Putting together a solar system

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monoloco
monoloco Solar Expert Posts: 103 ✭✭
Hi Everyone, Great forum here. I am building an off grid home in southern Baja and am thinking of purchasing some used equipment from a friend and thought I'd see what other forum members think. He has 8) [is that 8x ?] 75 watt BP solar panels, an APT powercenter 4B and a Heart Interface Freedom 25 inverter/charger 12v for sale for $2500. The equipment is about 10 years old but was only in service for about 5 years. I would like to know if it would be worth designing a system around this equipment or would I be better off purchasing new equipment. I also have 3) 55watt Kyocera panels, 1) 75watt BP panel and 1) 75watt Evergreen panel that I would be adding to the array. Looking forward to hearing your suggestions.

note: some number text combination are converted to smilies... -Bill B. Moderator

8 ) (without the space) becomes 8) cool face
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
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    Re: Putting together a solar system

    In general, 10 year old equipment is probably not worth much more than the scrap value...

    Electronics have been progressing so quickly that after 10 years, many of the parts need to repair electronic devices are no longer available (and vendors have ended paid support).

    Before I offer anything for the existing equipment--I would suggest that you get a good handle on the loads you want to support (watt*hours per day) and how much sun you get--then size a system that meets your needs.

    Go through a price out a couple of systems types and see what the parts costs would be--then you could compare with the used system and see how much it would be worth to you.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: Putting together a solar system

    I agree with Bill about the electronics. If however you are interested in getting rid of the BP panels let me know.

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
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    Re: Putting together a solar system

    And I agree with Tony that 5-10 year old good quality solar panels have probably 25-40+ years life in them...

    The bigger issue is mixing panels together on a system... In general, you can match Vmp withing 10% (parallel connections) and Imp within 10% (series connections).

    When you have a mix/match solar panel setup--you need to know exactly what model panels you have (their Vmp/Imp ratings), what voltage battery bank, and what type of charge controller (PWM or MPPT) charge controller you will want to setup.

    It is sort of like trying to take a junk drawer full of batteries and trying to mix series/parallel connections of D cell, AA cell, 9 volt radio batteries, Lithium, etc. into a integrated power source... It can be done, but it does take work and some panels (i.e., solar batteries) may not be compatible with the system you end up designing (or it would take more hardware/$$$ to integrate into the system).

    Not to say never to buy the used equipment--but make sure you understand its value to you.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
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    Re: Putting together a solar system
    BB. wrote: »
    And I agree with Tony that 5-10 year old good quality solar panels have probably 25-40+ years life in them...

    The bigger issue is mixing panels together on a system... In general, you can match Vmp withing 10% (parallel connections) and Imp within 10% (series connections).

    When you have a mix/match solar panel setup--you need to know exactly what model panels you have (their Vmp/Imp ratings), what voltage battery bank, and what type of charge controller (PWM or MPPT) charge controller you will want to setup.

    It is sort of like trying to take a junk drawer full of batteries and trying to mix series/parallel connections of D cell, AA cell, 9 volt radio batteries, Lithium, etc. into a integrated power source... It can be done, but it does take work and some panels (i.e., solar batteries) may not be compatible with the system you end up designing (or it would take more hardware/$$$ to integrate into the system).

    Not to say never to buy the used equipment--but make sure you understand its value to you.

    -Bill

    If I was to go with a MPPT charge controller on a 12v system, ideally what would be the voltage input from the solar array? Would a 1kw solar array be too much for a 12volt system?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
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    Re: Putting together a solar system

    The larger MPPT controllers are 60 amps of charging current maximum... Assuming 14.5 volts charging, and roughly 0.77 typical panel efficiency (if you are in cold/snow covered ground areas, you can get more power--but 0.77 derating works well as nice average to size a system):
    • 60 amps * 14.5 volts charging * 1/0.77 panel-system derating = 1,130 watts useful maximum per 60 amp MPPT controller
    Regarding the choice between a 12 volt / 24 / or 48 volt battery bank... The charge controllers can "manage" 4x as many solar panels at 48 volts vs 12 volt system.

