Simple System - What to Buy??

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jped
jped Registered Users Posts: 8 ✭✭
edited April 2016 in Solar Beginners Corner #1
I would like a 'simple' system but the more I research, the more complicated it gets. First calculate my load. I know I don't need much. (ie. some lights for my trailer, charge some phones, cordless tools) That's about it for now but maybe want to expand. Can I maybe get a 250W panel (Poly or Mono? 12V or 24V???) to charge 2 - 6V batteries (Trojan T-105). Seems simple. Now what controller? PWM or MPPT. I've read all the pros and cons and can't decide. Also can't figure out the difference in amps (Morningstar 15, 20, 30?) I might want to expand in the future so maybe go 15 MPPT? Is that enough for expansion?
 I know figuring out Exactly what you want to run first is the best way but does someone have a simple - "buy this, this and this and ti will WORK" - kind of answer. I don't mind spending money on the right, quality stuff.

200-250W Panel - $250-$300
2 - 6V Batteries - $260
Controller  - MS Sunsaver15 MPPT - $350 (too much for what I need? but want to expand)
                   MS Sunsaver15 PWM - $230
Inverter - ??

Total $1000+ (CDN)

I know it's too many questions but I just want a system that works. Thanks
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    edited April 2016 #2
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    NOTE: I have updated two sets of equations below, in bold (thank you vtMaps)... They were using a wrong charging voltage (12 volts instead of proper 14.5 volts).

    OK... I like to start with Loads--http://www.solar-electric.com/inverters-controllers-accessories/inverters/moin/mosu300wasiw.htmlWhich then sets your battery bank size and solar array wattage.

    But, I can start with 2x golf cart batteries too and size the system/estimate its power output.
    • 14.5 volt * 220 AH batteries * 1/0.77 panel+controller derating * 0.05 rate of charge = 207 Watt minimum (weekend/seasonal usage)
    • 14.5 volt * 220 AH batteries * 1/0.77 panel+controller derating * 0.10 rate of charge = 414 Watt array nominal (full time off grid)
    • 14.5 volt * 220 AH batteries * 1/0.77 panel+controller derating * 0.13 rate of charge = 539 Watt array "cost effective" maximum
    Next, how much load can your battery bank support. For a full time off grid system, I suggest 1/4 per day discharge for two days, 50% maximum discharge for longer battery life. For an RV system, perhaps you can justify 50% discharge for 1 day (weight/area available).
    • 12 volts * 220 AH * 1/2 days storage * 0.50 max discharge * 0.85 inverter eff = 561 Watt*Hours per day (120 VAC @ 2 days storage)
    • 12 volts * 220 AH * 1/1 days storage * 0.50 max discharge * 0.85 inverter eff =1,122 Watt*Hours per day (120 VAC @ 1 day storage)
    More or less, that means if you have a 30 Watt laptop + 10 watts for a light + 10 watts for phone/radio/etc. = ~ 50 Watt load.
    • 561 WH per day storage (two days) * 1/50 Watt load = 11 Hour per day average loads
    Then there is the the amount of energy a solar array can output. I do not know where you are located... You can use the following link to get information for your camping region. Note that many folks flat mount arrays on RV roofs, but in the far north/winter months, tilting the panels may give you significant more harvest from the sun:
    http://solarelectricityhandbook.com/solar-irradiance.html

    Vancouver
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a horizontal surface:
    Jan Feb Mar Apr May Jun
    1.09
              		2.00
              		3.10
              		4.51
              		5.39
              		5.69
     
    Jul Aug Sep Oct Nov Dec
    6.00
              		5.15
              		3.92
              		2.14
              		1.27
              		0.90
     
    So, April through September would give you a minimum of 3.92 Hours of sun per day (long term average):
    • 207 Watt array minimum * 0.52 typical system eff  * 3.92 = 422 Watt*Hours per day
    • 414 Watt array nominal * 0.52 typical system eff  * 3.92 = 844 Watt*Hours per day
    • 539 Watt array cost effective max * 0.52 typical system eff  * 3.92 = 1,097 WH per day
    And then there is what a flooded cell battery bank can output (assuming 50% maximum discharge for longer battery life):
    • 12 volts * 220 AH * 0.85 inverter eff * 1/20 hour discharge rate = 112 Watt (AC load) 5 hours per night, 2x nights
    • 12 volts * 220 AH * 0.85 inverter eff * 1/8 hour discharge rate = 280 Watt (AC load) for ~3+ hours continuous
    • 12 volts * 220 AH * 0.85 inverter eff * 1/5 hour discharge rate = 449 Watt max short term AC load
    • 12 volts * 220 AH * 0.85 inverter eff * 1/2.5 hour discharge rate = 898 Watt max surge load (seconds)
    And a nice AC inverter that fits into the above, plus as remote on/off and "search" mode (low power standby) is the MorningStar 300 Watt TSW 12 volt input AC inverter.

    Before we start looking at exact equipment--How does the sizing of the above system look? Will it meet your needs?

    How many solar panels can you fit on the roof? Do you want to tilt the panels in winter?

