Updating system and Voltage throughput
Gonpostal
Registered Users Posts: 2 ✭
I think the basic question is - Is the panel voltage independent of the battery/inverter voltage?
I have a remote cabin with a small 12V system which I'm thinking of upgrading to 24V. I have an EPEVER Mppt Solar Charge Controller 80a 12v/24v/36v/48v Auto Max 200V 6000W. I have two NEA 320 Watt, 12V panels wired in parallel. I'm thinking of upgrading my inverter to 24v and rewiring my battery bank, which is eight 6V Duracell EGC2 Golf Car batteries.
1) I guess first question is, is it any great benefit to convert to 24 volts?
2) Do I have to rewire the panels?
3) Would this prevent me from being able to upgrade a SINGLE panel?
I have a remote cabin with a small 12V system which I'm thinking of upgrading to 24V. I have an EPEVER Mppt Solar Charge Controller 80a 12v/24v/36v/48v Auto Max 200V 6000W. I have two NEA 320 Watt, 12V panels wired in parallel. I'm thinking of upgrading my inverter to 24v and rewiring my battery bank, which is eight 6V Duracell EGC2 Golf Car batteries.
1) I guess first question is, is it any great benefit to convert to 24 volts?
2) Do I have to rewire the panels?
3) Would this prevent me from being able to upgrade a SINGLE panel?
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Comments
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24 volts is better , smaller wires more power to loads .You can add more solar panels to your controller .I’m thinking if you have 12volt solar panels you would need to have the panels in series so the mppt is working .
You really want your panel voltage about double so your mppt controler puts out max power .
But you have a 200 volt controller so you can series your solar panels but stay below 160 volts or so.You would need a third panel that had the same voltage or within 10 % .
With 8 215 amp hour battery’s you really need 4 if not 6 of those panels .I use the same batteries with 16 series/ parallel and when I figure it out I thought 3500 watts of solar would be good for my system
So in your case half the battery’s would need half the solar power (1750 watts )
4 panels could work if you aren’t drawing the battery’s down .I’ve never herd any one say I just have to many solar panels .Out back flex power one with out back 3648 inverter fm80 charge controler flex net mate 16 gc215 battery’s 4425 Watts solar . -
Gonpostal said:I have an EPEVER Mppt Solar Charge Controller 80a 12v/24v/36v/48v Auto Max 200V 6000W. I have two NEA 320 Watt, 12V panels wired in parallel.
Next Energy Alliance USNEA-320M (320W) Solar Panel (solardesigntool.com)
If so they are 32 volt (VMP) panels. They are fine to use as is in a 12 volt system, but would need to be in series for a 24 volt system.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites, Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects. -
Welcome to the forum GP,
I always like to design a "balanced" system... To do that, normally we figure out the loads (Amp*Hours @ xx Volts or Watt*Hours per day), size the battery bank to support that, then size the solar array to keep the battery bank "happy" and sized on location (hours of sun per day).
Don't have loads, so start with the battery bank. 8x 6 volt @ 230AH golf cart batteries.
First, generally size the battery bank to supply 2 days of power and 50% maximum discharge... Can do 1 day of storage and 50% discharge for a weekend/sunny weather cabin.- 2x 6 volt series string = 12 volt battery bank
- 4x 12 volt series strings of 230 AH = 920 AH @ 12 volt battery bank
- 920 AH * 1/2 days * 0.50 max planned discharged (for longer life) = 230 AH per day @ 12 volts
- 230 AH * 12 volts = 2,760 WH per day
There are some interesting things you can do with 24 Volt battery bank... For example, there are a fair number of 24 volt "RV" type water pumps (replace a 12 volt pump) and you can get a good selection of 24 VDC capable LED lamps, and even USB chargers--And leave the 120 VAC for the "rest of the system" (modern 120 VAC energy star rated appliances are almost as efficient as their DC counterparts). And let you only run the AC inverter when needed (inverters draw something like 6-20+ Watts just turned on with no loads--Tare losses).
