help me design my PV solar system.

Discussion in 'Off Grid Living' started by timtebow970, Feb 21, 2011.


  1. timtebow970

    timtebow970 Monkey+

    I am trying to build a system to augment my grid power for day to day living and to act as a backup system indefinitely if the grid goes down. Obviously in the backup mode it would be for "essentials" only. I consider the essentials to be as follows: A newer model (energy star) freezer, a newer model (energy star) fridge, some small lighting and the blower for my furnace. As far as the blower goes, we are planning on switching to a 97% efficient furnace with a DC blower for our main (propane) heater before next winter. We also have a wood fired central furnace the has a blower and is piped into the HVAC. I am working on getting that up and running. I am not sure what the blower motor is on that, but I could easily install a DC on there as well I imagine. In back up mode we could lower the temp inside to reduce the load from the blower. As it is we only keep it at 60 in the winter. I have a number of questions, and I am sure there are things I should know that I won't even think about so feel free to chip in with any info you can. As for my questions here are the big ones.

    Solar panels: How do you figure out how many you need? I understand I can consult my electric bill or a kill-a-watt meter and figure out how much I am using and compare that to the ratings of the panels. But I assume those ratings are peak power and I am sure the sunshine is variable. So how do you figure the real life variables?
    -also, do they all have to have the same rating to be in a system together? My imagination tells me no, that each panel will simply contribute it's share and they should all work together. ??
    -also can they be located in different locations and wired together at the box?

    Battery bank: How do you size the battery bank. Obviously if one of the things I want to power with this is the furnace blower, and it runs more at night than during the day, then I will need a considerable reserve.
    -also do they have to have the same rating to be in a system together? This seems to be more critical to me than the panels. I just can't seem to figure out why.
    -also what kind of batteries are best for this application? deep cell, marine, sealed, refillable, 12v, ???
    -also, what voltage do you use? all 12v batts in parallel for 12v system or sets of 4 12v in parallel for 48v system? etc

    to invert or not to invert: Seems silly if I have DC powered fans to invert to AC and then back to DC to run them. I also know there can be significant line voltage lost in DC wiring. I don't know where one overrules the other. Same question for DC lighting? I will have to invert some of it, since I have never seen (or at least don't own) a DC deep freeze. Can you run DC loads direct from the bank and run an inverter. Seems like these should both just be different loads on the bank.

    leaving room for expansion: I would like to get this size system up and running fairly soon and for as little money as possible. But I can see wanting to upgrade as funds permit. In what areas should I leave myself room to grow? Inverter, battery box ???

    Thanks in advance. I have been searching this forum and others to find some of these answers on my own but I appreciate whatever help you can offer. If some of these things are covered somewhere I would appreciate links as well.
     
  2. TEXAS REBEL

    TEXAS REBEL Monkey+

    I would like to have same info myself.
    I am planning on trying to do this myself in near future.
    So going to subscribe to this so can get some ideas myself.
     
  3. BTPost

    BTPost Old Fart Snow Monkey Moderator

    There is section in my Alaska Wilderness Building blog on these issues, as well as a section on Backup Power Generators, that you might be interested in reading. It is about a 15-20 minute Read. Some of the topics discussed will NOT apply, but many will.
    Alaska Wilderness Building - Survival Monkey Forums
     
  4. bobzilla

    bobzilla Monkey+

    Your location is critical

    Find out which zone you live in,PM me once you find out your amount of available solar energy.
    NREL: Dynamic Maps, GIS Data, and Analysis Tools - Solar Maps

    Next figure out your total wattage for all appliances
    Example:5ampsx120volts=600 watts
    10 amps x 240 volts=2400watts

    When you figure out available energy and how much you need,we can design a system.

