Battery to TV sizing

brownbearbrownbear Registered Users Posts: 22 ✭✭
Hello great folk!. So I watch a lot of tv when the sun goes down.  Sometimes up to 6 hours at night. I have two 100watt panels, a 20amp mppt charge controller.  And one 125ah battery.  I want to power my 65in tv all night.  Tv uses about 100watts then there's the modem, router, and roku.   Should I add a second 125ah batter to total 250ah or should I get two 200watt batteries to total 400ah.   My main concern is to power my tv for at least 6 hours after the sun goes down.   I was also thinking of getting a 3rd 100watt panel but my 20amp mppt charge controller only takes up to 260watts at 12v.   If I add a 3rd 100watt panel will it damage the charge controller?   Thanks in advance.  

Comments

  • ShadowWolf180ShadowWolf180 Registered Users Posts: 4
    Hi Brownbear!

    I already have two 200ah sealed lead acid batteries (400ah total at 12v), powered by two 100w Renogy panels - a setup I used a few years back getting into solar, and they still do work.  It has the 2014 version of the 20 or 30 amp PWM charge controller from Renogy as well.  So pretty close to your idea of switching out your batteries to 200ah and staying with 2 100 watt panels.  I use this old setup for one purpose these days: to keep a 20w LED flood light on all night.  So here's my experience, and hope this really helps you decide...

    During the long daytime hours of the spring, summer, and fall, I have no problem keeping my 20w floodlight lit all night.  It's not until late November until early February that I have to basically turn the light off, else that 20w light will run the batteries dry around 2am.  The reason is because after just one cloudy day, the batteries don't get fully recharged and it goes downhill from there.  So starting in the fall, I just decommission that light and let the 200 watts of solar keep the batteries topped off in the event I need to use them for emergencies with an old 1000w 12v inverter.

    So if in theory I were to take my batteries and 1000w inverter over to your place, you won't be happy with the results.  It would definitely power your system, but about mid to late evening, that kind of power draw would deplete the batteries.  Because you can only use really no more than half of an AGM battery, my 400ah of SLA's is really only 200ah usable power.  And with that small amount of solar, it won't fully recharge the batteries from an 11.5v cutoff in just one day.

    You CAN however - to get more solar on the current charge controller you have - is maybe go 24v.  Then you could add TWO more panels for a total of 400 watts and feed a bigger battery bank. So maybe two 200ah batteries AND two more panels?  It still wouldn't get you thru the night, but at least you'd do better charging during the day, and if you are conservative enough with your energy you'd still have your TV and such for at least 2-4 hours.  That's a pretty big TV, and if it consumes 100w by itself, a little math would tell you what size battery bank you would need to go 6 hours, about 600 watt-hours.  Convert to amp hours and you'll need twice that in an AGM battery bank setup.

    Reply back with any questions or concerns.  There's a wealth of good knowledge and good people here.  :smile:
    6.4kw solar, 3x MidniteSolar 150, 200ah LFP @ 24v off-grid
  • EstragonEstragon Registered Users Posts: 3,127 ✭✭✭✭✭
    As a general proposition, many/most charge controllers will just take enough wattage from pv panels to output their rated current.  Depending on ambient temp, airflow, etc, they may reduce output as they get hot.

    Also as a general proposition, pv won't produce their (STC) rated output in most conditions, and to some extent the size of the pv array can be increased to compensate.

    That said, some caveats...
    In some locations/conditions, pv can put out more than rated.  In thin air and/or breezy and cool condtions (eg high altitude), or with "edge of cloud" effect, it's possible the controller could be overpowered at least briefly.

    Running a controller at rated output continuously makes them run hot and reduces life expectancy.  Some controllers/installations may be more prone to this than others (depending on controller design, dusty conditions, etc).

    Adding a third panel in parallel on one controller means each should really be fused.

    20a is good for 125ah battery.  Depending on local conditions, it may not be able to regularly fully charge 250ah, especially in winter.  For 400ah, 20a is pretty marginal almost anywhere for a system in daily use.

