Concerned about Amp Hours

[davarney]

I have a small system installed om my utility shed with the following components:2 - 100 watt Renogy Panels, Renogy RoVER 20A MPPT Charge Controller, Renogy 700W Pure Sine Wave Inverter and 2 Renogy AMG 12 - 12v 100AH batteries.

Everything seems to work well but I am concerned that when I check the data on my controller the number of battery AH's on tap is always low (30-60 ah's) and when I put a load on the system unless I'm in really bright sunlight the system draws down from 100% capacity pretty quickly. Conversely when i take off the load the panels charge the system up pretty quickly.

Not being very well versed with electrical systems etc... should my available amp hours be much higher since I have two 100 ah batteries collecting the energy?

Any help to point me in the right direction to find out more information in lay mans terms would be much appreciated.

[SunEagle]

I would say your batteries are not able to charge back to 100% SOC because they are too weak.

With 200Ah battery system you need about 20 amps of charging. With 200 watts of panels you may get at most 16 amps which may not give the batteries what they need.

Also 2 12v batteries wired in parallel may not be charging or discharging equally so one is doing the most work and is getting weaker.

[davarney]

Thanks for the reply - is there a way to set up the batteries so that they are charging or discharging equally? I thought that this might be a problem but am unsure as to how it can be remedied if at all.

[SunEagle]

There is no positive way of charging/discharging batteries that are wired in parallel. Although by keeping all the wire lengths the same and using bigger wire size may help reduce the resistance and differences between each charging "path".

You can try to charge each 12v battery separately using a grid tie charger to see if you can get them back up to 100% SOC. That may get you a little bit of an extended life for your system. But wired in parallel has it's disadvantages of keeping them at the same charge level.

[littleharbor]

The charging and load connections need to be at opposite, diagonal corners of the battery pair to force both batteries to work relatively equally. The image on the right is what you're looking for.
batteries-series-vs-parallel.jpg