    Also, I like to recommend around 100 amps maximum rated current for your inverter... to power even 1,200 watts of AC loads:
    • 1,200 watts * 1/10.5 cutoff voltage * 1/0.8 inv eff * 1.25 NEC derating = ~179 amps rated wiring/fuses/breakers...
    So, my rule of thumb is a maximum of 1,200 watt inverter for a 12 volt bank and a maximum of 2,400 watts for 24 volt bank--Anything larger than 2,400 watts would be best served by a 48 volt battery bank.

    Vmp of the array for a MPPT controller would run from ~17 to ~100 vdc.

    Lower voltages tend to be a few percent more efficient. Higher voltage arrays reduce the current in the Array to Controller (typically the longest wire run of your setup). If your panels need to be a distance from the battery shed--then running at higher array voltages can save you lots of copper wire costs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Putting together a solar system
    monoloco wrote: »
    If I was to go with a MPPT charge controller on a 12v system, ideally what would be the voltage input from the solar array? Would a 1kw solar array be too much for a 12volt system?

    For MPPT controllers you should consider three things; not exceeding the controller's maximum input Voltage, not having the array Voltage too much higher than the system Voltage (for reasons of efficiency), and not having more panel capacity than the controller's maximum output (waste of money on excess panels you can't really use).

    Not exceeding the input Voltage limit is dependent on the controller. The Bluesky only allows 36V (I think) whereas an Outback unit will take up to 150 - but costs more and handles more Amperage.

    System vs. array Voltage is more of a rule-of-thumb thing; most controllers work best when they're not doing too much down converting, so you generally go with a nominal array Voltage that's "one step up" from the system Voltage. For a "12V" system that would be a "24V" array.

    Is 1 kW too much for 12V? That too depends on the charge controller. The maximum output on some is 15 Amps: basically 15 * 14.2 (charging Voltage) = 213 Watts (usable). An Outback FM80 can handle 80 Amps: 80 * 14.2 = 1136 Watts. And when I say "usable" I mean that panels don't put out their nameplate rating all the time. They'll average about 80% during "good sun". In some cases there is even more derating due to environmental factors like heat.

    As Bill & Tony have both mentioned, you have to figure out how much power you need before you can determine how to produce it. The array sizing is according to how much battery capacity you have to recharge.

    Once you figure out your system design, price it new. You'll probably agree then that used equipment isn't much of a bargain (especially since some of its lifespan is already gone, and you never really know how much). Used batteries are the worst thing to spend money on, in my opinion.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: Putting together a solar system

    UH Bill,

    I was trying to suggest that the panels were junk and he should send them to me for scrap! You misunderstood me!

    Tony

    As always, start with the loads and work backwards! (or forwards!)
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    Re: Putting together a solar system
    monoloco wrote: »
    ....thinking of purchasing some used equipment from a friend ...


    I have a bad feeling about this......
    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 ,

  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
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    Re: Putting together a solar system

    Thanks for the input, here's some more info. The area in which we live is very sunny, 300+ days a year, the load demands of our house will be quite nominal, 4 amp 120v pump with pressure tank, washing machine, occasional kitchen appliances, (blender, food processor etc.)and lights with maybe a Sunfrost reefer in the future. I also have a 3600 and a 6000 watt genset for running power tools and large loads. I know that it would be more efficient to go with a higher voltage 24 or 48v system but I'm trying to do this on a tight budget with the parts i have available. It seems to me that for $2500+ batteries I could have a fairly good system that would meet our needs considering that a good 2500w inverter alone would cost close to that not including the fact that I would have to pay 15% duty plus transport from the states on anything I bring down. Maybe I need to rethink this but I was also planning on running most of my lighting circuits at 12v and using MR16 LED's. I will be buying new batteries and am leaning towards 1 string of 6 2v cells. I am wondering if with this system I am better off running all the panels in parallel or wiring them as 2 strings at 24v into a mppt controller?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Putting together a solar system

    A couple of observations based on your last post which I hope will help:

    A washing machine isn't easy on power. Depending on the model, it could draw 800 Watts running. Trying to agitate a tub full of sopping wet cloth and water requires quite a bit of torque. You might want to run the generator on laundry day!

