First post, first solar project, very basic - Please critique / questions before buying

[quintinha]

Hello all,

This is my first post here. Thank you to everyone who contributes to this forum, it's a goldmine.

After a lot of reading I'm just about ready to buy stuff. The project is very basic and I'm trying to keep it as plug-and-play as possible: my goal is to place approximately 25-30 1w and 2w LED bulbs around my yard for nighttime lighting. I'm shooting for somewhere around 30 watts running for 4-6 hours per night.

Here are the specs of the items I'm planning to buy (Please excuse the Portuguese, I'm American but live in PT):

TLDR
1x 100W panel, 5ish amps, 18ish volts
1x lifepo4 12v 20ah battery, 10amp max charge, 4amp max discharge
1x victron 75/10 mppt controller
a bunch of low-watt outdoor lights

Panel
https://www.castroelectronica.pt/pt...taico-silicio-monocristalino-100w-12v--proftc
Potência nominal: 100W
Corrente de Potência Máxima (Impp): 5.39A
Tensão Máxima de Energia (Vmpp): 18.56V
Tensão de circuito aberto (Voc): 21.76V
Corrente de curto-circuito (Isc): 5.72A
Tensão máxima do sistema: 100V

Battery
https://innpo.pt/baterias-recarrega...ah-innpo-baterias-recarregaveis-de-litio.html
Tecnologia LiFePO4
Tensão nominal 12,8 V
Capacidade 20 Ah
Corrente máxima de carga 10A
Corrente máxima de descarga 4A

Controller
https://innpo.pt/controlador-de-car...ictron-energy-controlador-de-carga-solar.html
Tensão da bateria 12/24V
Corrente de carga nominal 10A
Potência nominal FV, 12V 1a,b) 145W

30w from a 12v battery is 2.5A, so the battery's max discharge of 4A should be good.
Running the lights an average of 5 hours per night is 150w of power. The battery should provide more than 200wh so at least on a sunny day it should be groovy.

I'm open to suggestions if I've overlooked anything, please let me know what you think.

The one question I have remaining in general about how this all works is about the relationship between the controller and the battery: the battery says 10A max charge current (although it states 20A in the spec sheet, I need to clarify this with the manufacturer) and the controller says 10A charge current. The panel produces max 5.39A and 18.56V. From reading this thread I understood that that controller will drop the voltage received from the panel to match the battery it's charging thereby increasing the amps:

An MPPT solar controller can be imagined as a specialized DC-DC converter that feeds the battery its desired charging voltage. By lowering the output voltage, a higher current can be drawn by the battery, so in a way, voltage is „turned into current“. However, there is no „waste“ in the sense that energy is purposely converted to heat, it is merely a side effect of the process that is not 100% efficient.

So (dirty example) if a panel sends the controller 20V at 5A, that's 100w, but the battery wants 14V not 20V, so the controller sends it 14V at 7.1A for the same ~100w it received from the panel (ignoring system loss and whatnot). As long as the battery's max charge current rating is greater than what the controller is sending, and the controller's max current rating is greater than what it's receiving and sending, it's all gravy. Is that right, if a bit oversimplified?

Thanks! and happy building

 

[Daddy Tanuki]

yes for a MPPT controller not sure it works that way for a PWM controller. I think the PWm is simply off on off on off on in a cycle that controls the voltage to the set points that are programmed in, as such I do not think (double check this please) that it would increase the amps.

 

[ScrotpusGobbleBottom]

As long as the battery's max charge current rating is greater than what the controller is sending, and the controller's max current rating is greater than what

Yes.
The only thing I would do different is add a second panel in parallel.
This would enable you to not worry about cloudy days much at all and would keep you up at night trying to figure out what else to do with the extra power during the sunny days.

This would firmly plant the solar bug in you and you wood be chasing your tail like the rest of us for the rest of our earthly existence.

 

[quintinha]

Yes.
The only thing I would do different is add a second panel in parallel.
This would enable you to not worry about cloudy days much at all and would keep you up at night trying to figure out what else to do with the extra power during the sunny days.

This would firmly plant the solar bug in you and you wood be chasing your tail like the rest of us for the rest of our earthly existence.

