To make it simple, a solar heat plant heats up water (or another fluid) by the radiance of sunlight. This energy can be stored either in a tank or it can be passed on directly to a process by a heat exchanger.
Ideally, a solar heat plant heats up water to approx. 95°C. Processes that require warm water can be supplied directly by a heat exchanger. In Processes that require steam, e.g. for softening bentwood, this water can be fed into a steam generator. It is then not needed anymore to heat up the water from supply temperature up to steam temperature.
Feeder water has to be heated up from supply temperature 10°C to steam temperature of 110°C. When heating up this water directly in a steam boiler, the required energy is to heat up this amount of water for 100K (consumption of electricity or fuels). When using a solar process heat plant, that feeder water is first heated up from 10°C to 95°C in the solar heat plant for 85K and then fed into the steam boiler, where it has just to be heated up from 95°C to 110°C for another 15K. In this way, 85% of the energy can be saved easily by a solar process heat plant.