New Self-Sustainable Home Build Project

XSive · August 2017

My wife and I are building a new home and want to be off grid in a high tech modern home about 2500 sq.ft. near Crater Lake, OR
Details so far:
Energy envelope: ICF Construction, closed cell roof insulation (R62), Windows .26u or better. 100% Low Voltage LED lighting (DC Buss)
Radiant floor heat and some passive solar design elements. HRV system.
5.24 kWh/m2/day solar energy with an unobstructed southern exposure. 16 inches precipitation per year (this is not Portland - lol)
PV details:
I have 625sq.ft. of 60deg. south facing roof dedicated for PV generation
I also have 900sq.ft SE facing roof for additional solar for experimentation of some pet projects.
I have purchased a starter batt set of LiFePO4 used batts to get us going. 48V design (16 3.2v in series x 3 banks) We will also have an EV in the garage we could draw on to extend capacity if ever needed.
I have 46 320W 72cell mono modules.
Water Collectors
7 4'x10' Chromagen Collectors for open drain back water heater system. 900 gallon ICF water tank (135 deg) supplies radiant floor heat for house and acts as a heat exchanger for the domestic hot water supply. (280,000 Btu optimal) One of my projects is to experiment with direct PV heating elements for the water tank - much less complicated system.
Backups - propane generator and propane tankless water heater

My question to the group is how would you control 10kw worth of panels to charge the LiFePO4 batteries. I have looked at all the tier 1 charge controllers and I guess I am looking for some real world experience as I am a novice at solar but do understand most of the theory. I like the midnight solar classics but I would be regulated to 2 panel strings. All suggestions are welcome. Thanks for your input on our little adventure.

Bob
MSCE, CNA, MCP, A+, N+ (Computer stuff)
NABCEP Associate

bill von novak · August 2017

XSive said:

I have 46 320W 72cell mono modules.

That's 300 amps of charge current at 48 volts. Are you sure your batteries can handle that?

You could do it with 3-4 Midnite 150's or 4 Flexmax 80's. If you are going with an Outback inverter there is some benefit to using the Flexmax (easier integration.)

What kind of DC bus will you be using for DC lighting?

mvas · August 2017

Tesla Power Wall vs Enphase AC Battery?

XSive · August 2017

One of the things we have been considering is only commissioning a portion of what we have as new battery options seem to come around the corner at an ever increasing pace. (good thing) So that is why I called our batts a starter set. Gets us on the road so we don't need all of the 10kw yet.
I was a fan of the Aquion tech but that is not going anywhere at the moment.

XSive · August 2017

What kind of DC bus will you be using for DC lighting?

Since we just broke ground I have a little time to define the lighting circuit. I want 48V native fixtures. Being a computer guy, I lean to programmable Power over Ethernet LED's but the residential availability is still sketchy or very proprietary. I might run cat6 and 110 to all outlets if I don't find what I am looking for by the time I need to wire this winter.

Estragon · August 2017

I assume you've tried a 3 panel string with midnite string calculator using your local temps and panel specs. I don't think of OR getting that cold. Anyway, if a classic 150 (198v with hypervoc) won't work, would a 200 not do 3?

Having said that, MN has a new product (b17) that looks close to production which will apparently have both 200v and 600v controller modules. From what I've seen, it looks like an interesting product. Others (Outback, Schneider) make 600v controllers also. I personally probably wouldn't want a 600v system as 600v scares me, and more smaller strings means a bird bomb doesn't put me out of business.

If your climate tends to have a lot of days with high thin cloud, being overpanelled (within reason) can be quite useful. Max current to batteries can be limited by (most/all?) controllers for full sun days, while a surprising amount of production can be had on all but the gloomiest days with extra panel.

The project sounds really interesting.

Dave Angelini · August 2017

Are you a Wrench?
I am testing and it is almost done the solution that Schneider solar will have. You can contact me.
Here is a link to the testing over the last year here on the Forum.
http://forum.solar-electric.com/discussion/351297/conext-bridge-for-xw-li-ions-from-lg-and-hoppecke-announced-for-2nd-half-2017
For Estragon, the Schneider high voltage controller does not have the problem you mention BTW
I would look for a one make system, that is mature for anything Offgrid.
Outback is a the only other at this time and they do not have a high voltage controller.
The screen shot is missing the generator logo as I do not have one at this latitude. The system can go out to the web and be read anywhere there is internet as does Outback thru the WEB portal Insight. Tons of data and pre-made charts and graphs on both.
Beautiful place, I was there last month! Good Luck!

Image: https://us.v-cdn.net/6024911/uploads/editor/vo/qlnzisljwng4.png

XSive · August 2017

Right now I am leaning towards the MS 200, the 150 cuts a little close on colder days. We can get -10 but generally 15-25F lows in the winter. I have so many panels cause I had to buy full pallets and 1 was not enough so at .52W delivered I could not pass it up. I like the micro inverter idea but being off grid I am not enough of an electrician to follow what some have done with a Schneider to fake it out to think it is on the grid.

Raj174 · August 2017

Hi Bob,
I think 2 panel strings would work fine with the Classic 150 CC for your LFP bank, and VOC shouldn't be an issue. In fact I have the same setup and it works well charging my LFP bank. I like the ease of use and precise control the Classic provides. The Local PC app is dated, but does allow management over a network. Their "My Midnite" web app is good also
Standard charging amperage for LFP is about 1/3 capacity or 130A for your bank. Quick charge can go up to 1/2 capacity, however I don't think I would go there to often. Gentle is better for battery life.

