solar calculations

[JDSquared]

The more I try to study this the more I get off track I think.

I've been using an off grid calculator and consistently coming up around 6500 watts daily use. This still seems high, but I can use this as a baseline at least.

If I set up a 24v system, that would equal 271 amp hours per day?
Assuming 50% discharge on batteries, I would need 542Ah bank?

And that would last me off grid only one day? Why does it seem like everybody else can go a few days with less power, and I don't feel like I'm using a bunch of energy. Especially in 24v vs 12v. I considered getting something to measure actual usage, but pretty much nothing I own electronically is coming. My laptop and coffee maker. Fridge will maybe be 24 volt or maybe through an inverter, but it would be brand new so I am using online estimates for that. Same as an instahot water heater. I am trying to use 12v/24v for everything else in the bus.


Anyway, assuming 6- 12v 100Ah batteries, I would run two in series and 4 in parallel? This is where I get lost in how many amp hours I have doing this. Connecting two in series gives me 24v but still only 100 amp hours. Adding the other 4 batteries adds 400 amp hours? For a total of five? (which puts me under my daily needs).

Edit: I think I just figured something out in my head; 400 amp hours at 24V equals 9600 Watts, which gets me 1 1/2 days off grid? That's still not very much.

The only thing I have set aside right now (on EBAY) are solar panels. They are 250W poly solar panels. "Panels are used, have been tested and have good output" I don't know what that means lol, but they have no negative reviews.

open circuit voltage 37.6v
max power voltage 30.3v
max power current 8.27A
max system voltage 600v

I want to put 6 up on my bus. 4 will fit perfect between the roof hatches, and two more probably toward the front of the bus.

I took a note from somewhere that i need 40V to run 24v system. So would I have to run these like the batteries? 2s4p (is that how you write that?) or is my note wrong about the voltage needed?

Last question... How would you wire these? They would all go into 2 wires in a combiner box yes? And come down into the MPPT? Is there an advantage to running only four of them together (that would be 1000W, double what I use in a day) and wire the other two to, I don't know, charge to another battery directly for some reason? That doesn't make sense I guess. I was just picturing some sort of back up plan.

I can get more panels, or more wattage, but I seem limited by the battery bank anyway. I don't want 12 batteries lol, and not ure I can spend money on lithium.

I know this info is out there still. I am trying to gather it all without asking needless questions. But maybe typing this all out will help me see the answer.

Thanks

[john61ct]

First off, you need to get your units straight.

"6500 watts daily use" is not a thing.

From your later statement, I infer you mean 6500Wh.

Yes that is a very large amount of energy to have to recharge every day on average off grid.

You don't want 12V batteries, won't last long, compared to the best battery value by far, Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, 2x6V, around $200 per 200+AH @12V pair from BatteriesPlus or Sam's Club. Deka labeled same batts also sold at Lowes.

Two pair for 200Ah @24V, double that for 400Ah, so yes 12 units at 65lbs each for 600Ah.

LFP would be half the weight and space but 7x the cost, IMO do not consider drop in type for this big a system.

For solar, I recommend Victron MPPT, one 75/15 will support two panels in parallel if your system is 24V.

Any panel voltage over 20V is fine, Voc 37 even better.

If you really do "need" 600Ah @24W, and hope to get most of your energy from solar, get 2-3000W of panels, should cover you OK on days when insolation is good.

A quiet inverter genset will help supplement that, can convert to propane if you don't want to carry three fuel types.

Conservation, going for super-efficiency is really the key for off-grid living. Compromises are required to keep systems costs under control.

Do not heat things using electricity, propane much more effective than that, or other camping type setups like a Jetboil.

Forget a fancy coffee maker, just boil water and pour over, maybe Aeropress or similar

https://expeditionportal.com/forum/t...ss-trip.211397

For a fridge use native DC compressor type, not one that needs an inverter, maybe 25-40Ah per day.

If you do insist on high-current heat-producing appliances, then just run the genny to support their use, help reduce the tonnage of lead you need to carry around.

[Danjo]

Can you post your energy budget?

[JDSquared]

Originally Posted by Danjo

Can you post your energy budget?

I thought about it but didn't want to bog down the post lol. Then I just reread what I posted and it seems pretty bogged down already lol.
I will post it here in a few.

[JDSquared]

Originally Posted by john61ct

First off, you need to get your units straight.

"6500 watts daily use" is not a thing.

From your later statement, I infer you mean 6500Wh.

