First Time Solar Setup - Need Your Opinions!

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ChevyNo1
ChevyNo1 Solar Expert Posts: 30 ✭
in Solar Beginners Corner #1
Hello! First post here, and just getting started in solar - will be moving to an off-grid cabin next spring and plan to stay there for the entire year. My goal is to setup a basic system, as we are just testing out this first year to see if we like it enough to stay permanently. Because of this, I know I am light on both storage (batteries) and input (solar panels). BUT I do also have a Yamaha 3000esib as backup. I understand that I for the first year will use this more than I'd like to. After the first year if we stay I will beef things up.

But for now - this is what I am thinking and I would certainly appreciate the collective knowledge of all you fine folks here :).

To start - I had initially planned on going with a 12V system, mostly because it is what I'm somewhat familiar with, and I really didn't know enough about 24/48V to change that decision. However, I've kept reading quite a bit, and think I will make a change to 24V. Mostly because of my choice of charge controller. Was going to go with just a regular PWM, but I have changed my mind to get the Morningstar 15A MPPT.

I plan on building 3 panels myself. Using the standard 3x6 cells off Ebay - 72 cells on each panel should work out to 12V @ 7.2A (2x36 cells, each 12V@3.6A, those in parallel). If I wire these three panels in serial, I should get 36V @ 7.2A (51-54v open circuit). Panels should equate to just under 130 watts, giving me maybe 380 watts into the controller, just under it's 400w max @ 24V. I have considered building a combiner box from an AC panel - but not sure if I can get away with a simple combiner box like this one: http://www.freesunpower.com/project2.php.

Either way - out of the combiner into the charge controller. Controller will be hooked up to a 24V battery bank. I am thinking for now of just 4x6V GC2 batteries (brand undetermined) wired in series to give me 24V @ 220AH (assuming that is the rating of the batteries I get). This way the Controller would see it as a 24V system. From my calculations, this should equate to a max 15A charge @ 24V, giving me around 360 watts. Average sunshine I expect to be 4-5 hrs yearly average, which only gives me (at best) 1440 watts in. Not enough given my estimated 1.7KW/h per day - for charging of the battery bank I will end up using the genny. Again, only for first year ...

For inverters, I have two in mind. One is a pure sine wave 1000W 24V inverter that also has a cigarette lighter output (24V). The other is a 1500W but is not pure sine. I am leaning towards the 1500 simply for the extra potential. However, the socket on the other is appealing, only because I have a Coleman 12V/120V powerchill cooler. I also have a 24 to 12V converter. Thinking power-consumption wise, wouldn't it be more efficient running from the socket on the inverter, through the dc-dc converter for 12V and then into the fridge? Or would it just be the same to run the fridge on AC from the 120 on the inverter? If the former, I will get the one with the socket. If I'm really not gaining anything, I'll be better off with the 1500. If we stay past the first year will end up getting a quality 12/24DC fridge anyway.

I understand that I should have a fuse between the controller and the battery bank, and between the battery bank and the inverter. The 1500 has a built-in 40amp fuse. Is that also what I would put between it and the battery? If 1000W/24V = 41 amps I'm guessing that's correct. Since amperage coming from my combiner is only 7.2, do I even need a fuse there? If I were to build a panel with breakers, would I need a fuse there at all?

As far as shunts - do I need one? Or does this controller just handle that without a shunt, or perhaps it has a built-in one? Not sure on this part ...

And wiring is another question - for the solar panels to the combiner - what type is best? And what size? From my calculations I should be OK with 12AWG with lengths under 18'. The only reason I can get away with it from my understanding is because of my move from 12V to 24V as the current halves. I have the same AWG going from the combiner to the controller since the current stays the same but voltage is increasing. I suppose in that sense I could even go with smaller cable from the combiner to the charge controller? Or just leave it the same?

Coming out of the charge controller into the battery bank will be 24V @ 15A. Unless I'm doing it wrong, I show that as 14AWG if under 10'?

