Solar Pannel for an rv

lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
Hi Guys,

I have a 40 watt notebook that I'd like to charge on the go. I have an old RV and have tried the cigar lighter, but I really want to go solar. I tend to use the notebook around 5-6 hours a day and it has a battery life of about 3 hours; sometimes less.

Could you guys suggest for me a solar panel size/manufacturer that is reliable? I was thinking maybe a 60 Watt panel, but I don't know if that will be enough because of lighting conditions and what not. I am limited on space, so the less panels the better. I think you also need x2 the power if you charge/power on the computer at the same time? If this is true do I need a higher wattage panel?

If possible I would like to avoid using a battery due to the space restrictions and because of the acid/fumes I keep reading about. I read somewhere that there is a special type of battery that doesn't leak acid/release fumes, but was told it is expensive.

I don't have a lot of money. My budget is about $200 usd, but can spend $300 if necessary though I'd really rather not.

I will only use the panel to charge my netbook and nothing else.

Currently I use this: Cobra CPI 480 400-Watt 12-Volt DC to 120-Volt AC Power Inverter with 5-Volt USB Output http://www.amazon.com/Cobra-400-Watt-12-Volt-120-Volt-Inverter/dp/B001RNOHBC?tag=vglnk-c2416-20 Oh one thing I should add is that the inverter has a modified sine wave... not sure if that will be a problem/or if it will be useable /w the panel.

I don't know if I will need to buy another type of inverter for what is needed. I'm a noob! This is my first time doing this.

I live in L.A. and usually park my RV under the hot sun Though in summer I do use the shade, but right now is winter so no need for that.
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Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Pannel for an rv

    Welcome to the forum.

    Two things: 1). invest $30 in a Kill-A-Watt and see how much power the laptop actually uses when charging and running. It will probably be less than 40 Watts on average, which is good. 2). think "monocrystaline" panel; they have slightly greater power per square area. They cost more, but when space is at a premium you pay a premium price.

    Don't worry about using an MSW inverter for powering your laptop: the computer's power supply can handle the higher THD of the MSW output. Lots of people think computers need really 'clean' power, but in truth their power supplies are designed to take poor input quality because the circuitry needs very stable power.

    Charging directly from a panel is possible, but not easy as you need a regulatory circuit designed to match the panel to the laptop. It's much easier to use the supply that comes with the computer running from the inverter, the inverter running off the battery, and the panel charging that battery. It may not be the most efficient, but it's far easier to bring about.

    You're correct in your suspicions that the flat mounting and high temps will hurt panel output. Another thing you'll find is that small panels cost more per Watt than large ones. A couple hundred dollars will buy you an 85 Watt polycrystaline panel. $50 more will buy you 190 Watts.

    Oh and you will need a charge controller regardless of what panel you get.

    The "special type" of battery is AGM - Absorbed Glass Matt - and yes they are expensive compared to standard flooded cells.
  • lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi there Cariboocoot!

    Thank you for the reply and information. I really appreciate the help :). I'm glad I found these forums.

    So it looks like I will have to get a battery after all. It will have to be the AGM type since I will likely have to keep it inside the RV. I too was thinking along the lines of monocrystaline due to my space restrictions....

    I looked through amazon at some panels and some AGM batteries, but there seem to be a lot of makers and I know nothing about them.

    Could you recommend two high profile solar panel makers, or would the maker not matter?
    For the battery would you be able to recommend any good maker?

    I just want to buy something that will be of good quality, and not have troubles too soon down the line.

    Do you believe the best deals for panels and batteries are online?

    I will get the kill-a-watt asap and report back with the results! Thank you once again for your great input :).
  • ChrisChris Solar Expert Posts: 135 ✭✭
    Re: Solar Pannel for an rv

    Just a thought here
    But to me, adding another battery inside the RV just to charge the laptop doesn't make any sense. Why not just set up a panel and charge controller hooked to your existing coach batteries? then run your inverter off the existing electrical system.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Pannel for an rv

    Usually we'd say the best deals on batteries are local, but in the case of an AGM the weight is not as high and they are not considered hazardous to handle so shipping is not as much of a concern. Still, it pays to shop around.

    Likewise the bigger the panel the more costly the shipping, and some places only want to sell you whole pallets full not individual pieces. Otherwise there's not a lot of difference between one panel maker and another.

    But you have to do this in the right order because the most important thing about the battery or the panel(s) is that they meet your needs. The majority of problems reported here on the forum come from people buying "bargains" that won't do what they need done.

    So first thing is to get your power requirements determined. Second is to find a battery that can supply those needs. Third is to pick panel & controller to charge the battery.

    A note on that last item: you may not have enough roof space to achieve full charging ability with even monocrystaline panels. When that happens you fit as much panel as is practical, and look for alternate charging sources such as a small generator. If you figure this out first you may decide to go for less capacity (expense) in panel to have more to spend on the gen.
  • lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv
    Chris wrote: »
    Just a thought here
    But to me, adding another battery inside the RV just to charge the laptop doesn't make any sense. Why not just set up a panel and charge controller hooked to your existing coach batteries? then run your inverter off the existing electrical system.

    That sounds great. I'd love doing that. The only issue is that this is an old RV 1975 dodge sportsman, and I'm afraid about the circuitry of the RV. I don't know how it will hold up to the charging/discharging.

