Solar power isn't cheap. Although energy from the sun is free and plentiful, the equipment needed to make solar power usable and reliable is expensive. The cost of harnessing this free energy has come down substantially but solar power cost trends show that the future for this technology will likely continue to be expensive.
The average solar panel is currently around 22% efficient - although efficiency continues to improve with technological advances. At 22% efficiency, though, that would mean that the remaining 78% of the energy is either reflected (ever noticed the bright glare off of a panel?) or lost as heat (touch a solar panel and notice how warm it is). Research into semiconductor material has improved the energy conversion process but the cost of high-efficiency solar panels is prohibitively high.
Mass production has brought down the cost of the existing technology, but economies of scale currently cannot match that of existing energy sources (i.e. oil refineries, hydroelectric dams, coal-fired generators) until a new breakthrough emerges.
Because of the high cost of doping semiconductor material and the low energy output of solar panels, exploiting the energy of the sun will always be more expensive than other types of energy.
The sun's energy might be available during the day but at night, energy is still needed to power TVs, computers, lights, ovens, and all the other appliances people consider essential for our modern lifestyles.
To utilize energy when the sun isn't shining, batteries can be used to hold the charge. The chemical compounds are very corrosive and harmful to both humans and the environment.
Several things could help to bring down the cost of energy storage systems:
Solar panels need full exposure to the sun to generate the maximum amount of power while the sun is shining. However, few cities are located near inexpensive desert land.
To move the power to the cities, long distance transmission lines need to be constructed but the cost trends for these utilities is increasing in most areas of the world.
The cost of land acquisition costs can be alleviated by erecting low-loss transmission lines to transmit the power from the desert regions to the cities. High Voltage DC (HVDC) lines are still very expensive and high-temperature super-conductors have not yet been discovered.
Populations could also center around solar power plants so that transmission lines can be shortened and electrical losses can be kept to a minimum. However, areas where solar power plants are built tend to be rural and may not be the most desirable places for people to move.
Sheltering workers in hot, remote locations is very expensive. To bring down the installation costs:
Solar power cost trends have come down drastically over the past few decades due to improved manufacturing techniques, economy of scales in manufacturing and massive government subsidies. It will still take much more research (or an accidental scientific discovery) to make solar power more cost-effective in order to convince homeowners to adopt it over traditional energy sources.