Connecting a solar suitcase to 100 watt panels

[garyb1st]

I have a Renogy 100 watt solar suitcase and two Renogy 100 watt panels. If possible, I'd like to wire them in parallel and run them through my Renogy contoller. The suitcase is wired in series which to me is the same as a 100 watt panel. Renogy says I can't do it but didn't really say why. At least I didn't understand the explanation. The specs for the suitcase and 100 watt panels are similar but not exact. Open Circuit Voltage is the same = 21.6V. Short Circuit Current is a bit greater on the panels = 6.14A vs 6.1A. Optimum Voltage and Current is slightly greater on the individual panels.

So If I can't combine the suitcase and panels I'd like to buy another 100 watt panel. However, the new Renogy 100 watt panels have slightly different specs than the ones I have. Voltage is higher but current is lower. So isn't this the same problem? And if so, how does anyone combine dissimilar panels?

 

[Mark_K5LXP]

The mismatch is only important if you're trying to eek every milliwatt out of your system. Guessing your controllers aren't spec'd for the open circuit voltage of panels in series, so you're going parallel by default. From there your system efficiency with disparate panels isn't optimum, but it will "work". Practically speaking in an RV application you would be hard pressed to measure the difference. (you get what you get).

Mark B.
Albuquerque, NM

 

[garyb1st]

The mismatch is only important if you're trying to eek every milliwatt out of your system.

I'm good with less than optimal.

Guessing your controllers aren't spec'd for the open circuit voltage of panels in series, so you're going parallel by default.

Don't understand the subject well enough to answer. The solar suitcase is wired in series and when I wired the two 100 watt panels together I did it the same way, positive of one to negative of the other. Don't know if that's the optimal way. Wired in series, they usually generate around 10 amps in full sun. What I just learned today is that by combining them in series I'm losing some amps. That's why I'd like to wire the two 100's and the solar suitcase in parallel.

I've got some 3 to 1 mc4 connectors so thought I'd combine the two 100 watt panels with the suitcase. I just don't want to damage the controller.

 

[Lou Schneider]

Is the combined voltage for the suitcase panels 21.6 volts or 43.2 volts? Your parallel connected rooftop panels produce 21.6 volts.

If the series connected suitcase panels produce a total of 21.6 volts (10.8 volts each) you can connect them in parallel with your 21.6 volt rooftop panels. If they produce a total of 43.2 volts you'll lose half of their potential power connecting them in parallel with your rooftop panels because lower voltage panels drag higher voltage panels down to their level.

Make sure your controller is capable of handling the extra current. You can "overpanel" to an extent i.e. connect more wattage than the controller can handle. When the panels can produce more power than the controller can handle, like when they're in full sun, the controller becomes the limiting factor in how much current is passed through to your batteries.

 

[garyb1st]

The volts on the suitcase are the combined voltage. Looks like the limiting factor is my controller. According to the specs, Max solar input power at 12V is 260 watts or 520 watts at 24V. If I understand it, with my 300 watts combined, at 12v I could be damaging the controller during peak sun.

I could wire my lithium batteries in parallel which would get me to 24V. My refrigerator which is wired directly to the batteries will run on either 12 or 24v. But I have no idea if the 12 v lights and other appliances, water heater, furnace etc., would be OK. Also, I don't know if my Aimes 1000 watt inverter would be OK.

Unless the battery rewire will work i'm back to square one. Even buying more panels means I need to upgrade the converter. Before spending more on my portable system, I need to seriously consider a roof mounted system.

 

[garyb1st]

Just looked at a 12/24 converter. Don't think I want to change the wiring on the batteries. This is not a project for a novice.

 

[Tulecreeper]

The volts on the suitcase are the combined voltage. Looks like the limiting factor is my controller. According to the specs, Max solar input power at 12V is 260 watts or 520 watts at 24V. If I understand it, with my 300 watts combined, at 12v I could be damaging the controller during peak sun.

I could wire my lithium batteries in parallel which would get me to 24V. My refrigerator which is wired directly to the batteries will run on either 12 or 24v. But I have no idea if the 12 v lights and other appliances, water heater, furnace etc., would be OK. Also, I don't know if my Aimes 1000 watt inverter would be OK.

Unless the battery rewire will work i'm back to square one. Even buying more panels means I need to upgrade the converter. Before spending more on my portable system, I need to seriously consider a roof mounted system.

If your fridge and lights are on the same circuit(s) then no, your 12v lights won't work with a 24v supply.

 

[Lou Schneider]

The volts on the suitcase are the combined voltage. Looks like the limiting factor is my controller. According to the specs, Max solar input power at 12V is 260 watts or 520 watts at 24V. If I understand it, with my 300 watts combined, at 12v I could be damaging the controller during peak sun.

I could wire my lithium batteries in parallel which would get me to 24V. My refrigerator which is wired directly to the batteries will run on either 12 or 24v. But I have no idea if the 12 v lights and other appliances, water heater, furnace etc., would be OK. Also, I don't know if my Aimes 1000 watt inverter would be OK.

Unless the battery rewire will work i'm back to square one. Even buying more panels means I need to upgrade the converter. Before spending more on my portable system, I need to seriously consider a roof mounted system.

You won't damage your controller. All that will happen when your panels are in peak sun and capable of producing more than 260 watts actual power is the amount of current the controller can deliver will be the limiting factor. You will get more charging current than you do now when the panels are in less than full sun and producing less power than the controller's limit. When they're in full sun and capable of producing more power than the controller can handle it will simply ignore the excess.

Leave your batteries as they are now, wired for 12 volts. If you re-wire them in SERIES to get 24 volts you'll need a DC to DC converter to reduce the 24 volts to 12 volts to feed everything that is not 24 volt compatible including the inverter. These converters use some power even when everything is turned off so they will negate any advantage you'd gain by going to 24 volts.

 

[Mark_K5LXP]

When they're in full sun and capable of producing more power than the controller can handle it will simply ignore the excess.

Yep. There will be the periods prior to and after peak sun where the additional panel output can be realized, so even if the system is controller limited at the peak there will still be a net increase in daily power delivery. Depending on season, panel angle, weather, pollution the controller limit might not be hit anyway so then you will get all the panels have to deliver.

Mark B.
Albuquerque, NM

 

[garyb1st]

I'll be checking things out when I'm in Quartzsite next month.

Thanks for the responses.