solar

[highdesertranger]

2 days ago Bob released a video on SanTan solar in Gilbert Arizona.  this is the same place I got my huge 430 watt panel for 200 bucks.  these guys have incredible deals on panels of all sizes.  just thought I would pass along the info,



and a special thanks to the YARC for letting me hang out at their camp.  it broke the run up as I never would have been able to do it in one day.

highdesertranger

 

[XERTYX]

2 days ago Bob released a video on SanTan solar in Gilbert Arizona.  this is the same place I got my huge 430 watt panel for 200 bucks.  these guys have incredible deals on panels of all sizes.  just thought I would pass along the info,



and a special thanks to the YARC for letting me hang out at their camp.  it broke the run up as I never would have been able to do it in one day.

highdesertranger

A very interesting write up. Most of the panels I looked at on their site seem to be 24V based on open circuit voltage. I'm more comfortable with 12 volt systems as that's all I've ever done. Advice?

 

[highdesertranger]

most 12v panels have an open circuit voltage in that range. 21-25 volts. the controller knocks it down to something a 12v battery can handle. highdesertranger

 

[Seminole Wind]

A very interesting write up. Most of the panels I looked at on their site seem to be 24V based on open circuit voltage. I'm more comfortable with 12 volt systems as that's all I've ever done. Advice?

the panels are more of what we call residential panels and are not made for any particular battery voltage. these larger panels are intended to be run in series strings upwards of 600 volts then through grid tie inverters. but we can benefit from them by using decent MPPT controllers that take advantage of the extra volts and down converts it to the voltage required by the battery you have. not really any different than what your used to with the exception of the different controller. still plain old 12 volt battery just fine

 

[Seminole Wind]

i got 2 of the panels hdr mentioned and a buddy got 4, we had them shipped to a ups freight terminal in southern oregon. was still a smokin' deal. when i get these mounted and wired up, i will have over 2000 watts on my short bus

 

[XERTYX]

So am I to assume then that I can get a 24V MPPT controller that supports a 12v battery bank in place of one designed for these panels using 24V bank and get a benefit from the increased wattage of these panels?

 

[B and C]

You don't get a 24V MPPT controller. You get an MPPT controller that supports high voltage panels in an amp rating that is higher than the panels can produce. The controller needs to support a higher open circuit voltage than the panels produce. You hook the controller to the batteries first so it knows what it is charging (12 or 24V autosense) and then connect the panels.

 

[XERTYX]

You don't get a 24V MPPT controller.  You get an MPPT controller that supports high voltage panels in an amp rating that is higher than the panels can produce.  The controller needs to support a higher open circuit voltage than the panels produce.  You hook the controller to the batteries first so it knows what it is charging (12 or 24V autosense) and then connect the panels.

Nice. So I should search for controllers that support the voltage of the panels and just keep within the amperes of the high volt panel/array?

 

[B and C]

You want the charge controller to be larger (in capacity) than the panels you are connecting to them, so yes. Most any MPPT controller will work but don't cheap out on some chinese ones. They may advertise MPPT but are really PWM (Pulse Width Modulation) and not suited for high voltage panels.

 

[Seminole Wind]

for example, lets say you have a 295 watt panel. that the open circuit voltage is 39.7

295v watts will be about 25 amps at 12 volts nominal. it can be a little higher or lower based on how low the battery has been discharged.

so the controller needs to be rated at least for 45 volts max, but i would prefer 50 volt max rating. controllers can and will be damaged if the open circuit voltage exceeds the max rating. do not cut corners here

then to get the full power from the panel most of the time you would want a controller that is rated for 25 amps at 12 volt. most modern controllers will not be harmed or damaged if the amperage available to the controller is exceeded. some will self limit, others will over heat and "trip" like a breaker. if they trip, some will reset by them selves, others will need to be rest manually somehow.

the 295 panel i used as an example is what i have on the roof of my bus. i run 2 of them in series (volts add together) and use a charge controller that is rated for 100 volts so i have 50 volts for each panel. and the controller will manage 50 amps wich is right about the 25 amp each panel can produce.

dont pay any attention to the amp rating on the back of the panel. that is at the panel voltage and really has no bearing on picking a controller or anything. it can come into play when deciding on fuses in the panel string

 

