In two years, tourists will likely be traveling to Alcatraz on green energy.

Australia's Solar Sailor has come up with a way to make large solar panels that can also act like sails. Put one or more of the sails on a boat and the boat gets converted into a hybrid. The boat still has a diesel engine, but it mostly gets around on wind or sun power. A tour boat in Sydney Harbor has an array of eight small solar sails.

"It makes three runs a day and uses 1/10th of the fuel," says CEO Robert Dane.

The sail itself is solid and not flexible like cloth sails, but it functions like regular sails, he said. The solar panels, which are made with the assistance of a German company, are also lighter than typical silicon solar panels.

Hornblower Yachts in San Francisco is currently trying to get Coast Guard approval for a ferry powered by one of Solar Sailor's sails. If all goes well, the boat will be ferrying passengers in 2009. The picture shows Dane and a model of what the San Francisco boat will look like.

Solar Sailor also won a contract to deliver a set of sails for a 150-passenger boat in Shanghai. Additionally, it is working on a contract for four 100-person ferries in Hong Kong.

Like hybrid cars, boats equipped with the company's solar sails get their best mileage results in short-haul trips. The results, so far, are pretty impressive, Dane notes. In Sydney, the boat with the solar sails can go 6 knots on either wind power or solar power. Wind and sun together allow the boat to go around 10 knots. (Cumulatively, the sails on the Sydney boat can generate 16 kilowatts.)

The San Francisco boat will likely be able to go several knots on wind power alone.

Solar Sailor doesn't make the boat. It makes the sail and consults with the boat builder to ensure that it gets integrated properly and safely. The San Francisco boat will likely cost $8.5 million. Of that total, $1.5 million will be for the sail.

The sail on the San Francisco boat will approximately be 15 meters high. The boat will only have one sail. The Sydney boat has eight shorter sales that can be sailed in unison or individually. Computer studies, however, convinced Dane that the best design involves only one or two sails.