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Project Focus: Floating solar panels for Thames Reservoir

Europe's biggest floating solar panel array has been installed on the Queen Elizabeth II Reservoir, near Walton-on-Thames, London. Just over 23,000 solar photovoltaic (PV) panels have been floated on the reservoir, utilising a normally redundant suburban space on the surface, following an agreement between Thames Water, Ennoviga Solar and Lightsource Renewable Energy.

The array has over 23,000 solar panelsThe array has over 23,000 solar panels

The energy produced will help power the nearby water treatment works as part of Thames Water’s bid to self-generate a third of its energy by 2020. Lightsource Renewable Energy, Europe’s leading solar energy company, has funded and managed the ambitious £6.5M project.

A total of 23,046 monocrystalline photovoltaic panels make up the installation, each with a peak capacity of 275 Watts. Together they are expected to generate 5.8 million kilowatt hours in the first year.

Rather than being connected to the National Grid, the site will be “hard-wired” directly into the Thames Water private network. Thames Water will off-take all energy generated by the system. Lightsource will own and operate the solar installation and Thames Water will purchase the energy produced by the system.


The individual solar panels were clipped onto specially designed air-filled floats, manufactured by Ciel et Terre, which were assembled to form a large raft.

The raft was assembled on the shore and pushed out onto the reservoir in sections. Boats were used to position the raft’s sections, and then they were attached to buoys on the water’s surface which are anchored to the bottom of the reservoir to keep the installation in place.

The solar PV panels on the floating array are connected via a submerged cable to inverters onshore. A new cable will then connect into the existing Thames Water private power network at the site.

The electricity produced by the panels is carried to shore using marine cable, ensuring it is protected from the water. The same specification is used under the ocean to connect the UK’s islands to the mainland, and to carry electricity between the UK and the continent.

The project was a “permitted development” and therefore did not require planning consent. The solar installation will contribute to Thames Water’s ongoing operations and the primary use of the site as a water storage reservoir will not change.

Wave resilience

Waves on the reservoir can reach up to a metre in height, so the floats and connectors are designed to allow the pontoon to flex. All of the components have been rigorously tested to withstand the conditions on the reservoir. The modules are tilted at a shallow angle of 12 degrees – they need to have a tilt so that rainwater will run off, but the tilt is kept shallow to reduce wind loading.

If the reservoir needs to be emptied, the rafts are able to sit on the reservoir bed. Thorough habitat surveys were conducted as part of the project’s development, as reassurance that the installation would not adversely impact wildlife.

While it might be imagined that solar power is not suited to the UK climate, the fact is that solar panels do not require direct sunlight to produce electricity, only daylight. The array will therefore still work well on cloudy days, and actually perform more efficiently in cooler temperatures.

This is the first floating solar array on a Thames Water site, but it has solar panels on 41 other sites; three large installations at Beckton STW, Walton STW and Crossness STW and 38 small scale installations on other operational sites.


Project Fact file

-Divers have fixed 177 anchors to the bottom of the reservoir.

- Individual solar panels are mounted onto specially designed airfilled floats which are connected together to form rafts.

-The island’s surface area is 57,500 m2, less than 10% of the reservoir’s surface

-Total PV capacity is 6.33 MWp (Megawatts peak)

-Total number of modules 23,046; Total number of floats 61,721

-Project cost £6.5 million

Topic: Energy/Water Nexus , Sustainability & social value
Tags: solar , Thames Water , reservoir


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