Solar cell grades

Will2020
Will2020 Solar Expert Posts: 62 ✭✭✭✭
Hello all, I'm considering buying a UL 130 watt solar panel from ebay for $350 shipped. The cell type is a multi crystalline silicon variety with type 12 A solar cells.

A second option is a 130 watt panel made by Best buy solar for $360 plus s&h which is made of polycrystalline with type A solar cells.

Is there a difference between 12A and A for the cell type?

What about polycrystalline and multi crystalline silicon?

Are these panels worth it, or should I go for a better brand, thanks.
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar cell grades

    Please compare it to this "name brand" Kyocera with 25 year warranty: http://store.solar-electric.com/kyso130wa12v.html

    In practical terms there is no functional difference between them. 130 Watts is 130 Watts.

    Be sure to check the S&H costs as well as the warranty.

    If it were me, I'd spend $15 more for the Kyocera.
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Solar cell grades

    exactly what are you trying to power, please stay away from the "Ready, Fire, Aim" syndrome.
  • Will2020
    Will2020 Solar Expert Posts: 62 ✭✭✭✭
    Re: Solar cell grades

    Thanks Cariboocoot. I like the sound of the Kyocera panels for around the same price, I have to call and find out how much the shipping is though.

    Both companies give a 2 year warranty and the shipping is included for the UL solar panel. But who knows if these offbrand companies will be around in the future.

    As for my "powering requirements" I am going off grid with my camper and will be running led lights, I have not bought all of them yet, but I am estimating no more than 20-30 watts maximum at night.

    Also have a 12 volt vent fan, which will be run intermittently.

    A laptop computer and a Power tool charger (occasionaly)

    If would also like to run an extension cord to 110 volt power tools if needed.

    I am moving to a cold weather area and would like to have additional power for the future, some other camping buddies may need some of my juice at night.

    I am not sure what size inverter I need, I was thinking around a 1000-2000 watt.

    I built a battery box which will hold 3 batteries. I am not quite sure which ones I need for this setup. I was thinking along the lines of Trojan t1275s with 150AH a each. Is this way too much for this particular setup? Could I use smaller less expensive batteries?

    Would 3 6 volt golf cart batteries do the trick? Or use 3 12 volts?

    Any help or product recommendations would be appreciated.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar cell grades

    What solar_dave said.

    I swear there's some evil, mad solar-scientist out there getting everyone to plan their systems backwards!

    You start out with "a few LED lights" and then before you know it your loads include "110 Volt power tools". There's a whopping great difference between these two load requirements, and it's a difference of "one panel isn't going to do it".

    What you can expect from a 135 Watt panel: enough charge current to handle 76 Amp hours of 12 Volt battery, which would be 450 or so Watt hours per day maximum. Looking at the "rule-of-thumb" harvest rate you get similar results: 135 W @ 80% efficiency average * 4 hours "good sun equivalent" = 432 Watt hours.

    Start running things and see how fast that power gets used up!

    To do it right (so that you're not disappointed with the results) you need to determine your loads. A good fix on maximum Watts and daily Watt hours is essential. Then you can get a proper size (and type - battery chargers tend to not 'like' MSW nor do power tools) inverter and the battery bank capable of supply the daily power needs. That determines how much panel you need to get recharged.

    Otherwise you find yourself in the "Oops! Out of power!" situation too often.
  • zeuspaul
    zeuspaul Solar Expert Posts: 59 ✭✭✭✭
    Re: Solar cell grades

    Will

    To get shipping cost I placed the Kyocera in the shopping cart then went to checkout. Then I put in my zipcode and hit *apply* and the shipping cost was indicated.
    It arrived by UPS quickly and in good shape. It is the largest panel I could get shipped by UPS.

    Zeuspaul
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar cell grades

    Shipping costs for single or small numbers of solar panels can be highly variable--I would suggest calling the vendor to confirm actual shipping and insurance costs for your order.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Will2020
    Will2020 Solar Expert Posts: 62 ✭✭✭✭
    Re: Solar cell grades

    Here are my specs

    1 vent fan which pulls 3 amps on high. I will most likely not run every day, 3 hours on hi will be 108 watts

    21 watts of led lights x 8 hours for 168 watts

    4 amp shurflo water pump x 1 hour 48 watts

    My laptop charger says 1.5 amp input, 3.42 amp output. Will use around 5 hours. I am not sure of the wattage on this. Maybe 18 watts/h, so 90 watts?

