diy solar

diy solar

Correct me if I'm wrong please..

RaySE

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Hi, I've read through different articles and answers. And I think I get the idea of calculating.


When I use a 24V battery bank and inverter who has to deliver 40W for 20hours and 200W for 4 hours that is pulling
((50*20) + (240*4))= 800+800 = 1.6 KWh on a 24h day.

With 0.85% of efficiency of the inverter that would need (1600W / 0.85) = 1882W

That on a 24V battery would then be: 1882 / 24 = 78 Amp hours.

Considering the Depth of Discharge on a lead acid battery of 50%.
78 Ah on a lead acid battery would mean I need a 156 Ah battery. (78 / 0.5)

Considering the Depth of Discharge on a lithium battery of 80%.
78 Ah on a Lithium battery would mean I need a 98 Ah battery. (78 / 0.8)

So a 98Ah battery would cover my needs for 1, 24h day.

So far so good, I think.

Considering 5 sun hours for charging the battery and the need to charge 1882 Watts.

Would that mean I need: (1882 / 5) a solar panel capacity of 376 Watts? - "Simplified"

Then taking in account losses for the Panel and the charge controller.

I think I am safe when I take 75% of capacity for the solar panels and then forget the loss in the controller.

My conclusion:

A 500 Watt Solar panel with one of the 2 batteries mentioned above would provide enough to power the inverter to deliver 1882 Watts on a daily basis.

(Not considered cloudy days or more usage then average etc etc)


Please comment

Thanks Ray.
 
You got it.

One important consideration.. If you run into a cloudy day and can't get a lithium battery charged, its no big deal.. Lithium is perfectly happy sitting discharged.

But this isn't so for lead acid.. If you leave a lead acid battery discharged, it begins to die and its life is severely shortened. In other words, lead acid requires more solar panels to ensure it is charged up every day..

Also, while your numbers seem mathematically correct, you also need to account for the fact that, unlike lithium with a >95% to 98% efficiency, a lead acid battery is only about 80% to 85% (on a good day!).. So add another 15% to the losses you calculated along with your charge controller.

Then for safety, whatever you come up with, double it.. Because mother nature will never cooperate with you. And don't forget, the low sun angle in the winter will reduce solar output by more than 50% in the northern states.. and sometimes reduce it by 75% for weeks on end. This effect is less severe in the southern states, but still plays a part.

The type of racking you use also matters.. Fixed angle racks (cheapest) only operate at their highest output for about a month of the year when the angle of the sun lines up perfectly. Generally, here in Michigan, a 400 watt panel will only put out 250 watts most of the time unless its a perfectly sunny day and the temps are cool.

Solar panels put out less power as they heat up... On a 90 degree day, even with perfect sun, a 400 watt panel might only put out 300 watts.

Solar panels are cheap.. get more.. too many is rarely a problem unless you exceed the capacity of your charge controller.
Lead acid batteries, as well as lithium to a much lower extent, are also dependent on their temperature. Lead acid don't hold as much energy when they're cold.. at just 40 degrees, you'll notice it. At 20 degrees, you're going to think something is wrong if you're not expecting it.
 
Hi MurphyGuy,
Thanks for your answer.

One important consideration.. If you run into a cloudy day and can't get a lithium battery charged, its no big deal.. Lithium is perfectly happy sitting discharged.

But this isn't so for lead acid.. If you leave a lead acid battery discharged, it begins to die and its life is severely shortened. In other words, lead acid requires more solar panels to ensure it is charged up every day..
Right, I get that. It wasn't so much for absolute numbers and back up.

Also, while your numbers seem mathematically correct, you also need to account for the fact that, unlike lithium with a >95% to 98% efficiency, a lead acid battery is only about 80% to 85% (on a good day!).. So add another 15% to the losses you calculated along with your charge controller.
What do you mean by "efficiency" on battery ? I thought I mentioned Depth of Discharge, or is that not the same ?

Then for safety, whatever you come up with, double it.. Because mother nature will never cooperate with you. And don't forget, the low sun angle in the winter will reduce solar output by more than 50% in the northern states.. and sometimes reduce it by 75% for weeks on end. This effect is less severe in the southern states, but still plays a part.