    BOB
     
  5. timtebow970

    timtebow970 Monkey+

    Excellent article. You must read faster than I do. Can you be more specific as to what type of L16 batteries you are using. I googled them and came up with a very wide range of prices and amp hours.
    I am still a little confused as to how/why you decided to go to 24vDC battery bank if you are running 12vDC motors. Are you using an inverter to reduce it to 12vDC to run those loads? If so why not just use a 12vDC bank and skip the inverter. I understand that increasing the voltage in AC, lowers the current and therefor reduces the I2R losses. Is this the same reasoning for DC?
    Also, if a higher DC voltage is desired, why start with 6V batteries? Is their a correlation between votage and amp hours or is it a cost issue?
     
  6. timtebow970

    timtebow970 Monkey+

    Thank you for the offer! I see that you are also new here. Are you a contractor? Can you tell me about your experience in this area please?
     
  7. timtebow970

    timtebow970 Monkey+

    how to compare batteries

    Thought of another question. As I understand it, when comparison shopping solar panels, it is best to compare $/Watt. 1st is this correct. 2nd how do you compare batteries? Is it $/Ah? [dunno]
     
  8. TnAndy

    TnAndy Senior Member Founding Member

    Listen Tim,

    IF you're serious about putting in an entire PV system, it's really unfair to expect to be guided thru every possible question from Step 1, on a forum like this.

    Can you ask specific questions ? sure.....and get some good answers.

    But the first thing you need to do is self educate.

    Spend 35 bucks on a good manual, like: THIS
    (It will be the BEST 35 bucks you'll ever spend)

    and after you get a grasp on the basics, come back with specific questions that you have. Otherwise, this thread will develop into pages and pages of rambling, none of which will give you clear direction.

    bobzilla gave you the starting point....figure out what you need in the way of power....until you DO THAT, forget batteries, inverters, comparing panels, anything else.....that is ALL entertaining, but irrelevant. You don't begin a journey from the east coast to the west coast asking about the weather in Flagstaff, AZ....you begin by checking the fuel gauge in the car sitting in your driveway.

    SO: to repeat BOB's post......GO FIGURE OUT WHAT YOU NEED IN THE WAY OF POWER, and quit thinking about how to get it.

    Don't take this wrong.....I understand your enthusiasm, and desire to jump in.....but you have ( I can tell from your questions ) a HUGE learning curve here....take it one step at a time, or you'll simply become overwhelmed with tons of info that will never congeal into an operating system....or at least not one that could be a good as it could have been.
     
  9. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    At the risk of mis-statement that Bruce or BOB will correct, $/w or $/Ah is one way to start. You also need to factor in the number of cycles of charge that the batteries might be expected to sustain. That will influence your life cycle costs for the system, including maintenance and replacements.

    I suspect (but do NOT know) that the wide range of prices is more closely associated with the Ah and cycling.

    The decision on bank voltage is based more on the cost of wire (and physical size of the loads) than much else. Higher voltage is almost always better, because the I^2R losses are minimized. To a degree, battery voltage is a choice, too, it's a matter of how the cells are grouped internally to the battery case. For example, your car battery is 12V, consisting of 6 cells, each of which are nominally 2 volts. (Yes, I know that is imprecise, but for the sake of illustration, it's close enough.) Going to industrial fork lifts, the same 2V cells are grouped to provide 48 volts in some applications.

    Forgive me for this, but I'm suspicious that there are some functional facts missing from your thinking. So, and these two items are pretty important to understand:
    Inverters are electrical gadgets that make AC out of DC. They don't work both ways. (AC to DC would use a rectifier. If you are charging from commercial power, the charge controller will have the necessary innards to do it. As does, by the way, your car's alternator making DC for the battery.)
    Controllers govern the battery charging, whether fed from solar panels wind turbines, or the gennie that you don't yet have.

    So far as running 12V loads from a 24V system, it is a matter of how the loads are segregated at the power panel. Remember that the 12 volt loads will require heavier (and more expensive) wire. Another way to get 12V from 24V is to put a dropping resistor in series with the load, not usually a good idea; they are power eaters that waste the extra voltage as heat. (Slightly oversimplified, but the waste part is true.)

