Inverters
Inverters - Installed
Inverters should be kept cool, as a hot inverter operates less efficiently.
Consider that a 2 kW inverter that is 94% efficient will generate 120W of heat in the middle of the day.
If this heat is not dissipated (perhaps because the inverter is located in an enclosure), the inverter will heat up, operating less efficiently and thus generating more heat in a reinforcing cycle.
Inverters attempt to de-rate system output power as they approach their maximum rated temperature. This means losses in energy yield.
Inverters that exceed their maximum rated temperature typically shut themselves down, possibly for the whole day. Again, this results in loss of energy yield.
Therefore:
- Good ventilation is essential in order to have a high-performance system.
- Inverters should be placed out of the direct sunlight.
Manufacturer's design tools cover many design criteria.
Inverter efficiency
Inverter efficiency varies with many factors, including temperature.
The maximum efficiency should not be assumed for performance calculations. The Euro Efficiency is a better gauge of operational efficiency.
Inverter's efficiency is typically higher for higher input power.
Inverter's efficiency may also be higher for higher voltage DC input.
Voltage windows
Most inverters have two voltage windows – a minimum and maximum input voltage, and a range over which the MPPT operates.
Be aware of the following "catches":
The array's Vmp must be higher than the inverter's minimum voltage when de-rated for operating temperature (assume 70°C).
The array's Voc must not exceeded the inverter's maximum voltage when the de-rated for minimum operating temperature (assume -10°C or 0°C depending on local climate). Also ensure the array's maximum voltage does not exceed the maximum permissible in the panel's specification sheets.
The voltage windows may vary depending on the grid voltage. The quoted values may assume VAC = 230V or 240V. However, in many situations grid voltage can be as high as 253V, and if the panels' output falls below the inverters minimum voltage then the system may simply sit idle.
Check that these factors are accounted for in the design tool.
Operation outside the MPPT window can lead to highly inefficient operation.
For some inverters, it is possible to exceed the maximum input current. However, the system will not operate nearly as efficiently, and the inverter may be overstressed and thus have a shorter life.
See below a picture of our Power One Aurora Inverter, then the Power One Aurora Inverter installed.
