Solar Forehead Slap

[c1ue]

Re: Solar Forehead Slap

Most importantly, by mistake he did not measure power outputs from the solar cells. Instead he measured voltage, without a load attached ("open circuit"). They are barely related -- in solar cells, voltage is actually almost a constant, independent of power.

Actually, this isn't quite correct either.

If Voltage = zero, there is no power.

The tree arrangement shows a longer period where Voltage = rated voltage, thus the assertion that the tree provides longer hours of power is actually correct.

What is true is that measuring voltage does not itself measure the amount of power.

Thus it is very possible that the power generated by the standard array during summer months is much higher than the power generated by the tree arrangement - even as the tree arrangement is able to generate power during more of the year than the fixed array.

It is debatable whether the former situation is better; one of the largest criticisms of solar is its inherently low capacity factor. The tree arrangement therefore potentially increases that - important for reliability if not necessarily maximizing your solar PV feed in subsidy.

The blog also indicates that the theory behind the discovery itself is problematic: "I'm not sure I understand the confusion by which people think there could be some advantage, to orienting panels at sub-optimal angles. That somehow combining sub-optimal panels, together, makes them generate more energy in the net." It then goes to demonstrate via equations that "if the individual angles in the 'tree' are worse then the 45°-tilted south-facing panels in the flat array (they obviously are), so is their combination."

Again the author shows his bias towards maximizing energy output even at the cost of capacity factor (ironic given his name).

Yes, his assertion is true.

However, it should be noted that the kid recreated a hypothetical tree.

A real tree - or any other plant - doesn't operate by fixed in stone fractal principles. The fractal nature of its leaves is a function of how they are grown, but the actual orientation and growth is often a function of the environment.

Anyone who has plants in their house will certainly have seen how many of these plants reorient their leaves to maximize sun exposure.

So the arrangement the kid put together might not be optimal from a total solar electricity generated perspective, but equally might not be optimal from a plant's perspective.

The point was simply that this experiment showed fundamental PV output behavioral differences vs. fixed installations.

That he doesn't get this point puts him equally in ignorance with the MSM he attacks.

A tree's goal, much like any electricity consumer's goal, is to get enough solar energy to live and grow.

[lektrode]

Re: Solar Forehead Slap

... Right now, the combination of solar cells and LED lighting is a winner. Just a simple comparison - the cost of a $3.50 solar landscape light from Home Depot costs as much as the low voltage copper wire needed to connect 2 conventional landscape lights 8 ft apart.

even if that is a function of the reality of ZIRPland and the bernanks fantasy that the price of copper is somehow irrelevant to his calculation of 'inflation'

But solar to run your refrigerator or washing machine isn't a viable option YET. ...

this simply is NOT true and my mobile office setup proves it every day.
and as goodrich4bk mentions, the payback is even better at the $.44/kwh we pay out here
i have an offgrid customer that was having a problem with the PV setup she had not keeping up with demand, mostly due to the refrig, but always had to run the genset to do laundry - i set her up with a 12vdc refrig and she hasnt had to run her generator since, NO MATTER HOW MANY LOADS OF LAUNDRY she does.
the primary offsetting factor was in NOT needing to run the inverter all the time to keep the refrig cold, this alone saved enuf PV output to cover most of the demand from the 12vdc refrig - the batteries are refilled/full just about every day, with enuf leftover to cover the occasional set of cloudy days - the point is: NO MORE GENERATOR required on a daily basis

dont know how it would be possible if the PV wasnt covering her _entire_ demand

and one more point, re LED's
one can get 90% (or better) of the benefit of lighting with LED's using CFL's that cost 90% less than LED's
since LED's use only _slightly_ less watts than CFL's do for the same output in lumens, while costing upwards of 10times as much as CFL's

[Ghent12]

Re: Solar Forehead Slap

c1ue, he was covering "zero voltage = zero power" by saying they "are barely related."

and one more point, re LED's
one can get 90% (or better) of the benefit of lighting with LED's using CFL's that cost 90% less than LED's
since LED's use only _slightly_ less watts than CFL's do for the same output in lumens, while costing upwards of 10times as much as CFL's

CFL's are fine and dandy until you have to turn them on or off frequently. Their lifespan drops substantially with "bathroom light" cycling. There are advantages to LED's in that regard I believe.

[c1ue]

Re: Solar Forehead Slap

c1ue, he was covering "zero voltage = zero power" by saying they "are barely related."

To say voltage and power are barely related is incorrect.

If there is no voltage, there is no power. The periods when voltage is below operating voltage, neither setup generates significant power.

Equally so when voltage is nominal, there is power being generated.

For those extra hours of operation in the tree setup, there is more power being generated during those periods than the standard array because the standard array isn't generating any.

So while I can agree that the standard array may generate more power overall, the percentage of time power is generated by the standard array is less than the tree setup. The kwh profile during the day is likely significantly different as well.

