off grid cabin in the woods!!!

Hello folks _ I am new to this site and have so many questions. I have just been on a roller coaster ride of trying to set up a solar system on an off grid cabin in the woods of the coast of Northern CA.
We got one 187w panel that is 24v for a 24 volt system with four 6 volt golf cart batterys. we have a BZ500 charge controller and an Exeltech 1100 inverter. plus a Iota 27-25 battery charger with a Honda EU2000.
The problem is the panel is not charging the batteries- Even when there were really sunny days. i know we have limited sun due to the sun being low and dropping behind the trees at times, But the sun would be on the panel and all i would see on the BZ was .1 or .2 charge. This was obviously not working and it was not long before the Battery voltage was reading 23.9 volts and the float LED never lit- which meant the batteries were charged. So After hours on the phone with different folks I find out the panel we were sold was not enough voltage to charge a 24 volt system.
So we get a Trimetric meter which is not hooked up yet and an Iota charger and the generator.
Now the company who sold us the panel is saying we can swap the panel for a 36 volt 175 panel.
my questions are:
1. Should I get a 36 volt 175 w panel? or should I get two and run them in series? we get sun on our roof at different times due to tree shade. If one is getting light at one time and then the other will they negate each other if they are in series?
2. I am not so sold on the BZ500- is it worth getting an Outback system.
one installer I was talking to was suggesting an outback mppt charge controller and inverter.
3. when the Iota charger and generator are hooked up and charging the batteries is it okay to run the inverter? We just charged the batteries and it seemed to be okay.
If I go with the outback MPPT charge controller and with the varying sun on our roof am i better off getting one 48v panel with a lot of amp output than the two panels in series? Or finding a spot where bothe panels are in the sun at the same time?
thanks to anyone who can shed some light on this subject.
MM

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,408 admin
    Re: off grid cabin in the woods!!!

    I will try and take your post in a few bites...

    First, the BZ 500 solar charge controller was not the best choice... You can read a couple threads here about some of the issues:

    BZ MPPT250 and other controllers
    BZ Controller thread

    Your first issue is you should replace your Solar Charge controller with a different brand/model. Depending on what your other choices end up--there are several good choices out there for you.

    Next, you have a 187 watt 24 volt panel... Really need to know the exact specifications for the panel... What is the Vmp (Voltage maximum power) and Imp (Current Maximum power) for this panel (brand and model number may help us too). Basically, to properly charge your 24 volt battery bank, you will need a Vmp that is > ~32 volts (~30 volts minimum to equalize your batteries, and ~1-2 volts for voltage drop across the charge controller and wiring).

    Morning Star makes a very nice 15amp 12v/24v volt MPPT controller (~400 watt panel maximum for a 24 volt system). If you end up with larger panels (over ~400 watts), the Outback or Xantrex (or other brands/models) will be a better choice.


    Depending on the solar charger you purchase--it may change which solar panels you can use for your particular installation (and how you series/parallel wire them).

    The Iota charger and Honda eu2000i are pretty good brand choices--in and of themselves, these should be fine.

    Next, you have 4x 6 volt golf cart batteries. Assuming they are ~220 amp*hour rated (20 hour rate), we use a recommendation of ~5%-13% as the recommended maximum charge rate for proper battery charging...

    220AH * 5% = 11 amps minimum (for a 24 volt battery bank)
    220AH * 13% = 28.6 amps maximum (@ 24 volts)

    Watt-wise, that would be at maximum battery voltage of ~28.4-30 volts during charging:

    11a * 28.4 volts = 312 watts
    28.6a * 30v = 858 watts

    Assuming your charge controller is round 90-95% efficient--then you would want your solar panels to be:

    312 watts * 1/90% = 347 watts of solar panels (rough minimum)
    858 watts * 1/90% = 953 watts of solar panels (rough maximum)

    So, just to properly charge your battery bank, you would need ~312 to 858 watts worth of solar panels to properly equalize and mix the acid in your flooded cell batteries (at minimum current) and not overheat (or waste money) on the high current side (for typical batteries--as always, check the requirements for your specific batteries with the Mfg. data sheets).

    Now, the above has not assumed anything about the loads you are going to require for your solar system--this is just based on the size of the battery bank you are using.

    To calculate how much daily load you can get from your system, use this link to estimate your average kWatt*Hours of energy you can generate.

    Note that the above website will require the panel size in kWatts (1kW=1,000 watts) and 1 kW is the minimum you can enter. If your system is smaller, just enter 1.0 kW, and then multiple the answer by your system size (example 312 watts of panel, multiply by 0.312). Also, answer the rest of the question (tilt, tracking type), and use ~0.52 for your derating factor--these accounts for losses in your batteries and AC inverter too.