    It has 2 batteries. The one that came with the RV was from another old car. It discharged fast and so we bought another. The old one went to a compartment in the back of the RV, and the new one went to the front. The new one is a durablast gold from autozone. We were told the bat at the back is for the lights of the inside of the RV. We only use the kitchen sink light at night. It is a tiny little bulb. It tends to last us about 30 - 45 minutes at best when used.

    It would be awesome to do that, but I am not sure how the old circuit stuff will behave. The old bat is old. I don't know how old it is, but we were told it was from another card. I don't know how that old bat will hold up to discharging and recharging. I think I should get it tested at autzone and see if it is a hazard having it around :(.

    What are your thoughts on that? I actually stopped using the cig lighter because I read some posts online that it could kill the spark plugs. I don't now how to change them and I'd hate to not be able to run the RV when I need to move it; which is every 2-3 days because of city parking laws.
    Usually we'd say the best deals on batteries are local, but in the case of an AGM the weight is not as high and they are not considered hazardous to handle so shipping is not as much of a concern. Still, it pays to shop around.

    Likewise the bigger the panel the more costly the shipping, and some places only want to sell you whole pallets full not individual pieces. Otherwise there's not a lot of difference between one panel maker and another.

    But you have to do this in the right order because the most important thing about the battery or the panel(s) is that they meet your needs. The majority of problems reported here on the forum come from people buying "bargains" that won't do what they need done.

    So first thing is to get your power requirements determined. Second is to find a battery that can supply those needs. Third is to pick panel & controller to charge the battery.

    A note on that last item: you may not have enough roof space to achieve full charging ability with even monocrystaline panels. When that happens you fit as much panel as is practical, and look for alternate charging sources such as a small generator. If you figure this out first you may decide to go for less capacity (expense) in panel to have more to spend on the gen.

    Thank you for that amazing reply! I have been so busy so I could not get a kill-a-watt however, I did look up the list of devices and their wattage:

    #1 - Netbook with 36 watts
    #2- Another Netbook 33 watts
    #3 - Small Wifi Device 3.7v 9.25wh min. capacity 2500mAh (I saw no clear wattage # on it)
    #4 - Small old Cell phone 3.v 850mah li ion battery

    And that is all folks! The main energy hogs should be the netbooks. I will try and get a kill-a-watt as soon as possible, but life right now is so busy. From this simple list of devices, and I have no other electronics, about how big of a panel do you think might be required? I was thinking at most a 100 watt panel, yeah?

    Thank you so much guys!
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Re: Solar Pannel for an rv

    Just as a starting point, very roughly assuming a minimum of 4 hour of sun per day (excluding winter) a 100 watt panel may give:
    • 100 watts * 0.52 end to end system eff * 4 hours of sun = 208 Watt*Hours of "useful" 120 VAC power per day...
    So your 33 Watt Netbook (may be closer to 20 watts or less for a Netbook):
    • 208 Watt*Hours / 33 Watts = 6.3 Hours of use
    So, that is the basic math. #3 sounds like a rechargeable USB battery pack, or it is a Wifi Hot Spot (mobile phone router with internal battery?).

    The AH numbers are not really useful unless you know the watts they use... For example guessing at your cell phone:
    • 0.850 AH * 6 volts * 2 hours charging = 10.2 WH per charging cycle...
    My Andriod running at as a wifi hot spot probably uses around 5 watts... If you use it for ~5 hours:
    • 5 watts * 5 hours = 25 Watt*Hours
    And you have (roughly) a 208 watt minimum budget--Just add all your (known) loads together for daily power needs.

    For example, using PV Watts for Los Angeles with panel mounted flat to roof, you would expect around (on average over 20 years):
    Month    Solar Radiation (kWh/m 2/day)
    1      2.88     
    2      3.87     
    3      4.77     
    4      5.76     
    5      6.57     
    6      6.79     
    7      7.00     
    8      6.60     
    9      5.13     
    10      4.15     
    11      3.21     
    12      2.72     
    Year      4.96      
    

    You will see around 2.72 to 7.00 hours of sun per day (average) per month. You plug the numbers into the equation and see what you get.

    Remember that the battery bank is the "heart" of your system... Your bank should be ~2-4x your daily load--Longer battery life and backup for bad weather/aging (don't discharge battery lower than ~50% state of charge too often--better battery life).

    Also, very large battery banks need a fairly large solar array to meet the charging requirements (~5% to 13% rate of charge is pretty good with solar). If you have too large of battery bank, it can force you to use a larger solar array/using more generator fuel than you really need (to keep the batteries happy).

    Of course, never plan on harvesting/using 100% of "predicted" available power per day... You should plan on using only ~66-75% per day "base loads" unless you have a backup power source (genset/grid power) and/or can go some days with less power usage (during bad weather).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi BB!

    Thank you for all that information. From the math you provided 208 watts [note from BB.: that is, technically 208 Watt*Hours--Not 208 Watts] would be amazing to have for use. Yes #3 is a mobile hot spot for my internet needs. I'll be getting a kill-a-watt device from homedepot tonight after work and I will report the actual numbers I get from it tomorrow. I also need to get that old battery checked at autozone to see if it is a hazard to have around or not. Once I report the numbers I get with the kill-a-watt I will likely ask what is a good size AGM battery to get?

    Another thing I should add is that when I step out of the RV I always take my notebook with me. So if I go eat I get to charge the notebook there for a little whilte. If I go to the library or school I get some charge there. This should give a little break to my watt needs I think :).

    Out of curiousty would it be too risky to withdraw the solar panel inside the RV during night time? Is it best to just mount it? I'm afraid of branches hitting it or the less likely event of someone stealing it.

