Solar Panel Voltages?

[97435207]

Hello,
i was just wondering about how i could make my 24v solar panel be 12v to go into a charge controller and i had an idea. Could i hook up a step down module to convert the solar panel voltage to 13.8?

Thanks for any infnomation

[Sunking]

Use a MPPT controller. You can charge a cell phone with a 100 volt panel.

[97435207]

Use a MPPT controller. You can charge a cell phone with a 100 volt panel.

Thanks for the reply. I know i could just use a mppt but would this methord work?

[Sunking]

Thanks for the reply. I know i could just use a mppt but would this methord work?

Cannot say it any clearer, use a MPPT Controller, that meets or exceeds your panel output and step down to any battery voltage you want. The whole point of using MPPT is to allow you to use much less expensive Grid Tied Panel operating at high voltages to gain efficiency and lower installation cost.

[97435207]

Cannot say it any clearer, use a MPPT Controller, that meets or exceeds your panel output and step down to any battery voltage you want. The whole point of using MPPT is to allow you to use much less expensive Grid Tied Panel operating at high voltages to gain efficiency and lower installation cost.

Ok i understand that mppt would work but thearecticly could the step down module work?

[Sunking]

Ok i understand that mppt would work but thearecticly could the step down module work?

A MPPT controller is a Step Down converter called a DC-to-DC Buck Power Converter. Power In = roughly Power Out minus small conversion losses. It can take 100 watts at 100 volts and 1 amp input, and convert it to 12 volts at 8.3 amps output, or 24 volts @ 4.15 amps or 48 volts @ 2.0775 amps, or whatever you want. You can even find a rare one or two that can do both Buck and Boost.

My answer has not changed. Use a MPPT controller. If you use a PWM controller using a 100 watt 24 volt panel, on a 12 volt battery, you now have a 34 watt system. Use a MPPT controller and you have a 100 watt system using a 100 watt panel. PWM controllers are obsolete and once you go above 200 panel watts is a lot more expensive than MPPT.

[97435207]

A MPPT controller is a Step Down converter called a DC-to-DC Buck Power Converter. Power In = roughly Power Out minus small conversion losses. It can take 100 watts at 100 volts and 1 amp input, and convert it to 12 volts at 8.3 amps output, or 24 volts @ 4.15 amps or 48 volts @ 2.0775 amps, or whatever you want. You can even find a rare one or two that can do both Buck and Boost.

My answer has not changed. Use a MPPT controller. If you use a PWM controller using a 100 watt 24 volt panel, on a 12 volt battery, you now have a 34 watt system. Use a MPPT controller and you have a 100 watt system using a 100 watt panel. PWM controllers are obsolete and once you go above 200 panel watts is a lot more expensive than MPPT.

Ok so are buck converters diffrent from a normal dc/dc step down converter regulator?

[Sunking]

Ok so are buck converters diffrent from a normal dc/dc step down converter regulator?

Much different. When it comes to DC, there are two ways to reduce voltage.
The ole fashion modern way with Transistors and integrated circuits was to use either a Shunt or Series Regulator. That is what a PWM Controller basically is, ANALOG. They all share one common pitfall of: Output Current = Input Current Bad, very very Bad. You take a 100 watt Solar Battery Panel which has a Vmp of 18 volts and Imp of 5.5 amps on the Input of the Regulator, and on the output you have 12 volts @ 5.5 amps. What is wrong with that picture?

Two things are wrong.

1. Battery panels (low voltage) cost 2 to 8 times more than GT panels. So instead of buying a 100 watt $100 GT panel, you just spent $200 to $800 for a low voltage battery panel.


2. This is the real fun and educational part you did not catch the first time, and still have not caught on to. Wake Up. INPUT CURRENT = OUTPUT CURRENT. You still do not get it do you? 5.5 amps x 12 volts = 66 Watts from a 100 Watt Panel. You need another 50 watt panel to make up for the 34 watts you lost being so cheap buying a $30 PWM controller rather than $100 for a MPPT unit. You just spent more money for being to cheap for less power.

MPPT is just a fancy name DC-To-Dc Power Converter. I did not say Voltage Converter. I said Power Converter. A Power Converter converts Power from one voltage to another voltage. Power In = Power Out. well minus 2 to 3% for conversion losses. On a MPPT Controller Current Out = Power In / Battery Voltage. So that same low voltage 100 watt solar panel, or a high voltage 100 Watt panel converts to 12 volts @ 8.33 amps (100 watts). Who would have ever thought a 100 watt panel could deliver 100 watts?

[jflorey2]

Ok so are buck converters diffrent from a normal dc/dc step down converter regulator?

A buck converter is a variety of DC/DC converter. An MPPT charge controller combines a buck converter with a semi-intelligent controller that will "find" the best operating voltage for the panel and keep it there. This maximizes energy out of the panel - and allows you to run your panels at a higher voltage than your batteries without losing the power implied by that extra voltage.

[inetdog]

Ok so are buck converters diffrent from a normal dc/dc step down converter regulator?

If you have a true DC to DC converter which can trade off higher voltage for higher current, rather than just a switching or linear regulator that drops the voltage but does not increase the current, then that type of buck converter could be part of what you need. '
The remaining problem is that you do not want to just connect the converter output, at a fixed voltage, to you battery. Too high a voltage will eventually fry your battery. Too low a voltage will not take full advantage of the power available from the panels. So I would want to put at the very least a PWM type CC between the stepdown converter output and your battery.

But there is a more serious problem:
If the converter output voltage would result in more current into the battery than the panel power at that moment can support, the converter may just shut down protectively and not deliver any power at all.
You would need to have an output current limit on the converter which is sensitive to the available input power. That makes up 95% of an MPPT circuit that you would have to build, so why not go with an MPPT CC in the first place?

[97435207]

Thanks for all the feedback,
Ok I think I understand now so if you had 24v 8amps (for example) going in a converter and you get 12v 16amps out that is a good sign, but if you had 12v 8amps out then that would be bad.

And I might go with a MPPT

[bcroe]

Thanks for all the feedback,
Ok I think I understand now so if you had 24v 8amps (for example) going in a converter and you get 12v 16amps out that is a good sign, but if you had 12v 8amps out then that would be bad.

And I might go with a MPPT

Let me try to explain it another way. A basic buck DC - DC converter takes a higher input voltage and
puts out a lower voltage of near the same power, in other words increased current. Generally its
feedback adjusts to maintain a constant output V with varying current. With a light load, a
buck supplied from a PV panel will pull some current and pull panel voltage down from Voc. As the load
current is increased, the buck will pull more current from the panel and lower its voltage. If panel voltage
drops to Vmp (for that sun), you will be getting the maximum power possible. However if the load
increases any more at all, panel voltage will drop below Vmp, the panel will no longer be able to
maintain the operation, and voltages will drop below regulation.

An MPPT is a special type buck. Its mission is to take the maximum power possible from the panel.
So the load will be capable of taking as much power as the panel can make. The MPPT will adjust its
output so that panel voltage is pulled down to Vmp, then keep adjusting to stay on that point. Its
feedback adjusts to maintain maximum power possible conducted. Bruce Roe

[Silver_Is_Money]

Merely another way to explain it is that with MPPT you get WATTS IN = WATTS OUT, but with PWM you only get AMPS IN = AMPS OUT.

[Bucho]

What is wrong with that picture?

The idea that your batteries will be at 50% DOD at noon.

1. Battery panels (low voltage) cost 2 to 8 times more than GT panels.

Until you pay the residential freight shipping, then the GT panels can be more.