The type of racking you use also matters.. Fixed angle racks (cheapest) only operate at their highest output for about a month of the year when the angle of the sun lines up perfectly. Generally, here in Michigan, a 400 watt panel will only put out 250 watts most of the time unless its a perfectly sunny day and the temps are cool.

Solar panels put out less power as they heat up... On a 90 degree day, even with perfect sun, a 400 watt panel might only put out 300 watts.
Okay so my 75% of capacity is a little optimistic ??
I was also considering that today's panels don't necessarily need full sun exposure. Hours where the sun is up they will already charge, however I understand considerably less that their full capacity.

So I should cut that number to 50% efficiency on the panels to be on the safe side ?

Knew about the working angle of the panels, but one can never get to much info. I'm thinking of a solution for our specific situation. I want something I can adjust during the year. Maybe not daily but adjustable as needed.
Solar panels are cheap.. get more.. too many is rarely a problem unless you exceed the capacity of your charge controller.
Lead acid batteries, as well as lithium to a much lower extent, are also dependent on their temperature. Lead acid don't hold as much energy when they're cold.. at just 40 degrees, you'll notice it. At 20 degrees, you're going to think something is wrong if you're not expecting it.
They might be cheap, but I have limited surface to install.
I won't exceed the controller for the moment, because I don't have one yet ;)
--> Will buy one that fits my needs as soon as all calculations are done. Gonna pick one of those very cheap chinese PWM things for now to do experiments on 2 old car batteries, 12V and 24V measurements.

The numbers given in the example are based on my newly acquired Watt meter.
For the moment I have it hooked up on the outlet for the internet modem, router, apple tv unit, and the tv itself. There also are some phone and laptop chargers connected. Just the things that are basically running 24/7. (not the tv)

We are in a house now, and fully on the grid. But I'm going to convert a semi trailer into a home because we are going to move and in the new spot will be nothing. Once there we need to build everything we want from the ground up and we like to stay off the grid forever.
Therefore panel space is limited. How ever I can set up some panels outside when we are on a fixed spot for some time. I understood I should be able to connect the second controller to the same battery bank.
I have a small gas powered generator as back up so batteries won't stay empty in case of to much non sunny days. Probably will continue to take that into consideration. It will be a lot cheaper to pay for some petrol from time to time then to invest an enormous amount of money into a huge battery bank for the extreme situations.

So don't worry, there is a lot more to be done. Because next to calculate is basic needs as the fridge, laundry machine, kitchen appliances etc.

This was only to see if I got the idea of calculations correct. And you corrected me on the capacity of the solar output ?
Also the holding capacity of the battery was not bad to mention because we are moving to a colder climate.

FYI, I understand what you mean by southern and northern states but we are not in the US...?
We are in Europe but in fact are going to move way up north, so things do change for us.

Ray
 
My conclusion:

A 500 Watt Solar panel with one of the 2 batteries mentioned above would provide enough to power the inverter to deliver 1882 Watts on a daily basis.
panel space is limited. How ever I can set up some panels outside when we are on a fixed spot for some time
Using no math I get a different answer.
I read your comments several times and thinking about stuff I have done for others plus my having been offgrid for nearly 4 years now (this year being my first overwinter attempt) and reflecting on my setup I have some thoughts. I probably could provide some math but I don’t think it’s necessary to make this simple overview opinion that might help.

First, for a small solar power system I would never myself nor recommend to others to use a single solar panel. Ever.
Why? In higher latitudes at least two strings facing SE and SW at 90* (or a bit less) separation will usually produce more watts per sun-day than single-direction panels.

Second, with an mppt controller and series strings my experience has been that you will get some charging slightly earlier and later in the day compared to parallel. Plus, when cloudy periods occur the series strings can sometimes (usually) make some small amount of usable power than when I was paralleled in similar conditions and typically would get no charge whatsoever.

So for 500W you can do much better with multiple panels imho

As far as 500W and your battery options… I wouldn’t use 500W setup to begin with. I’d use 600W 3S2P at a minimum. 500W isn’t divisible by 2 or 3 or 4 so it’s a funky number to maximize solar in northern latitudes. Having said that, my wildhat opinion (no math) is that you need at least twice as much battery capacity and 800- or perhaps better: 1200W of solar.
I got by at the beginning with 200W but the normalcy and convenience that keeps life from being tiresome or feeling like your constantly ’camping’ needs more power than 500W and 100Ah of usable battery bank.
If you are going to live at the new location and have a daily shower and some electrical conveniences like a coffeemaker and adequate lighting, refrigerator etc. you need more than what a 500W system will provide. Could you get by with it? Maybe. Probably. But it will become tiresome in the late fall/winter.

