The "perfect" 2500W system--Suggestions?

System
System Posts: 2,511 admin
in Solar Beginners Corner #1
Hi to all! I am a newbie, here, so please bear with me. I want to set up an off-grid, one room, emergency use system. At times, I may want to use this system for weeks at a time. I am in Austin, Texas, and sunlight is in great supply, here. I have a great southern-facing roof side and no trees in the way during the complete solar transit.

My room will have a portable AC/Heater, mini-fridge, notebook computer, portable TV which I'll run AC (can do DC, but don't want to, at this time), a lamp and fan. That's it. I have calculated that 2500W will do it for me. I have a 5000W generator that I will want to tie into the system if the batteries are low and the sun is not out.

So, what is the best way to go, starting from solar panels and taking me to two dedicated outlets in the wall, terminating my system? Wire runs should not be longer than 60' from roof panels to batteries, 15' from inverter to my inside outlets (with a breaker box in between). Be as specific as you want to be. Including wire gauges would be helpful. I think I will house the batteries, controller and inverter in a modular plastic shed which will be bolted to a slab.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: The "perfect" 2500W system--Suggestions?

    Hello and welcome to the forum!

    I think you need to start by re-defining the terms. 2500 Watts. Is that a maximum load of 2500 Watts at one time, or is it 2500 Watt hours per day? There's a big difference.

    Also, a portable AC/heater & a refrigerator each have big start-up surges. These are difficult to measure, but will shut-down a too-small inverter instantly. They would also both "prefer" pure sine wave rather than the much cheaper modified square wave inverters.

    Once you get a precise fix on your maximum load at any one time (size of inverter) and your total Watt hours per day (size of battery bank) you can determine how much PV you'll need to recharge those batteries properly and what size/kind of charge controller best suits the application.

    If you were thinking about a 2500 Watt inverter (by whatever calculation) you should know that is a bit large for a 12 VDC system. You'd be better off with 24 Volt nominal for that size. It's kind of "just over the threshold" so if your actual maximum loads are closer to 1 kW you could stay with 12 Volts.

    Once you get the basic equipment figured out, then is the time to calculate wire sizes. :D
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: Newbie looking for help!
    mike90045 wrote: »
    (snip)

    Welcome to the solar club, where you can get 6 different answers from 4 different people.

    I am finding that to be painfully true, in here, from reading so many threads. It actually seems that many are just blowing a bunch of hot air, full of techni-speak and half-baked math formulas.

    I am going to bail, for a while, and see what I can learn from books on the subject. I will also subscribe to some e-zines. When I come back, I aim to be able to answer the question: "What do I need to set up a system delivering X amount of volts at x amount of amps to give x amount of watts?" in a clear, concise way that ANYONE CAN UNDERSTAND. Right now, in reading responses to fairly simple questions along that aforementioned line, I read a bunch of garble. In truth, I have my suspicions that many in here are solar installers who don't actually want to make it all that easy for those getting started to get a firm grasp on the subject at hand.

    Take care, folks! Don't worry, I won't let the door hit me in the @##!
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  • KeithWHare
    KeithWHare Solar Expert Posts: 140 ✭✭✭
    #4
    Re: Newbie looking for help!
    sr guy wrote: »
    ...
    I am going to bail, for a while, and see what I can learn from books on the subject. I will also subscribe to some e-zines. When I come back, I aim to be able to answer the question: "What do I need to set up a system delivering X amount of volts at x amount of amps to give x amount of watts?" in a clear, concise way that ANYONE CAN UNDERSTAND. Right now, in reading responses to fairly simple questions along that aforementioned line, I read a bunch of garble. In truth, I have my suspicions that many in here are solar installers who don't actually want to make it all that easy for those getting started to get a firm grasp on the subject at hand.
    ...

    Good luck with figuring out how to explain it all simply. The problem is that there are a lot of variables, some unknowns, and even some unknowables.

    I recommend "Photovoltaics: Design and Installation Manual" from Solar Energy International. This does a pretty decent job of explaining everything except for battery banks.

    Keith
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #5
    Re: Newbie looking for help!
    sr guy wrote: »
    I am finding that to be painfully true, in here, from reading so many threads. It actually seems that many are just blowing a bunch of hot air, full of techni-speak and half-baked math formulas.

    I am going to bail, for a while, and see what I can learn from books on the subject. I will also subscribe to some e-zines. When I come back, I aim to be able to answer the question: "What do I need to set up a system delivering X amount of volts at x amount of amps to give x amount of watts?" in a clear, concise way that ANYONE CAN UNDERSTAND. Right now, in reading responses to fairly simple questions along that aforementioned line, I read a bunch of garble. In truth, I have my suspicions that many in here are solar installers who don't actually want to make it all that easy for those getting started to get a firm grasp on the subject at hand.

