The ideal situation for solar panels is facing due south, although they are effective facing anywhere between south east and south west. As a rule of thumb you need between 1 and 2 m2 of collector (solar panels) per person living in the house. Shade on the panels at any time of day will reduce the performance.
Solar hot water storage tanks can vary greatly in size, from 150L to in excess of 1000L.
Depending on the size of the tank a number of options are available to assist in the heating of water, at times when the sun shaded.
For smaller tanks an electric element can be used. For larger tanks gas or diesel boiler can be used.
Solar panels are a very effective way of heating your pool during those months when it's warm outside but not hot enough to heat the pool. A solar heating system can be used as stand alone or as a supplement to another heating system, whether that be a heat pump or an oil/gas burning system. If you're starting from scratch, and you're just looking to extend your swimming season, then a solar system is a great option.