I'm in the process of designing and installing a faux skylight that uses a large LED panel and I want to power it with a solar panel.
The LED panel uses about 70 watts at full brightness so I figured a 100 watt panel would be adequate for the job but I'm not sure.

All the solar panel specs. I've seen give me only maximum ratings but no clue as to the actual power available at different light levels.
I would have thought that solar panel specs. would include some sort of figure or figures that would indicate the actual power available at different light levels and would read something like:
Available Power at 10000 Lux: 50 watts.
or the illumination level at the panel's specified (labled) power (in this case 100 watt).

So, if buy a 100 watt panel will it supply enough power to keep my LED panel running at full brightness most of a sunny day or under cloudy conditions?

The way the specs. read I have no clear idea what panel I should buy. My 100 watts is an educated guess and I don't like making educated guesses in engineering.

 

I'm in the process of designing and installing a faux skylight that uses a large LED panel and I want to power it with a solar panel.
The LED panel uses about 70 watts at full brightness so I figured a 100 watt panel would be adequate for the job but I'm not sure.

All the solar panel specs. I've seen give me only maximum ratings but no clue as to the actual power available at different light levels.
I would have thought that solar panel specs. would include some sort of figure or figures that would indicate the actual power available at different light levels and would read something like:
Available Power at 10000 Lux: 50 watts.
or the illumination level at the panel's specified (labled) power (in this case 100 watt).

So, if buy a 100 watt panel will it supply enough power to keep my LED panel running at full brightness most of a sunny day or under cloudy conditions?

The way the specs. read I have no clear idea what panel I should buy. My 100 watts is an educated guess and I don't like making educated guesses in engineering.

The number I have heard often is about 1/2, but I have no first hand knowledge.

 

It would depend on your definition of cloudy day. Once you define that...........you get a panel that will put that out for your load.

Edit:
I am just plug and play when it comes to solar panels. Never have designed a system. I just randomly pulled up a couple of solar panel datasheets.
They have a I-V curve plotted against intensity. That should get you in the right direction.

 

It would depend on your definition of cloudy day. Once you define that...........you get a panel that will put that out for your load.

Thanks for your response.
Cloud cover wasn't a specific requirement.
Daily light levels vary widely. It depends on latitude, time of year, time of day, cloud cover, pollution levels, even elevation so it's not possible to be that specific but without a proper solar panel specification (which doesn't appear to exist) selecting a panel is purely guesswork and as such I could waste money by selecting the wrong one. If I buy one too small it won't work properly and if I buy on too big the I'm wasting my money.

I have a lux meter that I use to measure light levels, if I had proper panel spec I could use that to calculate the range of power outputs over over a range of day times, dates and weather conditions for my location and select my panel accordingly but the way it is I can't see any way do that.

 

The number I have heard often is about 1/2, but I have no first hand knowledge.

Sorry I don't understand, 1/2 of what?

 

I think they use a standard.....1000w per square meter or some such. Hi noon maybe. Anyhow.....if you can convert your light meter standard to the solar standard(there should be a fudge factor).......you'll get an idea of the size panel you require.
Did you find those graphs I was tellin you about? On the data sheets?

Edit: Solar panels are like antennas.......never enough and never too big. Always buy or build larger than needed.

 

Sorry I don't understand, 1/2 of what?

You can expect 1/2 of the panel rating. So if it is rated at 100 watts you might expect 50 watts on average.

 

Solar panel specs are marketing tools - basically optimistic lies, with plausible deniability.

I would say use 30% of the rated output as a reasonable guess, but I would be more concerned about the behavior of the system as the light falls off.

Will it flicker or blink in a super annoying manner?
Test the light with a variable power source first- avoid a nasty surprise.

 

I think they use a standard.....1000w per square meter or some such. Hi noon maybe. Anyhow.....if you can convert your light meter standard to the solar standard(there should be a fudge factor).......you'll get an idea of the size panel you require.
Did you find those graphs I was tellin you about? On the data sheets?

Edit: Solar panels are like antennas.......never enough and never too big. Always buy or build larger than needed.

Thanks for your response.
To me the 1000W/M squared figure is a bit too vague there's so many variables involved that it's not really practical.
"Standard sunlight conditions on a clear day are assumed to be 1,000 Watts of solar energy per square meter (1000 W/m2 or 1 kW/m2). This is sometimes called one sun, or a peak sun. Less than one sun will reduce the current output of the PV device by a proportional amount. For example, if only one-half sun (500 W/m2) is available, the amount of output current is roughly cut in half."
Sound good, doesn't say much.

I've always been skeptical about the solar industry (back 20-30 years) , a lot of what I have observed seemed to be a half baked, exaggerated (from a technical point of view) con job.
I was aware of the graphs, they don't really help in this instance.