    For example, using the defaults and 0.52 derating factor for Arcata CA:

    We get around 50-80 kWhrs per month (1kW of panels) with what appears to be affects from coastal fog cutting down output. Using 312 watts of panels and 30 days per month:

    50kWH * 0.312 * 1/30 days * 1,000W/kW=520 watt*hours per day (fall/winter production)

    Or, you can run a 100 watt light bulb roughly 520WH/100W=5.2 hours per day during the fall/winter months from just your 312 watts of solar panels with fixed mount panels at 41 degrees from horizontal facing south. Also, if you don't know your loads (and how much power you need, both in Watts and Watt*Hours), get a kill-a-watt meter.

    Regarding running your loads/inverter while charging with the generator is fine (may take longer to charge). It might even be better, assuming you have enough power from the generator to run both the charger and your load (say washer or vacuum cleaner) to run the AC loads directly from the generator while charging (more efficient--don't waste power converting from 120 vac to 24 vdc back to 120 vac).

    Other recommendations... Get the Trimetric connected--will really help you understand the state of charge of your battery bank at all times. Another is to get a hydrometer and thermometer to check the battery state of charge (not often--after you get your system under control).

    And read the Deep Cycle Battery FAQ too.

    Anyway, the above is a start and should help you understand your system better.

    Good luck,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: off grid cabin in the woods!!!

    Bill has it dialed,,,,as usual.

    I would loose the BZ right now! Consider a Morningstar or Bluesky mppt, or even a cheap pwm controller for now, and spend some of the difference on more panels capacity.

    I fear that you may have already damaged the batteries by having them discharged for too long before bringing them up to full. (Most newbies crash a set or two before the get the hang of it!) Get them on the Honda and the Iota right now, and as Bill suggests, get the Trimetric up and running.

    Your system sounds a lot like mine. We live off grid with ~200 watts of panels and (currently) 4 t-105's)

    Good luck, read all you can, there are some very sharp people here.

    Tony
  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
    Re: off grid cabin in the woods!!!

    Good advice already posted here, I'll chime in a bit as I went through a pretty similar process in growing our own system:

    1) Regarding the recommended watts and such that Bill pointed out, you could get away with less, but you'll end up needing to run the generator more. This still could be a good option to start out with if it allows you to buy better components, don't know what your budget is like...

    2) Some one can correct me if I am mistaken, but I don't believe that the Iota chargers can really do an EQ or at least mine can't. Other than that I would agree that they are great little chargers. How high of a voltage did you recharge your batteries up to, you may want to give them an EQ charge if they've been severely undercharged for a bit.

    3) Regarding the Outback system, that's what we finally ended up doing piece by piece. That did mean getting a bit of an oversized Inverter for about 90% of our average loads (though it is nice to be able to run all of my power tools through the inverter now and then). With the VFX 3524 inverter we are able to do most of our EQ charging with the Generator, as the PV that we have is not quite enough most of the time (but is usually more than enough for our loads/demands). Having the MPPT charge controller (MX60) is great in terms of flexibility, we have even mix and matched our panels somewhat due to availability issues. I think Bill hinted at the key issue; for the most part Outback power system components and systems start to make a lot more sense with a bit bigger system, less so for a 1 or 2 panels set up.

    Good luck, enjoy the learning process.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: off grid cabin in the woods!!!

    A few other ideas, as I sit with my feet in the fire on a winter afternoon.

    A couple of things to remember for all those that are building small cabin type systems.

    First, your loads will ALWAYS be bigger than you estimate, and they will always grow with time. You start out using a few lights, then you add a radio, and a cd player, then a tv, satellite modem, water pump,,,, all the things we like, and since the energy is free there is a big temptation to use it.

    Second, it is way cheaper to build a nice little system if you leave the big loads to the generator. You are going to need a genny anyway, so why not use it to run the skill saw, or the table saw (and maybe the shop lights) when you need them rather than building a big solar system to support those sometime peak loads. This equation might be a bit different if you are full time off grid, using shop tools all the time however.

    Depending on how you are doing your water, and your climate (freezing etc) a large holding tank filled with either a genny powered pump, or a gasoline pump, using a small gravity or pump augmented system to pressurize the house MAY make sense.

    When you are building a system, keep your eyes on the idea of expansion. Try to buy components with some significant "headroom" to grow. This is especially true of charge controllers. Inverters should on the other hand be sized for their average load. It makes no sense to run a 2 kw inverter for a 50 watt load. You may be way ahead buy buying a couple of inverters and using them as the load requires. For example a low wattage inverter like the TS 300 for the general lighting circuits, and a 1.5 kw Exeltech or Xantrex for the high draw circuits that get used occasionally.