[highdesertranger]

a 24v panel is what you call a 12v panel. a 12v panel does not make 12volts it would never charge the battery at that voltage. for the same reason a 24 volt panel will not charge a 24v battery bank.

yes you could wire them in series but on large scale solar projects that would not be practical, grid tie panels are much higher voltage.

highdesertranger

 

[tx2sturgis]

dont pay any attention to the amp rating on the back of the panel. that is at the panel voltage and really has no bearing on picking a controller or anything. it can come into play when deciding on fuses in the panel string

Everything else was correct, except, the amps at Isc (current, short circuit) is the full amperage the panel produces when shorted thru an ammeter or current shunt. Of course, some panels also have a rating for Impp (current, maximum power point) which is usually a bit less than Isc. 

Most controllers do have a rating for max current, so that number on the panel (or panels) does need to be taken into account.

 

[Seminole Wind]

tx2 you are mixing up some numbers. the max amp Isc is at panel voltage, not the open circuit volts as it will be a little lower. it is not the amps the charger is passing on to the batteries. the charge controller amp rating is how many amps it can deliver to the batteries after it has been down converted. for example, the 295 watt panels i used in my example have a 9.6 amp Isc, but by the time the charge controller convert the voltage to the battery voltage the amps at max power will be around 25 amps 12 volt. so as i said, the max current rating on the back of the panel is not used for determining the controller. so just ignore that figure

 

[tx2sturgis]

tx2 you are mixing up some numbers. the max amp Isc is at panel voltage, not the open circuit volts as it will be a little lower. 

Respectfully, no.

Panel amp ratings are measured into a short circuit, that's what Isc (or ISC) means. NOT amps at full panel voltage, because there are no normal solar panels (we can buy) that can put out their full voltage at their full rated amperage under the standard test conditions and rating system.

For example, a 100 watt panel typically puts out 22 volts (Voc), OR about 6 amps (Isc) but not both at the same time, which would be 132 watts. It is rated at 100 watts, not 132. 

The more current that is pulled from the panel, the lower the panel voltage becomes. All the way down to zero voltage at maximum current. (Isc).

PWM controllers pull the panel voltage down to just above battery voltage under a heavy load. MPPT controllers dont do this, they 'sweep' the panels and then settle on, you guessed it, the Maximum Power Point, where voltage and current are 'balanced', which results in an efficiency gain. 

For me, with my ham radio hobby, and multiple receivers on a wide range of frequencies, MPPT controllers are mostly unusable because of the RF noise they create and radiate, but I do still own one, mainly used for testing.

 

[Seminole Wind]

yes the voltage at isc will be lower, much lower than the max open circuit voltage. but when you have a panel connected to a battery via a charge controller you will not see the isc amps going to the battery threw the charge controller. the only time you will see the max current short circuit is when/if it is ever short circuited. the spec is put there to know what fuse protection/wire size would be needed in case of a short circuit. when the panel is short circuited and putting out all those amps the volts will drop tremendously. they dont even post the volts in that situation.

the spec you need to consider when sizing a charge controller is the max power current. you will find that spec on the back along with the max power volts. if you multiply both of those you will get the rated watts of the panel. i will acknowledge that with pwm controllers on 12v nominal panels the difference is slight. but it is not right and has you confused. then when you or someone else steps up to higher voltage panels or 12v panels in series with mppt controllers the discrepancy is huge and if you use the isc to size your controller you will be shooting your self in the foot.

here are the typical specs for a 12v panel
Maximum Power: 100W                        Maximum System Voltage: 600V DC (UL)
Optimum Operating Voltage (Vmp): 18.9V Open-Circuit Voltage (Voc): 22.5V
Optimum Operating Current (Imp): 5.29A Short-Circuit Current (Isc): 5.75A

if you multiply the optimum operating (max power) current times the optimum operating (max power) voltage you get 99.981 watts. and they call it a 100 watt panel. now that is the max power you can get out of that panel. if the volts go up or down the current will change as well but at any other point the volts times the amps will be less than 100 watts.

