Pre-Sale Questions | First Post! :)

SolaRAC
SolaRAC Solar Expert Posts: 52 ✭✭✭✭
Hello all!

This my first post and I want to ask a few questions before I make my first purchase. I have no experiance with Solar Panels but I did spend quite some time reading through guides online and posts on this forum.

I've been searching for through Amazon, Froogle and broad searches on Google for the best prices on panels. The best prices I found thus far was on sunelec dot com. I have found panels on this site for as low as $1.34 per watt. Do you guys have any experiance with puchasing from this site?

Right now I have my eyes on this panel: SV Solar Panel 200 Watts 18.30 Vmp
$268.00 Any experiance with this brand/model?

I'm looking to get the best bang for my buck on a small system. I already have a marine 12v 79AH battery and a 400watt inverter. All I need now is a panel and a charge controller. What I plan to get from my setup is a goood understanding on Solar Panel systems and exactly what all this talk about watts/watt hours/amps/amp hours really means.


Thanks in advance,

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Pre-Sale Questions | First Post! :)

    This forum is actually paid for and hosted by Northern Arizona Wind & Sun--We try to avoid turning threads into hunts for the cheapest prices on the Internet and/or free advertising for their competitors. NAWS tries to offer pre and post sales supports for their brick and mortar store and their Internet store front.

    Other than the two admins here (Rick and Windsun), the rest of us are moderators and folks posting questions+answers.

    Specifically, Sunelec has sold many panels for very low prices--And most folks posting here have had pretty good luck with them. It is recommended that you do your homework (system design, researching components) when working with Sunelec.

    Here is a Google search of this forum where you can read about them in various threads.

    And with all vendors, make sure you understand their shipping and return policies. Packing, shipping, and insurance costs can be high on small shipments (vs pallet loads of panels). They are, for the most parts, single weight glass in thin aluminum frames. So it can be expensive to get them on your front steps.

    Sunelec tends to have a lot of good prices on overrun panels, blems and such... They may not offer complete guarantees on all products (I don't work for them, and I have not purchased anything from them--so I cannot really help you more).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Pre-Sale Questions | First Post! :)

    I'll just go for the easy one and mention that you aren't going to be happy with a "Marine" battery as they are not true deep cycles. For 79 Amp hours of battery you only need about 123 Watts of panel to recharge it.

    Generally the recommended recharge peak current should be 10% of the battery's Amp hour rating. That works out like this (rough calculations):
    7.9 Amps * 12 Volts nominal = 94.8 Watts, less the 77% efficiency derating = 123 Watts.

    Watts: Volts * Amps
    Watt hours: Watts * hours.

    If something draw 1 Amp @ 12 Volts that's 12 Watts. If you run it for an hour that's 12 Watt hours.

    Amp hours is the usual method of rating a battery's power storage capacity. It relates to Watts hours by dividing by Volts: 12 Watt hours / 12 Volts = 1 Amp hour.

    When designing a system for any type of use the procedure is to start with the loads. If you need a maximum of 500 Watts you need at least a 500 Watt inverter. If you need 1000 Watt hours daily then you need to supply that with a certain amount of battery capacity, vis: 1000 Watts hours / 12 Volts = 83.3 Amp hours.

    BTW, our host NAWS sells quality panels at reasonable prices: http://www.solar-electric.com/hiposopa.html

    Never heard of SV panels myself. Perhaps someone else has?
  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    Re: Pre-Sale Questions | First Post! :)
    I'll just go for the easy one and mention that you aren't going to be happy with a "Marine" battery as they are not true deep cycles. For 79 Amp hours of battery you only need about 123 Watts of panel to recharge it.

    I intend to get something better but for now I'm gonna start my testing with this marine battery.

    As for the wattage requirements to charge a battery... the idea I got was that any panel can charge my battery. The concept I had in mind was that a 10 watt panel could charge my battery only it would take 10 times as long as a 100 watt panel. Could you please elaborate a bit more on this?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Pre-Sale Questions | First Post! :)

    For a variety of reasons... A good rule of thumb for charging current for a flooded cell lead acid battery should be around 5% to 13% of the battery's 20 Hour Rate (in Amp*Hours).

