searching for comments on my proposed off-grid system

retroboltedretrobolted Registered Users Posts: 6
hi everyone,

I'm trying to put together a system for an off-grid house in Ontario, with a projected use (year round) of 2.5 KW/day. This will be my first time off-grid, and I am hoping I can get some comments on my proposed set-up. I could be making a big (and costly) mistake somewhere here, and would be grateful for any tips and pointers.

Here's what I'm thinking:


1.4KW array of Sharp 175 watt Single Crystal Silicon Photovoltaic Modules (NT-175U1). This is to start -- I would expect to bump up to 1.75 KW or 2.10 KW within a year.

8 Trojan L16H-AC 6V at 435AH, for a 24V system at 870AH

A 4000W 120/240 split phase Magnum Energy inverter/charger with generator auto-start.

A Flexmax 80 MPPT charger controller.


Does anyone have an opinion on whether these components will work well together? I'm thinking mostly sizing. For instance, I sized the batteries based on 3.5-4 days of backup. But are they an okay size relative to the planned solar array? Etc.

Many thanks for any help!



  • DapdanDapdan Solar Expert Posts: 313 ✭✭
    Re: searching for comments on my proposed off-grid system

    hey ret,

    Everything looks good. My only comment is that the recharge current is approx 7% a little on the low side in order to equalise but your systems looks good.

    My only other comment is if you are going with 4000w why dont you consider going 48v you have enough batteries and you would use a smaller wiring to complete your set up. Also I understand that the xw cc is more eff than the FM (apparently have some bugs and they are about the same price except the xw comes with it own TBS and FM you have to buy one). Also the cost of the 24v magnum is about the same as the 48v magnum. for that matter why dont you look at the xw hybrid it is about the same price range of the magnum with the same split phase and it has a grid tie option.

    Other than that you choise seem good. I just wanted to outline some other options. I myself run a 24v set up as indicated by my signature. My set up allows me to be off grid as well with an averager use of about 6kw per day. So I know you setup should adequately more than supply your needed 2.5kw per day.

  • BB.BB. Super Moderators, Administrators Posts: 32,813 admin
    Re: searching for comments on my proposed off-grid system

    You don't say where in Ontario Canada you are (not that it would mean a lot to me)... But lets choose Thunder Bay ON from the PVWatts program. Assume 1.4 kWatts of solar power, off-grid with a derating of 0.52 (52% of panel nameplate rating) assuming flooded cell batteries and 85% efficient AC inverter for power. Assume defaults for the rest of the questions:
    Solar Radiation (kWh/m2/day)
    AC Energy (kWh)
    Energy Value (Can$0.0862 per kWhr)
    1      3.80          94     8.10 
    2      4.83          104    8.96 
    3      5.58          128   11.03 
    4      5.41          113    9.74 
    5      5.57          115    9.91 
    6      5.41          105    9.05 
    7      5.64          112    9.65 
    8      5.14          102    8.79 
    9      4.69          94     8.10 
    10     3.47          74     6.38 
    11     2.89          62     5.34 
    12     3.03          73     6.29 
    Year   4.62          1175 Cn$101.28 [/FONT]
    2.5kWhrs per day * 30 days per month = 75 kWhrs per month

    Looks like a good fit (several low months of 62-74kWhrs per month) for Thunder Bay (southern Ontario). That what a genset/conservation is for.

    And you can pretty much double your solar panels with the battery bank you have--so room to grow once you nail down your usage and system performance.

    Battery bank (assume 3 days no sun, 50% max. discharge, 24 volt):

    2.,500 Whrs per day * 3 days * 1/50% * 1/24 volts * 1/85% invtr eff = 735 Amp*Hours

    So, you are fine with the batteries!

    Somebody has been working hard on planing their system. ;):D

    Leaves little for us to do.

