wifibeagle
New Member
I have an existing 180 watt solar panel on our boat dock charging 2 12V 55 Ahr gel batteries in series. It has kind of worked for 11 years before the 2 previous 55Ahr batteries died. It turns out the guy who sold me the solar panel and the Morningstar PWM controller either didn't know what he was doing or took advantage of my ignorance. The Vmp/Voc of the panel are specified as 25.8/32.7V. I have learned this is not a good match to bulk charge my batteries at ~29 volts. I plan to add another panel in series and change to a MPPT controller, probably a Victron Energy SmartSolar MPPT 100V 15 amp 12/24-Volt Solar Charge Controller. The batteries power 2 cameras ~1A for 12 hours/day, charging boat batteries ~2-3A 2 hours 3 times a week and ~22A occasional boat lift blower ~2-3 minutes..
My question is what criteria should I use to select the additional panel? I understand the current will be limited by the the lower of the two panels. I don't understand the criticality of matching the other parameters especially the Vmp. Most of the readily available panels on Amazon are nominal 12V with a Vmp less than 20V. This one "24V" panel is the closest match I have found. Panels with a Vmp around 25V don't seem very common.
Existing panel Potential 200 watt new panel
Vmp 25.8 24.38
Imp 6.98 8.2
Voc 32.7 28.98
Isc 7.65 8.7
Today (1/2/24) in full sun I measured Vmp/Imp/Voc/ as ~24/5.64/31.68 with my EY1600 solar multimeter. The local weather station reported a solar radiation of about 460 at that time. I suspect in late June the Vmp might be closer to the 25.8V in the specification.
So, is this potential new panel a reasonable match? Do I need to match the Vmp or only the Imp. I recognize paring it with the old panel will limit it to a max output of ~170 watts. However, The resulting bulk charge current would be in the range of 8-12 amps in full sun. A big improvement over the ~3A max I get now.
My question is what criteria should I use to select the additional panel? I understand the current will be limited by the the lower of the two panels. I don't understand the criticality of matching the other parameters especially the Vmp. Most of the readily available panels on Amazon are nominal 12V with a Vmp less than 20V. This one "24V" panel is the closest match I have found. Panels with a Vmp around 25V don't seem very common.
Existing panel Potential 200 watt new panel
Vmp 25.8 24.38
Imp 6.98 8.2
Voc 32.7 28.98
Isc 7.65 8.7
Today (1/2/24) in full sun I measured Vmp/Imp/Voc/ as ~24/5.64/31.68 with my EY1600 solar multimeter. The local weather station reported a solar radiation of about 460 at that time. I suspect in late June the Vmp might be closer to the 25.8V in the specification.
So, is this potential new panel a reasonable match? Do I need to match the Vmp or only the Imp. I recognize paring it with the old panel will limit it to a max output of ~170 watts. However, The resulting bulk charge current would be in the range of 8-12 amps in full sun. A big improvement over the ~3A max I get now.