LOL

Thanks for your replies.

Hmm hadn't thought of that in quite the way you've presented it. It is the cheapest part of the system to upgrade.

Taking this as a learning opportunity then, a second panel in parallel would double the amps. If one panel's max amp rating is 5.4A then two panels could on paper max out at 10.8A.

The victron 75/10 data sheet lists the following two specs:

• Rated charge current 10A
• Max. continuous load current 15A

I wanted to ask what the difference is between these two ratings in my original post. Max charge current is the max amps able to be sent to the battery, max load current is the max amps being received from the panels? If I've got that right then there would be no need to upgrade the controller by adding a second identical panel..?

 

[ScrotpusGobbleBottom]

• Rated charge current 10A
• Max. continuous load current 15A

It seems that this charge controller has a load port for 12v stuff. This is where it can't exceed 15 amps/ 180 watts

That its the difference. I wouldn't use it for anything but lights.

The only benefit of using the load port would be being able to switch it on off via Bluetooth or whatever

 

[Delmar]

This would firmly plant the solar bug in you and you wood be chasing your tail like the rest of us for the rest of our earthly existence.

Welcome! This is a perfect starter project to learn solar.

Per above you will catch the bug and immediately start looking to expand the system, especially for grid-down usage. I would also upgrade the battery to as much as you can afford. There is endless stuff you can buy including 12V fans, interior lights, phone chargers…

 

[Daddy Tanuki]

yes panels are the cheapest part of the equation, the most effective part of the equation however is conservation. cheaper to save then to produce. in your proposed system it is purpose made with the size of the load matched to the batteries with no inverter tare loss. this is good for small scale projects like this.

give it time and you will be building a portable that can power a window a/c through the day.... and after that.... well its your wallet and family life

 

[ScrotpusGobbleBottom]

Yes, welcome to the forum!

 

[ScrotpusGobbleBottom]

I'm just sitting here thinking of how much money I've spent on copper....

.. well its your wallet and family life

That is so true

 

[Daddy Tanuki]

I'm just sitting here thinking of how much money I've spent on copper....



That is so true

You??? thank god I have multiple income streams that my wife does not necessarily know the remuneration of

 

[quintinha]

Thanks a lot yall for the warm welcome.

It seems that this charge controller has a load port for 12v stuff. This is where it can't exceed 15 amps/ 180 watts

That its the difference. I wouldn't use it for anything but lights.

The only benefit of using the load port would be being able to switch it on off via Bluetooth or whatever

Well now I have to admit how little I still know/haven't yet learned. For some reason I've thought up until now that - at least for little stand-alone setups like this - the load always/normally comes out of the load ports of the controller, whether PWM or MPPT. But your response makes me think that people bypass the load ports of the controller and pull their load directly off the battery..? Sorry if I misunderstood your reply.

And following up on the extra panel idea, if the 15A rating is for the load from the battery, that would mean the 10A rating is for the load to the battery..? And that would mean that the "Rated charge current 10A" of the controller would not suffice for the two panels, as on paper the max current could go above 10amps (5.39 x 2)..? Hope I'm not turned around here.

Welcome! This is a perfect starter project to learn solar.

Per above you will catch the bug and immediately start looking to expand the system, especially for grid-down usage. I would also upgrade the battery to as much as you can afford. There is endless stuff you can buy including 12V fans, interior lights, phone chargers…

Thanks for the advice. If I (read: wife) want the lights to stay on longer into the night then it doesn't seem too difficult to add another battery in parallel. I want to get the system built and see it working first...I'm very comfortable with DIY but electricity bugs me out a bit, going to go slowly at first.

yes panels are the cheapest part of the equation, the most effective part of the equation however is conservation. cheaper to save then to produce. in your proposed system it is purpose made with the size of the load matched to the batteries with no inverter tare loss. this is good for small scale projects like this.

Thanks, and good advice, I hadn't thought about it that way. In a sense though that perspective is exactly why I swapped an AliExpress PWM controller out for a more reputable MPPT controller while planning this out. For another $30 to drastically increase the efficiency of the system it seems like a no-brainer.

 

[ScrotpusGobbleBottom]

pull their load directly off the battery..?