Rick

karrak · August 2017

XSive said:My question to the group is how would you control 10kw worth of panels to charge the LiFePO4 batteries. I have looked at all the tier 1 charge controllers and I guess I am looking for some real world experience as I am a novice at solar but do understand most of the theory. I like the midnight solar classics but I would be regulated to 2 panel strings. All suggestions are welcome. Thanks for your input on our little adventure.

To get a better lifespan out of your LFP battery you should limit the maximum charge current to 0.5C (200A for a 400Ah battery) and a maximum discharge power of 1.0C.

One reason I asked if you knew what the internal resistance of your cells is that at high charge and discharge rates the energy loss within the battery if the resistance gets too high will heat the battery up which will further degrade the battery. This is made worse by the fact that at high charge/discharge rates the heating becomes uneven within the battery.

There is no problem with running multiple charge controllers in parallel.

I would make sure that any charge controller that you choose will allow you to program the bulk/absorb and float voltages, and the end current to switch from bulk/absorb to float or the absorb time down to minutes. I think one important feature to look for is the ability to shut down the controller via an external input so any battery BMS that you might install can stop the battery charge if it detects a fault within the battery. The same feature should be available with any inverters that you choose.

Simon

XSive · August 2017

Thanks Rick,
2 panels do work well, I was trying to squeeze 3 in there and it gets too close. I have 2 Classic 150's in follow me mode sketched out with 16 2 panel strings. I am just trying to see if there is a better way or something in the works like Dave is working on that I might want to consider. The Classic is solid from what I have read and is probably a safe route for me to get my feet wet in this endeavour. Do like that bleeding edge sometimes...

BTW Dave I am a wrench, we are building the entire house minus concrete flatwork ourselves. We are both retirees and we are having a second childhood because the first one did not kill us.

XSive · August 2017

karrak said:

To get a better lifespan out of your LFP battery you should limit the maximum charge current to 0.5C (200A for a 400Ah battery) and a maximum discharge power of 1.0C.

Thanks Simon,
Those were my thoughts too, I was shooting for 160A charge rate with this pack to be as gentle with it as possible considering its history. I have had a full plate the past two weeks so my battery testing has suffered getting completed. Thanks for the input.
Bob

karrak · August 2017

XSive said:
Since we just broke ground I have a little time to define the lighting circuit. I want 48V native fixtures. Being a computer guy, I lean to programmable Power over Ethernet LED's but the residential availability is still sketchy or very proprietary. I might run cat6 and 110 to all outlets if I don't find what I am looking for by the time I need to wire this winter.

What are your reasons for using 48Vdc?

When I designed my off-grid system solar panels cost ~$8.00/Watt! Because of this I went for a 24V system with a 24V DC circuit that runs the LED lighting, all low voltage equipment like computers etc. and a 24V DC fridge/freezer. This means that my inverter is on standby most of the time which saves ~1/2kWh/day. If I were installing my system today, due to the huge decrease in the price of solar power I would go for 48V and wouldn't bother with running a separate DC circuit. I think you will find that there is far more mains AC equipment that can be remotely controlled than DC 48V equipment. I would also be looking at wireless control rather than using cat6. Depending on your software/hardware capabilities, small wireless connected microcontrollers running Open Source software that can control 110V AC equipment are now really cheap and readily available.

Simon

mike95490 · August 2017

The new Magnum/Sensata Power Track-100 (PT-100) MPPT controller is good to 200Voc & 100A output

Going to 48V DC lighting - I think you should review some of the new PoE lighting systems.

It may not be possible in your inspectors code book, to mix ethernet & 120VAC in the same outlet box

Also note, the Classic series, has high speed cooling fans that will operate day time,

jonr · August 2017

For anyone doing energy efficient home design, I recommend the free BEopt software to optimize the price/performance.

With low PV prices, I think PV makes sense for water heating. With a heat pump or direct.

mcgivor · August 2017

@XSive Going back to the original post, you mentioned roof mount PV, if ground mount is an option, I would highly recommend doing so, from the standpoint of maintenance, angle change to suit seasons, cleaning and so forth. Ground arrays are are much friendlieler to trouble shoot and natural cooling is an additional benefit, just a suggestion to ponder, of course if space is a consideration, roof mount may be the best solution.

Dave Angelini · August 2017

It is cheaper to mount on a roof. It just is not better in any other way offgrid.

XSive · August 2017

Roof mounting is our only option because of space so we optimized house orientation and design for that purpose.
Thanks Jon for the BEop link. Our design is somewhat unconventional so several of our elements don't seem to be options in the program. Still checking it out.

XSive · August 2017

mike95490 said:

The new Magnum/Sensata Power Track-100 (PT-100) MPPT controller is good to 200Voc & 100A output

Going to 48V DC lighting - I think you should review some of the new PoE lighting systems.

It may not be possible in your inspectors code book, to mix ethernet & 120VAC in the same outlet box

Mike,

I looked at NULED and IGOR and Genisys systems and even met the Genisys founder at Lighting West last spring. Working with POE for 20 years, it seems that the aforementioned companies are injecting very proprietary control components that could become non mantainable should they not be around in 2 years. Cisco and Phillips are involved in some promising collaborations but it is all commercial in nature. It is all a balance of function and affordability. The NULED solution comes in around 4.5K without the fixtures. ouch I am in search of POE fixtures.
I do like the Power Track100
I learned years ago that low voltage can pick up a lot of noise from AC of any type. A separate low voltage network/buss is in the works. All the computer/audio is fiber.

New Self-Sustainable Home Build Project

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