Photovoltaic power plants produce electricity from sunlight. : GMAT Critical Reasoning (CR)
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# Photovoltaic power plants produce electricity from sunlight.

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Photovoltaic power plants produce electricity from sunlight. [#permalink]

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11 Mar 2005, 14:45
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12. Photovoltaic power plants produce electricity from sunlight. As a result of astonishing recent technological advances, the cost of producing electric power at photovoltaic power plants, allowing for both construction and operating costs, is one-tenth of what it was 20 years ago, whereas the corresponding cost for traditional plants, which burn fossil fuels, has increased. Thus, photovoltaic power plants offer a less expensive approach to meeting demand for electricity than do traditional power plants.
The conclusion of the argument is properly drawn if which one of the following is assumed?
(A) The cost of producing electric power at traditional plants has increased over the past 20 years.
(B) Twenty years ago, traditional power plants were producing 10 times more electric power than were photovoltaic plants.
(C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants.
(D) Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20 times the cost of producing power at traditional plants.
(E) The cost of producing electric power at photovoltaic plants is expected to decrease further, while the cost of producing power at traditional plants is not expected to decrease.
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11 Mar 2005, 15:27
I would go for C

as if C is true, then the new technology would not allow a reduction in the cost for productin biological energy, brining only reduction for photovoltaic power.
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11 Mar 2005, 15:30
My choice is E.

Since cost effectiveness is discussed
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11 Mar 2005, 15:51
I go with D.

20 years ago, cost for photovoltaic <= 20 * cost of traditional

now, one-tenth of the cost, so now, cost for photovoltaic <= 2 * cost of traditional

in the stem, it states "the corresponding cost for traditional plants, which burn fossil fuels, has increased", so during long run, Photovoltaic is more cost-effiency.
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11 Mar 2005, 18:10
C.

If the advances can be applied to traditional plants, the cost advantage mentioned in the argument falls apart.
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11 Mar 2005, 19:01
prep_gmat wrote:
C.

If the advances can be applied to traditional plants, the cost advantage mentioned in the argument falls apart.

Hello, I think it is not necessary.

No matter what kind of technology advances, only if the cost of producing power at traditional plants doesn't decrease less than that at photovoltaic plants.

The conclusion is still effective.

However, if not, then it will weaken the conclusion.

SO, I go with E.

'The cost of producing electric power at photovoltaic plants is expected to decrease further, while the cost of producing power at traditional plants is not expected to decrease.'
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11 Mar 2005, 20:39
chunjuwu wrote:
prep_gmat wrote:
C.

If the advances can be applied to traditional plants, the cost advantage mentioned in the argument falls apart.

Hello, I think it is not necessary.

No matter what kind of technology advances, only if the cost of producing power at traditional plants doesn't decrease less than that at photovoltaic plants.

The conclusion is still effective.

However, if not, then it will weaken the conclusion.

SO, I go with E.

'The cost of producing electric power at photovoltaic plants is expected to decrease further, while the cost of producing power at traditional plants is not expected to decrease.'

I go with E on this. E states that the cost of the new stuff will decrease further...but does this need to be assumed to draw the conclusion that the new stuff is less expensive approach?
Let us see it the other way - say we negate E - the cost of the new stuff is going to increase in the future - this will definitely prevent us from concluding that the new stuff offers a better approach.
whereas negating C would mean all the tech. advancements have been applied to the traditional approach...in this we will also have to make an assumption that tech. advancements can be applied to traditional approach
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12 Mar 2005, 09:40
the conclusion, "photovoltaic power plants offer a less expensive approach to meeting demand for electricity than do traditional power plants."[/color]

(A) The cost of producing electric power at traditional plants has increased over the past 20 years.
- Not important.

(B) Twenty years ago, traditional power plants were producing 10 times more electric power than were photovoltaic plants.
- Out of scope

(C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants.
- Not important.

(D) Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20 times the cost of producing power at traditional plants.
- So D still does not tells us for sure that photovoltaic plants are more cost-efficient.

