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Electrical grid as backup

EscapedAritst

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Costa Rica
I am planning my new home to run on a residential off-grid solar system (I never want to feed back onto the grid or power equipment from the grid). But, I want to choose either the grid or a generator to backup the panels when the batteries are running low. Right now, I am trying to price a grid backup system. The distance from my meter to my main panel is 1000ft. A "normal" grid service that would power the entire house from the grid would typically require a 200amp service with two power cables, a neutral cable, and a ground cable running all the way from the meter to the main panel. Obviously, this would be very expensive.

My first question: When using the grid power to only charge batteries (i.e. never for equipment), do I need the neutral and/or the ground cables?

Second question: Since I'm only using the grid to charge batteries, can I limit the amperage at the inverter/charge controller in order to use smaller cables for the long run? If so, how do you typically do that?
 
When using the grid power to only charge batteries (i.e. never for equipment), do I need the neutral and/or the ground cables?
There are a couple of answers to that. (I assume you are in North America).

  • If your inverter/charger takes 240 in (and no neutral), you could get away without neutral,
  • If your inverter takes 240 *and* requires neutral.... it would be a problem.
  • If your inverter only takes 120, you could run just one hot and the neutral.
  • In both cases 1000ft is a long way, so you will need some big wire. (Bigger if it is 120V).
  • In both cases, I would highly advise running the ground wire.
  • I do not know what the code says about this. I don't know why it would deny running neutral if the load does not need it.... but you should check
Since I'm only using the grid to charge batteries, can I limit the amperage at the inverter/charge controller in order to use smaller cables for the long run? If so, how do you typically do that?
Most of the inverter chargers have a setting that allows you to set the max charge current. However, you don't want it to ever switch to grid mode. Most of the inverters have various settings that allow various priority settings (Example: Solar and battery first, then grid) You want to make sure the inverter you select has a 'battery & solar only' setting.
 
Here is my take on this scenario.
I am building a system for a friend of mine in this same situation. as i explained to him you will have many days during the winter where there will be no sunshine at all and to build a battery back to endure this is completely out of the question let alone the huge solar charging needed to charge between 10am and 3pm for that very large battery bank. there will be times where the solar is not charging and the battery is empty so you are forced to charge with utility. the problem with this is it will take the whole day to charge the battery and you are left with no power at your home, not a good idea in the winter time.
what i an doing is running larger utility wires to the 12k split phase inverter charger so that in case there is no power from the solar and battery needs charged the utility can power the house at last resort while charging the batteries. this is using utility as back up only and is good insurance for 25 dollars a month for the service connection fee.

sure the cable will cost a lot to run 1000 ft but just how cold will you get with no power to your home while the batteries charge?????
in my case though the utility is on the same wall as where i am going to install the split phase inverter. that and the fact that it is not grid tie so i do not need a blue print of the system for the utility company's review/acceptance.

so basically you have two choices,
1. run smaller utility wire to charge only and freeze a few times in the winter.
or
2. run normal utility line and allow power to house and battery charge as back up only at the cost of 1000 ft of cable.
 
Great thread as this is something I have been working through in my mind. My current build uses the grid to recharge the batteries this winter as I don't have enough PV. 4 days in a row right now without sun and don't expect it for a couple of more.

Forgot to add: The way I am connecting to the grid is via an extension cord. I plug into a wall outlet and then to my inverter's input.
 
According to the 12K split phase manual in order to do this you have to increase the size of the incoming AC line to accommodate the house and charge of the batteries compared to just using utility to charge. in this way every thing is taken care of and you do not freeze in the winter. setting the inverter with solar, battery priority allows the utility grid to still be used for charging and worse case scenario power your house while charging your batteries. since there is no grid feedback one does not have to provide grid feedback blue prints for utility provider approval. thus in my area it will cost 25 bucks just to keep it active which in my opinion is good insurance.

Quote from manual; " When in AC mode the AC input power will supply both the loads and AC charger, a heavier wire gauge for
AC Input is required. Please consult a qualified electrician about the specific wire gauge required." which by the way is the standard feed to a house circuit breaker pannel.


Just my two cents worth of opinion and reasoning.

PS. Battery bank will be LiFePo4 48 volt @ 400 to 500 ah.
 
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If you are worried about cost run wire for a smaller service. Is it over head or through the ground? We ran ours under ground for 280 feet and it was under $500 for a duel 200 amp service.

The power company usually doesn't provide a ground from the service. They usually provide 3 wires, L1, L2, and a neutral.

Run like a 100 amp service to charge your batteries if needed and only use them for that.
 
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Or better yet buy a used meter pole and set it yourself. utility providers will generally work with you like they are and have with myself and neighbors.
 
The distance from my meter to my main panel is 1000ft.
You cant run a "service drop" a 1000'. For that distance they run high voltage to within a reasonable distance (50 ish feet) and set a padmount transformer. The high voltage run is typically just a 3 wire and that is usually not symetric. so the current carrying conductors are larger, the neutral is smaller and they set a ground rod at the padmount for the earth (ground) 4th wire to the 200a service.
 
You cant run a "service drop" a 1000'. For that distance they run high voltage to within a reasonable distance (50 ish feet) and set a padmount transformer. The high voltage run is typically just a 3 wire and that is usually not symetric. so the current carrying conductors are larger, the neutral is smaller and they set a ground rod at the padmount for the earth (ground) 4th wire to the 200a service.
Never say never.....I have heard of 1000'ers....Call the electric company...they can let you know with little effort.
 
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