Off-Grid Design and Feedback

Anawa · October 2014

I am currently developing an off-grid design and about ready to “pull-the-trigger” within the next few weeks. I’ve concluded that a functional off-grid set-up is not something that one can select from a prepared menu or visiting a few on-line forums; but rather, it is developed to meet individual needs and designed for an intended outcome. My goal is to develop a PV system that, during daylight hours, both battery charging to 100% SOC, and “basic” power consumption is accomplished. The design will include propane generator back-up (and supply primary power on occasions) and two (2) days battery storage.

To begin, the location is in Carroll County, Georgia about 38 miles (as the crow flies) west and slightly south of downtown Atlanta. Although we are fairly close to an urban area, our home site is remote; the cost to run UG power is about $30k. We (my wife and I) agree that an off-grid lifestyle is certainly not an economic decision; indeed, we’ve learned that green energy is more appropriately expressed as “greenbacks” energy. We’re neither tree huggers nor prepper’s, but find living without total dependency on commercially generated goods (store bought food) and services (utilities) is good for the soul, on many different levels.

Our “basic” power needs will be somewhere, more or less, 4kW per day… without any A/C. This includes; refrigerator, TV, lights, computer, satellite equipment, well booster pumps, ceiling fans, etc. Heating will be primarily by wood stove, hot water and cooking by propane. For our A/C equipment, we are planning a single 14-16k BTU (or smaller) mini-split heat pump. The footprint of the primary residence is about 1000 sf, a simple configuration of two (2) bedrooms, two (2) baths with kitchen/living area in one (1) large room. The PV equipment, batteries, power distribution, and water systems area are housed in a contiguous structure that will also support the PV array.

Additionally, we have a small week-end guest house that will be used on occasion, maybe 8-10 times a year. The anticipated power consumption for this structure is less than 3kW. The floor plan is similar to the primary residence, but less than 1,000 sf and proportionally dimensioned. It will be connected into the primary residence power and water distribution systems, as well as, contiguous to the other structures.

Here is my preliminary design for a 48 volt system:
• Solar Panels: 6kW PV array: 24 ea. Kyocera KD250GX-LFB2 250 watt – 3 series, 8 parallel
• Combiner Box: Midnite Solar MNPV12- 8 ea. 15 amp breakers
• Charge Controllers: 2 ea. Outback FM 80
• Inverter: 1 ea. Outback Radian GS8048
• DC/AC Load Center: 1 ea. Outback GLSC175-PV10/240
• Batteries: 16 ea. Rolls-Surrete S-480 6 volt, 375 Ah (or Trojan L16-B 370 Ah) – 8 series, 2 parallel
• DC Monitor: Outback Flexnet DC
• Display and Systems Controller: Outback Mate3
• Communications Manager: Outback HUB4
• Genset: Kohler 12kW 120/240 – 50 Amp, 12RESVL LP

Some other considerations:

• Booster Pump: Grundfos 22 BMQE 05A-80 Ez Boost – This pump is a “slow” start without surge. It is a 1/2 hp at 230 V (or, either 115 V) and starting current is equal to the highest value on the motor nameplate. I have not confirmed this, maybe someone on the forum has expericence can verify this to be accurate. (The water source for the residence is supplied from two (2) existing 1,500 gal storage tanks filled by a Grundfos SQE 11 deep well pump powered by an existing 1.5 kW Kyocera array. The head pressure is 7.25 psi at the booster pump intake. We do a lot of gardening and have had the water storage in-place for about 2 years.)

• Planning a “dual” water heating system with both a propane tank and electrical tank that uses a diversion load thru one of the controllers. Not sure how to accomplish this, maybe with SSR to the A/C panel, or directly out of the batteries?

• Charge Controllers: I would consider Midnite Solar Classics in lieu of the Outback. But, I am not sure what I would give-up by not having by not having a fully integrated system with the Mate3. Would like some thoughts on this.