 

I never had anything to do with designing or marketing......but I put up many solar/battery powered stations..........and nothing is more reliable.....period.

I've seen panels covered with eagles nests and eagle poo poo......shattered by rutting buffalo.....to bullet holes, and still power satellite oven controlled transmitters for months.........without missing a beat.

 

Solar panel specs are marketing tools - basically optimistic lies, with plausible deniability.

I would say use 30% of the rated output as a reasonable guess, but I would be more concerned about the behavior of the system as the light falls off.

Will it flicker or blink in a super annoying manner?
Test the light with a variable power source first- avoid a nasty surprise.

As the LED panel uses 70 watts at maximum brightness I figured a $100 100 watt solar panel would do the job. Obviously that's not so when I can only expect 30 watts (say) on a clear sunny day.

Currently I have the system working with a 30 volt LED panel running off a voltage boost module off a 19 volt DC power supply and it works well. I've modified the voltage boost module so I can dim the panel to black if I need too.

The LED panel is a broken 55" LCD television, gutted and rewired to run the back light LED's off a 30 volt supply.

The system I've designed would use mains power in the evening and night and switch over to solar during the day. Flickering and blinking shouldn't be a problem as the voltage boost module would smooth out any voltage/current variation.

 

I never had anything to do with designing or marketing......but I put up many solar/battery powered stations..........and nothing is more reliable.....period.

I've seen panels covered with eagles nests and eagle poo poo......shattered by rutting buffalo.....to bullet holes, and still power satellite oven controlled transmitters for months.........without missing a beat.

My problem isn't about reliability, it's about getting good reliable data that makes sense so that I can build a cost effective device first time out.
Thanks for your input anyway.

 

In this case it may be... if you need it done right you have to do it yourself.

 

The system I've designed would use mains power in the evening and night and switch over to solar during the day. Flickering and blinking shouldn't be a problem as the voltage boost module would smooth out any voltage/current variation.

The boost module cannot make power out of nothing, what happens when the solar panel output drops really low? Like when it starts to get dark?

That's the flash and flicker moment.

 

The boost module cannot make power out of nothing, what happens when the solar panel output drops really low? Like when it starts to get dark?

That's the flash and flicker moment.

"The boost module cannot make power out of nothing,..." of course it can't,

When the solar output drops below a certain level the system will automatically switch over to the mains powered 19 volt power supply.
The voltage boost module is regulated to set the output to a particular constant voltage by the dimmer potentiometer no matter what the input voltage.
The boost module can maintain a constant output over a range of input voltage from 32 volts down to 10 volts so voltage variation from the solar panel is not a problem.
It's possible some damping or hysteresis control may be required but current tests indicate that it probably won't be needed.

The voltage boost module :
http://www.ebay.com.au/itm/401210812722?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

I'm new to solar, this project is to try and learn more about it with a practical application. So far I've come to the conclusion that the technology as it commonly used is very much a hit and miss affair. This is not the style of electronic engineering that I'm used too.

 

I've come to the conclusion that the technology as it commonly used is very much a hit and miss affair.

Agreed. But that also applies to other renewable energy sources. Nature's like that. I suppose one exception would be tidal energy.

 

Agreed. But that also applies to other renewable energy sources. Nature's like that. I suppose one exception would be tidal energy.

Off topic.
Roll on thermonuclear energy, that would solve all our energy requirements for a long long time.

It's bed time in Australia, I'm outta here.

 

Thanks to all that helped.
While I didn't resolve my original problem some of the comments made me aware of aspects of my project that I hadn't considered prompting me to refine my design.

 

Never sized a solar panel, but worked in the industry (basic research). I did tell a local manufacturer that they sized an array wrong for a particular inverter and that's why the system was for show and never worked.

I did design a system to do a demand side management study for that same installation hence the troubleshooting of the inverter. I didn't build or operate the system. I just designed it in a big hurry. The published study was done remotely, pre-internet.

Yes, the standard is AM (Air Mass)1.5 Global spectrum. https://en.wikipedia.org/wiki/Air_mass_(solar_energy) 100 mW/sqcm or 1000 W/m Clear day around noon in most places. Short circuit current is proportional to intensity,

OK, your right, crap shoot. You need a calculator e.g. http://solarelectricityhandbook.com/solar-irradiance.html
which can tell you on average how much solar energy your panel should get per day based on location, direction and angle of the panel.

 

My dental office has panels that look like this https://www.usaskypanels.com/products/cumulus-ii-skypanels.html on his florescent lights. Then, for fun, you could use something like these https://www.decorativelightcovers.c...ht-covers/astronomy-fluorescent-light-covers/ at night.