Yeah sorry, 6500Wh

Originally Posted by john61ct

Two pair for 200Ah @24V, double that for 400Ah, so yes 12 units at 65lbs each for 600Ah.

LFP would be half the weight and space but 7x the cost, IMO do not consider drop in type for this big a system.

Not sure what you mean by drop in, but I would go LifePo before making room for 12 batteries lol.

Originally Posted by john61ct

Any panel voltage over 20V is fine, Voc 37 even better.

20V panel would need to be in series right? To get 40V and cover the 24V battery? If I am remembering what little I learned from Will Prowse.

I like the panels I have saved. they are 75$ each. I could fit 8 up top but hoping to use 6. I was trying to ask how to connect them for best usage.

The fridge I used on the calculator said 69W so that's okay for calculations. Propane oven, didn't include any AC or anything. Planning on having a shore power outlet and a backup generator, but hoping to get what I can out of solar.

Going to post the calculator numbers here, they seem high.


I have 2 french presses for coffee and 2 percolators and a pour over ceramic filter for single cup pour overs. I roast my own coffee, but I am discarding the electric roaster and learning to roast with propane. I am all about my coffee. So the coffee maker is coming with me, even if I don't use it on cloudy days, I measure my usage in pots per day not cups.

[john61ct]

Originally Posted by JDSquared

Not sure what you mean by drop in, but I would go LifePo before making room for 12 batteries lol.

Not sure why you're laughing, plenty of rigs need big banks.

You could get there with fewer units weighing hundreds of pounds each.

Going LFP for many thousands of dollars won't mean fewer units at 3.2V each minimum is 8 to get to 24V nominal.

And 180Ah is a pretty big cell, 3 sets for 549Ah means 24 cells. But they are smaller and lighter.

Best as I said is to focus your spending on as high efficiency as possible, and only using electrickery where truly necessary.


> 20V panel would need to be in series right?

No, your panels at 37Voc are fine. Avoid series, output gets wiped out too easily by partial shade, even dust & leaves.

The 24V output is irrelevant to panel voltage with MPPT, but higher Voc panels get higher conversion efficiency.

The "75" in 75/15 means panels up to 60-65V will be fine. Victron gets you so much flexibility, you can test yourself what wiring scheme works best.



The fridge I used on the calculator said 69W so that's okay for calculations.

No useless number. You need actual measured Wh per 24hrs, to get 24V Ah. If a mains fridge (needs inverter) sold in NA market will be hugely wasteful to try to use off grid, don't bother IMO.



> So the coffee maker is coming with me

Electric?

I guess if you don't mind running the genset, charge the bank while making your cuppa, up to you.

[JDSquared]

Originally Posted by Danjo

Can you post your energy budget?

LOL I lost it. I have one saved in my email somewhere. I just did a new one and came out a little lower.


Appliance Watt Usage Daily WhAvg

MaxxAir Fan 60W 4 hours/day 7 days 240W
MaxxAir #2 60W 4 hours/day 7 days 240W
InstaHot 750W 1 hour/day 7 days 750W
Water Pump 100W 1 hour/day 7 days 100W
Fridge 69W 24 hour/day 7 days 1656W
Wash/Dry 1300W 1 hour/day 1 day 185W
Laptop 100W 4 hour/day 7 days 400W
TV/PS3 115W 1 hour/day 7 days 115W
LED lights x15 6W 3 hours/day 7 days 270W
Coffee/Grinder 1000W 1 hour/day 7 days 1000W


4956 daily average

Not sure what else I am forgetting now, but I like this total a little bit better. Especially if I put the washer with the AC unit and run generator only.
Not sure what the MPPT and monitors etc add to this either.

[john61ct]

All those W's on the right are

Wh (per 24hrs)

[JDSquared]

Originally Posted by john61ct

No, your panels at 37Voc are fine. Avoid series, output gets wiped out too easily by partial shade, even dust & leaves.

The 24V output is irrelevant to panel voltage with MPPT, but higher Voc panels get higher conversion efficiency.





The fridge I used on the calculator said 69W so that's okay for calculations.

No useless number. You need actual measured Wh per 24hrs, to get 24V Ah. If a mains fridge (needs inverter) sold in NA market will be hugely wasteful to try to use off grid, don't bother IMO.

Sorry the fridge was a 24V DC fridge. 69W per the specs. I don't have on so I don't know actual measured Wh. Same as everything else I am putting into the bus.

I must have misread something about that Panel Voltage then, too, because what you're saying about the controller is what I thought.

