I have a fairly similar size system. There are 90 tubes plus three flat plate panels. There is a separate system with sixty tubes for hot water. My system heats an overground clay store with straw bales for insulation. There is about 180 litres of clay and rock and the stores about 100 kwh per degree centigrade. It is just used to preheat water for a 3 kW heat pump but I now have a ground loop so I am planning to use the panels for heat in spring and autumn. There is a store in the attic with about 860 litres capacity or about 1 kW per degree. The panels can generate about 7 kW when the sun is shining so the main store would be needed in summer.

Because most of the piping in the store is plastic circulation is limited to 100C. This can happen after power cuts. The panels can take the heat but then clear skies are quite rare in Ireland, five days out of six are cloudy.