I have acquired solar panels and the tag reads:
Maximum Power (Pmax) 250W
Maximum Power Voltage (Vmp)30.3V
Maximum Power Current(Imp) 8.27A
Open Circuit Voltage(Voc) 37.6
Short Circuit Current(Isc) 8.85
Maximum System Voltage DC600V
Maximum Series Fuse 15A
Minimum Bypass Diode 15A
I read that the concern is the voltage. Can I get away with 5 panels? These are used panels and should not reach full manufacture specs.
Thanks
Connecting 3 panels in series on one input (DC1) and 2 panels in series on the other input (DC2) would work well with the Bluetti AC300.
Here’s why:
Advantages:
N.B. Stay clear from a parallel setup. They’re less efficient, more prone to accelerated ageing (hot spots, imbalances, etc. in case of uneven shading profile) and you woudln’t reap the full benefits given AC300’s limit to 12A (wasting whatever extra amps are available). And moreover, parallelism should only use even numbers, like 2P2S leaving one stray panel… and we don’t even want to imagine 5P1S 
NB2. “should” is not the best safeword here. Some people also argue that these systems mostly operate at Vmp, and almost never at Voc, so they’d go for 5 panels in series (151,5V … 1.5 volts above the limit is nothing, right?), especially considering they’re a bit used, so “Vmp should be a bit less than 150V”. It’s a gamble, might work, but be careful if given that sort of advice.
I should have stated that I have many more than 5 panels. I was looking at the Voltage limit and thought 5 would be pushing the limit. So if there is a way to use more panels, I have them available.
Thank you for the great response, I never thought of different orientations. Great Idea!
I have the cement and tubes for my frames’ foundation. I was going to start digging this weekend.
Much more to think about.
Where my panels are going, there is no shading at all. 100% clear!
I have 3-Renogy 320s on each controller, in series (6 total for the AC300) and when everything is perfect they almost max out, so I happy with the input. No need to max out system because peak performance varies.
Hello. I have a similar question along this same topic.
I currently have 6 panels total connected to my AC300…3 on each DC1 and DC2.
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I have a 7th panel just sitting in storage. I was originally planning on connecting the 7th panel directly to the battery, but it didn’t work out. And the panel needs to be up the roof…not where it is currently stored. So, I starting brainstorming hooking 4 panels on DC2 to be 2s2p. But, that was back in Oct 2023 when I was trying to decide IF and HOW to do so. I had posted to diysolarforum but I could never understand if 1) the AC300 system would allow it. And 2) if I would benefit from it.
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Having gone now through the ups and down of a winter…and a summer…I better understand the limits of the system. And more interesting, just how far north the sun passes over the top of the barn where the panels are facing due south. The angle was perfect for the winter…not so perfect for the summer. There were a few cloudy weeks…including the last few days, that I had to curtail power usage to make sure I had enough power. But, like today (in September), the sun is already moving south…and the sun came out this afternoon and charged the two B300 batteries right up even at 5:00 - 6:00 pm. In July by 5:00 pm, it was no better than 5:00 pm in December. Don’t get me wrong…I had plenty of sun on most days in the summer…and winter…just had a few strings of multiple cloudy days that were annoying.
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I think I understand that if I go to 2s2p on ONE of the DC inputs, I might get better production in the winter, but not the summer, depending on the circumstances? And I understanding that correctly? I don’t think I am understanding this. But I think the reason I don’t understand it is because of the specs of the AC-300, which was hard for me to communicate on the DIYSolar site. A couple of very patient posters tried to explain, I just don’t understand it.
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So, I guess the main question is…can the AC300 benefit and handle 3s on DC1 and 2s2p on DC2?
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The panels are:
Thanks for any feedback!
Can I put 3 Panels on DC1 and 3 Panels on DC2 in parallel?
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Are both DC1 and DC2 able to take 150V’s each?
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In other words, I can put on a total of 6 panels to the AC300? (I have them)
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How many degrees S-SW and S-SE should I go?
The only thing i know is that the panels should match up the best as possible, ie voltage I think, you can mix and match wattage. I don’t have anything hooked into the batteries separately, not sure how much more benefit there is to that. I think that is more for camping.
