Newbie Question About Battery Draining Overnight

[zot123]

I just installed a small solar system on a barn to power a few led lights and 2 outlets, specs below. I'm still understanding what the different modes on my charge controller do but without fail, my battery will charge during the day and starting at dusk, it will start to drain. I'm assuming that's what the "float" does. I only use the lights at night and in the early morning for maybe 5 min at a time (10 min total in a day) so nothing is left on that would drain the battery. I don't live in the most sunny place so it's frustrating that the power I gain during the day drains at night and I'm often left with a very low battery on overcast days. What can I do to mitigate my battery from draining at night? I've tried messing with the battery settings on the charge controller, set it up to the recommended settings for the battery type with no luck. I assume cycling the battery's voltage helps with battery life but draining the battery until it is so low the low voltage the alarm goes off doesn't help.

Setup:
2 - 100w Renogy Panels
30amp Renogy MPPT Charge Controller
1 - 100ah Renogy AGM Battery 12v
1 - Renogy 700w Inverter

 

[cdsolar]

What is the idle draw of the inverter?

 

[cdsolar]

What is the idle draw of the inverter?

 

[chrisski]

This time of year your panels likely produce around 400 watt hours. If its cloudy, less. Your battery has 1200 watt hours. At least 200 watt hours gets drained by the isle draw of the inverter, so probably half your daily production.

You can get more panels and if the battery charges fully every day, then you don’t need more batteries. If your batteries don’t charge fully every day, need more panels. You can charge the battery at what the spec sheet says, likely 50 amps. If you can limit charging of the charge controller to 50 amps, you can get more panels on it to avoid overcharging the battery.

In my signature block there’s a link to a solar calculator that will tell you how much energy your panels will produce based off location and time of year.

 

[Ronwattson]

200w PV is probably giving you 600w per day. Your scc will consume over night power and inverter as well if you leave it on. I would add at least 200w more in PV if not 400 if your solar peak hours are that low. The rule of thumb that I use personally is if my system functions as it should on good solar days and doesn't on several poor solar days add battery capacity. If it won't perform properly on good solar days add PV.

 

[Ronwattson]

This wine of year your panels likely produce around 400 watt hours. Your battery has 1200 watt hours. At least 200 watt hours gets drained by the isle draw of the inverter, so probably half your daily production.

You can get more panels and if the battery charges fully every day, then you don’t need more batteries. If your batteries don’t charge fully every day, need more panels. You can charge the battery at what the spec sheet says, likely 50 amps. If you can limit charging of the charge controller to 50 amps, you can get more panels on it to avoid overcharging the battery.

Well said and I didn't see you comment until I made mine. Spot on.

 

[Q-Dog]

Turn off the inverter when you are not using it.

 

[OzSolar]

Has anyone mentioned that the inverter's idle draw could actually be exceeding what the solar is producing?

Seriously though... NONE of the many "size your system" spreadsheets, tutorials etc. ever bother to mention that idle/tare losses are really going to add up and in many cases can exceed 1 kWh per day. In most off grid set ups that's probably 5X's more than all the lighting combined.

 

[zot123]

Thanks guys! Didn't know inverters have idle draw. I actually did start turning off the inverter everyday and only turned it on when needed, but of course it's been sunny so I haven't noticed a huge difference. I'll look into that calculator @chrisski! Sounds like I'll be adding a few more panels haha I guess building a solar system in the winter is a fast track to finding the weak points haha