Last summer had a solar power system installed. This comprised of 8-190watt panels mounted in a series array on eastern roof [now room on northern roof]connected to 1700 watt SMA inverter. At the quote stage the installer quoted for the addition 2 panels to be added at a later date. My question is would the 2 extra panels be able to be added in series with the existing series string and still be inside the inverters paramaters or would the panels need to be reconfigured to 2 - 5 panel series strings connected to inverter using both inputs ? Trying to wade through the technical data to answqer my questions is a nightmare. PS I am located in Brisbane. I suspect the efficiency of solar panels plays a large part in the calculations.
Adding panels to extra system
(11 posts) (3 voices)-
johnmath
MemberNeil, an extra 2 x 190 watt panels = 1900 watts which is potentially too much for the Sunnyboy 1700 Which is listed as 1850 watts maximum input. This would probably void your warranty. See
http://files.sma.de/dl/5682/SB1200_3000-DAU104411W.pdf
The range of voltage for strings is 147 to 320, so your panels would each have to be less than 32 volts for one string (320/10) or more than 29.4 volts (147/5) for two strings. The most efficient voltage for the inverter is around 180 volts; above or below this, the inverters efficiency falls of by as much as a couple of %. The maximum voltage for the inverter is 400, so the open circuit voltage of the panels must be less than 40 each, for one string. Also the maximum current is 12.6 amperes, so 6.3 for each string in a two string system. Your panels must be less than this. The power of a panel is the voltage x the current. On an individual panel, more cells = higher voltage (approx .49 volts per cell) bigger cells = higher current. It just depends on the design. A panel of 6 x 9 cells will be 6 x 9x .49 = 26.5 volts. If it is 190 watts, the current is 190 / 26.5 = 7.2 amps, if it were 250 watts, the current would be 250 / 26.5 = 9.4 amps.
If you run two strings, they must be identical and ideally have identical insolation or you will be wasting you money. Shade on one part of one panel will effectively shut down a whole string, leaving only the other string working, whereas shade on part of one panel in a single string will shut down just the one panel if it has bypass diodes. The reason for this is that the two strings are joined "in parallel" inside the inverter, and if one is lower in voltage than the other, it simply does not contribute any current.
I am about to put 9 x 190 watt = 1710 watts Qse panels on my Sunny Boy 1700 ( it started with 8). This keeps it inside safe operating parameters, but is not ideal for efficiency because it adds up to 239 volts, well above the ideal 180, but still below the maximum 320. The difficuly I had was getting another panel of the same type to match existing as the importer does not sell individual panels. I managed to get a single one ex a shop display. My 190 watt panels are 26.56 volts / 7.15 amps - so too low voltage for two strings anyway, and too high current as well.
I will be changing from a two by four array, to a three by three array, which is the same height but half a meter wider, but with the panels turned 90 degrees.Posted Saturday 16 Jun 2012 @ 11:33:11 pm from IP # -
Neil W
MemberMore tech info re panels in use they are JINKO type JKM 190M-72 panels VOC 42.2 volts Maximum voltage 36.6 volts maximum current 5.19 amps.I may have put the cart before the horse because on friday i have managed to get 2 brand new identical panels from the Jinko distributor. I still cant understand why the original installer company gave quote for 2 more panels which lead me to believe that 2 panels can be added to my current system and for me to go down this track. Your thoughts would be appreciated.
Posted Monday 18 Jun 2012 @ 3:51:13 am from IP # -
Lance
Key MasterTo be honest, I suspect the guy either didn't understand the specs for the inverter or for the panels, or both. There seem to be quite a few installers out there who don't really understand the tech they are working with (like many other industries!).
Posted Monday 18 Jun 2012 @ 5:08:04 am from IP # -
johnmath
MemberWell, with those numbers, you would need to make two strings of 5 panels, which gives you 10.38 amps and 183 volts. This is near perfect voltage for the efficiency of the inverter, minimising it's internal dissipation. That may give you enough margin of error to get away with the slight overload of the inverter. I am not an installer or an SMA expert so I do not know what happens to the inverter if the input power exceeds its capacity. I assume it would shut down. Another factor is that on a bright sunny day, the panels will get hot and that reduces their output, so again, you can probably get away with it.
Given that there are always design margins for worst case, if you are careful you should be ok. Make sure your inverter is in a shaded place where it gets adequate airflow for cooling, and make sure you have a low impedance (short/thick) power feed in lead going to your meter. The panels will lose about 1 % in output per year, so the 1900 watts will drop to 1845, I.e. within the rating, in about 3 years.
I would do it - but don't blame me if it goes to poo! You may want to disconnect the extra panels in peak season. You can run two strings of four panels with the voltage from your panels. Remeber to take note of what I said earlier about identical conditions needed for the two strings.
Posted Monday 18 Jun 2012 @ 7:02:34 am from IP # -
johnmath
MemberThere has been a discussion about an similar system on Whirlpool http://forums.whirlpool.net.au/forum-replies.cfm?t=1945655
The answer from SMA relates to QSE 190 watt panels and SB1700 inverter:
...with panel specs you provided and it’s no problem to add another panel to the SB1700 and in fact you can add another 2 panels if you want which brings the PV peak power to 1900W where inverter is capable of taking 1850W. This can ensure the capacity of your SB1700 is fully utilised that will give you higher energy yield generation. As I mentioned the previous email that the DC wattage is definitely fine for the inverter to handle and I have further confirm that putting either 9 panels or 10 panels in a single string will stay within the voltage limit range. Please refer to the summary overview of your design and please let me know if you need any further support.
I would say you are fairly safe, but maybe you can ask SMA directly. If they give you the same advice, it would protect your warranty.
Posted Friday 13 Jul 2012 @ 10:05:13 pm from IP # -
Lance
Key MasterWith those inverter and panel specs the array would definitely have to be reconfigured into 2 strings of 5, so it's not a simple install, as this obviously means rewiring, but it also means the current from the array to the inverter will double, so the cable that was installed may not be adequate. You would have to check the size and calculate the voltage loss at the new lower array voltage, or have the installer do it. I would double check it myself if it were my installation...
Posted Saturday 14 Jul 2012 @ 12:07:37 am from IP # -
Neil W
MemberThank you for your advice. I managed to obtain 2 190 watt panels identical to the 8 originals at the right price. I engaged the original Electrical Contractor to install them. He reconfigured my array to 2 strings of 5 panels in series connected in parallel.The paralleling was done on the roof with special T connectors, the cable from the roof to the invertor was the right current carrying capacity. It is a cloudy day to day, today the array has produced 3.1 DC Kilowatts total. At the moment it is producing about 700 watts @ 168volts DC, it is now 4-16pm . I feel since installing the extra panels the instant DC wattage at any point in time has increased about 200 watts. I am happy with the way the system is performing at the moment. The system eas only upgraded yesterday, so it is early days yet, It would be interesting to see how it performs during summer. Thanks again. regards
Posted Wednesday 18 Jul 2012 @ 6:25:15 am from IP #