Have I got the wrong Inverter?

[SolarCity]

Start up voltage? If you have 4kWp of panels on a roof I don't think you'll be getting much issue getting up to 350v, especially on the Fronius IG TL 36 as its characteristics tend to mean that the system is wired up on one string.

Generally speaking, it doesn't take much light to get a decent voltage and enough to fire the inverter and I think that the benefit of a low start up voltage is often overstated. Unless I have missed something?

 

[GaryM]

I do have 16 panels (4kWp) on a single string and as you say, they don't struggle to produce 350V.

 

[lewyames]

Are you sure you spoke to Fronius about this? There is no way that the 3000TL can output 9,350W. It may well cope with the higher power but it certainly won't process it. I believe the only way to truly damage an inverter is to use a voltage which is too high.

The 3000TL AC output is not 16A.

I think you may misunderstand me, you can input 9,350W of DC, not output it. If you check the SMA data sheet the max AC output for a 3000TL is 16A, have a look.....

 

[SolarCity]

I think you may misunderstand me, you can input 9,350W of DC, not output it. .....

I definitely did misunderstand you. While it probably won't damage the inverter by connecting too much power to it, I don't think the OP is concerned about this. I think it is the OP concern that he may have an undersized inverter as it will mean that he isn't getting the maximum benefit from his system.

If you check the SMA data sheet the max AC output for a 3000TL is 16A, have a look.....[/QUOTE]

I don't see how this can be. If the maximum power output of the inverter is 3000w then you would need a grid voltage of around 180v to get 16A.

The maximum current you would expect from the inverter at 230v is 13A - in reality, I'd imagine that the output current is dependant on two things - the DC power and the grid voltage. The output power will never be above 3000w.

Again, I'm always ready to be proven incorrect.

 

[clivep]

I posted a similar question following the installation of my panels in November.

I have 16 x Hyundai HIS-250MG panels connected in 2 x 8 strings to a Sunny Boy SB 3000TL-20.

This inverter and configuration is as recommended by Sunny Design. I was expecting a 4000TL to be recommended but this was not the case according to the company installing. I ran the Sunny design software for myself and sure enough the 3000TL-20 is the only one the software recommends. All the ones above 3000 and below 4000 were coming up as incompatible. Although not recommended, the software allowed the 4000TL to be selected as it was compatible (it was only recommended for 17 panels). The 4000TL gave an estimated annual yield marginally above the 3000TL-20 by about a half-dozen kWh so I'll be losing less than £5 per year by keeping the 3000.

 

[SolarCity]

I've checked the figures and the 4000TL looks fine to me for 16 Hyundai 250w panels, unless I'm looking at the wrong data sheet. What does Sunny Design flag up as being an issue for the panels? Oversized?

I'd say a 3kW inverter on a 4kW array is undersized.

 

[babba]

Start up voltage? If you have 4kWp of panels on a roof I don't think you'll be getting much issue getting up to 350v, especially on the Fronius IG TL 36 as its characteristics tend to mean that the system is wired up on one string.

Generally speaking, it doesn't take much light to get a decent voltage and enough to fire the inverter and I think that the benefit of a low start up voltage is often overstated. Unless I have missed something?

£ FOR £ Power one is the best, lower kick in and will peak over 3.68. Sorry to be so closed minded but I think power one have it all. I would prefer a warehouse full of P1 as not all have perfect 4 kw roof.

 

[clivep]

My reading of the data sheets also made me think that the 4000 would be recommended but the Sunny Design software doesn't agree.

If the 4000 is manually entered in then there are no incompatibility issues and the annual estimated output is calculated. I don't know why Sunny Design does not offer the 4000 as a recommendation... but it doesn't.

 

[SolarCity]

I'd agree that Power One takes some beating for the price. I think Fronius IG TL range is the best for pure, unshaded yield. SMA are best for features and range. Power One are a good all rounder. The 3.0 model especially. Kostal Piko are a very good alternative.

 

[SolarCity]

My reading of the data sheets also made me think that the 4000 would be recommended but the Sunny Design software doesn't agree.

If the 4000 is manually entered in then there are no incompatibility issues and the annual estimated output is calculated. I don't know why Sunny Design does not offer the 4000 as a recommendation... but it doesn't.

Very odd. I'm going to download the software and try to work out what I'm missing.

 

[babba]

I'd agree that Power One takes some beating for the price. I think Fronius IG TL range is the best for pure, unshaded yield. SMA are best for features and range. Power One are a good all rounder. The 3.0 model especially. Kostal Piko are a very good alternative.

Ye there are lots out there but some how I just keep comming back to P1. I think they lead, where others follow. They have not revised their inverters in a long while unlike sma, looking forward to the next generation of P1.

