small off grid solar options

nik · September 2020

Hi folks,

so I'm looking at loading up a truck with some sort of kit and moving down to my little patch in Baja California Sur. Lots of sun, not a whole lot of cash. Sufficient setup would probably be about a 2.2kW by my estimations, but looks like I'll need to start with 1/4 of that, so my calculations are backwards and sideways and I'm trying to make sense of the variables, but looking at maybe

4 used Sunpower 230W panels in series (for total $300)
Epever 40A controller (Tracer 4215BN) ($215)
4 Weize SLA 100Ah 12v batteries in parallel pairs for 24v ($700)
and then it looks like the minimum viable 24v inverter would be a 2000W Aussy Giandel ($390)

How do those numbers and value priorities seem for starters?

then there's the cabling (10 AWG from panels, about a 20' run) with a 15A breaker / fuse to controller
batteries and inverter (2 AWG short runs) with a 200A fuse
and maybe a combiner box of some sort but not sure if absolutely necessary or not (given it's only me that I can blow up and there's no code requirements) but I would like to be practical / semi-sensible.
Looking at a possible "ECO LLC 4 string combiner box with lightning arrester - Max.connection PV array---4; Max input current per array---10A; Total input current---40A" for $135.

So that configuration would run me around $1800 all told.

What are my main flaws in thinking, where am I better spending the money?

Thanks for your thoughts!!!

mike95490 · October 2020

Why do you choose SLA over flooded ? I'd consider 4 golf cart batteries wired for 24V @200ah instead, and when you get things tuned enough so that they last 2 years, then swap to the SLA. I prefer to direct you to SLA 6v 200ah golf cart batteries, all in series. Putting SLA in parallel causes current hogging issues

For a 24V system, having PV being more than 2x battery voltage (4 in series is way over 50V I think) and you loose efficiency in the downconversion to 24v battery . If the PV requires a long cable run, or you are at the conduit stuff limit, then higher voltage is worth the tradeoff.

nik · October 2020

Hi mike. Thank you for your input. I chose SLA's perhaps partly out of naivety, but primarily for apparent cost effectiveness (400ah for $700) but I will have another look. (the link you posted did not resolve)

I'm also making assumptions about 24v vs 12v series/parallel based on initial research. It may be smarter to start smaller though and work with 2 batteries / 2 panels, 20A controller, 12v inverter, but don't want to limit myself too much if I can get better gear for $1500-2000 max.

Cable runs will be short so don't need higher voltage for that reason - just juggling efficiencies all round with preliminary knowledge.

If I get (4) 230W Sunpower panels rated at 48v - less a few volts as they are a few years old (pulled off of a commercial application, but appear to still have plenty life left) connected in parallel (I did not mean to state "series" initially) - then am I still heading in the right direction!?

Thanks again!

littleharbor2 · October 2020

nik said:

If I get (4) 230W Sunpower panels rated at 48v - less a few volts as they are a few years old (pulled off of a commercial application, but appear to still have plenty life left) connected in parallel (I did not mean to state "series" initially) - then am I still heading in the right direction!?

Thanks again!

What are the specs of the panels? I doubt they are "rated" at 48 volts. They are likely 72 cell (24 volt, nominal) panels with a voc. in the high 40 volt range and a vmp. in the high 30's, maybe 41.

mike95490 · October 2020

Somehow the forum made my text into a link. That was not intended.

> 4 Weize SLA 100Ah 12v batteries in parallel pairs for 24v ($700)

Wired 2S2P gives you a 200Ah 24V battery for your $700.
Batteries in series add their volts. Batteries in parallel add their amps

That's an extremely good price you list for the batteries, Most AGM are in the $300 ballpark. I figure the GC2 (generic Golf Cart flooded battery) runs about $100 and you can get 2-4 years from them GC2 batteries are 6V, 200ah (some are 195ah, some rated at 230ah) weight is the indicator of how much lead (capacity in ah) you are buying.

nik · October 2020

littleharbor2 said:

What are the specs of the panels? I doubt they are "rated" at 48 volts. They are likely 72 cell (24 volt, nominal) panels with a voc. in the high 40 volt range and a vmp. in the high 30's, maybe 41.

Yes, 72 cell:

Model: SUNPOWER SPR-230-WHT-U

Wattage: 230
Voltage: 48.7

Here's a pic of the equivalent 210W panel boiler plate. (Could get these instead as they are only $65 each!)

nik · October 2020

mike95490 said:

Wired 2S2P gives you a 200Ah 24V battery for your $700.
Batteries in series add their volts. Batteries in parallel add their amps

That's an extremely good price you list for the batteries, Most AGM are in the $300 ballpark. I figure the GC2 (generic Golf Cart flooded battery) runs about $100 and you can get 2-4 years from them GC2 batteries are 6V, 200ah (some are 195ah, some rated at 230ah) weight is the indicator of how much lead (capacity in ah) you are buying.