With this inverter, the most it can pull from the battery bank is 40A - if under 3' I also show 14AWG - I'm used to seeing much larger cable with 12V - is that sufficient??

BTW, I am using this wire size calculator: http://www.freesunpower.com/wire_calc.php

If there is anything I am overlooking please also point it out - anything safety-wise especially!

I know I have a lot of questions - thanks for taking the time to help me out, it is much appreciated! :D
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #2
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    Re: First Time Solar Setup - Need Your Opinions!

    I will be shill for "the man" and tell you not to waste your time and money on building your own solar panels unless you just want a project for your own education. There are panels out there right now that cost almost the same amount as the components you will be using for your DIY project (~$3-$5 per watt--not including shipping). If you hunt around, you may even find some panels under $1 per watt (again, shipping can be a killer for solar panels).

    It is probably impossible for the average person to build their own solar panels at home that will both last more than a few months in the weather without failing, and, many people use wood and or plastic for their arrays which is a serious fire hazard (don't mount on on home roofs or over flammable grasses/plantings).

    That being said--if you are still interested in building your own panels, there are a few discussion threads here talking about how to do it and you are welcome to open your own thread for discussion.

    Regarding your hardware choices, 24 volts, MS 15amp MPPT charge controller--all fine picks.

    You can support more than 400 watts into the MS 15amp MPPT controller electrically... It will just limit its output current to 15 amps--so more panels may be a waste of money. I use the following as a rough break even point for sizing an array:
    • 15 amps * 29 volt battery charge * 1/0.77 system derating = 565 watts
    I would have no problem with a 565+ watt array on this controller/24 volt setup... Except in very cold / sub freezing conditions, the panels will never output even its rated power (as panels heat up from the sun, their Vmp voltage falls).

    For a combiner box--You do not need fuses/breaker if you have only one or two parallel solar array connections. If you have 3 or more parallel strings, you should have a fuse/breaker per string to prevent back feeding a panel short and starting a fire (two parallel arrays do not have enough current to start a fire/pop a series protection fuse in a properly designed setup).

    Inverters--for a full time / remote site--I would suggest going with True Sine Wave all the way. If cost is a big issue, get a small TSW for your computer/cell chargers/small TV/etc. and get a big cheap MSW for your power tools / pumps / etc:

    Morningstar SureSine, 300 Watt Sine Wave Inverter 115VAC (this is a 12 volt inverter--and for a smaller off-grid system--it is a good reason to stay at 12 volts)

    A couple inverter FAQ's:

    All About Inverters
    Choosing an inverter for water pumping

    Every wire/cable that leaves the battery bank should have a fuse/breaker rated to protect the wiring connected (14 awg wire, 15-20 amp breaker/fuse, etc.). Not everyone does it, and it is not cheap, but it is a fundamental requirement for fire safety (fuses are there to protect the wiring, not to prevent damage to the devices like inverters, lights, charger, etc.).

    24 and 48 volts systems use less current (for same amount of power), so fusing and wiring is much smaller (1/2 or 1/4 that of a 12 volt system) and the prices are also much less.

    I have to go right now--And we can discuss more of your wiring/fusing/etc... But this is a little bit backwards.

    It is normally better to start with your loads (peak watts, average watts, Watt*Hours your loads are running, etc.) first. If you design a system that is too small for your needs--it does not matter much if we designed it well... And if you design a system that is much larger than your needs--you will have spent a bunch of extra cash making a very nice installation.

    In the end, most people underestimate their loads and overestimate how much power an Off-Grid solar system can supply. Understanding your loads and working on conservation (the old Propane vs Electric Refrigerator question, etc.) is critical to getting a "right sized" system for your needs.

    Off Grid solar power systems are generally difficult to "up size" once you have installed one... Roughly, you can probably double its size (array or battery bank) if you have need--But more than that, you probably are looking at a complete tear-out/redesign. That is why is is critical to understand/map out your loads first.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #3
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    Re: First Time Solar Setup - Need Your Opinions!

