Hi, need some advice and guidance - I have recently installed a second 100w solar panel (in parallel to another 100w one) due to low light conditions, to my 75/10 mppt controller. Whilst generating more solar power, the load consumption (3w led light on for 12 hours) has increased from 40w to 60w with no other changes. Any ideas what has generated this additional load consumption? Many thanks.
Please provide more details - about the solar panels and the system.
In general, if you add a second, identical solar module to the input of an mppt, then as long as the input voltage is not exceeded, the performance will be better if the modules are in series. (assuming the same orientation)
Hi, my set up is as follows :- 2 off 100w solar panels connected in parallel, feeding into a 75/10 mppt controller, which in turn feeds a 12.8v LifePO4 18ah battery, and a load consisting of a single 12v 3w led bulb which is switched on via a timer for 12 hours over night. In my original post, I should have said that the consumption (as detailed by the app) has increased rather than the load. I am on a steep learning curve so trying to understand the system.
OK, so typically a 100W solar module has an open circuit voltage of ~20V and a peak power voltage of about 17.5V. Assuming both panels are mounted in the same plane, you will definitely be better off with them wired in series.
If the App is showing that your Wh from solar has gone up, that is probably to be expected - as you are charging the battery for longer. Typically once the battery gets to full charge, this will come back down to the Wh that you consume, plus a small amount to cover the battery charge / discharge efficiency - typically about 95% for lithium. plus of course the self / nighttime consumption of the MPPT. so this should come to about 38Wh, plus the night time consumption of the MPPT. Some additional power is also dissipated in battery cell balancing, this usually takes place at higher battery voltages, when the cells are near full charge.
Thanks Mike, I think that explains what I’m seeing (new to this solar topic) - my panels are in different planes, one to catch the morning sun and the other for the afternoon/late sun, so I guess parallel is probably best for this config (if I understand your explanation correctly).
If your panels are in different planes, then you should have different MPPT’s for best results.
Problem with the single small panel (<200W) is that the Voc is sometimes so low, the MPPT won’t start with a well charged battery. The Mppt needs 5V above the current battery voltage to start, so if your Battery is at 13.5V, this means the panel needs to get to 18.5V to start the mppt. Some small panels struggle to do this in poor light (<500W/m^2) and hence don’t charge the battery. This looses potential charging time.
Thanks for the feedback, it’s really helpful - I can now see why it maybe struggling to charge in low light conditions, and I’ll have a look to see if I can swap to a same plane panel configuration and series connection - I guess this will help with the 5v above situation as series will produce a higher voltage - thanks for the help, much appreciated.