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Posted by Amy Beaudet on Oct 19, 2015 04:27 pm

#21 -  Renewable Energy > Technical Discussion: Solar Electric System - Photovoltaic > Re: Extremely Long Run Solar Calculation

Yes, running a higher voltage panel (or panels) and running it through an MPPT charge controller is the way to go. Ideally, if you can do two 24V panels in series, that's even better. We've got a 100W 24V panel that can ship by UPS to control the shipping costs. two of them in series, 10AWG wire gives you 3.3% voltage drop for 69V at the charge controller! Then with a Midnite Kid charge controller, , that'll drop it right down to where you need it. Also note that the current you should be using for your calculations is the Imp of the panel, not the draw of the load. So it'll be down around 3A. High volts, low amps is the way to travel the distance.

Solar Queen
altE Store

Posted by Jeff King on Oct 19, 2015 03:56 pm

#22 -  Renewable Energy > Technical Discussion: Solar Electric System - Photovoltaic > Extremely Long Run Solar Calculation
Hello Everyone!

I have a small off-grid, low-amp (3-10) environment cabin, running 12v lights and charging cell phones only. No appliances, no radio...lights and charging only. So no major amp/power needs.

I'm currently using a 130w panel to charge 2 130 amp hour deep cell batteries..on site at the cabin. Works great! However, during the 4 winter months, I get no direct sunlight on the panels.

I do have a "sunny spot" on my property that gets sun all-year. However, the "sunny spot" is approx 400ft from my cabin (prob more like 360ft).

So,  I'm thinking that If I place 1 or 2, 24v panels in the "sunny spot" and run 10awg wire the 400ft, I figure I could get enough power. I have calculated an end voltage of 16.01 @ 10amps (this according to

I don't care about the loss of voltage, as I'm aiming for 12v anyway.

Question, does this seem right? AND could I then run that 16.01v through a properly rated 24v~12v charge controller to charge my 12v batteries on-site at the cabin?


Posted by Amy Beaudet on Sep 30, 2015 01:42 pm

#23 -  Renewable Energy > For Sale > Re: for sale used Reynolds solar hot water system
Dan, it may help if you say where they are located. It's easier to pick them up in person than to ship them by truck.
altE Store

Posted by Dan Majchrowicz on Sep 30, 2015 11:50 am

#24 -  Renewable Energy > For Sale > for sale used Reynolds solar hot water system
Reynolds whole house solar hot water system, complete minus hot water tank.  Includes 2 4x8 solar panels, crown top, heat exchanger and pumps.  Best offer.

Posted by Amy Beaudet on Sep 28, 2015 02:46 pm

#25 -  Renewable Energy > Technical Discussion: Solar Electric System - Photovoltaic > Re: newbie, here! had an oddly low state of charge
Gosh, you're making me blush.

I'm sure the batteries are fine, you are not the first person to get a bad start to their system. If you kept repeating what you were doing and had them deeply discharged often, you would certainly damage the batteries. But once, you're probably fine.

Looks like you are getting more rain in TN today, so I'm not sure if your trip out there today will be very telling. Maybe stay home and rescue another beer, and head out another day after you have a good day of sun.

Solar Queen
altE Store

Posted by Adam Meredith on Sep 28, 2015 02:33 pm

#26 -  Renewable Energy > Technical Discussion: Solar Electric System - Photovoltaic > Re: newbie, here! had an oddly low state of charge
Thank you so much for your reply, Amy!!!! After watching your tuturial vids it's a real honor to converse with u! First off thank u for clarifying the high voltage concern. I contacted the manufacturer this morning and they backed up exactly what you've stated... So no problems there.. I've kill a watted the fridge and it pulls 80 watts when running with a 160 watt surge. Not very effecient  fridge but I'm guesstimating a 10-12 hour run time. I never considered the inverter consumption!! When I got the cabin yesterday the state of charge was still at 43% at 25.04ish volts.. The display showed 0 amps going to the bank from controller even with verified pv input.. The manufacturer has emailed me a return shipping label and told me to just send the controller back to them...  I'm going to the cabin after work and I will check the voltages... If they haven't gone up with no loads today then I'm ripping the controller off the wall and stuffing it in a box. I'm going to stop by lowes on the way and see If I can pick up a cheap pwm controller to at least get my bank charged back up. It breaks my heart to see brand new batteries so deeply discharged... I prolly just cut the life of them in half!!!! Thanks again for your reply, Amy!!!! I look forward to learning so much more from you and this group!

Posted by Amy Beaudet on Sep 28, 2015 10:48 am

#27 -  Renewable Energy > Technical Discussion: Solar Electric System - Photovoltaic > Re: newbie, here! had an oddly low state of charge
OK, jumping in here a bit late, sorry, was away for the weekend. Let's step back and summarize the situation. Note that we don't sell Renogy products, so my knowledge of the details is from reading the manual.

Six Renogy 100W panels. 22.5Voc, 18.9Vmp, 5.75A Isc, 5.29A Imp
Renogy MPPT 40A charge controller
battery bank: 6=12v, 155 ah wired in 3 strings of 2 in series to make 24v and 465 ah.