If I were to do it over I would probably start with 400W and plan to expand to 1200W. Right now I’m functional at 600W and 300Ah of usable battery but just bare minimum for a dark day. I have the panels to do 1200W but I’ve decided to use 800W which should be better use on low sun days although on sunny days 600W is often way more than I need and 800W will definitely be way more than I can use come spring.

As far as space for panels: you say you are limited. But you could easily put 2000W of panels on a semi trailer. So if you were thinking 500W you have more than enough space to double that imho

I think 250W panels are the best value right now, but even if you used 100W or 200W commodity panels so you can ‘scale up’ over time you can make a decent 12V system. A 24V battery system has some advantages, yes. However, if you were thinking at the 500W level I think the convenience of widely available 12V lighting and the 12V RV products offset the 24V advantages for a smaller system and the living environment you describe.
 
1 important thing that I don’t see in your calculations is the consumption during solar charging. If you are producing say 45 amps and consuming 20 amps your battery charging is 25 amps. Lead acid efficiency, internal resistance is much higher than LFP and the closer to full charge the higher the resistance becomes. They get warm, I have 4000 lbs of them charging can raise the temperature 10 deg F. Easy. That is a lot of energy that was not stored as electricity but, as heat.
 
Hi MurphyGuy,
Thanks for your answer.


Right, I get that. It wasn't so much for absolute numbers and back up.


What do you mean by "efficiency" on battery ? I thought I mentioned Depth of Discharge, or is that not the same ?
If you pump 100 watts into a lead acid battery, it will only give you back 85 watts of energy. Regardless of the power source, the lead acid battery itself wastes 15% or more of the energy you put into it.
Lithium is better at greater than 95%, and as high as 99% by some figures.

Nickel Iron batteries, the cells with the crazy life measured in decades, are only 70%.

So yes, losses in the charge controller, then losses in the battery itself.

Okay so my 75% of capacity is a little optimistic ??
A little.. real world numbers always fall a bit short and mother nature never cooperates. As soon as you hang a solar panel, you're going to think mother nature is out to get you.

I was also considering that today's panels don't necessarily need full sun exposure. Hours where the sun is up they will already charge, however I understand considerably less that their full capacity.

So I should cut that number to 50% efficiency on the panels to be on the safe side ?
The efficiency of the panels isn't really an issue.. A 400 watt panel is a 400 watt panel.. The watt ratings are listed AFTER the efficiency has been accounted for.
The only thing the efficiency of a panel has any bearing on is the physical size of the panel. A 400 watt panel that is 25% efficient is going to be a few inches physically smaller and take up less space than a 400 watt panel that is only 16%. They will both put out 400 watts under ideal conditions.

There are some issues with temperature coefficients (performance when hot or cold) and performance under less than ideal lighting conditions, but these considerations are minor, mostly insignificant for our purposes, and hardly worth a discussion beyond the purely technical aspects one might find interesting. In other words, you can ignore the efficiency ratings.

Knew about the working angle of the panels, but one can never get to much info. I'm thinking of a solution for our specific situation. I want something I can adjust during the year. Maybe not daily but adjustable as needed.
The extra hardware required is not worth it.. If you have the money to spend on fancy mounting systems, you're better off putting it towards more panels.

They might be cheap, but I have limited surface to install.
I won't exceed the controller for the moment, because I don't have one yet ;)
--> Will buy one that fits my needs as soon as all calculations are done. Gonna pick one of those very cheap chinese PWM things for now to do experiments on 2 old car batteries, 12V and 24V measurements.
PWM controllers are VERY inefficient and will not take advantage of the full power of your panels. PWM is appropriate for very small applications like a solar yard light, chicken coop door, a lighted sign, etc. They are not appropriate for larger systems trying to power a microwave or something you depend on or need.

You get what you pay for when it comes to solar equipment.. Stick to an MPPT controller for any solar system over 100 watts.

