Inverter Temperature Derating

[scottliv]

As this was the hottest day of the year, I expected a high yield but was slightly disappointed. Having checked the inverter, it was the first time I had heard the fan on.

My system is a 3.75kWp (due south on the south coast with 15 x 250w Sanyo panels with an SMA SB 4000TL) with a loft mounted inverter. The ambient temperature in the loft was about 35 degrees C, but the cooling fins on the back of the inverter were in the region of 60 degrees C.

I understand that in the hotter weather will reduce the panel output but did not think it would be affected this much. I peaked at about 3.1kW, producing 24 kW in total. I assumed that as the loft temperature was so high and the fan was on the inverter was limiting on temperature, but I cannot find any information on this.

Will the inverter be derating on temperature and how would I know this was happening.

 

[poheZ]

if the inverter hits a critical temperature then an error code will apear. The fan is internal and for air circulation. Remember peaking is not as important as accumulation of kwh

Do you have any monitoring for your system?

 

[Gary K]

Do the inverters loose efficiency as they get warm. Even though it hasen't reached a temperature when it cuts out, would it produce more if it was running cooler?

 

[poheZ]

SMA inverters (i'm sure they are all the same) maintain their efficiency within their rated operating temperature thresholds. So, no!

 

[Gavin A]

they can derate if they go over a set operating temperature though.

 

[scottliv]

I have a sunny beam and there was no warnings. I have not checked sunny explorer yet. I know the inverters derate but cannot find a level that this happens.

 

[poheZ]

If no warnings on sunnybeam then dont panic as explorer wont say any different

why not send a picture of inverter location

 

[mdovey]

I understand that in the hotter weather will reduce the panel output but did not think it would be affected this much.

The efficiency of the Sanyo panel decreases 0.3% for each degree celsius - this is the temperature of the module itself which in full sunshine will be significantly higher than the ambient temperature.

Our outside thermostat hit about 30 in the shade today, whereas a few weeks ago it was reading about 15. The panels would therefore be a minimum of 15 degrees hotter which is a drop of 4.5%, but I'd suspect that in full sunlight they were probably closer to 20-30 degrees higher than a few weeks ago (which would be a 6-9% drop).

So, I'd suspect any reduction in output from your expectations is due to the panels being hotter, than any derating of the inverter.

 

[scottliv]

I have checked the SMA instructions and a 'thermometer' symbol will appear on the front panel of the inverter if it is derating due to temperature. This was not on so it must have just been hot panels.

 

[scottliv]

With a bit more digging, and in reply to Mdovey's post, the Sanyo HIT 250 will produce 188.9W @ 45 degrees C. This equates to around 2835W total for the 15 panels; so my output per panel, not including losses, would have been in excess of 205W giving a peak about 3100W.In conclusion it all seems to be running fine for the current environmental conditions.

 

[Earthstore]

Also you have not taken into account any cable loses, which there will be some.
The fan is on the inverter for a reason, just to help cool it when it has been working hard and the conditions may be warm, so it helps to keep the performance up, not unlike your car really.

The surface of a panel can get very hot in direct sunlight, far hotter than the air temperature, so, as you say all is well.
I feel some customers worry a little too much about the odd blip, they need to look at their annual performance, this takes into account all the changing weather conditions.

 

[SolarCity]

I've noticed that a few systems have failed to peak in our area in this recent hot weather. It often surprises people how much affect heat has on panels.

Regarding the inverter, there is a graph about somewhere showing how efficiency drops off on SMA inverters as they get hotter. You don't necessarily need to get the inverter up to a cricitical heat for it to have an effect on the efficiency.

 

[Gary K]

Regarding the inverter, there is a graph about somewhere showing how efficiency drops off on SMA inverters as they get hotter. You don't necessarily need to get the inverter up to a cricitical heat for it to have an effect on the efficiency.

so the answer is yes? -the cooler you can make run the inverter, the more efficient it is.
Has anyone got this graph please?

 

[overland]

Yesterday (25th) was by far the hottest day here since we've had 16 Trina panels installed in a 3.68kw system with a loft installed inverter. The peak power they produce is normally 3.62, but today they peaked at around 2.90kw which I assumed was down to the higher temps. However, overall for May they have achieved their expected generation for the month already.

Additionally I noticed that the expected generation figure for the month of June is lower than May which I assumed was partly down to one less day and also higher temps reducing the system's performance.

 

[mdovey]

so the answer is yes? -the cooler you can make run the inverter, the more efficient it is.
Has anyone got this graph please?

You can find the temperature derating graphs for the various SMA inverters here - http://files.sma.de/dl/1348/Wirkungsgr_Derat-TEN112110.pdf

In general below an ambient temperature of 40 degrees the inverter will be running at its maximum efficiency for the input of the panels. Above 40 degrees ambient temperature you may see derating (exactly how much above depends on the inverter model) but you should get a warning (on the inverter display, on a sunny beam etc) when this happens. If you aren't getting this warning there isn't much point cooling the inverter from a performance perspective. Cooling may help lengthen the life of the inverter, however.

 

[FB.]

so the answer is yes? -the cooler you can make run the inverter, the more efficient it is.
Has anyone got this graph please?

The Power One Aurora family of inverters are roughly as follows:

Air temperature / output

35-40'C: no loss of output (cooling fan gradually increases its speed to cool the internals).
40-45'C: 5-10% loss of output
45-50'C: 15-20% loss of output
50-55'C: 30-40% loss of output
>55'C: major power reduction and risk of shutdown due to overheating

It is also recommended to avoid mounting in direct sunlight as the inverter casing will absorb sun/heat and get hotter than if the inverter is in shade or in a loft/garage/utility room etc.

 

[FB.]

so the answer is yes? -the cooler you can make run the inverter, the more efficient it is.
Has anyone got this graph please?

And the SMA/SB family of inverters state an operating range up to 60'C, so probably fairly similar to the Power One family.
Unfortunately I couldn't find more specific temperature-derating data.

 

[mdovey]

And the SMA/SB family of inverters state an operating range up to 60'C, so probably fairly similar to the Power One family.
Unfortunately I couldn't find more specific temperature-derating data.

Err, you could look at the link I posted a few posts back!

 

[sambotc]

I've seen the cooling fans running in January when the sun was out, but still cold in the loft (2.4-2.7kw production). It's the process itself rather than the ambient temp in the inverter location (although this will no doubt have an effect)

Presumably the fans will use a small amount running full whack as well, so there will also be a slight loss because of this?

 

[Gavin A]

You can find the temperature derating graphs for the various SMA inverters here - http://files.sma.de/dl/1348/Wirkungsgr_Derat-TEN112110.pdf

In general below an ambient temperature of 40 degrees the inverter will be running at its maximum efficiency for the input of the panels. Above 40 degrees ambient temperature you may see derating (exactly how much above depends on the inverter model) but you should get a warning (on the inverter display, on a sunny beam etc) when this happens. If you aren't getting this warning there isn't much point cooling the inverter from a performance perspective. Cooling may help lengthen the life of the inverter, however.

So HF and TL inverters generally shouldn't derate even in warm UK lofts (as long as the temperature stays below about 50), but the SB series aren't so good, with some derating from as low as 30 degrees.

I think somewhere in the mists of time I'd seen those graphs before and reached the same conclusion, which is partly why we've mostly been installing HF and TL inverters, but I'd then no found the document again so I couldn't remember the specifics.