Good Day,

I am proposing to use a 12 V, 20 Watt solar panel to generate DC voltage and current directly to power a buck converter at 12 Volt, 1 Amps to a 11 Watts DC load continuously 24/7.

I do not want to use a battery to charge, discharge and store energy in alliance with the solar panel. Instead, I want to use a 12 Volt dc adapter to supply back up power by automatic switching to the dc load when the solar panel is producing low power and at night when solar panel does not work.

I tried searching for modules but couldnt come to a solution for this application. If this is possible pls link me to any module that can be used for this purpose. Any other circuit ideas would be greatly appreciated.

1. I need the 12 Volt solar panel to power the load through the buck converter. This is pretty straight forward since the buck converter would adjust itself to minor variations in voltage during daytime.

2. When the power output from the solar panel drops during cloudy conditions and at night, I need to automatically changeover to the 12 Volts from dc adapter connected to mains. Low power delivered from solar panel to the buck converter should be avoided.

3. When the power output at the Solar Panel is back to normal, which is the Voltage coming to 12 Volts, I need the load switching automatically to solar power disconnecting itself from the mains adapter.

Thanks.

 

The simple scheme to do this is to use two diodes, commonly called a diode or function. Use diodes with a low forward voltage drop and the load will always be supplied by whichever source supplies the higher voltage. Simple and automatic.

 

There are 12V "Voltage control relay modules" available on AliExpress for around $10.00 that will do what you want. This one is a dual mode one but ignore the timer mode. It will monitor the input voltage and switch the NC/NO contacts of a relay that will easily handle the power:
https://www.aliexpress.com/item/329...-url=scene:search|query_from:#nav-description

 

There are 12V "Voltage control relay modules" available on AliExpress for around $10.00 that will do what you want. This one is a dual mode one but ignore the timer mode. It will monitor the input voltage and switch the NC/NO contacts of a relay that will easily handle the power:
https://www.aliexpress.com/item/329...-url=scene:search|query_from:#nav-description

Thanks but I doubt if it can be used for this purpose. These are the applications from the maker for this module...

 

That is not the one. Here it is and how to connect it:
NOTE: You also need to connect the controller power input to the DC adapter.

 

What I read in post #1 is that the TS wants to power an 11 watt load constantly, either from the solar cell array or from an AC adapter.
I am a bit puzzled because not only does the TS not mention switching the adapter mains power off when not using it to power the load, The problem with that is that when the adapter is not delivering power to the load the efficiency is ZERO!!.
In addition, every one of the replies with a circuit show a battery, while the TS rather clearly stated NO BATTERY.
In addition, where did these responders find the information as to how that module functions?? My observation is that what it does was not explained in any of the printing that I was able to read.

 

What I read in post #1 is that the TS wants to power an 11 watt load constantly, either from the solar cell array or from an AC adapter.
I am a bit puzzled because not only does the TS not mention switching the adapter mains power off when not using it to power the load, The problem with that is that when the adapter is not delivering power to the load the efficiency is ZERO!!.

_____________________________________________________________________________________________________
When the adapter is not powering the load, it is only supplying a very small current to the Voltage switch controller. How can its efficiency be zero? (See my wiring diagram above).
______________________________________________________________________________________________________

In addition, every one of the replies with a circuit show a battery, while the TS rather clearly stated NO BATTERY.

______________________________________________________________________________________________________
The connection diagram that I posted does NOT show a battery. (See my wiring diagram above).
______________________________________________________________________________________________________

In addition, where did these responders find the information as to how that module functions?? My observation is that what it does was not explained in any of the printing that I was able to read.

______________________________________________________________________________________________________
Except for you, I am the only responder. The inserts were copied directly from the AliExpress pages. I drew the wiring diagram using the information provided. Below the illustrations on the vendor's page, there is a detailed description of the product.

 

What I read in post #1 is that the TS wants to power an 11 watt load constantly, either from the solar cell array or from an AC adapter.
I am a bit puzzled because not only does the TS not mention switching the adapter mains power off when not using it to power the load, The problem with that is that when the adapter is not delivering power to the load the efficiency is ZERO!!.
In addition, every one of the replies with a circuit show a battery, while the TS rather clearly stated NO BATTERY.
In addition, where did these responders find the information as to how that module functions?? My observation is that what it does was not explained in any of the printing that I was able to read.

Regret any misunderstanding. I have stated that the load must be powered primarily by the solar panel. When there is low voltage at the solar panel at cloudy conditions and at night I wanted the load to be powered by the dc adapter automatically and changeover to solar energy when solar panel is producing normal output.

I am not understaning the idea about the adapter efficiency. When adapter is taken over by solar power, the adapter supplies power only to the control module continuously. When sufficient voltage is available at the solar output terminals then the load is powered by solar power.

I posted those drawings from the maker to show that module could not be used for my purpose.

