Maximum AC Power

Inverter power limits are given in terms of the maximum AC output power of the inverter, which will be less than the DC power entering the inverter owing to the inverter efficiency being less than 100%.

Inverter maximum AC power is denoted \(P_{\text{inv,max}}(T_{\text{a}}(t))\) \(-\) this will be constant with time if there is no ambient temperature dependence.

If the inverter power, after applying the efficiency loss is greater than \(P_{\text{inv,max}}(T_{\text{a}}(t))\), then we limit the inverter power to the maximum.

$$P_{\text{inv,limited}}\left( t \right) = \begin{cases} P_{\text{inv,max}}(T_{\text{a}}(t)) & \text{if} P_{\text{inv}}\left( t \right) > P_{\text{inv,max}}(T_{\text{a}}(t)) \\ P_{\text{inv}}\left( t \right) & \text{otherwise} \end{cases}$$

The Effect associated with inverter maximum AC power for array at time t is then calculated as:

$$\Delta_{inv,PACmax}\left( t \right) = \left( \frac{P_{\text{inv,limited}}\left( t \right)}{P_{\text{inv}}\left( t \right)} - 1 \right) \bullet 100%$$

As before, the MPP values can be averaged over time and arrays to yield monthly or annual averages for the entire plant. Where an annually-representative result is to be calculated, it is important to de-season.

Temperature Dependence of Maximum AC Power

For many inverters, the maximum AC power output exhibits a temperature dependence and will be clipped at higher temperatures. SolarFarmer simulates this by allowing the user to specify a profile of Maximum AC Power as a function of ambient temperature using a series of points as shown in the figure below. SolarFarmer will interpolate linearly between these points to derive the Maximum AC power from the ambient temperature at each time step \(T_{\text{a}}(t)\).

Inverter temperature dependence