A heat pump is like a fridge working in reverse, using free heat extracted from the ambient air and then efficiently transferring it to the water.
Because they ‘extract’ heat from the air it only takes one fifth of the energy to run them as they produce.
A heat pump may produce 6 to 10kW of Heat energy for every 2kW it consumes.
We use and recommend Hot Water Heat Pumps Limited: waterheating.co.nz
For solar you need roughly 70-100% square meter area of the pool, available on the roof for the panels.
The area needs to be on NW, N, or NE exposure side of your roof. Initial install costs are roughly the same as a heat pump but of course the heat is free thereafter. As sunlight is not always dependable, speed of heating may be slow or non-existent.
We use and recomend this supplier: heliocol.co.nz
Pool Solar Bubble Covers
Remember also that a pool cover is the most energy efficient product for your pool.
Pool covers insulate and trap sunlight heat as well as preventing evaporation.