Help me start moving toward off-grid - Solar Edition

I'm starting two different threads in parallel because, while these are for the same project, the disciplines are different. 
 

I work from home, and just moved from Michigan to Florida. As soon as the Boost family started to look at houses here, we discovered that almost every house has a small shed. I wanted to use the shed as my WFH office. The house we purchased has an 8X12 shed, this will be my office. Currently is isn't insulated or powered, but it is wired internally for 120V power. I want to set this up off-grid, and I got the go-ahead from my wife. 
I just watched THIS VIDEO, and the price seems very doable, probably not a heck of a lot more than running power to the shed. Almost a no-brainer. But since I have no brain, I wanted to pick yours. Can you help me design a system?
The house is in SW Florida, so very sunny almost all the time. 
The electrical loads:

HP laptop computer - looks like a max of 90W power consumption.
3 monitors - figure 40 watts each to be safe (I suspect 30 is closer)
MAYBE my 3D printer - 160W
2 LED lights - 30W total (I plan on installing a few solar tubes so these lights will likely never be on)

Looks like a max of 400 watts per hour, but that's a worst-case. The laptop draws much less 90% of the time, while the printer will draw up to 400 watts for 5 minutes while the nozzle and bed heat up. 

I'd appreciate any input.

I'd spend some time sealing and bug-ridding the shed.  Up north we have the luxury that all the bugs die every winter.  Down there, the bugs are generations old!  

Aircon or just a fan ?

cold drinks ?

In reply to californiamilleghia :

AirCon for sure. 

Before I begin posting youtube links to content, you need to check Flaw-rida's laws in your area about solar. Some areas have the most restrictive laws in the nation, to the point where I don't even think you can have rooftop solar AND be on grid, anywhere.

Jehu Garcia - Most notable for making power walls like the one you want out of Ewaste. Very DIY, has his own website and tinkers quite a bit. Has built several homemade EV conversions.

Will Prowse - Does similar but with more of an off-grid focus on easily bought amazon stuff. Very down to earth. Tons of amazon product reviews.

David Poz - Nice mix between the two. Very OEM focused.

Interesting build for sure. I guess the first thing to do is figure out the maximum amount of power you expect to use in a 24h period, then run through some solar calculators and see what efficiency looks like in your neck of the woods so you can spec out your array. Figure you'll need enough battery for at least 24h of operation then add some fudge factor so you don't run dry. Take ineffeciencies into account as well, of course.

The monitor draw is probably directly related to what it's displaying - big bright whites vs "dark mode" text. I don't know this for sure, but that's what my LED arrays are like :) You can probably get a pretty good idea of draw by hooking up a Kill-A-Watt and run some sort of massive performance test on the laptop as well as setting the screens to maximum brightness.

Build a white aluminum "heat shield" a couple feet above your shed. It'll put your shed in the shade and take radiation out of the equation. Use sketchup to model the sun angles at your location and figure out how to shape the heat shield. 
 

Edit: also a good place to mount panels without drilling holes in your roof. 

Air conditioner will be your big load and require a decent size inverter to run, maybe a smaller unit from an RV that could run direct off of your DC battery bank is the way to go there to keep some costs down.

OHSCrifle is right about building a heat shield to shade the shed from the sun, if you can mount your panels with a decent sized air gap between them and your roof it will significantly help you keep things cool during the day, if you want to do some reading on that here you go - University of California San Diego Study. Otherwise doing a good job on your insulation will pay off by decreasing your load over the day and therefore helping you save on your setup (smaller battery bank, mppt, array, inverter if the A/C runs on AC). 

If there is already 120V in the shed keep it there as your back-up or to make sure you don't run out of juice in the middle of a print.

EDIT: now I see your other HVAC thread, sorry!

In reply to adam525i :

Or use the panels themselves as the sun shield, depending on if you're roof is in a good place for them.

Okay, stop me if I get man-splain-y. I jumped the gun on the system on my bus and have overengineered the version 2.0 that will go on it someday.

You have your wattages, that's a great start. Next you need to convert to amperage required for each. Watts = volts x amps. Assume all of those are 120v loads, so divide your wattages by 120 to get amperage draw for each. Then, as Keith suggested, estimate how many hours you expect to use each item in an average or slightly above average day (to be safe). Multiply your amperage by the time in hours to get the amp-hours needed for each load.

