On West Coast, more complex solar preheats water to wash old cans

A cold wind was blowing as we climbed the metal staircase to the roof of the warehouse at the Campbell Soup plant one bright, sunny day in April. Shivering, we finally reached the roof of the Sacramento plant, where we were confronted with a huge array of flat-plate solar collectors and metal concentrators that are used to heat water for washing chicken-noodle-soup cans.

"Even though there's a 50-degree [F.] wind today, there's plenty of sun," observed Steve Cirst, an electrical designer in charge of the solar installation at the plant.

"All you need is sun," he adds.

The Department of Energy sponsored the Campbell plant's solar system because so much energy consumed by industry and agriculture is used for low-temperature processes, such as washing containers. It's an experimental model, being used on only one line to compare efficiency, reliability, and operating costs.

A report shows that from September 1979 through February 1980 the system saved 69.2 barrels of oil. At a cost of $20 a barrel, that's $1,444. In Sacramento, these months are the cloudiest and rainiest of the year. Summer figures will most certainly show even higher savings.

On the cold, windy day we visited the plant, the temperature of the water in the solar collectors was 130 degrees F. The required temperature for washing soup cans in 195 degrees, but the collectors aren't expected to provide water that hot. They are the preheaters only. Final heating is done by the huge, curbed metal concentrators.

Acurex of Mountain View, Calif., designed the solar system, which was installed more than two years ago.

"It's a simple design," Mr. Cirst said.

"The only difficult thing is the concentrators," he reported, "because they are curbed."

He said these solar-powered concentrators have been used by Acurex in other industrial applications to heat oil as high as 450 degrees F. At Campbell Soup, photovoltaic cells are used to move the concentrators to prevent the water from getting so hot that it boils.

After heating, water from the concentrators flows through a 2-inch insulated pipe to a 19,000-gallon insulated steel storage tank.

"It fills the tanks at 30 gallons a minute when the sun is out," Mr. Cirst declared. "The water is pumped out at 7 to 12 gallons a minute."

The storage tank is used to ensure a continuous supply of water for two 8 -hour shifts every working day. From the tank, water is pumped through a steam-heat exchanger so it reaches the required temperature. The hot water is then routed to the can-washing lines.

Besides the Campbell Soup plant, Acurex also has designed and supplied a field of concentrators for an experimental solar-powered irrigation system in Albuquerque, N.M.

Near Coolidge, Ariz., Acurex is building a solar system to pump water from wells that are 380 feel deep. And at a Johnson & Johnson plant in Sherman, Texas, Acurex has designed and built a solar-energy system to produce low-pressure steam.