Off grid LED solar lighting without batteries

Thread Starter

Max20

Joined Mar 11, 2019
8
I have 2 COB LEDs (12-14V DC, 50W, I think with 3,75 A in data sheet). I need to run them with a solarpanel, it should only run when there is sunlight no batteries needed. So I figured out I could use a 270W panel (open circuit voltage around 38,8V, optimium volt+curr: 32V, 8,4A) with 2 parallel connected DC DC Step Down Buck Converters 8-40V 10or12A Constant, adjustable current+voltage to run them both seperately, but I am concerned because the maximum voltage of the solarpanel gets really close to the maximium the Buck Converters can handle. Or I could use just one LED with a 130 W Solarpanel (open circ. volt 22,8V, opt. volt+curr: 17,6V 7,4A) with a 7-32V DC DC step down buck Converter 8-10A also constant adjustable curr+volt. But here I am concerned that the input voltage may get too low for the Converter (because just 38% of the current of the max. output is needed and because the voltages of the solarpanel get even lower when the temperature gets over the 25°C Standard-conditions.) so that there is a bad efficiency when there is no perfect sunlight shining.

Or are my concerns unfounded

Please help…
 

pmd34

Joined Feb 22, 2014
520
Hi Max, certainly I would avoid the first possibility, that you have a bit too much sun and it pushes you over your voltage limit. (Though you could always put in some simple over voltage protection.)

Under voltage is not a too big a problem with a buck converter as effectively the "switch" in the buck just stays closed and runs the full voltage into your load, but it would give you annoying dimming of the LEDs.

To be honest I would just look for a higher voltage converter. You could opt for one that has an external mosfet, these are usually able to cope with higher voltages, you will also benefit from the additional possibility to dissipate the heat better as you are handing quite a bit of power. Texas instruments, has quite a good parametric search for things like this.

If you want ultimate flexibility you could look for a "SEPIC" converter this has step up and step down possibility.

Considering your application however I would look to see if there are any specific LED drivers available, as your really need to run them in constant current mode, rather than constant voltage which is the norm, for switching regulators, and it would be simpler if you could get this in one package, rather than having to trick the feedback on a normal DC-DC converter.
 

Yaakov

Joined Jan 27, 2019
3,757
I have 2 COB LEDs (12-14V DC, 50W, I think with 3,75 A in data sheet). I need to run them with a solarpanel, it should only run when there is sunlight no batteries needed.

Please help…
Could you explain why you are avoiding batteries? It might help making your goal more clear. It’s an odd constraint, and it complicates things.
 

Thread Starter

Max20

Joined Mar 11, 2019
8
Thank you very much for your Responses.
I just thought that I would not need them neccessarily, and I was unsure about the durability/longevity of solarbatteries, but I just read they can hold approx. 20 years what would be the lifespan of a solarpanel anyway so no problem I guess. I’m still unsure about the prices of solarbatteries.


I think you are right I could maximize the efficency and the shining time of the LED(s) with a small solar battery (20Ah? 12V maybe?) and a standard or MPPT Charge Controller (?) where the solarpanel is wired to the input of the Charge Controller, the battery is wired to the battery Output of the charge Controller and the LED is connected to the second Output of the Charge controller, right? (Or should I wire the LEDs directly to the battery, how can I be sure that the LEDs getting 12-14V, 50W?) Am I right that I can reduce flicker and dim of the LEDs to a minimum, because I think the COB LEDs are not dimmable.


What setup and size arrangement would you recommend me unfortunately I am not very keen on batteries,.. I only read about dc/dc converters etc the last weeks.

130W (or 270W) solar with mppt-charge controller and small(?) battery with one (or two) 50W cob LED? In the case of a 20ah battery with 12v it could provide the led for 4,8 hours when fully charged (0,24kwh), so a bigger solarpanel will just charge the battery more, but too big is bad too because energy is lost again because it can’t be storaged or used, am I right here?




Side Note: the effectivity of a such a system-size (130W solar / 50W LED) with no battery is just about 45% on a sunny day because overproduction cannot be used and it only works well when the sun is fully shining if my calculcations are correct. So that would be really bad from energy perspective.
 

Yaakov

Joined Jan 27, 2019
3,757
Thank you very much for your Responses.
I just thought that I would not need them neccessarily, and I was unsure about the durability/longevity of solarbatteries, but I just read they can hold approx. 20 years what would be the lifespan of a solarpanel anyway so no problem I guess. I’m still unsure about the prices of solarbatteries.

130W (or 270W) solar with mppt-charge controller and small(?) battery with one (or two) 50W cob LED? In the case of a 20ah battery with 12v it could provide the led for 4,8 hours when fully charged (0,24kwh), so a bigger solarpanel will just charge the battery more, but too big is bad too because energy is lost again because it can’t be storaged or used, am I right here?
In general, uncertain energy sources like solar and wind are best buffered through some storage, batteries being the most common for small systems.

It makes the design easier, and it provides benefits for times when the sun is not shining or the wind not blowing. Which brings me to a second question to understand your project: why do you need LED lighting when there is full sun? How will this be used? It's an odd situation that in strong daylight you want lighting.