I wanted a matched set, for both controllers that would be under the max yet provide leeway for when the sun actually is perfect. My panels are not on the roof because as you get older, falling really isn’t in the cards. I live in Az, and I have had my system for 1 year. I have only adjusted twice, once i figured it out…1=what i believe is the max for mid summer…I set this in the spring, and 2=I set in early Nov for what i believe will be the max in winter. It is a manual setup and a pain to adjust. To me winter is more important. Winter is dead on, and I maxxed out regularly. You need to find out the declination of your area to really get the benefit. I face almost true south anyway so the tweaking of the declination puts me in a good spot. Mine is about 9.5 degrees.
Summer, next year I will drop them lower but still got great solar service due to the long days, i didn’t mind it to be off. Summer also gets so hot the panels are not as efficient, but still good…might be better next summer when i apply the new setting. Unless you have a tracker, it is trial and error, but that adds to the fun.
You need the right combination of sun, temp, humidity, etc for them to max, I think.
Hello
your case is interesting.
My opinion:
-you can put 3S on DC1 and 2S2P on DC2 as long as you set “PV Parallel Enable” to OFF. (If it were ON, the AC300 would parallel your 3S and your 2S2P, which are not at all the same voltages, this is strongly not recommended.)
-Unfortunately, however, your 2S2P configuration is not the solution for you: on DC2 (as on DC1) you have a current limit of 12A on your AC300… i.e. if your panels exceed 12A on DC2, the AC300/DC2 input will limit to 12A. So your 2S2P configuration, when exposed to direct sunlight, can theoretically provide 2 X 13.34 = 26.68 A and you lose more than 14A (12 A limit). 2S2P gives you a maximum of 12 A x (2 * 34.48V) = 827 W whereas if you put 3S (3 panels in series on DC2) you get 12A * (3*34.48) = 1241 W! In short with 3 3S panels… you get more than 4 panels in 2S2P !!
The only solution in your case that I see is to use your last panel is therefore, in my opinion,
-keep your current configuration 3S on DC1 and 3S on DC2
-connect your last additional panel directly to the solar input of one of your B300 (they are equipped with a solar input): you will then recover an additional 200 W (limit of the B300 solar input) out of the maximum 460W. Of course you will have to pull additional solar cables. Eventually you can put your remaining panel in parallel on 2 solar inputs of your 2 B300… (with two Y solar cables) you will recover a maximum of 400W = 200W for each B300 (it’s unconventional but it should work).
I’m going to chime in here too because your panels are almost identical to mine. I also have used panels, 250 watts. I purchased 12 of them, so 3,000 watts total (and the pretty much meet the specs in output, roughly 80% of their output in real-world use). I made two arrays of the 12 panels. Each array uses six panels, with two sets of three panels in series, and each set of three wired in parallel. That gives me an array Voc of 111 volts, and a max current output of ~ 16 amps. Each of the arrays are identical, and are directly wired to each of the two MPPT inputs (do not use the parallel mode configuration either). With this set up I get a maximum of 2,400 watts solar input in really good conditions. I have been running this set up for two years now continuously.
I also live in AZ, down by the border.
All my panels match, they are exactly the same.
I am going with a ground mount system for the same reasons, age and easy maintenance. I’m starting my digging today to put in sono tubes.
As far as angel for me, it is: The most efficient angle is 8.2° in summer months and 46.6° in winter months. With 27° for stationary.
I’m going with the Signature Solar EG4 BrightMount Solar Panel Ground Mount Rack Kit.
I was lucky to be able to buy a pallet of panels for a great price, a one time opportunity. I have 17 panels for this project. I have two AC300’s that will be installed in time.
I like your setup, wish I could have afforded the nice mounts you have.
Do you have 2 AC300’s?
Having 16A, I thought the limit was 12A?
I purchased my used panels from SanTan solar, I think the price was around $65 per panel, plus shipping – less than $1,000 total. I only have one AC300, with 4 B300 batteries. Basically my home came with a 6-circuit transfer switch for an exterior generator connection. I re-wired that to allow for an indoor connection or the external connection, and none of those circuits need 240 volts. Having said that, I’d love to get a 2nd AC300 – and then get more batteries for them!
My son is a welder. We came up with the idea of this mount system together, and then he built it. It allows me to change the angle of the panels each month to keep them facing the sun, and the mounts face southward. He did a fantastic job of building them.