    Also, I like to recommend to derate the solar panels + charge controller by ~0.77 (77% of rated solar panel name plate).

    So, for a 79 AH @ 12 volt deep cycle battery, I would start with:
    • 79 AH * 14.5 volts charging * 1/0.77 panel derating * 0.05 rate of charge = 74 watt solar panel minimum
    • 79 AH * 14.5 volts charging * 1/0.77 panel derating * 0.13 rate of charge = 193 watt solar panel maximum cost effective [fix typo]
    Below ~5% rate of charge, it takes a long time to recharge the battery (can make batteries sulphate quicker), self discharge of older batteries becomes a significant loss, and proper mixing of electrolyte to reduce stratification (acid at bottom and mostly water at top of cell).

    13% is usually the maximum recommended long term rate of charge for a flooded cell battery... Higher rates can cause batteries to overheat (if done for many hours).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Pre-Sale Questions | First Post! :)
    SolaRAC wrote: »
    I intend to get something better but for now I'm gonna start my testing with this marine battery.

    As for the wattage requirements to charge a battery... the idea I got was that any panel can charge my battery. The concept I had in mind was that a 10 watt panel could charge my battery only it would take 10 times as long as a 100 watt panel. Could you please elaborate a bit more on this?

    Well, to some extent any panel can charge a battery providing it develops more Voltage than the battery can; the V difference equates to current flow and that means some charging is taking place. In practicality it doesn't really work that well.

    There was a time when panels were really expensive and batteries were really cheap and everyone was sold the idea that if you waited long enough a small amount of panel would recharge a large amount of battery. The batteries in these applications didn't last long, because batteries like to be recharged at a certain minimum rate and preferably all in one go. That helps them last for many years. Back then if you had to replace them every two or three years, so what? Now the economics have changed: the panel prices have come way down and the battery prices have gone way up. So now it's best to recharge at the recommended rate, which is usually a net peak current of at least 5% of the battery's "20 hour" Amp hour rating. Some manufacturers recommend higher rates; Trojan prefers 10%, and when it comes to "net" charge rate you have to subtract any current going out to run loads from whatever current is going in to charge the battery. So shooting for 10% tends to get a pretty good panel-to-battery ratio that will keep things going for years to come.

    On the fringe, batteries have a self-discharge rate which increases over time. It is entirely possible to have panel so low in Wattage that it literally does nothing for recharging the battery even though there is current flow because the self-discharge consumes any charging gain.

    And then there's the nightmare of sulphation. This will happen to batteries anyway, but batteries that aren't quickly recharged or that are left below optimum charge for too long end up getting their plates coated with an insulating layer of sulphur crystals from the acid content of the electrolyte long before they should. No matter what anyone says, it doesn't come off. It does decrease the battery's effective Amp hour capacity.

    Just about a week ago I pulled four that had suffered this fate. They charge up nicely to the Voltage set point. Quickly too. That's because the plates are coated and instead of having 160 Amp hours capacity they have about 25 now. They were 3 years old. Now they're scrap metal. :cry:
  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    Re: Pre-Sale Questions | First Post! :)

    where do you live? shipping on one panel might be %50 to 75% of the overall cost so gettting it to you is a major expense.

    Sunelec has messed up all 3 orders I've placed with them.
    1st one they had an intern size up a grid tie system with an inverter that needed more panels than they sold me to even meet it's start up voltage. Asked them if I could return inverter and they said it had to be in original box, but I threw away box already. should of double checked their math before the order and deffinetely before I threw out the box. Lesson learned.

    2nd order they said they did not have the 220W panels I wanted, but they could sell me the 185 watt ones. Less than a week latter they emailed me and said they had the 220W ones after all.

    3rd order. Again one of their interns took my order, I wired funds to them immediately. Then the intern ignored my emails for a week. Finally called and asked them what was going on and they said that intern no longer worked for them. Was told panels would be in two weeks, waited a month, still no panels and finally emailed them to cancel the order.

