New shed setup, sanity check

[trupper]

Decided to go solar for my 120 sq ft shed/office. Power will be used for lights mostly, will probably add through the wall AC next summer.
Was reading and watching for 2 weeks and I get more overwhelmed as I get familiar with components. I need to get some input before getting my order in. I welcome positive and negative feedback as well as suggestions to upgrade/downgrade. Also, would appreciate suggestions on awg wire I need and fuse amps.

 

[SkippyJonJones]

Funny, I was considering the same thing for my 12X10 shed. Mine is strictly storage but does not currently have any power. If yours is also just storage, I would think is is overkill (does that exist?). I guess that really matters if you are on a budget. I plan to use 4 100W panels to my two AGM 225Ah batteries in my RV. Then update the batteries to LFO. But...you did mention office, so maybe that power is required for office equipment.

Have you considered a 24v battery with a 24v pure sine wave inverter? I'm learning up on this approach now.

 

[MisterSandals]

Was reading and watching for 2 weeks and I get more overwhelmed as I get familiar with components. I need to get some input before getting my order in.

There is another thread with those panels and SCC. There was an efficiency curve that showed that lower voltage array (closer to 20V, which would be all parallel) was slightly more efficient.
Someone with actual experience said that they got the best results with the panels in 2S2P configuration.

Its a good read.

Adding 2 more panel, 400 watts total, 100 amp hr battery

Hi, I have this system, 12v 100 amp hr Renogy Smart Li batt with self heating Renogy 40 amp MPPT Li charge controller Renogy 1000w Pure sign wave inverter 2 x 100 watts NOMA solar panels The 2 panels are connected in parallel (want more amps, with voltage the same) I can get 2 more of the...

diysolarforum.com

 

[ghostwriter66]

Is there a reason you are going with 4 x 100 instead of like (1) 355 or something like that .... more panels - more issues sometimes ...

I'm a strong believer that if you can get 24V out of 2 batteries or 48V out of 4 -- then do that .... If this was for an RV I would understand (somewhat) why you want to keep everything 12V but for a homeshed -- i would be hitting 24 or 48 ... just more options out thee .. smaller ones ... etc

I would definitely ground the inverter -- but - do some research and see if there is actually a need to ground such a small current of panels .... won't hurt but from where I sit if the building and the inverter is grounded then you should be good -- but thats just me ... if you take a lightening strike no measure of grounding is going to save a shed ....

 

[trupper]

There is no reason for anything, I didn't realize 24/48 is better than 12. Is it also more expensive?
What about battery? Is it a good idea to have 2 in series here? Is 250ah reasonable with other equipment?

 

[trupper]

Funny, I was considering the same thing for my 12X10 shed. Mine is strictly storage but does not currently have any power. If yours is also just storage, I would think is is overkill (does that exist?). I guess that really matters if you are on a budget. I plan to use 4 100W panels to my two AGM 225Ah batteries in my RV. Then update the batteries to LFO. But...you did mention office, so maybe that power is required for office equipment.

Have you considered a 24v battery with a 24v pure sine wave inverter? I'm learning up on this approach now.

Mine was never a storage, always had power running from the main house. Of course it's an overkill for just lights, but I might add AC and heat, so I want to be prepared for that. I need to read up on 12 vs 24 vs 48, don't know anything on benefits vs price.

 

[MisterSandals]

I need to read up on 12 vs 24 vs 48, don't know anything on benefits vs price.

The best way to approach it (so i think right now) is to look at the number of watts you expect to be using at any one time. If you're looking at 2000W, you can get by with 12V as its just (2000W / 12.8V = 156A). So wiring, fusing and BMS to support over 156A (probably closer to 200A).
If 3000W, this is really pushing it for 12V. So 3000W for 24V is (3000W / 25.6V = 125A) which is manageable.

So figure out your expected loads and what different battery voltage and amperage scenarios look like.

If you figure out your usage numbers thru an energy audit, its fairly easy to run the numbers for you.

 

[trupper]

The best way to approach it (so i think right now) is to look at the number of watts you expect to be using at any one time. If you're looking at 2000W, you can get by with 12V as its just (2000W / 12.8V = 156A). So wiring, fusing and BMS to support over 156A (probably closer to 200A).
If 3000W, this is really pushing it for 12V. So 3000W for 24V is (3000W / 25.6V = 125A) which is manageable.

So figure out your expected loads and what different battery voltage and amperage scenarios look like.

If you figure out your usage numbers thru an energy audit, its fairly easy to run the numbers for you.

Ah thanks! Perfect explanation that even I can understand.
I don't think I will ever have that much load in that small space. AC would be the only thing and it will only be used a few hours a day in the summer.
What about pricing? All thing being equal per watt/amp/etc. Would 12v system be cheaper?