    You WILL destroy a battery bank as a beginner, especially if you don't have a good monitor. Don't buy the idea that you can draw your bank down to 20% soc and have good longevity. Personally, I don't believe in drawing a bank down to 80% soc before fully recharging. Battery bank sizing is more of an art than a science. Your intuition is to have a bank that is too big generally, thinking that you have more drawdown capacity. The problem is having the discipline to charge with the genny when the sun can't keep up. The obvious problem with a bank that is too small is drawing it down too far too fast. Remember adding battery capacity to an existing battery bank is not a good idea in most cases. (See Bill's reference to the battery FAQ site)

    Finally, consider the reputation of the people with whom you deal. As our host as noted, if they don't carry something there is probably a good reason. I have patronized NAWS for some things and have been very satisfied with their service. Having said that, I am a big fan of buying locally whenever possible. Aside from all other reasons, by buying locally, you are HELPING ensure that someone will be there tomorrow to take care of your needs. These local businesses need to earn our business but not just on the basis of cost. The net is a great place, but there still is a place for our local merchants.

    Good luck and welcome to the club,,so to speak,

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,408 admin
    Re: off grid cabin in the woods!!!

    Please feel free to browse our host's webstore... Most of the major component listings (solar panels, charge controllers, inverters, batteries, etc.) on NAWS' site include a link to a few pages of Frequently Asked Questions (FAQ)... There is usually enough there to provide you with 90% of the basic information you need--Then come here for to ask more questions on how it all fits together, or if you get more confused (happens to all of us). :confused:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: off grid cabin in the woods!!!

    Thanks everyone for the advice, though some of the tech specs baffle me.
    I think I understand the jist of it. I have a local installer on board who has given me a quote for this install.
    Equipment to be supplied:

    - 1 Unirac “Solar Mount” aluminum mounting rail kit for 3 panels
    - 1 Midnite Solar Combiner Box and 2 solar circuit breakers
    - 1 Outback Power Systems MX-60 PV charge controller and circuit breakers
    - 1 Outback Inverter, model VFX3524, 3500 watt output for 24 volt battery system
    - 1 Midnite Solar “E-Panel”, model MNE250ST, to mount inverter and house circuit
    breakers
    - 1 Outback “Mate” system display and controller
    - (1 Bogart Engineering Trimetric 2020 battery amp-hour meter) optional, not included
    in price
    - 2 Outback battery temperature sensors, one for MX-60, one for inverter
    - All wire, cable, conduit, and fittings required to comprise a complete, working, code-
    compliant system.

    I am going to take all the gear I got back Real Goods and do a swap I think.
    They suggested the Sharp 175w panels( I believe the store said they are 36volt panels- can I use a 36 volt with a 24volt battery bank?)
    if those work I can get 3 of those for the system above.
    I think it is realistic to say my power needs are going to keep getting bigger and so I will probably have to sell the HondaEU2000 and Iota charger and get a bigger propane generator eventually. because I don't come to to an off grid cabin to hear a generator humming all day.
    the batteries seem to be okay - we checked the water and they seem to be okay. the BZ charge controller read 25.4 volts.
    I figured the iota charger wont equalize the batteries since it only charges at 27volts and I need more voltage to equalize the 4 6 volt batteries.
    I wish the folks selling you these things would mention this stuff as you hand over your credit card.
    Anyway I have learned a few things by making a whole lot of mistakes.
    the installer is quoting about $6200 for all the stuff above and to install it all.
    that's without panels and generator. Seems like a lot of money but then I dont have electric bills.
    I guess I am interested to hear what you all think. I could just get one or two 175w panel and get the outback charge controller and stay with my Exeltech 1100w inverter stay small and then grow later or I can just go for it and get the installer to do what he does best.
    thanks MM
  • System2
    System2 Posts: 6,290 admin
    Re: off grid cabin in the woods!!!

    Also one more question.
    If I do go for a bigger generator that runs on propane what do you all suggest?
    Someone told me I would need 6k generator to charge for shorter periods of time.
    Also how does an inverter with a charger work?
    -MM
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: off grid cabin in the woods!!!

    Your "small" battery bank will not accept a high amperage charge, so don't be so quick to toss the honda genset. Best is to use the gen for an hour in the AM, to bulk up the batteries, and let the solar do the slow trickle charge fr the rest of the day.

    The MPPT controller does the "magic" of converting the higher voltage PV panels to the lower voltage battery, I think 36V panels will just barely work with 24V batteries, gotta read the specs before you can be sure. That is a class in itself, understanding what PV's to MPPT convert to what battery bank.

