I love this technology
a whole lot, but this is Hacker News so it is worthwhile to think critically about this kind of "press release"-style news posting. This article does a bit of hand waving with the numbers, and, while this is an amazingly cool project, I think that they are overselling its benefits.
First, let's get the terminology right. This plant has a capacity of 200 MW. That does not mean that it produces 200 MWh. The formula for converting MW into (annual) MWh is the following:
MWh = MWx365x24xCF
In the above formula, CF is the capacity factor. Capacity factor is basically the amount of energy that a plant is actually able to produce over the course of a year divided by the total capacity of the plant. Here are some common capacity factors for various industries (taken from a private document, so no sources but this stuff is easy enough to google):
* Coal - 65-95%
* Natural Gas - 35-65%
* Hydro - 25-65%
* Solar - 20-35%
* Wind - 20-35%
* Nuclear - 80%+
Capacity factors are never 100% for various reasons:
* Plants may need to be taken offline for refueling, maintenance, or inspection
* For renewables, the wind isn't always going at full speed and the sun isn't always shining
* A whole bunch of other things that I am too tired to list (read the references below, they have some more in them)
Now, let's look at this new project, and one of the claims made in this article.
According to the article, this plant will be able to provide power for 150,000 homes. According to the EIA, the average household annual energy usage is 10,896 KWh. Given this information and using a more generous solar capacity factor (35%):
Number of Homes Powered = (200x365x24x.35) / 10.896 = 56,278 homes
Hmm, well that's just a bit less than what the article claimed, so they must be assuming a really amazing capacity factor for this estimate. Let's solve the below for cf and see what we get....
(200x365x24xcf)/10.896=150000
cf = approx. 93%
Look, I'm all for scientific advancement and alternative energy, but can we try to be more sensible than this? This is a highly improbable capacity factor.
Documents available from Enviro Mission says that the simulated capacity factor will be more like 50%. When we plug that number into the equation we get about 80,397 homes, which is pretty sensible. However, we have to remember that these are only simulated numbers. There are no similar projects currently available that can be compared to this one, so the actual capacity factor may be either more or less.
Note: Please keep in mind that efficiency is a totally different concept from capacity factor. Efficiency is typically used to describe how well a plant transfers from its energy source into electricity^. The capacity of a plant is a number that already incorporates the plant's efficiency. The capacity factor is simply a measure of how much of that capacity is actually used on an annual basis on average.
^ I am not an electrical engineer. I am an economist, that is the best definition I can come up with.
Disclaimer: I am incredibly tired right now, so if any errors appear in the above posting please send me some coffee so that I can correct them before falling asleep.
References:
+ http://www.eia.gov/tools/faqs/faq.cfm?id=97&t=3
+ http://www.solarpaces.org/CSP_Technology/docs/solar_tower.pd...
+ http://www.enviromission.com.au/IRM/Company/ShowPage.aspx?CP...
Edit: Formatting was all messed up the first time. Forgot to include some additional information. Added clarification on efficiency.