    Take care, folks! Don't worry, I won't let the door hit me in the @##!


    First - What you will find, is that the formulas in the books are the same formulas that you see here. And everywhere else. Basic electrical math doesn't change.

    Second - You won't be able to answer that question at all, much less in a clear concise way - because the question is wrong. Watts, volts and amps are all tied together. Change one, it changes the others. This will make sense to you once you start to understand the formulas. By then you'll have a completely different question.

    Third - NO ONE here is trying to keep anyone in the dark. There is no conspiracy of installers trying to discourage you from doing it yourself. Most of the people here do it themselves. All the work that people around here put into giving detailed answers, what you call garble, is exactly the opposite - it's to explain everything so you can understand completely.


    You have to do the homework. You can do it from books that you pay for, or you can do it here for free. But either way - you still have to do it. If you don't have the patience to read what they are saying, or if you don't have the attention span to absorb more than a sound bite - then you probably shouldn't play with electricity.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #6
    Re: Newbie looking for help!

    Sr Guy, what "dwh" says is very true. And while someone not familiar with things electrical may find some of the answers rather confusing, or indeed unintelligible, and some answers unfortunately come across as somewhat terse, or talking over your head, they were indeed all aimed at giving help and support, not wanting to see you go down a wrong path and thus conclude that solar doesn't work. And, like was said earlier re all the different answers, there are some I personally take issue with because of my personal experience, however they were definitely not pointing you in a wrong direction, or trying to confuse you. And while we are all human and thus prone to mistakes, there has got to be over 200 years combined experience on this form you can freely tap into.
    I hope you at least continue to read posts on this form, and that in doing so, you will gain a greater understanding of the subject.
    Peace
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  • rafaelito
    rafaelito Registered Users Posts: 7 ✭
    #7
    Re: Newbie looking for help!

    Social skills are no different than solar skills... They can be learned. Sometimes the learned tone of this forum in response to the most basic questions, is tinged with sarcasm or simply comes off as condescending.

    Is this a great place to lurk and learn? Absolutely! But I am a 20 year refrigeration journeyman and I feel intimidated posting here.

    Welcome to this forum all who lurk and learn! You are in the right place even if you never post. But if you leave discouraged that is sad, because I cannot think of any of the "old-timers" here who do not sincerely wish, not only to answer questions, but to assist safe, efficient and affordable installations.

    Many of these folks are qualified engineers with collective decades of design experience. Most, including myself, have learned the hard way.

    I want to wish everyone happiness this holiday season and will post more frequently.

    These forums exist for the new comer. Your installation may very well benefit from toughing it out right here! We would certainly benefit! The input of 4 opinions, while diverse, will expand your horizons. The answers are not all black and white, but an engineered solution for free is a great outcome!

    Kind regards.
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  • Polychrest
    Polychrest Registered Users Posts: 17 ✭✭
    #8
    Re: Newbie looking for help!

    Sr Guy: Decoding a poster's "tone" in a web forum is a mug's game. Most experts in technical fields are better at solving problems than explaining them in neutral, clear, nuanced prose. This forum, from my experience, is one of the friendliest, most helpful ones you'll find on this here interweb thingy. Amateur DIYers like me are lucky to have access to the wealth of expertise and free advice shared here--particularly in a field where screwing up can get you fried.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #9
    Re: Newbie looking for help!

    I've been trying to 3 years, to build a spreadsheet, that a beginner can pick up and use to caculate for his area/climate : how much sun to expect, days of battery backup needed, size of battery, size of solar, how high the sun is, can neighbors trees be trimmed.
    but it all ends up being outside what I can put into a spreadsheet, and so each install need 80% hand caculations. Some plan for 1% loss, some accept 4% loss, another rejects 3 days of cloud, and runs a genset for 2.
    I was trying in a fun way, to prepare you for a wide range of responses. I don't think anyone here is trying to make it hard for you, and while there are a couple installers here, it's likely none are in your area, so nothing to gain.
    Solar is way more expensive then the media and ebay have lead most folks to belive.

    Mike
    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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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #10
    Re: Newbie looking for help!

    With all due respect to the Sir Guy and indeed those of us here responding. The bottom line is, you are asking what on their face seem simple questions, but once one delves into the gist, you realize that they are indeed very complicated questions. It would not be unlike asking "I've got 5000 widgets to get from California to NY, what's the best way to do it?" To given any reasonable answer one would need to know the size/weight/how fast etc. and indeed could come up a number of "reasonable answers".