• Mini-Split heat pump: Undecided, best price installed, or is there real differences in the energy consumption among the manufacturers? I’m guessing a summer time A/C comfort level can be achieved on a daily power consumption of 3.5kW, maybe less. Hopefully, some forum members can weigh-in on this. My local folks are absolutely no help on this. Thus, the realistic “basic” summertime power consumption would be about 7.5kW if my guesses are close. Charts reflect a May-Sep insolation of about 5.5 hours when the A/C will most likely be used. Is it realistic to assume that the summertime daylight hours will off-set the A/C power consumption and still properly charge the batteries?

• Occasional additional power consumption for guest house operation: Definitely problematic, but not opposed to generator operating on the 8-10 times a year it occurs. This maybe the times when the power consumption is diligently monitored. Would like some thoughts on this.

The older I get, the less I remember, therefore I am working on a wiring and equipment layout to help me keep on top of all this stuff. I will post it later, if there is any benefit.

Thanks for any input.

zoneblue · October 2014

Re: Off-Grid Design and Feedback

Welcome to NAWS. Your intial design seems to have the bones of a structure to it, and youve obviously done your homework on it.

For an off grid system it is quite large, and you may want to more closely compare costs with getting the grid wired in. And/or using soft conservation measures to reducing the air con demand. Money spent on shading and thermal mass, and insulation will always have a higher return on energy invested.

If your base loads really are 4kWh/d, then 6kWp , even without knowing your climate, seems pretty high to me. The guest house appears to be used infrequently enough that i wouldnt necessaryily add 4+3 to get 7kWh/d total load. Even if you did youd end up with an array closer to 3kWp than 6. However designing for peak load is usually not sensible from a cost tradeoff point of view. Running the gen for guesthouse/bad weather events will probably cost less, for the primary reason: batterys. All the other gear is more less one off, but the batterys have to be replaced every 7 years or so. If you work out what the battery replacement cost adds up to per kWh delivered youll see what i mean about grid being a close contender for this design. Inverters and charge controllers, we usually spec at 10 year replacements aswell so add that in your cost benefit modeling.

The 3-4kWh/day for summer air con/ domestic hot water, you should be able to largely run out of your opportunity load surplus. For example here with 1800Wp pV we can do 3kW/day for all but three days of the year. And an additonal 3 - 6kWh/day for about 75% of the year.

Now your choice of inverter. The radian is an expensive inverter, and primariliy because of its grid interactive "hybrid" features. Being off grid, most of those features are wasted, with the exception of gen support. However none of your loads appear to need gen support and an 8kW inverter should reasonably be expected to power two small residences, with conservative off grid appliances, as you appear to have generaly, and sensibly specified.

Given that you prefer outback gear, have you ruled out a flex power solution for a reason?

Controllers, if you did manage to get the PV under 4-5kWp, then only a single controller. Could save you a bit there.

Batterys: surrettes, arent that well loved here, as youll know if youve read a bit. All industrial batterys, take a bit of getting used to the way they take a while to form their plates, and can be tricky to absorb correctly in the early days. In any event, for a new design, id be really trying to avoid those parallel strings. This does push you to larger and bigger batterys, and you do kind of end up at the industrials as a consequence.

But i get the impression money is no object, or near so. So have you considered LifePo4? They appear depending on who ask, to be rapidly evolving into a strong contender for the prefered RE solution, with the caveat of high initial price.

The others will probably run your numbers, when the sun rises over there.

Anawa wrote: »

I am currently developing an off-grid design and about ready to “pull-the-trigger” within the next few weeks. I’ve concluded that a functional off-grid set-up is not something that one can select from a prepared menu or visiting a few on-line forums; but rather, it is developed to meet individual needs and designed for an intended outcome.

Photowhit · October 2014

Re: Off-Grid Design and Feedback

I'd suggest your inverter and battery bank is a bit larger than you need. If 4 Kwh will be your average daily load with out summer A/C, I suspect you would be better served with a 5-600 Ah 48Volt battery bank, and a 4 KW inverter and use the generator when you have guests.