For sure.
Most here use an inverter to grab thousands of watts off the battery.
You are doing native 12v lights. Native v doesn't require an inverter and is better in some ways.

I would do what you originally thought.
If the charge controller has way of switching and a low voltage disconnect. Use that for now.

 

[quintinha]

For sure.
Most here use an inverter to grab thousands of watts off the battery.
You are doing native 12v lights. Native v doesn't require an inverter and is better in some ways.

I would do what you originally thought.
If the charge controller has way of switching and a low voltage disconnect. Use that for now.

Nice. Yeah that makes a lot of sense.

Pretty sure I'll look back at this question and shake my head smiling in a couple years once the bug's bitten me and I'm 20k deep into a full-house multi kw system

So final answer, based on the specs of the panel and the controller, is it safe to add a second panel in parallel without overloading the controller?

 

[Mkgough]

Hello all,

This is my first post here. Thank you to everyone who contributes to this forum, it's a goldmine.

After a lot of reading I'm just about ready to buy stuff. The project is very basic and I'm trying to keep it as plug-and-play as possible: my goal is to place approximately 25-30 1w and 2w LED bulbs around my yard for nighttime lighting. I'm shooting for somewhere around 30 watts running for 4-6 hours per night.

Here are the specs of the items I'm planning to buy (Please excuse the Portuguese, I'm American but live in PT):

TLDR
1x 100W panel, 5ish amps, 18ish volts
1x lifepo4 12v 20ah battery, 10amp max charge, 4amp max discharge
1x victron 75/10 mppt controller
a bunch of low-watt outdoor lights

Panel
https://www.castroelectronica.pt/pt...taico-silicio-monocristalino-100w-12v--proftc
Potência nominal: 100W
Corrente de Potência Máxima (Impp): 5.39A
Tensão Máxima de Energia (Vmpp): 18.56V
Tensão de circuito aberto (Voc): 21.76V
Corrente de curto-circuito (Isc): 5.72A
Tensão máxima do sistema: 100V

Battery
https://innpo.pt/baterias-recarrega...ah-innpo-baterias-recarregaveis-de-litio.html
Tecnologia LiFePO4
Tensão nominal 12,8 V
Capacidade 20 Ah
Corrente máxima de carga 10A
Corrente máxima de descarga 4A

Controller
https://innpo.pt/controlador-de-car...ictron-energy-controlador-de-carga-solar.html
Tensão da bateria 12/24V
Corrente de carga nominal 10A
Potência nominal FV, 12V 1a,b) 145W

30w from a 12v battery is 2.5A, so the battery's max discharge of 4A should be good.
Running the lights an average of 5 hours per night is 150w of power. The battery should provide more than 200wh so at least on a sunny day it should be groovy.

I'm open to suggestions if I've overlooked anything, please let me know what you think.

The one question I have remaining in general about how this all works is about the relationship between the controller and the battery: the battery says 10A max charge current (although it states 20A in the spec sheet, I need to clarify this with the manufacturer) and the controller says 10A charge current. The panel produces max 5.39A and 18.56V. From reading this thread I understood that that controller will drop the voltage received from the panel to match the battery it's charging thereby increasing the amps:



So (dirty example) if a panel sends the controller 20V at 5A, that's 100w, but the battery wants 14V not 20V, so the controller sends it 14V at 7.1A for the same ~100w it received from the panel (ignoring system loss and whatnot). As long as the battery's max charge current rating is greater than what the controller is sending, and the controller's max current rating is greater than what it's receiving and sending, it's all gravy. Is that right, if a bit oversimplified?

Thanks! and happy building

Don't waste your time on 100w panel, get 200w as you will get 120watts or so from the 200 vs 60watt from the 100watt panel

 

[ScrotpusGobbleBottom]

Nice. Yeah that makes a lot of sense.

Pretty sure I'll look back at this question and shake my head smiling in a couple years once the bug's bitten me and I'm 20k deep into a full-house multi kw system

So final answer, based on the specs of the panel and the controller, is it safe to add a second panel in parallel without overloading the controller?

It's usually considered safe to overpanel a controller by 30 percent. Some people say 100 percent.

I would do it.

