Breaking News
Design How-To

Selecting a solar energy conversion method

NO RATINGS
Page 1 / 6 Next >
More Related Links
View Comments: Newest First | Oldest First | Threaded View
<<   <   Page 3 / 4   >   >>
HarrisMarcus
User Rank
Rookie
re: Selecting a solar energy conversion method
HarrisMarcus   7/9/2012 8:36:44 PM
NO RATINGS
You have stated ďAs the cell voltage rises, the current in the internal diode rises, leaving less of the photo current for the loadĒ. This is not so. If you follow the panel I-V curve shown in Figure 6 when the cell voltage increases the cell current decreases. The maximum cell voltage is the open circuit voltage, Voc, where the current is zero.

HarrisMarcus
User Rank
Rookie
re: Selecting a solar energy conversion method
HarrisMarcus   7/9/2012 8:35:36 PM
NO RATINGS
The maximum power available from the panel does not change but the power that is actually extracted from the panel does change and it is a function of the load resistance RL. This maximum power point occurs when RL = Rs. The boost converter decreases the value of RL by adjusting its duty cycle. The input resistance seen by the panel is RL x (1-du)^2 where du is the duty cycle internally set by the SPV1020. The SPV1020 duty cycle is internally adjusted so that RL x (1-du)^2 equals the panel output resistance Rs.

HarrisMarcus
User Rank
Rookie
re: Selecting a solar energy conversion method
HarrisMarcus   7/9/2012 8:34:29 PM
NO RATINGS
You are correct. The intent of using the Thevenin equivalent is to show that whatever the value Rs even though non-linear, RL must match it to provide maximum power transfer.

HarrisMarcus
User Rank
Rookie
re: Selecting a solar energy conversion method
HarrisMarcus   7/9/2012 8:33:35 PM
NO RATINGS
RL will normally be much greater than Rs. Interposing the SPV1020 boost converter between the panel and RL decreases the load resistance seen by the panel. The load resistance seen by the panel Rin = RL x (1-du)^2 where du is the duty cycle internally set by SPV1020. The duty cycle is set by the SPV1020 so that RL x (1-du)^2 = Rs, the source resistance of the panel.

Robotics Developer
User Rank
Rookie
re: Selecting a solar energy conversion method
Robotics Developer   7/7/2012 6:29:49 PM
NO RATINGS
A very nice article with good technical details! Very much appreciated, thank you! I am wondering if this level of complexity is needed when using solar power both locally and not at normal line voltages (ie. 12V or 24V DC lighting/systems)?

chrisrodgers
User Rank
Rookie
re: Selecting a solar energy conversion method
chrisrodgers   7/7/2012 2:40:06 PM
NO RATINGS
I see that my understanding is slowly beginning to clear. I found the found Fig. 3.7 on pg. 24 of the following article to be helpful: https://digital.library.txstate.edu/bitstream/handle/10877/3171/fulltext.pdf I think what was bothering me was that the boost converter cannot increase the load voltage to any arbitrarily high level. It is necessarily limited by the PV maximum power curve for a given set of conditions (illumination, temp., etc.) This Fig. (3.7) seems to bear that out that.

Brakeshoe
User Rank
Rookie
re: Selecting a solar energy conversion method
Brakeshoe   7/6/2012 8:14:28 PM
NO RATINGS
Yes, the Thevenin model applies in figure 2, as you are looking back into the terminals of the source. What's more, if you apply a variable resistive load, you will get a linear graph of voltage vs current.

Mineyes
User Rank
Rookie
re: Selecting a solar energy conversion method
Mineyes   7/6/2012 7:39:23 PM
NO RATINGS
"Southern Exposure is Obvious" That is true only in the Northern Hemisphere. A better statement, might be "Equatorial Exposure is required"

Trinity51
User Rank
Rookie
re: Selecting a solar energy conversion method
Trinity51   7/6/2012 9:50:45 AM
NO RATINGS
Rich - as far as I am aware the panel output is surprisingly constant with time. Most panels are guaranteed more than 90% rated output after 10 years and more than 80% output after 25 years (approx 100,000 hours of daylight use). Typical results are better than that, so degradation is just a fraction of 1% per year.

jg_
User Rank
Rookie
re: Selecting a solar energy conversion method
jg_   7/5/2012 10:30:41 PM
NO RATINGS
Thevenin is a poor approach, a better model is a current source, with a parallel clamp diode, and better curves would include constant power profiles (V*I = constants) which makes the MPPT seeking easier to visualize.

<<   <   Page 3 / 4   >   >>
Flash Poll
Like Us on Facebook

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Times on Twitter
EE Times Twitter Feed
Top Comments of the Week