Solar Photovoltaic Systems

This section covers the conversion of incident solar radiation at a panel to electricity.

NREL insolation map

This shows insolation in units of kWh/sq m/day.

You can thing of peak sun hours as equivalent duration of standard test conditions that would provide the same amount of energy.

E = P \cdot PSH

Where E is the energy per day, P is the power of the panel at peak sun, and PSH is the number of peak sun hours.

Peak sun hours is usually a yearly average of the equivalent hours of noon sun that a location gets during the year

We multiply peak sun hours by peak insolation to get total solar energy delivered.

We then multiply by the efficiency of the solar panel to get DC electricity energy.

We further multiply by the various system efficiencies to get the AC electricity energy.

Derating takes the many efficiency factors that change throughout the day and year and distills them to a single average.

A panel is rated according to its peak DC output at standard test conditions (STC)
From this ideal DC output, how much AC power is delivered?
What are the power losses?
We combine all these power losses into a single factor called a “derate”

The overall derate factor is the product of all the efficiencies

\eta_{overall} = \eta_{inverter} \eta_{mismatch} \cdots \eta_{temperature}

How do we go from derate factors that change hourly to an daily or yearly average?

We multiply the rated DC power by the hours of peak sun each day by the number of days each year and then we add the derate factor.

\textrm{AC Energy (kWh/yr)} = P_{DC-STC} \cdot PSH \cdot 365 \cdot derate