Yes, the maximum current is 12 amps. The MPPT controllers limit the current, so having more available than the maximum allows for longer periods of maximum solar input during the day. This technique is called over-paneling. The voltage is critical in the design stage and must remain below the maximum, but the current is managed by the AC300. It’s like if you have a desk fan that takes 2 amps, it’s no problem to plug it into a 15-amp, or 25-amp 120 volt circuit – the fan only uses what it needs. But don’t be plugging that fan into a 240 volt outlet!
hnymann
Thank you for the explanation on the wiring. I am a beginner and worried about making a mistake. Watching my system burst into flames is not the Friday night bonfire I want to watch.
SanTan solar is great. I’ve bought from them before. I drove there, just over 4 hours for me, and picked up panels. It’s a great excuse to go to Phoenix.
Your son did a great job on that mount!
Thanks for the reply…and solid advice with just “do this”. That helps!!
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So, it just so happens I have a place for the 7th panel that would be a flatter angle for the summer (blue shed above the barn) and it is right next to the Bluetti system.
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I actually thought to hook it up directly to one of the batteries. But you are saying I can split the one panel to both batteries?
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Also, I had done a little testing with a panel directly connect to a battery…with the panel facing due east…but it just didn’t seem to make a difference to the panel. GRANTED, it was limited about of time in the AM, and it was only 200…vs the 1200 coming in from the DC1. But, it seemed that the couple of weekends I had to experiment, but the battery did not take any charge from the direct input when the DC1 input was plugged in. It seemed like such a small deal, and I ran out of FALL days and morning sunlight to mess with it.
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BUT…if the one 460w panel could feed BOTH batteries 200w, that could be worth the effort…assuming it would work if the DC1 and DC2 inputs can in fact remain connected.
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So, what does the wiring look like from the leads from the panel to split to both battery inputs?
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Thanks for your time!!
First of all, very nice drone photo !
To put your panel in parallel on the solar inputs of your 2 B300:
You need to get two MC4 “Y” cables (photo below). You will definitely need some MC4 extension cables. You use the 2 “PV input cable” (XT90 - MC4 cable) delivered with your B300. Look at the diagram below.
Note: As you know, your AC300 will not see solar power arriving at the solar inputs of your B300. If you want to check that the power from your additional panel is reaching your 2 B300, disconnect your B300 from your AC300 to isolate your B300. Connect your B300 to your panel following the diagram. Normally you will see the green LEDs chasing. This will help you make sure everything is working. You can then connect your B300 to your AC300
Thank you for the reply…and the image!! Wow!! Excellent plan! I am eager to get that 7th panel in use…and this is perfect. Thanks! I went to Home Depot today to get another section of Superstrut, but that product has gone up 30% since last year! Crazy! So, I am going to cut the excess Superstruts off from the barn.
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Thanks for comment on the drone shot. I had gone out and shot that image just for the reply when I realized I didn’t have any of the shed behind the bar…and realized afterwards I still need a shot from side showing the angle difference. But I do think it will be a good angle to compliment the main panels. Below is a shot of a late, late afternoon in Mid October showing the sun still hitting the panels. But, during mid summer, the sun was further north and pitch did not help.
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Just a cautionary note about connecting one solar panel to two MPPT controllers though. I’m not at all sure that the two charge controllers can cooperate in this manner. Each controller is designed to take power from one or more solar panels, and they moderate the current, which also affects the produced voltage, to determine the best power point curve to use (Maximum Power Point Tracking). To have two MPPT controllers trying to do this same task on the same panel is, I think, going to mess both up as far as determining what power can be taken from the panel.
You are absolutely right in the general case: putting 2 mppt in parallel is often unstable: one mppt manages to draw all the power for a brief moment, then it is the other mppt a moment later and so on.
However there is a particular situation where it could work, I found it by conducting experiments of paralleling mppt: it is when the power delivered by the array of panels exceeds that which the mppt can take. In this case a stable point can be found. I have experienced this between a D050s and the mppt of an AC200max, between 2 ac200max and betwenn an oukitel bp2000 and a ac200max.
And for example it is the same principle which is activated on the dc1 and dc2 inputs of the bluetti ac300 when you activate the “PV parallel enable” mode when you connect for example on dc1 a array of panels with a power which exceeds the maximum that the mppt on dc1 can take, if dc2 is unused, putting parallel enable allows to turn part of the intensity/power on the mppt of dc2.
I made it clear that “it’s unconventional but it should work.” : there is a risk that it will not work but we are in the particular situation where I think it has a good chance of working!
Well, that is quite interesting! I hope that @DrewLoker will try it, and let us know how that works for him.
