Rookie here, help me design a small 24v system starting from the batteries.

[Daxo]

Hi there,
I'm new to the whole solar thing so I've been reading and listening to a lot about it lately. Obviously, the amount of information out there is overwhelming, to say the least.

I would really appreciate any help I can get to guide me through the design process of as efficient a 24V system for the batteries (I can afford to start with) as possible.


After doing the rough estimate for my power needs(tv, laptop, lights, sometimes small micro oven/kettle/power tools batteries), taking the price of batteries into consideration as well, I've come to a figure of 2400Wh storage. It's the best I can do at the moment, batteries are expensive.

With that said, I'd go with LifePO4 2x 12v 100Ah in series for a total of 24V 100Ah, roughly a 2400Wh storage.

If I've understood things right, these should be the following steps for me to find out what I need next.


Step 1 - Determining how much solar I'll need.
For a 2400Wh capacity, to get a full charge within 5 hours of direct sunlight, I'll need 480W of solar panels. 2400Wh/5h= 480W of solar.

Step 2 - Finding out which charge controller will do the job for the available solar wattage.
By dividing the solar wattage by the battery voltage I can determine the minimum required charge controller current(A) rating. 480W / 24V = Charge controller of minimum 20A rating, for precaution, should go 25-30A?

Is this correct so far?


I've also heard that in order to pick a good inverter for my system, I'll have to take into consideration the battery C rate in order to pick the maximum inverter wattage. ?

Please, feel free to correct me and share any advice/suggestions you can give me, highly appreciate it! Thanks.

[Daxo]

Gee, one at the time please

[SunEagle]

Gee, one at the time please

Starting a new thread on a Sunday may not get the response one expects. So please be patient. Answers to your questions will come.

I do have a question. You mention needing 2400wh storage but did not mention how many wh you plan on needing each day? That value and the manufacturer's claim of how much a battery can safely provide you each day it what you need to calculate your system size.

The other caution I shall mention is that if you use the "cost" as a reason to limit your system build you may end up wasting that money because the type and size of the equipment you start with is not enough to supply you what you need. That direction tends to end up costing you a lot more.

[EverAzure]

Hi there,
I'm new to the whole solar thing so I've been reading and listening to a lot about it lately. Obviously, the amount of information out there is overwhelming, to say the least.

I would really appreciate any help I can get to guide me through the design process of as efficient a 24V system for the batteries (I can afford to start with) as possible.


After doing the rough estimate for my power needs(tv, laptop, lights, sometimes small micro oven/kettle/power tools batteries), taking the price of batteries into consideration as well, I've come to a figure of 2400Wh storage. It's the best I can do at the moment, batteries are expensive.

With that said, I'd go with LifePO4 2x 12v 100Ah in series for a total of 24V 100Ah, roughly a 2400Wh storage.

If I've understood things right, these should be the following steps for me to find out what I need next.


Step 1 - Determining how much solar I'll need.
For a 2400Wh capacity, to get a full charge within 5 hours of direct sunlight, I'll need 480W of solar panels. 2400Wh/5h= 480W of solar.

Step 2 - Finding out which charge controller will do the job for the available solar wattage.
By dividing the solar wattage by the battery voltage I can determine the minimum required charge controller current(A) rating. 480W / 24V = Charge controller of minimum 20A rating, for precaution, should go 25-30A?

Is this correct so far?


I've also heard that in order to pick a good inverter for my system, I'll have to take into consideration the battery C rate in order to pick the maximum inverter wattage. ?

Please, feel free to correct me and share any advice/suggestions you can give me, highly appreciate it! Thanks.

Why not buy a finished system? Risk less.

[Daxo]

Starting a new thread on a Sunday may not get the response one expects. So please be patient. Answers to your questions will come.

I do have a question. You mention needing 2400wh storage but did not mention how many wh you plan on needing each day? That value and the manufacturer's claim of how much a battery can safely provide you each day it what you need to calculate your system size.

The other caution I shall mention is that if you use the "cost" as a reason to limit your system build you may end up wasting that money because the type and size of the equipment you start with is not enough to supply you what you need. That direction tends to end up costing you a lot more.

Fair point. Was just being sarcastic while checking if there's anyone on the other side or am I perhaps in the wrong forum section

In regards to your first question.
I'm on the grid so I do have the convenience to use the grid electricity to power things I need, yet, looking at how things are going in the world and here in Europe let's just say things aren't looking great in near future. That aside, I'm interested in having a solar system regardless of the possible near future electricity costs and/or possibly even grid blackouts, etc.

