Design and build a new heating system that uses a thermal heat store that is mainly heated by renewable systems and if required topped up by the existing oil fired boiler.
These radiators give out approx twice the heat output for the same water temperature, by having a much larger surface area, so can give out useful amounts of heat at 30 º C which is approx 50% of what most heating systems are set to.
Because they work at 30º C we should be able to get most of the energy required from the solar system each day, except when it is very cold or we have a number of days without solar radiation.