# Measure Daily Output of a Solar Panel

Discussion in 'Renewable Energy' started by Moneer81, Sep 28, 2008.

1. ### ronp849New Member

Joined:
Feb 27, 2009
Messages:
31
Likes:
0
Location:
West Midlands, UK.
With a fixed resistor the power is proportional to the sq of the voltage - sample the voltage on a regular basis and calculate the total ENERGY over a given time. (Ie Integrate the calculated power value.)

2. ### Mike_2545Super Moderator

Joined:
Jan 4, 2009
Messages:
1,057
Likes:
29
Location:
Toledo, Ohio
Sampling voltage won't give current.

3. ### ronp849New Member

Joined:
Feb 27, 2009
Messages:
31
Likes:
0
Location:
West Midlands, UK.
If the load is a fixed resistor, you do not need to measure the current:

Power = Volts x Volts / Resistance

Joined:
Jan 12, 1997
Messages:
-
Likes:
0

5. ### Mike_2545Super Moderator

Joined:
Jan 4, 2009
Messages:
1,057
Likes:
29
Location:
Toledo, Ohio

Give that a try and let me know how that works for you.

6. ### ronp849New Member

Joined:
Feb 27, 2009
Messages:
31
Likes:
0
Location:
West Midlands, UK.
If you have two identical solar panels then I suggest you test both panels at the same time - for the reasons Mike gives, duplicating the conditions for both panels at different times would be very difficult. You could monitor both voltages with a single micro and even calculate/display the energy/power difference in real time.

Ron

7. ### WillbeNew Member

Joined:
Aug 16, 2008
Messages:
1,236
Likes:
7
Location:
MD
Since a solar panel is a current source in parallel with a voltage clamp the voltage across your measuring device should probably never exceed <50% of the open circuit voltage of your solar cell.

8. ### Nigel GoodwinSuper ModeratorMost Helpful Member

Joined:
Nov 17, 2003
Messages:
39,380
Likes:
665
Location:
Derbyshire, UK
ONLINE
Did anyone understand that?.

9. ### Mike_2545Super Moderator

Joined:
Jan 4, 2009
Messages:
1,057
Likes:
29
Location:
Toledo, Ohio
No, that's why I said "Give that a try and let me know how that works for you."

10. ### WillbeNew Member

Joined:
Aug 16, 2008
Messages:
1,236
Likes:
7
Location:
MD
Well, if you open circuit the panel, each cell maxes out at about one diode drop, 0.7v or so, so you really can't tell what the cell is capable of by using a very high load resistor value.

If you short the cell, the Isc should vary with illumination but this also doesn't tell max power level, only max current level.

And you can't use the max. power xfer idea, where the load resistance = the internal resistance, because the internal resistance varies.

So, I guess keeping the load voltage at less than 50% of max. open circuit voltage will give some reasonable approximation to the max. power available.

11. ### Mike_2545Super Moderator

Joined:
Jan 4, 2009
Messages:
1,057
Likes:
29
Location:
Toledo, Ohio
Gibberish I tell ya

12. ### WillbeNew Member

Joined:
Aug 16, 2008
Messages:
1,236
Likes:
7
Location:
MD
Duly noted and recorded!

13. ### Mike_2545Super Moderator

Joined:
Jan 4, 2009
Messages:
1,057
Likes:
29
Location:
Toledo, Ohio
Actually Willbe,

.15 hp is around 111 watts. I know of many 3X5 panels rated for 170 watts and up to around 200 watts. So, a sq yard is 9 sq ft. you,re saying that if you can get 55% out of a solar panel you're doing pretty good?

14. ### be80beWell-Known Member

Joined:
Aug 23, 2008
Messages:
4,969
Likes:
147
Location:
morristown,tn
what happen to the 6 sq feet you lost and don't most calculate the power by the solar cell charging a storage battery. I don't see how you could get a power reading that would show you any thing about how much your cell can supply with out seeing how much it can save to storage.

Last edited: Feb 28, 2009
15. ### KMoffettWell-Known Member

Joined:
Oct 5, 2007
Messages:
2,498
Likes:
58
Location:
Minnesota, USA
We calculate the instantaneous (....well almost) maximum power output of our research panels by measuring the open circuit voltage, followed be the short circuit (0.1Ω) current, and multiplying by 0.6 (0.5-0.7 ranges depends on the type of panel). We also ran computer-controlled, swept-resistance loads to verify our calculations. And we switch between two panels, a polycrystalline and an amorphous, for comparison.

A ~24-hour sampling is shown.

Ken

#### Attached Files:

• ###### M-SolarPanel Output.JPG
File size:
107.7 KB
Views:
263
Last edited: Mar 1, 2009
16. ### umer27New Member

Joined:
Mar 1, 2009
Messages:
53
Likes:
2
Location:
Pakistan
I have a sunny boy SWR1700 inverter , in the application Im using it in ..

Tell me how to keep track of the output ?

17. ### WillbeNew Member

Joined:
Aug 16, 2008
Messages:
1,236
Likes:
7
Location:
MD
"The solar constant includes all types of solar radiation, not just the visible light. It is measured by satellite to be roughly 1,366 watts per square meter (W/m²)"

I don't know how much of this is converted by solar panels; maybe half?

18. ### Mike_2545Super Moderator

Joined:
Jan 4, 2009
Messages:
1,057
Likes:
29
Location:
Toledo, Ohio
Ulmer27 Get a sunny web box to hook to the inverter.

19. ### Nigel GoodwinSuper ModeratorMost Helpful Member

Joined:
Nov 17, 2003
Messages:
39,380
Likes:
665
Location:
Derbyshire, UK
ONLINE
Do you mean in space?.

No where near that sort of efficiency, at least not on earth.

20. ### Mike_2545Super Moderator

Joined:
Jan 4, 2009
Messages:
1,057
Likes:
29
Location:
Toledo, Ohio
The most expensive, carefully designed, and complicated solar panels in the world operate at about 40% efficiency.

The rest are about 10% efficient.

21. ### duffyNew Member

Joined:
Dec 22, 2008
Messages:
2,618
Likes:
73
Location:
nortern 'sconsin
Are they up to 40%? Last time I checked, it was only in the 30's, and that was an exotic concentrator cell with multiple layers and using a dang magnifying glass to "concentrate" the sunlight.