The long read: Feathered friends turn foe

From pv magazine, September 2019

In 2013, Frans van Herwijnen and his fellow project proponents began work on what they thought was a world first: a 2 MW solar array installed on a body of water. While during the course of the project he realized that floating PV systems had already been installed in China and Japan, the project team deployed a number of innovations to help the project rise to the top.

The Lingewaard floating array has a capacity of 1.845 MWp, and comprises 6,150 modules from Hanwha Q Cells. The project features Ciel et Terre’s floating structures, as well as 27.6 kW of SolarEdge inverters. The project was completed in mid-2018 and came with a total price tag of €2.2 million.

The town of Lingewaard itself has 46,000 inhabitants and is also the location of numerous expansive greenhouses. A large freshwater reservoir stores water alongside the greenhouse buildings. And it was on this body of water that van Herwijnen and his project partners saw an opportunity to install large-scale PV.

While the greenhouses are big consumers of heat and electricity, they are supplied by on an onsite gas-fired combined heat and power plant, so the floating PV instead supplies the community of Lingewaard.

Community focus

The Lingewaard floating array is owned by the local energy cooperative, Lingewaard Energie. Part of the project finance was crowdfunded by the locals themselves. “We have a lot of visitors to the project from the Netherlands and abroad and the community is very happy and very proud of the project,” says van Herwijnen.

Beyond the crowdfunding effort, the project’s proponents obtained financing through a combination of a grant from the Gelderland (Guelders) provincial government and a €1.7 million loan from Dutch lender ING Group. Ongoing revenues come in the form of the Dutch government’s SDE+ program, secured for a period of 15 years.

While the financing might be small change for a large, institutional lender such as ING, the process was not straightforward. “Despite the small size of the loan, it was a complex transaction,” wrote Eva Parro de la Paz, director of sustainable project finance for ING Structured Finance, in a recent blog post featuring the project on the ING Group’s website.

Given the project’s unique blend of crowdfunding, a government grant, and the relatively new technology of floating solar, ING Group’s due diligence took almost a full year to complete, explains van Herwijnen. “We learned a lot, but also ING learned a lot,” he adds.

Floating MLPE

The general assumption behind the use of module level power electronics (MLPE), such as power optimizers or microinverters, is that they are best suited to arrays in which shading is an issue. However, the Lingewaard Energie reservoir is not shaded by the adjacent greenhouses or the trees. “That is a question we often get – why optimizers?” The answer to this question came into focus once the array was in operation for several weeks, and the new reservoir feature attracted a number of feathered friends.

“At the moment, we have problems with birds on the panels,” explains van Herwijnen. “And they produce a lot of – what can I say? Shit.”

The issue turned up on the module-level monitoring used at the Lingewaard site. Customized alerts can be added to the monitoring systems, and they indicated to the operators that module cleaning and bird deterrent strategies were required.

“We cleaned the panels, of course, but after several weeks there was again a lot of shit,” says van Herwijnen.

Lingewaard Energy has since installed a laser deterrent. The device, commonly used for this purpose at airports, periodically activates a green laser to scare the birds away. Since its installation it has been effective, and van Herwijnen is now trying to determine how long it should remain in place – or whether the birds will return.

Bruno van Bost, the director of commercial sales in northwest Europe for SolarEdge, says that it’s not just birds that MLPE can assist with in floating PV arrays. He also notes how the impacts of module mismatch – the result of reflected and diffuse light from the water’s surface – can be resolved by the power optimizers. Additionally, DC cabling is kept to a minimum, with arc fault detection built in, to make work on the array – as well as O&M-related tasks such as bird waste removal – much safer.

“If you are placing PV on water, there are a few key benefits that SolarEdge brings that cannot be neglected,” says van Bost.

In terms of performance, Lingewaard Energie is exceeding expectations. It included plans for a 5% increase in power output, in comparison to a ground- or roof -mounted system, in its business case because of the cooling effects of the water. After one year of operation, the project is already exceeding this, with a 9% boost having been observed. Van Herwijnen believes this is because heat is radiating from the backside of the module, along with convection cooling – as wind travels underneath the modules, they are cooled by the water. “There is also a lot more diffuse light, reflected from the water surface, on the panels,” says van Herwijnen.