Any advantage of having multiple inverters?

[Ian S]

I guess that's one way to do it but I don't think that will work in Arizona. Circulated air from the outside is needed when the garage door is closed otherwise you're just circulating hotter air in the inverter.

It will help because the air in the garage will always be cooler than the heatsink. It just won't be as effective as air from the outside which will be cooler still.

Now, unless your inverter is undersized, the derating may not impact your installation significantly. A typical derating on a power supply might be 2% per C.deg. (starting from 45 or 50 deg C whatever your inverter's full power rating is) and I assume an inverter would be similar. But your solar panel output has already dropped significantly due to temperature being above STC of 25C which is well below the temperature at which the inverter starts to derate. At some point the steeper inverter derate curve will cross the solar panel output curve but I think that should always be higher than than the point where inverter derating starts.

[AZstars]

I guess that's one way to do it but I don't think that will work in Arizona. Circulated air from the outside is needed when the garage door is closed otherwise you're just circulating hotter air in the inverter.

Irrespective of inverter there or not, many times I thought why we don't care of the higher in the evening garage temps compared to outside. The garage with two cars' hot motors is like heatsink long in the evening. Just ventilate some air with outside based on temp differential. AC guys should offer such service..

[Naptown]

It's Arizona, Fronius starts to derate performance at about 101 degrees F and continues to do so as the temperature goes up, which means for about 5 months out of the year, your inverter is operating at reduced output. Power-One on the other hand won't derate performance until the temperature touches 120 F ambient, however few times that happens in a year.


Power-One also has the advantage of being rated NEMA4, which is of tremendous importance in Arizona where we often have dust storms that can result in debris ending up inside a lesser-rated inverter. I also believe that the Power-One will start up at a lower input voltage than most of the other central inverters, earlier startup time=more production throughout the year.

I believe that Sun power is recommending Power-One as their primary inverter selection since the Power-One's are higher efficiency and transformerless as well.


"Maximum performance: The panels that make up the new E20 Series are compatible with Transformer-less (TL) Inverters. This means that SunPower superior panel performance can now be matched with the highest performing inverters, maximising system output."

http://www.sunpowercorp.co.uk/homes/products-services/solar-panels/e20/

http://dcpower-systems.com/uploads/products/25366_1.pdf

But your panels have also derated substantially at that point also.
If the outdoor temperature is 120^oF you can add about 30^oC to that.
Do the math and you will see a dramatic reduction in the output of the array. As long as the array is not too oversized for the inverter there should be no reduction due to inverter derate.
Nmea 3 or 4 shouldn't matter if you put the inverter inside in conditioned space. Outside is another story same with temperature and derate

[Tucson Bass Player]

If I have the space, is having two (3000x2) instead of one (6000) inverter better? Thanks

I have always relied on multiple inverters for small systems. But they are of varied sizes for different task. And of they all count as spares.

[KRenn]

But your panels have also derated substantially at that point also.
If the outdoor temperature is 120^oF you can add about 30^oC to that.
Do the math and you will see a dramatic reduction in the output of the array. As long as the array is not too oversized for the inverter there should be no reduction due to inverter derate.
Nmea 3 or 4 shouldn't matter if you put the inverter inside in conditioned space. Outside is another story same with temperature and derate

Most inverters here are located outside as people don't typically air-condition their garages, thus its better to put it on a shaded side of the home rather than stick it in a heat sink of a garage that can go past 115 with minimal air flow happening.

[Naptown]

You are missing the point
An inverter starts to de-rate when temps get high so lets look at an example
Lets say it's 110 outside and you are using 20 Sunpower 327 modules
Noct or cell operating temps are generally abut 30C above ambient in full sun
Thats a cell temp of 73C
temp coefficient on that panel is .38% so 48 x.38=18.24% derate on the panels
Extrapolating that into real numbers 20 x327=6540 watts maximum and lower at PTC rating of about 301.4 =6020 watts
Assuming you have a 6K inverter at 25C you might feed in 6020 watts .
Now take the 18% off of that and what do you have about 5000 watts by my calculations or about 80% of maximum loading on the inverter. This assuming no humidity, smog and during the peak hours of the day. the likelihood of the inverter clipping is vastly reduced due to high temps on the modules.

