How To Size a Solar Charge Controller
Sizing Common Solar Charge Controllers
All renewable energy (RE) systems with batteries should include a charge controller. In this article we'll principally be referring to solar charge controllers . Charge controllers prevent battery overcharging and also prevent the batteries from sending their charge back through the system to the charging source (i.e., the solar panels). Think of a solar charge controller as a battery nursea"its job is to monitor the battery bank, feeding it what it needs and checking its vital signs. Since a solar controller does its work in line between the solar panel array and the batteries, it would make sense that its selection and sizing would be influenced by those components. And that's exactly the case.
Voltage and amperage (or current) are the parameters we use in solar charge controller sizing. The solar controller must be capable of accepting the voltage and current produced by the DC source (usually solar panels) and delivering the proper voltage and current to the batteries. This situation might make you think that the DC source, charge controller and batteries must all share a common voltage. While that is one system design strategy used in many installations, it's not the only one. More on the alternatives in another article. For now, it's one voltage for everyone!
Technically speaking, the DC source must always have a higher operating voltage than the battery bank in order for current to flow from one to the other. A handy way to remember this fact is the statement, "curent flows downhill." For the purpose of this discussion, we'll use nominal voltage which means common battery voltages. Nominal voltage in this sense is synonymous with battery voltage. Since batteries (where they are used) are in many ways the heart of an RE system, we can call the bank's voltage the system voltage. The system voltage selected for any given installation is usually, though not always, determined by the battery bank required by the application; the inverter, if one is used, will also influence the choice of system voltage.
Sizing comes down to this: there's the quick method, which will very likely give an acceptable, if perhaps oversized result, but won't describe the why here - we'll just show you the steps.
Short Method for Sizing Solar Charge Controllers
- For PWM and PWM shunt solar controllers, select one that is rated at your system voltage (same nominal voltage all the way through the system).
- Divide solar panel array total wattage by system voltage.
- Add 20% as a safety margin (i.e., (result of Step 2) X 1.2).
- Select a solar controller rated at or above the result of Step 3.
Example of the Short Method
- Two 125W, 12V nominal modules. System is 250 W, 12 Volt nominal. Solar charge controller will be 12 Volts.
- 250 A 12 = 20.83
- 20.83 * 1.2 = 24.996 amps
- You could use a Xantrex C35, a 35 amp solar charge controller; or a Morningstar Prostar 30, a 30 amp solar charge controller , for example. Any 12 volt solar controller greater than 25 amps will work.
Frequently Asked Questions
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QUESTION:
How do exactly solar charge controllers work?
I've been reading and reading online about solar projects and so on... But one thing puzzles my mind is when u have a charge controller that has a shut off what voltage will it supply to whatever is using the power? I mean what range of voltage will you be getting out of it? In between the min and maximum battery levels or a constant 12?-
ANSWER:
A charge controller monitors the battery's state-of-charge to insure that when the battery needs charge-current it gets it, and also insures the battery isn't over-charged. Charge controllers are rated based on the amount of amperage they can process from a solar array. If a controller is rated at 20 amps it means that you can connect up to 20 amps of solar panel output current to this one controller. The most advanced charge controllers utilize a charging principal referred to as Pulse-Width-Modulation, which insures the most efficient battery charging and extends the life of the battery. Even more advanced controllers also include Maximum Power Point Tracking which maximizes the amount of current going into the battery from the solar system by lowering the panel's output voltage, which increases the charging amps to the battery. If a panel can produce 60 watts with 17.2 volts and 3.5 amps, then if the voltage is lowered to say 14 volts then the amperage increases to 4.28 (14v X 4.28 amps = 60 watts) resulting in a 19% increase in charging amps for this example.
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QUESTION:
How do i connected solar charge controllers to charge 168volts batteries ?
The inverter is 10KVA 168volts. I cannot get a 168 Volts charge controllers. Only 48 volts are available.-
ANSWER:
You can't, you need the charge controllers that are configured for the battery voltage. You have to find companies that specialize in building charge controllers and contact them. Charge controllers are available for most voltages..
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QUESTION:
I 180V, 10kVA solar system. I only have 48V charge controllers available. How can I connect them?
For a 10kVA solar system having charge controllers and solar modules and batteries, there are only 48V charge controllers rather than one of 180V. How do I configure these charge controllers to give me the desired control?-
ANSWER:
I'm assuming you have a bank of batteries in series to get 180 volts DC, with a bunch of solar arrays in series to charge them.180 volts is high enough that you could get into breakdown problems, as well as shock hazard problems. Why not reconfigure them to a lower voltage series/parallel arrangement, so that your highest voltage is 48 volts, or even 24 volts. Then you can use standard charge controllers, as well as standard inverters.
