When it comes to getting hot water, you have two main options: solar hot water or a heat pump powered by solar panels.  

First, to make 100 liters of hot water from 25°C to 65°C, you need a 4.65 kW thermal unit. If you use a solar thermal panel, you’d need 2 square meters of it to do the job. 

Now, if you go for solar PV (photovoltaic), with those same 2 square meters, you’d generate 0.45 kW of electricity, which translates to 2 kWh of electrical energy. If you use this electricity to power a heat pump, it can produce 7 units of thermal energy. 

But we only need 4.65 kW of thermal energy for the hot water. This means you only need 1.32 square meters of solar PV panels. 300-watt solar panel is enough to get you the hot water you need. 

So, if you want hot water efficiently, a small solar PV panel powering a heat pump might be the more effective and space-saving choice for your home.