[chuco35]

You are missing the point
An inverter starts to de-rate when temps get high so lets look at an example
Lets say it's 110 outside and you are using 20 Sunpower 327 modules
Noct or cell operating temps are generally abut 30C above ambient in full sun
Thats a cell temp of 73C
temp coefficient on that panel is .38% so 48 x.38=18.24% derate on the panels
Extrapolating that into real numbers 20 x327=6540 watts maximum and lower at PTC rating of about 301.4 =6020 watts
Assuming you have a 6K inverter at 25C you might feed in 6020 watts .
Now take the 18% off of that and what do you have about 5000 watts by my calculations or about 80% of maximum loading on the inverter. This assuming no humidity, smog and during the peak hours of the day. the likelihood of the inverter clipping is vastly reduced due to high temps on the modules.

Are you saying that the effect of high ambient temperatures on the panels themselves degrade their efficiency to where we don't need to worry about the effect of such temperatures on the inverter?

[KRenn]

You are missing the point
An inverter starts to de-rate when temps get high so lets look at an example
Lets say it's 110 outside and you are using 20 Sunpower 327 modules
Noct or cell operating temps are generally abut 30C above ambient in full sun
Thats a cell temp of 73C
temp coefficient on that panel is .38% so 48 x.38=18.24% derate on the panels
Extrapolating that into real numbers 20 x327=6540 watts maximum and lower at PTC rating of about 301.4 =6020 watts
Assuming you have a 6K inverter at 25C you might feed in 6020 watts .
Now take the 18% off of that and what do you have about 5000 watts by my calculations or about 80% of maximum loading on the inverter. This assuming no humidity, smog and during the peak hours of the day. the likelihood of the inverter clipping is vastly reduced due to high temps on the modules.

If the temperatures here rarely exceeded 101, I'd say you have a point, but most inverters will START derating at 98-100 F and rapidly decrease performance as the temperature continues to go up.

Why even take the chance? Why not design systems according to the climate they will be utilized in? There's systems out here that flat out shutdown because the inverters check out at around 110-111 F, those might seem like incredibly high temperatures in Maryland but out here, they are fairly common in the summer, why not utilize the system that will provide the greatest high-temperature performance possible?

[billvon]

why not utilize the system that will provide the greatest high-temperature performance possible?

Because it might cost the end user a lot more for capacity he will never use.

[AZstars]

Extremes

If the temperatures here rarely exceeded 101, I'd say you have a point, but most inverters will START derating at 98-100 F and rapidly decrease performance as the temperature continues to go up.

Why even take the chance? Why not design systems according to the climate they will be utilized in? There's systems out here that flat out shutdown because the inverters check out at around 110-111 F, those might seem like incredibly high temperatures in Maryland but out here, they are fairly common in the summer, why not utilize the system that will provide the greatest high-temperature performance possible?

The Phoenix forecast for next days is a heat wave of temps in the 114F range. I am wondering what the panel temp can be on SSW orientation at 2PM and what is the garage temp if we have just arrived with two cars in the garage.
On the opposite, March (?) seems to be the best production month here. The system shall be designed to take in the high kW in March and to produce MAX possible in hot summer. How ? That I want to learn here...

[josefaz]

You are missing the point
An inverter starts to de-rate when temps get high so lets look at an example
Lets say it's 110 outside and you are using 20 Sunpower 327 modules
Noct or cell operating temps are generally abut 30C above ambient in full sun
Thats a cell temp of 73C
temp coefficient on that panel is .38% so 48 x.38=18.24% derate on the panels
Extrapolating that into real numbers 20 x327=6540 watts maximum and lower at PTC rating of about 301.4 =6020 watts
Assuming you have a 6K inverter at 25C you might feed in 6020 watts .
Now take the 18% off of that and what do you have about 5000 watts by my calculations or about 80% of maximum loading on the inverter. This assuming no humidity, smog and during the peak hours of the day. the likelihood of the inverter clipping is vastly reduced due to high temps on the modules.

I think I got your point. I don't have control of the de-rating of the mudules under extreme heat but I may be able to do something about the inverter. With your example above, wouldn't the inverter de-rate as well? So should the 6K inverters starts clipping at around ~5.7K? Keep in my mind I'm in AZ and it could reach up to 130F between now and end of Aug inside the garage. I read the SMA inverter specs and it de-rates at around 105F.
Kren mentioned the inverter should be placed outside but based on the suggestions I received from the installers, the inverter should be placed inside the garage since my main box is facing west. So the garage is my only placement option unless I pay extra to run it across the house.