    It would help to know your approximate location to estimate your available full sun hours, and more about your application (off-grid? Seasonal or weekend use? Alternate charging means such as generator/alternator?)
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mcgivormcgivor Solar Expert Posts: 2,506 ✭✭✭✭✭
    Your useage would be very close to the maximum the battery can support, simply adding battery capacity will not solve the problem because the PV is not large enough to recharge additional capacity, in fact it's marginal as is. Additonal battery capacity will create issues, the problems won't reveal themselves immediately, but once there is a bad sun day, the process of cronic undercharging will begin, by the time it's realized it will probably be too late. Adding another 100W panel may help with the current situation but the controller will be near maximum capacity. Rough calculation based on 4 hours of sunlight, depending on location it could be better or worse.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • BB.BB. Super Moderators, Administrators Posts: 28,315 admin
    In general, finding a more efficient TV would be a good start. Use a Kill-a-Watt type power meter and test a few TVs at the store (if they will let you), and/or confirm that yours takes 100 Watts...

    Here is the process for designing a "reliable" off grid power system for a residence.

    1. The battery bank. For full time off grid, you want a battery that will support 2 days of "no-sun" and 50% maximum discharge (for longer battery life). In general, Lead Acid batteries take a while to charge and there are not enough hours in the day (especially in winter) of sun to fully recharge a lead acid battery from 50% to 100% with less than 8-12 hours of electricity per day (i.e., plug into utility power, run a genset , etc.).
    • 100 Watt load * 6 hours * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/12 volt battery = 235 AH @ 12 volt battery bank
    Next sizing the solar array. There are two calculations to make. One based on size of your battery bank. 5% rate of charge for summer/weekend use and 10-13%+ for daily usage (9+ months of the year). And the second is based on your load and hours of sun per day.

    2. Charging based on battery bank AH capacity:
    • 235 AH * 14.5 volts charging * 1/0.77 solar panel+controller derating * 0.05 rate of charge = 221 Watt array minimum
    • 235 AH * 14.5 volts charging * 1/0.77 solar panel+controller derating * 0.10 rate of charge = 443 Watt array nominal
    • 235 AH * 14.5 volts charging * 1/0.77 solar panel+controller derating * 0.13 rate of charge = 575 Watt array "cost effective" maximum
    3. Sizing array based on hours of sun and load... In your case, it sounds like you want the system to run the TV in winter... I am not sure of your location, so taking a guess:
    http://solarelectricityhandbook.com/solar-irradiance.html

    Bellingham Washington State
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 26° angle from vertical:
    (Optimal winter settings)

    JanFebMarAprMayJun
    1.69
     
    2.80
     
    3.39
     
    3.99
     
    4.19
     
    4.25
     
    JulAugSepOctNovDec
    4.71
     
    4.87
     
    4.55
     
    3.08
     
    1.92
     
    1.50
     
    The basic math:
    • 100 Watts * 6 hours per night * 1/0.52 end to end off grid system eff * 1/1.50 hours of sun per day (ouch) = 769 Watt array "break even" in December
    Now, these are long term averages of solar radiation. In December, you will either need to use a backup genset at times, or make a larger array to support your usage:
    • 769 Watt array * 1/0.65 "minimum base load needing support fudge factor"  = 1,183 Watt array with 65% of predicted output
    • 769 Watt array * 1/0.50 "minimum base load needing support fudge factor"  = 1,538 Watt array with 50% of predicted output
    I am guessing at your location... So, if you are not in Western Washington state with the marine layer and rain... Your hours of sun may be better... 1.5 hours of sun per day is a pretty poor location for solar power.

