Power Inverter

Continuing to work backwards, we need a feed line that can supply 220 VAC at 100 amps.  This will run between the infeed breaker and the power inverter outlet.  If the inverter outlet is very far from the load center, you will need to derate the feed wire appropriately.  

Derating is used to adjust any load carrying wire for various conditions.  A wire that is capable of carrying 100 amps is only rated to do that for a certain length of wire.  After that, you may need to use larger wire to carry the load a longer distance.  This is typically due to voltage drop on the line due to length.  Other conditions may contribute to derating, but excessive length is the most common.

Keep in mind that the inverter is going to produce some heat, based on the efficiency and how it is configured.  So it is not a good idea to put it inside the house.  

Remember, any heat you bring in the house will have to be neutralized by a cooling system.  You get hit multiple times by these kinds of inefficiencies.

  1. wasted energy from the inverter.  Literally, energy you captured and is wasted by the inverter
  2. That wasted energy gets converted to heat in your house
  3. Your AC has to neutralize that heat that would not have existed without the inefficiency of the inverter
  4. the inverter has to supply more energy to the AC to neutralize the heat the inverter produced.
  5. that extra energy also causes the inverter to waste more energy
  6. the AC is not very efficient at all, so you are spending a large amount of energy neutralizing the effects of a small amount of energy
An example of this effect is as follows:

Inverter X is 90% efficient.
You are supplying 90 kWh of energy through that inverter.
The inverter is consuming 100 kWh of energy and supplying 90 kWh for use.
If the inverter is outside or in an area where it is not actively cooled, you are getting a 90% overall efficiency from the input of the inverter to the consumption of the energy.

Lets look at the inverter being housed inside a conditioned space.
Inverter X is 90% efficient.
You are supplying 90 kWh of energy through that inverter.
The inverter is consuming 100 kWh of energy and supplying 90 kWh for use.
BUT, the HVAC system is having to neutralize 10 kWh of heat produced by the inverter.
Since the HVAC system is 33.33% efficient, you need an additional 30 kWh of energy supplied to the HVAC system.  
Now your inverter is supplying 120 kWh in order to give you 90 kWh of useable energy.
The efficiency has now dropped to 75%
It gets worse.  To supply that extra 30 kWh of energy, the inverter has to actually consume 33 kWh due to its 90% efficiency.  
Now you are setting at 133 kWh consumed by the inverter in order to supply 90 kWh of energy.
that is just a 67.67% efficiency out of a system with a 90% efficient inverter.

This cycle continues, but the first two iterations show the effects without getting into calculus.

If you are in a climate that is primarily cool, you may be able to reclaim this heat and use it, but that is typically not a desirable place for a solar power system. 

Another idea is to reclaim the heat for other uses such as heating water, or heating the house in the Winter.  But, as you can see it is far more efficient to dump the heat outside than it is to try and neutralize it with and HVAC system.

It is much more efficient to place the inverter in a place where the heat can dissipate without needing to be actively neutralized. It is pretty common to place the inverter, charge controller and batteries in the same container. This allows you to make use of the waste heat in the Winter time since the batteries need to be kept warm to function at peak performance.  You can utilize all of this wasted energy to help do that.

Finally, the inverter selection is fairly simple.  You need an inverter that can supply 220 VAC at 100 amps.  There are features to consider, but this is the fundamental parameter for the selection of the inverter.

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