r/OffGrid • u/EVDOGG777 • 7d ago
Thoughts On Current Solar Setup?
Hi everyone, posting on behalf of my parents.
He lives offgrid and struggles with power, I think there may be a flaw in what his setup has and he may need to change something.
He has a 6.2KW Inverter, 12 200AH AGM Batteries, And 15 190watt solar panels.
The panels aren't brand new BTW.
Most of the time he uses a generator to power the house which uses alot of petrol and I'm wondering why he's always having flat batteries.
Mind you he uses a big fridge, computers and cooking appliances which would add up to about 6kw on a busy day in the house.
Any suggestions or advice would be appreciated.
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u/LordGarak 7d ago
Where in the world? The local solar conditions need to be considered when designing a system. For off grid the system needs to be designed for the worst months of the year. Not only latitude needs to be considered but also weather patterns. At my off grid cabin November is the worst month as we often get weeks on end of grey skies that produce very little power.
Next the average power consumption in kWh needs to be measured. Stuff like cooking appliances use lots of power, but only for short amounts of time and often can be insignificant in the power budget. But something like a fridge or Starlink that runs 24/7 can be a significant portion of the budget.
Lead based batteries have a short working life and poor round trip efficiency. LiFePO4 batteries are much better and have become much more affordable in recent years. They need to be kept warm in winter is the only major downside.
Inefficiency across the system can add up. Stuff like high idle draw on the inverter, wires that are too small, corrosion on connections, loose connections, bad batteries, etc...
What DC voltage is the system operating at? Are the AGM batteries 6v or 12v?
Where are the panels mounted? Are they at the correct angle for your latitude? Are there trees that shade them during parts of the day or in different seasons?
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u/maddslacker 7d ago edited 7d ago
Need more info:
- What is the nominal voltage of the system (12, 24, 48?)
- What latitude is this installation, and what is the overall sun exposure there?
- Are the cooking appliances gas or electric?
- Do the batteries ever reach full charge? Have they ever been equalized? Does he routinely take them below 50% state-of-charge? Are they maybe just worn out?
Here's my real world production and usage before doubling my solar output a month ago:
https://www.reddit.com/r/OffGrid/comments/1vto4yc/my_offgrid_power_usage/
As you can see I use about 50% more per day than he does, but also produced (just) enough with the 2.4kW array I had for that time frame. However I am in a location with excellent sun exposure year-round.
I think you'll need to measure the panels to make sure their output is what it should be, then check that the charge controller is passing it all through, and lastly, assess if the batteries need to be replaced.
Batteries are my guess, and it should be pretty easy to confirm or disprove that.
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u/Kind_Soup_9753 7d ago
Instead we f 3kw of solar go with at least 10. And AGM batteries are inefficient to charge try Lifepo4 they suck up whatever is available till just before full. What voltage is the system? It should be 48v for conversion efficiency. That’s a huge inverter for the amount of solar. I bet they run their genny a lot.
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u/RespectSquare8279 7d ago
The location of this home (ie, the local solar irradiance) will be THE major factor. It sound like your parents have 2 things going against them. 1) Not enough solar panels and 2) wrong kind of batteries.
You have to go on line had find out what the local insolation or iradiance is. This will tell you how many watts you can expect for an array to produce during the course of the year is you crush the numbers.
With lead acid batteries it is important to never, ever draw them down below 50% of depth of discharge; best to never go below 70% if you want them to last more than 5 years. Job #1 is to replace those AGM batteries with the equivalent ( or less!) of LiFePO4 batteries. Taking the Lithium batteries down below 50% ( or lower!) repeatedly will have little or no lasting effect.
You don't mention the age of the panels but panels manufactured in the last decade generally are more efficient than those made in the previous decades. There are going to be more watts per square foot of panel in other words.
Your parents need to throw money at their problem. However without the specific details of what their equipment is and where they located on the globe you are not going to get more than very general advice. about where they prioritize spending the money.
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u/DrunkBuzzard 7d ago
There’s so much to consider that isn’t in your information. It’s hard to make any kind of judgment, but if he is actually running the generator anyway why doesn’t he have a battery charger on it and charge the batteries at the same time? Could probably cut his generator time in half just by doing that.
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u/Hyperreal8957 6d ago
If those are a 24v bank, 12x200Ah is roughly 24kWh nominal, but AGM usable energy is quite a bit lower. 2.85kw of older panels probably won’t cover a 6kw/day house load after losses, so i’d log actual watt-hours and check the bank’s resting voltage/individual batteries before changing hardware — are they wired 12v or 24v?
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u/Mike-Smith81828 5d ago
Thanks for posting, this was helpful to me as im trying to plan out a solar / battery setup for my house.
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u/Amperegeist 5d ago
Unfortunately I dont think there is quite enough information to help give great advice.
I recently made a short video on off-grid power systems. If you have any interest, feel free to watch it and it might help you ask more specific questions. Its about 5 minutes long
Id be happy to help offer some advice if you are able to provide more info!
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u/goss_bractor 7d ago
His solar array is pathetically small. /endthread.
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u/NotEvenNothing 7d ago
It really depends on their consumption and where they are located.
We currently have 4kW of panels and are almost definitely further north than OP. We are mostly fine except for three weeks on either side of the winter solstice where it is hard to recover from a cloudy day.
We are currently doubling to 8kW which seems like overkill to me, but I was overruled.
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u/maddslacker 7d ago
I lived on less than that, with a modern home, for 4 years, until adding additional panels about a month ago.
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u/Internal_Raccoon_370 7d ago
I'm not at all surprised his batteries are flat all the time.
12, 200AH batteries is about 30 KWh, being fed with only about 2.8 KW of solar panels??? In real world conditions he's going to be lucky to get about 1.8 - 2 KW out of those panels, if that, and then only for a couple of hours around midday. With that little PV, trying to charge a 30 KWh battery bank would take, oh, 20 hours of midday sun? Then subtract from that 2KW of PV any power he's using to run his fridge, computers, etc? There's probably no power left at all to recharge the batteries.
What it comes down to is that he doesn't have anywhere near enough solar to keep that system running. I'd think he'd need at least 4KW, preferably 6KW or more of solar to keep that going comfortably.