    Anyway, will stop there for the moment and wait for your comments.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • jped
    jped Registered Users Posts: 8 ✭✭
    #3
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    That all looks great, Bill. Sizing looks to be exactly what I need for now. I guess in order to expand in the future, would it be as easy as doubling the panel and batteries? (Another 250W panel and two more 6V batteries). I guess it depends on what controller I have (which is my biggest question)? Also, I can tilt the panels, throughout the day even, if necessary. It's a wide open remote site. Would the whole system have to be altogether right beside the trailer? Or could it be further away?
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
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    BB. said:
    But, I can start with 2x golf cart batteries too and size the system/estimate its power output.
    • 2 * 6 volt * 220 AH batteries * 1/0.77 panel+controller derating * 0.05 rate of charge = 171 Watt minimum (weekend/seasonal usage)
    • 2 * 6 volt * 220 AH batteries * 1/0.77 panel+controller derating * 0.05 rate of charge = 343 Watt array nominal (full time off grid)
    • 2 * 6 volt * 220 AH batteries * 1/0.77 panel+controller derating * 0.05 rate of charge = 446 Watt array "cost effective" maximum
    Bill, you've totally lost me here.  For example, a 171 watt array derated to 77% is 131.6 watts.  Divided by charging voltage of 14.4 = 9.14 amps.  That is less than 5% charge rate for a 220 ah battery.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #5
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    Thank you vtMaps--I have updated the posts with the proper charging voltage (updated math in bold).

    Jped,

    In general, people don't change panel tilt/direction over the day on a long term basis... It is just easier to fix a tilt (perhaps adjust 2-4 times a year for winter/summer), usually is good enough. Getting a few more solar panels is much less  than trying manual tracking throughout the day.

    Where to mount the panels/battery system is your choice. However, if you are planning on using 12 VDC directly for your loads--The battery bank and charge controller should be either in or right next to the living space. It is very difficult (and expensive) to send 12 VDC anything more than a handful of feet--especially with larger loads (voltage drop of cable for 12 volt and high current is the problem). And, since you need to check electrolyte level, battery voltages, watch for corrosion/animal/other issues, "remote monitoring" cabiling, etc.--Keeping the main system components next to your living quarters can save a lot of walking

    If you need to send power any distance, than using a (small) AC inverter is generally a good choice. 120 VAC is 10x the voltage and 1/10th the current. All of a sudden a 14 gauge cable will send AC power 100' without any problem. And you can add another 15% or so more solar panels (and battery capacity) to make up for the AC inverter eff of ~85%.

    Charge controller--If cost is important and the array is small, perhaps you can use a PWM charge controller. Less than 400 Watt array, PWM plus "12 volt" (Vmp~18 volt) solar panels will work fine.

    However, if you go over ~800 Watt array, then a MPPT controller plus ~30 Volt Vmp panels (or other "GT designed solar panels) may make economic sense (MPPT controllers are expensive, GT Panels are about 1/2 the cost of Vmp~18 volt panels per Watt).

    Also MPPT controllers generally have more functions (larger micro processor). You can connect them to a computer to log your history, easier to reprogram/more charging options/settings/etc. Some even have native Ethernet connectivity.

    Also--If you are planning on making a larger capacity battery bank--Then you should look at the native battery bank working voltage--I.e., 12/24/48 volt battery bank. For various reasons, here are some rule of thumbs suggestions:
    • 12 volt battery bank--About a maximum of 1,200 to 2,000 Watt AC inverter (or DC continuous loads)
    • 24 volt battery bank--About 2,400 Watt maximum load
    • Over ~2,400 to 4,000 Watts, use a 48 volt battery bank
    • Suggest around 800 AH maximum battery bank Amp*Hour capacity. 10% rate of charge is 80 amps--That is roughly the maximum charging capacity of a "large" MPPT type solar charge controller... I.e., 800 AH @ 12 volt battery bank vs 400 AH at 24 volt vs 200 AH @ 48 volt battery bank--All store the same amount of energy--But, first one is 80 amps charging (at 10% rate of charge) vs 40 amps @ 24 volts and 20 amps @ 48 volt charging. Same charge controller can manage a 2-4x larger solar array with higher bank voltages.
    • It is very difficult to "cost effectively" expand a solar power system by ~2x or more in battery capacity without a major redesign and replacement of equipment (new batteries, new AC inverter at higher working voltage, new/larger charge controllers and/or second set of charge controller + solar panels, etc.). Design the system for your final needs (batteries last 4-8 years, electronics ~7-10+ years). If you plan on enlarging the system in 1-2 years--I highly suggest you cost out the major components for the larger design--Even if you install 1/2 the array and 1/2 the battery bank AH capacity now--Then spend the money as it becomes available/needs arise in the future.
    Note the above are rough rules of thumb to get your "close" to a workable system design. You should do several versions with different options and work out the design details and costs--Before you purchase any hardware. And make sure to include shipping/insurance costs--For example 140 Watt solar panel may cost $2 per watt, but be cheaper to ship vs a 280 Watt panel (at $1 per watt) that can only ship truck. Also, solar panels are shipped to the warehouse on pallets--When you order a fraction of a pallet at a time, it can cost near the price of the panel to package and ship that panel (I am not in the solar business--Just suggested "issues" to watch out for).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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