    This comes to a total of 414 daily watts if my calculations are correct. So if I had a 135 watt solar panel pulling 432 watts daily, it should cover this right?

    I believe the inverters pull some amps as well, but I am unsure which one will best suit my application.

    The numbers I have given are maximum and my daily usage could be cut down to make room for the inverter amps.

    I would like to keep it around 400-450 watts daily.

    What would be the best battery combo for this? Should I use 2 deep cycle 6 volt T-105 Trojans or Crowns? Or will a single deep cycle 12 volt work for this?


    I would like to build a battery bank and add more panels in the future for the fridge (which is on propane at the moment), and a power tool charger so I will not skimp on battery quality.

    Any help on what the best inverter or battery combo would be greatly appreciated.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar cell grades

    The problem is that the panel capacity has to match up with the battery capacity. If you stick with one 135W panel, the best you could expect to charge is about 150 Amp hour AGM type (they don't require as high a charge rate as the less expensive FLA type). So you'd be looking at something like this:
    http://store.solar-electric.com/de8a104ampho.html
    At 104 Amp hours, it would just make your needs at 400-500 Watt hours (if we can count on that figure).
    It is difficult to increase battery bank/panel size later, as it is not a good idea to mix older batteries with newer batteries. Absolutely never mix different types or capacity of batteries.

    Are we talking about a mixture of DC and AC loads? That can be problematic too.

    Otherwise there are several light-duty sine wave inverters from Samlex that might work:
    http://store.solar-electric.com/sasiwain1.html

    These do not have a built-n charger. If you're going to go "whole hog" consider the Magnum inverters:
    http://store.solar-electric.com/maenms2020wa.html

    Personally I think you're right to want to use a pair of T105's. At 225 Amp hours, you could safely use just 25% (longer battery life) for 600 Watt hours of power. But you would need more like 400 Watts of panel to charge them. At a minimum, it would require two of the 135 panels:
    270 Watts @ 80% = 216 / 14.2 = 15 Amps approximately 6.5 percent charge rate, daily harvest around 864 Watt hours.

    In any case you will need a charge controller. One example: http://store.solar-electric.com/pros15solcha.html (Would work with the example above).

    PLEASE keep in mind these are generalizations. Information just to "get you in the ball park". Solar is site specific. I don't know how good your insolation is or how long your downlead will be, et cetera.
  • azrc
    azrc Solar Expert Posts: 43
    Re: Solar cell grades

    I hate to be pedantic, but watt is a unit of rate, like GPM and Whr (or kwhr) is unit of energy...It makes things a little confusing when used interchangeably.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar cell grades
    azrc wrote: »
    I hate to be pedantic, but watt is a unit of rate, like GPM and Whr (or kwhr) is unit of energy...It makes things a little confusing when used interchangeably.

    :confused:

    This is in reference to what?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar cell grades
    Will2020 wrote: »
    Here are my specs

    1 vent fan which pulls 3 amps on high. I will most likely not run every day, 3 hours on hi will be 108 watts 3 amps * 12 volts * 3 hours = 108 Watt*Hours

    21 watts of led lights x 8 hours for 168 watt*Hours

    4 amp shurflo water pump x 1 hour 48 watt*Hours

    My laptop charger says 1.5 amp input, 3.42 amp output. Will use around 5 hours. I am not sure of the wattage on this. Maybe 18 watts/h, so 90 watts? 18 Watt*Hours

    This comes to a total of 414 daily watt*Hours if my calculations are correct. So if I had a 135 watt solar panel pulling 432 watt*Hours daily, it should cover this right?
    ...
    I would like to keep it around 400-450 wattHours daily.
    ...

    I am not trying to "pick on Wil"--Just showing where the confusion comes from...

    Watts and Watts*Hours=Watts in the above paragraph... They are not the same thing (Watts*Hours=WH)

    God knows I confused Watts and Watt*Hours through a fair number of classes in my day.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Will2020
    Will2020 Solar Expert Posts: 62 ✭✭✭✭
    Re: Solar cell grades

    I'm thinking about purchasing the Kyocera 135 watt panel from the store. That particular model has an upgrade to a junction box for $75 more.