 

[MisterSandals]

What about pricing? All thing being equal per watt/amp/etc. Would 12v system be cheaper?

In general, i think a 12V system will be cheaper and have more common equipment than a 24V system.
But a big 12V system is probably more expensive than a small 24V system...

If you have some numbers that would help: array size, battery size, max loads, max AC loads...

If you have a quality/price point (high, middle, low), that would help everybody offer up meaningful recommendations.

 

[trupper]

I'll think out loud... I try to always go for the "best bang for the buck", somewhere in the middle of price/quality, but won't settle for mediocre, even if it means paying more.
This is my first try and I want to do it right, but I have no immediate need for it. I have shore power running to the shed, it's on the 20 amp subpanel and it's sufficient to power up a couple of LED lights inside and a security light outside, plus some random chargers. I wouldn't want to hook up an AC to it, so this is how the solar idea came to life.
Just started to read up on 24v system and I'm liking it.
In terms of battery, I was thinking 4 of Trojan SPRE 06 255AH connected in series. I would love to hear CONS on this approach, I'm in love with these batteries for no apparent reason.
Max loads is kinda difficult to estimate since I haven't done my due diligence on researching cooling/heating systems. I wanted a mini split, but that might be too much money for something that is not used a lot.
As far as panels, 4x100 was always assumed, but now I question myself and thinking of maybe a single panel of 300+watts? Man, it's getting too overwhelming ?

 

[MisterSandals]

As far as panels, 4x100 was always assumed, but now I question myself and thinking of maybe a single panel of 300+watts?

No sense messing with tiny 100W panels. Look on craigslist in your area for big cheap panels. Or reveal your city/zip code and maybe someone will chime in with some deals.

Its pretty easy in most places to get big cheap panels for $.50/watt or less.

And mounting and wiring a couple big panels is a lot less work than a bunch of tiny ones.

 

[trupper]

I'm in Southern California, there are many many options here.
I was looking at 2 of these just now: https://a1solarstore.com/q-cell-qpeak-duo-blk-g5-315w-mono-solar-panel.html
These guys are right by me and have some cheap panels, but I don't know about their quality/reliability.

 

[MisterSandals]

Here are some 295W for $75

295 WATT SUNTECH SOLAR PANELS USED - general for sale - by dealer

WE DO NOT SHIP, BUYERS PICK UP ONLY, WE WILL ASSIST IN LOADING. Pick up address: 109 N. OLIVE AVE., SANTA PAULA, CA 93060 Loading hours: Monday-Friday 8am-4pm Any questions call: ***WE HAVE (1200...

losangeles.craigslist.org

right in southern california!
there are hundreds of options on craigslist down there.

 

[trupper]

Are used panels safe to buy? How do you check them?

 

[MisterSandals]

Are used panels safe to buy? How do you check them?

Its pretty easy if the sun is up. A volt meter will show you Voc and the Isc amps in just a few seconds.

If the price is comparable, i'd choose new for sure but i'd have no problem with big cheap panels that tested well.

 

[trupper]

Scrapped the whole thing from the OP

Liking it more, but still need help doublechecking wire gauges and fuses. Also, not sure about 4 golf batteries in series.

 

[MisterSandals]

but still need help doublechecking wire gauges and fuses.

More info needed. You need amps, volts and wire length.
At the end, double check the wire ampacity.

Here is a link to the voltage drop calculator to check wire sizing. Shoot for less than 3% voltage drop.
If its not clear how to use it, please ask, this is a very popular tool.

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

 

[MisterSandals]

Also, not sure about 4 golf batteries in series.

This is a solid solution and folks have great luck with Trojan.

Did you see all the new old stock AGM/solar batteries for cheap around LA on craigslist?
I don't know what the price is for the Trojans but i know they are spendy (a good investment!)

 

[trupper]

This is a solid solution and folks have great luck with Trojan.

Did you see all the new old stock AGM/solar batteries for cheap around LA on craigslist?
I don't know what the price is for the Trojans but i know they are spendy (a good investment!)

Yes, I have found some AGM on craigslist, they are NOS from 2019. They are only a little cheaper to get same ah. Know anything about this brand?

Solar Batteries AGM 105 Amp Hr New 33 Available - electronics - by...

Batteries are Brand New and Never Installed, Manufacture Date of 5/ 2019. They Have Been Charged and Maintained. These Will Not Last Long. These are Not Made in China These are Made in Mexico and...

losangeles.craigslist.org

 

[trupper]

This is a solid solution and folks have great luck with Trojan.

Did you see all the new old stock AGM/solar batteries for cheap around LA on craigslist?
I don't know what the price is for the Trojans but i know they are spendy (a good investment!)

I'd appreciate a little help with this calculator, I don't know what those input parameters mean except size and distance.