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Upgrading PV panels. Compatibility with inverter


GTP

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Hi all. I have read the other threads here with regards to calculating PVs. I did some calcs to determine what I can use with my Deye 5kw inverter. Hoping someone can verify my calcs and also shed some light on why my installer says I cannot proceed.

I have the Deye 5kw inverter with the following high level spec

1. Max PV array power = 6500w

2. Number of MPPT = 2

3. MPPT range = 125 to 425v

4. PV inout current = 11a + 11a

I currently have 6x 330w panels. The panels have  a 9.08a per panel max current rating

Therefore,

Max PV array is 6500w/330w = 19 panels max. Lets round this down to 18 panels.

As the number of MPPT strings is 2, this is 9 panels max per string.

If the panel VOC is 46.1v x 9 panels, this gives me 414.9v per string. Within the range of 125 to 425v.

Despite above, i only have the 6 panels currently.

I am restricted to number of panels i can have, so thought an easy way to increase my system spec is to upgrade my panels to for example 450w panels. These have a 10.8a rating.

Using the same logic as above,

Max PV array = 6500w/ 450w = 14 panels max

That allows for 7 panels per string. So lets make this 6 panels per string.

With a VOC of 45.9v x 6 panels, this gives me 275.4v per mppt. Well within the MPPT range.

So the thinking was to simply replace my 6x330w panels with 6x450w, But my installer reckons I cannot proceed and says the problem is the 10.8a rating of the 450w panels.

Why is this a problem if the MPPT is rated at 11a? Does it have to do with a safety consideration to not damage the MPPT?

 

Thanks, and I hope this post makes sense

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@GTP  You can go more than the "Max PV array power = 6500w" although the inverter will not use the extra power. 

It is useful for overcast days to still make enough power to run your essentials. 

You CAN NOT go more than the 425V per string voltage or you will end up with smoke and fire!! Is a very good idea to stay well away from the limit. 

Amps can be controlled by the inverter by increasing internal resistance in the inverter, Volts cannot. 

Is also important to note that panels can sometime show higher voltages that specced when they are very cold. 

I would leave the 6 x 330W panels on one string (maybe add 2 extra's) and maybe have a look for some slightly larger panels that will get you close to 11A max current for max efficiency from your inverter. 

 

8 x 330W panels = 2640W

11A x 400V = 4400W - so quite a lot of space for some extra power if you can find the right panels.

Maybe speak to your supplier and find out what other options that they have. 

 

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Go for the higher voltage with 330W panels. That will mean the MPPT starts earlier and works later and will also work better on overcast days.

The VOC you usually have to check against the inverter max voltage, IIRC that is 500V for yours, so you are still well away from that.

The MPPT range you check against the panel VMPP and make sure that you are within the limits.

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it feels as if inverters max current designs aren't keeping up with modern solar panels, with increasing difficulty in matching them.

don't forget the dc fuse of say 12A between the inverter and panels as a precaution. 

The 330w option would be safest, although likely not the most cost effective.

 

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Keith Gough suggests not going over 450V. Overvoltage will damage your kit. Amps are slightly less important, but it is easier for the MPPT to control amps, and if it does, then you will lose efficiency, at least it is not damaging, but you lose overall power.

Practically speaking, only if you have "perfect" Azimuth (true North facing) and panel tilt (around 26 degrees for most of SA) will you see the performance of the panel as per its specs at STC. You should try to use all of the information currently at your disposal, because you can get a good idea of projected panel performance from looking at your current panels' historical performance stats. How much they under perform vs their spec should give you a factor that you could apply to any similar panel (mono vs poly). If you have a year's worth of data, then it is better than nothing.

Then there is temperature co-efficient. Here you need to take into account the coldest day in winter for your location at 10H00 - 14H00, and use that to calculate how much voltage will increase if it is below 25 degrees (STC). There is a tool in the design tools section that can assist you with this if you do not wish to start your own spreadsheet.

 

Then there's cloud edge effect which can increase voltage, you might notice this when you do an analysis of your historical solar data. Building in a margin of safety in for this would be a good idea IMHO. 

Good luck, and once you have your data and sums logically laid out, post them here, we can all double-check for you .

 

Edited by YellowTapemeasure
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  • 2 months later...

Just an update. My supplier/ installer has been in touch with his supplier who has confirmed that the Sunsynk/ Deye inverters have built in buffering for current and voltage. As such, they were happy to upgrade my panels on the premise they wouldnt hurt the inverter. Happy days. I now have an extra 700w capacity. Changed from 330w to 455w. 

 

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