Will it never be useful to have lighting when the sun is down? I think we could understand better if you explain why you won't need light when it is dark.
 

Thread Starter

Max20

Joined Mar 11, 2019
8
In general its a proof of concept of something I am thinking about a long time already and I would like to do to get a better idea of solar panels, I already started a discussion about this topic in a german solar forum because I am from Germany

But I feel I need more assistance right now to make this. The inspirations comes from this DIY instruction https://www.instructables.com/id/DIY-Off-Grid-LED-Grow-Light/ (this one is in English)


The initial idea was just to convert sunlight into electricity and then back to light (which comes along with really bad effectivity, I know). And this only when the sun is shining, so sun shines, lamps shine. I would use this setup for pregrowing vegetables for a start and then eventually chilis, which would be nice to have the full year and therefore use the sun even in wintertime (with supportlight of course, which maybe can reduced with the battery idea because the lighting time of the LEDs could be longer bc the efficiency is better, if the LED could light up to 20 hours that would be perfect but I think its not easy to do efficient because the solaroutput in my area is “just” 1070 kwh per kwp solar installed, I know in the US especially California, Texas it would be 80 % more or so… ) So it basically doesn’t matter when the lights are on, daytime, nighttime, just photosynthesis has to go on, I just thought that it would be better if all (or now some) energy is used directly because there is no need to store all for later, the sunlight needs to be as effective as possible converted to Plant Full Spectrum COB LED light energy.


I hope that answers all questions and gives a background what the priorities of this project are.


And for this setup I am searching for a good assembling of the components.
 

Yaakov

Joined Jan 27, 2019
3,757
In general its a proof of concept of something I am thinking about a long time already and I would like to do to get a better idea of solar panels, I already started a discussion about this topic in a german solar forum because I am from Germany

But I feel I need more assistance right now to make this. The inspirations comes from this DIY instruction https://www.instructables.com/id/DIY-Off-Grid-LED-Grow-Light/ (this one is in English)


The initial idea was just to convert sunlight into electricity and then back to light (which comes along with really bad effectivity, I know). And this only when the sun is shining, so sun shines, lamps shine. I would use this setup for pregrowing vegetables for a start and then eventually chilis, which would be nice to have the full year and therefore use the sun even in wintertime (with supportlight of course, which maybe can reduced with the battery idea because the lighting time of the LEDs could be longer bc the efficiency is better, if the LED could light up to 20 hours that would be perfect but I think its not easy to do efficient because the solaroutput in my area is “just” 1070 kwh per kwp solar installed, I know in the US especially California, Texas it would be 80 % more or so… ) So it basically doesn’t matter when the lights are on, daytime, nighttime, just photosynthesis has to go on, I just thought that it would be better if all (or now some) energy is used directly because there is no need to store all for later, the sunlight needs to be as effective as possible converted to Plant Full Spectrum COB LED light energy.


I hope that answers all questions and gives a background what the priorities of this project are.


And for this setup I am searching for a good assembling of the components.
Well, consider this, at peak times you will not be able to use all the entire output of the solar array if it is scaled so that it has to run the lights directly in the average case. You've acknowledged the inefficiency, and this allows you to scale the solar array down since the battery can deal with the slack.

The proper way to do the design is to calculate the precise load of the LEDs over the time you expect to run them. There are rigorous design parameters once you know the solar availability and the actual load. That should be no problem to find online.

I understand this is a sort of intellectual exercise but I am not completely clear why you wouldn't want to use the direct sunlight both to charge batteries and provide growing light when that's possible, then use the LEDs when the sun becomes less or un-available. Why the isolation from the sun, that seems to be the goal, what's the idea behind it?
 

BR-549

Joined Sep 22, 2013
4,938
I have never installed a solar system for anything near that power. But I will throw some advice your way. Before you go buying stuff.....you need to confirm the amount of power that you THINK you're gonna get. And to get it you need a buffer....a battery.

It's hard to estimate or get reliable data without measurements. I have seen and read of a lot of disappointments AFTER a solar home brew installation.

In my opinion, a solar station is like radio communication.......it's all in the antenna.

My small power installations were successful, because I tripled solar area and doubled battery capacity specifications.

All of my systems were off grid and could still charge batteries with bullet holes or several inches of snow.
 

spinnaker

Joined Oct 29, 2009
7,835
In general its a proof of concept of something I am thinking about a long time already and I would like to do to get a better idea of solar panels, I already started a discussion about this topic in a german solar forum because I am from Germany

But I feel I need more assistance right now to make this. The inspirations comes from this DIY instruction https://www.instructables.com/id/DIY-Off-Grid-LED-Grow-Light/ (this one is in English)


The initial idea was just to convert sunlight into electricity and then back to light (which comes along with really bad effectivity, I know). And this only when the sun is shining, so sun shines, lamps shine. I would use this setup for pregrowing vegetables for a start and then eventually chilis, which would be nice to have the full year and therefore use the sun even in wintertime (with supportlight of course, which maybe can reduced with the battery idea because the lighting time of the LEDs could be longer bc the efficiency is better, if the LED could light up to 20 hours that would be perfect but I think its not easy to do efficient because the solaroutput in my area is “just” 1070 kwh per kwp solar installed, I know in the US especially California, Texas it would be 80 % more or so… ) So it basically doesn’t matter when the lights are on, daytime, nighttime, just photosynthesis has to go on, I just thought that it would be better if all (or now some) energy is used directly because there is no need to store all for later, the sunlight needs to be as effective as possible converted to Plant Full Spectrum COB LED light energy.