    Many other companies have prices pretty close now a days if you but pallets at a time.

    But if you are looking for a single panel, just hunt around, no one is going to be that eager to just sell you a single panel anyways.
  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    Re: Pre-Sale Questions | First Post! :)

    Wow.. You guys have provided soo much useful information.

    BB went alittle over my head with the electolytes and stratification but I will eventually get it.

    Apparently I misssed out an important part in my research; optimal charge rates for batteries. None of the solar tutorials I read thus far even mentioned it.

    One other thing I'm not clear on with regard to charging batteries is how to determing how long it will take to charge one. Am I right with this formular:

    A completely dead 79AH battery (zero amp hours) recieving it's optimal charge rate of 10.27amps (13% of 79AH) woud be fully charged in 7hrs and 42mins? Here's how I cam to that:

    79AH/10.27AH = 7.69 = 7Hrs:42mins
  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    Re: Pre-Sale Questions | First Post! :)
    where do you live? shipping on one panel might be %50 to 75% of the overall cost so gettting it to you is a major expense.

    I live in the Bahamas.. 4-5 sun hours on average almost year round :)
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Pre-Sale Questions | First Post! :)

    The "I hate to say this answer" answer... yes and no.

    Yes, you have figured out the equations and their relationships (technically, we are talking about the 8 hour rate; 1/8 = 0.125 or rounded up to 0.13).

    The details:
    • Batteries will take "full rate" up to ~80-90% state of charge. At that point, the charge controller will hit the absorb charging voltage (say 14.5 volts for a 12 volt bank) and the battery will start to reduce current to near zero amps. That "absorb" time is typically around 2-4 hours or so.
    • Next, lead acid batteries for the last 10% or so of charging will convert some of that into hydrogen and oxygen gases (electrolysis). So, you will have to restore a bit more than 79 AH to fully recharge the battery.
    So, ~6-7 hours or so under full current, and another 2-4 hours or so under declining current (remember, basically 8 hour rate of charge here).

    The battery Electrolyte is a mix of sulfuric acid and distilled water (roughly 30% pure sulfuric acid?). Over time, it is possible for the denser (heavier) sulfuric acid to sink to the bottom of the battery and leave mostly water at the top of the cell (stratification).

    This is more of a problem with "tall" batteries and less than 5% rate of charge (some vendors recommend 10% rate of charge). With 5% or greater rate of charge, there are enough hydrogen/oxygen bubbles to mix the electrolyte.

    Shorter batteries and batteries in moving vehicles tend to have less stratification issues (AGM and GEL batteries have no stratification issues--AGM's can have a different issue, but don't worry about it here).

    Again, very rough numbers and physical descriptions... Good enough to get a handle on the issues (I am not a battery engineer by and stretch of the imagination).

    A couple of things to read:

    Deep Cycle Battery FAQ
    www.batteryfaq.org

    Batteries are about the easiest component to mistreat and damage through neglect (short of connecting +/- connections backwards to your electronics).

    Understanding and monitoring them will help to ensure a long life for your batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Pre-Sale Questions | First Post! :)

    A completely dead battery will not recharge. Drag a 12 Volt down below 10.5 Volts and chances are you won't be able to bring it back up to 12.7. If not the first time, certainly with repeated discharge.

    As for recharging a battery that isn't below 50% (for standard FLA's), it's not as simple as "50 Amp hours used, recharge at 10 Amps, total recharge time 5 hours". Would that it were! But batteries aren't linear and neither are chargers. Look up the Peukart effect and you'll see what I mean.

    Basically, during discharge the Voltage falls off quickly at first, then settles down and drops slowly, then it falls off quickly again. This algorithmic curve will vary according to the battery and the rate of discharge. For charging it's reversed: the Voltage should come up quickly at first, then plateau for awhile. Getting the last 10% "back in" takes a long time compared to the first 10% or the middle 30%, so to speak. And as the Voltage rises the current inevitably tapers off because the internal resistance is increasing and the Voltage differential is decreasing.

