How Inverter Sizing Works for Solar
Inverters are a key part of solar panel installations, as they convert the solar power generated by your solar panels into AC energy – the kind that powers every other device in your home. AC power is considered the most stable form of power for transport, as it does not degrade and lose energy as quickly as DC power does.
The inverter’s job converts the DC power from your solar panel into AC power. You want an inverter that is large enough to handle the output of your solar panels.
However the general rule of thumb is that your inverter will be rated for about 80% of the watt output that your solar panels are rated for.
Yes, your inverters are typically rated for less energy than your solar panels are rated for! This is because your solar panel’s advertised watt-rating is peak power, which is the maximum amount of electricity your panel can produce under optimal conditions.
What are optimal solar conditions?
- Close to the equator so that your panels are parallel with the sun and light is not refracted by Earth’s atmosphere.
- No cloud cover or other shadowing.
- Proper alignment / face direction of your panels.
Now a good solar installation will take care of properly aligning your panels (to face the South in the Northern Hemisphere), but this doesn’t guarantee peak generating power unless you’re very close to the equator – something we are not here in Iowa.
So that means the peak power output of your solar panels will rarely be achieved. Maybe 5% of the time that your panels generate power will they be operating even within 90% of peak power. So trying to oversize your inverter to accommodate this small fraction of time will actually end up costing you money in additional wiring, inverters, and installation labor, reducing the payback period of your solar panels.
Manufacturers also recommend choosing undersized inverters – a process known as overclocking. It’s considered an effective best-practice when it comes to optimizing your system’s performance.
Is it dangerous to under-size an inverter? No! Not if your inverter lists the wattage of your solar panel in its acceptable input range. This means that if your inverter is under-sized, power will be “clipped” to the maximum output of the inverter if the solar panels produce more than peak energy. However this accounts for a small fraction of the overall amount of generating time, so it doesn’t affect your returns significantly enough to merit a larger – and significantly more expensive – inverter.