[Mike90250]

If I was in a high ambient heat situation, I would oversize the inverter by at least 20%

I would avoid one with an internal fan, and opt for a cheap desk fan on a timer to just stir the air around.
I feel internal fans would be ON a lot, and eventually require replacement which would not be easy.
$30 for a new desk fan, as I did.
My garage is closed days, and the south facing stucco wall is not insulated, and soaks up a lot of heat.

Maybe mount the inverter on a insulated plywood board (rigid foam insulation, foil backed plywood) to help reduce heat gain.
polyisocyanurate rigid foam insulation is a brownish color, and rated for high temps

Moving air removes more heat than stagnant air.

If your garage interior runs 130F, you need more venting in it, roof vents, floor intake vents.... something.

[josefaz]

If the temperatures here rarely exceeded 101, I'd say you have a point, but most inverters will START derating at 98-100 F and rapidly decrease performance as the temperature continues to go up.

Why even take the chance? Why not design systems according to the climate they will be utilized in? There's systems out here that flat out shutdown because the inverters check out at around 110-111 F, those might seem like incredibly high temperatures in Maryland but out here, they are fairly common in the summer, why not utilize the system that will provide the greatest high-temperature performance possible?

I agree. Heat degrades electronic parts and the suggestion that inverters loose a small percent of it's efficiency every year is magnified here in the AZ heat. Granted the system performance is warrantied for 20 years but who's to say the lessors are still around in 5 to 10 years. I may as well design the system to atleast reach my calculated ROI. My system will be designed to provide 110% of my current yearly energy usage and I would rather get a quality inverter. By my calculation, without factoring rate increases, my ROI is around 8 years.

[Naptown]

Are you saying that the effect of high ambient temperatures on the panels themselves degrade their efficiency to where we don't need to worry about the effect of such temperatures on the inverter?

For the most part yes unless you are at the upper end of the input watts. By that I mean that you're DC watts are above the output rating of the inverter

If the temperatures here rarely exceeded 101, I'd say you have a point, but most inverters will START derating at 98-100 F and rapidly decrease performance as the temperature continues to go up.

Why even take the chance? Why not design systems according to the climate they will be utilized in? There's systems out here that flat out shutdown because the inverters check out at around 110-111 F, those might seem like incredibly high temperatures in Maryland but out here, they are fairly common in the summer, why not utilize the system that will provide the greatest high-temperature performance possible?

Who's inverters are shutting down at that temperature. the Fronius I suggested is rated for an operating temperature to 131^oF It is also a 3 stage inverter meaning that the 6000W inverter is actually 3 2000W inverters so as things heat up and array output goes down it will track (derate) itself with little or no loss of efficiency. Over sizing and inverter to prevent it from derate or high temps will cost you more dearly when it is cooler outside. Efficiency will be reduced on the inverter if not operating within about 10% of capacity.

Because it might cost the end user a lot more for capacity he will never use.

Exactly correct and oversizing an inverter is just as bad as it will reduce efficiency at an even more rapid rate. They like to be loaded up not idling along.

The Phoenix forecast for next days is a heat wave of temps in the 114F range. I am wondering what the panel temp can be on SSW orientation at 2PM and what is the garage temp if we have just arrived with two cars in the garage.
On the opposite, March (?) seems to be the best production month here. The system shall be designed to take in the high kW in March and to produce MAX possible in hot summer. How ? That I want to learn here...

Add about 30^oC to the ambient temp and you will get pretty close.

[AZstars]

Take it, or..

panels1.JPG
With this panel orientation, I am told that the supplier's choice of (1) Fronius inverter is identical to two PowerOnes and that change of the inverter brand and model number is not possible at this stage of the project, without
affecting the quote substantially (note that I have the old pricing from June). So it seems that I am toast and have to go with the one Fronius. It would be interesting to make a calculation, how the "several percents" difference
mentioned to me will affect me monetarily over the long term (= missing on peak hour production).
The only change I was able to get was moving the inverter out of the garage on the east wall. No comment on the dust rating of the Fronius and how it can be affected outside.