    Assuming 100% living at off-grid home with spouse, kids, friends... I would highly suggest you get a Battery Monitor system. I can almost guarantee that you will save the cost of at least one early replacement battery bank (under charging, over discharging, sitting under 75% state of charge and not knowing, etc.).

    The Trimetric is supposed to be a very good low cost model (others here use it). I like the Xantrex LinkLite and LinkPRO as they have a programmable contact you can set for 50% State of Charge Alarm / turn off the inverter.

    You may be 100% on watching the battery voltage and using a hydrometer--but that is because you paid $$$$ for the battery bank. Others will not be as careful. ;)

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: searching for comments on my proposed off-grid system

    Welcome from the North,,

    Ditto what Bill has said. The only thing I would add is that your loads WILL grow with time, they always do. Consider the biggest Charge Controller you can. You could also consider a couple of inverter set ups,, 1 for one set of (bigger) loads,,, another for smaller loads. I would also consider adding batteries in the beginning since it is tough to do after a year or so.

    Good luck and keep us up to date.

  • retroboltedretrobolted Registered Users Posts: 6
    Re: searching for comments on my proposed off-grid system

    Thanks all for your helpful comments -- that was reassuring. Just a few quick follow ups.

    Damani, what would be the advantage of going to 48V? Is it just less line loss? Does that matter if the distance from the array to my batteries is only about 15-20 feet? Thanks for the tip re the XW over the Magnum....I will look into that. I'm not concerned about grid-tie capability since I'm $30,000 from power lines, but higher efficiency would be good.

    BB, thanks too for the info. My location is near Goderich, Ontario. November and December are noticeably worse (45KW per month). But the rest is about the same. A question about the battery monitor system -- I had planned to have a back up generator. My understanding is that I could set this up to automatically start at, say, a 50 percent drawdown of the batteries. Would it be better from your perspective to use the battery monitor and manually start? Or am I missing something here? (Would one still want a battery monitor if one had auto-start on the generator)?

    Tony, if I added batteries I would have to jump up to 1300AH (with the L16 H). Damani had suggested my charge rate was a little low (7%) with the smaller battery array. Do you know how I calculate how big my solar array should be for a larger size battery bank? Also, if I have a generator (which I will), is it as important to up-size the battery bank? That would be something like $1800 more, which would almost get me another 350W of panels.

    thanks again to everyone for their help.

  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: searching for comments on my proposed off-grid system


    Couple of points,, in no particular order. As for the battery monitor. Regardless of auto start for the genny, I would always have a battery monitor on the system... You will have enough investment in the batteries to keep them as healthy as possible.

    I would also consider setting your charging threshold higher than 50% soc/dod. I personally like to use an 20% discharge rate for longevity,,, others like 70%. Look at the battery mfts, charges of cycles vs longevity and come up with your own strategy. A bigger battery bank allows for similar number of AH draw down,,, without drawing the batteries down too far. That "too far" is a matter of great debate.

    As for battery capacity vs PV capacity. The general rule of thumb is between 5-13% of amp/hour capacity. The concern is that at the lower number you won't have the Pv capacity to equalize the batteries. Personally,, I wouldn't be concerned about that issue as long as you have the genny capacity to equalize. My thought is one should design your system for the average draw down, average solar charge per day, with some reserve added in. To design a PV system to cover every eventuality can get quite expensive.

    My one question is,, if you are near Goderich, why are you going with an off grid system? How far are you from grid power? Building a battery based system will cost about twice what a grid tie system will on a KWH basis.

    Good luck,

  • BB.BB. Super Moderators, Administrators Posts: 32,813 admin
    Re: searching for comments on my proposed off-grid system

    Regarding 48 volts vs other, lower voltages... If this is a "Large" (say >1,000 watts of load at any time) and you have no need for a 12 volt or 24 volt system (say native 12/24 volt devices like radios or such)--a 48 volt system will be better overall.

    1/4 the maximum current (smaller wires, less $$$ for copper, smaller fuses, circuit breakers, switches, less issues with voltage drop (2 volt drop on a 12 volt system--dead. 2 volt drop on a 48 volt system--no problem at all).