    What is the benefit of buying one already equipped with the junction boxes? Is it less wiring. less hassle?


    Here are my new specifications.

    13 amp Carrier a/c 8*13= 104 ah

    3 amp fan 3*3=12 ah

    2 amp Dometic fridge 2*24=48 ah

    4 amp water pump 4*1=4 ah

    30 watts led lights 30w*8=240/12= 24 ah

    1.5 amp laptop 1.5*8= 12 ah

    204 amp hours 204*12= 2248 watt hours?

    What is the "professional" way to calculate these numbers?



    Would 4, 135 watt Kyocera panels hooked to 3 Concorde Lifeline 105 ah batteries suffice for this kind of load?

    540*80% =432 watts * 4 hours full sun = 1728 watt hours?

    Am I in the ballpark with the numbers?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar cell grades
    Will2020 wrote: »
    I'm thinking about purchasing the Kyocera 135 watt panel from the store. That particular model has an upgrade to a junction box for $75 more.

    What is the benefit of buying one already equipped with the junction boxes? Is it less wiring. less hassle?
    If you are connecting a lot of panels together--the pre-cabled/connector panels are much easier/quicker to connect.

    I used to think that getting away from junction boxes was a mistake--But now, I am not so sure. The costs seem to be lower and the MC4 (and the older MC3) connections seem to be more weather proof (aka reliable).

    For a small system, just purchase some Male/Female jumper cables, cut them in 1/2, and wire the cut ends into the rest of your system. Getting the crimp tooling and components are really only cost effective for doing a large installation (something like $600 just for the manual crimping tool).
    Here are my new specifications.
    • 13 amp Carrier a/c 8*13= 104 ah
    • 3 amp fan 3*3=12 ah
    • 2 amp Dometic fridge 2*24=48 ah
    • 4 amp water pump 4*1=4 ah
    • 30 watts led lights 30w*8=240/12= 24 ah
    • 1.5 amp laptop 1.5*8= 12 ah
    • 204 amp hours 204*12= 2248 watt hours?
    What is the "professional" way to calculate these numbers?

    My first question is "at what voltage" are these Amp*Hour numbers (12 volts, 24/48 volts--Or even some at 120 VAC)?

    Assuming they are all at 12 volts (Carrier A/C?)--You have your "daily load" in Amp*Hours @ 12 volts (or Watt*Hours). Also need to know the peak current (sizing wiring, surge current for battery bank, AC inverter if used, etc.).
    Would 4, 135 watt Kyocera panels hooked to 3 Concorde Lifeline 105 ah batteries suffice for this kind of load?

    540*80% =432 watts * 4 hours full sun = 1728 watt hours?

    Now, we need to look at the deratings... A good starting point is 0.77 derating for solar panels and the charge controller. Another 0.80 derating for flooded cell batteries (discharge/charging power). And if you have an AC inverter, another 0.85 derating (ignore for now):
    • 0.77 * 0.80 = 0.616 = 0.62 DC derating for solar PV system...
    So, to figure out the amount of solar panels you would need for a minimum of 4 hours of full sun equivalent per day:
    • 2,248 WH per day * 0.62 derating * 1/4 hours of sun per day = 906 WH minimum of solar panels
    • 906W / 135 watts = 6.7 = 7 panels minimum...
    Would I suggest more panels (upwards of 14 panels) to allow for gradually increasing loads and system aging... Yea. But you could start with 7-8 panels and see how things work out... Typically, our battery recommendation of 3 days of no sun and 50% maximum discharge (for long life) would give you a 12 volt battery bank of:
    • 2,248 WH * 1/12 volts * 3 days * 0.50 max discharge = 1,124 AH @ 12 volts
    That would work well with an maximum array of:
    • 1,124 AH * 14.5 volts charging * 1/0.77 panel-controller derating * 0.13 max charging current = 2,752 Watts for a "large" array on that battery bank.
    One other thing to think about... Even with the ~900 watt array, you are looking at nearly 60 amps of charging current...

