Solar Panel Inverters

MASHER154

I have looked into solar panels for the last 3 weeks and had many quotations. It has been very hard deciding between the companies. They all seem to use different panels and inverters. I have narrowed it down now between 2 companies, both with 14 Suntech 280w panels, giving me a 3.92 system. One is using a Sunnyboy 4000TL and the other a Mastervolt 4300. One says its best to keep under the wattage of the panels, whereas the other the opposite. I know that you can be 10% either side, but what is best. Has any body got any views or experience on this.

Thanks

Cardew

This has been discussed several times, and no firm conclusion reached.

The 'logic' used is that the smaller inverter is more efficient and hence the gain for the great majority of time when the panels are producing below maximum output outweighs the very short periods the panel output exceeds the inverter capacity.

I suspect that the main reason is that a smaller inverter is cheaper!!!

Unless several 'side by side' tests were carried out I doubt the answer will ever be known

zeupater

MASHER154 wrote: »

I have looked into solar panels for the last 3 weeks and had many quotations. It has been very hard deciding between the companies. They all seem to use different panels and inverters. I have narrowed it down now between 2 companies, both with 14 Suntech 280w panels, giving me a 3.92 system. One is using a Sunnyboy 4000TL and the other a Mastervolt 4300. One says its best to keep under the wattage of the panels, whereas the other the opposite. I know that you can be 10% either side, but what is best. Has any body got any views or experience on this.

Thanks

Hi MASHER154

Please see my reply to your post where you posted on the other thread here ...

zeupater wrote: »

Hi

The debate on whether to undersize the inverter is a long running one, with many installers sizing the inverter to 80% of the nominal panel kWp .... as an array owner, here's my view ....

The arguement for undersizing inverters is probably based analysis of data collected by the inverters. The data which is recorded is based on the average generation performance of the system over a period of time, in the case of my inverter it's every 5 minutes. Looking at the data you will find that it is very rare to achieve over 80% - 85% of the total installed capacity of the array, this is mainly due to three main factors - firstly, system losses (inverter, cable runs, panel reflection etc) - secondly, temperature (in continuous sunshine the panels heat up and become less efficient) - thirdly, averaging, which seems to be something which is not fully understood by many.

Let me expand on the effect of averaging .....

Panels have a nominal power rating based on an operating temperature which is somewhere around 20C below what their temperature is likely to be after being in full sun for a while which usually reduces the performance by somewhere between 6% & 10% (depending on manufacturer/type). When the panels are cooler than the nominal rated temperature the efficiency increases. Taking this into account you will understand that the maximum performance will be achieved when the panels are cool and the sun shines brightly, which is exactly what you get when you have a blue sky with clouds, or a cloudy sky with blue patches.

As an example, and to keep things simple, let's say that the sky is 50% cloud/50% blue and see what we get. When cloudy let's say the system produces down to 40% of maximum capacity, and when sunny 100% and that there is a regular gradient in the irradiance between the two. This is not untypical.

The average generation of an unrestricted system will be (40+100)/2, so 70% and this is what will be recorded by the inverter for onward analysis, therefore there is an arguement that an inverter rated at 80% of kWp is sufficient in this scenario.

Let's now cap the maximum generation by introducing an inverter rated at 80% of kWp. We have now lost a third of the generation operating band above the baseline 40%, which effectively reduces the total generation in this band by 11.1% (1/9 - simple trig, the top 1/3 of the height of an equilateral or isosceles triangle accounts for 1/9 of the area).

Considering that a loss of 1/9th of 60% of the generation results in an overall loss of 6.7% we suddenly have an alternative position, being that in the conditions as described, an inverter rated at 80% of kWp will result in lost opportunity. This is something which is not apparent when analysing averaged data.

Enough to say, my inverter is sized to utilise the panel performance in conditions such as described in the example above.

HTH
Z

HTH
Z

MASHER154

That has me complety baffled , are you saying going above or below the array size.

zeupater

MASHER154 wrote: »

That has me complety baffled , are you saying going above or below the array size.

Hi

What I am saying is that the logic used for undersizing inverters is based on averaging generation performance over a period of time. If you look at averaging over a shorter period you will see that higher generation peaks are achieved and if you look at instantaneous power readings even higher peaks will be seen. The conditions over my system at the moment are very similar to the example given, so I would expect to have generated less over the past hour or so by having an inverter sized at 80% of the panel nameplate capacity (kWp) than one which would not clip performance.

HTH
Z

MASHER154

Ok Thank you

daytona600_2

MASHER154 wrote: »

I have looked into solar panels for the last 3 weeks and had many quotations. It has been very hard deciding between the companies. They all seem to use different panels and inverters. I have narrowed it down now between 2 companies, both with 14 Suntech 280w panels, giving me a 3.92 system. One is using a Sunnyboy 4000TL and the other a Mastervolt 4300. One says its best to keep under the wattage of the panels, whereas the other the opposite. I know that you can be 10% either side, but what is best. Has any body got any views or experience on this.

Thanks

sma 4000tl state of the art , mnastervolt only good for a skip , suntech mid range , much better modules with higher outputs/yields