I hope that answers all questions and gives a background what the priorities of this project are.


And for this setup I am searching for a good assembling of the components.

You have heard of greenhouses? Thy have only been around for about 1000 years or so and have been doing a pretty good job all that time.
 
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Thread Starter

Max20

Joined Mar 11, 2019
8
Haha, no I'not in a legalized state since I'm in Germany, but as i stated above :)
Thank you very much for your answers. I already got the LEDs and the Solarpanel it only cost me around 130 Euro including the cables.

https://de.aliexpress.com/item/DC-D...108.1000016.1.4b271687MNVqOZ&isOrigTitle=true

I got the idea to try it with a buck/boost converter (link) to hopefully solve the voltage problem that comes with a 150W Mono solar cell at higher temperatures (shift down to almost 12V in the worst case (75°C and 30-40% irridiance, so enough % of Peakwattage to power the LEDs )), what do you guys think does it work better that way than with a buck converter? So in this way: Solar panel -> Buck Boos converter -> LED

I mean the Buck boost converter only costs about 3$ so... Instead of a Buck converter.

If this doesnt work out I will give the battery + Charge Controller solution a try, but at first I want to try it that way bc battery and mpp Charge Controller will be 100 additional Euro.
I didnt know that the 12V LED only got 30% Efficiency so it would be better to take a 30-36V (50W) LED and a boost converter..?

It really sucks that the energy price in Germany is as high as 30 EURO-Cents per kwh (and still rising by 5-10% per year, already the highest in europe, maybe worldwide?) its ridiculous. So solar Experiments and Knowledge can be usefull i guess.
 

Thread Starter

Max20

Joined Mar 11, 2019
8
But yes I should have known that, higher voltage, lower amps mean less heat, so there Comes another Advantage with a buck boost converter i guess, because I can go higher with the voltage as I thought (13,5 instead of 12,5V with the buck converter to slightly better handle the temperature-caused voltage Drops) And for the Buck Boost Converter it should be of no or little concern if 13,5 or 12,5V are adjusted because it can both, also a Switch of the converter just stays opened when it gets the same vin as vout is adjusted, am i right? just the current gets witheld in that case)
 

spinnaker

Joined Oct 29, 2009
7,835
Haha, no I'not in a legalized state since I'm in Germany, but as i stated above :)
Thank you very much for your answers. I already got the LEDs and the Solarpanel it only cost me around 130 Euro including the cables.

https://de.aliexpress.com/item/DC-D...108.1000016.1.4b271687MNVqOZ&isOrigTitle=true

I got the idea to try it with a buck/boost converter (link) to hopefully solve the voltage problem that comes with a 150W Mono solar cell at higher temperatures (shift down to almost 12V in the worst case (75°C and 30-40% irridiance, so enough % of Peakwattage to power the LEDs )), what do you guys think does it work better that way than with a buck converter? So in this way: Solar panel -> Buck Boos converter -> LED

I mean the Buck boost converter only costs about 3$ so... Instead of a Buck converter.

If this doesnt work out I will give the battery + Charge Controller solution a try, but at first I want to try it that way bc battery and mpp Charge Controller will be 100 additional Euro.
I didnt know that the 12V LED only got 30% Efficiency so it would be better to take a 30-36V (50W) LED and a boost converter..?

It really sucks that the energy price in Germany is as high as 30 EURO-Cents per kwh (and still rising by 5-10% per year, already the highest in europe, maybe worldwide?) its ridiculous. So solar Experiments and Knowledge can be usefull i guess.
From what I see your panel produces ~38V. You already have plenty of voltage to light 12V LEDs. A boost converter does not reduce voltage it increase it. You don't need to limit voltage with LEDs. What you do need to do is limit current. There are LED drivers that do this.

Exactly what LEDs are you using? I have never heard of LEDs with a forward voltage of 12V. If it is one of those lights, it may already have a current limiter inside the light.
 

spinnaker

Joined Oct 29, 2009
7,835

Thread Starter

Max20

Joined Mar 11, 2019
8
https://www.ebay.de/itm/10DC12V-50W...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649


Here it is sorry..
But I thought Voltage needs to be limited too as it can bea above14v and i planned to use the LED at 13V / 3,5 A. But as i said the voltage of the panel can get as low as 12 V for the worst Case with 400 w/m2 irridiance and 75 Celsius Panel temp and in this Case i need to Booster the voltage a Bit altough it needs to lowered the Rest of the time.
 
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