Why cant i ?

moonbowmoonbow Registered Users Posts: 9 ✭✭
I live in Southern Colorado. Curious for your thoughts. I'm beginning to set up a small solar system for my off-grid cabin. Its my 500 sf dream home. My question is; If I only use a small amount of power from my batteries because my load isn't big (ceiling fan, laptop, small stereo, couple of small light) and my system to-be will only be used on weekends.Why can't I use traditional 12volt car batteries. My panel will be 180 Watt, a morningstar or rogue mppt CC, a morningstar sursine300 inverter(run into my AC breaker box). Seems deep cycle batteries are useful if your drainig your system regularly. With the tons of sun and the limited use I figure I can most likely keep the battery bank topped off most of the time. Am I fooling myself? (I'm thick skinned... gimme the truth) Thanks
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Comments

  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Why cant i ?

    Welcome to the forum

    My first reply got eaten, so here is another.

    I suggest that you consider reading the following links to better understand different battery types:

    http://www.batteryfaq.org/

    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

    tony
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Why cant i ?

    Second thing to consider. All solar calcs begin with the loads. The loads you define are not really small.

    For example, lets have a look for example:

    50 watt stereo 6 hours/day= 300wh
    3 15 watt cfl bulbs 6 hours= 270 wh
    Paddle fan 50 watt 24 hours= 1200 wh

    Just those three loads equals ~ 1770 wh/day.

    You 180 watts of panel might likely put out something like this, net/net though the inverter accounting for all system losses

    180/2=90*4=360 wh. (The four is the average number of hours of good sun one might expect on an ongoing average over the course of the year)

    So you can easily see that you are going to start out way in the hole.


    Deep cycle batteries don't like to be drawn down more than ~ 50%, and then they need to be fully recharged to 100% within a couple of days if you expect them to last. Ideally one would shoot for a daily discharge limit of ~ 20%, that leaves enough room for a day or two without sun.

    So to deliver ~1770 WH/Day ( Let's round that to 1.8 kwh/d) you would need a battery big enough to deliver a total of ~ 9 kwh. Translated to 12vdc amp/hours that would be a battery in the 750 AH range, or about 6 T-105 golf cart batteries. That 750 ah of battery would need to be charge at a minimum of ~ 35 amps, up to a high of ~ 80 amps. To deliver 35 amps one would need in the neighborhood of ~ 550 watts of PV.

    So plug in your own load numbers and you can begin to build your system around your loads, making the peg square as well as the hole, rather than doing it in reverse.

    As an FYI, we live off grid with 400 watts of PV, into 450 ah of battery. Daily we average between 600-800 wh. This system is almost perfectly balanced with the 4 hour rule. On a perfect day we can generate ~ 1.5 kwh, but on average, we keep pace quite well with the 6-800 wh use. We run lights, water pump, paddle fans, radio, phone, sat modem, lap top charging etc. What we do as well is load shift such that we try to only run the sat modem and charge lap tops when the sun is out, and pump water then as well, thus effectively reducing the total WH/D load. (Time shifting of loads) It is important to realize that for every 100 wh you take out of a battery, it requires ~ 120 wh to recover those whs, a 20% hit right out of the gate. Add in other loses and it becomes significant.



    Tony
  • moonbowmoonbow Registered Users Posts: 9 ✭✭
    Re: Why cant i ?

    Thank you for the resources. They are a wealth of info. Seems that I need to use my loads selectively, meaning use the fan when the temps are hottest/ coolest to circulate warm/cool air as needed. The morning star suresine 300 is rated for 300 watts continuous use. If I stay within that limit and use my loads with moderation I feel that I could come in way under the 1700wh. I understand what your saying and was not being realistic as to how quickly loads can add up. Commonsense thing to do is to get more watts into the system and meet myself in the middle with less load.I will look into the deep cycle batteries more indepthly. Can you direct me to a good source for the cables I'll be buying?
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Why cant i ?

    Our site host:

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

    PS, none of us here have any association with them, but most of us have traded with them over the years.

    Remember the other two rules of off grid solar,, the first is, loads always grow with time, so plan accordingly. Second, most people over estimate the amount of power they can actually harvest, while at the same time, they underestimate their loads. (The third lesson is that most newbies kill a set of batteries as they begin to learn how to use them, so consider buying a cheaper set before investing in large, exotic battery system. T-105 golf cart batteries are a good value, especially for beginers.