    The 2V cells are a great way to get a large bank of power. Much better than paralleling the equivalent Amp/hrs in 6V or 12V. But that one bank would be 1110 Amp/hrs and need more than 1500 Watts of panel to properly charge. They are also expensive, so be sure you really need all that capacity before buying them.

    Trying to do it on a limited budget is something we all understand here! (So far, Bill Gates is not a forum member.) :p But the biggest mistake you can make is to not plan it out carefully to begin with. I'm not saying you shouldn't buy the equipment, but you should look at all the options down to the last detail. That includes possibly buying a new but smaller inverter with a warranty rather than something which if it does quit tomorrow you're running on gen until you spend more money to buy a new inverter.

    I admit to knowing nothing about the Heart inverter you mention, including whether it's sine wave or MSW or what kind of quality rep they have. If the panels put out you've got 600 Watts right there, plus your others comes to 915. But remember that they are not identical panels, so their output won't be peak no matter how you arrange them. To that end, their Imp is likely most different, so you're probably better off keeping them in parallel. That would mean some arrangement with two PWM controllers.

    There doesn't seem to be any clear, obvious answer I'm afraid. :blush:
  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
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    Re: Putting together a solar system

    It depends on how many panels and what type of controller you have available...

    In general, below 200 watts of solar panels, it is generally not a great deal to go with MPPT controllers.

    Above 400 watts, a MPPT controller is typically more flexible and better able to charge your battery bank--at the cost of 2-3x as much money...

    If your panel array to solar charge controller is short (panels are on the side/roof of the home)--you can get away with a PWM (short but heavier gauge wiring). If your array is 10's of feet or longer away from the solar charge controller battery bank, then you my find a MPPT controller with high Vmp panel (closer to 100 vdc) a better fit.

    No black / white answers--You really need to do a paper design of several options and see which one will work best for you.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
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    Re: Putting together a solar system
    A couple of observations based on your last post which I hope will help:

    A washing machine isn't easy on power. Depending on the model, it could draw 800 Watts running. Trying to agitate a tub full of sopping wet cloth and water requires quite a bit of torque. You might want to run the generator on laundry day!

    The 2V cells are a great way to get a large bank of power. Much better than paralleling the equivalent Amp/hrs in 6V or 12V. But that one bank would be 1110 Amp/hrs and need more than 1500 Watts of panel to properly charge. They are also expensive, so be sure you really need all that capacity before buying them.

    Trying to do it on a limited budget is something we all understand here! (So far, Bill Gates is not a forum member.) :p But the biggest mistake you can make is to not plan it out carefully to begin with. I'm not saying you shouldn't buy the equipment, but you should look at all the options down to the last detail. That includes possibly buying a new but smaller inverter with a warranty rather than something which if it does quit tomorrow you're running on gen until you spend more money to buy a new inverter.

    I admit to knowing nothing about the Heart inverter you mention, including whether it's sine wave or MSW or what kind of quality rep they have. If the panels put out you've got 600 Watts right there, plus your others comes to 915. But remember that they are not identical panels, so their output won't be peak no matter how you arrange them. To that end, their Imp is likely most different, so you're probably better off keeping them in parallel. That would mean some arrangement with two PWM controllers.

    There doesn't seem to be any clear, obvious answer I'm afraid. :blush:

    The Heart inverter is a MSW. Do you think I'd be better off scaling down the battery bank?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Putting together a solar system
    monoloco wrote: »
    The Heart inverter is a MSW. Do you think I'd be better off scaling down the battery bank?

    Okay, there are some things an MSW inverter won't run and a lot of others it will run poorly. Like AC induction motors as found in refrigerators, washing machines, and some water pumps. Other things that "don't like" MSW include certain battery chargers and UPS units. It can be a bit of a crap shoot finding out if your devices will actually function with MSW, or function without significantly shortened life.

    As to the size of the battery bank ... This is where we start playing the broken record about getting a firm grip on loads. I know it's tough to do, but you need some kind of "ballpark figure" on how many Watt hours you'll use in any given day. There's no sense buying too much battery and having to spend even more to keep it charged and there's unpleasantness in suddenly running out of power and having to start a generator at 10:00 PM.