Based on that figure, we can start to decide how big the battery bank and inverter need to be to support the demand, and then (based on the aforementioned efficiency estimates in your geographical area) we can figure how many solar panels you need.

For example:

If you're thinking 400w (sans printer), you're asking for about 3.4 amp-hours at 120v for one hour of operating all that stuff. 

You *could* wire up a 120v battery bank (ten 12v batteries in series), if they were 1000ah batteries you'd have enough juice to run those loads for about 200 hours before they were down to the ideal discharge limit. That's a lot of batteries and more amp-hours than you really need.

More realistically, you'd run a 12v battery bank (say, four 12v batteries in parallel, giving you 4000ah) with an inverter. Because you're asking a 12v bank to provide 120v power, the inverter will need about 10 times the amperage input (12v) as it sends to the loads (120v). Running your 400w of loads would take about 8 hours to run the batteries down to the discharge limit. 

Then you just need to figure how much power you need to get from the sun to stay ahead of your usage. Panels are rated in watts, but output voltages and amperages vary depending on how intense the sunlight is and what angle it strikes the panel at. On top of that, the panels will need to run through a charge controller to reduce the voltage and/or amperage to a manageable level for charging the batteries, further restricting the efficiency of the system.

Doing all your math and speccing components (batteries, inverters, charge controllers, solar panels) to suit each other and your needs will help you end up with a better result. I wish I'd understood it better before I bought components that I thought made sense together.

That was super long-winded, sorry. Let me know if you have questions.

To be confident on your power, get a power meter, and plug all of those into a strip that you can connect to the meter.  Then track it over time to be exact- so you can get peak and average draw so that you can fully design the system.  Kill-A-Watt can be bought for less than $50, so that you get a better feel.

None of the original list have any surge issues, but the A/C unit surely will.  So the inverter needs to have X rating and normally 2X surge.  

BTW, there are some good sales going on for LiFePO4 batteries- relatively speaking, of course.  They will be more complex storage builds, but Will has some good videos on how to put a simple 24V system together with BMS.  Two packs of these https://batteryhookup.com/products/4-pack-etc-3-2v-176ah-563-2wh-lifepo4 will give you 4.2kW-hr of power.

In reply to alfadriver :

LiFePO4- Lithium Iron Phosphate- are always better than lead-acid in my opinion. To compare:

• Lead Acids for deep storage might last up to 5 years. Iron Phosphates can last twice that.
• Lead Acids cannot be discharged below 50% for more than 2 hours without damaging themselves. Iron Phosphates regularly can be 90-10% discharge range and still have over 2,500 cycles.
• Iron Phosphates can store more than twice the energy, reducing space.
• Iron Phosphates have internal BMS systems for safety and longevity. Lead Acids lack this and rely on external units, and can boil over and start fires.

Even fire risk for them honestly is overblown- it's pretty hard to make Iron Phosphates start fires even intentionally. There's plenty of fireboxes to contain them too.

GIRTHQUAKE said:

In reply to alfadriver :

LiFePO4- Lithium Iron Phosphate- are always better than lead-acid in my opinion. To compare:

• Lead Acids for deep storage might last up to 5 years. Iron Phosphates can last twice that.
• Lead Acids cannot be discharged below 50% for more than 2 hours without damaging themselves. Iron Phosphates regularly can be 90-10% discharge range and still have over 2,500 cycles.
• Iron Phosphates can store more than twice the energy, reducing space.
• Iron Phosphates have internal BMS systems for safety and longevity. Lead Acids lack this and rely on external units, and can boil over and start fires.

Even fire risk for them honestly is overblown- it's pretty hard to make Iron Phosphates start fires even intentionally. There's plenty of fireboxes to contain them too.

The first point is only kind of correct, some flooded cell batteries can last 5 years, but there's many that can last twice that. My last set lasted 8 years I believe.

The second point is totally true, flooded cell batteries shouldn't be discharged below 50 percent

The third point isn't something I'm very well versed in so I can't comment.

The last point is stupidly overblown, it's basically marketing. Every person here has dealt with flooded cell batteries a lot and I'm betting most haven't had them explode.

