Automatic Solar Switch

I would like to share a small project that I completed few months back. And hopefully it can help others also, who are looking for a similar solution.

In short it is a switching-system that turns ON a relay depending on the strength of sunlight.

Reason that I needed something like this was that I am using a UPS with Solar panels(through batteries) and wanted to power the load via solar-panels during strong-sunlight hours.
As per my understanding the Day-Night switching options found in Charge-Controllers are voltage dependent and nonadjustable(mostly). By the time when they switch to night/evening mode, it is quite late in evening and there is very little power coming in from panels, causing the batteries to be discharged to some extent.

I wanted something which I could adjust/set and would help me in keeping the battery-discharge to minimum when the sun was not strong enough to keep-up with the load(in evening, rain and fog).

DSC_0058_zpse7546aba.jpg

A separate 50 Watt Solar-Panel sits next to the main array. This panel is shorted via a resistor and a shunt, the voltage across the 50-watt panel and the current flowing through the resistor(and the shunt) is being measured by the DC Volt and DC Amp meter seen in the above image. On top of the box you can also see the resistor.

Value of resistor was chosen based on the panel's Max-Power Volt(Vmp) and Max-Power Current(Imp) and putting the values to the formula V = I . R
(I do have doubts if this is the correct way or not for getting the resistor value. But for now it is working)

As solar-panels are current source and their output is linked to insolation levels, I selected this method.

The volt and amp meters have Relay output. One can adjust the set-points to activate/deactivate the relays inside the meter.

DSC_0057_zps20be3789.jpg

The relay inside the ampere meter activates the timer seen above, this helps in avoiding short cycling when the current value is moving close to the set-point in the meter.

When time completes the external relay is turned On by the timer. It is wired such that the utility/wapda gets disconnected to UPS and the loads shift to battery power which is being topped via solar-panels.

Benefit is that the utility is disconnected when sun is strong. In evening, rain or fog when there is not enough power being produced by solar-panels, the UPS stays on utility and batteries are not drained. And whatever little power is being supplied by main array is helping to keep the batteries topped-up.

There will be better and cheaper options available but for me this has worked out as per my requirement.

I will try to update this post with more information. If anyone has any questions, I will be happy to help.

19-08-2014

Current setup prioritize the use of main pv array, first. Utility, second. And the batteries, third.

Looking at the current values of Volts and Amperes of 50 watts panel, provides a rough estimate of expected output from the main array.

For example as per the picture above at 13.21 V and 2.3 A, it is 30.38 watts. This 30.38 watts is 60.7% of the installed 50 watts panel.

((30.38 / 50) x 100)

And if the main array is of 1000 watts, then as per above the main array should provide with atleast 600 watts.

By adjusting the set-point on ampere meter, I can set the system to shift to utility when the main array's output is less than the average load on UPS.

For example if average load on UPS is 300 watts, I can set the ampere meter to 1.1

(600/300 = 2---> 2.3 / 2 = 1.15)

Surely, comparing a fixed resistor to an MPPT will not be accurate. But still it does give some figures to work with.

Idea is nice but this does not involve the battery volt as , in winter times, you still may have enough charge to be used but you are switching ON wapda that means you are not optimizing the solar energy acquired during the day.

I have made another setup with a light switch and a battery low volt together. This circuit charges battery in the day if the solar power is not enough only to a battery higher volt one cycle. This cycle may be repeated if required by the system.

In night time, the system will be a normal UPS once the battery goes down below a set value. That means if battery does not go, system remains on battery power.

Like this you uses maximum solar energy and wapda to least required level.

What does the timer do? Does it keep the system on batteries for 8-10 hrs of darknesz during night-time?

Aurangzeb

There is a separate Battery Low-Volt disconnect. So that there is no confusion, I haven't shown it here.

In winter days also, given that there is good sunlight the system will turn Off the utility to UPS.

I want my setup to minimize the use of battery. As charging-discharging cycles not only reduces battery life but also waste energy in inversion-conversion. Better to use utility directly rather than putting it into battery first and then inverting it back.

(with a sun switch for example, in evening the load on UPS is 200 watts. Panels are only producing 50 watts. Switch is On so that utility is disconnected from UPS. The UPS will discharge the batteries to make up for that extra 150 watts of load.
Some time later the sun sets and switch turn Off, supplying the utility to UPS, the UPS will now charge the batteries from utility.

I have tried to avoid this scenario.
I try not to let the batteries discharge(in day time) which the UPS has to charge again from utility(in evening).)

I understand that I am not fully utilizing the solar-panels but I am saving my battery bank, which only get utilized when there is no utility and poor/no sunlight.

I thought about the Sun/Light switch at first. As I understand it works on illuminance rather than insolation. And I guess(i am not good with electronics) the LDR in those switches cannot truly differentiate between the brightness and insolation.

How is your experience with light switch in late afternoon or fog. Where there is enough brightness but the solar panels aren't producing much output?

