Here is what the acolytes of solar power don't want you to know...

self | July 15, 2003 | Boot Hill

[Boot Hill]

harpseal says:   "Now the place where this increase is most likely is in the efficency of the PV cells themselves."

I agree with your general premise that the whole dynamic will change if PV cell cost decreases dramatically while efficiency increases. But here is the problem with the increasing PV cell efficiency. Notice in the table that the solar constant is 1,370 watts per square meter. While that is a very high intensity, it is spread over a very wide spectrum of wavelengths. PV cells have a sensitivity to a much narrower range of wavelengths. If the wavelengths of the sun's output matched the PV cell, efficiency would probably be in the 40-50% area. This lack of broadband detection is not a new problem and has affected virtually all applications of silicon/germanium detectors since their invention. I would speculate that billions have been spent on attempts to increase their sensitivity, but with very little progress to show for the effort. Does that mean that I believe it will "never" happen? I don't discount the possibility, simply because the word "never" (and variants like "always") are some of the most dangerous words in science and I don't believe in tempting fate!

harpseal says:   "...since an average home needs in the range of 5KWhrs ..."

You might want to check that number. The average home uses closer to 24kW-hr of energy every day, or about 720 kW-hr per month.

--Boot Hill

(PS I didn't use watt-hours in my table, just watts per square meter averaged over all the variations found during a 24 hour period.)

[Boot Hill]

Castroville, home of the world-famous artichoke festival, but Salinas is reasonably close.

--Boot Hill

[Boot Hill]

LN2Campy says:   "I would argue that since solar power is only collected once it has already passed through the atmosphere, this 'loss' really isn't a loss at all."

It doesn't alter any of the data in the table whether you start your calculation with the solar constant or after atmospheric effects. The numbers all remain the same.

--Boot Hill

[null and void]

Strange, I'm getting 800W from my ~ 2 m² array in downtown San Jose. (But then, the array is angled towards the sun, eliminating one of the main "power losses" in your table).

My PG&E bill runs in the $10-20 range...

[Protagoras]

However, it is currently being sold (and funded by your tax dollars) as a serious competitor, alternative and compliment to conventional electrical generation.

Government should not be funding anything like this. Which, however, does not mean that science will never find a way to convert it to power which does make sense. The whole concept is in it's infancy. No way to know if it will ever pan out.

[Boot Hill]

kegler4 asks:   "...do we just ignore the possiblity of technology improvements in the future?"

Choosing where to put our limited research dollars has always been a challenge. If you try to spread the money over all possibilities, you will get no where. But if I had to choose between, say, solar and fusion, I darn sure wouldn't pick solar.

--Boot Hill

[Wonder Warthog]

"I am an engineer. I've spent a life time in electronics and optics. I am thoroughly familiar with the technology and the economics of solar power."

You couldn't tell it from your vanity post. You aren't just comparing apples and oranges--you are comparing mustard seeds and watermelons. There "are" a few different sorts of solar cells, with widely differing efficiencies and costs. Hell, you don't even give the BASELINE PARAMETERS for your assumptions. Add to that the "strawman arguments" about hailstorm damage (the answer to that particular one is called "polycarbonate").

[null and void]

But if I had to choose between, say, solar and fusion, I darn sure wouldn't pick solar.

Your choice, but don't forget that, short of a hydrogen bomb, no-one has ever gotten more power out of fusion than was put in.

Solar is routinely producing power now.

Also, a diffuse power source (mutiple small generators) is much more robust, and less of a terrorist target than one big expensive central facility...

[r9etb]

You've got some valid points. However, you've also constructed a straw-man, in the sense that you've simply assumed that solar power advocates want/need to fully replace the current power sources.

There is a very broad middle ground here, based on paradigm of localized use. It doesn't get rid of the need for large, non-solar power plants, but it does offer some relief.

What you've done is made a case against solar cells in their entirety. Your set of "narrow exceptions" misses a whole range of possibilities.

For example, it's possible to run a home air conditioning unit using power generated by roof-top cells. The highest demand and best opportunity to use the system occur at the same time: during periods of sunlight.

