Need some advice on a frankenstein off grid system I might purchase

gtojohngtojohn Registered Users Posts: 20 ✭✭
First off, thanks! There's a lot of help and info here! I'm currently building a weekend cabin I would like to keep off the grid and self sustaining. I have a friend of a friend, a very smart EE who sells solar components as a hobby and extra money. He has for sale an off grid set up. It consists of 4x 100 Amp-Hour AGM batteries (Used) 80% life remaining, 2x 240 watt solar panels (New), 48Volt 30 Amp charge controller (New) I cant remember the brand, I know its not mppt. 100 Amp Fuse (Used). And a 2200 Watt APC Sine Wave Inverter (Used). The inverter is PWM, from a large ups. He has added a switch to disable the beep and the inverter fan is temperature activated. He is built and sold a few of these already. Asking price is $1200. I've tried pricing this out and it seems to be a good deal if everything works. Is there anything that I should run away from?


  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Hi "gtojophn", welcome to the forum.
    Reading your posts raised a couple of red flags. First was the AGM batteries with "80% life left". How does anyone know how much life is left in a lead acid battery - - - How old are they, have they been kept properly charged, have they ever been overcharged, have they ever been allowed to sit unused for a time while not being kept fully charged. I just don't get a good feeling about them.
    Next is the huge (for the battery size) 2200 watt inverter. the idle current alone on such an inverter would be a substantial overnight load on such a small battery bank even if the batteries were new, and there's no way you could put that full load on the batteries. Assuming 100% efficiency (which is definitely not reality) a 2200 watt load would demand close to 185 amps from your battery pack. This would quickly draw down the battery voltage, resulting in the inverter shutting down on low voltage disconnect.
    BUT - - so far we don't know the make and model of the inverter, controller, or panels - - so we can't even guess if the price is a deal, but to me, it seems quite high for used items of unknown quality..
  • gtojohngtojohn Registered Users Posts: 20 ✭✭
    thanks for the quick response Wayne. The panels are BP. The batteries are definitely the biggest concern. They were previously in use as a large ups for a large computer manufacturer. The 80% was his guess because of age, 2 years out of a 10 year service life, or was it 1 year out of 5? I had asked a lot of questions but not all of it stuck in my brain. My thoughts are this would be a starting point to add more panels and batteries. It seems I might want to start with a larger inverter, within reason, to expand into.
  • PhotowhitPhotowhit Solar Expert Posts: 5,650 ✭✭✭✭✭
    Keep the friend and don't buy the system. Friends are harder to come by the solar components. If he'll bleed for you and needs the money, you might buy it to help him out... but I'd rather have you start by finding the correct pieces for your self. I would have no idea about how long the batteries would live or how they had been treated in the past. I would want to know how efficient the inverter is, is it a pig? only passing through 80%. I have no problem with PWM charge controllers, Are the panels "true" 24 volt panels with a VMP around 35 volts? (NOT VOC)

    I think Wayne missed that it's a 48 volt system, also UPS inverters tend to be over rated, More likely a 1800-2000 watt inverter. I would be comfortable and have used a 1800 watt inverter on a similar battery bank, 4 GC batts, 215 amp hours at 24 volts.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former, 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    What are your present electrical loads you intend to apply to this proposed system?
    What are your projected future loads?
    It's far cheaper to save a watt than to generate, store and use a wasted watt.
    Is this a 48 volt system? Or a 12 volt system.
    Anything over 1000 watts total load should be at least a 24 volt system.
  • gtojohngtojohn Registered Users Posts: 20 ✭✭
    Thanks Photowhit and Wayne. I'll walk away from the package deal. He does sell new panels at a great price. Currently the cabin isn't finished. The walls are up but loft and roof are next. It'll be 1000 sqft living. I'm building it tight and well insulated. All the lighting will be led. Water is rainwater cistern I will have a couple of 12v pumps, one for hot water roof panels, one for water pressure. A little xtra power for entertainment electronics. Toilet will be composting, the better ones require a little power to run a heater and fan to speed up the process around 200watts when it cycles. I know thats all reasonably done, however the biggest wife requires a/c. I will be putting in 1-2 9000btu mini splits, gree terra 27 seer heat pumps to be exact. They draw around 450 watts each. I believe I won't need them for heating, between insulation, some hot water hydronics and wood stove I should be good. The gree are 240v so I might do a second inverter just for them that I can switch off 6 months when no hvac is required. My system hasn't been built yet, so 24-48volts where would the best value be for equipment cost? It seems like more selection for 24volt.
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    Don't buy any equipment yet....

    You really need to understand your loads (watts, peak watts, average Watt*Hours per day, etc.). And you need to look at conservation (insulation, very efficient hardware, etc.). Which it sounds like you are doing. It is almost always cheaper to conserve than it is to generate your power.