Basically, I'm looking to reduce my electrical bills and at the same time have a way to power essentials for a short period of time if needed. Considering inflation and how the market works, spending now sounds like a good idea if I'm to get a solar system built at any point in my life.

Initially, I'd look into using the Wh stored and the solar during the day as much as possible within the system capability I have at hand. For example, sometimes I'd power all lights, tv/laptop for the duration the storage capacity allows.

Eventually, I'd get at least 9600Wh storage at 48V. By that time, I should see what is the quality of the battery manufacturer I bought the 24v 100Ah from, and more importantly, I should know my way around solar not to burn such expensive battery storage. I hope The initial 2400Wh will not go to waste, It would just have its dedicated 575W max panel and dedicated charger.

Furthermore, I have space limitations, where I can place only a 1x 575W panel comfortably for now. Yet, even with potential 9600Wh later, the amount of sun I get where I live is pretty decent, near the sea, oriented South.

Hope I didn't bother you with all this, the list of limitations or 'parameters' goes on and on. Figure I probably should've said; It's complicated, to start with


So, the thing I'd be looking to spend the other half of the initial investment would be electronics that allow me to expand the system eventually. For instance, a charge controller that works with 12V-48V with enough voltage/current rating I could possibly use given the space limitations and the amount of solar I can fit for available space which is not much. Similar goes for the size of the solar panels, 480W up, obviously depends.

Btw, Is the math I wrote initially correct for calculating the basics of which panel/charger etc? Appreciated.

[Daxo]

Why not buy a finished system? Risk less.

Initially, I was interested in Bluetti 2048Wh, 350W, and a 2000w Inverter package. Then, I started reading and doing the math.

True, within 3000ish $ you can build a similar or slightly better system as far I can see. With a big difference in what you have in your hands for future expansion.

Without a doubt, I could be wrong, but you can get more for your buck initially and incomparably more later down the road going DIY from the get-go.

[SunEagle]

Fair point. Was just being sarcastic while checking if there's anyone on the other side or am I perhaps in the wrong forum section

In regards to your first question.
I'm on the grid so I do have the convenience to use the grid electricity to power things I need, yet, looking at how things are going in the world and here in Europe let's just say things aren't looking great in near future. That aside, I'm interested in having a solar system regardless of the possible near future electricity costs and/or possibly even grid blackouts, etc.

Basically, I'm looking to reduce my electrical bills and at the same time have a way to power essentials for a short period of time if needed. Considering inflation and how the market works, spending now sounds like a good idea if I'm to get a solar system built at any point in my life.

Initially, I'd look into using the Wh stored and the solar during the day as much as possible within the system capability I have at hand. For example, sometimes I'd power all lights, tv/laptop for the duration the storage capacity allows.

Eventually, I'd get at least 9600Wh storage at 48V. By that time, I should see what is the quality of the battery manufacturer I bought the 24v 100Ah from, and more importantly, I should know my way around solar not to burn such expensive battery storage. I hope The initial 2400Wh will not go to waste, It would just have its dedicated 575W max panel and dedicated charger.

Furthermore, I have space limitations, where I can place only a 1x 575W panel comfortably for now. Yet, even with potential 9600Wh later, the amount of sun I get where I live is pretty decent, near the sea, oriented South.

Hope I didn't bother you with all this, the list of limitations or 'parameters' goes on and on. Figure I probably should've said; It's complicated, to start with


So, the thing I'd be looking to spend the other half of the initial investment would be electronics that allow me to expand the system eventually. For instance, a charge controller that works with 12V-48V with enough voltage/current rating I could possibly use given the space limitations and the amount of solar I can fit for available space which is not much. Similar goes for the size of the solar panels, 480W up, obviously depends.

Btw, Is the math I wrote initially correct for calculating the basics of which panel/charger etc? Appreciated.

The math is not necessarily correct. It really depends on the quality of the CC and the amount of "useful" sun you get.

I can tell you that using FLA type batteries will require about 1/10th the Ah rating of the battery system to charge it. So if you have a 100Ah FLA type battery you would need about 10 amps of charging from your CC and panels. The panel rating in watts is not always the best data point and if you don't use an MPPT type CC you can lose about 1/3 the panel wattage in charging.

