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sciens-sciencia

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Posts: 2
Reply with quote  #1 
So, this may be nuts, but i need a pretty robust system to meet the needs/wants of myself and my family in regards to solar power.

I live in rural Oregon, power goes out for at least 20 days per year in the winter months not to mention the occasional summer "whoops, someone fell a power pole" instances.

I am running a data center from my shop for my tech business. A generator is pretty much a requirement for the days that power will be in blackout. Likely going to go diesel since it requires less treatment than gasoline to store for long stretches. The main focus for me is uninterrupted power during an outage event.

Grandma wants a solar system and likes the idea of grid-tied solar that "sells power" back to the company.

After a LOT of asking around I came to the conclusion that the whole "selling back" concept is both rather unfeasible and complicated with legalities and the like, not to mention the efficiency investments such as DC appliances and so on.

Oh yea, this is also for two houses across two acres. So I am planning on building a substation between them to house all the systems in a central area.

We have ~2000 sq/ft of roof space between houses and garages that get quite reasonable sun.

Power usage is pretty minimal except for the data center (~20A@110V)

SOmething that particularly spikes my frustrated confusion is phasing of power. I am not sure what the power company provides (1/3-phase) and i see inverters that are around my wattage needs (of which i have arbitrarily calculated out to ~10kW) and most are three-phase. Any ideas is single or triple phase is industry standard for residential?

I have an image of something i have drafted with my limited knowledge. At this point, i defer to the community for suggestions, criticism and guidance.

Power Systems Diagram.jpg 

stmbtwle

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Reply with quote  #2 
Grid-tie has some advantages:
It's usually cheaper and definitely simpler.
It doesn't have to be 100% of your usage, as the power company picks up the slack.
It doesn't need the expense and hassle of batteries, generators, etc. and is pretty much hassle free.
DC appliances are not required.

HOWEVER being "tied", when the grid goes down, your system does too.  Probably not a good choice where the utility power is unreliable.

Off-grid may be more reliable but with batteries, controllers, and backup generator it's going to be more expensive and complicated. 

There are also "hybrid" systems that have some of the advantages (and disadvantages) of both.

If the grid is "generally" reliable, you might consider a grid-tied system with a backup generator. 

These days I think most systems have an inverter, rather than DC appliances.  There MIGHT be some loss of efficiency, but you don't need the expense of DC wiring or pricey appliances. Your existing AC wiring and appliances work fine, they're cheaper, and you have a lot more choices.  

---------------------------------------

Do you HAVE to have two complete systems as shown? Seems to me you could save money with ONE system powering both homes (possibly a master/slave setup). 


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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
jjackstone

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Posts: 75
Reply with quote  #3 
You don't say how far your cable runs will be between the two houses. If you're running across a full acre to get to each house, then you will need to use some pretty heavy duty cable so as not to drop too much voltage on the runs. Plus you'll likely need to trench and run pvc conduit. It might end up cheaper and a lot less time consuming to build two separate systems, one at each house. Other than the proper permitting and inspection, what is the problem with connecting to the grid? Most people report decent results by selling back to the power company but YMMV. Maybe things are more difficult in your area.
Personally, once I collect enough battery storage I will go offgrid myself just because I can. This is as much as a hobby to me as anything else. But long run I expect to save a little money as energy costs here double about every eight to ten years and show no signs of slowing. That's assuming I live long enoough. Haha.

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sciens-sciencia

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Posts: 2
Reply with quote  #4 
Excellent replies from everyone!

stmbtwle:
I have two separate properties and the diagram is a logical diagram, not physical. The solar arrays will be set on roofs of two houses and two garages. Generators and batteries will be stored in/near a central substation-esque building. Electrical wires will have to be buried and the like.

jjackstone

The distance from service drop to service drop is roughly 260ft. This makes the midpoint for the substation between the houses roughly 130ft. Trenching and PVC conduit isnt an issue for me. I already have buried fiber/copper data cables so more trenching isnt an issue.

The issue isnt selling back itself as much as the actual realizable gains from being able to do so. Power consumption of the data center will likely consume most solar power generated, although i havent worked out exactly how much power i can potentially gain from the ~2000sq ft of roof space I have.
stmbtwle

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Reply with quote  #5 
So instead of one solar array as drawn, there are actually TWO arrays, presumably each connected to its respective inverter/charge controller.

If you connect the auxiliary DC to the battery side of the inverter, you are now down to only ONE pair of wires from the house to the central battery. Splitting the battery in two would eliminate even that and should be more efficient and less expensive, though I can appreciate the advantage of the central battery.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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