No panels, no fuel, nothing to switch. Watch a full day and night: in winter the solarium soaks up the sun and holds the heat overnight; in summer the high sun is turned away and the house stays cool.
Winter. Through the day the low sun pours onto the floor and the solarium climbs from cold to hot. The mass banks that heat and gives it back overnight — so the room stays warm long after the sun is down, and the heat flows into the house.
How hot is "hot"? On a clear winter day a Sophab solarium can reach the low 30s °C inside while it's well below freezing outside. Your house only needs about 20 °C — everything above that is free heat you can bank.
In winter the midday sun rides low across the southern sky; in summer it climbs steep and high. That seasonal swing is the whole opportunity — welcome one, refuse the other.
The glazing is steep down low and lies over up top. Low winter sun hits the steep part square and streams in; high summer sun hits the crown and is turned away — no switch to flip.
A dark floor or wall soaks up the daytime sun and lets it back out slowly overnight, flattening the cold. Add earth tubes and the ground lends a hand too.