    Fyi,

    We live off grid, with 400 watts of panels, 450 ah of batteries. On an average day, we use ~6-800wh of power, and generate about the same. On an ideal day, we generate 1-1.5kwh.

    A few rules of thumb. You will use more power than you expect, your loads will grow with time, and you will get less solar harvest than you predict.

    In my experience, take the ratings of the panels, divide that number by 2 to account for all cumulative system loses, and then multiply that number by 4 to represent the average hours of good sun you can reasonably expect over the year as a starting point.

    The most important thing to do is to design your system based on your expected loads, understanding that they will grow. I personally design for no more than ~ 10-10% daily draw on the batteries, leaving a three day reserve.

    Welcome to the forum, there are some very sharp, very experienced folks here who are more than willing to entertain any questions,

    Tony
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: First Time Solar Setup - Need Your Opinions!

    I'll throw my opinion in for what it's worth. :p

    First, I agree with Bill about the homemade panels; strictly a learning experience. What you will learn is that building them isn't as easy as the promoters claim and even if you do the best possible job they won't stand up to the weather the way commercial panels do.

    Second, I think you're a bit light with the 15 Amps charging for a 225 Amp hour bank. That's because it probably won't be hitting 15 Amps most of the time. Shoot for 10% charge rate; you'll probably get something between 5 and 10 that will suit.

    Third, to go with the rough estimates you've got I'd do something like this:
    225 Amp hour @ 24 Volt battery bank gives 100 Amp hours max to work with = 2.4 kW hours per day. This is really quite good for off-grid and would cover your 1.7 kW hour per day estimate at less than 50% DOD.
    To charge that you'd want 400-800 Watts of panel. I'd lean towards 800. :D And preferably a 30 Amp charge controller as you're trying to get over 20 Amps into those batteries. A bare minimum; 3 Kyocera 135. Four would be better. http://www.solar-electric.com/kyso130wa12v.html Then you put two in series for "24 Volt" and parallel two such strings. You could use a PWM controller on this without trouble and save money.
    As for the inverter ... the one thing missing from your post is the loads. Some things are fine on MSW, others not so fine. They'll draw more current or perhaps not work at all - or even quit. So it's important to know what you pan on using the electric for in order to choose an inverter.

    The system described in my sig runs an electric refrigerator, water pump, digester pump, computer/satellite/phone set-up, plus lights, radio, and the occasional microwave zap! It requires judicious load management, however; as in keeping the pumps off until there's a full charge in the batteries. It also requires more gen time than I'd like, and is no good in our ultra-short Winter days (6 hours - about 2 of sun if you're lucky). I intend to increase the panels to 1050 Watts and get a better battery bank. Perhaps even larger (with even more panels).

    Before you worry about fuses and wire sizes (which are dependent on distances and current and Voltage) let's see what we can figure out for your equipment first, eh? :D For instance, a 24 Volt 1500 Watt inverter with a 40 Amp fuse? Ought to be more like 90: W/low Voltage (21) = Amps * 1.25 "fuse factor" = about 90.
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #5
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    Re: First Time Solar Setup - Need Your Opinions!

    Bill - thanks for all the great info. I read the entire thread about the fire hazard - so I learned two things - do NOT roof mount, and to use glass, which should be pressed right up against the front of the cells to avoid any lifting. However - I know one of the reasons people use say plexiglass is for the strength against any impacts, ie hail. Building with glass only has this downside then?

    In terms of what materials to use for the frame - I am not clear on the best for a DIY setup, or at least what is somewhat economical yet safe.