[quote=“aurangzebhaque, post:3, topic:21447”]

What does the timer do? Does it keep the system on batteries for 8-10 hrs of darknesz during night-time?

Aurangzeb

[/quote]

The ampere meter is set to turn its internal relay On at the reading of 1.6. Meter relay turn the timer on.

Sometimes(usually clouds causes) the actual reading(current value) to fluctuate up and down of this set-point.

for example 1.4 ... 1.5 ... 1.6 ... 1.7 ... 1.8 ... 1.3 ... 1.4 ... 1.5 ... 1.6 ... 1.7.

the timer(delay-on) helps in avoiding the final/main relay to be turned on and off in quick successions. The timer turns on the main relay, only after the value of set-point has reached/crossed and the set time has elapsed.

The current setting is that when the ampere reading has reached/crossed 1.6 and 5 minutes has elapsed after reaching that value, the relay should turn On(disconnect utility). As soon as the reading of ampere meter drops below 1.6 it will turn the relay(and timer) Off; which will connect the utility back to UPS.

A circuit diagram and component list with or without prices will be a nice addition to this thread.

The components that I have used are;

50 watts Solar-Panel

DC Volt meter with Relay (optional)

DC Ampere meter with Relay
Sourced from Brandeth road, used/second hand market. Costed about Rs. 4000/- each. Good bargainer might get them at better prices.

50 watts, 6.4Ohm(if i recall correctly) resistor

Power relay(not shown here)

from Hall Road.

Shunt 100A/50mV

Control Relay, 11-Pin

Multi-Timer

Line-Up connector

Fuse block

Box

from Brandeth road

Wiring is simple. Resistor and Shunt are connected together in series. Panel and voltmeter across the resistor-shunt combo. Ampere meter across the shunt.

Ampere meter relay turns On-Off the Multi-Timer. Multi-Timer turns On-Off the control relay.

Control relay turns On-Off the Power relay(not shown here).

Power relay turns On-Off the utility line to UPS.

here is the difference of selection.

You dont want to utilize battery even it is fully charged because it is night. even for that, instead of making this big arrangement just to get the light switch, they are already available in market for much cheaper price and surely for easier use.

I got one made in US by F&P and it cost around 1000pkr.

http://www.fisherpierceolc.com/products.htm

Anyhow, in your setup the WAPDA is still used to the max while other scenario is to get maximum benefit from solar setup as you have already spent good amount of money of it. this is called ROI(Return Of Investment).

For that one you need use light switch and the volt switch together to keep battery charged to a good level and use wapda to the minimum.

As yousaf have already asked, please share the wiring diagram for others to get this idea in a more easier way.

@slightly on/off topic

@enlightenment

Bhai, no matter what, since your wiring diagram is not here and unabel to piece out what you accomplished and how, and what you intend to do with it,, your work is clean and wiring is stylish.. i like it already :)

Since we are discussing how to manage a hybrid system, this thread is worth reading too. http://forum.solar-electric.com/showthread.php?24059-New-user

[quote=“tufail_74, post:8, topic:21447”]

here is the difference of selection.

You dont want to utilize battery even it is fully charged because it is night. even for that, instead of making this big arrangement just to get the light switch, they are already available in market for much cheaper price and surely for easier use.

I got one made in US by F&P and it cost around 1000pkr.

http://www.fisherpierceolc.com/products.htm

Anyhow, in your setup the WAPDA is still used to the max while other scenario is to get maximum benefit from solar setup as you have already spent good amount of money of it. this is called ROI(Return Of Investment).

For that one you need use light switch and the volt switch together to keep battery charged to a good level and use wapda to the minimum.

As yousaf have already asked, please share the wiring diagram for others to get this idea in a more easier way.

[/quote]

I don't want to utilize the batteries unnecessarily. I try to keep them fully charged(on float) most of the day-time.

As wapda is kind enough to help in discharging the batteries 'every hour on the hour'.

Producing AC from batteries is expensive compared to using AC directly from utility.

Standard sun/light switches available in market are designed to differentiate between day and night.

I needed something which can differentiate and give an output for strong and weak sunlight(insolation levels).

In my setup, utility is turned off to UPS when there is good output from 50 watt panel. Complete load is then sustained by the main pv array and the batteries are not used.

When the output from 50 watt panel decreases, confirming decreasing sunlight and thus less output from the main array also, which will make the UPS take energy from the batteries, the system turn the utility to UPS on.

So in late afternoon, instead of getting 80 watts from pv-array and taking 70 watts from batteries(which will be charged using utility later, as there will be no sun); the system just shifts to utility and take all of 150 watts from utility directly. Leaving the batteries charged, which does eventually get cycled in evening/night when utility goes in load-shedding.

The I in ROI does include the high cost of batteries(VRLA). And I don't want to replace the batteries in 3~4 years time, in trying to get every last watt from solar panel in weak sun hours.

