Solar and Heat Pump Hot Water
Choosing solar or heat pump - http://www.energy-without-carbon.org/SolarOrHeatPump
Best alignment for solar collectors - http://www.energy-without-carbon.org/BestAlignmentForSHW
Selecting solar HW size - http://www.energy-without-carbon.org/SelectingSolarHotWaterSize
Efficiency of heat pumps COP - http://www.energy-without-carbon.org/HeatPumpEfficiency