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sciens-sciencia 08-27-18 12:01 AM

Pretty intense system requirements
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.

stevehull 08-27-18 06:06 AM

You are a planner - good. now lets get facts.

1) Call your utility and get their actual contract for a grid tie system. Don't just "talk around", get the facts and laws. They will also provide you with all the phase information if asked.

2) What is your kWt profile over the year? Do expect this to change in the upcoming years?

3) Your need for a system other that PV or grid will continue to be necessary (diesel generator). Remember, that on a sunny day, while generating kWhr with a grid tie system, if you loose grid power, than the PV system must immediately disconnect and likely shut down (by law).

4) Some solar inverter companies have some limited battery storage (2-10 kW). That is a real possibility.

5) I am confused with your DC reference. Solar is a 220 60 Hz ac system.

Excellent thinking, but make decisions and do do rather than talk talk.


NiHaoMike 08-27-18 08:12 AM

How much is the service charge? You might be able to save that if you do an interconnect between the houses. How practical it would be to have the interconnect in the first place would depend greatly on distance.

What's your usual heating fuel? It would probably make sense to build up a CHP system that doubles as a backup generator.

randen 08-27-18 11:13 AM

Sciens sciencia

Have you read my thread (Anyone working toward offgrid)
Not cheap but more than capable. Solar PV, Battery storage, and inverter 20kw. But capable of much more.


u3b3rg33k 08-27-18 01:56 PM

Selling back should not be hard in Oregon. last I checked, Portland was HUGE on that.

given your needs, you'll want a system that integrates the generator and solar. solar + generator means less fuel burned while the grid is down. there's a few options out there (xantrex XW comes to mind, might be outdated - grid tie inside of your transfer switch is another, but requires a completely separate UPS solution).

there is no ROI on a generator, just offset losses. there is ROI on solar. and remember, you do not necessarily want all your solar facing south. west and east may be useful, too. south is what gets you the grants, but if you diversify the direction based on your available space, you'll get more even load - this may be important depending on your battery bank size.

if you're looking for a diesel genset capable of running for 20+days, plan on having a 500 gallon (or larger) tank of diesel on hand, and spending at least 20k on a (new) auto-start genset. it's probably worth seeing what that money gets you in a larger battery+panel setup vs the spend on fuel/generator.

sciens-sciencia 08-27-18 04:45 PM

Excellent replies from everyone!


Ill make a call to the utility. I have been talking with people who have tried it (big shots who run/ran big name solar businesses in our area).

If i do some quick math, a rough estimate of daily kwh is 90kwh/month when everything is running in the data center +/- 10-20kwh for house uses.

I am aware of the legal requirements to ensure the grid is non-live in a POCO outage event. THis is common-sensical. I hate working on live lines too.

The solar batteries would really be to ensure power is uninterrupted while a generator kicks on. Massive battery arrays could be a future addition, but not completely necessary considering the cost.

As far as i was aware of, solar cells produce DC power unless you have the AC mini-inverters on solar strings. THis is why solar generation is often connected to DC batteries. Wind and hydropower however use the same function as a magnetic-coil generator but utilize hydraulic energy or wind energy to turn an alternator, thus providing AC.


The distance from service drop to service drop is roughly 260ft. THis makes the midpoint for the substation between the houses roughly 130ft. Service charges i presume would be the monthly service fees aside from kwh usage, this i am not certain of at the moment.

Heat is either wood stove or electric heaters.

Not sure what a CHP system is. I will look into this.


I will take a look at your post history and research the topic you referenced.


all points i ahve considered. The majority of my roofs are angled roughly southward. A few roofs face east and of course opposing west, but west downt get a lot of sun where I am located due to mountains.

Main consideration on selling back is i am not sure if i can generate enough power to run the datacenter (roughly 3kw/hr if things are running full bore), charge batteries from any outage or night loads and generate excess power to sell back.

Again, thank you all for your excellent responses!

u3b3rg33k 08-27-18 06:06 PM

The xantrex XW system - when I looked at it last, would use the grid to charge batteries when the pricing was advantageous. I'm sure it could be configured either way.

at work, we have UPSes between the generator and equipment so the equipment doesn't see the 10s downtime between power fail and genset pick up the load (we keep all the generators hot 24/7 so they're ready to go without warmup). this keeps battery requirements to a minimum (lower TCO on the UPSes).

CHP - combined heat and power. you can use the waste heat from your generators to heat your house when you need heat. this is usually done by tapping in to the cooling system to indoor radiators. any heat you need gets taken from the generator's waste heat, and the generator's radiator thermostat gets left alone so that when you don't need heat it maintains proper cooling.
you only get 35-40% fuel efficiency out of the generator when it's running, you can get another 25-30% fuel efficiency if you can use all the "waste" heat from the radiator.

also remember you can use the waste heat from your computers for space heating as well. not sure how you're managing that now.

sunspot 08-27-18 11:45 PM


Originally Posted by sciens-sciencia (Post 59699)
Likely going to go diesel since it requires less treatment than gasoline to store for long stretches. /Power%20Systems%20Diagram.jpg[/IMG]

Propane stores best.

jeff5may 08-29-18 09:07 AM

Ok here's why your DC connect idea is not such a great idea:

1. DC power equals big wires. Low voltage high current. Which induces loss at the square of the current per unit length. High voltage low current equals less power losses but way more deadly.

2. Everything tied to the DC feed must operate at that voltage or be converted. Yes, even battery banks need a charge controller. When the sun goes down, none of that dc stuff will work without being backfed from another power source.

3. Battery banks ain't cheap. Running night after night will wear them down in a few years. Then you get to buy new batteries.

It all depends on details and intentions. Being grid independent is satisfying but expensive.

pinballlooking 08-29-18 09:27 AM

Did you find out if your power company has net metering? What are the details for it?
The grid is the cheapest battery if they have net metering. I have 12.5 KW solar and even when charging my car 3.3 KW and running AC I am usually still putting power back into the grid.
My daily solar power average this year I am making 52 KW a day.

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