    I have read online that $4 to $5 per watt is a good price for a solar panel. Is this a good pricing per watt for a monocrystaline panel?

    -edit-

    There are times when I park right under a pole light at night and was wondering if the light from the pole light would charge the solar panel? If so, to what degree does the light help charge? Sorry for all the questions!
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Re: Solar Pannel for an rv
    lolcashcow wrote: »
    Hi BB!

    Thank you for all that information. From the math you provided 208 watts would be amazing to have for use. Yes #3 is a mobile hot spot for my internet needs. I'll be getting a kill-a-watt device from homedepot tonight after work and I will report the actual numbers I get from it tomorrow. I also need to get that old battery checked at autozone to see if it is a hazard to have around or not. Once I report the numbers I get with the kill-a-watt I will likely ask what is a good size AGM battery to get?

    In general, AGM batteries are several times more expensive than regular deep cycle batteries. AGMs are nice because their is less maintenance and they have very high surge current. However, if you do not need that, deep cycle golf cart batteries (a pair of 6 volt @ ~220 AH in series for 12 volts @ 220 AH) is probably the best bang for the buck. You will probably get around 3 years from either battery type (RV's have less than optimum charging conditions and frequently heavy/deep discharges because of the "undersized" bank)...

    Anyway, to give you an idea of what 12 volts @ 220 AH could do:
    • 220 AH * 12 volts * 0.85 inverter eff * 1/2 days of storage * 0.50 max discharge = 561 WH per day (for two days)
    And to recharge, 5% to 13% rate of charge:
    • 220 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 216 Watt array minimum
    • 220 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 431 Watt array nominal
    • 220 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 561 Watt array "cost effective maximum"
    So--In this case, unless you are able to get >216 Watt array on your RV, a pair of Golf Cart Batteries may be too large (unless you have 120 VAC charging source--Running your RV is probably not going to be a viable 12 VDC charging source. For the most part, a deep cycle battery needs 2-4 hours to recharge and >14.5 volts--running the RV engine that long will consume way too much fuel, and most automotive alternators run hot/too low of charging voltage (~13.9 to 14.2 volts) to recharge a deep cycle battery...

    AGM will probably charge better at 14.2 volts -- But vehicle alternator will probably not output that much current (for deep cycling AGMs either).

    A 100 AH deep cycle battery would probably be a better match for 208 WH and a ~100 watt array. Your choice AGM vs flooded cell (note that marine and marine/deep cycle batteries usually do not last very long when deep cycling).
    Another thing I should add is that when I step out of the RV I always take my notebook with me. So if I go eat I get to charge the notebook there for a little while. If I go to the library or school I get some charge there. This should give a little break to my watt needs I think :).

    Ye--You could save ~30-60 WH by charging at the library just the one netbook.
    Out of curiosity would it be too risky to withdraw the solar panel inside the RV during night time? Is it best to just mount it? I'm afraid of branches hitting it or the less likely event of someone stealing it.

    Your choice--Solar panels are "single weight" (~1/8" thick) tempered class. If it gets nicked/scratched--It can easily shatter (tempered glass shatters into small cubes). And you end up with a piece of "modern art".

    So, the extra daily handling vs permanent mounting and avoiding trees. Your choice. If you were parking at a camp ground, some folks will stake the panels to the ground (park in shade, put panels in sun). You have to stake them down so the wind does not pick them up and damage them. Panels are pretty tough--until they aren't.
    I have read online that $4 to $5 per watt is a good price for a solar panel. Is this a good pricing per watt for a monocrystaline panel?

    Small panels tend to cost more $$$/Watt (less than 100 watt). Panels that are over 200 watts tend to cost less (but cost more to ship). Our host has different size panels so you can get an idea of costs. Make sure you include shipping and insurance delivered "to your door" as shipping single panels (especially panels >~140 watts) is not cheap. Buying local (save shipping) may be cheaper.

    And note that large format panels have "non-standard" Vmp (voltage maximum power) output. To charge a battery with an "inexpensive" PWM charge controller needs Vmp~17.5 to 18.6 volts... Large format panels tend to have Vmp in the range of ~30 volts and need a more expensive MPPT type charge controller (to efficiently "down converter" high voltage/low current from the array to low voltage/high current needed by the battery bank.

    PWM controller will cost you way less than $100, and MPPT controllers will cost $230 and up (cheaper large format panel and expensive MPPT controller--get you coming and going).
    There are times when I park right under a pole light at night and was wondering if the light from the pole light would charge the solar panel? If so, to what degree does the light help charge? Sorry for all the questions!

    Wishful thinking... A solar panel will begin to output power when there is direct sun (or bright clouds) can cast a faint shadow on the array (morning/evening direct sunlight for example).

    You will not get any useful amount of energy from parking under a street light (light would have to be almost directly on the panel to generate any useful amount of power (like 1 watt or less--At best)....

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Re: Solar Pannel for an rv

    Also to clarify--That is 208 Watt*Hours of energy.

    Watts by itself is a "rate" (like miles per hour).

    Watt*Hours is an "amount" (like miles driven).

    Sorry, but need to be exact in our discussions--Mixing Watts and Watt*Hours (and amps vs amp*hours) can create a lot of confusion.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv
    BB. wrote: »
    Also to clarify--That is 208 Watt*Hours of energy.

    Watts by itself is a "rate" (like miles per hour).

    Watt*Hours is an "amount" (like miles driven).

