Solar Panel

[premkumar9]

Hi,
I have 40Watts load continuously for 24 hrs working at 12V DC. It has to be driven with solar energy. How to decide the solar panel and battery ratings?

 

[audioguru]

The solar panel will produce its rated current only at noon when the sun is directly straight up (in India is the sun straight up at noon?). The current is less at other times. You need a very expensive solar panel.

 

[kchriste]

Google for "solar panel calculator"
Here is some meant for the UK, but it'll give you an idea of how it's done:
Solar Panel Calculator, calculate your solar panel needs
Solar Panel calculator

 

[premkumar9]

Google for "solar panel calculator"
Here is some meant for the UK, but it'll give you an idea of how it's done:
Solar Panel Calculator, calculate your solar panel needs
Solar Panel calculator

In fact I also had seen such calculators in the net. I had a discussion with a panel manufacturer who suggested the panels. My intention in posting this question in the forum was to have discussion on various parameters to be taken in to consideration while deciding the panel and battery size. Discussion with experienced persons instead of trying to get the answers myself will save time to me . Also it may be useful to others in the forum who are interested in this subject.

 

[premkumar9]

The solar panel will produce its rated current only at noon when the sun is directly straight up (in India is the sun straight up at noon?). The current is less at other times. You need a very expensive solar panel.

This is for a commercial project. If I give the load details the panel supplier will do the rest. But I wanted to know the details for optimization as the panels are expensive.

 

[saturn1bguy]

The solar panel will produce its rated current only at noon when the sun is directly straight up

AG, do you have a repeat button to make this easier? (How many times have you had to point this out over the years...)

 

[blueroomelectronics]

It's an important point, most solar arrays are fixed and that makes the efficiency problem even worse. Tracking panels help but with large panels it can be cost prohibitive. Cloudy days, rain, location all make going solar an expensive initial investment.

I would love to get some panels on the homestead, just waiting till I find a bargain. I also wonder if a hot water storage system is worth the investment.

 

[premkumar9]

AG, do you have a repeat button to make this easier? (How many times have you had to point this out over the years...)

I don't think there is anything wrong in repeating as one may not go through all old threads before posting a question. But for me there was no wanted information in the answer.

 

[audioguru]

I assume that you know that a solar panel doesn't work properly when it is cloudy and raining. Frequently a windmill is also used to spin a generator to charge a battery on a cloudy day.

 

[premkumar9]

It's an important point, most solar arrays are fixed and that makes the efficiency problem even worse. Tracking panels help but with large panels it can be cost prohibitive. Cloudy days, rain, location all make going solar an expensive initial investment.

I would love to get some panels on the homestead, just waiting till I find a bargain. I also wonder if a hot water storage system is worth the investment.

Here in India there are government subsidies to encourage using solar energy.

 

[kchriste]

But I wanted to know the details for optimization as the panels are expensive.

Maybe you should look at the load instead. Can the power consumption of that be lowered, allowing you to use smaller panels? What is the load?

 

[Ubergeek63]

Hi,
I have 40Watts load continuously for 24 hrs working at 12V DC. It has to be driven with solar energy. How to decide the solar panel and battery ratings?

You should use a 250W solar panel and 2500WHRs lead acid as a starting point. Or 750WHRs of LiFePO4.

 

[premkumar9]

I assume that you know that a solar panel doesn't work properly when it is cloudy and raining. Frequently a windmill is also used to spin a generator to charge a battery on a cloudy day.

So I got two points.
1. Adjust direction for optimum performance (the panel supplier suggested the direction for my location) if we cannot afford a tracking panel.
2.Sufficient over rating for panels and AH rating for batteries to take care of cloudy days (of course depends on my location)

Anything else?

 

[premkumar9]

Maybe you should look at the load instead. Can the power consumption of that be lowered, allowing you to use smaller panels? What is the load?

LED signal lights.

 

[audioguru]

I guess you don't have winter when the sun is very low in the sky and night-time is longer than day-time.
I guess you don't have snow.

 

[premkumar9]

You should use a 250W solar panel and 2500WHRs lead acid as a starting point. Or 750WHRs of LiFePO4.

How did you estimate 250W panel with out considering my climatic conditions? How did you work out 2500WHRS(I think it has to be expressed as AH capacity of the battery. Am I right?). What is LiFePO4.

 

[kchriste]

LED signal lights.