I try to tell people not to waste their money first and to purchase quality equipment which usually means spending a lot more up front. But again I have heard people spending a lot of money only to determine they do not have the correct things so they start over and end up spending much more.

I do not know what it costs for a kWh where you live but in the US unless you have very high rates for electricity or are able to shift the usage to a lower rate and use the battery system during the higher rate batteries will never pay for themselves. Your POCO is probably still the cheapest power generator then any of the self generating systems. But again you have to do the math and determine if using a battery instead of your Grid connection is really cheaper in the long run.

I live in Florida and just solar will take over 10 years to pay for itself and batteries will never be cheaper for me. If I need emergency power when the grid goes down it will be less expensive for me to just run my 12kw gen set. But again each location may have different reasons and costs.

[SunEagle]

Initially, I was interested in Bluetti 2048Wh, 350W, and a 2000w Inverter package. Then, I started reading and doing the math.

True, within 3000ish $ you can build a similar or slightly better system as far I can see. With a big difference in what you have in your hands for future expansion.

Without a doubt, I could be wrong, but you can get more for your buck initially and incomparably more later down the road going DIY from the get-go.

I built a small system for about $550 (80 watt panel & PWM CC, 65Ah 12v battery, 250watt inverter, battery case and a small luggage trailer) which was comparable to ones going for over $1000. If you have any DIY abilities it will always be cheaper to put the system together yourself then to purchase a complete system.

[Daxo]

The math is not necessarily correct. It really depends on the quality of the CC and the amount of "useful" sun you get.

I can tell you that using FLA type batteries will require about 1/10th the Ah rating of the battery system to charge it. So if you have a 100Ah FLA type battery you would need about 10 amps of charging from your CC and panels. The panel rating in watts is not always the best data point and if you don't use an MPPT type CC you can lose about 1/3 the panel wattage in charging.

I try to tell people not to waste their money first and to purchase quality equipment which usually means spending a lot more up front. But again I have heard people spending a lot of money only to determine they do not have the correct things so they start over and end up spending much more.

I do not know what it costs for a kWh where you live but in the US unless you have very high rates for electricity or are able to shift the usage to a lower rate and use the battery system during the higher rate batteries will never pay for themselves. Your POCO is probably still the cheapest power generator then any of the self generating systems. But again you have to do the math and determine if using a battery instead of your Grid connection is really cheaper in the long run.

I live in Florida and just solar will take over 10 years to pay for itself and batteries will never be cheaper for me. If I need emergency power when the grid goes down it will be less expensive for me to just run my 12kw gen set. But again each location may have different reasons and costs.

Have to agree with you on the ROI on battery investment, it does not look good at all, that's for sure. Unless electricity jumps by 100+ % per kWh or something. So, I've part away from looking at ROI on batteries for now.

Basically, the mentioned 2x12V LifePO4 100Ah (2560Wh) I plan to buy, costs 1000ish $ here which is about 390ish $ per 1 kWh.

So far, I'm looking into getting Victron 150/45 Charge controller, still not certain but possibly a bifacial 455W(in the test condition 25% extra possible, not guaranteed ofc), 2x12V LifePO4 100Ah (2560Wh) - if I've understood it correctly 0.5C charge/discharge max recommended, still figuring out what Inverter should I be looking at.

Sun hours, range anything from 3 hours of direct sun during Winter and even 10 hours of direct sunlight during summer. Hope it helps give a rough idea of the sun available. Obviously, doesn't account for cloudy days, etc, hoping half-cut bifacial panels can help a bit with it.

In addition, I don't have the convenience of using a gas generator either.

Again, I'm new to this. I still don't have the full picture in regards to solar, but my expectations about it are not too high either.

Thanks for taking the time and effort to help me SunEagle, goes without saying, I appreciate it very much.

[EverAzure]

Have to agree with you on the ROI on battery investment, it does not look good at all, that's for sure. Unless electricity jumps by 100+ % per kwh or something. So, I've part away from looking at ROI on batteries for now.

Basically, the mentioned 2x12V LifePO4 100Ah (2560Wh) I plan to buy, costs 1000ish $ here which is about 0,39$ per Wh.

So far, I'm looking into getting Victron 150/45 Charge controller, still not certain but possibly a bifacial 455W(in the test condition 25% extra possible, not guaranteed ofc), 2x12V LifePO4 100Ah (2560Wh) - if I've understood it correctly 0.5C charge/discharge max recommended, still figuring out what Inverter should I be looking at.