    Sorry, but need to be exact in our discussions--Mixing Watts and Watt*Hours (and amps vs amp*hours) can create a lot of confusion.

    -Bill

    Hi BB,

    Thanks a lot for all that information. To be honest I really do not know much about this RV or about cars at all. I wouldn't know what type of alternator it has or the amount of volts it gives, so sorry! The RV has a small compartment at the back where it has the old battery, but it has no way to run any cables inside the RV. I would have to get some power tools and cut my way from the inside of the RV, or run the cables through a window then back into the RV; something I'd rather not do. I will have to bite the dust and get an AGM battery since I will have to have the battery inside with me. If I get the golf cart batteries I hear they leak acid and release fumes, so I don't think that will be good for me! There just is no other compartment to hold batteries in this old RV. I think hooking up a battery to the RV would be a great idea so the panel could charge them, but if I put them in the back then I won't be able to connect the inverter unless I run wires through the window. I'm also a little scared of the circuitry of the RV because it so old. I can always buy a really small rechargeable light to replace the kitchen sink light I use when doing things there. Truth be told with out the lights I'm able to sleep at around 8pm or 9pm and wake up as early as 3am with out feeling like a zombie.


    Here are the numbers I got from the kill-a-watt

    #1 Netbook 40 watts
    #2 Netbook 30 watts
    #3 Wifi 20 watts
    #4 Cell phone 15 watts

    I should also mention that the older netbook I use it as my work netbook and the other is my recreational netbook. I don't run both computers at the same time, so its always like I am running a single netook. They don't discharge at the same time basically, so its more like I only have one netbook. Could I then safely say that my wattage needs will be something like 65 to 75 watts per hour?

    Could it be safe to say that I can settle for a solar panel smaller than 100 watts? I always take my netbooks with me, my cell, and the wifi spot if I go out to eat, or at the library. While there I normally get to charge them for a little while :).

    The more watts I could get my hands on the better, but would it be too low to settle for a 60 watt solar panel or even a 50 watt?

    Hopefully I did not miss anything, sorry if I did. What kind of charge controller do you think I would need? I don't have any other electronics, so that would be the most wattage I'd be using.

    Thank you so much BB and Cariboocoot!

    Also, thank you for the information about the solar panel and artificial lighting :)
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Re: Solar Pannel for an rv

    The Kill-a-Watt type meters will also have a kWH (kilo-Watt*Hour) reading...

    For example, plug a charged laptop into the meter and measure the total power used over a 12 or 24 hour period... That 30/40 Watt is probably using the computer + recharging the battery bank...

    My old laptop would use around 0.420 kWH (420 Watt*Hours) over a ~10-12 hour per day usage... The average (something like 40 watts * 10 hours = 40 hours). For appliances that "cycle" (laptop charges battery, sleeps between uses, etc.)--The k-a-w meter does the hard work of monitoring total power usage over time.
    For 12 Volt & RV Systems - HandyBob's long discussion and rant is about 99% right on how to make RV and similar 12 volt systems work correctly. One of the few "non NAWS" articles that we recommend
    (from our host NAWS).

    Peak watts is important (for sizing inverter rated power), but overall "energy" use per day is important for sizing the battery bank and solar array. In general, people under estimate their power usage and over estimate how much power an off grid solar power system will generate.

    75 Watts for 1 hour is 75 Watt*Hours.... 75 watts for 10 hours is 750 Watt*Hours per day. Accurate measurements of the equipment, based on your usage profile, is critical to a successful/cost effective design.

    We can give you estimates of how energy a system will supply--You will have to decide if it adequate for your needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi BB!

    Oh ~! I remember reading the blog you linked me to. It was a while back, perhaps a year or more ago? I did recall book marking it, but sadly I think my older computer died and along went the link. I am glad to have found it again :) Thank you! Truth be told life has been so busy since we got an RV that I have not had time to search for it, nor did I recall it, but it is here now so thank you!

    I'd love to run the kill-a-watt for 24 hours, but when I checked the power I did it at a restaurant. I'm currently living in the RV and have no dedicated power socket to do this :(. Truth be told, I end up using the netbook for about 5 hours rather than six. I know I mentioned 5-6 hours before, but it was more of an estimate on my behalf. I'm sorry.


    http://www.midnitesolar.com/ A high quality, innovative US manufacturer who is cornering the market for very high quality alternative energy distribution equipment and maker of the best solar charge controller available as of 2013.


    Mr. Bob Mentions midnitesolar to be the maker of the best solar charge controller available. I was looking at the charge controllers they offer and the prices were 700 - 800 for the classics and400 to 500 or so for the KID. I've never looked up the prices on the charge controllers before, but wowzers I thought they'd be less expensive or the least expensive piece !

    From what I looked at last night the AGM battery prices were about 270 on amazon

    http://www.amazon.com/Vmaxtanks-Vmaxslr125-rechargeable-Solar-Inverters/dp/B00ACNO2AO/ref=sr_1_4?ie=UTF8&qid=1387761844&sr=8-4&keywords=agm+battery

    and from what I recall a 100 watt panel was 170 with the shipping

    http://www.amazon.com/RENOGY-Monocrystalline-Photovoltaic-Battery-Charging/dp/B009Z6CW7O/ref=sr_1_1?s=lawn-garden&ie=UTF8&qid=1387761736&sr=1-1&keywords=Mono-crystalline+Solar+Panel

    That is... unless I am looking at the entirely wrong items? I think the solar panel is the less witty choice, but the battery will be the tough part for me. Am I at least on the right track?
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Re: Solar Pannel for an rv
    lolcashcow wrote: »
    I'd love to run the kill-a-watt for 24 hours, but when I checked the power I did it at a restaurant. I'm currently living in the RV and have no dedicated power socket to do this :(. Truth be told, I end up using the netbook for about 5 hours rather than six. I know I mentioned 5-6 hours before, but it was more of an estimate on my behalf. I'm sorry.

