Capacity is the most they can produce at any given time. Solar only produces power during the day. Geothermal produces power 24 hours a day, without any regard for day or night. Therefore for the same “capacity” geothermal will produce more power per day because it produces for more hours a day at the same rate.

(This does not account for any complications such as the cost of that capacity or whether geothermal has other downtime to consider.)