Does your heat come with sun in summer? If so you should find the additional sunlight should compensate for the additional load. If your prone to 3-4 days of cloudy hot days then you might need the additional battery bank, but still likely to be cheaper to run the generator 2-3 hours a day.

Might consider a forklift battery. They tend to have long life, NAWS sells Crown and says "In a typical solar electric system they will normally last for about 20 years or more." and are mass produced so the price per stored Kwh is very attractive. I can send you a link to a direct site that sells 48 volt batteries.

mike95490 · October 2014

Re: Off-Grid Design and Feedback

If it's only $30K to get power brought in, do it. $+70K was my quote 5 years ago, being here now, knowing what I have learned, it's a PITA. I would have done the $70k, a transfer switch & backup genset, and be done with it.
The worries about batteries on cloudy days, driving into town to get distilled water, and filling batteries, changing engine oil, getting the new (50 hours) spare diesel genset into a truck and 300 miles to warranty center [the RobinSubaruHatz is unusable, the RPM's have climbed to 68Hz & 280VAC & inverter won't sync to it any more]. I'm not a retired electronics engineer anymore, I'm a full time power plant engineer, with the easy summer behind me, and winter coming up (again).

jcheil · October 2014

Re: Off-Grid Design and Feedback

I too would recommend the complete-pre-wired Outback solutions. For example the FP-2.

I just "built" one of these with all the parts individually and if I could have done it again I would have paid the extra $200 to buy the pre-wired panel.
Would have saved days of wiring, testing, etc. Just order an FP-2, it comes all assembled, mount it to the wall, run your solar, generator, battery and house wires to it and you're done in a couple of hours.

And absolutely go with the new inverter based mini-splits. I'm amazed at how little energy they use for both cooling AND heating.
You can buy them online, do the physical mounting of the units yourself (super easy) and then just have any AC guy come and connect the lines and evac the system.
I had an "off-the-clock" ac guy install all 3 of mine for $200 and it took him about 3 hours.

I just talked about them here: http://forum.solar-electric.com/showthread.php?25018-Fujitsu-heat-pumps

Anawa · October 2014

Re: Off-Grid Design and Feedback

Thanks zoneblue, I will checkout the Outback flex power. If I don't need all the grid functionalities, then I should save the money.

There is a bit more involved in just paying $ for the grid connection, the property has legal and topographical restrictions. Additionally, my wife has a say-so in what we do with this investment and that's an issue I live with up-close each day. I think in the long run, the grid may be best, economically, but for right now, I need to stay focused on an cost effective and efficient off-grid solution. You guys here at the NAWS forum are very helpful and I appreciate you guidance.

I'm not dedicated to any particular vendor, including, inverters, batteries, controllers, generators, etc. I do want high quality stuff that helps minimize all the downstream headaches and breakdowns. Also, I plan to do installation myself and want it simple. I'm open to substituion suggestions that are offered with plausible explanations. I just want to make an informed decision.

Roger on the battery paralleling. I will look at alternates for this solution.

I am very okay with generator operation during guest visits, so I am not overly concerned with that intermittent load. However, I can not say with 100% certainty that my daily power needs will be 4kW, but I believe it's close. I would rather err on the conservative side on an issue like this. Maybe I've been making some incorrect assumptions, but if my PV array can be any less than 6kW and still meet my load requirements, I would like to know. Do you think a 3kWp will meet my needs? Even with an additional 3kW A/C load during summer? This A/C stuff is really important to us boys down here in Georgia. Comments on this greatly appreciated.

Thanks Anawa

Anawa · October 2014

Re: Off-Grid Design and Feedback

Thanks Photowhit, reply to zoneblue addressed some of your comments. I'm very interested in re-evaluating array size.

Yes, I would like to look at industrial batteries. Fortunately, I am not encumbered at the battery storage area, fork lift accessable. Industrial batteries may be just fine. I just need to figure out how to get them from yonder to here in Georgia. No local vendors to deal with.

Any thoughts on the generator size? If I've got a hefty load for both residences? Also, if the array is down-sized, and the generator is used more often, any thoughts on that?

