How Is Voltage Set?

[DavidNJ]

In there spec sheet the different solar panels have their peak power output rated at different voltages. For example the Yingli 210w panels are at 26.6v/7.90a while the SunTech 210w are at 26.4v/7.95a. My guess that is the same panel. The Sunpower 39.8v/5.4a, which is quite different.

While it is hard to detect from the V/I curves which show lots of irrelevant data and are fuzzy around the important peaks, it seems the optimum voltage for peak power varies with different radiation intensities.

Question, how is the operating voltage set and is it optimized dynamically at different output levels?

Sidebar: is there an database of output levels at different radiation levels and do these vary with different natural light spectrums?

Thanks,

David

[DavidNJ]

Module Level Tracking: Enphase vs. Solar Edge

Module level tracking seems to offer significant advantages, especially for residential use where there may be some obstruction creating partial shade. there seem to be two solutions:

1) Micro Inverts which do the inversion at the panel level. They also have the advantage of transmitting AC away from the panel, which should have lower transmission losses. Enphase seems to be the only vendor currently: http://www.enphaseenergy.com/products/shipping units:

2) Panel level tracking with central inversion. SolarEdge seems to be the only vendor. http://www.solaredge.com/groups/technology/overview

Which is better and are there any other vendors?

Thanks,

David

[Mike90250]

So many questions....

Module level tracking

Only useful when shade covers some of your panels. Better to relocate panels, or not install there.

IV curves

are nearly identical for each style of cell construction. Good MPPT code can figure out the best place to run the array

[DavidNJ]

Those were supposed to be separate threads. One on how the voltage is set, and one which MPPT tracking is better.

There is no chance we won't use MPPT tracking; the question is which. I can't imagine a residential install anywhere near me that wouldn't have some varying shade from ground objects. All arrays are subject to variations from clouds and debris.

Otherwise, if Bambi her friends decide to eat in front of the array, we could be paying for lunch.

[Mike90250]

Enphase seems to have done a lot of work on their inverters, I don't know anything about the SolarEdge

And not every roof is suited for solar. You have to run the number for yourself, for each condition.

The MPPT software is supposed to be able to watch the array, and adjust for conditions.

[DavidNJ]

How is the voltage the solar panels, or a solar panel, runs at set?

[Mike90250]

How is the voltage the solar panels, or a solar panel, runs at set?

Each cell, produces about 0.5V Cells are wired in series to produce the desired voltage, and paralleled to get the desired current (amps)

[DavidNJ]

The IV graphs show nearly level current at varying voltage until a point, the the amperage decays rapidly. The peak power output appears to occur at Vmpp slightly above the voltage where the decay sets in.

What causes the cells to operate at their peak Vmpp rather than some other voltage?

[Mike90250]

Can you post the IV curve you are looking at?

some info:

http://www1.eere.energy.gov/solar/current_voltage.html

http://pvcdrom.pveducation.org/MANUFACT/LABCELLS.HTM

http://www.altestore.com/howto/Electrical-Characteristics-of-Solar-Panels-PV-Modu/a87/