    One last statement of the obvious: When it comes to solar panels, you get what you pay for; there are some, ah, "inexpensive" panels on the market that have the useful life of a gnat. TnAndy knows some s**t about panels, you might read some of his comments along with Bruce's and BOB's.

    Heh. Just noticed Andy's post. He's right.
     
  10. timtebow970

    timtebow970 Monkey+

    Thank you for your input, and I appreciate the book suggestion. Please allow me to clarify what it is I am trying to accomplish as I believe there has been a bit of a misunderstanding (fueled I'm sure by the title of this thread). I am attempting to self educate. However the only way to self educate short of hooking stuff up and seeing how it works, is to read what others have written and ask of those that know. If you don't know where to look (I don't) it is very difficult to find any viable information on solar energy. I started by contacting contractors and having them evaluate my energy needs and suggest systems to me. Turns out all of the contractors I can find are simply installers that have little knowledge on how a solar system operates. They are simply trying to capitalize on an increased market for green energy. While they are no doubt very knowledgeable on how to install it, they are much less knowledgeable on how to design it and what to expect for output. They seemed only to be interested in selling me on systems based on what even I could tell were outlandish claims of self sustainability. Not discuss system requirements and capabilities. So I turned to the internet for information. The bulk of information I can find on the internet is geared to what type of components people (most of them with the same level of knowledge of myself and some with less) had installed. Very little on what type of returns they were getting and by far the prevailing answer to the question why did you choose this or that was because that is what they were told to buy. And many of these people were disappointed by the performance of their systems. All of this to say I am having a hard time finding the information I need.

    I apologize if it sounded like I wanted you to tell me how many of what panels to go buy and then I was gonna come back and ask where to put them and then how to wire them in and on and on. In reality I am trying to find out how many of what type of panel I would need and how many of what type of battery I would need and what other components I would need. The reason I am trying to figure out this information isn't so I can go out to buy it tomorrow and try to install it. It is to figure out if this type of system is even a financially viable for us. In your road trip analogy, I am trying to figure out the mileage to sunny San Diego and what I would benefit by being there. With this information I can determine if the trip is even worth considering, let alone funding. I agree that I have a huge learning curve and that I need to take it one step at a time. I think we disagree on what step it is that I am on. I am not trying to build my system based on this thread. Simply trying to figure out what kind of system I am looking at and how much that may cost. I don't understand how to figure out what my power requirements will be. I can figure out how much my fridge uses while it is running, but how do I turn that into a daily, monthly and yearly average? How do I figure out how much energy I will need for components I don't own yet? How do I go about determining what size of system I need and how much that will cost me. If the answers to these questions are in the book you suggested then thank you again for that. Please don't think I am one who expects an internet forum to solve all the problems for them. I am merely looking for my starting point. Even if you told me exactly what I needed and what to buy, I would do my own research into why you would recommend those parts.
    Sorry for all the rambling but I guess your response hit me the wrong way.
     
  11. timtebow970

    timtebow970 Monkey+

    No need for forgiveness, that is the point of this post. To figure out what pieces are missing in my head. The inverter vs rectifier thing has always gotten me. It seems so clear until you read things like this on a solar company's website "Also we may want to use generator AC or grid AC if we are connected to the grid. Sometimes we take this AC and store it in the batteries so this is another conversion, this time from AC to DC. Usually this is done with an inverter operating in reverse as an AC charger or it can be done with a separate charger. This is why some inverters are actually correctly called "inverter/chargers." I'm not sure if inverters can and do actually operate in reverse or if this is oversimplification at it's worst. I spent 6 years in the navy generating electrical power and propulsion. However I was on the mechanical side and only got "cross-trained" on the electrical stuff. Also we dealt primarily in ungrounded 3phase AC and DC. The only way we switched between the 2 was with a motor-generator that was basically an AC motor/generator and a DC motor/generator coupled together. Both heads could be operated as the motor or the generator depending on which side was supplied with power. So while I do have some background in electricity it doesn't relate all that well to the topic at hand and while a lot of the words are there, the concepts may have been tweaked with the passing of time and oversimplification.
     