    Solar is really based on Location. If you have poor weather, any trees or buildings shading your array, or other siting issues (bottom of valley, on northern slope, etc.), these will all reduce your solar harvest. If you are under a forest canopy--That is even worse. Shaded (or even partially shaded) solar panels just do not produce much energy.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • brownbearbrownbear Registered Users Posts: 22 ✭✭
    I'm in Los Angeles its always sunny here.  My batteries are fully charged by 10AM every morning.  That's from draining it down to 12.4V every night.   In the afternoon when my two 100w panels are pulling in 119v I can turn on the big screen and watch tv for 3 hours but by 3pm I can see that I'm using more energy then I am taking in and so I'll unplug the tv and plug it back to the wall socket and let the batteries charge for the last hour of sunlight left.   Is that ok to do?  Am I damaging the battery?   I thought it might help if I get two 200ah batteries to total 400ah.   
  • jonrjonr Solar Expert Posts: 1,188 ✭✭✭✭
    edited December 2018 #7
    While Bill's method is best, adding another 100W panel (your controller is good for about 350W (nominal) of panels) and a second battery (250 AH total) sounds about right to me.   More if using utility power isn't an option in unusual circumstances.
  • BB.BB. Super Moderators, Administrators Posts: 28,315 admin
    Same as above, but Los Angeles and best year round harvest angle gives:

    Los Angeles
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 56° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    4.50
     
    4.82
     
    6.05
     
    6.78
     
    6.83
     
    6.80
     
    JulAugSepOctNovDec
    6.69
     
    6.67
     
    6.40
     
    5.85
     
    5.07
     
    4.41
     

    • 100 Watts * 6 hours per night * 1/0.52 end to end off grid system eff * 1/4.41 hours of sun per day (December) = 262 Watt array "break even" for December
    Your location is very good for solar...

    Since it seems like you want to learn about solar power and battery banks... Read up on batteries, get a hydrometer to measure specific gravity, and I highly suggest a Kill-a-Watt meter and DC capable Current Clamp DMM.

    Your lead acid batteries are not fully charged by 10am... They are (hopefully) bulk charged by then (increase in voltage during charging until you hit the setpoint of ~14.75 volts -- Which is then held for 2-6 hours or so---2 hours if lightly discharged and 6+ hours if 50% or more discharged).

    It really depends on what your desires are... Some folks just want the system to "work".... Other folks like to measure and fiddle and get into the details of their power systems.

    Unfortunately, with off grid solar power systems, there is fair amount of maintenance and measurement to ensure the system is running correctly.

    More or less, your battery bank is the "fragile" portion of the system. If you don't treat it right, it will die (either assisted suicide or murder).

    Solar power systems and battery banks just do not generate as much energy as people assume. Utility Power and Generators are amazing for what they do... With Off Grid Solar, you really need to understand the details and be careful about not over discharging your battery bank and doing your monthly maintenance checks for long battery life.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • brownbearbrownbear Registered Users Posts: 22 ✭✭
    Ok so I think I'm going to get one more 100w panel for a total of 300w.  My 20amp charge controller only takes 260w at 12v.  I'll get two 200ah batteries totaling 400ah.  I can use half of that so 200ah.  When my batteries are all charged up do you think I can power my 65in tv all night?  TV uses 100w then the modem router and roku.   For 6 hours?  
  • BB.BB. Super Moderators, Administrators Posts: 28,315 admin
    edited January 2 #10
    BrownBear,

    That is the $1,000 question (solar power questions are free--The answers can cost lots of money).

    First, a 300 Watt panel is going to be pretty close--Get a couple days of clouds, and you would need to cut back on TV usage until the battery bank gets >80-90% state of charge.

    If TV is "optional", then you read a book on some nights, or plug back into the utility power.

    If you want my 2 cents worth of advice... I would choose at least 10% rate of charge (443 Watt minimum array) for a full time >9 month a year usage system. Even then, there will be some times when the weather goes really bad (2 days of dark clouds and you may get around 5% or less of clear day harvest--almost nothing). If you go further (3-4 days on pure battery power), you run the risk of dramattically shortening the battery bank life (take a 1+ year old FLA battery dead and take a couple days to recharge it, the FLA battery will probably fail in subsequent use a few days or couple of weeks later).