    As far as my loads - I have figured it out to be 1700wh per day - a good lot of that taken by that PowerChill - but I will deal for the first year. I have added in 10 hours of laptop use per day for work, and a couple of CF AC lights for a few hours per day. Also have a propane lamp, portable flashlights, camping lights, etc. I have seen 24DC fridges that claim something in the range of only 150wh per day ( from Lehman's: http://www.lehmans.com/store/Appliances___Refrigerators___12V_24V_DC_Refrigerator_or_Freezer___33703166?Args= ). I thought that was very low, but they claim it's A++ rated. If that is in fact correct, my power needs would drop into my second year, assuming I didn't add anything new to my power needs.

    Tony - thank you for your input as well - good to hear from those with experience!
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #6
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    Re: First Time Solar Setup - Need Your Opinions!

    Coot - thanks! :)

    I do understand that I am underpowered at this point - the ONLY reason is because this is a BIG change for my wife - and after a year it may be decided that this will NOT be our fulltime residence, and only a cottage that we visit from time to time. Hence not wanting to dump a lot of $$ into the setup until I am sure.

    I really do not have any high load items that I know of - other than a 700W microwave from time to time. Other than that - a few power tools potentially. No pumps of any kind ...

    Does that make sense? With that in mind, I AM trying to build this system such that I can add on, to some degree, in the future without a complete rework. I think my power needs are low enough for that to be possible.
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #7
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    Re: First Time Solar Setup - Need Your Opinions!

    Also - to keep costs down initially - could I use the 15A Controller with 3 of these panels:

    http://sunelec.com/index.php?main_page=product_info&cPath=5&products_id=1173

    I realize that to handle some of the other high voltage panels I really need to step up the controller - but trying to avoid dumping that much money if possible - if you think I'm making a mistake, let me know ;)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: First Time Solar Setup - Need Your Opinions!

    Okay, a couple of other things you should be aware of:

    A "700 Watt" microwave will actually draw 1000+ Watts. They always rate them by "cooking power" which is substantially less than their consumption. Mine is 700 Watts - draws 1050 off the Outback! And that's another thing; the microwave will use more power from an MSW inverter than from sine wave.

    Power tools are occasionally problematic as well. Most corded tools will work fine. Big saws can have very high start-up surge and induction motors that will draw more power on MSW than PSW. Some battery chargers for cordless tools don't work properly on MSW or even fail. Just a "watch out" warning.

    I'm not sure about those particular panels. For one thing, their Vmp is just under what we'd normally expect in a "12 Volt" panel. For another, they've got that "Sun" in their name and there's one brand out there whose exact name I can't remember (but it has "Sun" in it) which are positive ground and therefor a bit tricky too hook up to the average charge controller. Bill will know; he always remembers these things!

    Sure can understand you're not wanting to dump a large amount of money into a trial thing. But on the other hand, if the electrical system doesn't work well that will severely degrade your quality of life and possibly make the off-grid experiment a failure. :cry:

    It's like the refrigerator issue: full time warrants electric, and the extra cost of powering it. Part time it's probably cheaper to go with propane (although the 'friges are expensive new). Maybe see what you can get in RV-type equipment. You'll be giving up space, but it's more likely you could re-sell it later if you need to "ramp up".
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #9
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    Re: First Time Solar Setup - Need Your Opinions!

    Yep, I actually have a Kill-A-Watt and have measured pretty much everything in the house, ha ha!

    So I have already observed my 900W microwave pulling 1300 - which is why I figured I should step it down to say a 700 which might pull 1000. Maybe I'll even drop that to a 600 version ...

    On the frig .. did you check that link from Lehman's? That seems VERY low consumption, I would think costing even less than running an LPG version ...

    I do not expect to be using any high-draw power tools often, and if so likely would fire up the genny for that. I plan on using it as a 'crutch' of sorts for my first year. But I do hear you on the quality of life - something I might not struggle with so much, but the wife might!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: First Time Solar Setup - Need Your Opinions!