The numbers given in the example are based on my newly acquired Watt meter.
For the moment I have it hooked up on the outlet for the internet modem, router, apple tv unit, and the tv itself. There also are some phone and laptop chargers connected. Just the things that are basically running 24/7. (not the tv)
Good.. you're starting off right by figuring out what your power requirements are.

We are in a house now, and fully on the grid. But I'm going to convert a semi trailer into a home because we are going to move and in the new spot will be nothing. Once there we need to build everything we want from the ground up and we like to stay off the grid forever.
Therefore panel space is limited. How ever I can set up some panels outside when we are on a fixed spot for some time. I understood I should be able to connect the second controller to the same battery bank.
I have a small gas powered generator as back up so batteries won't stay empty in case of to much non sunny days. Probably will continue to take that into consideration. It will be a lot cheaper to pay for some petrol from time to time then to invest an enormous amount of money into a huge battery bank for the extreme situations.

So don't worry, there is a lot more to be done. Because next to calculate is basic needs as the fridge, laundry machine, kitchen appliances etc.

This was only to see if I got the idea of calculations correct. And you corrected me on the capacity of the solar output ?
Also the holding capacity of the battery was not bad to mention because we are moving to a colder climate.

FYI, I understand what you mean by southern and northern states but we are not in the US...?
We are in Europe but in fact are going to move way up north, so things do change for us.

Ray
You're on the right path...
 
only thing the efficiency of a panel has any bearing on is the physical size of the panel. A 400 watt panel that is 25% efficient is going to be a few inches physically smaller and take up less space than a 400 watt panel that is only 16%. They will both put out 400 watts under ideal conditions.
That is a truth.
I have four mono panels coming (two arrived already) because I can put four on my existing mounts that only allow the width of three poly panels. I never thought I’d spend on mono but my tape measure convinced me.
 
Using no math I get a different answer.
I read your comments several times and thinking about stuff I have done for others plus my having been offgrid for nearly 4 years now (this year being my first overwinter attempt) and reflecting on my setup I have some thoughts. I probably could provide some math but I don’t think it’s necessary to make this simple overview opinion that might help.
Thanks a lot for your extended answer and thoughts, very much appreciated.
12VoltInstalls:

First, for a small solar power system I would never myself nor recommend to others to use a single solar panel. Ever.
Why? In higher latitudes at least two strings facing SE and SW at 90* (or a bit less) separation will usually produce more watts per sun-day than single-direction panels.
1. Sorry but with "A 500 Watt Solar panel with one of the 2 batteries...." I didn't specifically mean 1 / 500W panel.
It was more to round up the 376W, needed from the calculations, to a decent amount.
2. Got your remark about the facing SE / SW noted.;)

12VoltInstalls: Second, with an mppt controller and series strings my experience has been that you will get some charging slightly earlier and later in the day compared to parallel. Plus, when cloudy periods occur the series strings can sometimes (usually) make some small amount of usable power than when I was paralleled in similar conditions and typically would get no charge whatsoever.

So for 500W you can do much better with multiple panels imho
As far as 500W and your battery options… I wouldn’t use 500W setup to begin with. I’d use 600W 3S2P at a minimum. 500W isn’t divisible by 2 or 3 or 4 so it’s a funky number to maximize solar in northern latitudes. Having said that, my wildhat opinion (no math) is that you need at least twice as much battery capacity and 800- or perhaps better: 1200W of solar.
I got by at the beginning with 200W but the normalcy and convenience that keeps life from being tiresome or feeling like your constantly ’camping’ needs more power than 500W and 100Ah of usable battery bank.
If you are going to live at the new location and have a daily shower and some electrical conveniences like a coffeemaker and adequate lighting, refrigerator etc. you need more than what a 500W system will provide. Could you get by with it? Maybe. Probably. But it will become tiresome in the late fall/winter.
3. Again, the 500W was just a theoretical calculated number. But I get your point on the even numbers. Easier to expand and equilibrate your system.