    Real Goods DOES have knowledgeable staff, so either you got a solar hemp beach towel sales droid, that had no idea which end of a wind gennie goes round, or they did not understand your situation.

    Will you be living at your cabin, or just weekend trips to it? - how much power will you need, determines how much solar you must have to avoid excessive gen run time.
    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 ,

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: off grid cabin in the woods!!!
    monamoore wrote: »
    Also how does an inverter with a charger work?
    -MM

    When the inverter/charger senses Mains or Generator power, it stops inverting, and begins charging. The charge current and battery type must be programmed into the unit, and also programmed into the solar MPPT charger too.

    I think the HUB or the MATE will allow the 2 chargers to share 1 Bat temp sensor. ?? Someone with an outback system check me on that.
    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 ,

  • System2
    System2 Posts: 6,290 admin
    Re: off grid cabin in the woods!!!

    thanks Mike for the quick response. Living full time in the cabin.
    my energy needs are hard to figure out about 5x13 watt bulbs, a laptop computer and an external firewire drive that can run up to 8 hours ( I edit video) a tv to watch films occasionally. A small Ipod charger radio. Ideally i would like to get a small fridge so we can get out of the cooler and ice block life but may just get a little propane fridge for $400. Then there are the charger things - 2 cel phones and 2 toothbrushes. Occasionally charging a dustbuster and AA batteries. so I am not sure how to measure all that???

    here are the specs on the panel they suggested at Real Goods
    175 WATT
    Nt-175u1
    ElEcTricAl cHArAcTErisTics
    Maximum Power (Pmax)* 175 W
    Tolerance of Pmax +10%/-5%
    Type of Cell Monocrystalline silicon
    Cell Confi guration 72 in series
    Open Circuit Voltage (Voc) 44.4 V
    Maximum Power Voltage (Vpm) 35.4 V
    Short Circuit Current (Isc) 5.40 A
    Maximum Power Current (Ipm) 4.95 A
    Module Effi ciency (%) 13.45%
    Maximum System (DC) Voltage 600 V
    Series Fuse Rating 10 A
    NOCT 47.5°C
    Temperature Coeffi cient (Pmax) -0.485%/°C
    Temperature Coeffi cient (Voc) -0.36%/°C
    Temperature Coeffi cient (lsc) 0.053%/°C
    *Measured at (STC) Standard Test Conditions: 25°C, 1 kW/m2, AM 1.5
    mEcHAnicAl cHArAcTErisTics
    Dimensions (A x B x C below) 32.5” x 62.0” x 1.8”/826 x 1575 x 46 mm
    Cable Length (G) 43.3”/1100 mm
    Type of Output Terminal Lead Wire with MC Connector
    Weight 35.3 lbs / 16.0 kg
    Max Load 50 psf (2400 Pascals)
    Also on the Real Goods folks: they have been really very cool to me and have been nothing but cool since they realized they sold me a panel that would not charge the lame controller they sold me-maybe I just caught the guy on a busy day-and changed my mind once from 12v to 24v system-since I had no clue what i was doing I may have thrown him off.
    Anyway I wish there were just kits you could walk in and buy.
    So when you walk in you could look at a list of appliances and then know you need this set up or that one. it would probably make it easier for people to come over to the solar side.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,408 admin
    Re: off grid cabin in the woods!!!

    MM,

    You really need to figure out how much power you will need (and for the next 3-7 years--hopefully, so you don't end up with an undersized battery bank and the question of mixing old and new batteries together--not a great idea if you can avoid it).

    It will also help you size the rest of your system... Your system (if you pay for the install) is probably going to cost you around ~$15 (very rough guess +/- 50%) per solar panel watt to install.

    Get a Kill-A-Watt meter and measure all of your AC loads...

    wind-sun_2032_3349941Kill-A-Watt AC Power Monitor Meter

    wind-sun_2029_3303765Kill A Watt P4320 Power Strip
    Kill A Watt power monitor strip with surge protection
    Regular price: $99.95
    Sale price: $78.85

    Basically you will need to create a chart of Peak Watts, and Average Watts, and lastly, Total Watt*Hours per day (week, seasonal, etc.).

    The Peak Watts will size your inverter (and as you have seen a Pure Sine Wave inverter is not cheap)... If you have starting loads (pumps, fridge, motor)--you will probably have to get a pretty large inverter vs your average running load... For things that are optional, work to keep the "peak loads" low (for example, run your well to tank pump when everything else is turned off).