    Just to give you some rough ideas of how much power you may need:

    ~1,000 WH per day (1 kWH per day)--Small system that will supply lights, laptop computer, DC water pump, etc.
    ~3.3 kWH per day -- Add an energy star refrigerator, TV, well pump, clothes washing machine (close to "normal" electrical life, high level of conservation).
    ~10 kWH per day -- Add heat pump/AC for a room, fans, fairly normal life -- Again lots of conservation.

    A 3.3 kWH per day (or ~100 kWH per month) is a medium sized solar power system. Not cheap to build, but can be a good size for a first time do it yourself system (with lots of research).

    Larger systems tend to be very expensive and may require knowledgeable/professional help.

    Just to give you a "budget"--Very roughly off grid solar power, when all of the costs are rolled together (i.e., hardware, installation, new batteries every 5-8 years, new electronics every ~10+ years), works out to round ~$1 to $2+ per kWH for a full time home (~9 months or more occupation per year). Or roughly 10x the cost of utility power in much of the US.

    A few people have gotten their costs down to $0.50 or so per kWH--But that requires a lot of DYI and shopping for deals.

    Adding a refrigerator/air conditioning/etc. is a lot of load--Makes your power needs go up dramatically.

    For example, 2x 450 Watt units * 12 hours per day * 50% duty cycle = 5,400 Watt*hours per day

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • H2SO4_guyH2SO4_guy Solar Expert Posts: 213 ✭✭✭
    Hi and welcome to the forum. Here are some opinions that I understand to be true, as I have tried to go down the least expensive path to get alternative energy stuff up and running for over 20 years. UPS’s use more battery power to make power. The design isn’t for efficiency, it is to keep a system up and running if the grid fails. The idle draw is greater than a good inverter. A modified sine wave inverter may kill your mini split. It would also void the warranty.

    I run a Mitsubishi Mr. Slim 9000 BTU unit that is 26 SEER. It is wonderful but has a few things I don’t like about it. I mounted it high so it would cool the 175 sq ft I am currently staying in until I build the loft. The mounting works against you when it is heating as the floor is cold, but 4 feet and above is warm. Yes fans help, but the noise and the pia factor. When it was 96 degrees outside I can make it 62 degrees inside, so that works well. I do wish it had a backlighted remote so you could use it without additional lighting from overhead or flashlight. When you turn it on they it never shuts off, which is the nature of a heat pump. It it draws power 24/7 so there is no cycling to totally off, but it does not necessarily blow air all of the time as it has to do stuff in the outdoor unit.

    I run on used batteries, and bought them for not too much over scrap value. I also have spares of the same make, same model, and same age to plug in as they fail, and they will. If you wish to run what you are telling us, then the system is way too small.

    I suggest you figure out your loads and size the system accordingly. One challenge in the solar industry is the ability to find matching panels down the road that will work with the ones you already have. My new solution to this is to buy in increments of at least 5000 watts and put them on their own Midnite Classic 150 controller so they will play nice with the other Classics. Then it doesn't matter which panels you have and you can make them all work together.

    Get ready for the learning curve and many of us have made pretty expensive mistakes along the way. I try to learn from some of these guys to keep my costly mistakes down. This a great resource and knowledge base from people who are actually doing it.

    I would keep the friend and ditch the system offered. It is not near what your stated goals will cover.

    Good luck and let us know how it turns out.
    12K asst panels charging through Midnite Classic 150's, powering Exeltechs and Outback VFX-3648 inverter at 12 and 48 volts.  2080 AH @ 48 VDC of Panasonic Stationary batteries (2 strings of 1040 AH each) purchased for slightly over scrap, installed August 2013.  Outback PSX-240X for 220 volt duties.  No genny usage since 2014. 
  • MarkCMarkC Solar Expert Posts: 212 ✭✭✭
    It is interesting - what your friend is doing. I purchased a SUA3000 (APC) inverter for "scrap" cheap and plan on testing it's capabilities for off-grid emergency only use. It might be that your friend is selling a similar unit, maybe downrated -seems APC does that a lot. If so, it will come with a 48 volt battery pack with very minimal backup power (10 AH at 48 volts) and has a rated efficiency in mid-high 90% depending upon load - not bad. It will match the 4-12 volt batteries in series OK, but as stated will have limited backup power. I'd guess he's supplying a rather cheap PWM style charge controller. the panels are likely wired in series? Again, an interesting concept if what I'm guessing is true. Buying a good MPPT - 48 volt charge controller would likely cost about 1/4 of the total (Midnite KID) on its own, but is much better!