    Not a problem... It is purely your choices and decisions. It is easy for me to spend your money... For you, not so easy with me spending it. Having some solar power in your RV is probably a huge improvement over having next to no power available.
    http://www.midnitesolar.com/ A high quality, innovative US manufacturer who is cornering the market for very high quality alternative energy distribution equipment and maker of the best solar charge controller available as of 2013.

    Mr. Bob Mentions midnitesolar to be the maker of the best solar charge controller available. I was looking at the charge controllers they offer and the prices were 700 - 800 for the classics and400 to 500 or so for the KID. I've never looked up the prices on the charge controllers before, but wowzers I thought they'd be less expensive or the least expensive piece !

    Make no mistake, that is a very good, high end, MPPT charge controller. For an RV--It is overkill for the full sized unit. And at this point, you probably do not need the "Kid" either. Your choice of 100 Watt solar panel makes using a less expensive PWM controller a good fit.
    From what I looked at last night the AGM battery prices were about 270 on amazon

    A 100-125 AH AGM 12 volt battery should be fine.

    That solar panel is rated at:
    Electrical Specifications
    Optimum Operating Voltage (Vmp): 18.9V
    Optimum Operating Current (Imp): 5.29 A
    Open - Circuit Voltage (Voc): 22.5 V
    Short- Circuit Current (Isc): 5.75 A
    Maximum Power at STC: 100 W
    Operating Module Temperature: -40°C to + 90°C
    Maximum System Voltage: 600 V DC (UL) / 1000 V DC (IEC)
    Maximum Series Fuse Rating: 15A
    STC: Irradiance 1000 W/m2, module temperature 25°C, AM=1.5;

    There are a lot of inexpensive PWM type charge controllers that will work with AGM batteries.

    This one can actually charge both your vehicle and house batteries from the same solar panel/array:

    SunSaver Dual Battery 25 Amp 12 Volt Solar Charge Controller

    You might want to look closely at your solar panel choices... If you can get a bigger one for the same price (shipped), or justify getting a second 100 watt panel later (if you have room on the roof)--You probably will want to do that--Having electrical power "in your home" is addictive.
    That is... unless I am looking at the entirely wrong items? I think the solar panel is the less witty choice, but the battery will be the tough part for me. Am I at least on the right track?

    Metering your battery voltage is going to be an issue... An accurate DC volt meter at a minimum (if you could swing it, a DC Current Clamp DMM unit like this is pretty handy)--Or some sort of battery monitor would be very nice (but probably not worth money for your setup).

    Ideally, you want to not cycle the battery much below 50% SOC--But that is difficult to measure with a volt meter, and AGM/Sealed batteries cannot be checked with a Hydrometer for specific gravity.

    Another thing we have not discussed is an AC inverter--If you have DC adapters for everything, that may be the way to go in this case.

    However, if you do want/need to use an AC inverter--We will have to talk more. I like to recommend AC inverters, but they do waste some power. And for smaller off grid systems, you have to turn off the DC input to the AC inverter when not in use (the 6-10+ watts inverter idling current will drain the battery bank if left on 24 hours per day).

    Hope were are helping here.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi BB!

    You are all being a great help :) I really appreciate your time. Sears right now is offering 15% off their Die Hard Automotive Batteries + Additional $5 off /w free store pick up. This includes their AGM batteries. I am not sure if these are deep cycle(???) batteries and for whatever reason I can see their models, but when I click a battery the page doesn't load for me. Therefore I can't see the specs on the batteries :(. http://www.sears.com/automotive-batteries-car-batteries/b-1100206 Last month sears had 25% off on these batteries! The highest models, the platinum, cost about $200 which is $70 cheaper than the other AGM battery I listed in my previous post: http://www.amazon.com/Vmaxtanks-Vmaxslr125-rechargeable-Solar-Inverters/dp/B00ACNO2AO/ref=sr_1_4?ie=UTF8&qid=1387761844&sr=8-4&keywords=agm+battery The ones at sears look to be for cars, but I can't see if they are deep cycle or not. Would these AGM batteries be any good for the RV? Less so than the one at amazon?

    For the inverter I have the http://www.amazon.com/Cobra-400-Watt-12-Volt-120-Volt-Inverter/dp/B001RNOHBC it has battery clamps, and a cig plug that I was using before, but I am not sure if this inverter will work? Or if I need to change the wires that comes with the inverter? If this is no good I would have to buy another inverter?

    I will try calling some local solar panel dealers to see if I can get a better price on a 100 watt panel from them :)

    Okay I searched more and I see they have some marines batteries which I think are deep cycle, the others I'm not sure since they are for cars... do cars use deep cycle batteries to start up??? Here is the marine that they have and the page did load for this one :)

    http://www.sears.com/diehard-platinum-marine-battery-group-size-31m-price/p-02850131000P?prdNo=1&blockNo=1&blockType=G1
    It says on the side that it has a 10% off offer and I guess the $5 coupon will also apply? Would this one be a worse choice than the one on amazon?

    Thanks again !