Thanks for clarifying

Not finding anything close in price for equivalent GC2s, but these are the SLAs in case curious

Still not entirely sure which way to go, the real issue being, once geared up for my location (driving from California down to Mexico), there will be limited options for new supplies for some time!

Photowhit · October 2020

nik said:

Not finding anything close in price for equivalent GC2s, but these are the SLAs in case curious

Not sure where you are looking, Sam's Club and Costco sell flooded lead acid 6 volt batteries around $90 + core charge (I think around $15 currently, they have been VERY lenient on what they accept as a core, I've used a tiny lawn tractor battery easy to ask around at lawnmower repair shops offer $5 for them, much more than they get for lead)

If you aren't a club member there are some options too buy without becoming a member, find a friend who uses them, buy gift certificate. Ask for a 1 day pass to check them out, sometimes comes with a premium 5-10%.

Image: https://us.v-cdn.net/6024911/uploads/editor/ed/5ptjldxcrm2q.jpg

These will be 6volt, 200-210 amphours. 4 in series would give you a 24 volt 200-210 ah battery bank.

I've heard they may not be as good as in the past, I have purchase Energizer labeled GC batteries at Sam's Club several times. Them last set for me lasted 5 years even though I tortured them over the summer running them down to <50% of capacity every evening running an air conditioner, the last 4 years of their life.

mike95490 · October 2020

He's talking about sealed AGM batteries, not the ultra common flooded.

Trukinbear · October 2020

Photowhit said:

nik said:

Not finding anything close in price for equivalent GC2s, but these are the SLAs in case curious

Not sure where you are looking, Sam's Club and Costco sell flooded lead acid 6 volt batteries around $90 + core charge (I think around $15 currently, they have been VERY lenient on what they accept as a core, I've used a tiny lawn tractor battery easy to ask around at lawnmower repair shops offer $5 for them, much more than they get for lead)

The Interstate GC2's at Costco are rated 1.8 out of 5 by people who bought them - most give it a 1, probably isn't a zero option.

I can't speak for batteries from Sam's Club - but I took all my 'deep cycle' batteries back to WalMart for refund as they were not deep cycle in any meaning of the words. Garbage.

Batteries are where you probably shouldn't try to cheap out - $850 worth of WalMart batteries didn't last 3 months trying to cycle them down to 60% every day. My Trojans were still ok when I replaced them at 2 years, and the guy that bought them is still happy with them 2 years later.

Photowhit · October 2020

Trukinbear said:
I can't speak for batteries from Sam's Club - but I took all my 'deep cycle' batteries back to WalMart for refund as they were not deep cycle in any meaning of the words. Garbage.

As far as I know, Walmart doesn't sell true 'deep cycle' batteries. Maybe some 'Marine' batteries which are rarely deepcycle.

Trukinbear said:
Batteries are where you probably shouldn't try to cheap out - $850 worth of WalMart batteries didn't last 3 months trying to cycle them down to 60% every day. My Trojans were still ok when I replaced them at 2 years, and the guy that bought them is still happy with them 2 years later.

Sounds like a lot of batteries in parallel, never a good situation. I've not used the Costco batteries, I understand Costco is very good on returns, but I don't have one near me. The Energizer labeled GC batteries from Sam's had a better rep than the Duracell as I recall, and the Duracell have a 4.5 stars out of 5.

As I stated above; I have purchase Energizer labeled GC batteries at Sam's Club several times. The last set for me lasted 5 years even though I tortured them over the summer running them down to <50% of capacity every evening running an air conditioner, the last 4 years of their life.

Photowhit · October 2020

mike95490 said:

He's talking about sealed AGM batteries, not the ultra common flooded.

He stated;

nik said:

Not finding anything close in price for equivalent GC2s,...

Trukinbear · October 2020

Photowhit said:

I've not used the Costco batteries, I understand Costco is very good on returns, but I don't have one near me. The Energizer labeled GC batteries from Sam's had a better rep than the Duracell as I recall, and the Duracell have a 4.5 stars out of 5.

As I stated above; I have purchase Energizer labeled GC batteries at Sam's Club several times. The last set for me lasted 5 years even though I tortured them over the summer running them down to <50% of capacity every evening running an air conditioner, the last 4 years of their life.

The WalMart batteries were bought out of expediency and desperation. You are correct that what they sell, despite the label is NOT deep cycle. I'm 80 miles from a Costco (and wasn't a member) and almost 200 miles from a Sams Club (and wasn't a member). The Trojans seemed to be a decent upgrade from the WalMart batteries, and I got them locally for not much more than that low rated battery I just saw listed at Costco. I had 32 of them in 4-12V banks (split with 2 per system) - I hated watering 96 cells, and all the interconnecting cabling and fasteners required maintenance also. Once I realized I wasn't just temporarily off the grid I ditched them for a real battery and ditched my hastily cobbled together system (twin systems). I'm glad you had great service from your GC batteries, but do note you are using a real battery now, vs a bank.

small off grid solar options

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