The floating solar panels that track the Sun
In the search to find space for large solar arrays, many countries are looking to floating systems. Now the Netherlands is taking this one step further, with water-based arrays that follow the Sun.
On a lake in the Netherlands, a shiny circular island floats, covered in dozens of shimmering solar panels.
But this is no normal solar array, nor even simply one of the many new floating solar farms being installed in lakes, reservoirs and coastal areas across the world. That’s because its panels are doing something none of these other floating solar farms can do: meticulously tracking and following the Sun as it moves across the sky, to catch as many rays as possible.
This glistening installation, named Proteus after the ancient Greek sea god, is among the first to combine floating solar panels with Sun-tracking technology – all in an effort to maximise the amount of clean electricity it can produce.
The island, floating in Oostvoornse Meer, a lake in the south-west Netherlands, is covered in 180 of these moving solar panels, with a total installed capacity of 73 kilowatt of peak power (kWp). It’s a tiny amount in a world rapidly trying to switch to renewable energy, but SolarisFloat, the Portuguese company which built Proteus, believes this small installation could be scaled up to generate large amounts of clean electricity – and, crucially, without taking up valuable land.
From the Brazilian Amazon to Japan, floating solar panels are experiencing a boom around the world. Floating solar capacity has grown hugely in the past decade, from 70 MWp in 2015 to 1,300MWp in 2020. The market for the technology is expected to grow by 43% a year over the next decade, reaching $24.5bn (£21.7bn) by 2031.
“Floating solar is a rather new [renewable energy] option, but it has huge potential globally,” says Thomas Reindl, deputy chief executive of the Solar Energy Research Institute of Singapore (Seris). Covering just 10% of all man-made reservoirs in the world with floating solar would result in an installed capacity of 20 Terawatts (TW) – 20 times more than the global solar photovoltaic (PV) capacity today, according to an analysis by Seris seen by BBC Future Planet.
The rise of floating solar technology is among the latest trends in the revolutionary expansion of solar PV electricity in recent years. Globally, solar PV capacity has increased almost 12-fold in the past decade, from 72GW in 2011 to 843GW in 2021. The technology now accounts for 3.6% of global electricity generation, up from 0.03% in 2006. At the same time, solar arrays have seen an astonishing price drop which has made them the world’s cheapest source of power.
Further expanses in solar energy are expected – in fact, capacity needs to reach six times the current amount by 2030 to stay on track with a net zero emission world, according to the International Energy Agency. Global geopolitics are also playing a role in rising reliance on solar power: the European Union has proposed a massive ramping up of renewable energy as it aims to reduce its reliance on Russian oil and gas in the wake of the country’s invasion of Ukraine.
Alongside this massive growth, researchers continue to look for improvements in solar technology. Most of the solar panels installed so far across the world lie on solid land. But solar technologies which float on water offer a unique advantage: they don’t take up land space that may be needed for other uses.
“Renewable energy production is going to increase all around the world,” says Antonio Duarte, the lead technical engineer at SolarisFloat. “Solar installations are going to increase much more on water [than] land. Why? Because land is becoming a very precious asset.”
In a world looking to rapidly expand solar arrays, this gives floating solar a significant edge, especially for countries facing land scarcity. Conventional solar farms are often criticised for the amount of land they occupy – land which could otherwise be used to grow crops to feed the world’s growing population, or carbon-absorbing trees. Solar energy requires a huge amount of space, at least 40-50 times more than coal plants and 90-100 times more than gas, according to research by Leiden University in The Netherlands.
Conservationists have also expressed concern that land-based solar and wind farms can have a harmful impact on biodiversity, especially those that are built in species-rich areas.
Building sun-absorbing technology on water is therefore a smart way to free up land, while also making use of unoccupied lakes and reservoirs. Countries such as Japan and Singapore are investing heavily in floating solar farms because of limited land availability or very expensive land.
Floating solar installations offer a unique advantage: they don’t take up valuable land space
But currently less than 1% of the world’s solar installations are floating, says Michael Walls, a professor at the Centre for Renewable Energy Systems Technology at Loughborough University, in the UK. This is partly due to technical and financial constraints – saltwater causes corrosion and positioning panels at an angle is tricky and expensive on a floating platform, Walls says. Installations on freshwater bodies may also face opposition if they compete with other activities, such as swimming, boating or angling, he adds.
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Still, floating sun-powered farms also solve another problem plaguing conventional solar energy: inefficiency when solar panels become too hot. In fact, floating solar panels generate extra energy because of the cooling effect of the water they hover over.
Solar panels generate electricity using rays of light from the Sun – not its heat. But when they become too hot, their efficiency falls. This is because heat excites the panel’s electrons, which convert energy from the Sun into electricity, making the difference between the high energy and rest state smaller, which in turn decreases the voltage and the amount of electricity generated. Solar PV panels typically operate at peak efficiency between 15C and 35C (59F and 95F), but they can get as hot as 65C (149F), hindering efficiency.
The proximity to water of floating solar helps the panels operate more efficiently and increases their electricity production by up to 15%, says Nuno Correia, director of composite materials at the Institute of Science and Innovation in Mechanical and Industrial Engineering in Porto, who developed the Proteus project.