    Normally, as the system size gets larger, we suggest people look at 24 or 48 volt battery banks. Low voltage/large AH capacity battery banks (and their related charging/discharging currents) can be a real pain to deal with (lots of thick copper cables, heavy fuses/breakers, and multiple 60 amp charge controllers, etc.).

    Going with a higher voltage system make it much easier to send significant power any distance... With 12 volts, you can have ~1.0 volt drop in your wiring (11.5 volt loaded battery and 10.5 volt cutoff for many 12 volt devices).

    With 48 volt systems, you have 1/4 the current and a 4 volt allowable voltage drop (~46 volt battery and 42 volt cutoff)...

    If your system is entirely 12 volt DC--I can understand trying to design the battery / power system around 12 volts.

    But do a paper design first and make sure that you can get everything to work well for your needs (voltage drop, copper wire sizes, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Will2020
    Will2020 Solar Expert Posts: 62 ✭✭✭✭
    Re: Solar cell grades

    It is a camper which has both 12 volt and the 120 plug. I plan on using an inverter to run the Carrier a/c, and some of the wall sockets for the led lights.

    The panels will be mounted on top of the camper, so I can not see the cables being more than 25-30 feet in length maximum.

    Is there any way to upgrade the system to a 24v or 48v?

    What is the derating for agm batteries?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar cell grades

    You can use a derating of 0.90 for an AGM battery.

    And for AC appliances use a derating of:
    • 0.77 panel+controller * 0.80 flooded cell * 0.85 inverter eff = 0.52
    • 0.77 panel+controller * 0.90 AGM * 0.85 inverter eff = 0.59
    Now, remember the above are estimates and that a solar system's output is dependent on how much sun you had that day--Average values, best summer months, etc. are just guidelines. If you need the power regardless of the sun, you will need a generator+charger setup. If you don't need the power (optional loads), then you will have to turn them off when the power is not available (not much sun, discharged battery bank).

    If you are looking for a nice Off-Grid friendly A/C system--Take a look at the Sanyo Mini-Split thread. Very efficient and can be set on low and run on 300 watts all day long.

    However--Even the Sanyo is a very efficient and Off-Grid power friendly device--In general, I really doubt that any RV (short of a tractor/trailer or full size bus system) will be able to carry enough solar panels and battery bank to make for a practical/portable solar power system.

    Solar panels and battery may help reduce fuel usage / genset run-time. But, the physical size/weight may be too big a penalty for a typical RV'er.

    Also, if you do need to maximize your solar power generation--you probably need to look at panels you can tilt to the latitude of where you are camping and account for seasonal changes (summer/winter). A fixed flat PV panel array on the roof will only work fairly well for summer in the lower 48 states (and south).

    You can use a program like PV watts website to experiment with locations and panel arrangements to see what works well for your setup.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Will2020
    Will2020 Solar Expert Posts: 62 ✭✭✭✭
    Re: Solar cell grades

    After extensive measuring on the roof of my camper, I can not use the Kyocera 135s the way intended. (which really stinks because they can be shipped to my door for $400)

    One of them may fit, but then the mismatching of panels would be required. I would like to go with the same brand/size solar panels all the way around.

    They Kyocera are 26" wide, I need 21-22" panels in order to bypass the a/c, vents, and the smokestack. So it looks like I'll be downgrading to 100 watt panels (as these fit the measurement requirements)

    What do you think of these? http://store.solar-electric.com/sw100cpa.html

    The ad says they are not true 12 volt panels and the have to be wired in series. I intend on buying between 4-6 of the 100 watt panels. Is it possible to wire that many up to a 12 volt? It is also a tad bit over my measurement range.

    Another option are these Ja Solar from ebay with a 5 year full, and 25 year output warranty.

    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=290466139741

    These fit my measurement requirements perfectly and are 5 pounds lighter than the Sunwize.

    All bias aside, which is the better panel? The store sells an 85 watt Kyocera for $400, which is too expensive. I would like to purchase my panels from the store for further technical support on here, but is that required?
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Solar cell grades
    Will2020 wrote: »
    The ad says they are not true 12 volt panels and the have to be wired in series.

    Well, not exactly. Their Vmp (voltage max power - i.e., under load) is 23v which is quite a bit higher than what you'd want for charging 12v batteries. It would work, power would flow from high to low, but the voltage mismatch would be pretty inefficient.