[JDSquared]

Originally Posted by john61ct

All those W's on the right are

Wh (per 24hrs)

yeah the spacing got messed up after I posted it.

[john61ct]

Take out the electric HWS, use propane.

An efficient fridge maybe 500Wh per day.

Run the genset for laundry and coffee

MPPT supplies energy, not a significant consumer

[john61ct]

That 69W must be while the compressor's running.

With a low temp delta, duty cycle might be 15%.

Peak usage maybe 60%?

Buy your load devices first maybe 2pair GCs and a coulometer, and start actually measuring.

Buy the rest of the GCs within a few months of the first pair, keep well topped up.

[JDSquared]

This is probably the most difficult part of my build. Unless my engine fails at some point. I think I found some 3.2v 180Ah lithium cells for 80$ each. I think they would come from China, $258 flat fee for shipping. I sent an email looking for a quote on 16 of them.
If my numbers are right, that would give me a 24v battery with 360Ah (8640Wh). For $1586

I've been doing numbers all day on different systems. Used Valance batteries would be $1800 (6624Wh)

and 24V AGM would be $1300 (9600Wh). That's also good pricing but I would get only 50% usage on those. And fewer cycles.

The Valence make me nervous because I can't find their BMS to go along with it. Although I am not sure what I would need for these other 3.2V cells anyway. But I think I could ask the other JD for help, he's got a similar larger system that I hope to emulate.

This would not get me off grid for too long in the winter, but any place I am getting some sun would work. I'm hoping I found my batteries (even if I'm not even ready to use them for another six months).

[john61ct]

OMG do **not** spend thousands on any kind of bank, until you've got objective measured data to create an accurate energy budget!

Later on, if you do go LFP, get a set of genuine recently made Grade A cells from

Winston, CALB, GBS, Sinopoly

A123 (now Lithium Werks) out of the big prismatic space for now.

But would be silly to get bigger than you need.

As would AGM over FLA GCs without a compelling reason.

But for now you just don't even know how big a bank you need!

[JDSquared]

Originally Posted by john61ct

OMG do **not** spend thousands on any kind of bank, until you've got objective measured data to create an accurate energy budget!

Later on, if you do go LFP, get a set of genuine recently made Grade A cells from

Winston, CALB, GBS, Sinopoly

A123 (now Lithium Werks) out of the big prismatic space for now.

But would be silly to get bigger than you need.

As would AGM over FLA GCs without a compelling reason.

But for now you just don't even know how big a bank you need!

You're awfully hung up on 6v FLAs. I read a thread yesterday where you argued and argued about someone needing to use these batteries even though you stated you used the lithium for your own needs.

I read a thread this morning where you argued. And argued that they should get the system they need and not get one battery at a time. Which is what you're telling me to do here.

I appreciate the help but your advice is all over the place. And I can't find any place on here where you demonstrate your system, so I could maybe see it in real world applications.

There's a ton of other people on here with diagrams and pictures and examples of what works for them.

Especially JD ontheGo. You're telling me I can't bring a coffee maker and he's running a bunch of stuff on a 3000 watt inverter. On his third solar system and written blogs about his first two systems. I'm about to ask him a ton of questions and see if this is what I want.

In regards to using 16 6v FLAs to get the power I need. All that space and all those connections. And trying to top off the water every month? No thank you.

I know exactly the size bank I need. It's listed above. I know I sound like a dick, or ungrateful at least. But I'm really not trying to be. Everything I'm adding up, even the FLAs are coming out in the same price range. And right at my budget. But my research makes the lithiums really worth the effort.

[john61ct]

I'm not hung up on any one path, perhaps made wrong assumptions about your budget.

Of course you **can** run anything you like as long as the average energy input is higher than outgo.

But when starting out it is sensible to shoot for as efficient as possible; as you discover in actual use that you have plenty of surplus income, or are running ICE sources regularly anyway, then the more extravagant optional mod cons can appropriately be added.

If you really think you know the size bank you need, and are willing to pay the price for LFP, by all means go for it, just trying to help.

The "buy the whole bank at once" ideal can be compromised even with lead if we're only talking a few weeks or months of light usage to get a handle on the actual loads.

With LFP even years apart is fine.

[JDOnTheGo]

This is always a rather difficult topic - for a number of reasons. There is definitely no one 'right answer' and not everyone wants to learn all that is necessary to craft the "best" system for their needs. They really just want the recipe/parts list. Of course, when moving into 'RV style living' for the first time, it is impossible to know what you need (e.g. doing an energy budget and wondering how long your water pump will run each day. ).

