We have the F750 with us and are very satisfied with it. But as always, it depends on the details. Solar thermal can only save you about 70kWh of electricity in the summer months, so about 14EUR/month. In winter, the solar thermal brings about 20°C... so it doesn’t help you. Depending on the operator and billing model, I would recommend a photovoltaic system, but that costs about 10-15kEUR on top. The F750 operates very efficiently and economically. The problem here is unfortunately that almost no one is familiar with this pump and it is therefore set incorrectly. While with other pumps you don’t pay too much attention to the number of running times, the F750 should ideally run around the clock in winter. Since it is very efficiently inverter-controlled, it runs with about 100-1,300 watts at 3-5°C outside temperature... this is also managed by our photovoltaic system on a cloudy day in winter.
In principle, the COP of ground source heat pumps is higher and they are therefore more efficient. You just have to make sure that you have a proper borehole with the appropriate medium. If you drill in dry sand, this pump will not be able to provide you with any heat. For ground source heat pumps, the nature of the soil is therefore extremely important.
If it helps you, our COP, however including ventilation system, heating control and photovoltaic control, is about 3.0-3.5. (Ground source heat pumps should be 5 and above)