Which solar panels to buy?

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Very good!

I just have a problem with this:

When the solar panels are wired in series, then the voltage drop across all the panels is additive while the current remains constant from panel to panel. That is, if there were four 120 watt 12 volt panels producing 7 amps each, then the voltage drop across all the panels would be 48 volts (12 x 4) while the current would be just 7 amps.

I'm not familiar with saying 'voltage drop' in that context. Seems it would make more sense to drop 'drop'.

I agree.....but it is apparently just a matter of the original poster's semantics.

Read it. Good article and only one nit-picking deviance I would mention--all wire has resistance and it varies by amount of copper to carry the current. Heating the wire to initiate resistance is not correct and the temperature of wire, considering ambients and amount of current, isn't a contributing factor.

The effect of temperature across the junction within the solar cells is a factor and all panels are derated for temperature increase.

If I had a suggestion, it would be to skew the article's comments about wire size to instill a user to use larger wire and not plan or suffer the use of inadequate wire size. Typically, you install wire once but benefit or loose for the life of the installation.

Thanks westend. Bigger wire is definitely better!

As for "voltage drop," it was common terminology in all my physics classes. Maybe not so for electricians...

Just being picky (good article!) --the Voc of a 12v panel is more like 22 volts, not the 18v mentioned (that would be the Vmp) and on tilting, the tilt angle is not the same as your latitude (except twice a year at the equinox)

the tilt angle at high noon is 90 minus sun's altitude.(zenith distance) and ZD +/- Declination = Lat. So your tilt is changing with Declination every day.

EG-at a place on 21 June, Dec is 23N, Alt is 64 degrees, so ZD is 26 Lat is 26 plus 23 = 49N (tilt is 26)
-21 Sep and 21 Mar, Dec is zero, so ZD + 0 = Lat

Then there is "optimum tilt" which is not the high noon tilt :)

Great info, BFL13! We prefer to leave them flat and just have more, saving us from getting on and off the roof every time we pack and unpack.

Roads Less Traveled wrote:
Great info, BFL13! We prefer to leave them flat and just have more, saving us from getting on and off the roof every time we pack and unpack.

Yup, practical matters trump ultimate deployment nearly every time.

I have a four-way tilt platform and it is only usually used while in storage. It's nice to be able to tilt the module during Winter storage so the snow and ice melt off quickly. YMMV.

Roads Less Traveled wrote:
As for "voltage drop," it was common terminology in all my physics classes.

strange