    And, you need to know your Watt*Hours per day you will be using... For an off-grid system, power is expensive--probably around $1.00 per kWatt*Hour or more (1 kWH=1,000 Watt*Hours). Or about 10x what the typical cost people pay for home electric power (you are building your own power station and paying your own maintenance for batteries and such).

    An example for estimating power needs:

    10 hours * 40 watt = 400 Watt*Hours (laptop)
    10 hours * 20 watt = 200 Watt*Hours (firewire drive)
    5 hours * 13 Watts * 5 = 325 Watt*Hours (5 CFL's)
    2 hours * 5 Watts = 10 Watt*Hours (AA battery charger)
    0.1 hours * 1,000 watts = 100 Watt*Hours (well pump 6 minutes per day)
    ========================================================
    1,035 Watt*Hours per day.

    Assume 130 Watts for constant on power... The well pump would be 1,000 watts--but probably need 2x or larger inverter to start (others with well pumps can give better numbers than I).

    Here is where possibly getting two inverters--One small True Sine Wave inverter to run your electronics, and a second Modified Square Wave (or larger TSW) inverter to run your pump (assuming pump runs OK on cheap MSW inverter).

    Now, at a minimum, you are looking at needing 1,035 Watt*Hours (1.035 kWhrs) per day.

    Using the numbers from my first post in this thread, I estimated around 50-80kWhrs per month (winter/fog vs summer/fog if it is like where I grew up).

    Assuming you want to minimize the generator use--assume 50kW per month minimum (winter, base on 1kW of solar panels) to run your loads (more available for summer use).

    (1.035kWH per day * 30 days per month) /
    (50kWH per month per 1kW of panels) = 0.621 KW of solar panels

    So, for my "mythical load" you would probably get away with no generator use for 9 months of the year, and some generator use during the winter (probably a few dozen of hours of use--pure guesses).



    Battery size:

    6x * 1,035 Whrs per day / 24 volts = 258 AmpHours (@24v)

    Or, roughly in line with what you have now.

    With an MPPT Solar Charge Controller, you can effectively and efficiently use any panel voltage from Vmp =~32 volts to 100+ volts (there are rules to follow--can't just assume).

    Take a look at the MX-60 they are offering you--that unit is now out of production and you should be able to get something knocked off--or look at the FM-XX series. Both are very good controllers--but maintenance wise, it is best not to get an end of production unit for top dollar.

    And Mike is right about the Generator--Do not get anything bigger than you will need... Normally (from what little I have seen) if you run a genset at 50% or less load, you are still running 50% fuel flow.

    Or in your case, a 6kW unit running at 3,000 watts--can you make use of that much power or not... For charging your battery bank, you are looking at ~400-1,000 watts or so (and less, as the batteries are in the last 10-20% of their charging cycle).

    You may end up using 3x as much fuel (or more) with the larger genset than you really will need...

    In terms of gasoline--a]reasonably efficient genset gets around 5kW*Hours per gallon--A eu2000i running at 400 watts is still >5kWH/gallon (most are not so efficient at 25% load)...

    A generic 6kW unit at 3,000 watts will use:

    1 gallon * 3kW/5kWhr = 0.6 gallons per hour to generate 400 watts (0-3,000 watts)

    The Honda, roughly:

    1 gallon * 0.4kW/5kWhr = 0.8 gallons per hour to generate 400 watts (or more than 12 hours on a gallon of fuel--spec if 15 hours @ 400 watts on 1.1 gallons of fuel)

    So--unless you can run your generator at 50% load (or at least 25% load), a 6kW unit is probably way larger than you will need for a low-power off-grid lifestyle...

    Certainly, electric start (possibly setup for auto-start), propane vs gasoline, larger/more reliable unit, etc., has it attractions... If you need electric start, you may wish to look at the Honda eu3000i -- not as fuel efficient, but better.

    Regarding propane fridge vs electric fridge... I would price out your system assuming you get an electric fridge and see how much extra it runs you.

    A good Energy Start fridge is already very efficient. And if you are into do-it-yourself, look at converting a chest freezer into a fridge (basically, change out the thermostat, and maybe set up a drain to catch condensation on the walls)... Can cut your usage down to 1/2 or 1/4 of a standard energy star "fridge":

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: off grid cabin in the woods!!!

    mm,
    do note that the original 187w pv you liked, that you can have more of them wired in series when using an mppt controller like the mx60. just be careful not to exceed the voltage ratings on the mx60 going with a series arrangement so in some cases series/parallel pv arrangements are called for. the smallest number of those 187w pvs that would work in a 24v battery system would be 2 and this means pvs are bought in 2s. if you have 3 pvs you could place all 3 in series, but to add another pv in series for 4 would be closing in on the max voltage. just for your general knowledge pvs that are in series we refer to as a string of pvs or string for short. as i said before multiple strings can be paralled for more current if you ever cross that bridge, but they must identical to each other as i wouldn't recommend adding a string of 2 to a string of 3. in that example you will see that some numbers of total pvs just won't work with your 24v battery system. 2s x 2p, 3s x 2p, 2s x 3p, and 3s x 3p work so 5 pvs do not fit the arrangement as is the case for 7 of them also.
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: off grid cabin in the woods!!!

