Maxed out inverter

[scotth]

Hi

Last week during the good weather notice my inverter maxing out. 2k system sunnyboy 1700 installed for start was maxing out at 1700+- 20 watts then as week progressed was maxing out at 1550+-.

IS this correct size of inverter for my 2k system?
why would there be a drop in my max out wattage?

Thanks
Any advice would be great.


scott

 

[stuart99]

What panels are they?

Once the warm weather kicks in, the panels output will drop with the temperature of the panel.

Additionally, if the inverter is getting hot, it may also reduce power output to save itself!

 

[whinmoor]

Can you tell us your rough location, roof pitch & orientation?

We tend to use something a little larger for 2kWp systems but there may be an obvious reason why your installer chose this one.

 

[scotth]

Iam in north east scotland. 35 deg pitch and orientation of ssw. Get slight shading from late nov till early feb due to sun not quiet high enought to clear house next door in morning.

Pannels came from supper seal cant rememeber name of them off top of head and away just now. inverter out in my garage so not that warm. could not get any closer to pannels.

 

[Gavin A]

IS this correct size of inverter for my 2k system?
why would there be a drop in my max out wattage?

It'll make most sense to answer these in reverse...

the SB 1700 actually has a nominal rating of 1550W output, with 1700W being it's peak output that it can sustain for short periods.

This being the case, IMO the installer arguably shouldn't have specified this inverter for a 2kWp PV array as they should really be using the 1550W figure as their starting point for determining the maximum sensible array size, not the 1700W absolute peak.

This is compounded by the efficiency curve of the SB1700, which is unlike the HF or TL inverters has an efficiency curve that peaks at lower voltages and power of around half it's nominal output, and loses efficiency at the higher end of the power curve, so it's 2% less efficient at 1700W vs 800W.

There is a bit of a gap in the SMA range at 2kW though because while the HF inverters start at 2kW and the 2000HF would have been suitable, they're actually most efficient with 2500Wp of panels as the HF series work differently to the SB series.

 

[scotth]

so relay should have bigger inverter to get most out of pannels? think will have to chat to installer see what they say.

 

[mdovey]

It isn't an exact science. The SB2000HF would probably give you a little more output on a bright sunny day in summer over that of the SB1700, but we are probably only talking in the region of 100Wh. On the other hand, the SB1700 will be slightly better on cloudy days and sunny winter days.

If you use the figures from Sunny Explorer, overall the SB2000HF is estimated to produce about 40-50kWh more per annum than the SB1700 for a 2kW array, or £20 per annum in terms of FIT, but the SB2000HF typically costs about £200 more than the SB1700. Also the solar panels output will reduce over time so will be moving closer to the optimum range for the SB1700, whereas it would be moving further away from the optimum range for the SB2000HF.

I have a similar setup (2kW array, SB1700) and would have preferred the SB2000HF (but had to go with what could be installed during the dash last year). At the moment, I'm only seeing >1700 peaks on cloud days when the sun comes out from behind a cloud and hits cold panels. The panels soon warm up and the output comes down. On a clear day (with a nice smooth curve) it currently only reaches 1500. The real test will be in the mid-summer, if on a clear day you get a smooth curve with a noticably flat top.

 

[scotth]

It isn't an exact science. The SB2000HF would probably give you a little more output on a bright sunny day in summer over that of the SB1700, but we are probably only talking in the region of 100Wh. On the other hand, the SB1700 will be slightly better on cloudy days and sunny winter days.

If you use the figures from Sunny Explorer, overall the SB2000HF is estimated to produce about 40-50kWh more per annum than the SB1700 for a 2kW array, or £20 per annum in terms of FIT, but the SB2000HF typically costs about £200 more than the SB1700. Also the solar panels output will reduce over time so will be moving closer to the optimum range for the SB1700, whereas it would be moving further away from the optimum range for the SB2000HF.

I have a similar setup (2kW array, SB1700) and would have preferred the SB2000HF (but had to go with what could be installed during the dash last year). At the moment, I'm only seeing >1700 peaks on cloud days when the sun comes out from behind a cloud and hits cold panels. The panels soon warm up and the output comes down. On a clear day (with a nice smooth curve) it currently only reaches 1500. The real test will be in the mid-summer, if on a clear day you get a smooth curve with a noticably flat top.

What kind of system do you use to monitor your out put? IS it easy to install? Only way i see peck out put and how much generated for day is by looking at invertor.

 

[mdovey]

What kind of system do you use to monitor your out put? IS it easy to install? Only way i see peck out put and how much generated for day is by looking at invertor.

First you'll need to check whether you have a bluetooth piggy back card fitted on your inverter (The SB2000HF would have bluetooth built in but for the SB1700 bluetooth is provided by an optional add-on card) - the easiest way would be to ask your installer. Alternative you could install Sunny Explorer on a bluetooth enabled laptop/computer and see if you can find your inverter. If not you should be able to pick one up for under 100 (see SMA Sunny Beam Bluetooth Communication Piggyback Card - Saving Energy Online for instance). Fitting it involves taking the front panel off the inverter, and for that you need to isolate it from both the AC and DC first. The isolator switches should be sufficient but the manual says you should unplug the cables. It is probably prudent to do both (switches first, then disconnect cables). My recommendation would be to see if your installer to fit one you (they should be able to get the card at trade prices which would offset anything they charge for installation).

With that in place you have a number of options:

Sunny Explorer - SUNNY EXPLORER.*SMA Solar Technology AG this is some windows software which you can use if you have bluetooth on your laptop/computer. Laptop in built bluetooth tend to be low powered so may only pick up the inverter if the laptop is within 10m of the inverter! However, you can get long range bluetooth dongles very cheaply (look for class 1 dongles). The software allows you to see various values of the inverter (output, input voltage, input current etc.) and shows a daily graph. You can also export the data to a file which can be analysed or graph e.g. in excel.

Sunny Beam with bluetooth - SUNNY BEAM with Bluetooth®.*SMA Solar Technology AG A battery powered unit (which inbuilt solar charger) which displays daily graphs as well as current power etc. connecting to the inverter via bluetooth. You can extract the data via usb. You can find it online for about 150 but your installer may be able to supply it. There's apparently a new colour version due this summer.

Sunny Webbox with bluetooth - SUNNY WEBBOX with Bluetooth®.*SMA Solar Technology AG - This provides a similar interface to sunny explorer but in a web browser. It also allows upload to SMA own Sunny Portal or you could upload to other servers and/or save data to an SD Card. It is quite expensive (~500) and needs to be connected to a network router so may be overkill.

I use all three of these (Sunny Webbox to a web server with some web page graphing code I wrote for a historical record, Sunny Explorer as a backup for recording data, and Sunny Beam for just checking on the system - my inverter is up in the loft). For completeness there is also something called Solar-log (Homepage) which is similar to the Sunny Webbox but works with a range of inverters from different manufacters. There are also devices which involve placing a sensor around the AC cable from the inverter (e.g. OWL - http://www.theowl.com/index.php?page=using-owl-with-solar-power ). These are less accurate than devices which connect to the inverter directly but cheaper and less hassle to install (there are other threads on here about using those).

 

[Gavin A]

so relay should have bigger inverter to get most out of pannels? think will have to chat to installer see what they say.

I couldn't categorically say whether it should or not, as there are other variables as well such as the additional cost of the HF inverter. Arguably if for instance the HF would have added say 4% to the cost of the installation, and the improvement in output would only have been say 2%, then there would have been reasonable logic behind installing the SB1700 instead of the HF.

it's borderline basically, but could be worth just asking them to explain their reasoning given that it's obviously limiting significantly already.