    If you "had to run 6+ hours of TV a night" (your base load requirements), I would be derating your system output by 65% or even 50% to give you a larger solar array:
    • 262 Watt Array (Dec minimum) * 1/0.65 = 403 Watt array (65% derating for base load)
    • 262 Watt Array (Dec minimum) * 1/0.50 = 524 Watt array (50% derating for base load)
    And even then, there will be days/times when you simply do not have enough sun, and simply need to use generator, utility, or no-power until the weather clears.

    Granted, in Los Angeles, those stretches of bad weather are rare--So only use can decide how much you wish to overpanel... 443 Watt array (10% rate of charge--That is where I would be aiming (note: calculations are always approximate--If you are within 10% of a predicted value, that is pretty much "dead on" for solar power math).

    You asked about adding more batteries....  In general, it is not a great idea to add more batteries unless you add more solar panels too (see 10% rate of charge rule of thumb)... Double the battery bank AH capacity, then double the solar array too.

    I would stay with 2x 6 volt @ ~200 AH golf cart batteries in series for a 12 volt @ 200 AH battery bank. Golf cart batteries are pretty rugged and forgiving (and relatively cheap)--As long as you take care of the electrolyte levels and keep them from going below 50% state of charge (very often), and get back >~90% state of charge once or twice a week (not to 100% SoC every day--That is hard on FLA batteries).

    If you take care of your batteries--They should last 3-5 years. And if you make a mistake (most everyone "kills" their first battery bank or two), you will have burned a bit less cash.

    After you run the system for a couple of years, you can decide what to do next (upsize system, or whatever).

    If you want to run the TV 12 hours a night, then yes, 4x golf cart batteries would be needed (and a 2x larger solar array too).

    I asked if you are trying to learn how to build/use/understand a solar power system, or what... Getting a hydrometer, DC Current Clamp DMM, and possibly other power meters (like a Kill-a-Watt 120 VAC power meter, or some sort of DC AH/WH meter, or battery monitor) are pretty important to understanding and operating your system. Again, your choice.

    Another issue is selecting the correct AC inverter for your system... Many folks try a 1,500 Watt or larger AC inverter... For this small of battery bank, a 300 Watt TSW AC inverter is a better choice. They use less power, and a few have "on/off" switches and "search mode" that can help save energy too.

    If you go with a >300 Watt array, you will need a new/second PWM controller, or pick another controller (PWM or MPPT) that will meet your system's needs. You just have to accept the fact that larger solar power systems do cost more to build and maintain (and why we suggest the most energy efficient loads you can find, and smaller TV sets when practical). Reliable off grid power systems are not cheap.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Solar Expert Posts: 2,506 ✭✭✭✭✭
    The 300 watts of panels will not actually produce 300W unless in perfect conditions, usually thy produce ~70-80% in normal conditions, so you would be close to the controllers maximum capacity. The TV Roku and modem question, the 400Ah battery should support those without problems. The only area of concern is the array is not sufficient even at 300W, a couple of bad sun days could begin slippery slope of under charging, a very common occurrence with beginners. This can be compound by loads being used during the day, they are subtracting from charge current. For a part time use, weekends for example perfect, but full time use you'll eventually run into trouble, it's cheaper to do things right the first time than having to do it twice. Just my opinions.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • brownbearbrownbear Registered Users Posts: 22 ✭✭
    Hey guys do you think I'll be ok if I get a 3rd 100w panel to total 300w with a 20amp mppt charge controller that supports 260w at 12v and two 200ah batteries to total 400ah.  I'm in Los angeles and it is always sunny here like always 🌞.   Is that a good idea?
  • BB.BB. Super Moderators, Administrators Posts: 28,315 admin
    Exactly, what charge controller do you have? MPPT controllers (good quality) can be over paneled without too much problem (keep them cool/well ventilated).

    Over paneling a PWM controller (check the specifications), is usually not a good idea (PWM do not have the ability to "safely" throttle the output current--MPPT controllers can throttle the maximum output current).