    Take a look at the equipment in my sig. It manages to run a refrigerator, plus the computer/satellite set up and lights as well as water pump (1/3 HP) digester pump (septic - 1 HP) and microwave. The last three are only run under full sun, fully-recharge battery conditions. The 700 Watts of panel supply approximately 2.4 kW hours of power on a good Summer day. But it's cooler up here, I'm at 3000 feet (clearer air), and our Summer days are up to 16 hours long so our sun exposure can be 5-6 hours of 'good' light.

    That said, if you put all those panels together I wouldn't be surprised to see better than 3 kW hours harvest per day in Baja, despite the heat. It would be enough panel to recharge about 600 Amp/hrs of battery bank, so perhaps you might want a parallel set of L16's @ 320 Amp/hrs (640 total) or 2-3 sets of T105's (450-675 total). The L16's would give you approximately 3.6 kW/hrs per day to work with max (50% DOD), and the T105's would run either 2.7 or 4.0. Any of these configurations is potentially feasible with the total panel count (all 915 Watts). Heat derating I'm not sure of, nor any other losses that would be inherent in your particular system.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: Putting together a solar system

    "the load demands of our house will be quite nominal, 4 amp 120v pump with pressure tank, washing machine, occasional kitchen appliances, (blender, food processor etc.)and lights with maybe a Sunfrost reefer in the future."

    One might argue that the loads are indeed more than "quite nominal" Everything adds up. For a simple example, a 5 watt brick power supply running an extra 12 hours in my house (60 wh) would be the equivalent of ~10% of my daily total power use!

    The 4 amp 120 vac pump is 480 watts, , 12 minutes per day is 96 wh,, 1/6 of my daily use,,( I am not trying to hold myself up as a paragon of good virtue in low power use, but rather suggest that loads are loads, and they do add up. Three rules seem to exist in the PV world, the first is that people under estimate their loads, over estimate their potential solar harvest, and loads grow with time.)

    So, for simple comparison, we live off grid, no washing machine or DW, no TV, no toaster, LP fridge etc, and we use ~600 wh/day. We supply that with ~400 watts of panel, into 450 ah of battery.

    Tony
  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
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    Re: Putting together a solar system
    Okay, there are some things an MSW inverter won't run and a lot of others it will run poorly. Like AC induction motors as found in refrigerators, washing machines, and some water pumps. Other things that "don't like" MSW include certain battery chargers and UPS units. It can be a bit of a crap shoot finding out if your devices will actually function with MSW, or function without significantly shortened life.

    As to the size of the battery bank ... This is where we start playing the broken record about getting a firm grip on loads. I know it's tough to do, but you need some kind of "ballpark figure" on how many Watt hours you'll use in any given day. There's no sense buying too much battery and having to spend even more to keep it charged and there's unpleasantness in suddenly running out of power and having to start a generator at 10:00 PM.

    Take a look at the equipment in my sig. It manages to run a refrigerator, plus the computer/satellite set up and lights as well as water pump (1/3 HP) digester pump (septic - 1 HP) and microwave. The last three are only run under full sun, fully-recharge battery conditions. The 700 Watts of panel supply approximately 2.4 kW hours of power on a good Summer day. But it's cooler up here, I'm at 3000 feet (clearer air), and our Summer days are up to 16 hours long so our sun exposure can be 5-6 hours of 'good' light.

    That said, if you put all those panels together I wouldn't be surprised to see better than 3 kW hours harvest per day in Baja, despite the heat. It would be enough panel to recharge about 600 Amp/hrs of battery bank, so perhaps you might want a parallel set of L16's @ 320 Amp/hrs (640 total) or 2-3 sets of T105's (450-675 total). The L16's would give you approximately 3.6 kW/hrs per day to work with max (50% DOD), and the T105's would run either 2.7 or 4.0. Any of these configurations is potentially feasible with the total panel count (all 915 Watts). Heat derating I'm not sure of, nor any other losses that would be inherent in your particular system.
    Am I mistaken to think that a larger battery bank would last longer because it wouldn't be discharged as much as a smaller bank? Also it seems like another reason to go big on the batteries is that it would be better to add more panels than to add more batteries later.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Putting together a solar system
    monoloco wrote: »
    Am I mistaken to think that a larger battery bank would last longer because it would be discharged as much as a smaller bank? Also it seems like another reason to go big on the batteries is that it would be better to add more panels than to add more batteries later.

