Newbie needs help please!

[Chasba]

Hi, I'm a solar power newbie and I'm trying to set up a small system to power grow lamps in my greenhouse. At the moment I am unable to get the grow lamps to run for more than a few hours overnight, whereas I need them to run for about 12 hours. Clearly there is not enough charge in the batteries but I can’t see why this should be. Can anyone help me please?

The system is powered by two new 12V 30Ah LifePO4 batteries connected in parallel, charged by a Renogy 100W 12V solar panel, both connected to an Easun MPPT 6048 60 amp solar charge controller. The load, which is connected to the charge controller, is a set of 4 LED grow lamps strips consuming in total 36W at 12V, and has an in-line switch for on/off, timer (3,6,12Hr), dimmer and on/off for each individual grow lamp strip.

According to my limited knowledge, the batteries at full capacity should provide a total of 720W (60 Ah @ ~12V). This should be ample to run all 4 grow lamp strips for 12 hours. The PV panel is rated at 100W/12V though in fact runs at around 20V. Even at half power at this time of year it should generate around 50W, or 30A over a 12 hour daylight period, providing enough electricity for 10 hours at 36W.

If I switch on the grow lamps at nightfall, even running only two of the four grow lamp strips and after the batteries have been charging all day from the PV panel with no load, the grow lamps switch on correctly. At that point the charge controller says that the batteries voltage is 13.1V and the State of Charge 91%. Sometime during the night the lamps go out but I don’t know when as I’m not prepared to stay up watching them! In the morning the charge controller shows a voltage of 11.1V, current 0.1A and SoC of only 15%. I know that SoC readings on charge controllers are notoriously inaccurate and that the battery manufacturer indicates that at 13.1% the SoC is likely to be very low.

So clearly my batteries are not providing enough power to the load for long enough. They are brand new, good quality batteries as is the PV panel. By my calculations there should be enough capacity in the system to run the grow lights for 12 hours and recharge the batteries during the day.
Can anyone please give me a clue about what I might be doing wrong or what may be causing this issue? I really don't want my first DIY solar project to be a failure Many thanks. Chas.

[Mason Parsons]

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.

[Chasba]

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

[Bala]

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.

[SunEagle]

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.

[Chasba]

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.

[chrisski]

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.

[Chasba]

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