    Larger inverters are about the same price (24 vs 48 volt).

    A 60 amp MPPT charge controller can control 4x the number of solar panels at 48 volts vs 12 volts (fewer number of charge controller, less cost, less complexity).

    Regarding the battery monitor--The Xantrex has a programmable output that should be able to connect to a automatic generator start setup. The others may not.

    I believe that most auto-start systems monitor the battery voltage (and throw in an offset depending on the amount of current being discharged at the time, with some timers to average the loads--so every time your well pump starts up, the generator does not start).

    Monitoring battery system voltage is a very rough analog to "knowing" the actual battery bank state of charge at every moment.

    I live with a GT solar system--so take my recommendation for what it is worth--I would probably set up the "standard" off-grid with generator auto-start setup (probably voltage based) and just monitor it with a Battery Monitor.

    You can always start up the genset manual--or convert to a battery monitor based genset auto-start later (probably for not that much extra money if you get a Xantrex BM with external output) if you are concerned with how the system operates. For example, you know that the next few days are clear and sunny--so you delay the generator start based on the forecast because your battery bank will quickly be above 75% state of charge by mid-morning. A "gen-start controller" will not know what the forecast will be.

    My guess--is many people have the genset start too often and end up burning an excess amount of fuel per useful kWhr generated... And some don't start often enough and their battery bank dies and early death. The extra data will help you with the trade-offs.

    Which leads me to another suggestion--don't oversize the genset (big generators running light loads are very fuel inefficient). And 2nd, put a logging kWhr meter on the generator output and monitor fuel usage...

    Keep track of how many kWhrs / gallon (or per pound, etc.) you are getting. For a gasoline genset, they can run 5-6kWhrs per gallon of fuel -- when properly loaded--but it is very easy to get down to 1 kWhr per gallon when not (running a 10kW genset with 1kW of load).

    If you won't be using the genset much--perhaps the extra fuel flow won't hurt vs having a very nice propane 10kW 1,800 rpm prime mover water cooled generator vs a little manual pull Honda eu2000i to make up for a few cloudy days a year. Or even run the Honda manually--(cheap and easy)--but you still have the 10kW for backup/running the shop loads when needed.

    Make up some simple formulas for a spread sheet... Example cost per kWhr for an Off-Grid system:

    1,400 watt off grid * $15 a watt to install plus $2,000 for replacement batteries over 20 years of use (lifetime), assuming 1,175 kWhrs a year.

    (1,400 watt * $15/watt + $2,000) / (20yrs * 1,175 kWhrs per year) = $0.89 per kWhr

    How much does that $30k Power Line cost? Lets assume 20 year payback, 1,175 kWhrs per year @ 0.10 per kWhr:

    ($30,000 + 20yr*1,175kWhr/yr*$0.10 per kWhr) / (20yrs * 1,175 kWhrs per year) = $1.38 per kWhr

    So, from a solar RE point of view--Off-Grid is probably cheaper than Grid... Unless you use ~2x the amount of power you plan on--then it will be near break even.

    How much does a generator cost you in fuel. Assume $3.00 per gallon, and you are making up for 30 kwhrs per month for 2 months a year. Assume 5kWhr / gallon (efficient) vs 1 kWhr / gallon for inefficient fuel usage):

    2 months * 30 kWhrs per month * (1/5kWh per gallon) * $3/gallon = $36 per season
    $36/(2mn * 30 kWhrs per mn) = $0.60 per kWhr

    2 months * 30 kWhrs per month * (1/1kWh per gallon) * $3/gallon =
    $36/(2mn * 30 kWhrs per mn) = $180 per season
    $180/(2mn * 30 kWhrs per mn) = $3.00 per kWhr

    So--you can decide if a ($180-$36=) $144 a season savings. It would take you almost 7 years to "pay for" buying a small Honda (assuming a USD$1,000 price tag) to supplement your big genset on fuel savings...