Have you thought of dimming them at night to save power?
The only other way to getting the max output from a solar panel is to use a maximum power point tracker. These are usually only practical with larger arrays due to cost.

 

[Boncuk]

Hi premkumar9,

your total power demand is 40W for 24 hours which equals 960W/h. I assume that the sunlight duration at your location is similar to mine - 12 hours per day. Considering the rainy season with less sunlight (sky obscured, hence less power output from the panel(s)), I'd figure a safety factor of 25% which results in daily power rating of 1,200W/h.

The higher power solar panels start at about 170W. So using one of those your device is already overpowered. (2,040W/h)

If your panel manufacturer offers panels rated 100W they will suffice.

Other than stated there is no big deal with a solar tracking device. For a panel of the required size you might use 12V toy-motors connected to planetary reduction gear and make further reduction using a worm gear on the main drive shaft.

I am going to use a bathroom floor cleaner with a telescopic aluminum handle bar to make the drive water proof. The spindle will rotate inside the aluminum hose. Having a total length of 1m you might adjust for any desired movement angle.

Azimuth angle is fixed 180 degrees and elevation angle varies with the appearant sun movement, in Thailand over the top during the hot season (0 to 100 degrees, which takes care of latitudes of 13.5deg/N).

Using a worm drive has an additional advantage. Wind has no influence on the accuracy since driving a worm with a nut is simply impossible.

The circuit I designed includes an automatic "homing" circuit to have the panel move to face east for a selectable time after sunset. Further development is an automatic override which moves the panels according to the appearant sun speed if the sky is overcast for a while, in order to have full sunlight as soon as the sky gets clear.

One word concerning traffic lights: Out in the country side there are flashing lights at road intersections. They have a tiny solar panel (20X20cm) mounted horizontally on top of the light and they flash at any time of the day and of course at night.

Regards

Boncuk

BTW: the power output of solar panels is determined in California, about 35 degrees north of the equator. The power is then calculated for a loacation at the equator. Do you guess the calculation is perfect?

 

[premkumar9]

Have you thought of dimming them at night to save power?
The only other way to getting the max output from a solar panel is to use a maximum power point tracker. These are usually only practical with larger arrays due to cost.

Yes. I have thought of dimming at night through pulsed operation. Also using a charge control unit.

 

[premkumar9]

Hi premkumar9,

your total power demand is 40W for 24 hours which equals 960W/h. I assume that the sunlight duration at your location is similar to mine - 12 hours per day. Considering the rainy season with less sunlight (sky obscured, hence less power output from the panel(s)), I'd figure a safety factor of 25% which results in daily power rating of 1,200W/h.

The higher power solar panels start at about 170W. So using one of those your device is already overpowered. (2,040W/h)

If your panel manufacturer offers panels rated 100W they will suffice.

I think, 25% safety factor is not enough and we cannot take 12 hrs peak charging.

Other than stated there is no big deal with a solar tracking device. For a panel of the required size you might use 12V toy-motors connected to planetary reduction gear and make further reduction using a worm gear on the main drive shaft.

I am going to use a bathroom floor cleaner with a telescopic aluminum handle bar to make the drive water proof. The spindle will rotate inside the aluminum hose. Having a total length of 1m you might adjust for any desired movement angle.

Azimuth angle is fixed 180 degrees and elevation angle varies with the appearant sun movement, in Thailand over the top during the hot season (0 to 100 degrees, which takes care of latitudes of 13.5deg/N).

Using a worm drive has an additional advantage. Wind has no influence on the accuracy since driving a worm with a nut is simply impossible.

The circuit I designed includes an automatic "homing" circuit to have the panel move to face east for a selectable time after sunset. Further development is an automatic override which moves the panels according to the appearant sun speed if the sky is overcast for a while, in order to have full sunlight as soon as the sky gets clear.

I will come back later

One word concerning traffic lights: Out in the country side there are flashing lights at road intersections. They have a tiny solar panel (20X20cm) mounted horizontally on top of the light and they flash at any time of the day and of course at night.

May be efficient LEDs- good light o/p with less power- smaller duty cyle (flashing) and smaller size of the lamp (with less LEDs)

Regards

Boncuk

BTW: the power output of solar panels is determined in California, about 35 degrees north of the equator. The power is then calculated for a loacation at the equator. Do you guess the calculation is perfect?