    BB breaks it down like a scientist again :)

    BB you and installer? Just been at it for along time? You sure do know how to give people an accurate honest real life answer.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: off grid cabin in the woods!!!

    MM,

    Please give a quick scan of my previous post in this thread. Bill has it absolutely right, that you should get a handle on the loads. This is difficult because you are not living there.

    Your situation is not unlike mine. The difference is that you will be using your TV and we don't have one. You will also be using your lap tops more hours per week.

    Just for comparison, we use ~ 50 amp/hours/day in general use. (12vdc) that translates to ~ 600 watt hours/day. If I was starting over, I would double the over all numbers, and then add in for a hi-efficiency electric fridge. (Stay a away from compact "dorm type" fridges as they tend to be very inefficient).

    We use Propane fridges, because we always have, but if I was to do it over again I would go with 120vac. If you were living there part time, then propane would likely make sense, but full time, over time the 120vac will pay off pretty well.

    Pay attention to what I suggested earlier. (Not that I am always right,,, in fact maybe seldom,,,) You loads WILL increase with time, and it is much cheaper to start with a system that is too big now and grow into it rather than the other way around.

    As for generators, I would consider a Honda Eu2000. Very fuel efficient, easy starting, portable, reliable. It will easily run a Xantrex TC 40 amp charger, and probably a bigger IOTA. On the other hand, if you are going to live there for years, you might consider an industrial duty Onan or Kohler, but you will pay a price in fuel and noise. I use a Honda Eu 1000, powering a Xantrex TC 20 and am very happy. We only have to run it about 2 days/month.

    Good luck, try to avoid the ready, fire, aim by reading and learning all you can before you buy and build your system.

    Tony
  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
    Re: off grid cabin in the woods!!!

    Sounds like you're getting the idea. I have the same Outback system components, and as Mike said you only need one temp sensor. I would not spend the money on a bigger generator, if anything the two areas that I would look to spend some more cash first would be a bigger battery bank (perhaps) or more solar panels.
    As far as estimating loads for a full time residence, I'll repeat what's been said a few times: they tend to grow. Especially be aware of winter time, this is the tough time for off grid systems when there is often more power used and a lot less solar power available to harvest. One thing that hasn't been spelled out so clearly perhaps, and turns out to be kind of a major factor for off grid living is not just the raw power consumption itself, but when it's being consumed.
    Be sure to pay attention to your batteries with regards to using power, there is a bit of a learning curve to this but the basic idea is that they need to get their full charge on a regular basis. Sometimes your batteries will not get enough juice to finish off if you're also using some or all of the solar power available. If you are away most of the time in the day that's no big deal, but for those days when you are home it may prove challenging to run household loads and charge your batteries. During the winter especially, I would suspect (VERY rough estimate based on no cold hard numbers) that you might have trouble running loads AND giving your batteries a full charge with three 175watt panels. A standard strategy is to hold off on using a lot of power until the batteries are full (or near full), to do utilize this strategy well, you'll need to get a feel for how much power may still be available (solar wise), and how much more your batteries need to finish charging. Winter is tough, right now at our home for example, we start getting high output around 10:30-11:00 am, peak output from about 11:45 or so until about 1:30-2:00pm, and then the numbers start dropping. Since batteries need to hold absorb level voltage for two hours this means that there may not be sufficient juice to finish them off if they don't hit absorb voltage by about 12:30... a very narrow window all in all. Obviously there are many factors, and without all of the numbers it's all really just guessing.
    Probably the best questions to ask, and numbers to calculate out, will relate to how easy will it be to add to this system. With that Charge controller you'll be able to expand really easily with no additional costs other than mounting structure and possibly some additional wiring (assuming that you have space for more panels). The bigger limiting factor will probably be the battery bank, which you could figure that you'll replace with a bigger bank a few years away when you'll know a lot more and have a solid feel for your needs. Sounds like you're well on your way.
    enjoy
  • BB.
    BB. Super Moderators, Administrators Posts: 33,408 admin
    Re: off grid cabin in the woods!!!
    RWB wrote: »
    BB you an installer? Just been at it for along time?

