Solar-powered mass transit is key to U.S. energy sustainability. Did you know that one full city bus can keep 50 or more cars off the road? Or that a single solar array can remove one entire home from the electric grid? Both technologies, solar and mass transit, are getting extra special attention given the rising costs of fuel and home energy.

Public transportation and solar power have traditionally been independent of each other. However, the race to increase and improve mass transit infrastructure while reducing energy and fuel consumption is facilitating a close relationship between the two. It’s exciting and we’re getting amped up at the thought of widespread clean energy systems.

Let’s take a look at the different manifestations of solar-powered transit:

Solar On the Bus Line

In general, solar power technology is not advanced enough to power city buses in real time - that is, rooftop solar panels powering buses as they run daily routes. However, there is a steady rise among hybrid and electric buses that can power up at solar charging stations. Residential solar power is also being used to power transit facilities, bus stop shelters and to create alternative fuels for buses. It is in these somewhat indirect applications that solar power currently has its greatest effect on public transit.

Recovery Act in Motion

The American Recovery and Reinvestment Act of 2009 (ARRA), otherwise known as the stimulus package or recovery act, is having a profound impact on greening public transportation systems around the United States. And solar power is heavily involved. According to Clean Fleet Report, in September of 2009, the federal government announced $100 million in funding for 43 transit projects aimed at greening city bus systems. Here are several projects in which solar power will play a pivotal role:

1. California - AC Transit of Oakland received $6.4 million to increase solar photovoltaic capacity at a facility that generates hydrogen for Oakland's fuel cell-powered, zero-emission buses. The City of Santa Clarita got over $4.6 million to add PV modules to its maintenance facility. The panels will be installed on canopies to provide shade for buses. Also in California, North County Transit District (San Diego) will use Recovery Act funding to install solar power at a variety of facilities.

2. Delaware - Delaware Transit Corporation received $1.5 million for solar panel installations at its facilities to offset the transit system's electricity costs.

3. Georgia - In Atlanta, $10.8 million has been approved for the Rapid Transit Authority to construct a grid-tied solar-powered shade structure at a bus storage lot. It will be the largest PV installation in Georgia.

4. Illinois - The Chicago Transit Authority received $1.5 million to build solar-powered outdoor bus stalls that will provide power for up to 80 vehicles, as well as heating and air conditioning to buses that would otherwise be left idling during cleaning. Elsewhere in Illinois, Rock Island Metro received $600,000 for a solar thermal system to provide hot water for its operations and maintenance building.

5. Massachusetts - Lowell Regional Transit Authority will install a solar system on its Hale Street facility, where buses are stored, fueled, maintained and repaired. The 70,000 square foot building also houses LRTA's administrative and dispatch services. LRTA was awarded $1.5 million to install the solar system.

6. Washington - Clark County Public Transportation in Vancouver received $1.5 million to improve systems and install solar panels at several facilities. The projects will combine energy efficiency upgrades with solar electricity to reduce the overall environmental impact of public transportation in Vancouver.

Independent of Recovery Act funding, earlier in 2009, the Los Angeles County Metropolitan Transportation Authority (Metro) unveiled the nation's largest solar panel installation (1.2 megawatts) on one of its facilities. In recent years, Metro has installed solar power systems on several of its bus division facilities. Metro also uses many alternative-fueled buses, which in total, comprise the nation's largest public transportation fleet of its kind.

Solar Bus Shelters

Solar electricity is also having an impact at bus stops. Three major concerns, safety, lighting and weather protection, are easily alleviated by solar-powered bus shelters. Solar bus shelters are already in use in cities across the U.S. and Europe. One of the latest innovations in this area is the PV-Stop from the Urban Solar Corporation. These LED-lit, solar-powered bus shelters are exemplary of the safe, viable and appealing role that solar bus shelters can and do play in public transportation.

One high-profile example waits in San Francisco, where the city recently opened the first of 1,200 new bus shelters. At least one-third of them will be powered by solar panels on the shelters' roofs. The panels will power lighting, an LED arrival-time display and a push-button loudspeaker for visually impaired riders. The shelters will be grid-connected with excess power fed back into the grid.