    I'm not surprised about the 'frige; it's less than 6 cubic feet and a chest-style.
    You might want to have a look at this thread: http://forum.solar-electric.com/showthread.php?t=9
    And know that some others here have found the use of the chest 'frige/freezer to be a real pain in the anatomy. Your Mrs. may not like having to bend over and reach down and sort through to get at things. :blush:Mine sure wouldn't! :p
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #11
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    Re: First Time Solar Setup - Need Your Opinions!

    Great link on the freezers - other than the obvious bending-over issue - what a cheap way to run a frig!!
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #12
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    Re: First Time Solar Setup - Need Your Opinions!
    ChevyNo1 wrote: »
    Bill - thanks for all the great info. I read the entire thread about the fire hazard - so I learned two things - do NOT roof mount, and to use glass, which should be pressed right up against the front of the cells to avoid any lifting. However - I know one of the reasons people use say plexiglass is for the strength against any impacts, ie hail. Building with glass only has this downside then?

    My commercial panels survived a golf ball sized hail storm about 2 months ago. It was bad enough to cause over $4000 damage to one of my cars. Unless your in some freak hail zone then the commercial tempered glass panels are not an issue. Plus if using commercial panels you can just add them to you homeowners insurance for minimal added cost.

    Homemade panels will never get into your homeowners insurance and if there ever is a claim for fire now you have to deal with a possible source of ignition that the insurance company may use as an out on paying. This is true even if the panels may not be the source of the fire.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #13
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    Re: First Time Solar Setup - Need Your Opinions!

    Re your fridge, I used a 5 cu ft converted freezer for a few years. Worked great except for the problem of getting at the items, and the loss of useable space due to the need to get at things. Also the way too easy problem of items getting buried and forgotten about.
    Update - - I now have the following:
    http://www.sears.ca/product/kenmore-md-42-cu-ft-upright-freezer/646-000088526-DUF408WE
    Yes, it's slightly smaller cu-ft wise, but has far more useable space, have it elevated so no more bending over, and unless one stands there with the door open, gazing and wondering what to take out, it actually uses less power than the other one I had!
    Maintaining more or less 35F temp, it runs 5 minutes, once an hour (once everything has cooled down) and consumes more or less 100 Watts while running. Another thing I love, is that when set to run at this temp, I don't have water buildup like with the chest style. Why? Because the upper shelf/evaporator tends to stay below freezing, thus collecting the moisture as ice, which can be removed perhaps once a month by placing a good thick towel directly under that shelf to catch the drip, turning the whole thing off for most of a day to allow the collected ice to melt. then just remove the wet towel and turn it back on. No need to remove any food items. Way, far more convenient than trying to move things around to sop up the water that was omnipresent in the chest style. And after having the chest type for about 5 years, I LOVE the door shelves for all those little items. Power consumption has worked out to less than about 150 watt hours, per 24 hour day. Again, depending on how often and how long the door is opened and how much warm mass in put in to be cooled. Best of all, it's price. If you're interested, I can also give you info on what I used for temp control. (a modified home heating/AC thermostat with it's thermistor sensor remotely located inside the " fridge")
    After using this for for a couple of months now, I'd never go back to a chest type fridge!
    Food for thought :)
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    #14
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    Re: First Time Solar Setup - Need Your Opinions!

    I just cleaned out a 10cuft chest freezer yesterday, in about 10 minutes. Procedure is unplug (or shut off), by the time everything is pulled out and in boxes, laundry baskets or boxes you can use an auto ice scraper to dislodge the frost cake from the sides, then scoop it up with a dustpan. Putting the still frozen contents takes a little longer (do we keep this or let the dog eat it?), then plug in/turn on again. Total time 10 minutes or so. Letting the system truly defrost is messy and time consuming. The plastic ice scraper doesn't damage the freezer. Not sure if our American South friends know what an automobile ice scraper is, but Wayne and I sure do. Probably Neil by the sounds of last year's storms.;)

    Ralph
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #15
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    Re: First Time Solar Setup - Need Your Opinions!