    Tony
  • PhilSPhilS Solar Expert Posts: 370 ✭✭✭
    Re: Why cant i ?
    icarus wrote: »
    My first reply got eaten, so here is another.
    tony

    Sorry Tony, my computer had a case of the "muchies" and your post was easy pickin's!

    Have a great weekend, everyone!

    Phil
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Why cant i ?

    180watts PV? Round figures from my experience, averages perhaps 120watts X 4 hours = 480 watt hours per day.
    Like others have said over and over again down through the years, the first law of off grid solar, is Conserve, Conserve, Conserve. But if you can't do that, Honda makes a nice little 1000 watt generator, 1/4 load, about 2 liters fuel per 8 hours. http://www.hondapowerequipment.com/products/modeldetail.aspx?page=modeldetail&section=P2GG&modelname=EU1000i&modelid=EU1000IKN
    My cousin recently got one for his solar powered off grid camp deep in the forest, to supply his wife's excessive consumption habits which could not be broken. They are both VERY happy with it. He also added a battery charger, so the batteries get some charge while the generator is running.
    Food for thought.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Why cant i ?

    I think that 480 wh in 4 hours out of 180 watts is pretty optimistic net/net.


    I second the idea of a honda Eu 1000!
    t
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Why cant i ?
    icarus wrote: »
    I think that 480 wh in 4 hours out of 180 watts is pretty optimistic net/net.
    I second the idea of a honda Eu 1000!

    You're right about the 480 wh being overly optimistic. Guess I was trying to let him down easy. The idle power consumption of the SureSine300 alone is roughly 6 watts X 24 hours = 144 watt hours. I have two, one of which is on 24/7 and is supplying the power to send this message. The other is dedicated to doing a job which most would consider impossible for such an inverter, but it's been faithfully dong it for almost 3 years now, and to avoid being called a liar, I haven't revealed it's duties.
    If the gentleman still wishes to go completely solar, which most certainly can be done, he must do a major re-think of the whole project, building on the experience of those who've already traveled that road. Otherwise, failure, disappointment, and financial loss await.
    I wish him total success and happiness.
  • Ralph DayRalph Day Solar Expert Posts: 952 ✭✭✭✭
    Re: Why cant i ?

    ''and to avoid being called a liar, I haven't revealed it's duties.''

    C'mon Wayne!! Curiosity is piqued! Give it up...what load/duty are you talking about? My guesses:

    Pool circulating pump?

    Air conditioner?

    Hair dryer (unless you're like me and facially enhanced)?

    Walk in freezer for restaurant?

    Hot tub? Yeah, that's gotta be it!

    I know I tried to run my freezer off a 12volt 1000 watt Xantrex msw inverter... it made squeeky ''no, please, not me'' sounds, so a 300 watt inverter...hmm.

    Ralph

    careful here ralph as what the other one is powering is irrelevant as he made his point without it. let's not get into a match here over something dumb. niel
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Why cant i ?

    Ralph, I'll send you a message re the second inverter.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Why cant i ?

    Oh, c'mon, let the rest of us in on it!
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Why cant i ?
    techntrek wrote: »
    Oh, c'mon, let the rest of us in on it!
    See the note added to the bottom of Ralph's message.
    The explanation I sent Ralph is rather long and detailed and I don't have a copy, so perhaps Ralph can forward it to you, then you'll know too ;)
    Peace.
  • Ralph DayRalph Day Solar Expert Posts: 952 ✭✭✭✭
    Re: Why cant i ?

    The detailed explanation of Wayne's use is indeed detailed and great. If anyone is really interested I can pm the pm I got from him to whomever...or post it here.

    It's not dumb, he's just shy about his abilities.

    Ralph
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Why cant i ?

    Would rather you PM'd it Ralph. And thank you for your kind words. :blush:
  • Ralph DayRalph Day Solar Expert Posts: 952 ✭✭✭✭
    Re: Why cant i ?

    Gotcha Wayne. Will do if asked.

    Ralph
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Why cant i ?

    No clue why Niel felt the need to add that note, all good natured discussion here.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • PhotowhitPhotowhit Solar Expert Posts: 5,655 ✭✭✭✭✭
    Re: Why cant i ?

