Harvey D. -

your suggestion of attaching solar panels to the roof of a bus is intriguing, I had not come across it before. Unfortunately, panels that get 25-30% efficiency are still very expensive indeed. Also, city centers tend to feature high-rise buildings that cast shadows on the streets below.

Therefore, in the real world, I suspect you'd be lucky to get a third of the solar energy you estimate. On the plus side, the panels may have a longer life expectancy than the rest of the bus - if so, it would reduce the TCO. I suspect it would still be cheaper to invest in ultracaps for efficient recuperative braking to achieve similar fuel savings.

400 square feet of 25% efficient solar cells might produce 10Kw of electricity maximum, under fully optimal conditions. Since the bus takes about 10 times that much energy, I don't think it would help much and would cost a whole lot.

Carl, NBK:

CNG buses with oxidation catalyst is antiquated technology. With tree-way catalytic converter NG bus engine is cleaner then cigarette lighter.

SJC:

The high efficiency solar panels were not intended as the main power source but as a complemtary (optional) free power source for part of the on board HVAC. Solar panels may be too expensive now but the price per KWh should go down by about 10+% per year as did large LCD panels. If so, the price would be acceptable-affordable by 2012/2015.

Not all city street have 300/400-ft buildings. The average city bus is exposed to sunlight most of the time. Their large flat roof is an ideal place for solar panels.

The idea is to reduce dependance on ICE genset as much as possible by making vehicles as electric as possible.

Rafael & SJC:

Please check the MIT Technology Review (10 Nov. 2006) for 'Cheap Superefficient Solar Power Modules' using sunlight concentrators + very high efficiency wide spectrum tri-junction solar cells.

When mass produced those power modules could convert sun energy into useful electricity at a relatively low cost.

These power modules made replace the current steel bus roof-top.

Harvey D. -

do you really think sunlight concentrators are practical in a mobile application? Tracking mirrors would have to deal not just with the gross motion of the bus but also the elastokinematics of the suspension, plus vibrations. In addition, they would generate substantial aerodynamic drag and reaction forces on the roof structure at elevated speeds. The alternative, heavy fresnel lenses, is even less practical on top of a bus.

If Sharp's technology really is cheap enough, it should be used in stationary solar electricity farms to address energy security and climate change, cp.

http://www.greencarcongress.com/2006/10/solar_systems_t.html

For a public transport concept based on all-electric propulsion with occasional grid connectivity (at selected bus stops), please see

http://www.greencarcongress.com/2006/11/fraunhofer_test.html

Rafael:

These concentrators have no moving parts, are very rugged, relatively thin, light and could last up to 30 years. They can be made tile or strip shape of various size and could be fixed or glued to a flat roof tops.

The idea is to reduce the size of the very high efficiency (up to 50%) wide band expensive energy converter components in favor of low cost mainly plastic concentrators to reduce the total cost.

These panels have 10x concentration with no tracking, but you still have the 1/10 power generation to consumption fact to deal with.

http://www.siliconsolar.com/shop/catalog/Concentrator-Solar-Panels-SSPV-10-p-16339.html

Andrey-

Could you point me to a curret study or spec sheet detailing the emissions performance of a CNG bus fitted with the latest catalysts? I would like to compare it to the 2002 data presented in the studies that Carl linked mentioned.

A bus-type diesel engine with gears, generator and rectifier gets roughly 10 kWh out of every gallon of diesel. That means that the cost of electricity is three times as high as wholesale electricity for consumers. Thus, PVs mounted on buses should be three times as economical as home installations, no matter what efficiency is employed. Furthermore, the electric control unit needed in home installations is already paid for. Last, but not least, I will claim that installation of PVs in mass/series production (of cars/buses) is cheaper than installation in homes with all their variability.

But in the end, it is a matter of economics - including marketing. Will diesel savings pay for the solar panels or not? And will "solar driving", however small percentage, entice more customers?

I would agree that the payback would be better with busses than with homes. You could produce enough energy to power the A/C, or use absorption cooling and save fuel with PV electric for the motors. PV payback for the home might be 40 years, PV payback for the bus might be 20 years. Absorption cooling payback might be 10 years. Since city busses can cost $500k each, you have to ask if they want to spend another $100k with a 20 year payback when the bus might last 10 years.

Federal regulations aim for a transit bus lifespan of 12 years. Payback for any extra technologies should therefore take place within that time frame, accounting for the time-value of money. This assumes that the bus will be scrapped at the end of that period and not live on with a secondhand operator. If some of these suggested technological units can be expected to outlive the bus, they might be salvageable -- they can be stripped from the junked bus, refurbished, and installed in a new bus. The residual salvage value can therefore be subtracted from the extra up-front cost.

City buses tend to cost $350,000 or so for conventional models. A $500,000 figure is more accurate for hybrid city buses.

If a bus were 40 feet long and ten feet wide its top surface would have 400 square feet. That is less than 40 hp at full sunlight and only 4hp with a standard 10% solar cell conversion factor, at $10 a watt fabricated and installed the solar collector would cost $30,000. The average output over day and night would be one horsepower or less. Solar energy is too weak and too expensive and inefficient to convert for transportation units.

Super light weight street cars on tracks drawn by horses fed with grass from Central Park is a better option. Corn from the midwest could also be fed to them instead of making ethanol. Oh wait, every even slightly advanced nation has tried using biomass energy with the result of the nearly total destruction of Virgin forests and grasslands.

Low pollution power plants that feed power to plug in electric hybrids is the answer to all stop and go bus service. Recharge facilities can be built at every stop.

APUs, probably small diesel piston engines(OPOC), would be used after ten miles without a recharge stop. Very high speed, super-charging and exhaust-energy-turbines would allow high power output from low weight units, but only simple units should be installed in buses on routes where they would seldom be used.

Because of the maintenance costs, any battery other than ZEBRA batteries are too expensive for HEV use in busses. L-Ion batteries of all types are too expensive to monitor and cool. If large numbers of ZEBRA batteries were built on an efficient assembly line they could be one fifth the price or less.

With careful design of components, a hydraulic hybrid bus would be the least expensive bus to build and operate. The UPS hydraulic hybrid points the way, add a large flywheel, as in PARRY PEOPLE MOVERS, and you have a lot of regenerative power. Put in a small Zebra battery for lights and air conditioning from the engine generator...HG...