Lastly I'd also note that this tree setup was not specifically optimized; it was a pure conceptual experiment.

The logical step is to then experiment with different variations of non-aligned solar panels to see if there are better ways to position a solar array - not just for total power generated but for real life factors like daily demand profiles, seasonal demand profiles, etc etc.

[dcarrigg]

Re: Solar Forehead Slap

A tree's goal, much like any electricity consumer's goal, is to get enough solar energy to live and grow.

I don't think so. A tree's goal is to survive long enough to propagate - just like all life. Growing outward in a spiral pattern like that is likely more an adaptation designed to ensure that it has sufficient leaves outside of the shade cast on it by its competitors.

A tree's goal is not to maximize solar power, but to grow with the minimum required power possible.

Making the argument that a tree is like an electrical consumer is akin to saying that the more food you pump into a person, the healthier and stronger they will be (or the more O2 they take in, etc.) Nature doesn't work that way.

If trees were to work that way (and they were still relatively immobile), they'd work together to create south-facing shelves of leaves at ~45% angles (depending on latitude and time of year), just like solar panels.

The point is that any panel pointed directly at the sun will be generating more power than one angled obliquely. To calculate the sun's position at a given latitude and time is not too difficult. It can be done (if you're a bit of a programming wonk) with the data here: http://www.nrel.gov/docs/fy08osti/34302.pdf.

The sun's angle changes throughout the year, of course. The point of this is that optimum efficiency will not be gained by having one small panel on a spiral picking up sunlight more directly around sundown. There are two-axis trackers that can always make sure panels are pointed directly at the sun already.



The graph above shows the effect of adjusting the tilt. The violet line is the amount of solar energy you would get each day if the panel is fixed at the optimium winter angle. The turquoise line shows the energy per day if the panel is fixed at the optimum full year angle. The red line shows how much you would get by adjusting the tilt four times a year (for each season). For comparison, the green line shows the energy you would get from two-axis tracking, which always points the panel directly at the sun. These figures are calculated for 40° latitude. (from http://www.macslab.com/optsolar.html with data from http://www.nrel.gov/rredc/solar_resource.html and http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php). The European tool is great if you're in that neck of the woods.

[c1ue]

Re: Solar Forehead Slap

I don't think so. A tree's goal is to survive long enough to propagate - just like all life. Growing outward in a spiral pattern like that is likely more an adaptation designed to ensure that it has sufficient leaves outside of the shade cast on it by its competitors.

A tree's goal is not to maximize solar power, but to grow with the minimum required power possible.

Making the argument that a tree is like an electrical consumer is akin to saying that the more food you pump into a person, the healthier and stronger they will be (or the more O2 they take in, etc.) Nature doesn't work that way.

If trees were to work that way (and they were still relatively immobile), they'd work together to create south-facing shelves of leaves at 45% angles, just like solar panels.

I'm unclear what you're trying to say.

Having enough energy to live and grow is exactly not optimizing for maximum solar power.

So you're actually arguing my point - and furthermore my point is that maximizing solar power is only useful in a feed-in tariff sense.

Maximum solar power doesn't help if said power is generated when demand is not at peak or when seasons change - both of which are design issues and not random events like clouds/rain.

[dcarrigg]

Re: Solar Forehead Slap

I'm unclear what you're trying to say.

Having enough energy to live and grow is exactly not optimizing for maximum solar power.

So you're actually arguing my point - and furthermore my point is that maximizing solar power is only useful in a feed-in tariff sense.

Maximum solar power doesn't help if said power is generated when demand is not at peak or when seasons change - both of which are design issues and not random events like clouds/rain.

I think I misread your post above. Re-reading it I get the feed-in tariff / economic optimization vs behavioral requirements argument you were making originally. It did escape me upon the first run-through. Sorry about that.

[Starving Steve]

Re: Solar Forehead Slap

Just out with my mother walking this morning, I paid special attention to California poppies along the way. And to my astonishment, most of them, like 95% of them, faced to the South-east where the Sun was at 10:30AM PDT.

So here is my dumb question for to-day: If poppies open-up for the bees between 10AM and 4PM solar time, then why would the California poppies on our walk face East or South-east?

Now, I'll pay special attention to the Cal. poppies when I walk in the afternoon in order to see if the poppies swing around to the South-west or the West. And if I observe that result--- I may not, but if I do observe that result--- then that would suggest that the poppies open to collect sunlight, not so much bee pollen.

This is an interesting question, and I hope kids in school are reading this. A real scientist is a close observer of nature, and without bias. Real scientists try to ask simple questions and make simple observations; and real scientists do NOT base their science primarily upon esoteric computer models.

So, let's wait for the afternoon in California to see what the poppies do.......

[Ghent12]

Re: Solar Forehead Slap

To say voltage and power are barely related is incorrect.