    For a system over 12v, such as a 24v system, the 23v Vmp of those panels is too low to push the batteries up to a full charge at 28.8v. So, for a 24v or 48v system you must wire them in series.

    So, for a 12v setup, you can wire them in parallel, but you pretty much have to use an MPPT controller since it will lower the voltage and minimize the mismatch inefficiency. On the plus side, by lowering the voltage you kick up the amperage, so not only will the batteries absorb the juice faster (because of the decreased mismatch inefficiency), there is more amperage available for them to absorb.

    Actually, to use those panels to charge batteries at all you pretty much have to use an MPPT since wiring two in series would give 46v, which would be a hefty mismatch when charging a 24v system, and wiring three in series to get up over 48v would be 69v and once again you have a significant mismatch.

    I intend on buying between 4-6 of the 100 watt panels. Is it possible to wire that many up to a 12 volt?

    Sure. You just have to make sure you have a big enough controller to handle the amperage.


    EDIT: Oh, and the tech support question. NAWS owns and runs this forum, but it's moderated by volunteers who are not affiliated with NAWS and NAWS employees pretty much just leave us to do our own thing.

    So it doesn't matter where you buy your gear, you can still get help on this forum. Just *please* don't call NAWS for support on gear you bought from their competition. That would just be rude. :D
  • Will2020
    Will2020 Solar Expert Posts: 62 ✭✭✭✭
    Re: Solar cell grades

    Okay then , I looked at the measurements again and I can not use the sunwise, they are too wide at "22.81" I need something under 22"

    Does anyone have recommendations for a 100 watt panel for a decent price? Is JA Solar a reputable company?

    Also, will a 100 watt panel be enough to charge a 105 ah agm battery?

    100*80%=80*4=320 wh <is that correct?

    I have a battery rack built for 3 batteries and will have 315 ah total, how many 100 watt solar panels would it take to fill these up daily?

    What type of charge controller would handle this load?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar cell grades

    You might try calling NAWS and other dealers--They might have some orphan panels (a handful or less) that are not worth advertising in their webstore, in the warehouse, that may meet your needs and at a good price (neither Niel nor I work for NAWS or any other solar vendor--so we cannot tell you what they may have available).

    As to a recommended solar array size... Assuming 315 AH @ 12 volts and the 5-13% rule of thumb for charging current/power, and 0.77 derating of solar panel marketing specs. + charge controller efficiency:
    • Panel Watts = 315 AH * 14.5 volts charging * 1/0.77 derating * 0.05 charge ratio = 297 Watts minimum
    • Panel Watts = 315 AH * 14.5 volts charging * 1/0.77 derating * 0.13 charge ratio = 771 Watts maximum
    So, the optimum array for charging an average flooded cell battery bank would be in the ~300-800 watts of solar panel.

    AGM's will give you about another 10% more power (over flooded cell batteries). AGM's are almost perfect lead acid storage batteries (don't leak, don't normally vent hydrogen gas, ~90% efficient vs ~80% for flooded cell, no electrolyte maintenance)--But that costs you about 2x what flooded cell batteries would.

    Also, I would recommend a Battery Monitor too--Almost mandatory if you have AGM/Sealed batteries as you cannot use a hydrometer to measure their state of charge.

    Regarding:
    100*80%=80*4=320 wh <is that correct?

    I am not quite sure what you are asking/telling me... I am guessing you are trying to figure out how much useful energy is in a 100 AH 12 volt battery?
    • 100 AH * 12 volts = 1,200 WH = 1.2 kWH of Energy
    • 100 AH * 12 volts * 0.80 max discharge = 960 WH of "Useful" Energy
    • 100 AH * 0.80 = 80 AH of useful "Amp*Hours" (same as useful energy without knowing the bank voltage).
    If you discharge below 20% state of charge (80% state of discharge) you run the risk of taking a "weak cell" through zero volts and actually begin "reverse charging" of the cell--Pretty much instant cell death. (battery cell AH storage can vary by upwards of 20% in a string of cells).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Solar cell grades
    Will2020 wrote: »
    Okay then , I looked at the measurements again and I can not use the sunwise, they are too wide at "22.81" I need something under 22"

    Does anyone have recommendations for a 100 watt panel for a decent price? Is JA Solar a reputable company?