 

[ScrotpusGobbleBottom]

Pretty sure I'll look back at this question and shake my head smiling in a couple years once the bug's bitten me

Funny thing here is, you will never be done learning.
So with that said, it's was just your first step. Nothing to cringe at.

Pretty sure everyone is here because we all know that we don't know everything, But good conversation can be had while learning.

We will keep your chair at the table here.

 

[Delmar]

It's usually considered safe to overpanel a controller by 30 percent. Some people say 100 percent.

I would do it.

But the 20AH battery would be full in a couple of hours. I would spend my money on more storage.

I don't know how reliable the grid is in Portugal. You will get a dirty look from the wife when the grid is down, and your expensive hobby system is useless.

 

[ScrotpusGobbleBottom]

But the 20AH battery would be full in a couple of hours.

That is the point. Only got 4 hours in a day to charge in most places

 

[ScrotpusGobbleBottom]

expensive hobby system is useless.

We are doing lights. That is the plan.

 

[Delmar]

We are doing lights. That is the plan.

How long have you been married?

 

[ScrotpusGobbleBottom]

How long have you been married?

Long enough to be stubborn af.

 

[quintinha]

LOL @ replies

It's usually considered safe to overpanel a controller by 30 percent. Some people say 100 percent.

I would do it.

Interesting. OK I'll take that into consideration. In this particular case it's only on paper that the two panels would peak above 10A into the controller, and even then just barely. In the real world 10A into the controller is likely never going to happen.

But the 20AH battery would be full in a couple of hours. I would spend my money on more storage.

I don't know how reliable the grid is in Portugal. You will get a dirty look from the wife when the grid is down, and your expensive hobby system is useless.

That is the point. Only got 4 hours in a day to charge in most places

We are doing lights. That is the plan.

Yeah the wife wouldn't be happy at all grid-down but for better or for worse this system is indeed just for garden lighting. I'm not (yet) dabbling in home energy storage. Although I suppose I could uproot one of the strings of lights and drag them inside from the garden when the candles burn down.

I think this whole rig will run around 300-350 euros all-in with cables, bulbs, etc. I've thought about cost effectiveness while thinking through this project and my approach is a sort of "price per lumen" mentality, since all I'm after is cheap outdoor lighting. The good standalone solar lights with little panels and batteries built in - not the crap in the big box stores with 2 lumens that die in one season - seem to run at least 10-15 euros each. 30 of them around the yard and I'm already at or above the price of this setup, the main difference being that about half of the area I want to illuminate is part or full shade so those standalone lights wouldn't get the love they need. Doing it this way I can plant the panel for maximum exposure and run the lights wherever.

I think you're right about 4 hours charge time here, the solar insolation number (I believe that's the name) averages out to around 4.5 over the course of the year.

Grid's pretty good here. Over half on renewables, over 25% by wind turbines and almost 25% on hydroelectric. I've never lost power for more than a few hours and that was once in four years.

Thanks again all for the replies. I think I'm going to pull the trigger and order tonight. If you have any last minute considerations I'm all ears.

(Married eight years...more than enough time to be stubborn af)

 

[ScrotpusGobbleBottom]

on paper max out at 10.8A.

Yeah, that is perfect.

You do realize you might never hit 10 even with 2. And there is zero possibility of harming the controller.

 

[quintinha]

Yeah, that is perfect.

You do realize you might never hit 10 even with 2. And there is zero possibility of harming the controller.

Yep yep for sure. I don't know what the real-world average difference is between paper numbers and real-world numbers, I see people say 50%, 60%, 80%. Of course each installation is different. I read one guy here who lives a million miles up in the mountains say he gets over 100% rated output on his panels on clear cool days IIRC.

The most I have planned for optimization is a post mount that allows for angle adjustment maybe once a month or whenever I'm inspired. I figure that plus ditching the planned PWM for an MPPT controller is enough to call it good.

 

[Delmar]

Of course each installation is different. I read one guy here who lives a million miles up in the mountains say he gets over 100% rated output on his panels on clear cool days IIRC.

In the south Texas winter, on a clear 40’s day with brisk breeze my 400W of panels will actually produce 400W. Otherwise in the summer heat its barely above 300-320W.