Aena, the world’s largest airport operator in terms of passenger numbers, announced on Tuesday an ambitious plan to run most of its operations using solar energy in just seven years’ time. The proposal is an expansion on the previous company’s plans, which will now see the firm install solar panels on around half its airport sites including Madrid and Barcelona.

It’s the latest in a series of reports that airports are making the most of large swathes of land to provide clean energy. El Pais reports that the operator, which handled 280 million passengers in 2017 through its 46 airports in Spain and one airport in the U.K., originally planned to simply purchase renewable energy from a provider and generate just five percent of its own electricity. A newly-installed management team has now decided that the company should generate more of its own electricity using unused land located near its sites.

The project will see Aena invest €250 million ($282.4 million) to install panels in 20 of its 46 Spanish airports, prioritizing those with the most sunlight and available land. The company expects Madrid and Barcelona to reach carbon neutrality by 2030, airports that currently account for the majority of the firm’s emissions. The firm’s total carbon emissions are expected to decline 40 percent by 2025, cutting 167,000 tons.

Airports are major energy hogs. Research from resource site Business Energy Advisor shows the average airport uses 19.7 kilowatt-hours per square foot per year, with 46 percent used for lighting and cooling. Professional education firm Energy Class Factory found an airport uses around 180 million kilowatt-hours per year in total, around 60 percent used for the terminals. By comparison, the average American home uses just 10,399 kilowatt-hours per year.

Airports: a major energy hog. Unsplash / Bna Ignacio

A number of sites are taking steps to reduce their output. New York’s John F. Kennedy Airport announced last month it plans to install up to 13 megawatts (or 13,000 kilowatts) of solar capacity, comprising a five-to-eight-megawatt solar array for the authority’s consumption, plus a further five megawatts to bring energy to low-income houses at a reduced price. Honolulu Airport in Hawaii announced in July 2018 plans to install 4,260 panels as part of its goal to reach 100 percent clean energy by 2045. Moi International Airport became the first in East Africa to install solar when it announced its 500-kilowatt array in November 2018.

Others have gone for more drastic measures. Cochin International Airport, based in the south Indian state of Kerala, claims to be the first airport run entirely on solar, with a 29-megawatt array that’s set to scale up to 40 megawatts. The owners use the land underneath to grow 60 tons of vegetables per year, a technique known as “agrophotovoltaics.” A team based at the University of Hohenheim found such steps can increase land use efficiency by 60 percent versus separate land used for crops.

These projects are proving economical, as the price of solar has continued to decline. On the bills side, Aena’s plan is expected to save €52 million ($58.7 million) from its current €75 million ($84.7 million) annual energy costs.

Beyond its solar project, Aena also aims to make a big move into electric vehicles. It’s planning to replace all of its passenger vehicles with zero-emission vehicles by 2025, while placing 2,500 charging points for airport visitors. It’s a far cry from earlier projects, like Portland Airport’s installation of 42 chargers in 2015 that ranked as the largest such project at the time in the United States.

With airports moving to clean electricity, the next step could be transferring the jets themselves onto renewables. Unfortunately, Tesla CEO Elon Musk claims that such a shift won’t occur until batteries reach a density of 500 watt-hours per kilogram, where a Tesla car today uses a 250 watt-hour battery. At least when it arrives the airports will have transitioned further onto solar.