In theory, solar power should be one of the most promising alternative energy sources around. The process has a virtually perpetual source (the sun), creates no dangerous exhaust and would not leave a lasting carbon footprint on the Earth. But there are a number of disadvantages of solar power which have kept it from joining ethanol and hydrogen as viable alternative fuels for commercial vehicles and power plants.

One of the main disadvantages of solar power is consistency and reliability. Solar-powered devices rely on the steady delivery of special atoms called photons to keep the electricity generating process going. As soon as the sun disappears behind thick clouds or falls below the horizon at night, the photons stop striking the solar panels and the power drops instantly. Some solar power can be stored in large battery arrays, but this arrangement would be impractical for motor vehicles and insufficient for major power stations. Solar power would only be viable with current technology as long as the sun's photon atoms can strike a solar panel directly. If there is no sun, there is simply no power.

Some disadvantages of solar power are economic in nature. At present, solar panels designed to generate electricity are fairly expensive to produce. Since a single solar panel can only generate a relatively small amount of electricity, an expensive and bulky array of solar panels would be needed to provide a sufficient level of electricity for homes or vehicles. These solar panels also have to be adjusted throughout the day in order to maintain a direct angle with the sun. Indirect sunlight is only marginally better than no sunlight at all, so a mechanical orientation system would also need to be implemented to turn all of the solar panels. An entire field filled with mirrors could focus the sun's energy on a power generator, but maintenance of such a system would be prohibitively expensive.

Other disadvantages of solar power are technical. The materials used to create a solar panel are constantly exposed to other things besides photon atoms. The constant bombardment of ultraviolet(UV) rays and other solar radiation often causes the panels themselves to deteriorate, much like any other material left exposed to the sun for extended periods of time. If current solar panels were used to provide electricity for private homes, there might be an entirely new industry dedicated to the maintenance and replacement of failed panels.

Perhaps one of the most noticeable disadvantages of solar power is the sheer volume of solar panels needed to generate very little energy. A solar-powered vehicle, for example, might solve many of the world's energy problems, but currently these vehicles are clearly not commercially viable. In order to generate enough electrical power to the vehicle's motor, virtually every square inch of the exterior must be covered in solar panels. Even then, the sole driver is often wedged into a small compartment with little more than a steering wheel and an electric meter. Commercial passenger vehicles would require significantly more electrical power, and a better battery system would have to be developed for any driving on cloudy days or at night.

Overall, the current disadvantages of solar power appear to outweigh the advantages on a large scale, but solar power has proven itself to be a viable alternative to chemical batteries or fossil fuels for smaller applications.