    RWB,

    Thank you very much for the kind words... Believe it or not, I have one Grid Tied system, professionally installed, on my home. Other than playing with the usual small solar cell chips as a kid, and other electromechanical stuff--no involvement with solar industry at all.

    The rest of my knowledge comes from reading (here, i.e., you guys and gals, and other places), and from my design engineering background (larger computer and communications equipment).

    With engineering, you quickly learn that things (and people) don't work they way you hope they will--only the way they will.

    So, being dispassionate about analyzing your needs and what your situation is (from site, hardware available, money available)--it pretty much boils down to what can be done with available resources.

    And, I am cheap... Hate seeing people waste there money and wasting of resources (natural and otherwise).

    Merry Christmas and Happy Holidays to all!
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,408 admin
    Re: off grid cabin in the woods!!!

    Also, to add one more place to look... Outback has a nice page of drawings and parts lists to show how everything connects together.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: off grid cabin in the woods!!!

    Thanks everyone, and happy holidays.
    I was really relieved the folks at Real Goods took my whole system back with the exception of the 4x 6volt golf cart batteries and a 30 amp disconnect. Now i can start again and do some more research. I will definitely assess my loads first then talk to my installer some more.
    I have a question for Bill. i am confused about what WH means. like say i call apple and they say my laptop draws 100watts is that per hour? does that mean if i use it for 8 hours that it takes 800 watts a day. how does that translate to watt hours?
    I guess when I get the kill-a-watt meter there will be instructions. I am on the grid for a few weeks so maybe i can try to measure my usage and add it all up.
    I think I am heading for 6x175w sharp panels on a combiner box (because some panels will always fall in the shade of the redwoods) Also the outback system(inverter charger and charge controller) with the Honda Eu2000 or maybe the 3000 for back up.

    Not sure about more batteries- I thought I couldn't get anymore and still be 24v?
    Anyway happy holidays and thanks again for the help.
    MM
  • BB.
    BB. Super Moderators, Administrators Posts: 33,408 admin
    Re: off grid cabin in the woods!!!
    monamoore wrote: »
    Thanks everyone, and happy holidays.
    Happy Holidays back to you and your family!
    I was really relieved the folks at Real Goods took my whole system back with the exception of the 4x 6volt golf cart batteries and a 30 amp disconnect.
    Always happy to hear good things about companies too!
    Now i can start again and do some more research. I will definitely assess my loads first then talk to my installer some more.
    I have a question for Bill. i am confused about what WH means. like say i call apple and they say my laptop draws 100watts is that per hour? does that mean if i use it for 8 hours that it takes 800 watts a day. how does that translate to watt hours?
    Just to be clear, it is not Watts per Hour, but Watts that you are taking about...

    Watts is already a "rate" based measurement... It is equivalent to Miles per Hour.

    Watt*Hours is the unit we measure "work" in for electricity (really kilo-Watt*Hours or equivalent 1,000 Watt*Hours--there are other units used in your physics and chemistry classes--Jules and Ergs and such--but those are really small numbers so the kWhr was used instead for most utility power).

    Watt*Hours is equivalent to Miles Driven (if Watts=MPH)...

    Watt = MPH = Rate per unit time
    Watt*Hour = MPH * Hour = energy used or miles driven

    It is confusing--even for me--first in physics and chemistry--and even here years later when I started posting--it is really easy to mix-up the units...

    So, when you call Apple and they say your computer uses 100 watts... That is really 100 watt*hours per hour (if that makes sense).

    So, if you use your computer for 1 hours, then 100w*1h=100Watt*Hours of energy used (drive at 100 MPH for 1 Hour = 100 Miles driven).

    Run your computer for 10 hours at 100 watts = 10H*100W=1,000 Watt*Hours or 1 kWhr of electrical energy (power is a rate / per unit time, energy is the amount used -- equal to miles driven).

    Now, 1,000 Watt*hours = 1 kWhr and a typical electric rate is $0.10 per kWhr, so you have used $0.10 of electricity.

    If you are off grid, your costs are probably around $1.00 per kWhr, so your power use would be 1kWHr*$1.00/kWhr=$1.00 of energy used.

    Also, the reason a Kill-A-Watt meter is so important is that the "ratings" of appliances are typically maximum/worst case ratings... You need those, but you also need your "average" to size your solar panels and batteries.

    Your car may average 65 MPH on the freeway, but when you take all of your time together (stop lights, stop and go driving, etc.), you will find your average motor on time is around 35 MPH average...