12VoltInstalls: If I were to do it over I would probably start with 400W and plan to expand to 1200W. Right now I’m functional at 600W and 300Ah of usable battery but just bare minimum for a dark day. I have the panels to do 1200W but I’ve decided to use 800W which should be better use on low sun days although on sunny days 600W is often way more than I need and 800W will definitely be way more than I can use come spring.
For now I made some pre calculations with all kinds of daily things running, modem, fridge al the sort of things you don't want to think of constantly, like you said it shouldn't look like camping if you are living off grid year round. It adds up to 3100W at moments I put the watercooker on or another kitchen machine.
When I guess the time we use it per day, I come around 40-ish Amp hours.
I know it's possible to look up our usage on our electricity bills, but we are on electrical heating in our current house, so that screws up the estimations.


12VoltInstalls: As far as space for panels: you say you are limited. But you could easily put 2000W of panels on a semi trailer. So if you were thinking 500W you have more than enough space to double that imho

I think 250W panels are the best value right now, but even if you used 100W or 200W commodity panels so you can ‘scale up’ over time you can make a decent 12V system. A 24V battery system has some advantages, yes. However, if you were thinking at the 500W level I think the convenience of widely available 12V lighting and the 12V RV products offset the 24V advantages for a smaller system and the living environment you describe.
As Will Prowse states in his video's, and with him others too, a 24V system requires smaller cables and you can save good bucks on that. But 24V to 220V inverters are less common and as you said all 24V products are less widely available. 12V can be found everywhere and relatively cheap. So I don't know what is best yet. I don't have the experience yet to judge.
 
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If you pump 100 watts into a lead acid battery, it will only give you back 85 watts of energy. Regardless of the power source, the lead acid battery itself wastes 15% or more of the energy you put into it.
Lithium is better at greater than 95%, and as high as 99% by some figures.
The efficiency of the panels isn't really an issue.. A 400 watt panel is a 400 watt panel.. The watt ratings are listed AFTER the efficiency has been accounted for.
The only thing the efficiency of a panel has any bearing on is the physical size of the panel. A 400 watt panel that is 25% efficient is going to be a few inches physically smaller and take up less space than a 400 watt panel that is only 16%. They will both put out 400 watts under ideal conditions.
Okay, learning.?

The extra hardware required is not worth it.. If you have the money to spend on fancy mounting systems, you're better off putting it towards more panels.
Well what is fancy.? We have a lot of stuff laying around here what I think I can use. If we leave this place we have to throw it away anyway. And I think I may call myself a handy enough DIY guy. If I can put something together that can tilt to make a better angle why wouldn't do it?

PWM is appropriate for very small applications like a solar yard light, chicken coop door, a lighted sign, etc.

You get what you pay for when it comes to solar equipment..
Absolutely right. Learned that already.-->> Read some stories of burned and cooked batteries due to cheap PWM chargers. I didn't really get that, your batteries are the most expensive part of you system. Why risk them with a cheap charger??

But yes I DID order PWM.... 2 in fact. ?
1 for 6,28 Euros and 1 for 10,78 Euros. So I probably get what I paid for yes. But I can connect to the panel I have and an old battery I have so I can do experiments.

And well, as they continue to work I can find some use for them later on.
This year the nice lovely deer we like to see so much, ate our entire winter garden. Every vegetable we had planted to harvest for winter is gone... So I'm gonna put an electic wire around the foodgarden next year. Hope the controllers are good for that. But I won't risk a 500$ battery on them.

You're on the right path...
Thanks
 
And well, as they continue to work I can find some use for them later on.
This year the nice lovely deer we like to see so much, ate our entire winter garden. Every vegetable we had planted to harvest for winter is gone... So I'm gonna put an electic wire around the foodgarden next year. Hope the controllers are good for that. But I won't risk a 500$ battery on them.


Thanks
Our garden is surrounded by six 12 gauge galvanized wires stretching up to 7 feet and energized using a 6 Joule electric fence charger rated for 200 miles of fencing. The 200 mile fence charger is being used on 200 yards of fence...

You can't just shock the deer to keep them away... they'll just forget about it for the night and come back later to try again. The shock needs to hurt... it needs to be 10,000 volts or more.. and the secret to a good electric fence is good ground rods.. sink at least 3 of them and spread them out as far as you can.
If your controller comes with lightening arrestors, remove them! They reduce the fence charger's output and they don't really work anyhow. If a big storm comes around, just disconnect the fence for the night.. deer don't feed when its storming anyhow, nor are they waiting for you to disconnect the fence.. once they learn the area of your garden = pain, they won't come around anymore.