It's true that there are cost/energy return issues. But those are not unsolveable.

[Boot Hill]

Just to nitpick...You are technically correct. However if I had used the word "flux", instead of power, how many non-engineering types here would have had any idea what the heck I was talking about?

--Boot Hill

[Boot Hill]

null and void claims:   "I'm getting 800W from my ~ 2 m2 array in downtown San Jose."

I can guarantee you that you are not getting 800 watts from a 2 m² PV cell array.

--Boot Hill

[Boot Hill]

By the very act of funding such a poor system, the government is inhibiting the very research that could lead to an honest break through in the field.

--Boot Hill

[Protagoras]

By the very act of funding such a poor system, the government is inhibiting the very research that could lead to an honest break through in the field.

I agree, which is why I started my previous post with the statement I made.

[upcountryhorseman]

Are these items available to the average business
at a reasonable price?

[dark_lord]

There is an interesting article in the current issue of Discover magazine for a device that uses a bunch of mirrors (96 partial parabolic mirrors) to focus sunlight on the base of a Stirling engine. Light sensing photocells are hooked to thermocouples and a computer to keep the mirrors focusing the sunlight on the engine, which turns a generator which produces the electricity. The heat focus on the Stirling is about 1,200 degrees Fahrenheit. The prototypes have been built and work well. It looks very interesting. In mass production they think they can sell a unit for about $250 bucks, and it produces 250 peak watts of power. They get that $250 per unit figure by assuming a production run of 100,000 units. Target customers will probably be commercial customers with flat roofs (think light industrial or office parks) in the deep South. Of course it won't work as well on cloudy days etc. but there is nothing fancy here, no special technology. It looks like they can produce electricity at $1 per watt or a little more (assuming they can mass produce the units) which is reasonably competitive.

My guess is that this venture will be successful, but I wonder about maintence costs as well since these things do have moving parts. The design looks good (and you should be able to read it online in a couple weeks, Discover doesn't post the online issue until after the print issue has been out a while and this is the August 2003 issue). I bet that they will need maintenance every year or 6 months, at a miniumum to wipe of the glass enclosure that protects the unit from the weather but probably also to check the moving parts.

[MainFrame65]

"...I'm getting 800W from my ~ 2 m2 array in downtown San Jose."

And how many watts at midnight, with a new moon, in mid-winter? In other words, what is the average output over a full year, which would tend to average out daily, seasonal, and weather variation?

[Boot Hill]

r9etb suggests:   "For example, it's possible to run a home air conditioning unit using power generated by roof-top cells.."

You just couldn't do it and make any kind of economic sense (without government subsidies, that is). Let's look at an example.

1. We have a 3,000 watt window air conditioner unit running 8 hours per day for 180 days per year at a utility rate of 15¢ per kW-hr. Cost per year = $648.

2. When calculating PV output we will use no loss for night time, sun angle or dirt. The starting value of 790 W/m^2 is reduced by PV loss (85%), packaging loss (20%), heat loss (15%), inverter loss (20%), leaving 64.5 W/m^2. For 3,000 watts, that's 46.5 m^2 of PV panel array needed. The area of the SP-150 (for instance) is 1.32m^2, meaning that you need at least 35 of them at $700/unit or $24,500. Plus another $3,000 for the 3kW inverter and another $5,000 for someone to install and wire this system. Now we're up to $32,500. I'll give you the building permits for free.

3. But for that same $32,500, I could have run the air conditioner off the power grid for 50 years! And this does not even begin to account for the time-value of the $32,500 I had to plunk down on day one to start this venture!

So maybe you could explain to me again just why it would be such a good idea to buy the solar cells to run the air conditioner?

--Boot Hill

[mvpel]

You make the assumption that the price of electricity from the grid will always be 15c for the next 50 years. I don't think that's likely. In California, you'd be paying upwards of 25c per kWh for that A/C unit after you burned through your monthly peak usage limits.

[balrog666]

By the very act of funding such a poor system, the government is inhibiting the very research that could lead to an honest break through in the field.

Bump.