    -edit- I was looking at the list of sears for sears and the 25% off for batteries deal seems to come back up often enough. If this is a good battery I might just end up waiting for the deal to come back up again!
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Re: Solar Pannel for an rv

    I really cannot help you much with these batteries. In general, if they do not give you a AH Capacity number (at 20 hour discharge rate, for example) and only talk about CCA (cold cranking amps), group size, Marine/deep cycle, etc... Many times they are not true deep cycle batteries.

    Check the warranty--If it is 3 year 100% replacement guarantee--I probably would risk it. If it is a declining warranty (18 months, 50% coverage)--perhaps not.

    For an RV with moderate use and less than ideal amount of charging (solar, occasional driving, etc.)--2-3 years is probably the expected life. If you do better--Great.

    If you can, you want to get "fresh batteries" (you don't want something that has been sitting on a self for a year+). Bring an accurate volt meter and make sure that it is >~12.5 volts (resting). Any think much less is, probably, an improperly stored battery at at risk for already having some early sulfation.

    Regarding the AC inverter--It is a typical 400 Watt MSW inverter. The cigarette lighter plugs are usually only good for around 10 amps @ 12 VDC maximum. If you need more than 100 watts, you will have to hard wire it to the battery directly (short heavy cables bolted directly to the battery bank with a 50 amp (minimum) fuse or breaker. Circuit breaker would be nice to use as the DC on/off switch too).

    MSW vs PSW--Probably 80% of your stuff will work OK on MSW, and 10% will not--The problem is figuring out which is which. Just watch for overheating/hot plastic smell from your AC power bricks/devices.

    I would not use the USB charger from the Inverter unless you are already running other AC devices. Get a simple cigarette plug type USB adapter to charge cell phone/etc. when the AC power is not needed (more efficient).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi once again :)

    I looked at the warranty on the battery and the amazon one is marked with a 12 month warranty.... I did find another battery on amazon that has a 24 month warranty, but has no amp hours either....

    http://www.amazon.com/Exide-RF-31D-Maintenance-Free-Heavy-Duty-Commercial/dp/B003FFQ9L6/ref=sr_1_13?ie=UTF8&qid=1388027368&sr=8-13&keywords=agm+battery+solar

    On the other hand the battery from sears has: Free Replacement Warranty Term: 36 months
    but it does not have the AH marked.

    The AH is the amount of time the battery will provide energy for, right? Does this mean if I connect it a 0.5 watt LED light bulb it will still drain the battery fully only in that short amount of time? Even if the wattage that is being drawn is so tiny? That would only be 1 watt in one hour, I think. So two hours and .. if the AH on the battery is two hours... it will be dead by then? Is that right???

    I read online that the military uses odyssey batteries, does this mean they are really good because of the military grade quality?
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Re: Solar Pannel for an rv

    I really am not the guy to ask about batteries--I can give you an "engineering/specifications" answer--But this is not my field.
    lolcashcow wrote: »
    The AH is the amount of time the battery will provide energy for, right? Does this mean if I connect it a 0.5 watt LED light bulb it will still drain the battery fully only in that short amount of time? Even if the wattage that is being drawn is so tiny? That would only be 1 watt in one hour, I think. So two hours and .. if the AH on the battery is two hours... it will be dead by then? Is that right???

    Lets use 6 watts for LED lighting--That is a goodly amount for a work space.

    6 Watts / 12 volt battery voltage = 0.5 amps.

    A 100 AH battery * 0.50 maximum discharge / 0.5 amps = 100 Hours to 50% discharge

    The above is an estimate--But close enough for now. We use the C/20 hour discharge rate (100 AH / 20 Hours = 5 Amps)--Since the 0.5 amps is much less than 5 amps--The apparent capacity of the battery will be somewhat over 100 AH (depends on battery). For an AGM, that 100 AH battery may appear to be ~120 AH capacity when discharge at 0.5 amps (~C/200 rate).
    I read online that the military uses odyssey batteries, does this mean they are really good because of the military grade quality?

    I don't know... They probably are a perfectly good battery. Remember that the government uses the low cost bidder for many things they buy--That may or may not be the best quality product.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Solar Pannel for an rv

    STOP. Know that there are SLI-only batteries, and dual-purpose batteries. You don't want the SLI only types.

    Here is the scoop on those Sears batteries you were looking at. The Sears Platinum AGM's, are rebadged Odyssey batteries. GREAT dual-purpose batteries (SLI & deep cycle). Overkill for most casual solar installations. Major problem is that Odysseys require 0.4C charge current to stay healthy, and which most casual 12v systems don't meet unless you have a LOT of panel power. Odyssey is VERY stringent on charging properly to stay within warrantee. That is one reason the Platinum Charger at Sears defaults to 40A charge current which most consumers don't know how to circumvent - a good thing actually. Otherwise, fantasticly low internal impedance resulting in very high voltage under load. But since you aren't starting a vehicle with it, that feature will go unused. My own tests with low charge current started to show a drop in capacity, so they aren't kidding. Odysseys like to be hit HARD, absorb at 14.7v, and mandatory 13.5v float or higher.

    Sears Die-Hard "Advanced" Gold. Not the regular gold agm but "Advanced" gold. It is a rebadged East-Penn/Deka agm. Very good dual-purpose. Eased charging requirements of "up to" 0.2C recommended for longest cycle life. 14.4v absorb, 13.5v float, which is common for many low-cost PWM charge controllers. Good internal impedance with high voltage under load. This would be the better choice of the two due to this.