    Same thing with your computer and fridge--at certain times they take more energy, and other times less (fridge only runs 1/3-1/2 of a 24 hours day, your computer and diskdrive use more power when computing/accessing files, less when not, and less when the backlight is off)--the Kill-A-Watt meter allows you to total all of the energy use and average it over 24 hours, a week, whatever.
    I guess when I get the kill-a-watt meter there will be instructions. I am on the grid for a few weeks so maybe i can try to measure my usage and add it all up.
    Exactly correct...

    And because your electric power will be so "dear" in cost--you will need to see what you can do to reduce your needs.
    I think I am heading for 6x175w sharp panels on a combiner box (because some panels will always fall in the shade of the redwoods)
    The combiner box will do nothing about shading.

    Don't kid yourself--solar panel arrays need full sun to work correctly... Look at your site right now--hopefully, you are getting full sun from around 9am to 3pm--at least. You can do with less (or east, or west, facing panels)--but you have to account for the loss in overall power generation.

    Some people have morning fog, so they face their panels west... Others have hot afternoons with thunder showers, so they face their panels east.

    Others have limited space and face 1/2 the panels east, and the other 1/2 west... But--when you split panels based on available light--it is very important that a string (a set of series connected panels) all have the same sun... If one panel in a series connected string has even 10% shadow--it is possible that the effective harvested output of the entire string will drop to near zero (if there are two or more strings in parallel).

    There are lots of issues that you cannot take for granted with designing/building your own solar power station... And solar panel location/positioning is very important (solar panels only generate usable power when subjected to full sun--shaded panels and panels facing away from the sun will not generate any useful power--no matter what some people post or write articles about).
    Also the outback system(inverter charger and charge controller) with the Honda Eu2000 or maybe the 3000 for back up.
    Either Honda would be good for a backup and/or low cost entry level system where solar power provides the majority of your electricity (don't run these 24 hours per day and expect long life).
    Not sure about more batteries- I thought I couldn't get anymore and still be 24v?
    Not quite sure what you mean by this--if your batteries are still in good shape and pretty new, you can add more in parallel (for more energy storage at 24 volts) and/or more in series (for more energy storage at 48 volts).

    In any case, the voltage of your battery bank is dependent on how much power you want to draw (I would suggest trying to stay at below 100 amps typical current maximum) to keep your wire size low and so as not to overheat your batteries with high current...

    100 amps * 12 volts = 1,200 watts maximum
    100 amps * 24 volts = 2,400 watts maximum
    100 amps * 48 volts = 4,800 watts amximum

    For battery sizing, you want them to be sized appropriately with the charging system... Too many batteries--can't charge well on small solar system... To few batteries, deep discharging will lessen battery life and cause you to run the generator more in bad weather.

    The above numbers are recommendations--and other things can be done for the right reasons with the correct parts. Pretty much everything within +/-50% of the above numbers is not a big difference to fret over.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Moe
    Moe Solar Expert Posts: 60 ✭✭
    Re: off grid cabin in the woods!!!

    Voltage is a measure of instantaneous pressure (electromotive force).

    Current in amperes is a measure of instantaneous current flow. Current flow over time is measured in ampere-hours. For example, 5 amps current over 2 hours = 10 amp-hours.

    Power in watts is equal to volts times amps. Wattage is a measure of power at one particular instant. Power over time is measured in watt-hours (or kilowatt-hours for large amounts). If your laptop draws 100 watts and you use it for 2 hours, you've used 200 watt-hours or 0.2 kilowatt-hours.

    I suspect you'll find your laptop only draws 100 watts when you are using it on the adapter after running down the laptop battery, meaning it's drawing power to both operate the notebook for you AND charge the laptop battery.

    I edited this to add some more, as I understand it. Critique by the gurus here is welcome.

    If you put the six Sharp 175W panels all in parallel to minimize the effect of shading, you'll have a max continuous current of 6 x 5.4 x 1.25 = 40.5 amps (in other words, even if it was rated for 100%, the 30A disconnect is too small). If you put them in three parallel strings of two in series for 48V nominal (2 x 44.4 V = 88.8 V x lowest temperature factor), you'll have a max continuous current of 3 x 5.4A x 1.25 = 20.25 amps and the 30A disconnect will be sufficiently large, even if it has to be derated to 80%.

    If you get four more 6V batteries and wire them in series with themselves, you will have 24 volts just as you do with the 4 you now have wired in series. If you put the two series strings in parallel, you will have twice the amp-hour or watt-hour battery capacity. If these are 220AH T-105 batteries, you'll have 440 amp-hours and the 29.7 amp Imp total of the six panels will be 6-3/4% of the battery bank capacity (and would be over 5% even at 80% output)...in other words a good match.