    Anyway--some of what I have done to figure out the "better" solution. Your mileage (and assumptions) may vary. ;)

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • retroboltedretrobolted Registered Users Posts: 6
    Re: searching for comments on my proposed off-grid system

    Thanks again, Tony, for the info on the advantages of a battery monitor -- I will be sure to add one to the shopping list.

    As for why I want to be off-grid if I'm near (20km inland from) Goderich: The building site is on a dirt road with the power lines at the neighbours, about $25,000-$30,000 away, per an estimate from a couple of electrical contractors. That's enough reason to make me interested in going off-grid. But the other factors are (i) the people at Hydro One were really, really annoying and unhelpful in our discussions about a line extension, and (ii) the building site is very beautiful in part because there are no power lines anywhere nearby. It would be great to preserve that.

    thanks again,

  • retroboltedretrobolted Registered Users Posts: 6
    Re: searching for comments on my proposed off-grid system

    Hi Bill,

    thanks again for an incredible wealth of information.

    Regarding the 24/48 issue: We were planning on having a 24V March pump for the in-floor heating system. This draws about 40 watts, compared to 80 watts for the Grundfos 120v pump. I don't know how much that pump will have to run, but it could add up pretty quickly if it runs for 10 to 12 hours a day. If I went 48v, could I 'step down' to 24v?

    The Outback spec sheet says the recommended size of the solar array for a Flexmax 60 at 48V is 3000W, which is about twice what I would start with, and about 1000W more than I would expect the end size of the system to be. Would that be a problem, in the sense that if I went 48V, should I shop for some other controller?

    I was happy to hear you bring up the genset. That is a big question mark for me, as I figured I should spec the rest of the system and then decide on a generator to fit. A manual start is out as the house I've been talking about is actually for my mother, who turns 66 tomorrow (April 27). I need her to be able to start the thing with a flick of the switch at most.

    As I see it, there are three generator options:

    A $2500-$3000 8KW propane generator like the Briggs/Stratton back up power ones you can buy at Home Depot.

    A $6000 8KW generator like a Winco standby. Still air-cooled, but presumably a better build.

    A $10,000 liquid-cooled propane generator (if I could even get one for that).

    The third option just about kills me in terms of $, and I find it hard to imagine that it would pay itself off, given the light use I'm expecting. The $2500-$3000 option is tempting, but it's hard to believe it wouldn't die pretty quickly, for no good reason. Do you have any thoughts on this? I wouldn't be worried about the engine wearing out, so to speak, because I don't think it would run all that much. The worry instead is with general build quality.

    I am also very interested in the question of what it costs to run a generator. Suppose an 8KW generator takes 1 gallon of fuel per hour at half load. That means, I assume, 1 gallon per 4KW. But if I am using the generator to charge the batteries, how many of those watts actually make it into the battery? Are there any guidelines on this?

    One of the reason I am interested in this question is because although I really don't want to run the generator a lot, there is obviously a breakpoint where it makes more sense to run the generator than to stock up on yet more panels for winter. If, for instance, it costs $1 per KW to run the generator, it would make a lot more sense to run the generator in December than to buy panels. But if it costs $4 per KW, the calculations might go the other way. I am also jumping through a lot of hoops to trim every last bit of electricity (e.g., 40W 24V pumps versus 80W AC pumps, a pricey bathroom fan that is only 13W instead of 30W, etc.). If it really costs only $1 per KW, I could relax a bit on those measures. This info about cost per KW into batteries is something I haven't been able to find out from generator dealers/manufacturers.

    thanks again,

  • BB.BB. Super Moderators, Administrators Posts: 32,813 admin
    Re: searching for comments on my proposed off-grid system

    Tony/Icarus would have more information on Canadian and generator specific availability questions...

