A new "green" Plymouth library, lit largely by the sun, will open at 9 a.m. Saturday with double the space, twice the parking and at least 11,000 more books and other materials than the old library it replaced.

The $10 million building at 15700 36th Av. N. abounds with glass to capture natural light.

The result is a library that is light and airy, colorful and joyful, said librarian Trudy Hanus. "I think people are going to be so happy to come into this space."

The old library was closed on May 31, 2008, and torn down after Hennepin County determined that it defied efficient expansion.

The new library has a spacious 30,000 square feet on one floor. That's medium-sized for the 41-library Hennepin County system -- bigger than the typical 15,000-square-foot community library but smaller than the 60,000- to 90,000-square-foot, multi-story regional libraries.

A key convenience feature is an always-open drive-up book dropoff that will allow library patrons to return materials without leaving their cars. "That is really nice during the winter," Hanus said.

To save time for librarians, returned materials will be checked in by a machine that reads bar codes and sends items via conveyor belt into the right bin for reshelving.

Bookshelves in the new building are just 5-feet-6-inches tall instead of the 7-foot shelves used in older libraries. This gives librarians an easy view of all library activity, Hanus said.

The green design of the building is aimed at saving energy, said John Wicks, county project manager. "The county has a great interest in being frugal regarding the expenditure of energy," he said.

The building cost more than a traditional library but will be cheaper to operate and maintain, Wicks said. It's expected to last at least 50 years.

The building has no furnace, boiler or gas appliances. It's all-electric. Heating and cooling will be supplied by more than 100 geothermal wells sunk 200 feet into the earth. Heat exchangers will extract the warmth or cold and circulate it with fin tube radiators and an air-handling system.

The abundance of glass will reduce the need for artificial light. Sensors attuned to sunlight in the building will automatically raise and lower the brightness of the lighting fixtures.

Some space on the roof will be used to grow plants. Hardy native plants were bedded there in nutritious soil last fall to provide added insulation, protect the membrane that waterproofs the roof, and absorb rain.

Once it's established, the roof should be self-sustaining: no watering needed.

Eventually the library will train a webcam on the roof to show views of it on the library website, Wicks said.

The exterior of the library will never have to be painted, Wicks said. Exterior finishes are glass, polished metal panels and local brick and cast stone. The interior features maple millwork.

Another green feature of the building is a storm-water retention pond that has been designed and landscaped as a small park with outdoor seating around the shore.

The library will offer 72 computers -- 24 more than before -- and three public meeting rooms that can be reserved. The old library had only one interior room with no windows, Hanus said. The largest meeting room in the new library has a wall of windows. One has comfortable furniture suitable for book club meetings.

Many new materials have arrived since the old library closed its doors, Hanus said. Besides the existing collection, 500 boxes of new materials were purchased for the library while it was under construction. Last week an opening day collection of classic titles arrived in 600 boxes. All are shelved and ready to go.

The old library was one of the busiest community libraries, Hanus said. "We know when we open our doors, the materials are going to fly out of here pretty quickly."

Laurie Blake • 612-673-1711