    No, you are correct: the larger bank will suffer a lower Depth Of Discharge percent for the same amount of Watt hours delivered and that adds to battery lifespan.

    Unless you don't have enough panel to recharge the bank. It's a balancing act.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
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    Re: Putting together a solar system

    If you can find the cycle life chart for your batteries---they do last longer if not discharged as deeply--but it is not an obvious solution.... If your set of 4 batteries last 3 years, then a set of 8 batteries may last 6-8 years. Twice as much money for a bit better than 2x the life...

    For many folks, replacing batteries 1/2 as often is not a bad thing.

    If you start out with a properly sized battery bank and only 5% rate of charge -- then you can double the panels or a bit more upwards of 13% rate of charge later...

    Running batteries below 5% means you probably will be running more genset time to keep your bank up (AGM batteries will probably run better at low charge rates--Forklift type batteries are probably a bad choice for a 5% or less charge rate because of their higher self discharge).

    Above 13% -- that is about the useful limit to charge current for flooded cell batteries. AGM's can accept higher charge rates--but do you need it?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
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    Re: Putting together a solar system

    Thanks for all the suggestions. I can see that there is a lot to consider. One more question: What is the rule of thumb for matching the battery bank to the solar array? I think that now I'm leaning towards buying a new inverter and controller and trying to buy just the panels from my friend.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Putting together a solar system

    An expansion on the 5% minimum charge rate: that's without loads. The net charge rate is the gross minus whatever power is going back out to run loads while charging. It's important to remember this because we generally don't shut down systems while they recharge. Thus if you calculate for 5% initially, you'll find you don't actually get that rate in practice. This is why I repeatedly recommend 10% as a target.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,477 admin
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    Re: Putting together a solar system

    For battery sizing--a reasonable starting point is to plan for 3 days of no sun and 50% maximum discharge--or 6x your daily load (don't forget inverter efficiency of 80-85% if you want to account for all loads).

    A bigger bank is more expensive and requires more panels/charging current to keep happy. A smaller bank may cause you to run the genset more during strings of bad weather...

    A bigger than 6x battery bank is probably a waste of money--below 4x your daily load may be a bit on the small size.

    Also, check out your maximum power (surge power/current)--too small of bank may not start your well pump without browning out the rest of the inverter AC loads.

    If you are looking at spreading out your costs--probably a 6x battery bank and 5% set of solar panels--run for a few months or a year--then look at how many panels you would like to add to reduce genset run time.

    Another thing I like to look at is genset / AC battery charger sizing... For Diesel motors, you generally want to run them at 50-60% load.

    For gasoline based gensets, running them below 50% load can be waste of fuel--For below 50% electrical load, the generator fuel flow hardly drops any further...

    A few gensets, like the Honda eu2000i family, can run pretty fuel efficient down to 25% load or a bit less...

    So, I like to look at the battery bank to generator load ratios too when sizing a system... Many people put a 7-12 KW, very nice prime mover, genset in--and run it at 3kW or less loading when charging the battery banks. A second small genset dedicated to battery bank charging may be worth the time and money (and fuel saved). And keep the big guy to run the shop and pump water once a week. There are not that many reliable/quite/cost effective small gensets out there--so that can be a issue trying to find one too. Sometimes getting a smaller Onan or equivalent from an RV wreckers can be a good source.

    A properly sized genset my use 1/2 the fuel (or even less) vs what many people started there initial off-grid experiences with.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
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    Re: Putting together a solar system
    BB. wrote: »
    For battery sizing--a reasonable starting point is to plan for 3 days of no sun and 50% maximum discharge--or 6x your daily load (don't forget inverter efficiency of 80-85% if you want to account for all loads).

    A bigger bank is more expensive and requires more panels/charging current to keep happy. A smaller bank may cause you to run the genset more during strings of bad weather...

    A bigger than 6x battery bank is probably a waste of money--below 4x your daily load may be a bit on the small size.

    Also, check out your maximum power (surge power/current)--too small of bank may not start your well pump without browning out the rest of the inverter AC loads.

