Inverter Focus - Nominal and Apparent Power

How does HelioScope model inverter power?

HelioScope models inverter power using nominal power. This is because HelioScope simulates production in hourly increments. To model on an hourly basis, we must use the power and voltage values that can be sustained by an inverter for a full hour in normal operating conditions. Occasionally we have requests to upload inverters at their AC Apparent Power, at an odd nominal voltage range, or inverters that overpower to a certain value. Here we will describe how HelioScope models inverters based on these different conditions:

1) Modeling with Nominal Power

HelioScope models inverter power based off of the listed nominal power. This models performance of inverters on the DC side well, but does not take grid conditions and apparent power into account. Apparent power is the sum of real and reactive power. Because reactive power depends on the phase matching with the grid, it is not modeled. Apparent or reactive power has the units VA/kVA. The real power value that HelioScope can use will have units of W.

2) Voltage Range doesn't update with temperature

Inverters can have a nominal power measured at an irregular temperature. However, HelioScope does not model the change in the inverter's voltage range when the inverter's internal temperature changes. While we have external temperatures from available weather data, there is not yet a model for calculating internal inverter temperatures, which would be the temperatures affecting nominal power. This means that if a nominal power is measured at an odd temperature, we do not consider the effect of that temperature.

3) Inverter Overpower Boost

HelioScope inverter power does not vary based on grid conditions. This means that the program does not model “overpower boosts” in inverters, as these are typically only possible for less than an hour. HelioScope weather files predict production on an hourly basis, so the program can only be used to simulate behaviors that can be sustained for the full hour.