate that the investment toward installing FPV [floating photovoltaic] systems on the dams’ reservoirs leads to a significant improvement to the overall system reliability, minimize load curtailment, and could potentially add more flexibility to the operator to dispatch power generated by hydropower plants during peak demands,” they concluded.
Floating Solar Panels Save Water
As the researchers note, Brazil has a head start on hydro + solar. Earlier this year PV Magazine surveyed the state of affairs and took note of a large scale, 30-megawatt project in the State of Goiás. The total includes re-use of a former construction site for ground-mounted solar panels as well as floating ones.
In Bahia, a 1-megawatt pilot project that launched in 2016 is expanding to 5 megawatts.
One question is why Brazil should invest in floating solar panels, instead of building more conventional solar arrays or, for that matter, wind farms.
The land use conflict issue answers that question in part, but another factor is in play. The Michigan State team took a look at previous studies that examined wind and ground-mounted solar options. They noted that floating solar panels offer an important advantage over wind and ground-mounted solar, in that they help conserve water by reducing evaporation.
The researchers also mention another study that assessed the benefits of installing floating solar panels on the Gavião reservoir in Northeast Brazil, which found both economic and environmental benefits.
Another study cited by the authors involves hydropower plants in the São Francisco River basin. “Besides the environmental gain, the results also indicate installing FPV could potentially increase the hydroelectric plant production flexibility by 76% and the capacity factor by 17.3% on average,” they calculated.
Solar + Hydropower In The USA
The US Department of Energy, for one, is impressed with the potential for floating solar panels to make a significant contribution to the national energy mix.
About 18 months ago, the agency’s National Renewable Energy Laboratory produced a report on floating solar panels that included human-made ponds, lakes, and other water bodies in addition to hydropower and pumped energy storage reservoirs.
“Our results demonstrate the potential of FPV to contribute significantly to the U.S. electric sector, even using conservative assumptions,” the NREL team explained.
By conservative, they mean conservative. The NREL approach centered on water infrastructure in stressed areas where the dampening effect of floating solar panels on evaporation would add value to a project. They also focused on areas with high electricity costs, where floating solar panels would be competitive. That meant rejecting a large number of water bodies that could technically host solar panels.
That left a group of 24,419 qualifying water bodies, which accounted for just 12% of the total area of human-made water bodies in the 48 contiguous states.
The researchers eliminated more than two-thirds of the water bodies in that group for various reasons. They calculated that if only the remaining 27% were developed for floating solar panels, that could still produce almost 10% of the nation’s electricity supply.
With more companies throwing their hats into the floating PV ring, costs will continue to fall, and that may expand the number of sites where development is competitive.
Keep an eye on the largest floating PV array in North America, a 4.6-megwatt array completed last year in Sayreville, New Jersey.
Thought not located at a hydropower dam, the new array does illustrate use of existing infrastructure along with environmental benefits. It was constructed on retention ponds serving the town’s water treatment plant. The ponds are surrounded by a public park that is apparently a popular fishing site, and the developer anticipates a healthier habitat for the fish due to increased shading and reduced algae growth.
In another interesting twist, the developer is pretty sure that sunlight reflecting from water in the afternoon has provided the panels with an unanticipated boost in late-day solar conversion efficiency.
Spearheading the project is the firm Ciel & Terre, partnering with local solar companies J&J Solar Power LLC and Solar Renewable Energy LLC. The firm RETTEW takes engineering credit and apparently it is already laying plans for more and bigger floating PV projects, so hold on to your hats.
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Photo: Floating PV array courtesy of Ciel & Terre.