(E) The cost of producing electric power at photovoltaic plants is expected to decrease further, while the cost of producing power at traditional plants is not expected to decrease.
- If this is the case, then we're sure one day photovoltaic plants will be more cost-efficient.

E it is.
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12 Mar 2005, 23:52
Fact: P's cost is reduced to 1/10 of its original cost. T's cost has increased.
Conclusion: P is less expensive than T.

Clearly it is a leap from the facts to the conclusion. Think about this: How much do they differ in cost originally? What if P's cost was $1000000 20 years ago and T's cost was only$10? Who's more expensive now?

(A) The cost of producing electric power at traditional plants has increased over the past 20 years.
Not enough to answer our question.

(B) Twenty years ago, traditional power plants were producing 10 times more electric power than were photovoltaic plants.
We are only interested in cost, not quantity of outputs.

(C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants.
It doesn't matter. The facts already said that T's cost has increased.

(D) Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20 times the cost of producing power at traditional plants.
There, answers our questions perfectly. Of course it would be even better if the number is 10 instead of 20. But as it is now, with the words "less" and the fact that T's increased it's more or less sufficient for this one to provide a rough estimate to suppor the claim.

(E) The cost of producing electric power at photovoltaic plants is expected to decrease further, while the cost of producing power at traditional plants is not expected to decrease.
Still we can't get to the conclusion that P is less expensive today.

(D)
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13 Mar 2005, 01:11
Hello HongHu.

Even if we can get that 20 years ago the cost of producing power at Photovoltaic power plants is less than 10 times of the cost of producing power at traditional plants.

How can we make sure that now photovoltaic power plants still offer a less expensive approach?

Just because the corresponding cost for traditional plants has increased and the cost of producing electric power at photovoltaic power plants has decreased due to the technological advances.

I initially considered choice D, but the figure 20 is really tricky.
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13 Mar 2005, 07:28
chunjuwu wrote:
Hello HongHu.

Even if we can get that 20 years ago the cost of producing power at Photovoltaic power plants is less than 10 times of the cost of producing power at traditional plants.

How can we make sure that now photovoltaic power plants still offer a less expensive approach?

Just because the corresponding cost for traditional plants has increased and the cost of producing electric power at photovoltaic power plants has decreased due to the technological advances.

I initially considered choice D, but the figure 20 is really tricky.

Let's look at (D) again.

The passage says:
- Photo plants operate now at 1/10 the cost of what it was 20 yrs ago
- Cost of traditional plant has increased

Choice (D) says:
- 20 yrs ago, the cost of operating a photo plant is less than 20 times the cost of operating a traditional plants.

Let's put in some figures to get a clearer picture:
we assume the following costs:
- 20 yrs ago, cost of operating traditional plant: $1 - 20 yrs ago, cost of operating photo plant:$19 (less than 20 times cost of traditional plant)

- Today, cost of operating photo plant: $1.9 - Today, cost of operating traditional plant:$1+delta

Since we do not know the value of delta, we can't say for sure that photo plants are going to be more cost-efficient. If this delta value is >0.9, then yes, photo plants are more cost-efficient. If delta value is <0.9, then no, photo plants are not more cost-efficient.

On this premise, we can rule out (D). Although (E) is not perfect, it is better than (D)
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13 Mar 2005, 07:45
I had changed my mind to D on this and Hong's explanation clinches it.
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13 Mar 2005, 07:48
prep_gmat wrote:
I had changed my mind to D on this and Hong's explanation clinches it.

(D) can be challenged. Look at my post above with the numerical workings.

(E) although isn' a nice choice, at least offers a suggestion that cost of operating photo plants will go down further. It does not ask if photo plants are cost-effectivie today, but whether it offers a cost-effective solution. This could be today, tomorrow or further down the road.
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13 Mar 2005, 13:17
The conclusion is:
Quote:
photovoltaic power plants offer a less expensive approach to meeting demand for electricity than do traditional power plants.