    One of the other reasons for shooting for "10% charge rate" is so that the whole Bulk, Absorb, and maybe a bit of Float charge process can be completed in one day before that 4 or 5 hours of "equivalent good sun" is gone.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Pre-Sale Questions | First Post! :)

    the sv pvs are sovello and are similar to the evergreens, but no certification here in the states. the company in question selling the pv has had issues and is reflected in their bbb rating.

    i agree that a pv of that size may be overkill for a 79ah battery, but there is always a but. you may wish to draw from the battery while charging and that would detract from the charge reaching the battery by the amount of the load. if you expect a larger battery in the future then just put a load on the pv instead of the battery to draw down the power sent to the cc and battery for now and that would automatically stop when no there's no sun. fans can be a useful load to do this with if they can take the voltages involved. it can be put to the battery too if you are there to connect/disconnect at the right times. if you always intend to have a battery about at the 79a capacity then gear it down to a smaller pv roughly in the range bb explained. btw, that 12.5% or 13% isn't all that concrete as most batteries can have higher charge rates usually with a bit more water usage. this can vary too much between manufacturers with the maximum charge rate and a good compromise on the maintenance so we roughly go with a 13% max overall. i wouldn't worry too much if the % was say 13.5% or even 14% in most cases if you can handle the extra maintenance.

    coot,
    just to clarify, a battery drawn down to 10.5v at rest voltage with no cell reversal, shorts, or opens may only suffer a severe degrading on the cycle life of the battery. a battery can only do this so many times and is at risk of catastrophic damage to a cell going reversal, shorting, or opening every time it happens.
  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    Re: Pre-Sale Questions | First Post! :)

    I didn't noticed until a few minutes ago that my thread went on to a second page.

    niel/Cariboocoot: Thanks for clearing things up for me. I was speaking hypothetically with the 0Ah (completely dead) battery. Your answer however was very helpful. This battery stuff has alot of factors involved.

    I'm glad I created this thread because you guys helped me realise how little I knew and still don't know about batteries. One key point I learned recently is that I need to shoot for double the Amp Hour capacity required for my load to ensure that I don't go below 50% of my stored charge. I actually found a good calculator that helps you spec a system starting from your watt demand:

    http://www.batterystuff.com/solar-calculator.html

    Funny thing is, I don't even know how good my battery is; I don't have a volt meter yet and I haven't applied a charge or load to it in more than 10 months. The last time time it was connected it was probaly powering my bilge pump while my boat was docked (in a discharge state); hopefully I don't need a new battery.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Pre-Sale Questions | First Post! :)

    I would suggest this DC Current Clamp Meter for first DMM when working with solar/batteries/etc... Current clamp meters are much safer and more useful for DC power systems--You don't have to break wires to measure current and these meters will read up to 400 amps--much higher than the 10 amp maximum for typical DMMs

    Note: DC current clamp meters are not that accurate at lower currents and tend to drift--Like every tool, they have their limits.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Pre-Sale Questions | First Post! :)

    10 months is way too long between charges. you need to charge it now and hope that no severe sulfation has taken place. you could charge it with a regular battery charger, but due to there being no regulator in most standard chargers you will have to disconnect it before it goes beyond the absorb set point voltage. i don't remember if you said it was a standard fla battery or an agm. the fla will take overcharge voltages better so you could go .1 or .2v higher than the absorb point. agms are sensitive to overcharge voltages so do not go beyond the absorb voltage setpoint on this type. this will only get it to 80 or 85% charged and a good absorb charge is needed to finish it up.

    i forgot you said you don't have a voltmeter so take it somewhere that can get it charged up and in the meantime if you can put jumper cables to it from a car that might get it semi started. engine running of course.
  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    Re: Pre-Sale Questions | First Post! :)
    BB. wrote: »
    I would suggest this DC Current Clamp Meter for first DMM when working with solar/batteries/etc...