Thanks
Anawa

Anawa · October 2014

Re: Off-Grid Design and Feedback

Thanks mike. I am troubled by the very issues that you have so eloquently expressed, but there are other factors in play (see earlier reply to zoneblue) that make a grid connection difficult at this time.

The older I get, I'm gonna remember your post.

Thanks
Anawa

Anawa · October 2014

Re: Off-Grid Design and Feedback

Thanks jcheil, good advice on the pre-wire. Got any vendor recommends, I'm planning to do this myself.

I'm glad you responded to my post. I would like more info on your experiences with the mini-splits. What size do you have? What kind of wattage? And, most importantly, does it keep you cool down there in Florida?

Thanks
Anawa

zoneblue · October 2014

Re: Off-Grid Design and Feedback

Anawa wrote: »

I'm not dedicated to any particular vendor,

I wasnt suggesting theres better than Outback, and for inverters, in fact there probaly isnt! European SMA, Victron maybe. But Midnite charge controllers are worth every penny, even though they wont necessarily integrate with the Outback ecosystem. BUT, if it was me, id lose the hub, the FNDC and the two FM80s, and replace that all with a single Classic 150 plus Whizbang Jr. Just saved you over 2K.

However, I can not say with 100% certainty that my daily power needs will be 4kW, but I believe it's close. I would rather err on the conservative side on an issue like this.

We hear this from engineers a lot. If 4kW is good, well lets double it and call it good. The thing is, with the marginal economic proposition that RE represents, thats the difference between a system that will pay for itself and one that wont. Adding to that cost factor,, you have the fact that lead acid batterys are about as tempermental a thing as youll find in this world, and they like a very narrow set of operating conditions. Hence for these reasons, its essential that you accurately spec the system.

To temper this view, over-panelling is workable, even desireable in some situations. With batterys now the achiles heel of RE systems, the smallest battery you can get away with it is the goal. You can in many situations make up for reduced storage with over panelling. Local weather patterns will be the deciding factor there. While it is completely true that double nothing is still nothing, in terms of PVs, in my climate, small breaks in the otherwise grotty weather, can provide a suprising amount of energy.

Of course, high charge currents create further impetus for a storage tech that can sustain those C rates... like 0.3C for AGM or 1C for LiFePO4.

Generators are a mixed bag. Once you design in a genset, you may as well use it. Keeps the oil circulating through the crankcase, and the fuel stable. See posts by Chris Olsen. But some of us are just hopeless with mechanicals, and prefer not to touch the things.

jcheil · October 2014

Re: Off-Grid Design and Feedback

Anawa wrote: »

Thanks jcheil, good advice on the pre-wire. Got any vendor recommends, I'm planning to do this myself.

I'm glad you responded to my post. I would like more info on your experiences with the mini-splits. What size do you have? What kind of wattage? And, most importantly, does it keep you cool down there in Florida?

Thanks
Anawa

The host here has great prices on the pre-wired systems. I am 50/50 on the "mixing" of equipment. Yes the Midnight charge controllers have awesome features, but the outback FM80 are solid. And the fact that they all integrate together and work with the FNDC, you get great "logging" potential. Look at the logger I use in my SIG. Sure you could do some logging with mixed equipment, but I personally like to have the one-stop shopping. And the pre-wiring is a blessing.

The FP2 system with the X240 transformer is great because it can produce 240v just using the transformer up to 1000w while it puts the other inverter to sleep to save power. If your 240v load increases, it instantly comes on just for the time needed. If you look at my graphs you can see where inverter#2 rarely comes on (the yellow line). Plus if you buy now (and in the future) Outback gives you the cloud based OpticsRE logging at no extra charge.

The mini-splits kick butt down here in the middle of super hot-humid FL. And lately (past couple of nights) I am even more impressed with their heating ability! - Yes I know, we are a bunch of wimps down here because it got into the low 50's and we were cold

For cooling, they actually use about 1/3 of the power that my 6000btu window-unit was consuming. Plus they are DEAD-QUIET. Both inside and outside. You'd never even know they are running. Not to mention not having to run duct-work is a plus.
I was standoffish of them for while concerned about service/parts/etc, but now that I have them I am SOLD. And at the price they are down to now, it's a minimal investment even if they have to be replaced every 5-10 years.

If you look at that link I posted above, it goes to a thread where I listed the ones I am using.

vtmaps · October 2014

Re: Off-Grid Design and Feedback

jcheil wrote: »

I too would recommend the complete-pre-wired Outback solutions. For example the FP-2.

Personally, I would recommend the prewired Midnite ePanel over the FP-2.... It is a bit easier to work in and to customize. Of course, if it's prewired and not to be customized, then that consideration doesn't matter. It's hard to predict what changes you might make in a few years, but likely you will be better off with the ePanel.

--vtMaps

Blackcherry04 · October 2014

Re: Off-Grid Design and Feedback

jcheil, Looks like you have Designed and Installed a very nice system, you should be proud. Watching your data is addictive, I almost couldn't wait to see it this morning. Being a cracker myself, I know what you mean about the heat at 50° outside temps. I assume all the dips in the output is the mini split cycling. I hope your system keep's on meeting you needs.

Anawa · October 2014

Re: Off-Grid Design and Feedback

jcheil, in another one of your posts I saw that you installed 3 minisplits. Are they 240's or 120's? How many total btu's are you running? When they are all operating, any idea of the wattage?

I'm thinking to do the same, buy the units and have local HVAC contractor install to get the warranty. Got any suggestions (things to avoid) from doing this yourself?

Thanks Anawa

creeky · October 2014

Re: Off-Grid Design and Feedback

This is part concurring/part ...

... I would add: look at TBS inverter/chargers if you decide not to go the full "prebuilt" option.

Then, as posted, look very carefully at LifePO4 or LFP batteries. A lot less maintenance. And for your use/budget an excellent choice. (4.5 years off grid. No way will I buy another FLA. Yuck.)

Also, I see you're reconsidering the issue of system size. .02. If you can modify your behaviour (set the dishwasher to start at two in the afternoon on a sunny day instead of loading it and running) you can achieve the same lifestyle for less overhead. When I first looked at off grid I was told I needed a 4kw solar panel system minimum (at $6/watt, 24k for panels) . Um, that was about right. But with behavioural modification I'm doing fine on 1.5 kw solar. And did well on 1 for 3 years. bark bark. do I get my cookie now?

jcheil · November 2014

Re: Off-Grid Design and Feedback

vtmaps wrote: »

Personally, I would recommend the prewired Midnite ePanel over the FP-2.... It is a bit easier to work in and to customize. Of course, if it's prewired and not to be customized, then that consideration doesn't matter. It's hard to predict what changes you might make in a few years, but likely you will be better off with the ePanel.

--vtMaps

But you can't fit the X240 balancing transformer in that panel unfortunately and if you have 2 inverters you have to get 2 midnight panels (AFAIK).
I still have my original epanel from before I upgraded to the FP-2(ish) system. I toyed with the idea of getting another for the second inverter but the Flexware 500 enclosures are SO clean and neat... My original epanel will be on ebay soon.

jcheil · November 2014

Re: Off-Grid Design and Feedback

Anawa wrote: »

jcheil, in another one of your posts I saw that you installed 3 minisplits. Are they 240's or 120's? How many total btu's are you running? When they are all operating, any idea of the wattage?

I'm thinking to do the same, buy the units and have local HVAC contractor install to get the warranty. Got any suggestions (things to avoid) from doing this yourself?

Thanks Anawa

Sorry for the delay in the reply, got busy with real life for a tad

I installed 2x9000BTU and 1x12000BTU units. They are all 240v units. I went that way because they had the higher SEER (20/22) vs the 120V units.
Looking at my data (online) I COULD have gotten by with a single 3600 inverter and just used the X240 transformer for the 240v. But, I wanted some extra room plus I like having a backup. Right now as you can see from the data the 2nd inverter only wakes up once in a while anyways.