    In general, conservation and solar panels will be the answer to most of your questions--a generator will be a requirement--but how often and how much you will run it vs paying for more solar panels is your question to answer (of course--if you have weeks of heavy cloud cover--solar panels will never be the solution there).

    Used gensets (I think Tony has a yard full of them on his island ;) ) should not be that expensive. But there is always the maintenance costs (can you do it yourself?) and the fuel + transportation costs.

    The reality is that large gensets need large loads (typically around 50%) to be "efficient"... And charging batteries, you can start with the rule of thumb (13%) and make an equation:

    870 Amp*Hours * 24 volt * 0.13 * 1/0.8 charger efficiency = 3,400 watts from genset...

    So--if you get a 3-5kW genset, you can assume 3,400 watts (~maximum wattage through charger) if the battery is below 80-90% state of charge up to ~80-90% state of charge, when most chargers will start to back down on power requirements.

    On the other end, 5% min. charge rate:

    870 Amp*Hours * 24 volt * 0.05 * 1/0.8 charger efficiency = 1,300 watts from genset... (minimum charge rate)

    And a 2,000 kW max (1,600 watt max cont.) genset start making sense--plus since you are at a lower energy rate--you can probably keep the efficient use of power past the 80-90% state of charge (and the Honda is efficient down to 400 watts)--so it will taper charge very nicely...

    Let Tony, who has more experience than I type about his experiences and recommendations... But--again easy use (electric vs manual start) vs costs (purchase and fuel) will be an issue.

    Also, finding a charger with the appropriate current output and sized for your genset will affect your choices too...

    Lastly, many battery chargers are not very "electrically friendly" (have low Power Factor or no PFC--PF Correction)--that means you are left with a battery charger that can only use 50% of the generator's rated capacity before it pops a breaker or overheats the alternator.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: searching for comments on my proposed off-grid system

    Nick,,, Roger that on Hydro 1!

    About generators. The reality can get run into a series of complicated equations that lead to somewhat ambiguous conclusions.

    First you seem to have gotten a handle on the conservation side. As too many people learn too late,,, that their cheapest RE $ is conservation,,, all the way down to the pumps you buy! The 40 watt savings on the pump system is huge over the life of the hardware. (40 watt/ 24 day=.960kwh,,, 50% more than my total use in the average day. Using our 50% rule of PV name plate rating to get that 960wh you would need something like 300 watts more panel,,, at $4 (USD) per watt that simple pump change saves $1200 up front.

    Now for generators. I would stay away from Briggs and Stratton/Coleman/Canadian Tire type generators UNLESS they are almost free. The reality that they are not very fuel efficient,, they are noisy and they have trouble holding steady voltage. They are commonly wired with floating neutrals that make it difficult for many Battery Chargers to run well. (The Xantrex TC series being one exception) From a fuel efficiency stand point,, there is no beating the Honda Eu series. Take into account running at the most efficient loading given your expected use will lead you to a size. They are quiet and very fuel efficient, but pricey. You could certainly consider a Kipur clone instead,,, but I would shy away from one. My neighbour has one and has been fine.

    I am a big fan on older Onan generators. They can be had quite reasonably and if they are taken care of they can run virtually forever. They can be had with auto start systems as well. Many can or are already configured to run on LP or Natural gas. The rub is that they tend to be fuel hogs,, especially the 3600 rpm versions. (Many are 1800 rpm units). Your choice of fuel is largely dependent on availability and price. Propane would be preferable from a fuel stability issue,, but in my case it come at ~twice the price per litre. If you can get home delivery in bulk at a good price,, surely consider it.

    Finally, consider diesel. From a fuel efficiency point of view with larger loads there is no comparison. Diesels also can last forever if you take care of them. The issue with diesels is noise,, and smell,, and fuel handling. Once again,, proper loading is critical both for fuel efficiency as well as good engine running. (Running a 1 kw load on a 10 kw not only burns a ton of fuel,, relatively,, but it also very hard on the engine,, causing carbon build up,, piston ring ridges etc.

