In answer to the question of “why are my solar panels underperforming their rated capacity” I have some information that you might find useful. The rated capacity of these 4 panels is 400 watts. You probably already know that panel angle and whether the weather is sunny or cloudy can have a effect on power output. What you may not know is that how you connect your solar panels to the power station can also have a huge effect.My power station is rated at having 500 watts maximum solar input power so I assumed that I should have no problem connecting it to 400 watts of solar panels, but my power station has maximum solar input voltage of 60 volts and maximum solar input current of 15 amps. Each of the 4 solar panels has normal output voltage of not more than 12 volts but a peak output voltage of 19.5 volts and peak output current of 8.33 amps.If you connect the panels in parallel (positive of one panel to positive of the next panel and negative to negative of the next panel), the peak output voltage would stay at 19.5 volts but the peak output current would be 33.32 amps which exceeds the input current capacity of the power station. The power station would reject the current over 15 amps, so power output would be reduced by a little more than half and the excessive current could damage the power station. If you connect the panels together in series (positive of one panel to negative of the next panel), the peak output voltage of the 4 panels would be 78 volts and the peak output current would stay at 8.33 amps which exceeds the input voltage capacity of the power station. Power output would be reduced by about a quarter and you would again risk damage to the power station.In this example, I should be able to maximize power output by connecting the panels in series using a solar power controller. There are two types of solar power controllers, PWN and MPPT. PWN controllers are cheaper but they only reduce the voltage without a corresponding increase in the amperage so you lose power output. The MPPT controllers cost more but they increase amperage as they decrease voltage with no loss in power output. I have ordered an MPPT controller and am optimistic of getting optimal power production.