  12. TnAndy

    TnAndy Senior Member Founding Member

    And see.....I said "don't take this the wrong way" :D

    OK..I have a self installed system. I stumbled and fumbled and screwed around, JUST LIKE YOU ARE, trying to figure things out.

    But I DID start with a premise......that I wanted to replace 1/3 of my kilowatt hour use per month, and at that time, we were using about 900kw/hrs/mo, and had been for 30 years. We've since reduced that to about 700/mo.

    What I wanted was a system that would provide the basics of electrical power, assuming the grid died ( Lights Out situation ). What was important to ME was:

    Refrigeration. My fridge ( which we replaced with a model that uses 550kw/hr/yr versus the old 1200/yr model ), at least one freezer ( we have 2 mid sized uprights and a small chest ), some lights, and occasional use of the clothes washer. I figured THAT was the difference in living in the 20th century and all those previous ones.

    SO, what I did was use a Kil-a-watt meter, and measured my appliances use.. (THAT is how you measure, over time, what your appliance uses....get the 2nd Gen version with the battery to hold the readings when you unplug it....lot handier )..then I calculated lighting ( based on bulb watts and approximate time used ), and I came up with 250kw/hrs/month would do us just fine.

    THIS is where you are. You need to know WHAT you need ( or want ) to replace. IF you don't know that now, you simply CAN'T get a price on a system...you are simply doing what those installers are doing.....pulling numbers out of the air that may or may not work.

    ONCE YOU HAVE A KILOWATT HOUR PER MONTH ( or day or week or year....you pick ) FIGURE, you can proceed.

    Get that.
     
  13. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    Tim, we are not here to belittle your lack of knowledge. The quality of your questions shows your level of understanding of the problem, and that is fixable. Get the book Andy recommends, then ask for clarification of anything that's obscure.

    I sympathize greatly with your experience with contractors, but giving them their due, they are builders, not designers and have an axe to grind. The experts in the field of solar and wind are the designers, and ALL of them work for people that want to sell something. The only alternatives are to hire your own designer, or DIY. Alternative energy designers that are worth a poop are going to get a couple hundred bux an hour, and there's little point in spending the money for them to gather data that you can get.

    First step after getting the book is to go 'round the house and sum up all the wattages of all the things you want to run off your system. Don't account for the fact that not all of them will run simultaneously, that comes later, and also ignore that AC wattage is not directly convertible to DC wattage. Do this nameplate reading while waiting on the book; no matter what, that is the first thing you need to know.

    BTW, I was a nuc MM (3355/3356) on a fast attack (and "surgeon's assistant" on the boat) after a stint as instructor at the prototype, so I know what training you had. Fuggedaboudit, there isn't a lot other than the math and really basic theory that you can use for solar.
     
  14. BTPost

    BTPost Old Fart Snow Monkey Moderator

    The L16 type Batteries are fairly generic, in that Trojan built the original design, but it has been copied by just about every Battery OEM on the planet. I get mine from Interstate Battery, as they ship to Alaska every week. The smaller version is called a T-105, and is generically called a "Golf Cart Battery". These are BOTH 6 Vdc Batteries, and you string them together in Series, to increase voltage, and parallel to increase AMPHours. These are what 75% of the Solar-Inverter/Charger systems are using to build their Battery Banks. For those folks that need BIGGER Batteries, (more capacity) they move up to Traction Battery Systems. These are commonly found in industry, running electric Forklifts, and PalletJacks. These are made up of individual 2 Vdc Cells, and you just stack up as many as required, to get to the DC Buss Voltage that you need.

