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One large solar array to service two different physical locations on a property?

AlaskanNoob

Solar Enthusiast
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Feb 20, 2021
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Is this doable? I have an off grid property and one area gets good sun, the rest doesn't. But I built our cabin 500-700 feet away from this good solar location and we have another cabin we're gonna build on a different part of the property that's also about 500 feet from the good sun location. I'm wondering...

Could I build a large ground mount solar array in the good sun spot, then trench 4/0 wire (whatever) to location A and also trench another wire from the solar array to location B and have the solar array know which location needs the energy the most and send it on the appropriate line?

Location A and location B would have their own MPPTs, inverter/charger, and battery bank. Would like the array to send the power to whichever location has the lowest battery bank level or highest current power demand. Are there any devices geared toward this kind of use?

Many thanks for any help!
 
I think the general consensus is that having multiple MPPT charge controllers attached to the same array is not a good idea...

My guess is that the "maximum power point tracking" of the controllers will end up fighting each other and never settle onto reasonable voltage/current optimums at any one time.

You could probably work something out with relays to programmatically control which cabin system gets to draw power from a single solar array, but there are probably better options.

My guess would be that it would be better to build a shed or something near the solar array and put your batteries/inverter/etc there, then run power out to each cabin. You can use power loss and voltage drop calculators to determine where the sweet spot is in terms of cost/efficiency, but you probably want to run as high of voltage as possible over that long distance to minimize losses - possibly stepping the voltage back down at the end for your actual devices.
 
One big solar/battery/inverter and distribute AC to wherever you want. Why complicate things with separate batteries, inverters, ...?
 
I hadn't even thought of that, but that seems like an obvious solution. Must be why I missed it.

There will be times potentially when there isn't enough power for Location A and Location B at the same time though. In the winter, we probably won't have anybody in Location A (guest cabin) and we'll get less power generated in the winter. But we'll be living in Location B. How would that work when we'd want all the power (or most of it) to go to Location B?

What happens if AC power is supplied to Location A's breaker box and nothing is using power there as nobody is there at the time. Does that power get lost in transmission? Or at least some of it through the wire's resistance?

If I haven't made my ignorance abundantly clear already, I would imagine another advantage of sending AC power to the locations as you both have brought up, would be a smaller wire would be needed since it's AC power rather than DC being transmitted?
 
What happens if AC power is supplied to Location A's breaker box and nothing is using power there as nobody is there at the time. Does that power get lost in transmission? Or at least some of it through the wire's resistance?

Nothing. In an ideal system there is no transmission loss associated with a circuit until you complete the circuit by plugging devices into it. This is the reason all those power loss and voltage drop calculators take the amperage as an input - because without a closed circuit and current flowing, there are (should be) no losses.

In practice there may be some small losses from things you might not think of like your GCFI/AFCI protection devices, but they are probably negligible.

Since you should have a breaker panel near the inverter and another one at each of the cabins, you can turn off the breaker going out to a given cabin if it will be unused for a long time if it turns out those loads are significant.

One thing this strategy does involve is only using AC power which means you'll incur the power usage of running the inverter(s) all the time. Depending on the size of the system that could use on the order of 10s or even 100s of watts even with nothing else running.

I would imagine another advantage of sending AC power to the locations as you both have brought up, would be a smaller wire would be needed since it's AC power rather than DC being transmitted?

Yes and no. It's mostly* the voltage and amperage that matters, not whether it is AC or DC. Theoretically you could transmit the power as high voltage AC or high voltage DC and still get the advantage of lower line losses - and potentially smaller/cheaper wire. You could even get that high voltage DC by putting many solar panels in series - the trade-off being that you'd need a more expensive charge controller to accept the high input voltages involved (and it still wouldn't solve your specific 2 cabins problem).

* The "mostly" above refers to the fact that with AC power you could have multiple phases sharing a neutral. e.g. 120v/240v or 3 phase - see https://diy.stackexchange.com/quest...uctor-sometimes-undersized-in-ac-applications

That said, making most of the system AC has the advantage over DC for this application for two reasons;
  1. You can use super standard (and mostly cheaper) hardware; charge controllers, inverters, breaker panels, wire, etc
  2. Most of the system can be safely installed/serviced/understood by any competent electrician
 
Thanks for taking the time to share all that info with me. I appreciate it and have lots of thinking to do.
 
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