Further reading:
Passive solar Building tips Great Ideas from Green Builder
Solar Thermal history A history of the solar thermal industry
How solar panels work A great site that tells all the fancy physics stuff

            Every 40 Minutes enough solar energy hits the United States to power everything in that country for a whole year.  That is a lot of power!  In fact just about everything on this planet is solar powered.  Plants we eat come from the sun, fossil fuels are really just old plants and animals, wind power is caused by the sun creating different hot and cold areas on the planet, hydro energy is caused by rain which in turn is caused by the heat from the sun, even tidal energy is caused by the gravity of the sun.  Only nuclear and geothermal energy is produced without the sun (and an argument could be made that the plutonium and earth crust materials were formed in the core of some star if not our own sun)  

              Our sun is a medium type yellow star, pretty average really.  It has been around for about 5 billion years, and isn't scheduled to burn out for a little over 5 billion years.  So we can safely consider it an unlimited source of power.  There are many ways to use this free energy from the sun below is a short background on each.

PASSIVE SOLAR

            Passive solar is the use of the light and heat from the sun.  Having a sun light, or a glass enclosed porch, or even building your house facing the rising sun are all examples.  Passive solar was first used in ancient civilizations.  The ancient Greeks build there homes in such a way that the morning sun would heat there house and the noon sun would be shaded.  They gained warmth when they wanted it and protected against excess heat as well.  Many homes in the northern part of the United States are still built with there front doors facing the rising sun for extra warmth. 
            When you are building a structure the light from the sun can cut your lighting costs during the day.  Building designed with passive solar in mind are more efficient and use less money for heating, cooling, and daytime lighting.  Most passive solar heating is accomplished by creating a thermal mass, or rather a big area to soak up heat.  If you want to heat your home with passive solar you can do something as simple as putting a large brick wall behind a window and paint it black and then allow the hot air that is created to enter the room.  Of course there are more appealing ways and a good architects can help you create a myriad of passive solar designs. 

SOLAR THERMAL

            Solar thermal devices are gadgets that concentrate the sun to do something.  Be it producing steam to create electricity, or heating your house or a pool.  The basic way they work is that the sun shines down on them, and be it through mirrors or water filled black pipes, or some other method, the sun is collected and then used for what you want to use it for.  The most common of these are the solar thermal panel.  It can be seen on the roofs of many homes.  Your basic set of solar thermal panels can produce enough hot water to heat your home, or just provide you with hot water.  Even in the depths of a northern winter (below 0 temps) a solar thermal panel can produce 80-100 degree heat with relative ease.  There is a lot of energy in the suns rays and when you start concentrating it neat things can happen. 
            Solar Thermal can also be used to create electricity.  Using many mirrors and a giant collecting tower, the sun can be used to heat water till it becomes steam.  This steam is used to turn giant turbines that in turn produce electricity.  Solar thermal energy can even be stored in huge tanks of water and used later. Even on cloudy days a solar thermal device will work because it is concentrating solar energy instead of converting direct sunlight to electricity the way solar panels do. 

SOLAR PANELS (PHOTOVOLTAIC PANELS)

            Solar panels are the slick pimp daddy of the renewable energy world.  Solar panels have been around for a long time.  Modern solar panels were developed in the 50's for NASA, but people have realized that certain things produced electricity when exposed to light as early as the late 1800's.  You will find them in calculators, on homes, on space ships, on boats, even on cars trucks and RV's.  A solar panel is also known as a photovoltaic panels (photo for light, voltaic for electricity or "electricity from light").  Most solar panels are made from silicon.  A very common element, also used in computer chips, glass and a million other things.  Solar panels work because silicon is crazy.  Well not really crazy but rather a semi-conductor.  That means it sort of conducts electricity well, and sort of doesn't.  With out getting into all sorts of physics (although if you want to give me an email) silicon when formed into a crystal has the property of having not enough electrons in some atoms and too many in others.  What this usually means is that the atoms with too many electrons have them scoot over to the atoms with not enough and they then just sit there.  Not very exciting right? So if you take two chunks of silicon crystal and add (its called doping) boron to one, and phosphorus to the other you get a neat effect.  What happens is the boron layer ends up having lots of atoms with too many electrons, and the phosphorus layer ends up having lots of atoms with way too few electrons. 

            So if we connect the two guess what happens?  The answer, not a whole lot, the extra electrons zip over to the side with not enough and well then it doesn't do much of anything.  But wait!  If we sit this little setup out into the light some renewable energy magic happens.  The suns energy (single units of which are called photons) comes screaming down at the speed of light (which is very fast) and crash into the top layer's atoms.  This gives them enough juice to shoot down to the bottom layer, the bottom layer now has too many electrons, so where you do think these extra baddies go?  That's right into your light, or your battery, or your cell phone, or whatever else you hook up to the solar panel.  If you hook up another wire to the top layer and hook that up to your device you get a little loop of electrons that keep moving around and around doing work (lighting up the light, or keeping your cell phone working or whatever) until the sun goes away.