Reference, Questions and Help > Nuke Q&A
Press Question
Rennhack:
If anyone can help this guy, please send me an email.
--- Quote ---Mr. Rennhack--
I'm a reporter at the St. Paul Pioneer Press, and I came across your website and found it interesting. I'm trying to track down some generating figures for Xcel Energy's nuclear and conventional power plants, though, and I was having difficulty reconciling some numbers, so I'm writing to you to see if you might be able to provide some insight.
In particular, I'm trying to figure out how to determine "net capacity factor." FERC seems to have one formula, NERC has another and it appears the individual utilities may even have their own.
Since you cite the '97 "average capacity factor" numbers on the plant pages of your website, I'll use that year as an example. If you look at the NRC's 2002 annual report, it shows that in '97, Monticello had a capacity factor of 83.6; your site lists it as 76.7. Similarly, the '97 NRC figures for Prairie Island's Unit 1 and 2 capacity factors are 98.9 and 91.1 respectively; your site lists the '97 figures as 78.4 and 81.2 respectively. I checked with the NRC and they said they use the capacity factors that are provided by the licensee.
Compounding the problem is that when I use figures that NSP provided to FERC in its Form 1 covering '97 and plug them into the equation that FERC told me to use, I come up with a capacity factor of 97.1 at Monticello, and a combined capacity factor of 76.8 for Prairie Island. (In the FERC Form 1, all figures for the two units are combined into a single total.)
The raw numbers from the Form 1 that FERC said are relevant are Total Installed Capacity (Max. Gen. Nameplate Ratings-MW), Plant Hours Connected to Load and Net Generation Exclusive of Plant Use. Given that, the relevant figures for Monticello for '97 are:
Total Installed Capacity: 631.2 MW
PHCL: 6776
Net Gen.: 3,876,322 MW
I guess this is a rather long-winded way of asking:
-- Where did you get your figures?
-- If you came up with them on your own, what equation did you use and what were the raw numbers for it?
-- Are you able to provide any insight into how to come up with figures that would be considered reliable by the industry?
Thanks. I appreciate your help.
--- End quote ---
I borrowed the statistics from the Nuclear Energy Institute (http://www.nei.org/documents/2001_Plant_Capacity_Factors.pdf) And the EIA http://www.eia.doe.gov/cneaf/nuclear/page/at_a_glance/reactors/monticello.html
EIA states 2001 AVERAGE capacity factor as 74.1% (Monticello) NEI states 76.5 Net Capacity Factor…
I would say that the term ‘average’ and ‘net’ might have something to do with the difference.
I have found no ‘formula’, just a definition:
Capacity factor (gross)
The ratio of the gross electricity generated, for the period of time considered, to the energy that could have been generated at continuous full-power operation during the same period.
Capacity factor (net)
The ratio of the net electricity generated, for the period of time considered, to the energy that could have been generated at continuous full-power operation during the same period.
Pet_Cow:
It is also interesting to note that a utility can produce beyond 100% capacity with cold injection water for cooling the condenser. I believe there are actually 2 capacity factors, one is for operability, one is for power generation, although I may be wrong about this. The numbers would be similar, but slightly off.
HydroDave63:
Mike, your definition of
Capacity factor (net)
The ratio of the net electricity generated, for the period of time considered, to the energy that could have been generated at continuous full-power operation during the same period.
is essentially correct, when you also subtract out power used by the generating station on its aux loads, like air conditioning/HVAC loads, HP break trailers, lighting, etc.
It can exceed 100%, for factors like colder ultimate heat sink temps, turbine efficiency, nuclear instrument rating increases,etc. The last two factors have become more and more commonplace throughout the industry in recent years. The baseline number of what the plant should produce is based on its original year of manufacture rating. Several utilities have changed turbines for greater efficiency, and many have recalculated some statistical properties of their nuclear instruments, and allowed to run at 102% rated thermal power. So, in a good year, at a top performing plant it is not impossible to have a 103% capacity factor year. Hope this helps!
rlbinc:
There are many versions of "Capacity Factor", utilities customize the stats to meet their needs. I have seen "Net Dependable Capacity Factor" which considers age related de-rates, usually provided to State Commerce Commissions for rate case analysis in regulated states. More applicable to fossil boilers accumulating scale and slag, many nukes are owned by fossil utilities and use these numbers for corporate conformity.
With Power Uprate projects across the industry, many plants are now "Electrically Limited" due to Transformer capacity or grid limitations.
From an operator perspective, the only thing that matters is Licensed Power Level, given in Tech Specs.
For the company, the Megawatt Hour meter is all that matters, that's how the bills get paid.
DainJer:
Downtime has to be factored in...the outages in '97 had'nt shortened quite as much as now. emergency outages and scheduled outages should be averaged in to any net or average. 30 days offline can make a difference.
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