I find myself occasionally answering some question here with "my perspective" in mind or sometimes with the "group perspective" - neither are necessarily the best. Some folks only need a 12V battery connect to an LED light for a weekend trip, others 'need' much more.

Digging into each question/thread to figure out what the OP is looking for usually takes some time and patience.

[kazetsukai]

Originally Posted by JDSquared

MaxxAir Fan 60W 4 hours/day 7 days 240Wh
MaxxAir #2 60W 4 hours/day 7 days 240Wh

I have one of the fantastic fans and they don't use even close to 60W at full tilt, seems a bit high to me.

Originally Posted by JDSquared

InstaHot 750W 1 hour/day 7 days 750Wh

I'm skeptical this is actually 750W, or that it'll only run for an hour a day, or in that case, that it'll do anything beyond provide lukewarm water. I gave up on hot water planning a 30kWh battery bank, I say go propane.

Originally Posted by JDSquared

Water Pump 100W 1 hour/day 7 days 100Wh

How many GPM is your pump? Do you have at least 60 times that in water capacity? lol, your estimate is too high.

Originally Posted by JDSquared

Fridge 69W 24 hour/day 7 days 1656Wh

Wash/Dry 1300W 1 hour/day 1 day 185Wh
Laptop 100W 4 hour/day 7 days 400Wh
TV/PS3 115W 1 hour/day 7 days 115Wh
LED lights x15 6W 3 hours/day 7 days 270Wh
Coffee/Grinder 1000W 1 hour/day 7 days 1000Wh

All of these, use a Kill-a-Watt or other meter and actually measure your weekly usage. Your grinder really runs for an hour?



Yesterday my yield was 1.62kWh. I used about 600Wh (25W load running 24/7) Net yield, ~1kWh. 24/7 loads are the killers.

Originally Posted by JDSquared

This is probably the most difficult part of my build. Unless my engine fails at some point. I think I found some 3.2v 180Ah lithium cells for 80$ each. I think they would come from China, $258 flat fee for shipping. I sent an email looking for a quote on 16 of them.
If my numbers are right, that would give me a 24v battery with 360Ah (8640Wh). For $1586

I went EV lithium/Tesla. Systems with an internal BMS like the battle-borns and others are more or less plug-and-play. Everything else you will be doing it all yourself. If you enjoy tinkering with electrical, go for it. If you don't like watching voltages, or are uncomfortable in the slightest with any of this stuff spend the extra $ on the premade solutions.

[JDSquared]

Originally Posted by JDOnTheGo

This is always a rather difficult topic - for a number of reasons. There is definitely no one 'right answer' and not everyone wants to learn all that is necessary to craft the "best" system for their needs. They really just want the recipe/parts list. Of course, when moving into 'RV style living' for the first time, it is impossible to know what you need (e.g. doing an energy budget and wondering how long your water pump will run each day. ).



I find myself occasionally answering some question here with "my perspective" in mind or sometimes with the "group perspective" - neither are necessarily the best. Some folks only need a 12V battery connect to an LED light for a weekend trip, others 'need' much more.



Digging into each question/thread to figure out what the OP is looking for usually takes some time and patience.

I will have a few questions for you JD and when I get to ask them I promise I'm asking for your opinion directly. Your sister may or may not be the best fit for me, but how it's actually working for you is a great guide for mine.

I can't figure out what you using for a BMS though I think that's my biggest hang up right now. I only see the one picture and you've got a great electrical diagram, but I'm not sure what your components are to monitor your batteries.

[JDSquared]

Originally Posted by john61ct

I'm not hung up on any one path, perhaps made wrong assumptions about your budget.

Of course you **can** run anything you like as long as the average energy input is higher than outgo.

But when starting out it is sensible to shoot for as efficient as possible; as you discover in actual use that you have plenty of surplus income, or are running ICE sources regularly anyway, then the more extravagant optional mod cons can appropriately be added.

If you really think you know the size bank you need, and are willing to pay the price for LFP, by all means go for it, just trying to help.

The "buy the whole bank at once" ideal can be compromised even with lead if we're only talking a few weeks or months of light usage to get a handle on the actual loads.

With LFP even years apart is fine.

I really appreciate the help. Everything is still in a folder I've been tied up a few weeks again. I'll still in planning stages, so when I start asking more questions I'll be happy if you chime in.