Renewables Just Keep Getting Better

whoosh.

NT is the specialist in horseshit around here. He knows very little and most of what he thinks he knows seems to be wrong.

His positive opinion of his own credibility is one of the many areas where he deludes himself.

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Bill Sloman, Sydney

That kind of argument does go over NT's head.

--
Bill Sloman, Sydney

A solar cell is like a (photo)current source in parallel with a diode. The current source's polarity is in the forward direction of the diode, which is why the voltage across a single cell is limited to one diode forward voltage drop, about 600mV, give or take.

To see what happens when a cell is inhomogeneously illuminated, one could model a large cell as several small ones in parallel. It's easy enough to see that the photo current is proportional to the illuminated area while the voltage is is affected only by the logarithm of the current, that is, only a little.

In a PV panel, many cells are put in series and it's easy to see that the current produced by one cell flows in the reverse direction through the others. If one cell in a series string is not illuminated, it blocks the passage of the current from the other cells! Of course, it's natural to include a reverse diode in each cell to defend against such cases, but the loss is still

*two* diode drops for each dark cell, so it's important that a panel is homogeneously illuminated.

Now I'm left wondering why no one in this discussion took the trouble to answer this properly, but I'm sure that several will now pipe up to pick nits.

Jeroen Belleman

Precisely. That is why small shadows can cane the output.

If you look at a PV array's v/i curve you'll straight away see that having one string with significantly reduced V_out means it provides less current than the others - and that's a bit of an optimistic case. If your shadow or uneven illumination affects all the strings, it doesn't go well.

I don't know what %age of PV arrays have diodes to work around this, but th e ones I've tried this with did not do well, so I expect they didn't have t hese diodes.

NT

g one string with significantly reduced V_out means it provides less curren t than the others - and that's a bit of an optimistic case. If your shadow or uneven illumination affects all the strings, it doesn't go well.

If you look at a PV array's v/i curve without thinking about what's actuall y going on you can probably duplicate NT's mistake.

the ones I've tried this with did not do well, so I expect they didn't have these diodes.

Given that NT has a rather poor grasp of the subject, his lack of success i sn't really surprising.

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Bill Sloman, Sydney

And not all the photocurrent comes out of the terminals - some biases the d iode.

There's an optimal bias that trades off the extra bias you can get with a s maller current at a higher bias against the extra current you get at a lowe r bias.

But the "leakage" current that has to flow to sustain the diode bias voltag e is subtracted from the photo curren tyou can exploit.

You can arrange photovoltaic cells in a PV panel any way you like.

el

If you can make cheap micro-inverters parallel would work better.

Not necessarily. Within limits, the highly illuminated cells will produce m ore photo current, but use more of it to generate a higher bias voltage, so that they deliver the same current through the string as the less well-ill uminated cells that will deliver a higher proportion of their photo current while using less of it to sustain a lower bias voltage across the cell.

Neither of them will be operating at their optimal power generation bias, b ut they won't be far off it.

If it is wired in series, which is a matter of choice.

As with all technical questions, the answer is complicated and the audience inclined to ignore complications. Detailed consideration always looks like nit-picking, particularly to people who have made up their minds premature ly.

--
Bill Sloman, Sydney

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I guess I have no idea what you mean by, "use the energy in the light for p hotosynthesis or electricity; make your choice" because my point is you do n't need to optimize anything to capture every last bit of light. I guess you just aren't grasping what I'm saying. By leaving space between the row s it maximized the utility of the solar cells for receiving the direct sunl ight, while leaving un-captured light to fall between the rows. By "un-cap tured light" I mean the light from parts of the sky that are not direct sun light.

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Ok, you seem to be intentionally ignoring the meaning of my words.

"other than selected species"

What do you think I meant by that???

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Not intended to be an insult. It is a summary of everything you have told me. I believe it was you who tried very hard to impress upon me the densit y of housing, the crowding, the lack of adequate parking on top of the lack of adequate electrical infrastructure as well as the lack of generation ca pacity in the UK. I am simply agreeing with the obvious, that the UK is in such bad shape it will take a ginormous effort for them to accommodate EVs and many forms of renewable energy.

I think one of us doesn't understand the meaning of alt-right.

ery

al

No prejudice and it is YOU who has educated me regarding the UK and energy. Thank you for the education.

Yes, I'm sure the coal generation will never be missed... unless it is. Wh at did the cause of the recent black out turn out to be when all the dust s ettled? I seem to recall it had to do with a couple of hundred MW of fossi l fuel generation going off line. How will the country cope with losing AL L the coal generation? I guess Hinkley will supplant that... except it won 't be online until 2025 and even then only if you believe the latest schedu le.

I guess they will need to find a way to install a bunch of renewables... re ally???

--

  Rick C. 

  ---- Get 2,000 miles of free Supercharging 
  ---- Tesla referral code - https://ts.la/richard11209

More ignorant "guesses", which you could easily have checked but chose not to. I leave others to assess why you chose those particular inaccurate "guesses".

Firstly the power source was irrelevant; what mattered was that a source, *any source*, went offline unexpectedly.

The cause was a lightning strike. That took 737MW from Hornsea *windfarm* off line. Then 885MW from Little Barford gas station went offline.

So your statement is /false/ in /every/ important respect.

Nothing you have said is even relevant. The issue is that the UK grid is friable, fragile, brittle, delicate. Then you talk about how they plan to retire GWs of coal based generation BEFORE they can bring up the nuclear generators at Hinkley.

Besides, what I wrote wasn't wrong. Read it again. Or better, don't. You clearly are wound up regarding this issue. Just give it a rest. You'll feel better.

--

  Rick C. 

  ---+ Get 2,000 miles of free Supercharging 
  ---+ Tesla referral code - https://ts.la/richard11209