    I think your link is dead.. what's the brand/model info?

    I'm actually looking up data loggers with a computer interface (prefferably USB or Ethernet). Might be overkill for a small system but I would like to be able to analyze this info.. see how close the theory I'm studying now lines up with practical.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Pre-Sale Questions | First Post! :)

    Sorry, both my link and your copy have been fixed. $60 from Sears:

    www.sears.com/shc/s/p_10153_12605_03482369000P?

    Note that this meter is still handy for debugging systems...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Pre-Sale Questions | First Post! :)
    BB. wrote: »
    Sorry, both my link and your copy have been fixed. $60 from Sears:

    www.sears.com/shc/s/p_10153_12605_03482369000P?

    Note that this meter is still handy for debugging systems...

    -Bill

    I definitely have to get me one of those! Thanks for the link BB !
  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    Re: Pre-Sale Questions | First Post! :)

    Bad news.. I just put a voltmeter to my marine battery and got an 11 volt reading? :cry:

    Update: It appears this cheap voltmeter isn't all that accurate.. it's now fluctuating betwen 11 and 12 volts. I'm guessing my battery is 11.x volts but this dumb meter is rounding down :/
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Pre-Sale Questions | First Post! :)
    SolaRAC wrote: »
    Bad news.. I just put a voltmeter to my marine battery and got an 11 volt reading? :cry:

    Under what circumstances?
    As a resting Voltage (nothing attached, no current in or out for at least two hours) that's not good. You definitely need to charge it some way and see if it comes up to a usable level.

    As a recently discharged Voltage it's lower than you'd want to go on a regular basis. Again; get it charged and see what happens.
  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    Re: Pre-Sale Questions | First Post! :)

    Here's what I did..

    First remember that the battery has been sitting for a long time and it was last in a discharge state; it powered my boat then I might have used it to jump start my vehicle a months ago.

    Initially, I attached my cheap multimeter off it and got an 11 volt flat reading. I got a little impatient and attached my DC power supply to it for 20-30 minutes (250watts). It now reads 12 volts flat. Once again I think the meter doesn't read down to the tenth decimal place.

    Using the formular I learned from this forum, I should be charging this 79Ah AGM battery at 10.27 Amps.(13% of the amp-hour capacity). I think my power supply pumped 250watts/12v=20.8 Amps to it (double my suggested charge rate).

    I know I know.. I will be properly charging this battery soon with either a propper charger or my first panel. Could I have done any damage in my ~21 Amp 20-30minute charge?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Pre-Sale Questions | First Post! :)

    First problem: leaving a battery sit in a semi-charged state. Not good; shortens the lifespan.
    Second problem: a power supply isn't a battery charger. It isn't going to even approximate the 3 stage charging profile. If it's fixed at 12 Volts it's not gong to do as good a job as even a cheap automotive-type charger. You really want to get it up to 14.4 Volts and keep it there until the current drops off to about 1-3 Amps.
    Third problem: putting 20 Amps to it when 10 Amps is the most it should have can heat the plates and boil off a lot of water. Briefly may not have done much damage, but repeatedly will.

    You sure aren't doing that battery any good. :cry:
  • SolaRAC
    SolaRAC Solar Expert Posts: 52 ✭✭✭✭
    Re: Pre-Sale Questions | First Post! :)
    First problem: leaving a battery sit in a semi-charged state. Not good; shortens the lifespan.
    Second problem: a power supply isn't a battery charger. It isn't going to even approximate the 3 stage charging profile. If it's fixed at 12 Volts it's not gong to do as good a job as even a cheap automotive-type charger. You really want to get it up to 14.4 Volts and keep it there until the current drops off to about 1-3 Amps.
    Third problem: putting 20 Amps to it when 10 Amps is the most it should have can heat the plates and boil off a lot of water. Briefly may not have done much damage, but repeatedly will.

    You sure aren't doing that battery any good. :cry:

    .............Duly noted.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Pre-Sale Questions | First Post! :)

    interesting that it wasn't duly noted in my post #15.:roll: