The Ergosphere
Saturday, October 14, 2006
 

Great strides

More evidence proof that events are getting ahead of me:  GE has a SOFC fuel-cell stack which hits 49% efficiency.  The GE stack is estimated to cost $254/kW for a 5.4kW system (under $1400 for 5.4 kW), exclusive of fuel reformer and electronics.

It's not clear if the efficiency is for the stack alone (probably) or for the complete system, or what the cost and efficiency loss of fuel preparation would be.  If the cells are aimed at use in coal plants, it seems likely that they will take scrubbed syngas (CO + H2 + inert gases) as their fuel and require no further reformation.  If fuels like methane and propane require no preparation and the 49%-efficient stack is followed by a 95%-efficient converter, the fuel-to-juice efficiency would be 46.6%.  That's not half bad.

The system cost for cells such as these is not easily pinned down [1], but if we assume $600/kW we probably won't be far off.  Last, we need a total system efficiency.  Condensing furnaces exceed 95%, so that seems like a completely reasonable assumption.

If we assume 46.6% electrical efficiency and 95% total efficiency (48.4% output as heat, 5% losses) here's what we'd get out of a therm of natural gas, assuming a price of 65¢/therm for gas and $.68/therm for the produced heat:

  Product     Quantity     Units     Value/unit     Total value  
  Electricity     13.65     kWh     $0.08     $1.09  
  Heat     0.484     therm     $0.68     $0.33  
TOTAL     $1.42  

Looks like the unit would just about double your money.  If you had a 5 kW unit running at 25% capacity factor for the year (providing both space heat and DHW), it would consume 802 therms of gas at a cost of $521 and yield heat and electricity worth $1139.  The gross profit before depreciation and maintenance would be $618/year, sufficient to pay off a $3000 unit in 5 years.

Most households don't use 5 kW of electricity during the heating season except for electric stoves or heat pumps.  I haven't looked at the net efficiency of the fuel cell plus heat pump in at least a week, so it's time to scribble on another envelope.  5 kW into a heat pump with an EER of 12 would yield 60,000 BTU/hr.  The example fuel cell system producing 5 kW would burn 0.366 therm/hour of gas and yield 17,700 BTU/hr of heat; together, the two could produce 77,700 BTU/hr of heat from 36,600 BTU/hr of gas.  This is an EER of 212%, cutting fuel requirements by 54% compared to a 98%-efficient condensing furnace.

I'll come back and look at the combo of FC/heat pump plus wind power and PHEV later.  For now, it looks like a replacement of gas furnaces with FC/heat pump combos could offset quite a few years of natural gas depletion, and make it even cheaper to adopt alternative energy supplies when we develop them (so long as they're SOFC-compatible).  Samples suitable for these purposes are in testing at the Department of Energy, and the projected price is right.

[1] I found Assessment of Solid Oxide Fuel Cells in Building Applications which specifies the cost of an inverter as $400/kW and so forth, but the exponents for scaling most of these costs with size are specified as zero.  I can't tell if the authors assumed that the cost would be roughly the same across the 1-5 kW power range (which seems likely for elements such as the water heater), or if this is a typo.  This report is also 7 years old and way out of date.  The SECA report 10 kW SOFC Power System Commercialization SECA Semi-Annual Report 41244R04 states a goal of $400/kW system cost for the third and final phase.  It is far more recent, and probably more trustworthy. (back)

 
Comments:
Wow, costs really are falling on SOFCs. Is GE actually selling these fuel cells now, or are these estimates of costs when they commercialize a prototype?

How large do they scale their SOFCs? These could be very efficient devices for use in industrial processes to provide both electricity and process heat/steam.

As you said, if SOFCs replace natural gas co-gen boilers, they could greatly extend the depletion time for natural gas.
 
I doubt very much that GE is selling these; the price appears to be a projected price in volume production.

That's still darned impressive; if we asked GE to make us a million stacks a year in 2009 and 10 million a year by 2012, $254/kW would be cheap enough to accomplish a whale of a lot.
 
I don't remember why I posted a comment or how I came to view your "work." Regardless, the one feeling I get reading you. You use the web to crap out your thoughts because you don't have the ability or nerve to speak your mind to someone's face. I sure hope you get paid to come up with all this crap. You have the ability to research, write and present. It would be a huge waste if this was your only outlet.
 
Post a Comment



<< Home
Talk largely about energy and work, but also politics and other random thoughts


Mail Engineer-Poet

(If you're mailing a question, is it already in the FAQ?)

Important links

The FAQ
Glossary
The Reference Library

Blogchild of

Armed and Dangerous

Blogparent of

R-Squared




The best prospect for our energy future:
Flibe Energy

ARCHIVES
January 1990 / February 2004 / March 2004 / June 2004 / July 2004 / August 2004 / September 2004 / October 2004 / November 2004 / December 2004 / January 2005 / February 2005 / March 2005 / April 2005 / May 2005 / June 2005 / July 2005 / August 2005 / September 2005 / October 2005 / November 2005 / December 2005 / January 2006 / February 2006 / March 2006 / April 2006 / May 2006 / June 2006 / July 2006 / August 2006 / September 2006 / October 2006 / November 2006 / December 2006 / January 2007 / February 2007 / March 2007 / April 2007 / December 2007 / January 2008 / May 2008 / June 2008 / August 2008 / October 2008 / November 2008 / December 2008 / February 2009 / March 2009 / April 2009 / May 2009 / June 2009 / July 2009 / August 2009 / September 2009 / October 2009 / November 2009 / December 2009 / January 2010 / April 2010 / May 2010 / June 2010 / July 2010 / August 2010 / September 2010 / October 2010 / November 2010 / December 2010 / January 2011 / February 2011 / March 2011 / April 2011 / May 2011 / July 2011 / August 2011 / September 2011 / October 2011 / April 2013 / November 2013 / December 2013 / January 2014 / February 2014 / March 2014 / April 2014 / July 2014 / August 2014 / September 2014 / October 2014 / November 2014 / February 2015 / April 2015 / October 2015 / March 2016 / April 2016 / May 2016 / June 2016 / July 2016 / November 2016 / December 2016 / February 2017 / May 2017 / June 2017 / September 2017 / October 2017 / November 2017 / March 2018 / May 2018 / June 2018 / October 2018 / December 2018 / January 2019 / March 2019 / June 2019 / October 2019 / November 2019 / March 2020 / June 2020 / December 2020 / March 2021 / April 2021 / May 2021 / July 2021 / January 2022 / February 2022 /


Powered by Blogger

RSS feed

Visits since 2006/05/11: