Water has always been a ‘cool power’ 

Two stories about water caught my attention this week – how an ancient technology is helping to cool a Spanish city, and how abandoned coal pits and stone quarries are increasingly popular in Europe as a site for ‘floatovoltaics’ – floating solar panels.

I have been interested in ‘floatovoltaics’ since I read about the plans to install solar panels on two wastewater treatment plants in Healdsburg, California, in November 2021. At the time, it was thought to be the largest such installation in North America. Researching further, I discovered that Asia was far, far ahead of North America, although it wasn’t easy to find an authoritative overall source for such an emerging technology.

Now it has really caught on in Europe, and governments, businesses and utilities are “scouring out-of-use industrial areas for available bodies of water,” says a recent Bloomberg story. “At the top of the list are ponds and lakes that don’t attract many visitors, and which have steady water levels that won’t disappear beneath snow pack in winter.”

Baywa.r.e photo

This was, in part, because of the huge success of putting solar panels on European rooftops and resistance from farmers and local residents to using land for siting solar panels on the ground. “Agriculture still sees solar panels as a threat that competes for the same land,” Matthias Taft, chief executive officer of Baywa.r.e., told Bloomberg. (Although agrivoltaics is blending agriculture and solar power in positive ways.) But gravel and sand pits that are no longer used are ‘low-hanging fruit’, Taft says.

Since Baywa.r.e installed its first array of floating panels back in 2018, it has become Europe’s leading producer of floating photovoltaics and expects to triple its current 28 gigawatt output by 2025. It has already installed floating panels capable of generating half a gigawatt of energy in Europe and Asia, and is assessing new sites in South America.

The World Bank estimates that Europe could cover at least 7% of its annual power consumption by deploying floating solar panels on just 10% of artificial lake surfaces, Bloomberg reports. If this were scaled globally, the amount of electricity generated would rise to 5,211 terrawatt hours a year — more than all the electricity consumed annually by the US, the world’s largest economy.

There are some other equally imaginative approaches. The Netherlands, which has more than 48 million panels nationwide, has put solar panels over car parks and on commercial lakes, sheep grazing fields, strawberry farms, disused churches, train stations and airfields. In the countryside, 23,000 solar panels on an 80 foot hill made from 15 years’ worth of household and business waste now generate enough electricity for about 2,500 households.

The qanat is originally part of a traditional communal water management system which is still used in arid regions of Iran (and adapted by the Spanish in Spain and in territories they controlled, where it is known as acequias). Vertical shafts brought cool air from the water in the tunnels to the surface.

Now the CartujaQanat, a pilot project in Seville designed by researchers at Universidad de Sevilla, has added some modern twists with the goal of “recovering the street life in a climate-changing world”.

Seville, the largest city in southern Spain, can get very hot in summer –  as hot as high as 50℃. The grid of aqueducts can lower surrounding temperatures by as much as 10C using just air, water and solar power, says Emasesa, the Seville public water company that helped to build it.

The ‘Souk’ – photo by Cartuja Qanat Project

The two auditoriums, green spaces, a promenade and a shaded area with benches are cooled with cool air pumped through small openings in the floor and steps by solar-powered fans. A channel with water goes 20 meters deep underground and, through air vents, drives the coolness of the water upwards. Below the ground, the water temperature drops 10 to 15 degrees, and above it results in a drop of 6 to 7.

Funded through the EU’s Innovative Actions programme, Cartuja Qanat is located on the Isla de la Cartuja, which became a showcase for innovative technological in bioclimatic architecture and temperature control solutions during Expo’92.


No land, no problem: Netherlands innovates to lead EU solar drive. Context, Mar. 2, 2023

Floating Solar Panels Turn Old Industrial Sites Into Green Energy Goldmines. Bloomberg, Aug. 2, 2023

Transforming Unused Bodies of Water into Clean Energy Generators. Baywa.r.e

One of Europe’s Hottest Cities Rediscovers an Old Cooling Technique. Bloomberg, Aug. 8, 2023

Cover image: the Ampitheatre, Cartuja Qanat Project