    I've lived off grid with 180 watts of panels and a couple golf cart batteries, and a 300 watt inverter, it's not imposible, but If your starting with a 500 sf cabin, I'd allocate a bit more for the solar system, I think the tax credit applies to 2nd homes now(please check)

    I'd suggest dumping the ceiling fans in favor of 10" O2cool fans run 12-15 watts (from some what faulty memory) using an effiecient 10 watt stereo Check out the T amp's with an MP3 or CD player, and compact florescent lights a few hours of laptop time. would be doable on @200 watts of panels.

    If your good at budgeting your time, planning ahead, and the like... living on an electric 'budget' will likely be OK. I would rather have an additional 200 watts of panels than depend on a genny. But I have not had a catastrophic failure in my 8-9 years off grid. I have backup inverters, charge controllers,(largely from expansion) but not a backup system.

    4 years ago I decided I wanted to run and AC and have increased my system for this, I still have the 4 golf cart batteries I was using when I had a 220watt system(I broke a30 watt Noname and replaced it with a 60 watt solar world) As others have said the storage and life span of true deep cycle batteries will make a difference.
    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 backup...lol), 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.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Why cant i ?

    A paddle fan running on slow speed moves a lot of CFMs with only ~ 30-35 watts of draw. I would be hard pressed to assume that any other fan would move as much air as a paddle fan per wh.

    We use a good quality 12 vdc auto radio (Pioneer) wired into convention speakers. Draws only ~12 watts and sounds great. (and there are not inverter loses associated with running a conventional stereo).

    Tony
  • Peter_VPeter_V Solar Expert Posts: 226 ✭✭✭
    Re: Why cant i ?
    icarus wrote: »
    A paddle fan running on slow speed moves a lot of CFMs with only ~ 30-35 watts of draw. I would be hard pressed to assume that any other fan would move as much air as a paddle fan per wh.

    We use a good quality 12 vdc auto radio (Pioneer) wired into convention speakers. Draws only ~12 watts and sounds great. (and there are not inverter loses associated with running a conventional stereo).

    Tony

    Not sure which kind of paddle fans you folks are talking about.

    I bought a couple four speed 42" ceiling fans that run on 12V and draw 18-20 watts max. They are designed for RVs but would work perfectly for something like this.

    With careful selection of appliances, you could avoid using an inverter entirely.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Why cant i ?

    I also have a 12 vdc paddle fan. Even though it burns a few less watts, I don't personally like it as well as it make a odd little noise on slow speed. Moves lots of air though.

    T
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: Why cant i ?
    icarus wrote: »
    A paddle fan running on slow speed moves a lot of CFMs with only ~ 30-35 watts of draw.

    do you think they move more air than blower fans? in a small space, I'd prefer to have that directional, concentrated gust, but I don't know how much current those types of motors use.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Why cant i ?

    In general AC induction motors are quite inefficient when operated at reduced speed, compared to PM rotor 3 phase inverter controlled motors, or brushless DC motors. Most, especially the cheaper fans have cheap induction motors which can be fine in many cases, but when every watt counts - - - - not so much.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Why cant i ?
    moonbow wrote: »
    If I only use a small amount of power from my batteries because my load isn't big (ceiling fan, laptop, small stereo, couple of small light) and my system to-be will only be used on weekends.Why can't I use traditional 12volt car batteries.
    The short answer to your question is that car batteries are designed to deliver a lot of current for a short period of time, whereas batteries suitable for solar applications are designed to deliver less current over a longer period. Car batteries will wear out much sooner than deep cycle batteries in your application. You can do it and it will work for a little while, but you'll be replacing the batteries so often that the money you save in the short term will be far outstripped by the expense over the long term.
  • moonbowmoonbow Registered Users Posts: 9 ✭✭
    Re: Why cant i ?

    As always, these forums are a wealth of knowledge. I have spent the past few days doing some research on my "system" as I envision it. 180watt PV panel( to start) running into a blue-sky 2512i CC or the BZ 500 45 amp CC to my Battery bank (deepcycle... I've since learned, thanks for that), running into a Morningstar SS300 inverter (hardwired to my breaker box). I'm having trouble finding an inverter between 300 and 1000 watts that can be hardwired. Most seem to simply have GFCI plugs in that watt range. My cabin is wired and I don't care to run extension cords if I don't have to. Any ideas on a 600 watt hard wireable inverter? I would like to be able to leave room to grow but can't afford or justify going "big" right off the bat. This system would allow me to add a panel or two in the future. Contemplating the whole fan issue....seems there are a few routes to go. Stereo would really only be an ipod speaker system. Penny for your thoughts.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Why cant i ?