Note that the MPPT solar charge controller (like you have) array size supported is directly related to the battery bank voltage... The controller will output 80 amps (in your case) at 12, 24, or 48 volts... Which means that you can, for example, manage a 2x larger array at 24 volts vs 12 volts with the same controller... (AC inverters are "captive" to there base battery input voltage--No 12/24/48 capable AC inverters out there (in the mass market) that I have seen.
Your present system is almost what I suggest as an "aim point" for a very efficient near normal off grid existence in a conservation minded family/home (3,300 WH per day for Lights, full size 120 VAC fridge, clothes washer, water pump, laptop computer, cell charger)...
If you are ever planning on a larger system (full time residence)--You could probably justify 48 VDC too...
Anyway, back to "keeping your battery bank happy". Generally suggest 5% minimum rate of charge for weekend/non-winter cabin. 10%-13% for full time off grid. And >13%-20% or so for winter harvest (oversize solar array to save genset runtime).- 920 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 866 Watt array minimum
- 920 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1,732 Watt array "nominal"
- 920 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 2,252 watt array "typical" cost effective maximum
Re-configuring your 8 batteries as 2 series * 4 parallel (12 volts @ 920 AH), or 4 series * 2 parallel (24 volts @ 460 AH), or 8 series * 1 parallel (48 volts @ 230 AH)--Same energy storage, just battery bus voltage changes, and as you get higher voltage, the lower DC battery bus current (and smaller AWG wiring you can use). For example, the above 5/10/13% calculations give identical results with the same 8x Golf Cart Bank.
Next, sizing the battery bank based on your daily loads and location... Lets use 2,760 WH per day somewhere near Denver Co, with a south facing fixed array:
http://www.solarelectricityhandbook.com/solar-irradiance.htmlDenver
Measured in kWh/m2/day onto a solar panel set at a 50° angle from vertical:
Average Solar Insolation figures
(For best year-round performance)
For the moment, assume you are not there in winter (Nov thru Jan)--Pick February at 4.85 hours of sun (no shade from trees, buildings, deep in valley), the array would be:Jan Feb Mar Apr May Jun 4.27
4.85
5.58
5.62
5.81
5.90
Jul Aug Sep Oct Nov Dec 5.72
5.60
5.87
5.60
4.52
4.12
- 2,760 WH per day * 1/0/.52 off grid AC system eff * 1/4.85 (Feb) break even hours of sun per day = 1,094 Watt array February "break even" harvest
- 80 amps * 14.5 volts charging * 1/0.77 panel+array deratings = 1,506 Watt array "cost effective" maximum for your 80 Amp controller on a 12 volt battery bank
- 866 Watt array minimum suggested array (5% rate of charge)
- 1,094 Watt array "break even" February (long term daily average) harvest
- 1,506 Watt array "12 volt suggested max" array
- 250 Watts * 1/100 AH (@ 12 volts) * 920 AH (@ 12 volt) battery bank = 2,300 Watt max AC inverter for your present bank
- Suggest around 1,800 Watts max for a 12 volt battery bank (basically copper wiring AWG/Costs/Voltage drop design issues)
- 2,300 Watt inverter / 2 = 1,150 Watt "nice size" inverter for your bank
- 2,720 Watt*Hours per day / 5 hours per night (example) of AC power = 544 Watt "average" draw (5 hours per night from existing battery bank)
Cheaper to do "paper designs" first and figure these issues out first--Then look at the hards?are designs next (array/solar panels, charge controller, AC inverter, battery bank)--Again paper designs before buying hardware.
Your thoughts/corrections to my guesses?
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Photowhit. Apparently I do. I just looked up the stats and they're 32V. I have no idea what let me to believe they were 12V. Probably because the cheap 100W pair I had upgraded from last year were.
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Note: I had a typo in my previous post... Suggest a maximum AH size for battery bank is ~800 AH or larger to step up to next higher bus voltage (not 80 AH).
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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