    Dunno. Never heard of them.

    I should probably also have mentioned that it's somewhat frowned upon to link to NAWS competition or do comparison shopping on the forum. The reason is not that NAWS doesn't like the competition - but what happens is that when people see a link here in the forum, then go out and buy that product, they somehow get the impression that NAWS endorses the product and they end up calling NAWS for support on products they bought from someone else.

    It's not a hard and fast rule and the mods generally let it slide unless it's some blatant attempt by NAWS competition to drum up business - but still...frowned upon.

    We try to be polite to our hosts for providing the best solar forum on the net.

    Also, will a 100 watt panel be enough to charge a 105 ah agm battery?

    Around here, it's generally recommended that you need a charging current of from 5% to 15% of the battery's amp hour capacity. 10% seems to be just about perfect all around, with maybe a touch higher for AGM and a touch lower for GEL.

    So for a 100ah battery, 5a would be right at the bottom of the sweet spot. 10a would be better.

    100*80%=80*4=320 wh <is that correct?

    The math checks, but what are you trying to figure out?

    EDIT: Just noticed a missing step. Formula also needs 320w x 1h to equal 320wh.

    I have a battery rack built for 3 batteries and will have 315 ah total, how many 100 watt solar panels would it take to fill these up daily?

    Depends on how much you take out daily.

    First of all, to keep batteries alive a long time, you want to drain them no more than 50%. Battery life is rated in cycles - drain them 20% and recharge and they might be rated to last 3000 cycles. Drain them 50% and they might only last 1500 cycles. Drain them 75% and they might only last 300 cycles. Drain them 100% and recharge, and depending on the battery, they might last 10 cycles or 100.

    But the deeper you discharge them, the more you shorten their life. Best is to plan on regular discharges of no more than 50%

    So if you have 300ah of battery, that means you would have about 150ah per day available to use.

    6 x 100w panels = 600w
    600w x 4 hours/day of good sun = 2400 watt*hours
    2400wh / 14.4 (battery voltage) = 167 amp*hours.

    So there is your max theoretical harvest. Now take some away for system losses and inefficiencies and you might actually get as much as 150ah actually into the batteries.

    So, with 300ah of battery and a daily power budget of 150ah, 600w of PV for 4 hours/day would be just about right to replenish the 150ah/day you use.

    HOWEVER...see the next question.

    What type of charge controller would handle this load?

    Wrong nomenclature. Type would be either PWM or MPPT. You mean size.

    600w of PV / 14.4v (battery voltage) = 42a

    So, to take full advantage of the PV output, you'd need something that can handle at least 42a of current on the output side to the batteries. Something like a TriStar 45a MPPT would be about right.


    But...10% charge current on a 315ah battery bank would be 31.5a.
    42a would be up just above 15%, which might be a just a touch too high - depending on your battery. Check your battery specs and find out what they need for charge current.

    In reality, they can probably handle 15% charging current, and it wouldn't be for long anyway, since the controller will back it down as the battery charges up.


    So...with 600w of PV and 300ah of battery and a 45a charge controller you would be just about right on the money and would have a 150ah/day power budget.
  • Will2020
    Will2020 Solar Expert Posts: 62 ✭✭✭✭
    Re: Solar cell grades

    Will do, no more competitor link posting from me.

    How do you find the charge current for 12v?

    When buying a panel for a 12v system, what should the "specs" be?

    Open Circuit Voltage:
    Short Circuit Current:
    Maximum Power Voltage:
    Maximum Power Current:
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar cell grades
    Will2020 wrote: »
    Will do, no more competitor link posting from me.

    How do you find the charge current for 12v?

    When buying a panel for a 12v system, what should the "specs" be?

    Open Circuit Voltage:
    Short Circuit Current:
    Maximum Power Voltage:
    Maximum Power Current:

    The main issue is the Vmp: it has to be above the charging Voltage for a "12 Volt" system, typically 14.2-14.4 Volts, and preferably above the equalization Voltage point of 15.

    Otherwise it's a matter of having sufficient current for the particular battery (5-13% of the Amp hours).

