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neilzero
2012-Feb-15, 12:09 AM
Please correct, embelish or refute how I answered calculating power and energy for a concentrating photovoltaic system: What is DNI? If you have one large reflector such as 100 square meters, the reflector efficiency might be 90% when the steerable reflector is facing the sun, approximately. Exactly means the solar panel is partially shading the reflector, which could halve the efficiency of the reflector.
If the sun and the solar panel are 90 degrees apart; then the angle of incidence and angle of reflection are 45 degrees; that is 0.707 (if I recall correctly) times 0.9 = 0.6363. Average sunlight at your location might be 100 watts, so the beam from the reflector is 6363 watts. On the average 10% of the beam may miss the solar panel, so multiply by 0.9 again = 5727 watts. Dust and bird poop (on the reflector and the solar panel) may reduce that to 5000 watts times 0.2 if that is the efficiency of the solar panel = 1000 watt generated. That likely assumes a near perfect impedance match between the solar panel and load, which is not realistic, but a set of new batteries might return 90% of the 1000 watts to a 900 watt load connected 24/7. I have not seen specs on a grid connect inverter, but my guess is a premium priced inverter will also put 90% of the 1000 watts on the grid by using switching power supply technology. Most of the numbers I suggested are a bit optimistic and I missed some items such as the shape of the beam changes with the angle between the Sun and the solar panel, changing how much of the beam misses the solar panel. Failure to illuminate all the area of the solar panel is like the gob of bird poop = it reduces the panel efficiency considerably.
If you have multiple concentrating reflectors much the same happens except one reflector will occasionally shade another reflector near sunrise and sunset at certain times of year. In hot weather, you likely get lower efficiency from your solar panel, unless you have an active cooling system for your solar panel.
So, you may average 900 watts 24/7/365. 900 times 24 is an average day of 21,600 watt-hours of energy = 21.6 kWh worth about $3 retail. Neil

publiusr
2012-Feb-17, 08:12 PM
EMP is a threat to photovoltaics. I wonder if there maybe a way to slave water wheels and link them to solar collectors

http://gas2.org/2012/02/07/concentrating-solar-power-projects-will-rise-again/

So you would have a constant supply of water so that both thermal and mechanical forces generate power...

neilzero
2012-Feb-18, 05:21 PM
Yes I am sure very strong EMP = electromagnetic pulse can destroy the PV panels, but the electronics used to control the steam turbine and stearable mirrors are also vulnerable to strong EMP, and manual operation is often not included in the design nor the job skills of the only operator on duty. Worse, a major redesign may be necessary for even a very skilled operator to produce electricity without some of the electronic subassemblies. Staffing alternative energy facilities is difficult as at least one person is needed 24/7 but most of the time the system is fully automated, so you use a highly skilled person to wash mirrors, sweep the floor, answer the phone, security guard duties etc. With 5 full time people and 5 part time people, most of the money from the electricity sold goes to payroll, so the facility operates at a loss. With two of the 10 persons still learning the basics, the system may shut its self off fairly often. Likely at least 2 skilled persons are required to restart the system following an unscheduled shut down. Family housing in or near the tower for some of the employees may be a good move.
The best locations for solar are typically very dry, but there may be a small stream from nearby mountains. Very unlikely enough water for a practical water wheel, and they may have to be very careful about evaporation, and other water usage to avoid trucking water to the facility. The well water available is typically very deep, with high concentrations of corosive minerals, so they may need a small desalination plant which can run off the concentrated light. Algae in transparent pipes may also be another practical use of light that misses the opening at the top of the tower.
Possibly both steam and PV = photovoltaic is practical at the same facility as cheap PV panels can catch some of the light energy that misses the opening at the top of the tower. A wind turbine above the tower opening may also be practical to provide essential power at night, with the aid of a small battery bank. High wind speed though the tower opening will carry away up to half of the energy that would have heated the molton salt, so it may take more than one hour following sunrise to start delivering energy, some mornings. Worse a small biomass burning furnace may be necessary following several cloudy days to prevent the molton salt from solidifing, which would damage the equipment and/or make restart difficult = Several more employee skills required. Neil

publiusr
2012-Feb-24, 10:47 PM
Clockwork mechanisms would resist EMP. I just wonder that perhaps combining disparate power generation systems might give us a break-though otherwise unsuspected...

Ivan Viehoff
2012-Mar-01, 03:26 PM
EMP is a threat to photovoltaics. I wonder if there maybe a way to slave water wheels and link them to solar collectors
What does EMP stand for in this context? I've searched around and followed links and not been able to work it out. No doubt there will be a "silly me" moment coming up shortly.

I noticed a rather interesting renewable energy design that converted the water energy directly to pumped storage, that you can run at your convenience. This is a wave-operated water pump, that uses the wave energy directly to pump sea water up into a storage reservoir on the cliff above, which you could then run back through a turbine at your own convenience. I think the suitability of the wave motion for this makes it a more useful conversion of energy than some others. Though of course the total quantity of wave energy along the world's coastlines is not large in comparison with our energy consumption, (see http://physics.ucsd.edu/do-the-math/2012/01/the-motion-of-the-ocean/) so this can only ever be a niche source.

Strange
2012-Mar-01, 03:38 PM
What does EMP stand for in this context? I've searched around and followed links and not been able to work it out. No doubt there will be a "silly me" moment coming up shortly.

EMP (http://en.wikipedia.org/wiki/Electromagnetic_pulse)

Silly you. :)

Ivan Viehoff
2012-Mar-02, 10:20 AM
I did not consider it plausible that was the subject of their discussion.

