PWM or MPPT

I have a 175 watt solar panel with 36.5V and 4.80A, from which I have to charge a 12V battery through a PWM charge controller, means 14V x 4.80A = 67W , so the panel works on 67watts? If I use a MPPT charge controller will it makes any difference?
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|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
If the panel were connected directly to the battery for an extended period time, the voltage would continue to rise above the safe limits which would generate heat and ultimately damage the battery, hense the need to control.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
Solar panels output current in proportion to the amount of sun. Full noon time sun, panel pointed at sun, you will get ~Imp (current maximum power) from zero volts to Vmp, then current will fall to zero amps at Voc (Voltage open circuit). Note--This is an approximation, but works good enough for this explanation. If you have 50% sun, then you get 0.50 * Imp worth of current).
Power is = Voltage * Current... If you have 4.8 Amps from the solar panel, the power "into the battery" depends on the battery voltage:
- PWM charging a 12 volt battery with a "24 volt" solar panel:
- Pbatt ~ Vbatt*Ibatt = 10.5 volts battery * 4.8 amps (near dead battery) = 50.4 Watts
- Pbatt = 12.8 volts * 4.8 amps (charging battery) = 61.44 Watts
- Pbatt = 14.75 volts * 4.8 amps (~80-90% state of charge) = 70.8 watts
- PWM charging a 24 volt battery with "24 volt" panel:
- Pbatt = 29.5 Volts * 4.8 amps (80-90% SoC battery) = 141.6 Watts
An MPPT (Maximum Power Point Tracking) controller "matches" the high(er) voltage / low(er) current from the solar panel to the battery's low(er) voltage / high(er) current requirements.Think of the PWM controller like a 1 speed transmission.
Think of the MPPT controller like an automatic transmission that matches the "optimum" panel voltage+current input (i.e., RPM and Torque from engine) to that of the battery bank (i.e., RPM and Torque at wheels).
-Bill
Regarding loss factor. I use the same loss factor for both pwm and mppt controllers of 0.77 ...
More or less, solar panels are rated under standard sun and room temperature (75F or so).
In real life, panel Vmp is roughly 81% of factory spec in warm to hot weather in full sun. Add a few percent of loses for controller and dust on panels, you get a nominal 75% 77% end to end efficiency (solar array to charge controller to battery bank).
Add battery charging loses (80 to 90% efficiency for flooded cell lead acid batteries), ac inverter loses (120/240 vac), and you are looking at panel to ac load efficiency of 52%.
For 400 Watt or less array, a pwm system usually is more cost effective.
For systems over 800 Watt array, mppt systems usually make more sense.
My suggestion is to paper design 2 or more different systems and cost them out. And see what works better for you.
Bill
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
https://www.solar-electric.com/learning-center/batteries-and-charging/mppt-solar-charge-controllers.html
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
Things t note in designing small-scale systems, MPPT type controllers also need some 'head space' so solar panels should present about 30% higher voltage than the system will be charging at. Hence a 12 volt system that is charging at 15 volts should present about (15x1.35=) 20.25 volts. This is higher than the VMP of 12 volt nominal panels so multiple panels or panels with more than 36 cells should be used.
MPPT shines when solar panels aren't matched to battery voltage, like cell configurations of 54 and 60 cells. There are some very large panels made with 72 cells now, making large 24 and 48 volt arrays on PWM more cost effective and some what reason to consider. Having run a small cabin on a 24 volt 16-1700 watt array and a 60 amp PWM controller for 5-6 years I am comfortable in saying it works out nicely.
I've seen production curve charts at Midnite Solar website, but they're for larger controllers. I don't know if they would apply to smaller controllers. At altitude, you'll want to derate the controller output, but classics may still be big for "extremely small scale systems".
If high altitude is also high latitude, self consumption could be an issue. Many (most, all?) mppt controllers take more power just being on and waiting for input vs pwm. This self consumption would be a factor in any case, but could be a deal breaker in an unattended high latitude winter application.
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
http://www2.exide.com/Media/files/Location Data/Battery Charging & Storage Specs 11_13_15.pdf
I am available for custom hardware/firmware development
As far as I know MPPT charge controller revert to PWM at some point after reaching absorb, once in float it is likely receiving a pulsed current flow once in float.
A PWM controller can't control peak current or voltage - when it turns on, how can it avoid > 5A flowing?
I am available for custom hardware/firmware development
I am available for custom hardware/firmware development
Except that most 12V inverters will complain or turn themselves off if battery voltage gets to 16 volts. or so. Sometimes less.
boB
A pwm controller will be at or near battery voltage. Unless the battery is very small (like a capacitor) the pulsed voltage at the battery won't get to anything like Vmp.
I'm still learning this stuff though, so I stand to be corrected. I don't see how ripple is a problem for batteries.
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
Do you understand that 'Float' is a stage of charging when the charge controller limits the voltage, using pulses and the electrochemical nature of batteries to limit the system voltage. At these lower voltages very minimal amounts of current flow to the battery.
By definition, Float is a state of full or nearly full charge. If the charge controller is allowing higher voltage then it is not in 'float' stage and we have no reference to problems from your source. If you just don't want to understand... Don't.
It's not in 'Float' the parameters of your argument.
570W mono / 220AH GC
Photowit, if you think that a PWM controller can limit peak voltage (ie, during msecs of on time) or that a PWM controller never switches on in float, I'm fine with you "going away".
fratermus is correct - ie, if only 5A flows out of 20A of panels, the voltage produced (and seen by the battery when a PWM controller is switched on) will be close to Voc.
I am available for custom hardware/firmware development
Hope some will find this information useful, interestingly this use of high frequancy pulses is used in desulfators, for what that's worth.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.