March 4, 20233 yr Hi all. Need help with panel sizing please. I have a 3kw / 3kva 24V Mecer inverter running with 2 x 100ah Gels. I know I can't add much, but would just like to cover the afternoons as much as possible, with general load at around 300 - 400w. See attached pics for inverter MPPT specs. Thank you.
March 4, 20233 yr You can ad 600 Watt of panels. 2 x 300Watt panels. The max VOC of the mppt is 75volt. If the total volts of 2 panels exceeds 75v you will have to connect them in parallel. You can exceed the panel wattage safely by 10%
March 6, 20233 yr I have the same inverter. And also want to add PV. Would the 605w canadian panel do? The question i have. What is the target when adding panels? 2x 300w panels in series normally puts the Voc above 75V. Putting 2x 300w panels in parallel will have the same result as one canadian 605 panel. What is the rule of thumb? Is the target to get as close to the max VOC?
March 6, 20233 yr 4 minutes ago, Flouw said: I have the same inverter. And also want to add PV. Would the 605w canadian panel do? The question i have. What is the target when adding panels? 2x 300w panels in series normally puts the Voc above 75V. Putting 2x 300w panels in parallel will have the same result as one canadian 605 panel. What is the rule of thumb? Is the target to get as close to the max VOC? @Flouw2 * 300Watt panels in series do exceed 75 VOC . Canadian 605 Watt panel will be fine. The VOC of 605W panel is 50.2v .Your MPPT voltage range is 30-66v. The max VOC must never be exceeded and it is best to stay within the MPPT voltage range. I used 300 Watt panels because that was the largest I could get in 2015.
March 6, 20233 yr thank you @Chris Louw the data i have of the Canadian panel is as below - 605w panel has a operating voltage of 35.1V. VOC at 41.5V. operating V is at the lower spectrum of the working range for the MPPT. the question still, is the target to get as close to the max VOC? or aim for middle of working range?
March 6, 20233 yr The target is to stay in the working range . Everthing above the working range is lost and you can blow the mppt when exceeding the VOC. The 35.1v will be ok.
March 7, 20233 yr Author Thanks all, very interesting. If you go ahead, please send pics here. I was told by another electrician, not really a solar installer, that we could do 4 x 300w panels? 2 in series and another 2 in parallel? The ones in parallel will increase the voltage, and the ones in series will increase the amperage?
March 7, 20233 yr 16 hours ago, NeilJ said: Thanks all, very interesting. If you go ahead, please send pics here. I was told by another electrician, not really a solar installer, that we could do 4 x 300w panels? 2 in series and another 2 in parallel? The ones in parallel will increase the voltage, and the ones in series will increase the amperage? The electrician need to pay attention to his advice. Series increases the voltage not parallel.
March 8, 20233 yr Author My apologies, that could have been me getting it the wrong way round. Either way, could he be right?
March 8, 20233 yr Generally, you should not add panels with nominal power more than 120% of the rated power of the inverter (for Voltronic Axperts). The reason is that the control algorithm is poor, and overshoots are common. More than 20% more than the control algorithm is expecting can damage your battery and cause various problems. This 24 V model has an exceptionally weak solar charger (600 W). Connect it to a maximum total of about 720 W of panels (hard with today's giant panels), and if you need more solar power, add an external MPPT that connects directly to the battery. Use a type where you can set the absorb and float voltages, and set them slightly (about 0.1 V) lower than the same setting on the inverter. You have to be a bit careful not to charge the battery with too much current, though with only 600 W from the inverter's built-in solar charger, it's not too hard. I note that there are other 24 V models (usually with "PLUS" in the name) that have a much more powerful built-in solar charger.
March 8, 20233 yr im Sure he means you can install them as (2p2s) (or is it 2S2P) but yes, what he means is you will install two panels in series, and connect those two series panels in parallel. you can read my comment from earlier, you cant exceed the VOC. putting two in series will exceed the max VOC. to save on cabling, connections and mountings - and in general panel costs. just install 2 larger panels (2x350w) in parallel. or just buy 1 x 650w and get it over with. thats what im going to do. 1 x 6xxW panel, and it makes it rather easy to add another in future when i expand. realistically, calculate your solar needs during the day. and go from there.
March 8, 20233 yr 3 hours ago, Flouw said: im Sure he means you can install them as (2p2s) (or is it 2S2P) but yes, what he means is you will install two panels in series, and connect those two series panels in parallel. you can read my comment from earlier, you cant exceed the VOC. putting two in series will exceed the max VOC. to save on cabling, connections and mountings - and in general panel costs. just install 2 larger panels (2x350w) in parallel. or just buy 1 x 650w and get it over with. thats what im going to do. 1 x 6xxW panel, and it makes it rather easy to add another in future when i expand. realistically, calculate your solar needs during the day. and go from there. The problem with adding another 2x350W or a 6??W is that the inverter can only handle 600W of PV input as the detail info Coulomb provided in his reply. Refer to the specs by the OP.
March 8, 20233 yr You can exceed the watts by some margin (eg10% - 20%. do not exceed the VOC. MPPT will "chop" the excess. this will however mean that you will have better PV early in the morning, late afternoon and on cloudy days. that is my understanding, and im happy to be corrected.
