Berniea Posted February 21, 2020 Share Posted February 21, 2020 I currently have two x 150w solar panels on the roof which don't generate anything more than 220w on the brightest sunny days. They are connected to a victron 30amp MPPT controller. I want to add two additional 120w panels giving a theoretical total power generation of 540w - can I use the same MPPT for all four panels, or will I exceed the capacity of 30amps if I connect all four to the same 30amp MPPT? This is the spec of the two new 120w panels I'm wanting to use: Battery voltage 12/24 V Auto Select Maximum battery current 30A Maximum PV power, 12V 440 W (MPPT range 15 V to 100 V) Maximum PV power, 24V 880 W (MPPT range 30 V to 100 V) Automatic load disconnect no Maximum PV open circuit voltage 100V Peak efficiency 98% Self consumption 10mA Charge voltage 'absorption' 14.4V / 28.8V Charge voltage 'float' 13.8V / 27.6V Charge algorithm multi-stage adaptive Temperature compensation -16 mV / °C resp. -32 mV / °C Continuous/peak load current 15A / 50A Low voltage load disconnect 11,1 V / 22,2 V or 11,8 V / 23,6 V or BatteryLife algorithm Low voltage load reconnect 13,1 V / 26,2 V or 14 V / 28 V or BatteryLife algorithm Protection Battery reverse polarity (fuse) Output short circuit Over temperature Operating temperature -30 to +60°C (full rated output up to 40°C) Humidity 100 %, non-condensing Colour Blue (RAL 5012) Power terminals 13 mm² / AWG6 Protection category IP65 (electronic components) Weight 0,5 kg 1250g Dimensions (h x w x d) 130 x 186 x 70 mm Thanks Link to comment Share on other sites More sharing options...
spirou Posted February 22, 2020 Share Posted February 22, 2020 Use a separate controller for the extra 2 panels. What you pasted are not panel specs but controller and what you need to worry about is its input voltage ceiling, not amps. If you went over the current limit the controller would just shed it as heat (within reasonable overload) but if you go over the 100V limit it could do some serious damage. While it might be possible to stay under the voltage limit it's still not good practice to mix different spec panels together on the same controller as the smaller ones would limit the output of larger pair. In simple terms, you would have 4x120W. Also, 220W max you've had might also be because the batteries couldn't accept more than that at the time. They might have been getting closer to full by the time the panels were at max output as it's likely they were on charge for several hours by that point. It's a different story if you consistently don't see the controller completing its 3 charging stages and mostly stay in bulk. That's easy enough to check with VictronConnect app if you have a bluetooth connection. Link to comment Share on other sites More sharing options...
Ocsid Posted February 22, 2020 Share Posted February 22, 2020 Are the existing panels wired in series to best exploit the use of the MPPT controller? Whilst it will not significantly alter peak performance it can alter what to most of us is the real world need, optimising off peak yield. I would also use a second controller if I could not satisfy myself how well matched the panels would be, new to old. Plus, if adding new they would be selected from those with a high maximum power point voltage, not the more modest type marketed for use with PWM controllers. ie look for 36V or more PPPV panels not 17 V, and still wire these in series with a MPPT controller. Edit: I would also be ensuring I regularly cleaned them. Link to comment Share on other sites More sharing options...
Berniea Posted February 22, 2020 Author Share Posted February 22, 2020 Many thanks for your answers guys, and sorry for confusing things by posting the spec of the MPPT and not the panels! The two existing panels are indeed wired in series and the panels were clean when I saw a "spike" of 220w. I would say the average best wattage is around the 150w mark. I have a Victron BMV712 battery monitor fitted and at the time the 220w was produced, the three 170ah batteries were showing 80% charged and if I recall correctly they were being charged in the absorption state. The panels are going to be fitted at the front of a 9metre van roof and they are supplied with a 6metre cable. I'm going to need about 10 metres to reach the place the new controller will be fitted. Would you suggest I fit an extension cable to the 6m cable, or would you rewire the panel with a complete 10m length. If you think an extension is OK, do I need to make the joint withing a waterproof box or are the joints already waterprrof? Thanks again. Link to comment Share on other sites More sharing options...
spirou Posted February 23, 2020 Share Posted February 23, 2020 If they were in absorption then it's no surprise panels weren't producing more than they possibly could. Again, if you routinely see the controller spend most of the day in bulk phase (easy to check duration of each in history chart) then your consumption is indeed too high for existing panels. But if your history says float phase already lasts for several hours most days then adding more panels doesn't make much sense. Your batteries might already get enough charge, it just happens at lower power earlier in the day and panels don't need to develop full power. Perhaps post your history screenshot? As far as wiring, MC4 connectors are waterproof and also give you the option of easily disconnecting a panel if required. I'd consider rewiring if you have 4mm2 cable and wanted to go with 6mm2 to minimize voltage drop. Less of an issue with series wiring though. Link to comment Share on other sites More sharing options...
Berniea Posted February 24, 2020 Author Share Posted February 24, 2020 Many thanks Again I now have a better understanding of how to increase the panels and how my current set-up works. Good advice and well written Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.