What made you pick 180 volts? I don't think you can get inverters that operate at that voltage.
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QUESTION:
i need schematics or circuit diagrams for solar charge controllers?
i have a solar panel that can give up to 20v dc supply.....i need to make a charging circuit that can charge a 12v gel cell battery....anyone know any site with useful circuit design??-
ANSWER:
I did two Google searches.
The first for [solar charge controller circuit diagram]
http://www.google.com/search?hl=en&q=solar+charge+controller+circuit+diagram&rlz=1R2GGLL_en&aq=2&oq=solar+charge+controller&aqi=g10
Did not see much there till I got to the bottom of the page.
Several links equaling other searches.
[solar battery charger circuit diagram]
http://www.google.com/search?hl=en&safe=off&rlz=1R2GGLL_en&newwindow=1&q=solar+battery+charger+circuit+diagram&revid=1321056361&ei=sSYtSo75IKXoswOQrqmCCw&sa=X&oi=revisions_inline&resnum=0&ct=broad-revision&cd=1[solar wiring diagram]
http://www.google.com/search?hl=en&safe=off&rlz=1R2GGLL_en&newwindow=1&q=solar+wiring+diagram&revid=1690969710&ei=RigtStSUMp-ctgPxhZzmCg&sa=X&oi=revisions_inline&resnum=0&ct=broad-revision&cd=3[solar battery charger circuit diagram]
http://www.google.com/search?hl=en&q=solar+charge+controller+circuit+diagram&rlz=1R2GGLL_en&aq=2&oq=solar+charge+controller&aqi=g10
This the most promising thing so far.
Voltage Doubler for Solar Battery Charger -
SolarFind out how to make a current controlled
solar battery charger using an LM317T ...
Find out how to construct an AC voltage doubler circuit. ...
Part way down the page is this link;
Solar Charge Controller
Find out more about Solar Charge Controllers
Article Last Modified: 15:43, 29th Jul 2008
solar | electronics | electric circuit
http://www.reuk.co.uk/Solar-Charge-Controller.htm
To another link:
Solar Charge Controller
Find out more about Solar Charge Controllers
solar | electronics | electric circuit
http://www.reuk.co.uk/electric-circuit.htm
Ok I quit, lots to look at though.
Next search [solar charge controller schematic]
http://www.google.com/search?hl=en&q=solar+charge+controller+schematic&rlz=1R2GGLL_en&aq=5&oq=solar+charge+controller+&aqi=g10
This again, most promising, several circuit projects and
schematics there.You are only allowed 10 links in an answer here.
The last result is where I would start.
Sounds like an interesting project, best wishs to you.
Wingman
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QUESTION:
Solar Charge controllers?
A charge controller usually has 3 terminals, solar panels, battery and
load. If i measure the amperage and voltage of each of the terminals,
the results i got was the amperage and voltage flowing through the
cable at that very instance?Cables from the solar panels to the charge controllers mean the
charging state?What about the cables from the charge controllers to the battery?
And also the cables from the charge controllers to the load?
Can someone clarify the amperage and voltage that i got in every
section that i mentioned above means...?The results that i got from the battery and the load is about the
same. Why?Thanks.
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ANSWER:
Okay, let's do this a bit at a time.
When the sun shines the solar panel will produce power, this is passed to both the battery and the load with the load taking preference. When enough power is generated to power the load, the excess is diverted to the battery to charge it. Under these conditions when you measure currents in the circuit you will find that the sum of the currents in the battery and load circuit will equal the solar panel current. Note that if the battery current is negative in value, this means that the sun cannot provide all the power for the load and the battery is supplimenting the solar panel output.The cables from the charge controller to the battery carry current in both directions depending on the load at that time and the output of the solar panel, see the note above.
Cables from the charge controllers to the load carry current in one direction only, this current is supplied either from the solar panel or the battery.
Cables from the solar panel to the charge controller carry current in one direction only.
The results that i got from the battery and the load is about the
same. Why? Looking at the first parragraph and assuming the sun is producing enough power in the solar panel, your results indicate that half of the panel output is going to the load and half is being used to charge the battery, this is a very good position to be in.BUT
If the ammeter reading in the battery line is negative, then half of the load power is being supplied by the solar panel and half from the battery, this is not a good position to be in as tha battery will eventually go flat.If you want to study this circuit, you need ammeters in the battery line, the load line and the solar panel line, the battery line ammeter must be able to indicate a negative or positive current flow to show if the battery is being discharged or charged.
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