    Exide - most of the agm's you are looking at are SLI, even if marketing says "2X the cycling over conventional batteries". In this case, the comparison is with FLA and not against another agm, and 2X is still basically an SLI (starter-lights-ignition) type. Of the recent Exides, the Exide "Edge" has only ONE model which is dual-purpose - it will state so on the case. Again, be aware of new/old stock dumping online where you can't put your voltmeter across it until after purchase.

    You want to avoid new/old stock in any case, so try and find a reputable counter. If you can, take a voltmeter with you and reject those that are reading much lower than 14.4v as this signifies that they have been sitting around on the retail shelf for a year or more, or under hot storage. Fortunately Odysseys can go 2 years in retail dormancy, BUT the voltage upon receipt should not be under 14.4v, otherwise you are taking your chances. Most retail outlets don't properly maintain aging stock to my knowledge with occasional bulk boost charges, so it behooves you to find a reputable place that will let you get the newest one.
  • lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi PNjunction

    Thank you for all of that information. Then the sears platinum AGM are overkill for what I am intending to do? I see that you recommend the Sears Die-Hard "Advanced" Gold. Not the regular gold agm but "Advanced" gold. I went to sears.com and did a search for "Die-Hard Advanced Gold", but all the hits were for Die-Hard "Advanced" Gold AGM battery. I got 8 hits for Die-Hard Advanced Gold AGM the only difference was the group size. The other four left were Die-Hard Gold with no "Advanced" wording to them and they too varied in group size. Am I looking for the wrong item or is this one the one? Here is a link to one of the AGM's listed that was 'Customer Preferred Item'; whatever that means! Also one of the more expensive ones as the others were $140ish. Though if this is a good one and since it costs less than the platinum I could put the extra money into the solar panel and maybe upgrade to a slightly higher wattage.

    http://www.sears.com/diehard-advanced-gold-agm-battery-group-size-94r/p-02850793000P?prdNo=1&blockNo=1&blockType=G1

    It is marked as deep cycle, but I see no Amp hours listed. Do I need to look for a specific group size that I might need? Free Replacement Warranty Term: 36 months, so this is 3 years only. Is that good enough for what I am intending? I will only charge one netbook at a time. I will also try my best to not discharge it below 50%. Unless that is not good enough? If that is not good enough then what % should I aim for?

    If this is still no good are you able to recommend a battery? Thank you so much!

    Hi BB,

    Thank you so much for all of that information. I honestly got lost there a couple of times with the numbers... from what it looked like the 100hrs do turn into 120 AH which basically is just 2 hours of use? If not, then I am deeply sorry I have a hard time understanding the mathematics :(. I see it as simple, but I cannot seem to wrap my head around it easily.

    I also did not know that about the military. Who would have thought I always thought they went for the highest!


    Sorry for the late reply I was just so busy because of the holidays. Happy holidays to all!
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Re: Solar Pannel for an rv

    It is OK--Talking math on Web postings is not always the easiest thing in the world.

    Think of AH like gallons of water.
    • 100 gallons of water, use 0.5 gallons per hour = 200 Hours till empty
    • 100 AH of energy / 0.5 Amps = 200 Hours till empty
    I threw a 50% derating for your battery--Lead acid batteries start to "wear out" quicker when discharged below ~50%... So, one of the rules of thumbs we use is to only use 1/2 of the stored energy in a battery.

    So, a 100 AH battery discharge by 1/2 would be 50 AH of useable energy.
    • 50 AH / 0.5 amps = 100 Hours of "useful" energy (with 50% reserve)
    The 50% reserve is also helpful because it gives you some extra room to allow for battery aging (loss of capacity).

    If you have a 2 amp load, then:
    • 50 AH capacity / 2 amps = 25 amps

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi BB!

    Yes, that does help me understand it. Sorry you had to go that extra mile to help me clear that up. I appreciate the effort :). Hey do you think the Die-Hard "Advanced" Gold AGM battery I linked is the one PNjunction mentioned? There really are not that many listed for that name, so I am almost certainly certain that it is the one. I kind of hope so since it does cost less and with that discount, once it comes around, it will drop the price even further.

    Thanks BB!
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Re: Solar Pannel for an rv

    Our pleasure.

    I have no idea what to tell you about that battery... I don't have any off grid experience other than killing a couple RV batteries from time to time.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv
    BB. wrote: »
    Our pleasure.

    I have no idea what to tell you about that battery... I don't have any off grid experience other than killing a couple RV batteries from time to time.

    -Bill

    Hi once again :),

    I called around and found someone willing to donate a used solar panel. He says he can give me a 160 watt solar panel, and that he has another one he does not use. This panel is not monocrystaline, but it is free so I am willing to take it. I am also thinking on taking the other solar panel if it can fit on top of the RV. I'm thinking on just asking him to install the panels for me on top of the RV, as he has experience with installing panels on homes, and pay for his handy work. The only thing that worries me is the inverter since it is a MSW. It is a 400 watt power inverter. I'd actually be quite happy with 400 watts of available power to me! Though I am worried on what to say when he talks to me about a charge controller and the type of battery. If he has suggestions on the chargers and batteries... what should I say? I know nothing about them.
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Re: Solar Pannel for an rv

    As always, get the specs and do a "paper design" first. You have to have the "correct" combination of panels, charge controller(s), and wiring. Without knowing the exact hardware--It is difficult to give correct answers.