We no longer have an issue with deer, and we have so many around our property that I can just open a bathroom window and shoot them anytime I want, but they give the garden a good 100 foot berth.
 
1 important thing that I don’t see in your calculations is the consumption during solar charging. If you are producing say 45 amps and consuming 20 amps your battery charging is 25 amps. Lead acid efficiency, internal resistance is much higher than LFP and the closer to full charge the higher the resistance becomes. They get warm, I have 4000 lbs of them charging can raise the temperature 10 deg F. Easy. That is a lot of energy that was not stored as electricity but, as heat.
Well good point.
This thread actually is about getting the pre- calculations right to prepare myself to get the best fitting installation for our needs.
And besides the mentioned reduced output, efficiency on charging, losses in battery charging etc. I think this is a good one to think about.
So the answer for now is: I don't know yet.

We now have a double meter. Night time electricity is cheaper, so the laundry machine, dryer and dishwasher we have running at night.
I already have been talking with my wife to change that kind of routines. I guess those things should run in day time when you are on "free" solar power.
That can save on battery storage capacity I'll guess.
 
Our garden is surrounded by six 12 gauge galvanized wires stretching up to 7 feet and energized using a 6 Joule electric fence charger rated for 200 miles of fencing. The 200 mile fence charger is being used on 200 yards of fence...

You can't just shock the deer to keep them away... they'll just forget about it for the night and come back later to try again. The shock needs to hurt... it needs to be 10,000 volts or more.. and the secret to a good electric fence is good ground rods.. sink at least 3 of them and spread them out as far as you can.
If your controller comes with lightening arrestors, remove them! They reduce the fence charger's output and they don't really work anyhow. If a big storm comes around, just disconnect the fence for the night.. deer don't feed when its storming anyhow, nor are they waiting for you to disconnect the fence.. once they learn the area of your garden = pain, they won't come around anymore.

We no longer have an issue with deer, and we have so many around our property that I can just open a bathroom window and shoot them anytime I want, but they give the garden a good 100 foot berth.
Okay thanks good one.
We have poultry net for the chickens on solar. But I bought that as a plug and play kit.
-->> A galvanized box with a little 25W (not sure) panel on top. A little controller and battery inside with the wire charger.
Installed it and never looked at it again. Only charged the battery one or two extra times last winter. This years winter we switch off the wire charger unit at night as we close the door from the coop once the chicks are inside. This works fine for the moment, it saves the battery. Once days are longer again we will leave it back on 24/7 again.
 
You need 220? Not North America?
So, no. Why? Except for the difference in 110V / 220V on the Grid.
Well I had a suggestion but I saw the 220 and realized it might be irrelevant. And it is.

So I see your point on 12V
For a small system you may not have any wiring/cable savings more than a pizza or two. Big systems usually have enough stuff and more of it so the cable savings are often significant.
 
Okay thanks good one.
We have poultry net for the chickens on solar. But I bought that as a plug and play kit.
-->> A galvanized box with a little 25W (not sure) panel on top. A little controller and battery inside with the wire charger.
Installed it and never looked at it again. Only charged the battery one or two extra times last winter. This years winter we switch off the wire charger unit at night as we close the door from the coop once the chicks are inside. This works fine for the moment, it saves the battery. Once days are longer again we will leave it back on 24/7 again.

My chicken coop has a solar powered automatic door I fabricated from a motorized car antenna.. (the type that extend up when you start the car).

I used to have a 5 watt panel on the coop but it wasn't enough for winter so I changed it to a 25 watt panel.. I also switched out the 12 volt motorcycle battery to a couple of reconfigured IMA sticks from a Honda Civic hybrid electric car.. The IMA sticks are NiMH and aren't harmed if discharged. I put them into a 10s config to make a 14 volt battery and they give me about 10 amp-hours of capacity. I got a whole bunch of them free a few years ago from a battery recycling center.. about 20% were bad, but the rest were good as new.

No problems this winter..
 
Hi, I've read through different articles and answers. And I think I get the idea of calculating.