 

[babba]

My reading of the data sheets also made me think that the 4000 would be recommended but the Sunny Design software doesn't agree.

If the 4000 is manually entered in then there are no incompatibility issues and the annual estimated output is calculated. I don't know why Sunny Design does not offer the 4000 as a recommendation... but it doesn't.

You cant believe that rubbish...The computer says no...

 

[lewyames]

I definitely did misunderstand you. While it probably won't damage the inverter by connecting too much power to it, I don't think the OP is concerned about this. I think it is the OP concern that he may have an undersized inverter as it will mean that he isn't getting the maximum benefit from his system.

If you check the SMA data sheet the max AC output for a 3000TL is 16A, have a look.....

I don't see how this can be. If the maximum power output of the inverter is 3000w then you would need a grid voltage of around 180v to get 16A.

The maximum current you would expect from the inverter at 230v is 13A - in reality, I'd imagine that the output current is dependant on two things - the DC power and the grid voltage. The output power will never be above 3000w.

Again, I'm always ready to be proven incorrect.[/QUOTE]

Yeah I see where you're coming from! Product specifications can be very misleading, the most common inverter I've fitted is the Fronius IG TL 3.6 which for instance has on its data sheet a max power output of 3680W but they will regularly generate up to 4000W - my assumption is that as you allude to this is down to high grid voltages, but it also leads me to believe that when it comes to product specifications, the most important value is the max output current as this is the real limiting factor, especially for a G83/1 certificated inverter (as per DNO requirements). This is what leads me to believe that the max ac output in Watts can be misleading. SMA are probably the only ones who can really answer this (I've never fitted an SMA 3000TL) if I had an hour to spare to spend on hold I'd give them a call! If you're right and it won't go over 3000W then this guy has definitely had the wrong inverter fitted!

 

[clivep]

I've just downloaded the latest Sunny Design software and there are a couple of changes. The SB 3000TL-20 is still the recommeded inverter (in dark green) but the SB 3600TL-20 and SB 4000TL-20 are now shown as options (in light green).

No other single inverter is shown as compatible and I believe this to be because of yield loss (Min PV voltage for a string of 8 is 198V but inverters need 209V... 1 string of 16 is too high voltage).

Using my data of 16 x Hyundai HIS-S250MG panels, located in Leeds with azimuth of -30 degrees and inclination of 30 degrees gives the following comparison of design suggestions:

SB 3000TL-20 - Annual yield 3348.30 Usability factor 99.5% Performance ratio 83.7%
SB 3800TL-20 - 3327.70 100.0% 83.1%
SB 4000TL-20 - 3356.80 100.0% 83.9%

So the 3800 actually produces less than the 3000 and the 4000 only produces 8.30 kWh more per year than the 3000. Presumably the 3000 is recommended over the 4000 as the extra cost of the 4000 wouldn't be recovered over it's lifespan.

I still can't fathom why the yield of the 3000 and 4000 is so similar. The spec on the 3000 definitely states max AC power of 3kW so I would of thought that in summer there would be a lot more power being wasted.

 

[FB.]

I still can't fathom why the yield of the 3000 and 4000 is so similar. The spec on the 3000 definitely states max AC power of 3kW so I would of thought that in summer there would be a lot more power being wasted.

It's probably because inverters work best when they're working at a medium to high capacity, relative to whath they were built to handle. When there's only a trickle of electricity coming in from the panels (on cloudy days, or when the sun was not in the panels arc, or in winter) the big inverter is well off its "sweet spot" and might only be 80% efficient at converting the DC to AC, while a smaller inverter might be only just off its "sweet spot" and be 90% efficient.
In recent cloudy days my SE-facing 3.75kWp system has only been generating about 3kW total per day, or about 0.6kW per hour at peak late-morning output. My P1 Aurora has a maximum input of 3.75kWp, but with only 0.6kW coming into the inverter (even at the peak in recent days), it was only running at 16% of the maximum that it can handle. Once the sun was out of its arc in the afternoon, it's probably only generating 0.3kW; about 8% of maximum potential.

I extracted this from an ealier posting of mine:

If we had a hypothetical 4kW inverter, it would most likely have efficiency something like this:

0.25kW DC -> 0.2kW AC (80% conversion efficiciency)
0.5kW DC -> 0.45kW AC (90%)
1kW DC -> 0.95kW AC (95%)
2.5kW DC -> 2.4kW AC (96%)
4kW DC -> 3.8kW AC (95%)

In short: the smaller inverter is optimised to deal with smaller DC input, whereas the bigger inverter is optimised to handle higher DC input. To some extent it depends on the exact make/model of inverter as to how well they convert on dull days.