If there is no voltage, there is no power. The periods when voltage is below operating voltage, neither setup generates significant power.

Equally so when voltage is nominal, there is power being generated.

I think you're just splitting hairs here and making more of a semantic point, but what you are offering could provide some clarity to some readers here.



Overall I don't see much use for this type of design. Complexity generally means higher costs than simplicity; combining that fact with its trade-off of power for increased up time imply a narrower set of useful applications than more traditional PV setups. Decorative street lighting, perhaps.

[Starving Steve]

Re: Solar Forehead Slap

The largest demand for electricity in the desert S.W. is mid-day until about 7PM. The most demand is late afternoon and early evening.

Solar is OK in summer at mid-day to help with air-conditioning power demand. But solar drops-off to almost zero by late afternoon and evening, so solar is a joke. Meanwhile, power demand is at a peak then. And using batteries to store solar-electric power captured during mid-day cuts down on the output of the system, and battery storage adds to the cost of power bled-off and used late in the day.

And don't even try to use solar in the winter for anything. It's a joke.

The jewel of the solar buffs is their solar power plant in the Mojave Desert which is (or was) built by the U.S. Army. Yes, probably that jewel would provide power for 165,000 homes in the desert in summer, at mid-day. But there are not cities near-by in the Mojave Desert with that number of homes. The power would have to be transmitted long distance by wire, and that would negate a huge chunk of the power generated by the solar power plant.

Ah, but no-one hired geographers to do any engineering. No-one heretofore was ever allowed to question the viablility of solar power. The solar power lunacy was a dead-end financed by government grants. Even now, deep in the Great Recession, challenging the viability of solar-electric power brings on controversy, and as one can see just from the length of this thread.

Yes, one could use solar power to light a few bead lights during the night. But conventional and nuclear power plants have a surplus of power during the night, so solar-electric bead lights would not help solve the power-generation shortage during the day.

Stay tuned to this thread for what the poppies say about solar, later this afternoon in California.

[c1ue]

Re: Solar Forehead Slap

I think you're just splitting hairs here and making more of a semantic point, but what you are offering could provide some clarity to some readers here.

I would agree with you if I were also just pushing solar as a way to maximize feed-in tariffs.

However, as someone with hands on experience with power systems engineering, the shape of the supply curve is just as important as the area under the curve (total power).

Overall I don't see much use for this type of design. Complexity generally means higher costs than simplicity; combining that fact with its trade-off of power for increased up time imply a narrower set of useful applications than more traditional PV setups. Decorative street lighting, perhaps.

Again, as I note above, the concept of optimizing a solar install for a different output characteristic - that in interesting.

A typical household doesn't demand/use electricity in the same fashion as a solar array generates it:

http://itee.uq.edu.au/~aupec/aupec02/Final-Papers/Ali-Al-Alawi1.pdf

Middle East electricity usage profile.png

In California, the profile at the utility level is:

http://www.mpoweruk.com/electricity_demand.htm

CA electricity demand profile.gif

Note that while both the ME household and the CA utility overall curve is reasonably well matched with what you might expect for peak solar PV electricity, the residential curve is skewed towards a peak at 6pm.

A residential install for the purposes of household consumption thus would be positioned radically different than a residential install for the purposes of raking in a feed-in tariff.

[Starving Steve]

Re: Solar Forehead Slap

Here is what the California golden poppies had to say at 4:45 PM PDT ( approximately 3:45 PM solar time ):

Nearly all ( about 90% ) of the poppies were standing straight-up, and they were closed-up for the rest of the afternoon and evening. Of the 10% that were still open, most were facing South or South-west, but about 2% of the total poppy population was facing odd directions, including East and North and West.

So the poppies were saying, the solar output wasn't worth opening-up for and they were cooking their plant-food dinners.

There were bees all over the place, but the poppies closed-up and ignored the bees. No interest in pollination, but interest on the part of the poppies in the Sun. The poppies were fixated on the Sun, and I did not observe such a dramatic response on the solar position in other plants along the route of my walk.

Once again, the verdict was to close-down and stand-up straight. About 90% were so arranged.

The poppies work a six-hour day in California because the sunlight is NOT worth collecting for longer than that. The poppies concentrate on mid-day sunshine....... But I hate to confuse the solar energy buffs with the obvious facts, and the facts of this matter are that their solar trees would be a joke late in the afternoon and early in the morning. Next to nothing would be collected by solar panels arranged perfectly to collect late day sunshine or early day sunshine.

To prove that poppies open for the sunshine and not the bees, the next step would be to grind-up a sample of poppy flowers and see if there is something in the flowers that poppies convert to plant food with the help of sunlight. But that would take a bio-chemist or biologist to do.... The only other solar energy possibility is that the weight of the flowers pulls the stems down into the most optimal position to collect sunlight during the day. The stems, of course, make plant food because the stems are green and have chlorophyl (spelling?).