    Personally, I have used lots of MSW inverters--But I would suggest TSW inverters if you can swing the costs. It is less of a chance for things to go south (old 80/20 rule--80% of your hardware will probably work OK, 10% can fail, and 10%--I have no idea).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: Solar Pannel for an rv

    with what you will save on the cost of the panels, invest it into an MPPT CC, so if/when you want to upgrade the panels or inverter you do not have to buy another CC.... ie you might find a smokin' deal on a GT panels and a PWM CC will only give you a portion of that panels potential...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv
    BB. wrote: »
    As always, get the specs and do a "paper design" first. You have to have the "correct" combination of panels, charge controller(s), and wiring. Without knowing the exact hardware--It is difficult to give correct answers.

    Personally, I have used lots of MSW inverters--But I would suggest TSW inverters if you can swing the costs. It is less of a chance for things to go south (old 80/20 rule--80% of your hardware will probably work OK, 10% can fail, and 10%--I have no idea).

    -Bill

    Hi BB,

    Out of curiosity about how much would a TSW inverter cost? When you mention about the combination of panels does this mean linking different panels of different brands/watts is more difficult than say two panels of the same wattage/brand? Do you need more than one charge controller if you have two solar panels? I was looking at the size of a 160 watt panel on amazon and I think the RV could fit two of them. Perhaps three, but I feel like I am stretching it. What kind of questions should I ask about the panel?

    Hi WestBranch,

    Oh I remember reading that there are Charge controllers out there that are able to control more than one solar panel? I am not sure if this is the type of charge controller you mentioned. I did find this article on ebay about it and read it: http://www.ebay.com/gds/Why-MPPT-PV-Solar-Charge-Controllers-Are-Important-/10000000176770209/g.html Though it did not sound to me like the other charge controller I read about. I'm sorry.
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Re: Solar Pannel for an rv
    lolcashcow wrote: »
    Out of curiosity about how much would a TSW inverter cost?

    MSW inverters can be "silly inexpensive"... The "good ones" made for off grid use are not as cheap (our host, note these have built-in AC chargers too):

    Magnum Energy ME2012 2000 Watt MSW Inverter with Charger $1,119.20
    Magnum MS2012 2000 Watt Sine Wave inverter w/charger $1,719.20
    Samlex 2,000 Watt 12 Volt Sine Wave Inverter: $625.30
    Exeltech XP2000 12 & 24 Volt, 2000 watt sine wave inverters $1,280.00
    Outback Power FX2012T 2000 Watt Sine Wave Inverter: $1,633.00
    Morningstar SureSine, 300 Watt Sine Wave Inverter 115VAC 12 VDC $232.70

    Whistler Pro-2000W 2,000 Watt Power Inverter (MSW-Amazon) $150
    BESTEK Dual 110V AC outlets and Dual USB 3.1A 300w power inverter $27

    All 2kW 12 volt AC inverters--3:1 pricing ratio for just 2kW pure sine.

    For an RV--I would be looking more for the ~200-300 watt inverter vs the 2,000 watt--Just saying there are lots of options and you can spend an hour or more reading about each.

    For an RV, you need to look at efficiency (including "tare" or "idle" losses--Just being turned on for a smaller inverter is ~6 watts with no load--Larger inverters are many times that amount).
    When you mention about the combination of panels does this mean linking different panels of different brands/watts is more difficult than say two panels of the same wattage/brand? Do you need more than one charge controller if you have two solar panels? I was looking at the size of a 160 watt panel on amazon and I think the RV could fit two of them. Perhaps three, but I feel like I am stretching it. What kind of questions should I ask about the panel?

    More panels need more/heavier copper wire. Possibly series protection fuses per panel... Are you using MPPT vs PWM charge controller.

    If placing panels in parallel, the Vmp voltage needs to be pretty close (Vmp~17.5 to 18.6 volts or so). If in series (for an MPPT controller), the Imp needs to be within ~10% or so.

    For example the 160 watt panel could be a Vmp~17.5 volt panel or it could be Vmp~30 volts. I do not know.

    The Vmp-array and Imp-array have to match the capabilities of the charge controller (and battery bank voltage).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lolcashcowlolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi BB,

    I think I could definitely think about getting a true sine wave inverter... much later down the line! The 300 watt true sine wave inverter you linked me too does look like a possibility! Just not at this time... I wanted to ask you if panels usually have their specifications listed uhm on the back of them? If not, then how do you get to figure out their specifications? Like if for example someone gave you a used solar panel? I think it would just be much easier to install a single large panel instead of two or more....
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    Re: Solar Pannel for an rv

    Ideally, Label on the back of the panel. It is possible to estimate the panel ratings by measuring the open circuit voltage and short circuit current (and counting the number of cells--i.e., 36 cell is Vmp~18 volts, 72 cell can be 18 or 36 volt Vmp, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Solar Pannel for an rv
    PNjunction wrote: »
    You want to avoid new/old stock in any case, so try and find a reputable counter. If you can, take a voltmeter with you and reject those that are reading much lower than 14.4v as this signifies that they have been sitting around on the retail shelf for a year or more, or under hot storage. Fortunately Odysseys can go 2 years in retail dormancy, BUT the voltage upon receipt should not be under 14.4v, otherwise you are taking your chances. Most retail outlets don't properly maintain aging stock to my knowledge with occasional bulk boost charges, so it behooves you to find a reputable place that will let you get the newest one.

    YIKES! Sorry to quote myself but the voltages I listed were written hastily - it should have said 12.4v not 14.4v at rest with the voltmeter... Sorry about that...
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