The charge controller is MPPT, so you can input more than the nominal 24V and it will adjust the output voltage down and current up. 100V max is the temperature adjusted Voc output. You are in TN, so it doesn't get insanely cold (compared to up here in New England), so let's say 1.15% increase in voltage when it gets cold. 100V max \1.15 = 87V max Voc input. 87V / 22.5Voc of your panels = 3 panels max in series. So you can do 2 parallel strings of 3 in series. The MPPT charge controller will drop the voltage to the 24V battery bank, and increase your output current to about 12A per string x 2 strings = 24A out. (This is all theoretical without system losses calculated).

The manual is confusing on page 22. What it is saying is that for a 24V battery bank system, the most power you can put in is 800W. It's not saying the most voltage you can put in is 24V. You can do strings of 3 panels in series.

So, let's figure out what is going on. It's good that you got a display, that will help with troubleshooting. Did you set the amphour on the display? The default is 200Ah, you have to change it to 465Ah.

Now that you took care of the beer (good thinking), and have the fridge unplugged, it will be very good to see if the solar is able to recharge the battery bank without a load on it.

I think the meter shows the amps going from the charge controller to the battery bank. Next time you are there when it is sunny, see what it is saying. On a perfect day, you should be seeing in the 20A range. Also, it should be keeping track of amp hours added to the bank, that will be important to see. Are you making about 80Ah a day?I'd also like to confirm the power used by the fridge, I'd recommend getting a Kill-a-watt meter to keep track of the actual power usage of the fridge plugged into the inverter ( It may not work perfectly with a modified sine wave inverter, but you should get a good feeling for it. Being a "cheapo modified sine wave", the inverter itself may be using a lot of your power as well, not just the fridge.

Now let's look at the system as a whole, to see if it is correctly sized. 600W of panels, although you started with 400W. Let's guess 4 sun hours. 400W x 4 sun hours x .6 system losses = 960Wh generated a day. Fridge draws 80W. Continuously? Or is it on half the time? The Kill-a-watt meter will tell you that. Let's be nice and say it's on 12 hours a day. 80W x 12 hours = 960Wh a day (which is what you estimated). So you started out theoretically making exactly what you needed for the fridge, but not figuring any losses by the inverter. It's maybe 85% efficient, so you are losing 15% through that. So you started out at a deficit. You then added 200W of solar, giving you 1440Wh. If you always have perfect sun, that's probably fine. but you had a rainy day, so you lost 1140Wh for that day. Plus starting a bit low from when you had 400W of PV. I think it just started to snowball down from there.

Sooooo, long way of saying, let's see what you get this week without the fridge plugged in, and go from there next weekend.

Solar Queen
altE Store

Posted by Tom M on Sep 28, 2015 01:01 am

#28 -  Renewable Energy > Technical Discussion: Solar Electric System - Photovoltaic > Re: newbie, here! had an oddly low state of charge
Well i feel i answered you question several times as well as referred you to the manual.  The controller requires a pv input of 12 or 24 volts, not just some random voltage which is why most pv panels come in 12, 24, 48 volts DC. If you reread my fourth post and look at the ratings on your panels, you will see that the panels operate in a range of voltages, from V oc to nominal rating. It is when these higher voltages are reached and added that it may be possible to near the upper limit of the controller.   *search for "Max solar input voltage" if you want to read up on it's purpose. Otherwise panels are hooked up using nominal voltages to work in conjunction with other components in the system, eg. your 24 volt battery bank.

Also, that controller automatically detects 12 or 24 volts and switches accordingly, if it is reading anything different then........

  And if you want to run long distances you can increase voltage by putting 10 in a string and using larger inverters as opposed to small controllers.  But you still must conform to 120, 240 etc volts.
  The way your doing it would be like saying you can use any voltage coming off your breaker panel at home because you have a 200 amp service so it should be able to handle any voltage appliance you want to put into it, eg. plugging in a 12 or 9 volt appliance into a 120 outlet.

Posted by Adam Meredith on Sep 27, 2015 08:35 pm

#29 -  Renewable Energy > Technical Discussion: Solar Electric System - Photovoltaic > Re: newbie, here! had an oddly low state of charge
Dang, man... Not much of a people person are you? I understand exactly what you are saying... But you haven't answered the question as to why the higher voltage is bad or not commonly used or whatever before you assume I'm a retard... If I took took that too harshly then my bad but geez!!! I came here for insight... Anyway... I got beer in my fridge that I unplugged that I gotta drink now before it goes bad lmao! Let me digress for the sake of argument .... I have pv voltage coming from the panels... Be it 99.9 volts or 24.... My controller doesn't seem to be charging my bank.... I do appreciate your input... I guess I picked a bad day to join a solar forum... Cheers!

Posted by Tom M on Sep 27, 2015 07:43 pm

#30 -  Renewable Energy > Technical Discussion: Solar Electric System - Photovoltaic > Re: newbie, here! had an oddly low state of charge
24 volts!!!!!! What gauge wiring comes from the panels?  Connecting two in series will not increase wire gauge significantly. Not sure why you can't understand, very simple.

so 3 strings...24 volts...200 watts ..8 amps per string...with 12-14 gauge the combiner block......for a total of ....24 10 gauge wire from the combiner to the controller

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