    If you are looking at spreading out your costs--probably a 6x battery bank and 5% set of solar panels--run for a few months or a year--then look at how many panels you would like to add to reduce genset run time.

    Another thing I like to look at is genset / AC battery charger sizing... For Diesel motors, you generally want to run them at 50-60% load.

    For gasoline based gensets, running them below 50% load can be waste of fuel--For below 50% electrical load, the generator fuel flow hardly drops any further...

    A few gensets, like the Honda eu2000i family, can run pretty fuel efficient down to 25% load or a bit less...

    So, I like to look at the battery bank to generator load ratios too when sizing a system... Many people put a 7-12 KW, very nice prime mover, genset in--and run it at 3kW or less loading when charging the battery banks. A second small genset dedicated to battery bank charging may be worth the time and money (and fuel saved). And keep the big guy to run the shop and pump water once a week. There are not that many reliable/quite/cost effective small gensets out there--so that can be a issue trying to find one too. Sometimes getting a smaller Onan or equivalent from an RV wreckers can be a good source.

    A properly sized genset my use 1/2 the fuel (or even less) vs what many people started there initial off-grid experiences with.

    -Bill

    Thanks for the info. I currently have an Onan 3600 Microlite LP and an Onan 6.5 KW diesel generator that I use for running my wood shop tools, but I try not too use it too much because it's quite loud.
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
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    Re: Putting together a solar system

    Lots of things here;

    On the battery bank for a first time solar electric system, I would rather see you NOT invest in a big AmpHour system. The mistakes you learn in the first couple years may cost you a lot less.

    If your running a home, not a weekend cabin in the woods, I'd go with a 24 volt system minimum.

    With a generator back up for long periods of cloudy days, particularly in a 300+ sunny day area. I would go with a somewhat undersized battery back. Try to load shift as much as possible (running things during those sunny days, this will save you 15-25% as storing cost's you watts)

    Areas with 300 sunny days are often hot, you won't need AC?

    Ananda went out of business in the mid '90's, I love the Pulse power center I have from about 2000, but in a year or so, when I finally replace the PWM charge controller (there is a recent thread about my trying to replace the charge controller), it will just be an AC and DC breaker box. Indeed, I think Ananda only used a fuse on the Battery disconect.

    Power centers make life setting up easier. If the Ananda is setup for a generator it might be worth a trying to use for your initial setup, but it's value I would find no more than the $250 I paid the the Pulse PC250 Power center, New Old Stock 3 years ago(a good deal). The inverter might be worth something as a backup, but thats all. 10 year old Quality solar panels might be worth as much as $2 a watt, you can get new for $2.50-3.
    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.
  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
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    Re: Putting together a solar system
    Photowhit wrote: »
    Lots of things here;

    On the battery bank for a first time solar electric system, I would rather see you NOT invest in a big AmpHour system. The mistakes you learn in the first couple years may cost you a lot less.

    If your running a home, not a weekend cabin in the woods, I'd go with a 24 volt system minimum.

    With a generator back up for long periods of cloudy days, particularly in a 300+ sunny day area. I would go with a somewhat undersized battery back. Try to load shift as much as possible (running things during those sunny days, this will save you 15-25% as storing cost's you watts)

    Areas with 300 sunny days are often hot, you won't need AC?

    Ananda went out of business in the mid '90's, I love the Pulse power center I have from about 2000, but in a year or so, when I finally replace the PWM charge controller (there is a recent thread about my trying to replace the charge controller), it will just be an AC and DC breaker box. Indeed, I think Ananda only used a fuse on the Battery disconect.

    Power centers make life setting up easier. If the Ananda is setup for a generator it might be worth a trying to use for your initial setup, but it's value I would find no more than the $250 I paid the the Pulse PC250 Power center, New Old Stock 3 years ago(a good deal). The inverter might be worth something as a backup, but thats all. 10 year old Quality solar panels might be worth as much as $2 a watt, you can get new for $2.50-3.