[quote=“farhan_ds, post:9, topic:21447”]

@slightly on/off topic

@enlightenment

Bhai, no matter what, since your wiring diagram is not here and unabel to piece out what you accomplished and how, and what you intend to do with it,, your work is clean and wiring is stylish.. i like it already :)

[/quote]

Thank you for liking the wiring :)

The diagram I have is all hand done on paper(a bit messy). I will try to make something simple on paint.

How do you deal with "partial shading" e.g something is obstructing 50W panel for more than 5 mins at noon. Solar array will be under high isolation.

I think you did not get my point or did not read my setup details.

First thing, this is highly exaggerated to get VRLA battery down in 3-4 years. They should be good for at least 7-8 years. Second, I do not DISHARGE battery but battery has to just once to lower voltage ( adjustable to any safe level) then it comes to normal UPS. Your setup has some things to be reviewed. like yousaf already mentioned partial shading. moreover, in winter, you may be getting enough power to keep home on solar yet you switch to wapda coz light goes low. this makes no sense.

I think you have not used the light switches available. I am not talking about experimental kind of or cheap china made ones. The switch I am using usually switches around one hour before sunset and same happens in the e vening. it turn when there is enough sun to bring power from solar.

My point is that you have to run in a way where it is long lasting and cost reducing both.

BTW, as farhan has also pointed out your wiring does show your like to have a nice looking setup. That is very good job by all means.

First, let me appreciate your idea + efforts to implement it regardless of how much useful it is and what flaws it has. Good Work......

Without going into the functionality details, I would just invite your attention to the 50W resistor on the top of panel. It looks like this is the load on a separate 50W panel and you are measuring current through it using a combination of shunt + Panel Ampere meter. Am I right ?

If so then it is dissipating 13.21 (V) x 2.3 (A) = 38 Watts which is too much heat. You should better mount it directly on the panel top without any gap and using some thermal grease in between.

[quote=“yousaf465, post:13, topic:21447”]

How do you deal with "partial shading" e.g something is obstructing 50W panel for more than 5 mins at noon. Solar array will be under high isolation.

[/quote]

If the Shading(clouds mainly) causes the output of 50W panel to go below the set-point in ampere meter, the UPS is shifted to utility.

Shading from trees or nearby walls is no problem due to the mounting location.

[quote=", post:15, topic:21447"]

First, let me appreciate your idea + efforts to implement it regardless of how much useful it is and what flaws it has. Good Work......

Without going into the functionality details, I would just invite your attention to the 50W resistor on the top of panel. It looks like this is the load on a separate 50W panel and you are measuring current through it using a combination of shunt + Panel Ampere meter. Am I right ?

If so then it is dissipating 13.21 (V) x 2.3 (A) = 38 Watts which is too much heat. You should better mount it directly on the panel top without any gap and using some thermal grease in between.

[/quote]

Thank you for the kind words and the appreciation.

Absolutely correct regarding resistor being the load on the separate 50 watts panel. And the current through the resistor being measured by the shunt and the ampere meter.

The Panel/Box is not metal. It is some kind of mixture of PVC+Fibers(glass i guess). That is why I have this gap to let some air move around it and not melt the panel-box. I did thought of putting a small panel fan near it. But now that it has endured June-July, I think it will be alright for the rest of the months.

I did check the insulation of wires at this power. They did seem to be holding well, not too soft or mushy.

[quote=“enlightened, post:16, topic:21447”]

If the Shading(clouds mainly) causes the output of 50W panel to go below the set-point in ampere meter, the UPS is shifted to utility.

Shading from trees or nearby walls is no problem due to the mounting location.

[/quote]

Partial shading is a classic problem for a MPPT charge controller. One of the factor which determines their quality is how quickly and efficiently they manage it.

In your case amount of Insolation on the 50W panel and time determines whether to switch to Utility or stay on solar. That is indeed a good simple solution for areas where Net-metering/ on-grid solar installation is not an option.

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I have alternative solution, I don't how viable it is. Instead of installing separate 50W panel, we can measure the actual current being produced by Solar array using a hall effect sensor (I'm getting too obsessed with Hall effect ;) ) . Set the timer at 5mins as you have done. the rest of the solution remains the same.

A slight modification on the above, Shunt + timer method but measuring actual current being produced by Solar array.

With these methods, shading on a single panel (clouds etc) will not have any effect on switching.

Any comments are welcome.

Hall effect sensors are great. But since I am no good with electronics, I keep away from them. :)

Main array output is directly linked to SOC of battery, load on UPS and if mppt the current tracking point.

Sometimes the main array might be sitting idle(almost), in no load situation and batteries fully charged.

Or might be at full output, with maximum load on UPS and battery at 50% SOC.

How do you intend to switch the utility from UPS. And at what power levels of main array.

There was PIC controller based project using multiple hall effect sensors. I need to find it.

I'm not suggesting you should modify your project. These will help anyone designing something similar in future.

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Edit:

  1. http://forum.solar-electric.com/showthread.php?6762-Project-Designing-Solar-Meter
  2. DIY battery monitor/charger