Keithwalker clearly explained that module was a different one. Also thanks a lot Keithwalker for pointing out the correct module and also for the wiring drawing, I will try to look into that setup.

Any other method or circuit also will be greatly helpful. Thanks a lot for the responses.

The idea here is to conserve power from the mains by using solar power without using a battery during daytime when solar power is available and switch over to mains power when solar output is not sufficient.

 

KeithWalker,

Unfortunately this module is not available for delivery to my location so I have to let go of that option.Thanks for making the circuit drawing and suggesting this solution.

I am thinking of using this emergency power swiching module here:

https://www.xcluma.com/xh-m350-back...utomatic-switching-battery-power-12v-150w-12a

It switches to battery power when the mains power is completely out. So I am planning to connect the solar power to the main source and adapter power as emergency source. When solar power goes off, the adapter power will take over.

But the problem here is the solar voltage should be fully off for this to work. It does not use a voltage sensor in which settings could be made. So I am planning to incorporate this battery protection module which is used for disconnecting load when battery voltage drops below certain level. I connect the solar output voltage to the input of this module and the output is connected to the other emergency switching module.

https://www.electronicscomp.com/xh-...HGCzDDMmGDYBN5dSfVSzdm0CmNdPXxihoC8V8QAvD_BwE



I hope this should do the trick.

 

This is pretty straight forward since the buck converter would adjust itself to minor variations in voltage during daytime.

You really think so? Seems like a rather naïve understanding of the workings of solar panels to me. You need an MPPT!
A 20W solar panel will give you 20Watt-hours per day in winter and 80 in summer (depending on your location which you don't state) somewhere between 7.5% and 30% of the energy required, actually rather less because the 9W spare when the solar panel is at full power cannot be used, and the adaptor will probably be consuming its legal maximum standby power of 0.5W when the load is powered by the solar panel, that's probably another 6Wh lost energy every day.
Doesn't seem like it's worth the bother.

 

You really think so? Seems like a rather naïve understanding of the workings of solar panels to me. You need an MPPT!
A 20W solar panel will give you 20Watt-hours per day in winter and 80 in summer (depending on your location which you don't state) somewhere between 7.5% and 30% of the energy required, actually rather less because the 9W spare when the solar panel is at full power cannot be used, and the adaptor will probably be consuming its legal maximum standby power of 0.5W when the load is powered by the solar panel, that's probably another 6Wh lost energy every day.
Doesn't seem like it's worth the bother.

Yes you are right, I do not have much understanding about solar panels. So the minimum power a 20 Watt solar panel can supply per day is 20 Watt hours in winter and 80 Watt hours in summer. If I run a 11 watt load continuously for 12 hours from sunrise to sunset then I need 132 Watt hours of energy. You are right, I looked into the details now. Before in some sites they said it produces 20 watt hour of energy in one hour. That is not right. Especially in my case I do not want to use a battery to store the energy.

So, could you please suggest me the rating of solar panel that could be used for this purpose. Could a 40 watt solar panel provide the power directly to this load (without a battery to store and discharge energy).

I live in Chennai, Sothern part of India in Asia. Always get 12 hours of sunlight from morning 6 am to evening 6 pm. Mostly hot weather from March to July. Max temp will reach to 40 degrees Celcius, average 37 degrees during summer. November to February will be coloer compared to that and min temperature does not fall below 22 degrees celcius.

Please look into the circuit I made using the emergency switch over module and the battery protection module. Battery protection module takes power supply from solar power then supplies to emergency switching module. It changes over to adapter power only at night when solar power is insufficient and no power is consumed at standby condition from the adaptor so the 6 Watt hour energy loss per day you mentioned is avoided (a controller taking power from adaptor is not used to switch the power supplies).

Thanks.

 

I live in Chennai, Sothern part of India in Asia. Always get 12 hours of sunlight from morning 6 am to evening 6 pm. Mostly hot weather from March to July. Max temp will reach to 40 degrees Celcius, average 37 degrees during summer. November to February will be coloer compared to that and min temperature does not fall below 22 degrees celcius.

Thanks.

The figures from Britain are just an example. We get a variation in daylight hours from 7.5 in winter to 16.5 in summer, and that makes a big difference.
My brother-in-law lives in Denver, Colorado, which is the same latitude as the south of France. Colorado gets much better solar in the winter, because the air tends to be clear and dry, but southern France had rainy winters.
Chennai being coastal (I know where most of the Test Match grounds are!) probably has more cloud, and seasonally, monsoon probably makes much more difference to solar yields than daylight length.
The power varies with the angle of the sun, so 12 hours of sun from a clear sky does not equal 20Watt.hours from a solar panel.

 

Any time the power out from a device is zero but the input power is not zero, the efficiency is zero. And not all power supplies have a "very small" no-load power input. Certainly some are better than others, though. And OK, not every post contained a circuit with a battery, but several of them did.
And it is not clear where the operation information for the modules came from, I saw none of it in the links given. Perhaps there was more if one went farther in, which I did not do.
The requirement for having a maximum power circuit is based on the need for obtaining the maximum possible power, which is quite different from just getting enough power to supply the intended application. It would certainly be appropriate for a battery charging system with the goal of collecting the maximum possible amount of energy in a storage system.

