About five hundred times more solar energy falls on the lower 48 states each day than the inhabitants of that area use in a day. Harvesting that energy is seen as a panacea to our energy problems for, on average, one half of each day.
There are many ways to harvest solar energy from as basic a form as a turtle basking in the sun or a beachgoer collecting their tan, to industrial scale steam generation.
Passive solar energy is commonly taken advantage of in architectural design in the orientation of buildings and their fenestration, the application of materials and even the positioning of landscaping elements to maximize collection of solar energy. This reduces the load on conventional heating systems to save electricity or fuel.
Some industrial solar power is provided by a large-scale array of flat mirrors to track the sun during the day, reflecting the energy that falls on them to a central tower that collects the concentrated energy provided by the entire array generating high temperatures which create high temperatures in a fluid, normally an oil to collect the heat and transfer it through heat exchangers to water which generates steam, which in turn drives a steam turbine. The turbines in turn generate electricity. This is seen as a method of centralized electrical generation whose drawback is providing the acreage required to accommodate these mirror arrays on land that has a higher than average number of sunny days throughout the year. This normally means desert land, which at least does not subtract from arable acreage, but it is also remotely located relative to the population centers requiring the energy. Another method is a type of mirror called a parabolic trough that focuses solar energy on a Dewar tube that operates on the same principle as a Dewar flask or thermos bottle that runs along its focus providing thermal energy.
One drawback for flat mirror arrays and parabolic arrays that are oriented in a north/south direction is the requirement for solar tracking mirror mounts with motor drives. There will, of course, be wear and tear on these mechanisms from daily use and environmental exposure that make them fairly high maintenance items. The parabolic troughs oriented along east/west axes do not need tracking motors, although that comes at a small cost in reduced efficiency.
Another common and remarkably scalable method of generating electricity from solar energy is photovoltaic chips, which can provide power for systems as small as your pocket calculator to as large as a household and beyond. The requirement for such a system is to provide enough collection area for these fairly inefficient units to provide useful amounts of power for the specific energy needs. The expense of such a system is another high hurdle for many desiring to provide for their own energy use.
Great strides are being made in efficiency with these units, and there are even solar collecting coatings that are being developed as I write this.
Large-scale development of geothermal energy has been around for more than a century. It is accomplished by taking advantage of hot water (up to 700 degrees Fahrenheit) from the geothermal source to generate steam or collect steam directly from the source to drive generator turbines. It is a cheap and renewable source of energy.
Use of this form depends on proximity to a geothermal energy source, as they cannot be moved to where they are needed.