Strange
2012-Mar-02, 10:29 AM
I was surprised. I doubt the PV panels themselves are susceptible (directly) but the associated electronics may be. And the wiring could induce spikes that do some damage to the panels. I had quick web search and a lot of the comments regarding this seem to be on survivalist web sites and I'm not sure how credible that info is.

publiusr
2012-Mar-03, 08:25 PM
You have to have a faraday cage to protect them, I think. Somebody said the mesh in a stucco house might be enough--but it would have to house over the roof too I think...

cjameshuff
2012-Mar-04, 05:26 AM
I did not consider it plausible that was the subject of their discussion.

Electromagnetic pulses are not a noteworthy threat to much of anything apart from some industrial equipment, so assuming something else was meant seems entirely reasonable.

EMPs aren't exactly a common problem, but apart from the lack of EMPs around to cause damage...

The power distribution network at a solar plant is likely to be heavily filtered to cut down on noise (a bunch of small, cheap switching converters feeding into long conductors is otherwise likely to radiate a lot of EMI), plus well protected against damage from lightning strikes. The converters themselves at each panel are built for power switching in the first place and will be relatively robust. Not necessarily EMP-proof, but not the first things to go.

Photovoltaics themselves have enormous junction areas compared to other semiconductor devices, and the conductors along their surface aren't the lowest resistance things around and are connected to the semiconductor material along their length. I'd expect them to be essentially immune, or at least one of the last things to fry.

Even in a global nuclear war scenario, I expect blast effect would be a much bigger threat than EMP. It would not take much of a blast to ruin an entire field of panels, and faraday cages aren't going to help. I'm rather wondering why anyone would consider EMP worth worrying about.

neilzero
2012-Mar-06, 10:19 PM
Disparate power generating systems have both advantages and disadvantages. In a hybrid vehicle, multiple systems may mean you can limp to a repair place instead of being towed. But, a minor defect in one system can cause major damage to another system, such as the tower elevator needs a major overhaul because some molten sodium-potassium nitrate solidified in it's mechanism. The more different systems you have, the harder it is to train employees to be experts in even most of the systems. I agree clockwork mirror pointing systems can be more easily protected from EMP, but they are likely more vulnerable to a sand storm which is likely in the best solar locations. Aren't clockwork systems that adjust to the changing seasons lots more complex without electronics or a knowledgeable human? A solar concentrating system peresently under construction has over 1000 steerable mirrors, so fully automatic steering is important. Neil

HenrikOlsen
2012-Mar-08, 05:40 AM
Aren't clockwork systems that adjust to the changing seasons lots more complex without electronics or a knowledgeable human?
The required adjustments are very easy to describe as sums of periodic terms which is something that is really easy to implement with gears.
I think I could design one with 10-20 gears, making it simpler than the average gearbox of a car. Main design challenge would be the 1/487 ratio needed in one gear set.

cjameshuff
2012-Mar-08, 01:23 PM
The required adjustments are very easy to describe as sums of periodic terms which is something that is really easy to implement with gears.
I think I could design one with 10-20 gears, making it simpler than the average gearbox of a car. Main design challenge would be the 1/487 ratio needed in one gear set.

Or you could use a simple cam.

HenrikOlsen
2012-Mar-09, 06:30 AM
You still need to drive the cam at the right speed, which means you need a shaft turning once per year.

The cam just translates the period to the periodic term, the period still needs to be provided.

cjameshuff
2012-Mar-09, 04:37 PM
You still need to drive the cam at the right speed, which means you need a shaft turning once per year.

The cam just translates the period to the periodic term, the period still needs to be provided.

You make this sound like a problem. You've already got the panels/mirrors going back and forth once a day, and there's plenty of ways to use that to advance the cam a fixed increment each day...a motor with an encoder and some relay latches, a stepper motor, etc. Shouldn't take 10 gears. There's still the question of why EMP is such a concern in the first place...what about other dangers, like...meteors? Falling space junk? Rogue cropdusters loaded with spraypaint?

As for sandstorms, while vastly more likely to be an issue than an EMP, any sun-tracking system is likely to involve gearmotors just to produce enough torque to move the panels around, hold them against wind and gravity, etc. You do what you can to protect the mechanical bits, just like you do with everything else that uses such things. It's the panels themselves that I would be concerned about in a sandstorm, not the mechanical bits for tracking the sun.

HenrikOlsen
2012-Mar-09, 05:05 PM
You make this sound like a problem. You've already got the panels/mirrors going back and forth once a day, and there's plenty of ways to use that to advance the cam a fixed increment each day...a motor with an encoder and some relay latches, a stepper motor, etc.
The problem given was to do it with clockwork.
If you have electrical components it's a different problem.

neilzero
2012-Mar-09, 07:04 PM
EMP is one of a million things that may disable a power plant long term. Since we did not plan for EMP at most power plants, There is about one chance in a google that 99% of world's power plants will be inoperative long term starting one minute from now. It sort of makes sence to make efforts to insure that a new power plant of any kind will be in the 1% following a powerful EMP that is all but certain, some time in the next billion years. Obviously the new facility will never be funded if we try to provide for most of the unlikely contingencies. In any case, the analysis may prepare us for a more practical contingency of an entirely different sort = I can't believe I just typed that mass of generalities. Neil

publiusr
2012-Mar-10, 06:47 PM
It is always good to overbuild things if possible. Reactors need to be floating, as was the case with the command and control facilities in Cheyenne Mountain--so that any cracks from a fault do not propagate into the reactor housing.