    As to the posters here, there is no reason to be intimidated by anyone. If you don't understand an answer, or the terms used, ask for clarification. People here are more than willing to spend great amounts of time tutoring those that request it, and seldom in a patronizing way.

    That said, this is a somewhat technical field, and some here are more technical, and (perhaps a bit less real world practical) than others, but the bottom line is there is a core of very smart people who have forgotten more about RE/PV/Battery/EE than most of us will know. Many are EEs, some are commercial installers, some are serious hobbiests, and others are just trying to live off the grid in some more civilized form.

    If you are serious about PV, you will find (on balance) the best, most unbiased advice and information available any where! No one is interested in selling anyone anything, including our site host. If you find yourself put off by tone of some posters, don't take it personally, and when it doubt ask for clarification. In the rare even when one of us steps over the line, the community is quick to put them in their place.

    Good luck. Understand that these are all real answers from real world experience . Just because one doesn't like the answer(s) doesn't mean those answers are wrong.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,622 admin
    #11
    Re: The "perfect" 2500W system--Suggestions?

    Sr Guy,

    I have moved your 2nd post and the commentary to your own thread.

    Perhaps the point you are missing is that we need to know how long you will need your 2,500 watts of power...

    Assuming your fridge uses 500 Watt*Hours per day (4 hours per day at 125 watts), your laptop 500 WH per day (10 hours per day at 50 watts), your heater 2 hours per day at 1,500 Watts or 3,000 WH per day, and 50 watts of lighting 10 hours per day for 500 WH per day... Total of 4,500 Watt*Hours per day

    Using PV Watts , 0.52 off grid derating (solar panel to AC inverter losses) for Austin Texas--Starting with 1 kW of solar panels (round number):
    "Station Identification"
    "City:","Austin"
    "State:","Texas"
    "Lat (deg N):", 30.30
    "Long (deg W):", 97.70
    "Elev (m): ", 189
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 30.3"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 9.7 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 4.32, 65, 6.30
    2, 4.96, 67, 6.50
    3, 5.47, 81, 7.86
    4, 5.52, 77, 7.47
    5, 5.54, 78, 7.57
    6, 5.93, 79, 7.66
    7, 6.21, 85, 8.25
    8, 6.22, 85, 8.25
    9, 5.77, 78, 7.57
    10, 5.65, 80, 7.76
    11, 4.60, 65, 6.30
    12, 3.96, 59, 5.72
    "Year", 5.35, 900, 87.30
    Say you want to run the system 9 months of the year (use grid or generator for 3 months of the year during bad weather). That would make February as the minimum solar month to support:
    • 4.5 kWH per day * 30 days per month = 135 kWH per month
    • 135 kWH per month / 67 kWH per February per 1kW of panels = 2.0 kW = 2,000 Watts of solar panels
    For an off-grid system, we normally recommend 3 days of no sun battery backup and 50% maximum battery discharge for long life. The size of battery for a 24 volt battery bank:
    • 4,500 WH per day * 1/24 volt battery * 1/0.85 inverter eff * 3 days no sun * 1/0.50 max discharge = 1,324 Amp*Hour @ 24 volt battery bank
    The minimum battery system would be 1 day of no sun:
    • 4,500 WH per day * 1/24 volt battery * 1/0.85 inverter eff * 1 day no sun * 1/0.50 max discharge = 441 Amp*Hour @ 24 volt battery bank
    That small of battery bank should really be limited to a maximum continuous load of around C/8 (for long life and efficiency of battery):
    • 441 AH * 1/8 discharge rate * 24 volts * 0.85 inverter efficiency = 1556 watts of AC load (just your heater on high).
    Anyway, that was what the original question was about--We need to know your loads and time they operate to size the rest of the system...

    Otherwise, I am just going to take a SWAG and give you numbers that may, or may not, meet your needs/expectations.

    And, as a suggestion, in general, Off-Grid solar PV electric power will cost you around $1-$2+ Per kWHour (total equipment cost, replacing battery ever 3-8 years, etc.)... Running an electric heater is generally a very expensive way to go (around $3-$6 per day for 2 hours of use per day using my above example).

    -Bill "Moderator" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #12
    Re: The "perfect" 2500W system--Suggestions?

    Checking in. Thanks for the input. I was getting very frustrated when I last posted, and I know that came through. My apologies if I offended anyone.

    I am working on my calculations and will check back in when I have more to post.
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