March 8, 20233 yr 22 minutes ago, Flouw said: You can exceed the watts by some margin (eg10% - 20%. do not exceed the VOC. MPPT will "chop" the excess. this will however mean that you will have better PV early in the morning, late afternoon and on cloudy days. that is my understanding, and im happy to be corrected. Refer to the 2 responses by Chris Louw on Monday. The Voc is a maximum. No point in getting to over 66V Vmp which is the upper limit of the MPPT. Even if you are below Voc maximum the moment you hit temps of say 10 degrees C you will cook the MPPT due to Voc rising from the 25 degree value in the spec.
March 8, 20233 yr 3 hours ago, Scorp007 said: Refer to the 2 responses by Chris Louw on Monday. The Voc is a maximum. No point in getting to over 66V Vmp which is the upper limit of the MPPT. Even if you are below Voc maximum the moment you hit temps of say 10 degrees C you will cook the MPPT due to Voc rising from the 25 degree value in the spec. Agree with you. Hence me saying one single panel. Or 2 smaller panels in parallel. That should keet the VOC low enough
March 9, 20233 yr Author Ok, so to keep things "simple" and in a safe range, the Canadian 605w will do the trick for this little inverter?
March 9, 20233 yr I have a similar set up that I installed for my parents. They have the axpert ps 3kva it does not say the solar watts. But assuming that the 50a x 24v it is a max of 1200w of solar I have since added 4 ja solar 365w panels. 2s2p. But the inverter registers the solar panels but it is not charging the batteries or using it for the load. we also added a Hubble cloud link in order to monitor and check the production. when the panels are disconnected from the inverter they are generating 77v but as soon as they connect, the voltage drops to 42v but does not charge or power the load. Does anyone have any solutions or have expected the same problem. And am I misunderstanding the 80v max solar voltage.
March 9, 20233 yr 1 hour ago, charl said: I have a similar set up that I installed for my parents. They have the axpert ps 3kva it does not say the solar watts. But assuming that the 50a x 24v it is a max of 1200w of solar I have since added 4 ja solar 365w panels. 2s2p. But the inverter registers the solar panels but it is not charging the batteries or using it for the load. we also added a Hubble cloud link in order to monitor and check the production. when the panels are disconnected from the inverter they are generating 77v but as soon as they connect, the voltage drops to 42v but does not charge or power the load. Does anyone have any solutions or have expected the same problem. And am I misunderstanding the 80v max solar voltage. 2 panels in series with a Voc=41V would have exceeded the maximum voltage allowed of 80V. This is at 25 degrees C. At lower temps the voltage would have been higher. This is one voltage you never want to exceed. Best to have the solar controller checked out if it did not pop.
March 10, 20233 yr @NeilJ Similar inverter at our complex. Yesterday we added a 545W Canadian Solar pv panel on to it. It works like a charm. 👌
March 10, 20233 yr 18 hours ago, Scorp007 said: 2 panels in series with a Voc=41V would have exceeded the maximum voltage allowed of 80V. This one is a PWM model; you would not have gotten any more power from more voltage anyway; when bulk charging (most of the time), the panels are directly across the battery. And of course at the end of charging when it does its PWM thing, the voltage would have swung too high, probably damaging the solar controller. As you say, the maximum PV voltage is always a "never exceed even on cold winter mornings" figure.
March 10, 20233 yr Oh no. Probably should have paralleled all of them. Would have been under the 50amps I'll try open it up over the weekend and see if I can see anything Does anyone know if the charge controller is a separate module and if I could buy a replacement one from somewhere
March 11, 20233 yr 11 hours ago, charl said: Does anyone know if the charge controller is a separate module and if I could buy a replacement one from somewhere 90-99% of it is usually in one module, yes. You should be able to get it from a reputable reseller that is willing to go to some effort to please their customers. If you bought from a clone maker or the likes of Ali Express, my guess is it's highly unlikely. It's difficult to get the exact right part for your exact model, too. There are so many models with slightly different specifications, and wildly different names for the same thing.
March 11, 20233 yr On 2023/03/06 at 8:22 AM, Flouw said: thank you @Chris Louw the data i have of the Canadian panel is as below - 605w panel has a operating voltage of 35.1V. VOC at 41.5V. operating V is at the lower spectrum of the working range for the MPPT. the question still, is the target to get as close to the max VOC? or aim for middle of working range? 11 hours ago, charl said: Oh no. Probably should have paralleled all of them. Would have been under the 50amps I'll try open it up over the weekend and see if I can see anything Does anyone know if the charge controller is a separate module and if I could buy a replacement one from somewhere Spares is difficult to get in South Africa. If the AC charger and inverter is OK you could install a lose SCC. You can then use a PWM or MPPT.
March 11, 20233 yr 55 minutes ago, Chris Louw said: Spares is difficult to get in South Africa. If the AC charger and inverter is OK you could install a lose SCC. You can then use a PWM or MPPT. Great suggestion😀. I use such an external controller. Just pay attention as you have a 24V system and the controller is a 20A unit you will only be able to harvest 20x24V=480W from the panels. This power can be used from the battery directly for loads and charge the battery for use during LS. Perhaps the cheaper option than to replace the whole inverter.
March 11, 20233 yr Thanks for all the replies. I'll try find a replacement charge controller as we just install a Hubble cloud link to be able to control when the inverter uses solar battery or grid. Not sure how it will work if it uses a external charger
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