# '''The Size of the Storage Tank''': a bigger tank will keep water hotter longer. Homemade tanks are less expensive than commercially bought ones.
# '''The Surface Area of the Solar Collectors''': a bigger surface area for the sun to hit results in more water being heated. In hot climates increase the storage to 2 gallons (7.5 litres) per square foot (0.09 m²). If you don't get this ratio right, there's a possibility that the system will overheat during summer or not heat the water enough during winter.
# '''Collector Materials Used''': Traditional traditional (commercial) solar collectors have copper tubing attached to copper heat absorbing fins because this provides the best thermal performance, but at a premium price. Homemade solar water heater collectors can be made at a much lower cost using copper tubes mated to aluminium fins and obtain almost the same performance. Pex tubing/aluminium fins cost about 1/6th the price of commercial ones with approximately 15% loss in performance.
# '''Tilt Angle and Orientation of Collectors''': homemade solar water heater collectors in the Southern hemisphere should face due north and in the Northern hemisphere, due south. The optimal tilt angle you mount the collectors at should be equal to the latitude of your location but the performance difference only becomes noticeable if the angle is more than 10% out.
# '''Coil Heat Exchanger Material and Dimensions''': Copper copper heat exchangers are the best but at a high cost. To make things more affordable a pex/copper hybrid or pure pex heat exchanger is acceptable but they will be less efficient than the copper equivalent. The longer the coil, the more water can be heated at a time, so a 1 inch (2.54 cm) diameter 300 foot (91.44 meters) coil of pipe can hold 12 gallons (45.42 litres) of water, which will be very efficient because many hot water draws are less than that volume.
# '''Insulation on Tanks and Piping''': it's important to insulate properly because the less standby heat lost the longer the water will stay warm and the less the homemade solar water heater system has to work to heat it up again. It also helps to extend the time hot water will be available under cloudy conditions.
# '''Hot Water Demand''': The the more hot water you use, the worse your system will perform due to the fact that it has to heat up a larger volume of incoming cold water to the desired temperature.
# '''Site Obstructions''': your commercial and homemade solar hot water collectors should be situated so that they get as much exposure to the sun as possible and that means making sure that obstructions such as trees are taken into consideration before deciding on where to locate them.
# '''Geographic Location''': the closer you get to the equator, the more energy the sun will provide to heat water, due to the fact that the surface of the earth faces the sun directly there.