Newbie troubleshooting

[michael_dem]

Current setup: 4 Renogy 100W 12V panels, Renogy Voyager 20A PWM controller, 3 deep-cycle marine batteries 12V, 2 at 100Ah and 1 at 75Ah, Cantonape 1000W inverter, and the only load is a greenhouse roof blower of approximately 1A. All wiring after controller is 12GA.

I know the controller is not sufficient with full panel output, but in the winter I'm getting well less than 20A, and plan to replace it with an MPPT controller before summer.

My problem is battery life. Several times with just 2 panels and 2 batteries the batteries were depleted below threshhold voltage and the inverter shut down. I added 2 more panels, and then another battery. There should be 275Ah available with full charge, but I'm consistently getting 40-70Ah showing on the controller. The whole setup seems to me like overkill, but it still shuts down after 2 days of overcast.

What am I doing wrong? This is the first time I've used solar. The greenhouse is a good distance from the house, and we were hoping to keep it off-grid and use the solar for the blower and maybe an LED light when it's dark and a USB charger for a speaker or phone. I've screwed up somewhere, but I can't figure out where.

[SunEagle]

I see a few issues.

First you have 3 batteries wired in parallel and are not all the exact same type. Parallel wiring tends to cause uneven charging and discharging. When you add the variable of all 3 batteries not being the same you induce much different resistance paths which also causes uneven current paths.

Next with a 275Ah battery system you really need at 27 amps of charging. With that PWM type CC you are not getting even 25 amps of charging. It should get better with an MPPT type CC but will still be marginal for a 275Ah battery system.

Next, I believe you are discharging the batteries more than 50%. Going that low every day will kill off the batteries quicker as well as make it harder to get them back to 100% SOC with insufficiant charging amps each day.

I really think you first need to determine your daily watt hour requirements and THEN size your battery system using high AH low voltage cells all wired in series. Once you determine your watt hour usage and battery AH rating you can then size your panel wattage for worse case (Winter) days of sunlight. Maybe then you will get more out of your system.

And finally I understand your desire to keep the greenhouse off grid but once you have determined the size of your system to keep your loads happy you might want to think about running a power line from the house to your green house. It will be cheaper in the long run.

[michael_dem]

So with 2 panels and 2 equal batteries I should still expect to run out of juice after 2 days of overcast? Why are the batteries not charging up with full sun in October in Indiana?

[littleharbor]

Is your inverter on 24/7? Many inverters draw more power while sitting there doing nothing than the intermittent loads on them. Do you need a 1000 watt inverter for a 1 amp load? Phone charging and led lighting can be done via DC, avoiding the inverter. So a smaller inverter and only running when you need it should help your situation. Oh and remove the 75 ah battery.

[SunEagle]

So with 2 panels and 2 equal batteries I should still expect to run out of juice after 2 days of overcast? Why are the batteries not charging up with full sun in October in Indiana?

With 2 x 100Ah batteries you can safely generate about 600watt hours a day (200ah x 12v x 25% = 600 wh). If you are using more than that you will never be able to charge the batteries back up to 100%. The next day they will be even lower until you end up discharging them so when the systems shuts down you now have a bad set of batteries the can't be charged back to 100%.

Besides 200 watts of panels generate maybe 10amp and you have a 200Ah system. That calculates out to a C/20 charge rate which is way too little to keep the batteries happy every day.

Again. You first have to determine the number of watt hours you NEED for every day and then build a battery system that is 5 times what you need. That provides you a couple of days without sunlight and you may still have some power left

[michael_dem]

Lots of good info, thank you all... I'm buying a meter this weekend to measure exactly what the blower is drawing... and it does run 24/7 to keep the layers of roof plastic inflated as a thermal barrier. I also am now using 400W of panel. And I wondered about that 75Ah battery, I'll remove it. If the other 2 are still good I should get about 4 days out of a full charge. They're probably not optimal anymore though. Is there an advantage to using pairs of 6V instead of Marine 12V? The 6's seem to be more expensive.

[SunEagle]

Lots of good info, thank you all... I'm buying a meter this weekend to measure exactly what the blower is drawing... and it does run 24/7 to keep the layers of roof plastic inflated as a thermal barrier. I also am now using 400W of panel. And I wondered about that 75Ah battery, I'll remove it. If the other 2 are still good I should get about 4 days out of a full charge. They're probably not optimal anymore though. Is there an advantage to using pairs of 6V instead of Marine 12V? The 6's seem to be more expensive.

Yes the 6V would be better. But using 4 x 6V to create a 12V system is not as good as using 2 x 12V batteries. Although you will find 6V at higher Ah ratings then you can find 12V. Also the 12V are also a lot heavier.

Using lower voltage batteries (2V, 4V, & 6V) allows you to build a system with a high Ah rating with the batteries all wired in series.