    One thought that might make the most sense,,, is set your house up,, buy a cheap genny to start that is big enough to handle your charging and other needs. (I also use the genny for all the shop tools rather than sizing the solar for that occasional use) For 1300 ah of 24v battery,, lets say you wish to charge at 15%. You would need ~ 195 amps @ 24 vdc or ~ 4700 watts,, factor in maybe .65 power factor (just a guess) would leave a genny of ~ 7 kw. Now an old Onan would run day and night for years at 100% of rated without breaking a sweat. A Cheap Briggs might run a year if it were fully loaded a bunch of hours a week. A non Eu Honda might well run a bunch of years at or near load,,, but most would like it better to run ~75% load.

    The long and short of it is this. You need a genny big enough to charge your batteries quickly and to equalize them. It seems that there are tons of "cheapo" gennys out there 5 kw and under. Above 5 kw you begin to limit yourself somewhat. There is a ton on Onan models right around 5 kw. (I would avoid the newer Emerald series of RV Onans. They are fairly good units, but not the brick outhouses that the CCK series were.

    At five + kw for a cheap short term (few years) you could get a Honda or Mitsubishi, Robin Subaru, Makita type construction genny. It will do what you need it to do and still be here in a couple of years. After you get your usage pattern down,, THEN you can find the best, most fuel efficient, quietest etc genny for your needs.

    Hope that helps,



    Between Craigs list, Kijiji, E-bay there are tons of gennies out there. The last one I bought is a 2800 Mitsubishi for $50. Needed a control board that Mitsubishi sent me gratis after I complained that it had gone through 4 in the previous few years,,, true story. My little honda eu 1000 cost me $350 USD nearly new. It is amazing how many people get new gennies and with in a year or so realize that they don't use them and then sell them.
  • retroboltedretrobolted Registered Users Posts: 6
    Re: searching for comments on my proposed off-grid system

    Hi Bill,

    I was hoping to ask you just one thing about the calculations you did on the recommended generator size for my set up.

    13% charge rate would be:

    >870 Amp*Hours * 24 volt * 0.13 * 1/0.8 charger efficiency = 3,400 watts from >genset...

    5% charge rate would be:

    >870 Amp*Hours * 24 volt * 0.05 * 1/0.8 charger efficiency = 1,300 watts from >genset... (minimum charge rate)

    Am I right to understand that you're saying that I don't need any more than 3400W from the generator? I am puzzled because I had read in Bill Kemp's book that people usually need 7500W for battery charging.

    >Also, finding a charger with the appropriate current output and sized for your >genset will affect your choices too...

    This remark reminds me how clueless I am. I thought the generator was hooked either directly to the batteries or to the inverter/charger that I already have. Am I right to understand I need to buy both a generator and a separate charger?

    thanks for your patience.

  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: searching for comments on my proposed off-grid system

    1) the wattage needed will vary, depending on the size of the battery bank.

    2) The type of charger that runs off 120/240VAC - if it has good power factor
    you will need less generator watts, if poor power factor, you need larger generator.

    A good power factor spec is >.9 bad is less than .9
    perfect PF = 1.00
    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: ,

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: searching for comments on my proposed off-grid system

    reread bill's last sentence as i believe he addressed it there and confirms what you have been told elsewhere.
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: searching for comments on my proposed off-grid system


    The PF of the Magnum 4000 inverter/charger suggests that the PF is >.95. Pretty good by most standards.

  • BB.BB. Super Moderators, Administrators Posts: 32,813 admin
    Re: searching for comments on my proposed off-grid system

    As Niel and others said--many chargers have very poor power factor (do not take current in a nice sine wave that follows the voltage wave form)--so the genset needs to be amost 2x to handle the "non-linear" current draw of the typical battery charger.

    Xantrex also makes a nice "TC-2" line if their TC line is indication (which is end of production). The TC-2 appears not to be shipping yet to retailers.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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