    Haha Hey Ralph, I was referring in both cases, to defrosting units which had been designed as freezers, but which have since been converted to super high efficiency fridge use, so are no longer being used as freezers. I did have a couple of things freeze in them, until I got the temp properly regulated, but not since. And yes, we sure do know about ice scrapers! Gonna have to start using them again any day now. Hahaha :p
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #16
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    Re: First Time Solar Setup - Need Your Opinions!

    Hey Wayne, thanks for the info - good to know that by being smart with usage an upright is very economical also. That is likely the way I will go as well.

    FWIW - I am in the deep southwest now - moving to the northeast - grew up in eastern Canada - so very familiar with the winters. My wife not so much - California girl so she's in for a shock or two I figure :D

    But we're both excited about getting off the grid and going green - a new direction for us.
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #17
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    Re: First Time Solar Setup - Need Your Opinions!

    Dave - thanks as well for your information. I figure since this is a 1-year probationary period for us - I will make my panels and if they only last one year, so be it. Big learning experience for me, I am researching this quite a bit to do it right and safe. I will build with the tempered glass as suggested.

    After that first year - if we stay permanently there will be a lot more changes to happen!
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #18
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    Re: First Time Solar Setup - Need Your Opinions!

    What size interconnects between batteries should I use for this? Based on what I have read, I probably would want to support up to 100A load (1500W 24V inverter) on the interconnects - would these be sufficient? http://www.solar-electric.com/43010.html
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #19
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    Re: First Time Solar Setup - Need Your Opinions!

    The basic current calculation for a generic inverter:
    • 1,500 watt *1/21 volt cutoff * 1/0.85 inverter eff * 1.25 NEC safety factor = 105 amp designed circuit
    A pair of 4 awg cables will have about 0.9 volt drop at 105 amps and 15' one way run--Looks fine to me.

    In any case, the shorter the better for inverter cables.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #20
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    Re: First Time Solar Setup - Need Your Opinions!

    Awesome, thanks Bill! Great knowledge going on here :)
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #21
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    Re: First Time Solar Setup - Need Your Opinions!

    I also am trying to figure out the best way to charge the bank with my generator when I need it. I already have a Stanley 25A charger (3 stage with equalization) but it is 12V. So I was thinking about getting another one. Then I would break the connection in the middle of the 4 battery bank, creating two 12V batteries, each being charged by it's own charger. 25A on a 220AH bank should be where I want to be right? This way I figure I can max my genny run time.

    I am guessing that if I did this, I'd also want to be able to disconnect the entire bank from both the controller as well as inverter-side. Is the power-off switch on the inverter enough, or would I want some sort of disconnect switch there?

    I've seen the knob controllers that I think would work. Could I also use one of these in between batteries 1/2 and 3/4, to make my two 12V batteries quickly?

    And between the controller and bank - just another knob switch would do?

    Thanks for all suggestions!
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #22
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    Re: First Time Solar Setup - Need Your Opinions!
    ChevyNo1 wrote: »
    ... So I was thinking about getting another one. Then I would break the connection in the middle of the 4 battery bank, creating two 12V batteries, each being charged by it's own charger. ....


    While this might work if everything is isolated, and no common grounds on the chargers, you would also disable any inverters while this is happening.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #23
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    Re: First Time Solar Setup - Need Your Opinions!
    mike90045 wrote: »
    While this might work if everything is isolated, and no common grounds on the chargers, you would also disable any inverters while this is happening.

    Which I can be OK with - I have two powerboxes (300/400 watt units) that could carry any smaller loads I might have.

    Although I better get clarification - if both chargers are running off the same generator - wouldn't they have the same ground? How does this cause problems?

    I also have a 1200W 12V inverter that I would have hooked up to a standalone 80AH marine deep cycle I have - so while the genny is running I think I'll be OK.

    However - is there a better config for charging with the generator? Obviously a controller that also charged - but that will be the following year should we stay.

    Thanks!
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #24
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    Re: First Time Solar Setup - Need Your Opinions!