    First,,, research this forum on the opinion of BZ controllers! The consensus is that they are POS! I have one that I used on a bench test and it performed worse than no controller at all. The Bluesky is a reasonable controller, albeit dated technology. Consider the Rogue 3024 MPPT controller.

    Second, depending on your peak loads, you can wire two Shursine 300s, one to each leg of a split phase load center, providing two separate 300 watt legs. If you peak load never exceeds 300 watts for any one device that might be a perfect alternative.

    Going back to your original post by memory, I don't think that you have any individual loads that come close to 300 watts. If you do, you could wire one side of a split phase panel with a 300 watt inverter for your routine loads, and load the other side with a larger one for a given peak load, (like a pump) shutting it down when it sits idle. Be careful doing this and get some advice on the grounds and the neutrals. (The shuresine will be fine this way, mixing a different inverter, (especially a MSW inverter) might cause some problems. The dedicate the proper circuits in the load center to the proper inverter.

    Once again, define the loads, and then design the hardware around those loads.

    Just for the record, we live off grid with a single Shuresine 300 and it powers everything in the house. (No fridge however).

    A couple of other thoughts. Get a good 12vdc car radio, and wire it to conventional speakers. This will sound fine, get better reception than most component stereo recievers, and net/net use less power.

    Also, realize that the BS controller can only be wired with 12 vdc input/12vdc output, so much of the advantage of an MPPT controller is lost. With most other MPPT controllers, you can wire the panels for 24 vdc (or higher) reducing the line loss, and have the controller down convert to 12 vdc. If it were me, I would buy the Rogue over the Bluesky any day. If you are ever considering adding panels, get the bigger CC now. You can run as much as ~ 500 watts of panel through the Rogue into 12vdc.

    Tony
  • moonbowmoonbow Registered Users Posts: 9 ✭✭
    Re: Why cant i ?

    Looking into the Rogue MPPT 3024 CC. Thanks for the suggestion. Any opinion on the roof mounted solar attic fans with their own mini-panel? Could it actually be as advertised or is it a waste of money?
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Why cant i ?

    We have had a few threads here... I think that adding inlet and outlets as appropriate probably does as much or more vs a solar powered attic fan.

    Here is a Google Search of past threads.

    On an earlier attic fan thread here (actually post is here), I remember reading a post, where after several years, their attic fan failed and they did not even notice. Just adding the extra ventilation (from installing the solar powered attic fan) was enough to reduce their attic temperatures...

    DC attic fans have typically around 10-20 watts of solar panels. The typical AC attic fan is probably 10x or larger and will have much more effect than the typical 12 volt fan.

    That being said, one person here used an old electric radiator fan from a car and is quite happy how it works, moves a lot of air--Although, it is quite noisy.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DerikDerik Solar Expert Posts: 82 ✭✭✭✭
    Re: Why cant i ?

    I ran a small weekend cabin off of a 65 watt panel for 5 years. I ran two lights, a small LCD televison, and a sterio. My cabin was a bit smaller.. yes smaller than 500 square feet but the fact is that even with 500 square feet you will never need more than one light, and you will not be running the tv and the sterio at the same time. My Sterio used way less than the 50 watts stated here and my televison used 35 watts, lights 8. I also get or got way more than 4 hours of sunlight, that would be an average for winter which is only 2-3.

    The other thing is who runs their lights for 6 hours a day in Southern Colorado?

    In the winter you may run them from 5:00 pm until 10:00 pm or so but other than that unless you stay up until 2-3 a.m you will not run lights for 6 hours on an average.

    I have an attic fan that does nothing for my house but warm it when the attic is colder than the outside air.

    The other thing is that it's a weekend cabin so if you use all your power on Sat, and Sunday you have all week for the batteries to re charge so who cares.. if you use more than what you make for two days.
  • DerikDerik Solar Expert Posts: 82 ✭✭✭✭
    Re: Why cant i ?

    I left my first paragraph hanging. WInter is only 2-3 months so his average sunlight or harvest in S. Colorado will be more than the 4 hour average stated.

    I am guessing that S. Colorado is much more like what I experience here in CA than what my nothern solar brothers experience.
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