Technically speaking, solar energy is the only energy we have. Every other “energy” is a derivative of the sun's energy hitting the earth. Fossil fuels, wind power, biofuels, and even wood are all products of the sun. It is the most abundant and basic forms of energy. Unfortunately, it is difficult to capture without some technology. Using the sun to heat something, like water, is the most basic form of using this energy, but with this, you can produce heat, electricity or hydrogen. Combining these cycles increases the efficiency, so that you get heat and electricity from the same system. The key with solar is simplicity. The simpler, the better, and the longer it will last.

Photovoltaic energy is electricity that is produced by cells than convert the energy in sunlight into electricity. These are the solar panels we all know about and see in many forms. PV panels have been on the market for at least 30 years now, and in that time they have increased in efficiency, but not decreased in cost. This is in part due to the fact that they are rather complex to make and require high grade silicon, which is becoming short in supply. This makes PV panels the most expensive option for alternative energy. So why would anyone buy them? Because they are as simple as off-grid electricity gets. Plug and play, you might say. All you need is a panel and a battery, and maybe a controller. That's quite a bit different from a wind generator that has several systems working together just in the generation part of the system. But cost is usually an issue, so most home-based systems use a bit of solar PV and lot of other types, like solar thermal, wind , and biofuels.

Solar Thermal
Solar thermal production is the next step up the ladder of complexity. Basically, you heat a fluid with the sun and that heat is then used to heat water, air, or maybe generate electricity with a heat engine. This is by far the most common use of solar energy, mainly because it is simple and inexpensive to implement. Heating is also very inefficient when using electricity as the source of energy, so with a solar thermal system, you can kill two birds with one stone. Get your hot water and space heating for free, and reduce the drain on the batteries, requiring a much smaller electrical system. These systems come in all sorts of shapes and sizes, depending on what you want to heat and how hot you want it to get.

Solar Tower
A Solar tower is basically a large scale solar thermal system. When I say large scale, I really mean mega scale, way beyond a backyard system, but the components are essentially the same. The sun's energy is concentrated to a fixed point and high temperatures are generated, which then can be used to generate electricity or be used directly as heat for homes and water. These massive designs are for populated areas where individual solar thermal or PV systems might not be practical. How does killing a million birds with one stone sound? Its a very attractive sort of system for some areas that get a lot of sun throughout the year.

Combined Heat and Power
Solar PV or thermal systems by themselves don't enjoy great efficiencies. Maybe 10-20% of the sun's energy is actually converted into usable energy. So, to make these designs more efficient and practical, we use combined heat and power cycles. The idea is that you need a bit of cold to generate electricity, or rather, you need a temperature difference to generate usable power. To create that difference, you can either heat the atmosphere around your device, or you can use that heat for another purpose. Think of the radiator in the car. It is actually cooling the engine to make it run smoother and cooler. Now, that hot water could then be used for heating a home. That's the basis of a Solar Combined Heat and Power system. Generate a bunch fo heat with the sun, then use that heat to generate electricity, and use the waste heat to heat your house or water or dry your clothes. These combinations are common in steam and coal power plants where there is a lot of wasted heat and systems efficiencies are very low. When these “wastes” are then used, overall system efficiency can easily double or triple.

Although Solar energy is widely abundant, capturing it and putting it to use can be tricky. It is an attractive are of research, however because these systems are relatively simple and enjoy long lifetimes of maintenance-free service. The key to making them work is in the design. With a little forethought, a solar energy system can virtually power your entire infrastructure with very little continued cost.