    Instead of monkeying around with two chargers, and disconnecting batteries etc, why not bite the bullet now and get a good 24 volt charger? Eventually if you system works as you hope, you will want a real charger anyway.

    http://www.solar-electric.com/bach1.html

    Tony
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #25
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    Re: First Time Solar Setup - Need Your Opinions!

    Generally, you would like to load your genset to at least 50% of rated power for best fuel economy...

    For 25 amp 24 volt worth of charging, assuming 50% genset loading and 80% charger efficiency:
    • 25 amps * 29 volts charging * 1/0.80 eff * 1/0.50 generator loading = 1,812.5 watt rated genset
    With AC loads (particularly generic battery chargers), the input stage has very poor power factor--It can be down as low as 0.6 for battery chargers pretty easily. Power Factor is a "correction" for less than ideal current usage of 50/60 Hz AC power (genset or utility power):
    • Power = Voltage * Current * Power Factor
    So, if you want to load your genset more than ~50% loading--You have to measure or find out the power factor of your AC battery chargers.

    Power wise, your chargers would use:
    • 25 amps * 29 volts charging * 1/0.80 eff = 906 watts
    So, that would be pretty close to running on a 900 watt genset.

    But, because the "bad power factor" that most AC battery chargers have, you need almost 2x larger genset to prevent current overloading of the generator, wiring, and breakers.

    As Mike said, if the two 12 volt battery chargers have isolated (or floating) inputs with respect to their AC power cord (and safety ground, if present)--you could connect each supply across a 12 volt bank and charge the bank nicely.

    But not knowing the guts of your power supplies, it would be unsafe for us to tell you that is OK. And you might not find any charger vendor that is willing to give you information about output isolation (in theory, a modern UL/NRTL approved battery charger should be isolated to the AC power line by 1,800 VAC--But we don't really know about the third wire safety ground and how that is handled--it could be connected to the DC output and would short your bank out if you tried two 12 volt chargers on a 24 volt bank).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #26
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    Re: First Time Solar Setup - Need Your Opinions!

    I agree with Tony; if you have to buy another charger, get a 24 Volt one and save yourself some hassle.

    That said, you don't have to "break the bank" (couldn't resist) when charging a 24 Volt system from two 12 Volt chargers; their DC is separate from one another and having the same AC source is irrelevant.

    And if you like to mess around with such things, most 12 Volt battery chargers will put out 24 Volts with a bit of tinkering inside. There won't be any regulation and the Amperage will be low and the life will be shortened. But it can be done in a pinch. This is because most of them center tap a "24 Volt" transformer and then rectify the two "ends" to (+). You get a rather impure DC this way, but it ups the Amperage capacity.

    Oh yes, and the caveats: Don't try this at home, professional tinkerer, closed course, and your actual lifespan may be severely shortened. :p
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #27
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    Re: First Time Solar Setup - Need Your Opinions!
    icarus wrote: »
    Instead of monkeying around with two chargers, and disconnecting batteries etc, why not bite the bullet now and get a good 24 volt charger? Eventually if you system works as you hope, you will want a real charger anyway.

    http://www.solar-electric.com/bach1.html

    Tony

    Well - unless I am misunderstanding - for me to buy a 24 volt charger capable of charging this - wouldn't I be looking at least the 24 volt, 25A charger, which is $270? And if I had to go with the 40A, then it's $472. Another 12V charger like I have is $67 delivered to my door. Unless I'm looking at the wrong chargers. I can handle the disconnecting for a year if the price is that steep ...
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #28
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    Re: First Time Solar Setup - Need Your Opinions!
    ChevyNo1 wrote: »
    Hey Wayne, thanks for the info - good to know that by being smart with usage an upright is very economical also. That is likely the way I will go as well.

