Solar Company Shortcuts – Oversizing the Inverter

A majority of solar companies like to “oversize” the inverter, or as it is better known in the industry, “clipping the inverter”. However, most companies do this to the detriment of the customer in order to give themselves a cost advantage. For example, a customer will buy a 7 KW solar system, but the inverter used for the installation will be a 5 KW inverter. So what is the point of a customer paying for the benefits of a 7 KW system, but the solar system peak power be capped at 5KW (the size of the inverter)? That absolutely makes no sense.

So your next question will be, how is this even legal or possible? Great question. Let’s go straight to the source (i.e., one of the leading manufacturers of inverters). Once again, an installer can oversize the inverter, but there are certain risks attached to that. Let’s take a look at its response on this issue:

Oversizing the inverter maximizes power output in low light conditions, thus allowing the installation of a smaller inverter for a given DC array (or alternately installation of more DC power for a given inverter). Oversizing the inverter is typically not a requirement, however an experienced PV designer may choose to oversize the inverter in order to maximize the power production, due to the following:

  • Actual PV module power vs. module nominal power
  • Financial considerations

On the other hand, too much oversizing may negatively affect the inverter power production: Inverters are designed to generate output power up to a maximum AC power that cannot be exceeded, and they limit (clip) the power when the actual produced DC power is higher than what the inverter can output. This results in loss of energy. Oversizing the inverter also causes the inverter to operate at high power for longer periods, thus affecting its lifetime. Operating at higher power also increases inverter heating and may heat its surroundings. Inverters will reduce their peak power generation in case of overheating.

Ok, let’s break this down by discussing a few key points that I bolded:

  • Financial Considerations – By using a smaller inverter than the installer should, it saves the installer a few hundred dollars. Over time, that $200-$300 savings on each customer becomes a huge profit for the company. So, it pays off for the company to shortchange the customer in order to keep costs down.
  • Operating at Higher Power Can Affect Its Lifetime – If your inverter is capped and always running at its limit because your solar system size is bigger than the inverter size, that is going to affect the lifetime of the inverter. It’s similar to buying a new car. Which car will last longer?:  (A) the person who drives normally; or (B) the person who continually pushes the car to its limits, driving like a maniac 24/7? The answer is obvious; so, it’s fruitless to make a long-term investment when your inverter is going to malfunction in 3-5 years because of excessive wear and tear.
  • Operating at Higher Power Increases Heating and Its Surroundings – “Excessive heat is generally good for electrical appliances correct?” “No?” “Oh, well I am sure we can use the extra heat during our cool summers”

Again, you are allowed to oversize the inverter, but only in a few limited scenarios. A lot of solar companies are more concerned with saving a few more dollars versus actually giving the customer the most bang for their buck. If your solar company is taking shortcuts with the inverter, what other shortcuts is it taking to save money?

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