I have 1.5k Solar panels - which should make it 150 MW. But production shows as max 1.1 GW. Could be due to (additional 6 MW) mixing of Solar panels, Shelter, Gas Power Plant and Wind Turbines...
Solar panels energy production is based on what time it is ingame, if its night it will not generate any power at all. Second the system will not produce more energy than you are using. So most likely you have 6MW spare energy that you can pull out.