Last week saw the United States pulling out of the Paris climate accord, as decided by President Trump. Despite this, the President has said that the United States would be “the cleanest” country on Earth. It is unknown how the President plans to achieve this, but apparently part of this plan may include a large border wall covered in solar panels.

According to Axios, the President recently pitched Republican congressional leaders the idea of a border wall covered in solar panels, though not as a definitive solution. Theoretically, the electricity generated by the panels would cover the costs of the wall. The wall pitched by Trump is envisioned as being 40 to 50 feet high, with solar panels installed all over them.

Back in March, the United States Department of Homeland Security requested designs for border wall prototypes. Gleason Partners of LLC of Las Vegas submitted their proposal to cover the wall in solar panels, which would power light and sensors across the wall.

As for what the solar panels would cost, estimates float somewhere between 12 to 15 billion dollars, assuming that the panels cover some 1,000 miles of wall space (roughly the distance of the unobstructed land between the US and Mexico). Assuming certain types of solar panels were used, the wall has the potential to generate 7.18-gigawatt hours of electricity a year, about 300 million dollars worth.

Other estimates have been given, as according to Generate Capital, would generate some 6.5 billion kilowatt hours of electricity, collecting roughly $15.8 billion over the solar panels’ 40 year lifetime.

This may sound good in theory, but there are some logistical issues which would make constructing a solar wall very difficult, perhaps unattainably so. For instance, it assumes certain types of panels are available and leaves out the transmission, storage, and possible security costs. The costs of the wall itself are not, solar panels excluded, fully nailed down either, as Washington experts say it could cost up to 22 billion dollars. Given these facts, it may be wise to hold off on expecting a solar wall to emerge on the southern border anytime soon.