You have a preview view of this article while we are checking your access. When we have confirmed access, the full article content will load.Fifty-five years after the first Earth Day, climate activists organized a nationwide celebration of solar power.Susan B. Millar, a retired scientist emeritus from University of Wisconsin Madison, is hosting open houses this weekend at her solar-powered home to talk about solar energy.Credit...Kaleb Autman for The New York TimesSunday Was Also Sun DayFifty-five years after the first Earth Day, climate activists organized a nationwide celebration of solar power.Susan B. Millar, a retired scientist emeritus from University of Wisconsin Madison, is hosting open houses this weekend at her solar-powered home to talk about solar energy.Credit...Kaleb Autman for The New York TimesListen · 6:03 min Published Sept. 20, 2025Updated Sept. 24, 2025On Friday morning, Susan Millar was readying her home in Madison, Wis., for an open house. But she wasn’t trying to sell it. Instead, Ms. Millar opened her doors to a dozen strangers curious to see her heat pump, solar panels, battery storage and electric induction stove.It was an early peek at one of more than 450 events taking place as part of “Sun Day,” a nationwide demonstration of solar power and renewable energy. Most of the events spread across nearly all 50 states, including E.V. parades, church sermons and house tours, are set to take place on Sunday, the day before the Autumn solar equinox. Ms. Millar was getting a jump on the action.“You can live in a 90-year-old home like this one without burning anything,” she said. “Now all those fossil fuels are gone.”Bill McKibben, the climate activist who also writes for The New Yorker, got the idea for Sun Day a few years ago as the cost of renewables began to drop. Solar power has become the world’s cheapest form of energy, with costs declining by nearly 90 percent in the last 15 years, according to Our World in Data. Solar power is no longer the ”Whole Foods of energy — nice but pricey,” Mr. McKibben said. Instead, it’s become the “Costco of power — cheap, available in bulk, and on the shelf ready to go,” he said.ImageThe back of Ms. Millar’s home in Madison. “You can live in a 90-year-old-home like this one without burning anything,” she said.Credit...Kaleb Autman for The New York TimesThank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.Thank you for your patience while we verify access.Already a subscriber? Log in.Want all of The Times? Subscribe.AdvertisementSKIP ADVERTISEMENT