I'm trying to understand an efficiency curve from PVsyst, using this documentation

However, I'm not sure what this sentence means:

  • This production is penalized by an ohmic loss$^1$ of the internal components (transformer and transistors), which increases quadratically$^2$ with power (like R · I²)$^3$. *
  1. What is meant by ohmic loss in this instance?
  2. When it mentions that it increases quadratically, does it mean in quadratic form (equation) i.e. $ax^2 + bx + c = 0$ and how does this relate to the efficiency curve of an inverter, relative to power loss?
  3. What does the equation represent, and what does it suggest when either parameter $R$ or $I^2$ is greater than the other?

1 Answer 1


I believe what this sentence is trying to convey is that all circuit components have a small resistance associated with them if you look at them in enough detail. For example a transformer circuit can be viewed as (this is from electrical academia website:

enter image description here

The reason that the resistance is there is because there are wires in the system (unless of course you happen to have superconductive wires). When current pass through that resistance energy is converted to heat, and cannot be reclaimed. The higher the current passing through the system the higher the energy lost.

Regarding the quadratic. If you double the current through the system, then the heat losses will quadruple.

Regarding the third part of your question I am not certain what equation you refer to, and what is the exact meaning of your question.

  • $\begingroup$ The link did not address the page intended. Although, when clicking on the link documentation, then referring to "See also the construction of automatic efficiency profiles", when on that page, under the sub-heading Automatic-efficiency profiles it makes reference to the equation here: "in a quadratic way as function of the power (R * I²)" I'm not sure what R * $I^2$ represents. And thank you for the previous explanation, they're very helpful! $\endgroup$
    – Lime
    Commented Jan 28, 2021 at 16:50
  • $\begingroup$ Whilst looking at this it seems that your previous 2 explanations fulfil what the equation meant. Many thanks! $\endgroup$
    – Lime
    Commented Jan 28, 2021 at 16:52

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