Every outdoor pool runs short of the same thing in August, and it is not water. You show up at eleven, the lawn is already full, and the few trees along the fence have towels under them. A town utility northwest of Frankfurt spent the spring building more shade at its pool. Then it wired the shade into the building.<\/p>\n
Stadtwerke Oberursel runs the TaunaBad, the public pool in Oberursel, a town of about 47,000 at the foot of the Taunus hills. Before the outdoor season opened it put up three pergolas on the lawn beside the children’s pool, each one 34 by 38 feet (10.4 by 11.5 meters). The roofs are made of 180 solar panels. Stadtwerke Oberursel<\/a> forecasts about 69,500 kilowatt-hours a year out of them.<\/p>\n A pergola is a freestanding frame with a roof on it, the thing you put over a patio when there is no wall to hang an awning from. The TaunaBad version swaps the slats for photovoltaic modules, so the panels are the roof instead of sitting on top of one. Three of them cover about 3,862 square feet of grass next to the kids’ area.<\/p>\n That distinction matters more at a pool than it sounds. The buildings on a pool site are small and the open ground is enormous, so the roof area everybody wants to fill barely exists. Anybody who has priced a patio cover also knows the frame costs more than whatever you lay across the top of it, which is the honest argument against doing this anywhere you have a roof sitting empty. The argument for it here is that shade over the lawn was the thing families actually wanted.<\/p>\n The second half of the job is stranger, and I think it is the better idea. A fence already ran between the pool grounds and the parking lot. The utility bolted 64 bifacial modules onto it and forecasts about 38,000 kilowatt-hours a year off that line.<\/p>\n So why put solar panels on a fence at all?<\/p>\n Bifacial modules collect light through the back of the cell as well as the front, which makes standing one upright less wasteful than it looks. One face takes the direct sun and the other takes whatever bounces off the parking lot behind it. Stadtwerke Oberursel says the fence modules work on direct and reflected light together. A vertical panel does give up the middle of the day that a tilted array is designed around, and picks up more of the early morning and the late afternoon in exchange. We went through the same physics on a Queens rooftop where about a hundred kilowatts of solar panels stand on edge above a garden<\/a>.<\/p>\n So I did the division myself. Running the utility’s two forecasts against its own module counts, each fence module works out at about 594 kilowatt-hours a year, against about 386 for each pergola module. Stadtwerke Oberursel has not published the wattage of either type, so I cannot tell you how much of that gap is bigger panels and how much is the bifacial gain.<\/p>\n Both installations together come to more than 107 kilowatts peak and a forecast 107,000 kilowatt-hours a year. That lands at roughly 1,000 kilowatt-hours per kilowatt installed, the ordinary rule of thumb for German sunshine rather than an optimistic one. It is still a forecast. No full year has gone through the meter yet.<\/p>\n Almost all of it stays on site. Stadtwerke Oberursel says the electricity feeds the TaunaBad’s own technical equipment rather than the grid, and it planned the pergolas alongside a replacement of the pool’s pumps. Hessen’s state funding program for municipal climate protection and adaptation projects paid into the pergola half.<\/p>\n Pool pumps suit solar well. Circulation and filtration run through the whole operating day, all season, at a fairly flat load, and the panels make their power in the same window. You do not need a battery to line those two up.<\/p>\n Set that against Disneyland Paris, where 82,000 solar panels cover 11,200 parking spaces<\/a>. The Swiss builder that developed it sells the entire output, and the park self-consumes none of it. Both are real projects. Only one of the two runs its own equipment on what it makes.<\/p>\n Stadtwerke Oberursel puts the pergolas at the annual consumption of about 28 households and the fence at about 15, so 43 between them. Run the same output past an American meter and it shrinks fast. The Energy Information Administration<\/a> had US residential customers averaging 865 kilowatt-hours a month in 2024, about 10,400 a year, which turns 43 German households into roughly ten American ones.<\/p>\n American houses are bigger and most of them run air conditioning, which the EIA’s own survey work keeps finding to be the largest single use of electricity in US homes. German homes also do much of their heating and hot water on gas rather than electricity, which keeps the electric half of the bill smaller before anybody turns anything on.<\/p>\n None of this is exotic hardware, which is the appealing part of it. The modules are ordinary and the pergola is a patio structure with a stiffer roof, and the whole idea rests on putting them where the ground was already committed to something else. The airport at Frankfurt, on the other side of the same metro area, ran solar panels down the side of a runway<\/a> on the same logic.<\/p>\nSo what is a PV pergola?<\/h2>\n
The fence was already there<\/h2>\n
The pumps get the power<\/h2>\n
The same array covers 43 German homes, or ten American ones<\/h2>\n