    I'm about to run an extended test with the 3000 based on 8 - 155 AH batteries - powering a couple of ceiling fans, a small refrig, some lights and a newer TV in my rural cabin. As I have a separate Priups generator (with a SURT6000 APC UPS), I felt this could be a good match for almost all usages EXCEPT the air conditioners and water well pump - they will definitely need the "Priups" generator (240 volt split phase). Again, this off-grid system is for emergencies (hurricanes, etc) only. I'd be cautious about going with UPS style inverters for continuous off-grid use - only the double conversions are built for continuous usage and they are not the most efficient - I'm quoting on this one, no experience!

    Long story - short, If you would like the results from the test, email me a private message and I'll send them to you.
    3850 watts - 14 - 275SW SolarWorld Panels, 4000 TL-US SMA Sunny Boy Grid tied inverter.  2760 Watts - 8 - 345XL Solar World Panels, 3000 TL-US SMA Sunny Boy GT inverter.   3000 watts SMA/SPS power.  PV "switchable" to MidNite Classic 250ks based charging of Golf cart + spare battery array of 8 - 155 AH 12V Trojans with an  APC SMT3000 - 48 volt DC=>120 Volt AC inverter for emergency off-grid.   Also, "PriUPS" backup generator with APC SURT6000/SURT003  => 192 volt DC/240 volt split phase AC inverter.  
  • PhotowhitPhotowhit Solar Expert Posts: 5,650 ✭✭✭✭✭
    Well, I'm one of those people who has gotten the costs down significantly, but still more than being on the grid, about 26 cents a Kwh with out counting the tax credit. This only works since I have an undersized battery bank and have the heaviest load in the summer, running an air conditioner. This system being used part time will NOT be cheap electric! but I suspect you're well off grid?

    I agree with most of what has been said, people going to a solar electric solution often waste a great deal of money early, buying undersized systems or bad components. Talk to us and we can let you know what worked for us. I think you may end up with a similar sized system to mine. I figure I have about $7K after tax credit, and have yet to buy my planned inverter. I've been chugging along though for almost 2 years now and you tend to live with what you've got. I might pop for the inverter this year as the tax credit will end in 2016. For your information, Primary AND secondary residences qualify in the U.S. for a 30% tax credit on solar systems. This is a credit off your liability!

    Well I started a reply earlier and will post it now 4 hours later, I had stopped to hunt up info on an autotransformer, another option to run your mini splits off a standard 120 volt system.
    From earlier; More selection for inverters, but less wasteful to go to 48 volt. To run those AC units you will end up with a good sized system. If the cabin is in the hills/mountains you might not need as much storage to run the AC at night so that might help make for a smaller system that would be 'over paneled' for the storage, but running the ACs during the day.

    A 48 volt system will save money on charge controllers likely. I'm guessing you will end up with a system in the 3-4000 watt array size, the Midnite Classic Charge controller can handle about 2500 watts at 24 volts but about 4400 at 48 volts so one charge controller rather than 2. Quality large inverters will generally have 48 volt options.

    Since you need 240 for the AC's might just look at those options now, Magnum makes a 4448 that is 240/120. Outback require pairing of their units.You will likely want to run that mini split at full power at least to cool down the cabin. so it's likely to run around 1000-1200 watts at full power. If you can use a smaller battery bank, you could go with a Schneider 2524 (2000 watt 24 volt, @$1200) but might be safer with the 4024 (3500 watt, 24 volt,@$1450) units. They use a bit more energy at idle than other units, but will give you the 240 you need.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former, 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • gtojohngtojohn Registered Users Posts: 20 ✭✭
    Thanks for all the fast responses guys. Figuring the load is definitely a difficult task. I've had a killawatt for some time and I'm awaiting for a panel mounted power monitor to arrive. I've been working hard to make our current house and habits efficient, but our best power bill still avg 19.8 kwh day. We are by no means roughing it though. The point of the cabin is for our family to get away and experience the outdoors and nature however the reality of keeping everyone happy with modern conveniences will be a balancing act. Its amazing how much power refrigerators eat up. My dream is off the grid, Reality is there is a power pole not too far away. Grid tie might be the best option, I can sell power back for pennies 5 days of the week and buy a little back on the weekends after the sun goes down, and my wife gets a/c!
  • mike95490mike95490 Solar Expert Posts: 9,358 ✭✭✭✭✭
    [lets not go there. -Bill B.].
    They were previously in use as a large ups for a large computer manufacturer.
    That means with 99% likelihood, that that they are "float service" batteries, and only good for about a dozen deep cycles, and maybe a couple hundred shallow cycles. Less than a year of usage when they were fresh from the factory. 90% chance they are GEL batteries and cannot be quickly charged by solar.
    Pairing a huge inverter with a limited solar and battery is a large warning flag that the system is not anywhere close to balance.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

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