The tax credits of the energy crisis of the late 70s early 80s created a surge in solar thermal systems. Because of Denver's cold winters and plenty of sun, a lot of solar systems were installed in the area. These systems were done by alot of different companies in different ways. Here's a look a some of the more common experiments that were used to create hot water.

db tank
This insulated square tank that can hold about 600 gallons of 180F water. The insulation is to help keep the heat in. If these tanks aren't made well, the heat will distort them over time.

This exploded view of a plastic square tank shows angle iron used to brace the tank walls.

This heat exchanger inside a plastic square tank is the heart of the system. The fluid around the coil heats up fluid moving through it.

fin coils
This tank contains the older style fin coils and newer smooth surface coils.

A typical bray oil module from Western Solar. These expansion
tanks dont have a bladder and are tricky to charge up.

Spas work well with solar thermal systems. The tub can be
used like a heat storage tank and the system can also be set up
to heat domestic hot water.

A typical package system installed on the storage tank.
This one by Enerworks has a small heat exchanger,
very uncommon fittings and non drainback panels.