Have an off-grid system with a new higher load. Question about combining ssytems.

[RiverCityCont]

We have an off-grid system set up to run a radio telemetry module. The current system is a 20W panel with a controller charging a 12V battery which runs the radio module. We have now installed a new module which has a higher load and is running down batteries. We also have, on the shelf, another 20W panel and controller that were taken from a dismantled system elsewhere. My question is what would be the best way to combine these two solar panel systems to come up with a system that will handle new load. A simpler way to ask may have been, "How do I properly combine two 20W solar panels into one system?" Thanks.

[inetdog]

We have an off-grid system set up to run a radio telemetry module. The current system is a 20W panel with a controller charging a 12V battery which runs the radio module. We have now installed a new module which has a higher load and is running down batteries. We also have, on the shelf, another 20W panel and controller that were taken from a dismantled system elsewhere. My question is what would be the best way to combine these two solar panel systems to come up with a system that will handle new load. A simpler way to ask may have been, "How do I properly combine two 20W solar panels into one system?" Thanks.

If your controller can handle the current produced by two panels (~2 amps??), then just connect both panels in parallel to the same charge controller.
If your controller is really limited, you can also connect two panel/controller combinations to the same battery as long as the settings on the two controllers are the same.
Chances are very good that you will not need to add more battery capacity, but you should check to see how far the battery is discharged each night. Once you have the second panel in place, if the battery goes down to only 80% of full charge, you are OK. If it goes down to less than 50% you are in trouble. In between it is a judgement call.

The one important piece of information which you left out, however, is what type and size battery you are using? AGM or FLA?
If it is FLA and less than 10AH, then just putting two panels on it may end up charging it faster than it is comfortable with.
If it is AGM, then you should be OK.
IF it is a GEL battery, do NOT increase the charging rate without looking at the specifications for that particular battery. And do not get GEL for this service again.

[Sunking]

One other thing that sticks out is now that you have increased the load, you might very likely be over discharging your battery too deeply each day. So not only do you not have enough panel wattage to recharge the battery fully, you most likely do not have a large enough battery and destroying your current battery.

You need to work out how many watt hours per day the system will use, location, and time of year use. Get all that together and you can design a system to do the job. My best guess is the system now is undersized. Get a handle on this or yu will likely have a catastrophic failure (destroyed battery). If it is a small battery, no big deal because you will likely new a new larger one to do the new work you have added onto it.