Earlier quoted context omitted.
They have very good thermal coeffiency: ground source heat pumps will typically generate 3-6kWh of thermal energy from 1kWh of electricity. By reversing the flow you can also use ground source heat pumps for cooling as well.
Doesn't sound like "basically free" to me... It still uses electricity, which doesn't help with climate change (even if it mostly comes from renewables).
Charge the battery from the solar and it powers the AC in the evening.
You'll generate more than enough during the day to run AC and fill the battery to run it overnight.
Still using grid sources in winter, but you aren't using the AC. Although you might find air-air AC in heat mode is better than your gas boiler.