    Usually we see "not-quite-24-Volt" panels that have a Vmp of 26 or so. Looks like it might work until you realize that "24 Volt" systems actually charge at around 28.4 Volts!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar cell grades

    It is OK to post links for questions--We just try to avoid the "best deal" type stuff (once in a while is not going to get somebody banned here)... It also helps us to identify spam when somebody new just starts posting links to off-site stuff to, what turns out, to be their store.

    Generally, Vmp-stc > 17 volts (when used with a PWM/MPPT charge controller).

    If your Vmp-stc > 20 volts or so--then you should look at an MPPT type solar charge controller.

    If your array is less than 200 watts--probably only a PWM type controller.

    If your array Pwatts is less than 400 watts or so, either a PWM or MPPT controller would usually be fine.

    If your array is larger than 400 watts, a MPPT controller is probably a good idea.

    If your array is mounted a fair distance from the batteries/charge controller, you should also look at a MPPT controller.

    Isc--Does not matter--It is just defines the series fuse/breaker for the solar PV string.

    Voc--It depends on the charge controller... A PWM on a 12 volt battery bank, Voc is not going to be much over 21-22 volts anyway.

    For MPPT charge controllers, Voc may be ~35 volts, 57 volts, 75 volts, 140-150 VDC (or sometimes more). It just depends on the model that you select.

    For a larger MPPT charge controller, they typically max out at Voc=150 VDC. Because Voc rises as the temperature drops, it works out that Voc-max of 150 VDC means a Vmp-stc of ~100 VDC max for very cold climates (well below freezing).

    For many MPPT charge controllers, the optimum Vmp is ~2x Vbatt... But I would not go out of may way to configure a string for exactly that setup... The differences in efficiency are not that great (the battery voltage choice of 12/24/48 probably has a greater effect on efficiency).

    If the system is installed the Caribbean, then the Vmp can be higher because the panel never gets very cold (and Voc-cold does not go up very high).

    That is why many vendors make String Sizing Calculators for their products... There are a lot of variables/calculations to be made to find the right series/parallel configuration.

    Usually, the better questions to ask are--How many watts of solar panels do you want. Do you have a brand/model of solar panels you would like to use, where will the panel be mounted (close/far from charge controller), where is the system located (hot/cold/temperate climate), what type / brand / model / options like networking of charge controller are you interested in, and such.

    Also battery bank capacity (AH and volts), and any details about the loads would be helpful.

    We can walk you through a set of calculations and then you can tweak them yourself the next time.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Solar cell grades
    Will2020 wrote: »
    How do you find the charge current for 12v?

    Watts / Volts = Amps

    So, 600w of PV / 14.4v (the battery) works out to (roughly) 42a.

    A normal 12v "nominal" battery will be completely dead at 10.5v and fully charged when it reaches 14.4v. Then, once it has sat a while and normalized (no charging or discharging), it should settle down at about 13.5v fully charged.

    The charging voltage has to be higher than whatever the battery voltage is at "right now". So if the battery is at 11v, then 13v would be high enough to overcome the internal resistance of the battery and allow watts to flow into the battery.

    But 13v isn't enough to fully charge the battery. For that, you've got to get the battery up to 14.4, which means you have to supply the power at a voltage which is higher than "14.4 + battery internal resistance".

    So a "12v solar panel" would normally put out at least 17vmp (voltage max power - under load). But if you get the voltage too far above the battery's voltage, then you end up increasing the resistance (the mismatch I talked about before) and while it will still charge the battery, it just won't do it as efficiently.

    With MPPT, you don't have that problem, since an MPPT controller will lower the voltage - which also increases the amperage (see the math above).


    So, what is the current? It depends on what you plug into the formula...

    If the PV puts out 100w at 23v then the formula looks like:

    100w / 23v = 4.35a (rounded off)

    If the MPPT down converts the voltage to say 16v, then it looks like:

    100w / 16v = 6.25a

    Same watts being produced by the PV, but by lowering the voltage the controller increases the amperage - and the amperage is the "current" that is flowing into the battery.

    Either one will charge the battery, but at 16v you get less mismatch resistance and also more amps of charging current - out of the same 100w of PV. That's the beauty of MPPT.


    When buying a panel for a 12v system, what should the "specs" be?