It says P is less expensive. It didn't say P will be less expensive one of these days in the future.
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13 Mar 2005, 16:08
D would make sense though it was not my initial choice. mine was C. but makes sense what HongHu has said..
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13 Mar 2005, 18:25
But can you work out a figure with the constraints given and show me that not a single case will not refute the statement in (D). I think not.. if so, we can't be sure (D) is true.
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13 Mar 2005, 20:41
Depending on how much T's cost has increased the analysis can actually be meaningful, the figures are close at the least. For E we don't have a starting figure and their cost difference could be in millions, there is no limit in saying when the day would be when P can be less expensive then T. This would render the analysis non sensical.
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13 Mar 2005, 22:03
HongHu wrote:
Depending on how much T's cost has increased the analysis can actually be meaningful, the figures are close at the least. For E we don't have a starting figure and their cost difference could be in millions, there is no limit in saying when the day would be when P can be less expensive then T. This would render the analysis non sensical.

Honghu, I do agree E is not a good choice but referring back to your original post:

"What if P's cost was $1000000 20 years ago and T's cost was only$10? Who's more expensive now?" P cannot cost $100,0000 20 yrs ago and T$10 according to choice (D), since P is only less than 20 times cost of T.
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13 Mar 2005, 23:00
hi, ywilfred
Now I've been convinced that D is better than E.

Let's look the passage carefully, and I will divide the passage into several parts.

1, the cost of producing electric power at photovoltaic power plants is one-tenth of what it was 20 years ago. Let's set (1/10x, now) and (x, 20 years before).

2, the corresponding cost for traditional plants has increased

3, conclusion: photovoltaic power plants offer a less expensive approach than do traditional power plants.

Caution: there is a big gap between 1,2 and 3, we need to compare the cost of photovoltaic plants with the cost of traditional plants so as to get the conclusion.

in Choice E, the cost of producing electric power at photovoltaic plants is expected to decrease further, while the cost of producing power at traditional plants is not expected to decrease.

We don't need to assume any further decreasing of photovoltaic plants. As long as the cost of photovoltaic plants is less than the cost of traditional plants now or 20 years before, we can attain the conclusion.

(D) Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20 times the cost of producing power at traditional plants.

This exactly supplements the big gap.

That is to say, the cost of traditional plants is 20x in my example.
Moreover, becaus of technology advance and the corresponding increasing cost for traditional plants, we can get the conclusion: photovoltaic power plants offer a less expensive approach than do traditional power plants.

Hope this helps.

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13 Mar 2005, 23:20
chunjuwu wrote:
hi, ywilfred
Now I've been convinced that D is better than E.

Let's look the passage carefully, and I will divide the passage into several parts.

1, the cost of producing electric power at photovoltaic power plants is one-tenth of what it was 20 years ago. Let's set (1/10x, now) and (x, 20 years before).

2, the corresponding cost for traditional plants has increased

3, conclusion: photovoltaic power plants offer a less expensive approach than do traditional power plants.

Caution: there is a big gap between 1,2 and 3, we need to compare the cost of photovoltaic plants with the cost of traditional plants so as to get the conclusion.

in Choice E, the cost of producing electric power at photovoltaic plants is expected to decrease further, while the cost of producing power at traditional plants is not expected to decrease.

We don't need to assume any further decreasing of photovoltaic plants. As long as the cost of photovoltaic plants is less than the cost of traditional plants now or 20 years before, we can attain the conclusion.

(D) Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20 times the cost of producing power at traditional plants.

This exactly supplements the big gap.

That is to say, the cost of traditional plants is 20x in my example.
Moreover, becaus of technology advance and the corresponding increasing cost for traditional plants, we can get the conclusion: photovoltaic power plants offer a less expensive approach than do traditional power plants.

Hope this helps.

Point noted. Thanks I do not know how i got my math for this question all wrong.
13 Mar 2005, 23:20

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