    A lot of good points there. This is not my first solar system, I lived for nearly 10 years with a much smaller system. The batteries are really the hard choice for me, the system I had in my old place used 16 T105's and I had a 400 watt array. I managed to nurse those old Trojans along for 6 years but it was a real PITA to maintain that many cells. For simplicity sake I would like to have fewer batteries but at the same time would be really easy to go to Costco in Cabo San Lucas and buy a load of Kirkland golf cart batteries whereas if I went with 2 or 4v cells I would be looking at hauling them from Az or Ca., another consideration that I have is space, my solar room is only about 4x6 so bigger cells would be a more efficient use of space. Ah so many questions and no clear cut answers.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: Putting together a solar system

    16 T-105s and only 400 watts of panel?

    Talk about under charging! Something like 2000ah of battery (12 volt) with ~20 amps of charge current! 1%,, just barely enough to keep in float!

    Tony
  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
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    Re: Putting together a solar system
    icarus wrote: »
    16 T-105s and only 400 watts of panel?

    Talk about under charging! Something like 2000ah of battery (12 volt) with ~20 amps of charge current! 1%,, just barely enough to keep in float!

    Tony
    Well they worked good for 6 years and I didn't even have an AC charger. I think that the key was that they never discharged more than 15-20% and I was meticulous about maintenance.
  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
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    Re: Putting together a solar system
    Photowhit wrote: »

    Areas with 300 sunny days are often hot, you won't need AC?

    .
    Actually, we are on the Pacific coast so the only really hot months are September and October which aren't really that hot, (mid 90's) just humid, but totally bearable. Sometimes it would be nice to have an AC in the bedroom for sleeping but there are trade offs when living off the grid.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Putting together a solar system
    monoloco wrote: »
    Well they worked good for 6 years and I didn't even have an AC charger. I think that the key was that they never discharged more than 15-20% and I was meticulous about maintenance.

    There is a classic example of under-panel sulphation failure: it doesn't show up right away, and everything appears to be working. You can replace the "used Amp/hrs" but not properly re-mix the electrolyte (not enough charge current). Slowly the battery capacity decreases until one day it reaches zero. This problem will not show up as a drop in either Voltage or Specific Gravity. Basically, the batteries just get 'smaller' inside.

    If you'd had enough panel the batteries could have lasted twice as long, believe it or not. Why, one poster here recently reported she got 15 years out of a set of L16's! That has to be a record.

    1800 Amp/hrs (16 T105's @ 12V) would require about 1500 Watts of panel, two charge controllers to handle it, and a whole lot of very well-balanced wiring to keep current flow even. 400 Watts of panel will charge one set of T105's @ 14.2V (two batteries in series). Six years is the manufacturer's "expected lifespan" BTW.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: Putting together a solar system

    With a battery bank that big, you could probably draw ~10% off of just surface charge. I too made the same "mistake". I am still running a pair of l-16s that were on a system with ~100 watts of panel. ( was originally 4 batteries, two have croaked) I never drew them down much as they were so big, but they never got much current. The remaining two hold a charge just fine, but they have nearly no capacity to draw down. I leave them on a small system just to run a fridge igniter and a couple of lights.

    It has taken me a long time to realize the economy of proper sized batteries, well balanced between draw depth, draw current, charge current and charge times. Bigger is often not better. I have one pair of t-105s that are now in their 12th year, in limited service. These on the other hand have been on a system with ~5% charge, and they seem as strong as ever. Not bad for a pair of cheap batteries.

    Tony.

    PS BTW, 'Coot makes a point, if not in this thread, then another. Designing a system to have a minimum of ~10% charge current relative to battery Ah capacity, leaves some headroom for NET charge current. Just because you can make X amps, you have to factor in the on going loads so that the NET charge current is at least 5%. Makes me wish for another couple of panels!
  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
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    Re: Putting together a solar system

    One more question: What would be a fair price to offer my friend for his 8 10 year old BP 75w solar panels? I have to figure that if I buy new ones I will have to pay 11% duty to import them into Mexico and his are already imported.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: Putting together a solar system

    How good a friend?

    Personally, I would be hard pressed to pay more than ~$.50-.75/watt for them, plus a bit for shipping and importation. If the guy was a real friend and I had tons of money, maybe $1/watt.

    The reality is,, they are worth what someone is willing to pay. Since shipping is not an (easy) option (away from there) then the market is only those in the neighbourhood.

    Tony