LOS ANGELES — Harold Hay wants to help the world save itself, but he's running out of time.

Forty years ago, Hay invented a simple, inexpensive way to heat and cool a home using the sun's rays, but without the panels and wiring that come with conventional solar energy systems.

He has been pushing for its adoption ever since, trying to find footing in each of the solar industry's last three boom-and-bust cycles. Yet, despite the merits of his pioneering technology, the energy establishment has shown only fleeting interest.

At 98, Hay is making what he knows will be his final push.

The retired chemist promotes his cause by funding research and vents his frustration in letters, e-mails, phone messages to pretty much anyone who will listen, and on his own Web site, www.2and50needles.com.

Hay is unyielding and scathingly critical of other people's efforts and the solar business as a whole. He dismisses the U.S. Energy Department as being "in the research-forever stage" and the solar trade as "a bunch of money grubbers."

Hay has no interest in softening his message. He doesn't have time for subtlety.

Over time, people lost patience with Hay and then lost interest in his creation, says Ken Haggard, who designs buildings that use solar energy. Hay's combative personality and reluctance to let others join his mission scotched one potential deal and might have turned others off, Haggard says.

"He's a caricature of the mad inventor," says Haggard, who met Hay in 1972 when the architect was a young professor at California Polytechnic University, San Luis Obispo. "He's a genius. But he's also impossible. And he has not mellowed one iota."

MESSAGE STILL RELEVANT

It's tempting to write off Hay as a bitter solar has-been, hoping for immortality at the end of his life. But, given today's energy and climate challenges, ignoring his message and achievements could be a mistake.

"His invention and what he's been saying for all these years is still very, very relevant," says Becky Campbell-Howe, operations director at the American Solar Energy Society, which gave Hay its Passive Solar Pioneer award in 1986. "The main point that he's trying to make now is that all of our hopes are pinned on all of these complicated technologies, and it's not that complicated. We could solve a lot of the problems by building our buildings correctly."

Hay calls his invention the Skytherm system, and it was a wonder in the 1960s because it used the sun to heat and cool a home. The earliest version operated without any electricity, making it a purely passive solar technology.

Skytherm was the first of what's known today as a roof-pond system. It includes a large mass of water, contained water-bed style in plastic bladders on top of a house. A steel liner substitutes for regular roofing. The flat roof also holds an insulation panel that moves on rails to cover and uncover the water with the help of a motor, an upgrade from the original rope pulley.

The concept relies on water's tremendous ability to absorb heat. During hot summer days, the water sacks are covered by the panel, which deflects the heat of the sun while the sacks draw warmth from the house, keeping the interior cool. At night, the panel moves aside and the sacks release their heat into the night sky. The process is reversed in the winter.

Hay explains the basic theory by pointing out his bedroom window: "Take the black pavement out on the street. It gets extremely hot every day in the summertime — much too hot to walk across barefooted. The next morning it's cold."

Hay attempts what passes for a shout these days: "You don't need electricity to cool! You don't need an air conditioner! You do it with the sky."

EARLY SUCCESS

In 1967, Hay scraped together the money to build a one-room test home in Phoenix. The results were encouraging, but yielded no flood of support or funding. It took him several more years, but Hay finally got a full-scale model built in Atascadero, Calif., near the campus of Cal Poly SLO.

It was completed in 1973. The next year, Hay testified before Congress, imploring senators to fund research into solar heating and cooling. Two years later, Hay's Skytherm house was recognized by the American Revolution Bicentennial Commission as one of the country's 200 most promising inventions.

In his rundown apartment near downtown Los Angeles, crammed with a lifetime of research, Hay holds up a brightly colored poster celebrating the award; he points to the spot where the Skytherm house is mentioned. "That was an award from the president of the United States," he says. "My house was one of the unique things, and it's gone nowhere."

For more than two decades Hay has lived in a tiny apartment, surrounded by dozens of boxes full of magazine articles, scholarly treatises and government reports. One entire wall of boxes is devoted to medical topics. Asisclo "Butch" Carnaje, who takes care of Hay, says the clutter is organized loosely by subject.

Amid the mess, Hay keeps a magazine display rack that holds copies of his congressional testimony as well as conference papers with titles such as "Wet Steps to Solar Stills " and "Roofponds En Route."

SEEKING RECOGNITION

Hay is strong for someone who has lived 98 years. But age and illness, witnessed by the long rows of medications on his dresser, have left their inevitable mark. His daily routine is dictated mostly by meals and sleep, which leaves pockets of time for him to read, watch the BBC and business news, check e-mail and track his stocks online.

Hay used to board a crosstown bus to do research at university libraries. Now his social schedule is defined mostly by doctors' appointments.

But not entirely.

In December, he spent nearly a month in a mountainside bamboo house in Manila, Philippines, with Carnaje and his family. He then made a side trip to an international meeting on the history of medicine, with a stop to lecture a Habitat for Humanity group on the benefits of the Skytherm design.

"I'm happy here," Hay says. "The thing I'm not happy about is that my ideas aren't recognized."

Hay's prized Skytherm house is in disrepair. A family lived in it for a while, but there were leaks. When fuel got inexpensive again in the late 1970s, enthusiasm for the project petered out along with the entire solar movement. The Skytherm house's benefits were never documented beyond the prototype stage, and no one worked out how much mass production would cost.

Over the years, Hay has given $500,000 to the University of Nevada, Las Vegas, and $50,000 to Indiana's Ball State University to fund Skytherm research. The studies confirmed the heating and cooling benefits of Hay's design but didn't go further.

Encouraged by a $1 million research grant from Hay — along with title to the Atascadero house — Cal Poly periodically has revived the project.

Mike Montoya, a professor of construction management, recently secured permits to bring the house up to current building codes. He hopes to re-open it and quantify its merits.

"The thing that sparked my interest is the fact that it is supposed to be able to heat and cool the house with no power," Montoya says.

"There are a couple problems, but it clearly works. It's a design that's very, very simple and that can be applied pretty much anywhere."