Also a plus for flooded cell is they are much cheaper than any other options. They aren't always the answer but they are very proven tech, cheap and have a long track record for off grid reliability and ruggedness.

In reply to Antihero (Forum Supporter) :

I'm pretty sure he was commenting LiFePO4 vs. LiIon, where the latter has had fire issues many times, whereas the former does not have chemistry that is flammable.  And never comparing LiPo, which are a real issue.

As for the BMS- those are only as good as the one they put in- some are great, some suck, and there are some very doable DIY ones if you just want to get raw cells.

One thing to add, though, anymore, I would not say that LiFePO4s are that much more expensive, anymore- as you can get a 100ahr batteries for about $350.  Which is getting REALLY close to 2 100ahr lead acid or AGM batteries that actually have the same storage.  https://www.amazon.com/LiFePO4-Lithium-Battery-Overland-Applications/dp/B08ZJ48ZK3?dchild=1&keywords=weize%2Blifepo4&qid=1634756853&sr=8-4&linkCode=sl1&tag=vehicledwelling-20&linkId=f8302f7a606134d19f908390d07997a8&language=en_US&ref_=as_li_ss_tl&th=1 was tested by Will Prowse, and it turned out to be quite good- even though he approached it as a cheap rip off.

In reply to alfadriver :

The Trojan t105, which is kind of the go-to for smaller setups and what I've used, is a 225ah battery and cost about $150-175 a piece. That's still pretty cheap compared

In reply to Antihero (Forum Supporter) :

So it would come down to total cycles that one can use....  At least now.  If you are only going to run in a few times, the lead acid would be the choice, but if it's cycled every day for a few years, well...

alfadriver said:

In reply to Antihero (Forum Supporter) :

So it would come down to total cycles that one can use....  At least now.  If you are only going to run in a few times, the lead acid would be the choice, but if it's cycled every day for a few years, well...

Literally all my power runs thru 4 of those t105. They last about 7-8 years of every day usage 24-7 and I'm using them right now.

They are very rugged, very dependable and very proven. This is not an opinion based on research or theoretical, this is experience thru 20 plus years of using them

In reply to alfadriver :

No, I was doing LiFePO4 vs Lead Acids. I agree you're going to have to make sure you have a reputable one with a good BMS, but that's why I posted lads like Will Prouse.

But I'll admit, part of that on Lead Acids is just what I've seen as an outsider on other people's builds. Seemed like too many were having them boil over.

GIRTHQUAKE said:

In reply to alfadriver :

No, I was doing LiFePO4 vs Lead Acids. I agree you're going to have to make sure you have a reputable one with a good BMS, but that's why I posted lads like Will Prouse.

But I'll admit, part of that on Lead Acids is just what I've seen as an outsider on other people's builds. Seemed like too many were having them boil over.

Whose builds are these? I've literally never seen anyone have this problem, there's a lot of off grid people around here and I haven't either.

Lead acids aren't some weird technology, pretty much every car has one, have you ever boiled over your car battery?

This guy (Russell Graves) has a bunch of very detail-oriented articles about setting up a solar-powered office for himself in a shed.  He is more concerned with heat than A/C (being in Idaho rather than Florida), but it is an interesting read.

This is the first article on his blog about the "solar shed":

Solar shed part 1

The big hurdle is going to be cooling.   Some napkin math below.   6000 BTUs of Cooling is not a ton in a shed in Florida, and this whole spreadsheet assumes 100% efficiency and no disruptions in your solar during charging.  

Ive looked at running A/C off my solar, and its a real challenge if the expectation is to actually cool something.  I would trench it out and run power if it was my decision.  The reason folks can make it work in the mountains is they are concerned with heating, and a gas furnace or a pellet stove use a whole lot less power than an A/C unit, and a wood stove uses no power. 

alphahotel said:

This is the first article on his blog about the "solar shed":

Solar shed part 1

Looks like he didn't update anything after insulating the shed. Bummer. 

What is the temperature of the ground - say 2 feet down? Could you bury a pipe and let the ground condition the air some?

NermalSnert (Forum Supporter) said:

What is the temperature of the ground - say 2 feet down? Could you bury a pipe and let the ground condition the air some?

Congrats you just invented geothermal cooling!