Newbie needs help please!

One possibility is that your charge controller settings might need adjustment, particularly in terms of voltage thresholds for charging and discharging. Additionally, double-check the wiring to ensure there are no losses or inefficiencies there. It's also worth considering factors like temperature, as extreme cold can affect battery performance.

Thanks Mason. Useful advice. I’ll check the charge controller settings. I’m not quite sure what I would be looking for in terms of losses or inefficiencies in the wiring? Does that mean for instance cables that can carry either too little or too much current than I need? I don’t think temperature is the problem as it’s now Spring here in the UK and getting a bit warmer. Chas

A few things to consider.

Did you measure the actual current draw of the lights, timer ect when running or is your 36w from specifications.

I have a couple of 12V lithium systems. Budget on getting about 80% of the Ah capacity. They drop of very quickly at the end and will cut out on low voltage.

Your example started at 91% Soc, so you were already down.

You will not get 12hrs of full charge from your panel. If you chase the sun with it you will get more. Watch what it is doing during the day and you will be surprised how little you are getting.

IMO a singe 100watt panel will not provide the amount of current a 60ah battery system needs to get back to 100%. Also be aware that the lights may use more then 36 watts and that your battery system may not really provide the calculated power for 12 hours.

First off I would get more panel wattage to charge the battery system. Also anytime a battery system has parallel wired batteries one of them may not get fully charged back to 100% SOC. Better to have 2 6volt batteries wired in series to provide a 12volt system.

Many thanks both for your helpful comments. The 36 watts consumption of my grow lights comes from the suppliers specification so it could easily be wrong. I tried to check this by measuring the amperage between the load output of the charge controller and the lights but the result calculated out at only about half of the quoted 36W so that wasn't helpful! I charged the batteries from the 240V mains supply during yesterday and both the charger and charge controller finished at about 13.7V which I assumed to be full capacity. I left the lights on at full load overnight and duly got my target 12 hours of lighting. So it's clear that my 100W panel just isn't powerful enough, especially if the weather isn't sunny which is mostly the case here. I didn't realise that with two batteries in poarallel one might not get a full charge. Using two 6V batteries in series seems like a better answer and something to think about for the future. Meanwhile I'm now convinced that I need to swap out my 100W panel for a 200W. Thanks again for your really useful advice. Chas.

This is what a 100 watt panel will produce year round using a 720 Wh battery year round in england for 32 watt LED strips running 24 hours (768 Wh load), with panels sloped at 45 °. This site does adjust not only for lenght of sunshine, but for weather which explains the abysmal results. Recommend you put your own numbers in.

eNGLAND sOLAR.jpg This shows not a single day has enough power.

Even changing the numbers to thousands of watts of panels, not enough power.

You may not run the LEDs 24 hours, so that may bring the daily power requirement down. I reccomend using the longest run day as the time for the LEDs, normally the shortest day of the year or the closest to the winter solsitce you have these lights on.

The Data from this sight is fairly accurate in my section of the sunny SW of USA.

Thanks chrisski. I'd completely forgotten about using the PVGIS dataset to model the viability of my system. I've now done so and you're quite correct, a 100W panel will give me nowhere enough power. But it also tells me that if I run the load at only 75% capacity for 10 hours a day in the months of April through September (which would cover the UK growing season), I could probably just about manage with a 200W panel. So, again, I now feel sure I need a 200W panel. Thanks for your help. Chas