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>> You keep using that word; I do not think it means what you think it means.  -- [[https://www.youtube.com/watch?v=G2y8Sx4B2Sk|Inigo Montoya in the Princess Bride]]

====== "Efficient" ======


The word //efficienct// is often mis-used in vanworld to mean something like:

  * //better// 
  * //preferable//
  * //makes more power//
  * or, perhaps more cynically, //the thing I bought// 

... without describing the use case. 

It will simplify matters if we think of efficiency as ''power in / power out''.  Round numbers example:  if a component requires 220W in to make 200W out then it is ~90% efficient with ~10% lost, typically as heat.

Made up examples:

  * 200w inverter, 85% efficient
  * 1000w inverter, 80% efficient

Which one can make more 120v power?   The 1000w one.  Which one is more //efficient//?  The 200w one.  



===== getting it wrong =====

==== solar panels ====

[[electrical:solar:panels#efficiency|Solar panel efficiency]] doesn't mean //how much power the panel will make// or anything like that. A more efficient panel and a less efficient panel **of the same rated wattage** will harvest the same power, all other things being equal. 

Panel efficiency is a mathematical relationship between the panel's **area** and its rated power.  **Efficiency makes no difference** unless you are maxxed out for panel space. 


==== solar charge controllers ====

MPPT are not more //efficient// than PWM controllers.  MPPT have DC-DC conversion losses (typically ~5%) and PWM do not.  

Will the MPPT harvest more in Bulk?  Yes, on average MPPT controllers will harvest ~13% more energy (Watt-hours) from sunlight than the same system on PWM.  But it incurs losses while doing so.  There are [[electrical:solar:charge_controller#when_pwm_beats_mppt|scenarios where PWM can harvest more power than MPPT]] because of MPPT's buck/boost losses.  


===== getting it right =====


[[electrical:inverter|Inverters]] are the usual case where efficiency is discussed accurately;  see the examples at top.  Even then we often do not account for standby losses.
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