 

Can someone please tell me why @MisterBill2’s suggestion in post #2 is being ignored? It seems to me that it does exactly what is desired. It uses power from the solar panel as long as it can produce 12V+ at the needed current and switches to the 12V adaptor when it cannot. And with the simplest circuit imaginable.

 

The maximum output would be obtained from the solar panel if its output were kept at its MPPT voltage (which varies with temperature, but hardly at all with current). So, if the power supply were chosen (or adjusted) to output the MPPT voltage of the panel, rather than 12V, then diode-or with the solar panel, then regulated to 12V, it would maximise the use of the free power.

 

The "buck converter" mentioned in post #1 will tend to avoid wasting power, to some extent. But the TS already has the buck converter, I think. The Maximum Power Point Translator is a great invention, but certainly not a small and simple device. Even the math involved for the MPPT function is not simple. So the added power gained would be rather expensive in an area described by the TS as having a lot more free power available than where I live. So there does seem to be a cost to benefit ratio to consider in this case.
Besides that, there is the issue of simplicity. Connecting two adequately sized and rated diodes is a much simpler task than even just selecting an MPPT package. And the diodes will not require any adjustment or calibration.

 

BobTPH, MisterBill2 and Ian0,

Thanks all for your responses. Yes I already have the buck converter. I also looked into the possibility of using the low forward voltage drop diodes. I am not well versed with design using diodes in circuits. So it would be greatly helpful if you could link me to the details of how this circuit can be designed and what is the type and rating of the diodes that could be used in this required circuit.

The MPPT module be incorporated into this as an add on to improve efficiency I suppose that is available at a fair cost.

https://zbotic.in/product/cn3791-12...qlm6qTs0dKijKcw46SfFxUqYU6c_e5m0aAoh9EALw_wcB

But those are designed for batteries, could I be able to use it for direct power transfer to the load. The main reason I do not wish to use a rechargeable battery is the cost of low energy battery and they last for 2 years losing capacity over time. The cost of replacing them will be avoided if I could use the solar panel directly to power the load and secondary power from the adaptor.

 

The maximum output would be obtained from the solar panel if its output were kept at its MPPT voltage (which varies with temperature, but hardly at all with current). So, if the power supply were chosen (or adjusted) to output the MPPT voltage of the panel, rather than 12V, then diode-or with the solar panel, then regulated to 12V, it would maximise the use of the free power.

The problem with that is that the max power will often be below what is needed, so the gain is only in that region where the output is below the needed voltage but above the needed power. How large is that region? Beats me.

The OP says he is using a buck converter from the solar panel OR a 12V supply. I read this as the panel produces more than 12V when it has enough sun to power the load, and the load requires 12V. If that is the case, the diodes would supply power pretty much during the same periods as the MPPT controller would. MPPT controllers work best when charging a battery, where any amount of power is useful. That is not the case for this project. Adding a battery and an MPPT controller would maximize the free energy used.

To the OP:

Solar panel to buck converter to diode to load.
12V adapter to diode to load.

Assuming I am right about the load needing 12V power. The solar panel would then power the device as long as the output if the buck converter was more than 12V at the required current.

 

To the OP:

Solar panel to buck converter to diode to load.
12V adapter to diode to load.

Assuming I am right about the load needing 12V power. The solar panel would then power the device as long as the output if the buck converter was more than 12V at the required current.

I think I am misunderstood. The project is that the buck converter powers the load in both cases of the adapter and the solar power at 12 V (in case of solar panel, voltage rating is 12V and it varies depending upon sunlight and other factors). The input power to the buck converter is powered by the solar panel when daytime and the 12V dc adaptor automatically switches to power the buck converter at night and reduced power output. The adapter does not power the load directly.

In both cases, the load takes power supply through the buck converter. The load connected to the output of the buck converter is a constant current dc inductor and I set the current to constant 2.5 A on the buck converter module. When adapter supplies power at 12V, the buck converter reduces it to provide a constant 2.5 A current to the load. When solar panel takes over, that might have changes in Voltage to the input of the buck converter, but since the current is set to constant 2.5 A the buck converter would adjust to the varying voltage from the solar panel, providing constant current to the load.

Thanks for your understanding.

 

Thank you for the clarification.

In that, case, the diodes would go between the solar panel and converter and between the 12V supply and the converter. But 12V may not be the right voltage to use.

To really design this we need to know the characteristics of the solar panel and the load.

Solar panel:

Open circuit voltage?
Short circuit current?
Max power point voltage and current?

Load:

Voltage at which it draws 2.5A? This should be constant if it is just an electromagnet.

Buck converter:

Any specs you have?