Now, I didn't REALLY need that much cooling, however due to the layout of my place (a OLD 10' by 50' single wide mobile home) there was no way for me to get the air into the center room down the long hallway without a bunch of fans. So I put a 9000 in the end bedroom, the 12000 in the livingroom/kitchen area and ended up having to put a 9000BTU (smallest they make) in the tiny 6x8 room off the center of the hall. But all my computer equipment is in there and that generates a lot of heat so it's good having it in there anyways. All in all it doesn't really matter because it uses very little power. It only comes on when it needs to.

I keep the thermostats on 77-78 most of the time for cooling, and 70-72 for heating (used quite a bit the past few nights when it was in the 30's and 40's!). I just read my meters Friday (I hooked up electric meters on each unit to be able to monitor the individual consumption -- $25 on ebay + $30 for the mounting panel). Here are my kwh readings for the past month:

Total House (includes AC units): 542, avg=18.1kwh per day
AC1 (Bedroom): 47, avg=1.6kwh per day
AC2 (Small Office): 41, avg=1.4kwh per day
AC3 (LivingRoom/Kitchen): 65, avg=2.17kwh per day

So as you can see, they use VERY little power. And we have had some HOT (and cold) days this past month here in FL so they were working 24/7. And my insulation factor on this place sucks. These 1960's mobile homes were made with 3/4" - yes 3/4", a 1x2 basically on edge, exterior walls. So there is only 3/4" of insulation between the inside finished wallboard and the exterior metal siding. I debated on adding an extra 4" foam to the outside and going over it with vinyl siding, but that is a project for someday.

As far as the AC hookups? I did just what you are proposing. I "physically" installed the inside and outside parts (super easy), drilled the hole in the wall, ran all the pipes and wires and just left the ends of the pipes hanging on the inside and outside. The AC guy I had come and do it charged me a total of about $200ish to evacuate and make the final connections on all 3. Took only a couple of hours and most of that time was just sitting around drinking beer waiting for the evacuation pump to do its job.

Added: As far as the "running" watts for the mini-splits? Not EXACTLY sure on each one but if you look at my data you can see the "peaks" when they come on. 99% of the time it is the bedroom one at night cycling. In the day it is either the office or living room one (or sometimes both). The 2nd inverter only comes on when the load to the x240 exceeds 1000watts, so that should give you a ballpark also.

Photowhit · November 2014

Re: Off-Grid Design and Feedback

jcheil wrote: »

... and if you have 2 inverters you have to get 2 midnight panels (AFAIK).

I have an Epanel lite and have 2 inverters, but doing it in a manner not recommended by midnite, using a 90 amp Din rail breaker for the small 1100 watt inverter. I had it already installed for the 3rd array which isn't installed yet. When I do get that installed, this fall is the theory. I'll put a panel mount breaker where a GFCI breaker would go (I don't use one). Most E-Panels are made so you could mount the main breaker on either side. In larger boxes I suspect mounting one on either side would work out fine, though a tight fit, you would need to use the bottom and perhaps the back or to for wiring coming from and going to the charge controller.

Here is clip of the Epanel lite;
Attachment not found.

I've got a pretty crowded box E-Panel now with 2 arrays coming in from the back to 2 panel mount breakers and out to CC and back from CC to 2 panel mount breakers as well as the main inverter breaker and small inverter breaker. I have the room to add the last array, as I said moving the inverter breaker to a panel mount breaker where the GFCI break would mount. I couldn't use the opposite side main breaker mount since I have my CC wiring there. Most(all?) other Epanels are larger than this one. so it would be easier. I'll have to change the location of the shunt to put in the Whiz Bang Jr. and while I could, I won't run a breaker for the AC into the Panel, I'll use a stand alone box for that. currently relying on the internal fuse and the breaker at the sub panel.

Photowhit · November 2014

Re: Off-Grid Design and Feedback

If you chose to do 2 E-Panels if you order ahead and ask, they can be made with the door on either side so they would open unencumbered.

Off-Grid Design and Feedback

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