Sun hours, range anything from 3 hours of direct sun during Winter and even 10 hours of direct sunlight during summer. Hope it helps give a rough idea of the sun available. Obviously, doesn't account for cloudy days, etc, hoping half-cut bifacial panels can help a bit with it.

In addition, I don't have the convenience of using a gas generator either.

Again, I'm new to this. I still don't have the full picture in regards to solar, but my expectations about it are not too high either.

Thanks for taking the time and effort to help me SunEagle, goes without saying, I appreciate it very much.

It will be great backup power for you. Great system you did.

[SunEagle]

Just a side note. If you have a battery system you can't always rely on the sun being able to charge them. Which is why you still need another power source or generator. The fuel that the generator uses can be different depending on where you live and what is available.

[Daxo]

Just a side note. If you have a battery system you can't always rely on the sun being able to charge them. Which is why you still need another power source or generator. The fuel that the generator uses can be different depending on where you live and what is available.

Unfortunately, I can't use a gas generator since I own a small apartment within a residential building. Although it's small, only 5 stories high, some considerations have to be made towards my neighbors. It's mostly how it is in Europe. There are folks that own a house too. Just not me, obviously Not that I would like to get into the expense of maintaining a house, etc, either.

That's a great tip tho, maybe I could at least consider some sort of wall charger for the battery storage if such exists and charge the batteries during late hours when it's the cheaper rate per kWh to keep the batteries charged during rainy days?

[SunEagle]

Unfortunately, I can't use a gas generator since I own a small apartment within a residential building. Although it's small, only 5 stories high, some considerations have to be made towards my neighbors. It's mostly how it is in Europe. There are folks that own a house too. Just not me, obviously Not that I would like to get into the expense of maintaining a house, etc, either.

That's a great tip tho, maybe I could at least consider some sort of wall charger for the battery storage if such exists and charge the batteries during late hours when it's the cheaper rate per kWh to keep the batteries charged during rainy days?

Having a separate charger besides the panels is an insurance policy but if the grid is down and the sun is blocked by clouds those batteries will die requiring a new purchase. IMO if you own batteries you still need multiple ways to charge them especially if the sun is not available.

Another question is if you live in an apartment then where will you be able to mount solar panels?

[Daxo]

Having a separate charger besides the panels is an insurance policy but if the grid is down and the sun is blocked by clouds those batteries will die requiring a new purchase. IMO if you own batteries you still need multiple ways to charge them especially if the sun is not available.

Another question is if you live in an apartment then where will you be able to mount solar panels?

I guess if it gets that serious, I'll borrow a gas generator and use it to keep the batteries healthy for sure, here and there ofc.

Oh, did I mention, it's complicated? Sorta

Long story short, I'll be making the panel installation on my balcony, the reason why I'm considering using the 'larger' solar panels from the get-go. As far as I can see they are more cost-effective and provide more power for the space they occupy.

It will have to do for now, because all of us owners got together and decided to invest and refurbish our building roof and facade with a higher energy efficient one using proper insulation.

Basically, It wouldn't be wise for me to make any roof installations until the work on the building is done.

The only thing going in my favor at the moment is that my balcony is facing south and is 'bathed' in sunshine the whole day. Yet, I'll only know how good or bad it will be once I actually start using the system. Cross fingers

[Daxo]

Was curious to check the home load path for a backup system of 8 hours for a 'small' load for essentials.

For a 300W load at 24V, It would require a 12.5A (rounded 15A) of DC current. If my math is correct(300W*8H)/24V, that would require a 100Ah battery capacity.

It's recommended to charge the batteries at the current of 10% of its capacity? That's 100Ah*0,1= 10A charging current. (valid for LifePO4 too? )

Solar panel bit as far as I've understood it. Solar Array Current, Battery charging current +load current, 10A + 15A = 25A. So, apparently, it's said that Solar Array power is V*I, 24V*25A = 600W of solar.

Here's the bit It gets confusing for me.

If it's recommended to charge the battery with a current of 10% of its capacity which is 10A.

If I understand correctly, CC(charger) will always take solar W / Battery V = Charging current?? 600/24= at 25A?

Am I missing something or did I mess something up here? It sure looks contradictory to the recommended battery charge current. ?

As always, I appreciate the help.