    And, if you only go to 300 Watt of solar panels, then do not double the AH capacity of the battery bank. You would need 2x the array size (2x the 5% or 10%+ calculations a few posts above) to keep a larger battery bank "happy" unless you plan on using a Utility or Genset powered AC Battery Charger to assist.

    300 Watt array is just too small for a 12 volt @ 400 AH battery bank... A 5% minimum array would be:
    • 400 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 377 Watt minimum array
    • 400 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 753 Watt nominal array
    And for daily use year round, I would suggest a 10% rate or charge--Much larger than you are asking for...

    If this is an experiment/learning situation... Keep your 12 volt @ 200 AH battery bank and add the extra panel for 300 Watt total array (if controller supports it), and see what happens. You can always add a second charge controller if you wish... And if you "murder" the first set of batteries, then get your 4x golf cart batteries for 12 volt @ 400 AH.

    If this is something you want to work rain or shine, and support larger loads (modem, routers, Roku boxes are not Zero Watts). Measure your actual system loads (Kill-a-Watt meter or similar) and figure out where to go next... Or, again, if reliability is important and cost less so, go with a 10% or bigger array for your 400 AH battery bank.

    I feel bad not being able to give you an "exact" answer--I just don't know enough about your needs and expectations. 

    Off grid solar energy is (at this time) never going to be cheaper than utility power in the USA. Generators are, for many folks, a better backup system (storm/earthquake damage) for a few days or a week (assuming you can store fuel/have a safe place to run a genset).

    Backup solar power systems--You generally have to pick the minimum "necessary" loads (laptop+cell phone, small LED TV, some LED lighting). When you have maybe 1x 2 hour power failure every few years--Backup solar is very difficult to justify (when you need to check batteries every month, and replace the "golf cart" batteries every 3-5 years).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Solar Expert Posts: 2,506 ✭✭✭✭✭
    brownbear said:
    Hey guys do you think I'll be ok if I get a 3rd 100w panel to total 300w with a 20amp mppt charge controller that supports 260w at 12v and two 200ah batteries to total 400ah.  I'm in Los angeles and it is always sunny here like always 🌞.   Is that a good idea?
    Not really a good idea, Los Angeles has on average ~106 days pre year with partial sun, string 3 of those together then the process of undercharging begins, it's like a cancer for batteries, at first everything looks healthy but underneath the damage grows, by the time the symptoms start to show, it's usually too late to remedy. A seasoned operator may be able to monitor the ballancing act but would be unlikely to be in that situation in the first place, probably because he/she has been there before to learn the lesson.
    https://www.currentresults.com/Weather/California/annual-days-of-sunshine.php
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • brownbearbrownbear Registered Users Posts: 22 ✭✭
    edited January 6 #15
    So it's a good idea as long as I don't let the batteries drop low especially on a cloudy day?  Is the discharging to a low level what we don't want to do?  Besides that do you think that set up is a good idea?
  • mcgivormcgivor Solar Expert Posts: 2,506 ✭✭✭✭✭
    edited January 6 #16
    There are so many variables involved in solar, a system should be designed to account for worst case scenario. Personally I believe information provided points out shortcomings which should be addressed. They are a collective knowledge base, offered without  charge, you can choose to ignore all suggestions but I'm confident in my assumption you'll be back asking why your batteries no longer work as they once did. The ballancing act is extremely difficult, you are correct, limiting discharge will be advantageous, but extensive knowledge is a prerequisite, knowing the details is something gained over time, for this reason I would think your approach is not ideal. Sorry, but just an option, others may disagree.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • jonrjonr Solar Expert Posts: 1,188 ✭✭✭✭
    @brownbear ;    You haven't made it clear if you are willing to use utility power whenever the sun is lacking.  If so, you can safely design right to the limit.
  • brownbearbrownbear Registered Users Posts: 22 ✭✭
    Yes I'm using utility power when my battery is below 12.2v I just unplug from inverter and plug into the wall
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