    As for 12 Vdc from a 24 Vdc Battery System, what I did, was to take a 24/12 Vdc 25 Amp Switching Power Supply, that draws power from the Main Battery Bank, and then charges a small 12 Vdc Group 27 Battery, to supply any 12 Vdc loads that I might have. The Power Supply is set to float the 12 Vdc Battery and Buss at 13.4 Vdc. This keeps the 12 Vdc Battery topped off, while only drawing enough power from the 24 Vdc Batteries to do so. These Power Supplies are very common in the Marine Electronics Industry, from which I have extensive experience. As I explained in the blog, most off-Griders will have 120 Vac Inverter/Chargers, and only use 12 Vdc as a backup system. Like one light and outlet in each room, while everything else is running of the Main DC Battery Bank, and Buss, thru the Inverter/Charger.
     
  15. TnAndy

    TnAndy Senior Member Founding Member

    Buy and apply:

    Kil-a-wat 4460


    [​IMG]

    About 25 bucks.
     
  16. timtebow970

    timtebow970 Monkey+

    Sometimes it is as effective as telling someone not to worry about it.[fnny]

    I checked out a kill-a-watt from the library a while back, then we bought a new freezer! I suppose I'll just go buy one, but...

    Is there anyway to account for things you don't own? We are planning replacing our furnace soon with one with a DC blower motor. Just request motor plate info from manufacturer?

    No kidding. I guess we really are everywhere. I learned how limited the application was when I started remodeling houses. Will do as you say. I'm not worried about being belittled about my lack of knowledge, I know it's lacking. I just don't want to get blown off as a leach thats too lazy to do their own leg work. So far my research has been misguided and ineffective. So I appreciate everyone's responses.
     
  17. TnAndy

    TnAndy Senior Member Founding Member

    No, believe me, if I WANT to piss you off, I'm fully capable of it.....ahahaaaaaaa



    So, you should have some idea what things you already own DO use, right ?


    Well, first off, why are you going with a DC blower ? Do you plan to run it exclusively in the future off solar ?

    As to the power requirements, yes, you should be able to get a horsepower rating on it....like 1/3 or whatever. 745w per HP, figure the running watts. THEN you'll simply have to guesstimate the time it runs....how much does the current one run ? 4 hours in 24 ? 6 ? 8 ? ( and that is going to vary with temps outside/heat loss )...so pick some number....even if it's high...say it runs 8 hours out of 24.

    8 x the watts ( say it's a 1/2hp...375w ) = 3000watt/hrs, or 3kw hours per day (24hr).....or 90kw/hrs/mo ( at least in the coldest months....I assume that would taper off early fall and late winter.

    THAT is how you would do it.

    Now, keep going...add your fridge, your freezer, your lights, WHATEVER you think you would want your system to cover.....eventually, you'll arrive at some figure.

    THEN you can start to design a system to fit your needs.

    AND I'm not doing that.....I'm trying to GUIDE you thru the process. And it doesn't involve randomly jumping from one area/question to another AS THOUGHTS HIT YOU.....because what you will end up with is a jumbled up mess of info, WITHOUT a clear direction of how to proceed.

    I can already SEE the confusion beginning, and am simply trying to cut it out from the git-go. You can waste a whole lot of your time, and other folks energy with random questions.....or you can take this a step at a time, and come up with a good system.

    I've already got enough invested in this that I'd like to see that as the result....ahahahaaaaaaaaa
     
  18. timtebow970

    timtebow970 Monkey+

    I need to redo all my readings because based on what I saw on the kill-a-watt, we replaced most of what we had.

    As far as the DC blower goes, it is more efficient and keeps a more consistent temp in the house.
    from here

    Thanks for the good intended help. I will get back when I get some numbers figured out.
     
  19. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    There are VS drives available for AC motors, even single phase soft start to hold inrush current down. Dunno what the efficiencies are, but worth checking. I suspect that they throw voltage spikes back on the mains, might not be so good.
     
  20. Mountainman

    Mountainman Großes Mitglied Site Supporter+++

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