    FWIW - I am in the deep southwest now - moving to the northeast - grew up in eastern Canada - so very familiar with the winters. My wife not so much - California girl so she's in for a shock or two I figure :D

    But we're both excited about getting off the grid and going green - a new direction for us.
    Awesome man! Very best of luck with your off grid plans. I could now easily cut the grid wires, but as I'm getting older, I figured it best to keep them there as backup.
    For all intents and purposes, I am off grid. Use extremely little grid power and what I do use, is definitely NOT a necessity. When I get that second full size freezer emptied (Yeah, I have 2 full freezers) I won't be using any power from the grid. One of these days I'm just going to empty out the second one out and pull it's plug. I keep putting it off.
    Hopefully your wife will see the awesome beauty that Winter can bring, and not just the negative :)
    Would be awesome if your new place had a reliable brook nearby that you could tap into for micro hydro. Mine only puts out 135 watts, but it keeps the batteries full up on charge throughout the night and heavy overcast days, and I use all I want, just don't waste any. Never did waste, so no big change in lifestyle needed. Any heavy loads are saved for sunny days (or hours). Living with nature, not fighting it. Appreciating more every day, that I'm in a position, energy wise, that once was beyond my wildest dreams. Never thought I'd progress so far with it. Now I never want to go back!
    Totally dark outside, the sun's been gone for almost 4 hours, and all the following are on and running: Fridge(converter freezer), full sized freezer, TV, outside lights, inside lights. air exchanger, and this laptop, all running off my system (wired fridge and freezer so they don't run at the same time) and battery voltage is holding at 13.2, Gotta love that! :p
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #29
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    Re: First Time Solar Setup - Need Your Opinions!
    Cariboocoot wrote: »
    I agree with Tony; if you have to buy another charger, get a 24 Volt one and save yourself some hassle.

    That said, you don't have to "break the bank" (couldn't resist) when charging a 24 Volt system from two 12 Volt chargers; their DC is separate from one another and having the same AC source is irrelevant.

    And if you like to mess around with such things, most 12 Volt battery chargers will put out 24 Volts with a bit of tinkering inside. There won't be any regulation and the Amperage will be low and the life will be shortened. But it can be done in a pinch. This is because most of them center tap a "24 Volt" transformer and then rectify the two "ends" to (+). You get a rather impure DC this way, but it ups the Amperage capacity.

    Oh yes, and the caveats: Don't try this at home, professional tinkerer, closed course, and your actual lifespan may be severely shortened. :p

    OK now this confuses me - are you saying that if I have a 24V battery bank - that I can hook up two 12V chargers and it will charge at 24V? Is that because technically by hooking chargers to batteries in parallel that I'm adding the voltage?

    Sorry for all the silly questions - I am a newb! ;)
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  • ChevyNo1
    ChevyNo1 Solar Expert Posts: 30 ✭
    #30
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    Re: First Time Solar Setup - Need Your Opinions!

    Bill - wow ... I have much to learn!

    OK - this is how my basic mind thinks about things. I have a 12V charger. It takes 120V @ 6.5A as input - if I work the #'s, that should be about 800W draw .. if I have two chargers, each charging a 12V bank - that should be 1600W draw. Of course there are the various efficiencies which you have quoted - is that another way to come up with your 1812 #?

    Either way - shouldn't a genset rated at 3000W be fine? Still trying to wrap my head around the isolated ground etc that you were mentioning. If each charger is connected to it's own 12V bank - is there still an issue?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #31
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    Re: First Time Solar Setup - Need Your Opinions!
    ChevyNo1 wrote: »
    OK now this confuses me - are you saying that if I have a 24V battery bank - that I can hook up two 12V chargers and it will charge at 24V? Is that because technically by hooking chargers to batteries in parallel that I'm adding the voltage?

    Sorry for all the silly questions - I am a newb! ;)


    Right. or you may get a lot of smoke. We have no way to tell what you will buy, how it is made, and where the grounds in your system are. And sometimes the best stuff is wired such that you could not do this without letting all the internal smoke out. :cry:
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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