When I use a 24V battery bank and inverter who has to deliver 40W for 20hours and 200W for 4 hours that is pulling
((50*20) + (240*4))= 800+800 = 1.6 KWh on a 24h day.

With 0.85% of efficiency of the inverter that would need (1600W / 0.85) = 1882W

That on a 24V battery would then be: 1882 / 24 = 78 Amp hours.

Considering the Depth of Discharge on a lead acid battery of 50%.
78 Ah on a lead acid battery would mean I need a 156 Ah battery. (78 / 0.5)

Considering the Depth of Discharge on a lithium battery of 80%.
78 Ah on a Lithium battery would mean I need a 98 Ah battery. (78 / 0.8)

So a 98Ah battery would cover my needs for 1, 24h day.

So far so good, I think.

Considering 5 sun hours for charging the battery and the need to charge 1882 Watts.

Would that mean I need: (1882 / 5) a solar panel capacity of 376 Watts? - "Simplified"

Then taking in account losses for the Panel and the charge controller.

I think I am safe when I take 75% of capacity for the solar panels and then forget the loss in the controller.

My conclusion:

A 500 Watt Solar panel with one of the 2 batteries mentioned above would provide enough to power the inverter to deliver 1882 Watts on a daily basis.

(Not considered cloudy days or more usage then average etc etc)


Please comment

Thanks Ray.
By George I think you've got it
 
Good thread. A couple things to think about...

Whatever power you use at night you'll need enough solar to replace that in the batteries and run the loads you need during the day. So just enough solar to replace the energy in the batteries won't be quite enough. I know some will be used during the day too but you get the concept :)
More wattage from the panels on days that aren't ideal is advantageous as well.

If you use 3100 watts you'll be pulling from the batteries
258 amps at 12 volts
129 amps at 24 volts
65 amps at 48 volts

So that could have a bearing on your battery voltage selection. Another plus for a higher battery voltage is your charge controller can handle more watts of pv input too.
 
Good thread. A couple things to think about...
Thanks :cool:
But indeed a lot of things to consider.
So I see your point on 12V
For a small system you may not have any wiring/cable savings more than a pizza or two. Big systems usually have enough stuff and more of it so the cable savings are often significant.
Well yeah what is a small system and when is it becoming a big system?

@12VoltInstalls I get the point on the savings for cable costs. On the other hand, the cabling is all in your technical room.
From there you run it through an inverter to 110V or 220V, whatever your case.
Then you proceed with cable to run 110V / 220V through your house, trailer or what so for all your devices. Maybe you keep some lights direct on 12V/24V but not so much I would think.
So how many meters of cable for the actual solar/charger/battery/inverter part are we really talking about??
Maybe I'm not seeing things right for the moment because I didn't build a system yet.

On the other hand,
If you use 3100 watts you'll be pulling from the batteries
258 amps at 12 volts
129 amps at 24 volts
65 amps at 48 volts
the 48V version sounds a lot better to me.
On 12V I would need an enormous amount of battery power/back-up.
258Amps on 12V is 1 day of power.
258Amps on 48V is 4 days. So actually: 1 day of power and 3 full days of back-up.
Besides that, working lower amps sounds more safe to me.
 
Thanks :cool:
But indeed a lot of things to consider.

Well yeah what is a small system and when is it becoming a big system?

@12VoltInstalls I get the point on the savings for cable costs. On the other hand, the cabling is all in your technical room.
From there you run it through an inverter to 110V or 220V, whatever your case.
Then you proceed with cable to run 110V / 220V through your house, trailer or what so for all your devices. Maybe you keep some lights direct on 12V/24V but not so much I would think.
So how many meters of cable for the actual solar/charger/battery/inverter part are we really talking about??
Maybe I'm not seeing things right for the moment because I didn't build a system yet.

On the other hand,

the 48V version sounds a lot better to me.
On 12V I would need an enormous amount of battery power/back-up.
258Amps on 12V is 1 day of power.
258Amps on 48V is 4 days. So actually: 1 day of power and 3 full days of back-up.
Besides that, working lower amps sounds more safe to me.
Concerning the last part.
It doesn’t sound like you understand that it takes 4 times the battery to equal the same Amp hours in 48 volt system than a 12 volt. That is why “Watts “ is a much better Value to use and less chance of math errors moving from one voltage to another.
 
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