Posted on 07/07/2003 5:06:51 PM PDT by PeaceBeWithYou
Its all controled buy an intertie, which is a charge controler and inverter that is connected to the AC main panel and the electric meter. Batteries or a genset are for backup only.
Excess goes into the grid, deficiencies come from the grid.
They say a picture is worth a thousand words.
Let's review some basics about photovoltaics (solar cells) and see how much sense this really makes.
WHAT HAPPENS WHEN WE USE SOLAR CELLS TO
CONVERT THE SUNS ENERGY TO ELECTRICITY:
| SOURCE | LOSS - % | POWER - W/m2 | |
|---|---|---|---|
| 1. | solarconstant | -- | 1370W |
| 2. | atmosphere | 27 | 1000W |
| 3. | clouds | 21 | 790W |
| 4. | sun angle | 40 | 474W |
| 5. | night | 50 | 237W |
| 6. | cell efficiency | 87 | 31W |
| 7. | dirt/reflection | 10 | 28W |
| 8. | packaging | 20 | 22W |
| 9. | AC convert | 25 | 17W |
| 10. | storage | 30 | 12W |
Net efficiency = 0.85% (!)
The current rate of U.S. energy consumption is 3.3 trillion Watts. Based on the above data we would only need to cover the entire state of Nevada with solar cells! And because of a 6% annual growth in our energy consumption, in another 12 years we would also have to cover the entire state of Arizona with Solar cells! Yet the current world-wide production of solar cells is so small that it couldn't even keep up with the annual growth rate in energy usage, much less supply enough solar cells to produce the base amount of energy usage.
I don't know whether to laugh or cry.
We were told that under the PURPA act, the utility had to reimburse co-generators at the deferred capital rate. Has that been usurped by some California law?
Got a source or a link?
How about an equal breakdown for fossil fuel sources (ancient sunshine) showing the losses that occur from the ground to the wall outlet?
Just curious how it would compare.
If you're speaking of the table of efficiency in post #23, the answer is no, I have no single link. The data for compiling that table I assembled from numerous and commonly available physical, mathematical texts and commercial sources.
For example, items number 1-3 are from the CRC handbook of physical data. Item #4, sun angle, is simply calculated from an ordinary understanding of trigonometry (and a practical understanding of why tilting the PV cells does not increase efficiency). Item #5 is self-evident. Item #6, raw PV cell efficiency, is derived from manufacturer data sheets and a life time of experience in electro-optical engineering. The contribution of dirt to Item #7 is a practical estimate based upon experience with optical systems exposed to an open environment and the contribution of reflection is based upon Fresnel's Law of reflection and a understanding of the practical limits of anti-reflection coatings. Losses due to packaging, item #8, is derived from manufacturer literature and data sheets. Items #9 and 10, AC conversion and storage losses, reflect published data for the available state of the art circuits for both processes.
Now if you were referring to the claims about total U.S. energy consumption, that was DOE information and the area information was calculated from the energy consumption and the ~12Watts per square meter figure from my table.
BTW, one thing I forgot to mention in my post #23 is that the capitalization cost of solar power (exclusive of land costs) is about 10 times that of a conventional natural gas power plant. (Basic rule of thumb is $1/W capital expenditure for a conventional power plant, although in the last few years I've noticed the cost dropping to as low as 75¢/W.)
PeaceBeWithYou asks: "How about an equal breakdown for fossil fuel sources (ancient sunshine) showing the losses that occur from the ground to the wall outlet"?
To be a fair comparison, we would have to limit that comparison to placing the power on the power transmission lines, rather than all the way to the wall outlet.
There are several basic categories of losses that solar electric power has that conventional plants don't have. First, there is no need for storage, as night time doesn't affect generating capacity. Second, there is no need for an inverter to convert DC to AC. (The inverter is a bigger deal than it first sounds like, because the inverter for a public utility must produce a very pure sine wave and that is much harder to do with high efficiency.)
The principle losses in a conventional gas or coal fired power plant are (a.) conversion efficiency of fossil fuel to either hot gases or high pressure steam, and (b.) conversion efficiency of the gas or steam to (rotating) mechanical energy, and (c.) the conversion efficiency of the electrical generator. The overall conversion efficiency of these conventional generating systems is quite high, something on the order of 60 to 80% (depending on a number of factors).
However, the real importance of the efficiency factor that I posted for solar power, is in calculating the amount of land that would be needed to supply that much energy. The land area needed for a typical large (1000 MW) conventional plant is "mouse nuts" compared to the 33 square miles(!) needed for an equivalent solar electric power plant. The effect that this need for large land areas has on the initial capitalization costs for solar power, cannot be over stated. And this is over and above the already high capitalization costs of just the solar installation.
Sorry about taking so long to post answers to your questions. Hope this reply addresses some of the issues you asked about.
Regards,
Boot Hill
In other words, there's no actual advance here, it's just a small redesign that provides a small benefit. When solar power is economically viable, then I'll be interested in it.
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