Follow the Sun
But there are also other ways to boost the energy production of solar panels – such as by tilting them to follow the Sun’s path in the sky, similar to the way young sunflowers follow the sun from east to west during the day. Tracking technology, which is already in use on some land based solar arrays, helps increase the overall electricity production, as the panels constantly adjust to face the Sun.
Double-sided panels that track the Sun could increase energy production by 35% and reduce the average cost of electricity by 16% compared to conventional systems, according to research by SERIS. Demand for tracking technology for solar panels is expected to grow by 16% per year between 2022 and 2030 due to this efficiency boost.
By merging the two technologies, SolarisFloat says it can increase electricity production by up to 40%, compared to static land installations.
SolarisFloat built Proteus as a pilot project, to test this cutting-edge technology and analyse how it boosts the generation of clean energy. The prototype landed them a position as a finalist for the European Inventor Award this year.
Proteus’ single-sidedpanels slowly rotate every few hours on two axes, using mechanical, geospatial and light sensors to precisely follow the elevation of the Sun’s path, as it moves from east to west.
There are plenty of suitable locations for tracking systems such as Proteus, but the most likely niches are installations in higher latitudes that will not experience strong winds, says Reindl. Locations must be chosen carefully to avoid tidal forces and stormy weather from destroying the panels as well as their mooring and anchoring systems.
Tracking systems will also not make much difference at locations near the equator, where the panels are installed almost horizontal and face the Sun throughout most of the day, notes Reindl.
Adding trackers increases the overall capital and maintenance costs of the installation, says Walls. But the electricity gains make this technology a worthwhile investment, “especially in sunbelt locations,” he says.
Another downside to Sun-tracking solar arrays positioned on water is that they are challenging to install, Duarte acknowledges. “Land tracking systems are [typically] ‘anchored’ to the ground by poles and only a platform with the [solar panel] modules on top of the poles moves,” he explains. To ensure stability on water, propellers and engines have been installed on Proteus’s platform to anchor the panels.
“It remains to be seen what the maximum wind speeds and wave heights would be which the system can absorb while still working smoothly and reliably over time,” says Reindl.
Floating solar installations cool water temperatures by shielding the surface from the sun. This prevents the growth of toxic blooms of blue-green algae, which thrive in warmer waters and can produce harmful toxins that cause eye and skin irritation as well as vomiting among humans and serious illness or even death in animals.
The cooler temperatures also prevent evaporation of water – an especially important advantage in arid areas where water is a precious resource. A 2021 study found that floating solar panels on a reservoir in Jordan, one of the world’s most water-scarce countries, reduced evaporation by 42%, while producing 425 MWh of electricity annually.
“If done well in the right place, floating solar has the potential to provide much needed low carbon energy without taking up land and whilst improving [the] water body condition,” says Alona Armstrong, senior lecturer in energy and environmental sciences at Lancaster University and co-author of a study reviewing the environmental benefits and risks of floating solar farms. “Our research shows that floating solar cools the water body and reduces phytoplankton biomass.” High concentrations of phytoplankton biomass can boost the growth of algal blooms.
However, there could also be ecological disadvantages to wider use of floating solar. Floating solar panels decrease the period of stratification, when the Sun heats the water surface and creates distinct layers of water with different temperatures. This decrease can cause the bottom layer to become deoxygenated, “causing undesirable increases in nutrient concentrations and killing fish,” Armstrong’s study notes.
“Floating solar could cause beneficial and detrimental impacts to the water body, and likely a combination of both,” says Armstrong. “It’s all about ensuring it’s done well and in the right place.”
Floating solar panels can also offer useful advantages when combined with other clean technologies. For one thing, there is a “huge opportunity” to merge floating solar with existing hydropower infrastructure, says Reindl. This would help tackle one of renewable energy’s biggest challenges: how to provide a steady power supply during variable weather conditions.
“You could use solar during the day and hydro at night,” says Reindl. “If you do it in a smart way, you could in principle use the reservoir as a giant battery.”
Hydro dams are the world’s largest renewable energy source. But in some areas of the world, such as Africa, increasing droughts caused by climate change could threaten their future potential, the International Energy Agency has warned. One study found that solar panels floating on just 1% of Africa’s hydropower reservoirs could double the continent’s hydropower capacity and increase electricity generation from dams by 58%. There is “strong potential” for an installation such as Proteus to be used in combination with existing hydropower infrastructure to boost electricity generation, says Duarte.
As demand for renewable energy soars and climate impacts such as droughts increase, SolarisFloat says their technology offers a “win-win solution”. The high cost of materials, such as steel and plastic, needed to build the panels and the complex installation are the major hurdles which are stalling the global rollout of installations such as Proteus.
To be a commercial success, SolarisFloat not only needs to demonstrate an increase in electricity production, but also show that initial investments in the entire system and operational costs can be kept low, says Reindl.
Still, it seems clear that the future for floating solar overall is bright, with the global market expected to grow by a fifth in the next eight years to $180.2m (£151.5m).
Considering the world rapidly needs to ramp up renewable energy to avoid dangerous levels of warming, it needs all the help it can get. Floating, sun-tracking solar could help put the most efficient panels where they are urgently needed.