the 11-14 volts or so is well below the max power volts so the panel will not be producing the full 100 watts. also, going through/into the battery is not a short circuit so you wont get to the short circuit amps that way either. and we are talking about less than half an amp from max power current to max short circuit anyways. any time you can post a pic showing a 12v panel putting more amps into a battery via a pwm controller than the max power amp ratting, i will tip my hat to you. now if you had a good mppt controller that could work with the lower volts of the 12v nominal panel it would be possible to see more than max power amps going to the battery. the mppt controller would allow the panel to put out the full 100 watts by running the panel at the max power volts of 18.9 and then down converting to the 12-14 volts at the battery. and if we divide 100 watts by 12 volts that gives us 8.3 amps into the battery and through the charge controller. if you had sized your controller on the short circuit current of 5.75 you would be significantly under gunned. so there again, the isc/short circuit current is irrelevant when sizing a controller

but we are not talking about 12 volt panels or pwm controllers. the original post was about 435 watt panels that have an open circuit voltage of 85.6volts! the short circuit amps is 6.43 amps so if like you are professing the short circuit amps is used to calculate the controller size then i would be fine with a 10 amp controller but that is so far from reality it is laughable. that big 435 watt panel has a max power current and voltage of 5.97 amps by 72.9 volts and that gets us 435.213 watts. (i find if funny that renogy and other low end companies have 100 watt panels that max out close, but under 100 watts. but sunpower and other high quality companies have panels that max out slightly higher than their rating.) now to find out what size (amperage) controller we need. we dont look at max short circuit, instead we look at max power. because the mppt controller will run the panel at the max power all the time (assuming standard test condition for all examples) we need to divide the max watts by the battery voltage when low in the morning. say 12 volts, and that is 36.25 amps.

like i have been saying, use max power in watts to calculate the charge controller amps that is needed. at no time is max open circuit current going to give you the information needed to select the right controller.

you might get away with it in the smaller 12v nominal panels with pwm controllers. but that does not make it the right way to figure it out. then if/when you take that wrong way of doing the calculation and apply it to larger panels and mppt controllers you are stearing folks down the wrong path and causing needless confusion. if you dont understand gridtie high voltage panels with mppt controllers, stick with the systems you are used to

 

[tx2sturgis]

I never said any of that other incorrect stuff, or implied any of it. Putting words in my mouth, as they say. 

As I said, you had provided good advice, which I mostly agreed with, except for the one point where you made an error in regards to how solar panels (of any wattage) are rated.

And I DO understand how PWM and MPPT controllers work, and will continue to monitor your statements, as you have done with me in several other threads. The desired 'product' here is correct information presented, not the soothing of egos, mine, yours, or anyone else's. 

If I actually state facts that are incorrect, please, be sure to help me understand the error, I do not wish to make errors and continue to post the wrong information. But if you extrapolate from that and make it sound as if I said something I didn't, the end result might be misunderstood by the readers and/or the OP.

 

[Seminole Wind]

Everything else was correct, except, the amps at Isc (current, short circuit) is the full amperage the panel produces when shorted thru an ammeter or current shunt. Of course, some panels also have a rating for Impp (current, maximum power point) which is usually a bit less than Isc. 

Most controllers do have a rating for max current, so that number on the panel (or panels) does need to be taken into account.

i am not putting words in your mouth. ALL panels have a rating for max power voltage and amps. the max power amps dont tell you anything without the max power volts. you either need both of those, or just use the wattage of the panels. the isc or short circuit current tells you nothing about the size of the controller needed. and all controllers have a max amp rating. some handle or behave differently if you exceed that rating

so again. the amps alone, mean nothing as they are amps at the panel voltage not the amps going into the battery passing through the controller. you need to know the max power from the panel and figure how many amps will be going to the battery. thus is is much easier to just use the max watts and divide by the volts at the battery to determine the potential amps the charger would need to handle going to the battery. yes you can calculate that by multiplying the max power current times the max power volts. but why, it is the same as the panel watts

trying to keep it simple for a new person trying to understand is much easier to use the panel watts to calculate. if you want to do the extra math for no reason, go ahead.

 

[XERTYX]

Well this was very informative indeed and a game changer for my plans I must say. It was my understanding that if I used what is marketed as a 24 volt panel I'd need a 24v system. It does make logical sense that if the controller is rated for the max voltage that it would work no differently that if using what is marketed as a 12V panel. The variable being that watts are still watts and youd need to divide the battery voltage by the array wattage to size a controller beefy enough to do the job.

Given the prices listed on their site this is the way to go. I'll give another look on craigslist locally as well as I found a source on there some time ago for 48 volt panels on the cheap but I didnt think they would be compatible.