Adelaide and the Electric Bus

In Adelaide, Australia, the public can ride (for free!) the Tindo, an all-electric city bus which gets its power from a solar PV system mounted onto Adelaide's central bus station. The bus can drive 200 km (124 miles) on a single charge and carry up to 27 passengers at a time. It is the first public bus in the world to use 100% solar electricity. Its name, Tindo, is the Kaurna Aboriginal word for sun.

Solar Rides the Rails

New York City's subway system and Chicago's El Train are famously successful examples of public transportation by rail. Operating on a wider scale are Amtrak in the United States and Europe's well-travelled spider web of international train routes.

Trains travel long distances under the sun's energetic glow, making them at least theoretical hotspots for solar power. Trains, however, require a lot of fuel and power to run and at present technology levels, solar has yet to make much of a dent in mass transit by train. But a dent, however small, has been made.

The most straightforward example comes out of Italy. In 2005, Italian company Trenitalia set in motion its first PVTRAIN, a prototype passenger/cargo train with solar modules integrated into its roof. The panels produce 1.36 kW of peak power, which is used for air conditioning, lighting and safety systems.

In Japan, which boasts one of the world’s most extensive bullet train networks, has been using solar power for years to provide some power for its fleet of trains. Trains typically charge up while stopped at stations equipped with PV arrays.

One of the most aggressive concepts for solar-powered trains comes from Arizona. The Solar Bullet train is designed to run from Tucson to Phoenix (to start), traveling at 220 mph beneath a canopy of solar panels. Its co-creators point out that all the technology to build the train and railway is already available in Europe and could alleviate major commuter problems in Arizona and elsewhere, while providing excess power and economic gain for local communities. The Solar Bullet remains in development at this time, but Solar Bullet LLC hopes to be operational by 2018. If not technology, then money may be their biggest obstacle. Their ideal cost is about $20-40 million per mile of track which, according to some estimates, puts that overall cost at $27 billion for the first phase. The company claims that the train would need 110 megawatts of electricity to run, which is readily available in the Southwest's very sunny climate.

In Wales, solar power provides electricity to a miniature railway that runs around a lake in Rhyl. The train is wholly powered by solar panels mounted on the train station and museum building. It is designed to demonstrate the potential for solar power in Wales by offering visitors a ride on a solar-powered train.

If a small lakeside ride is just too big for you, then ride on down to the South Florida Science Museum in West Palm Beach, where you'll find the Solar Express, a unique, solar-powered outdoor model railroad complete with push-button controls for curious visitors.

Solar On the High Seas?

Just a few weeks ago, in Japan, the Auriga Leader set out of the Port of Kobe on a test run. The Leader is a partially solar-powered automobile carrier with 328 solar panels equaling 40 kilowatts mounted on its deck. The ship is no dinghy. It is 60,213 tons, 200 meters long and can transport 6,200 vehicles.

Yet the Leader is far from solar-powered. The PV array offsets 0.3 percent of the ship's total energy consumption and 6.9 percent of its electricity usage. But it does represent the first ship of its kind and is only a test to determine whether larger PV systems are viable for big ships. The panels will remain on the ship and be monitored for the next two years. Some important variables include how the system holds up against salt damage, wind, mechanical vibration and swaying.

The Auriga Leader is no public transit vehicle, but it could prove an important test run. For if a 60,000-ton cargo ship can successfully (if partially) run off solar power, then why not a cruise ship or a passenger ferry?

For buses, trains and boats - not to mention cars - direct solar-powered travel is far off. The best we've gotten to date is an electric bus that charges up with solar power, which admittedly, is just as effective. Perhaps the future for eco-friendly mass transit lies in alternative fuels, such as hydrogen, biodiesel and natural gas, but don't count out solar power. It's already powering plenty of transit facilities, stops and stations. And it is but one quick jump from rooftop to bus-top.