    Open Circuit Voltage:
    Short Circuit Current:
    Maximum Power Voltage:
    Maximum Power Current:

    If you use an MPPT controller, it doesn't really matter since the MPPT can take a whole range of input voltage and down-convert it to the best voltage for charging the battery.

    For instance those Sunwize panels - even at 23vmp they are still perfect for charging a 12v battery - IF you use an MPPT controller. If you used a PWM which just connects the panel straight through to the battery, they wouldn't be as good since 23v - 14v is a pretty big mismatch and would be correspondingly more inefficient.

    If you used a PWM controller, then you would want to pick a PV module that was rated "12v nominal", which as Bill mentioned, would normally have a Vmp somewhere between 17v - 20v.

    And with MPPT it wouldn't matter if you wired them in parallel or series either, since you could feed an MPPT controller 23v or 46v or 69v or 92v or whatever - and it would still down-convert the output to be whatever is most efficient for charging that 12v battery.

    Two things that really matter are A) the voltage coming into the controller is higher than voltage of the battery (MPPT controllers down convert, but they don't up convert), and B) you don't wire up your PV modules in such a way as to exceed the input voltage specs of the controller (too many in series).
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Solar cell grades
    Will2020 wrote: »

    I have a battery rack built for 3 batteries and will have 315 ah total, how many 100 watt solar panels would it take to fill these up daily?

    Are you going to pull 150A daily ? You have to recharge at least 120% of what you use, if you just use a few LED lights, a single panel will replace that.

    AGM batteries are more efficient, in both recharging, and stand-by losses, than flooded batteries. That will allow your charge to go further.
    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 ,

  • Will2020
    Will2020 Solar Expert Posts: 62 ✭✭✭✭
    Re: Solar cell grades

    This is my dc load only.

    I have a Fantastic vent fan that pulls 3 amp on high, 2.29 med, and 1.86 on low.

    Run the fan on med for 8 hours.

    8*12*2.29=18.32 amp hours?


    The I have a 4 amp water pump to run for half an hour.

    4*.5=2 amp hours?


    Then I have 20 watts worth leds.

    20 watts *8 hours = 160 watt hours? How do I convert this to amps?


    Correct me if I'm wrong here, I'm a tad bit slow in the calculating department :roll: I want to get my dc basics down.
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Solar cell grades
    dwh wrote:
    160wh / 12v = .83ah

    Um..wth?

    <runs it through (again) handy little promo ruler/calculator that I picked up somewhere years ago and have used a million times>

    = 13.3

    I have no idea how I flubbed that one. Must have put a thumb in the wrong place.


    www[dot]freshpromotions[dot]com[dot]au/desk-accessories/calculators/business-ruler-and-calculator.html
  • Will2020
    Will2020 Solar Expert Posts: 62 ✭✭✭✭
    Re: Solar cell grades

    It is a dc fan. Is this the right formula for 8 hours use? If so I will seriously have to cut my fan running time down to a couple of hours daily.

    8*12*1.86= 178.56 amps

    8*12*2.29= 219.84 amps

    8*12*3= 288 amps



    If I have 20watts*8 hours= 160 watt hours /12= 13.33 amp hours total right?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Solar cell grades
    Will2020 wrote: »
    It is a dc fan. Is this the right formula for 8 hours use? If so I will seriously have to cut my fan running time down to a couple of hours daily.
    • 8hours*12volts*1.86amps= 178.56 Watt*Hours
    • 8hours*12volts*2.29amps= 219.84 Watt*Hours
    • 8Hours*12volts*3amps= 288 Watt*Hours
    If I have:
    • 20 watts * 8 hours= 160 watt*hours
    • 160 watts / 12 volts = 13.33 amp*hours total
    I think the above is what you are asking about?

    Since for a 12 volt battery system Amp*Hours*12Volts=Watt*Hours--You have 12x larger numbers than you expected, if you were expecting Amp*Hours

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • zeuspaul
    zeuspaul Solar Expert Posts: 59 ✭✭✭✭
    Re: Solar cell grades

    No
    8*12*1.86= 178.56 amps

    8*12*2.29= 219.84 amps

    8*12*3= 288 amps

    8 hours * 1.86 amps = 14.88 amp hours
    If I have 20watts*8 hours= 160 watt hours /12= 13.33 amp hours total right?

    Yes

    Zeuspaul