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The Fuel Cell For Home

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Re: The Fuel Cell For Home

#11

Post by maxerickson »

jimmcslim wrote: post #9
marvin wrote: post #2

Does anyone know what makes this more compelling than static power generation over the electric grid? Gas-fired power plants are pretty efficient. Is this significantly better?

A potential factor is improved efficiency due to not relying on an electricity transmission and distribution grid, and generating the electricity where it is needed... 1. Electricity grids have to account for a loss factor due to the accumulated resistance of the wires between the power station and where the electricity is actually used. This power is lost as heat radiating from the transmission wires. That said, I'm…

Grid losses aren't that bad:

EIA estimates that national electricity transmission and distribution losses average about 6% of the electricity that is transmitted and distributed in the United States each year.

http://www.eia.gov/tools/faqs/faq.cfm?id=105&t=3

Compare that to more than 50% thermal loss at the point of generation.

Re: The Fuel Cell For Home

#13

Post by brc »

otterley wrote: post #7
maxerickson wrote: post #3

Earlier quoted context omitted.

The big win is having the waste heat available at the house.

What if you live in a warm climate?

People in warm climates still have hot showers and need to dry their clothes on rainy days or at night. Or maybe they want to heat up their pool to use all year round. There's always a use for waste heat.

Re: The Fuel Cell For Home

#14

Post by jgamman »

marvin wrote: post #2

Does anyone know what makes this more compelling than static power generation over the electric grid? Gas-fired power plants are pretty efficient. Is this significantly better?

FCs don't operate via the carnot cycle so in theory can be 90+% efficient in electricity generation. in practice, 35-50% electrical efficiency is possible (although this isn't a ceiling, just a current tech benchmark). coal fired is 25-30% and gas fired 30-40% ish - i think the carnot efficiency maxes out somwhere 40-50% so no matter what you do (and we've been doing this for 100 years now) you aren't going to get 60+% electrical efficiency from burning stuff to drive a turbine. the FC remainder is thermal and in the situation of a combined heat and power unit, this is very useful as a lot of energy is just used for space heating - why waste high grade electrons if you've got some waste heat kicking around anyway. from the users perspective, 50% electrical and 50% thermal is getting close to an ideal 'efficiency' for actual use. i used to work on these systems in the late 90s and there's nothing new here. the dream of having a complicated steam reforming unit coupled to a Faraday device that is expected to run like a fridge with zero user maintenance for 3-5 years at a time is tremendously difficult.

Re: The Fuel Cell For Home

#15

Post by jws »

marvin wrote: post #2

Does anyone know what makes this more compelling than static power generation over the electric grid? Gas-fired power plants are pretty efficient. Is this significantly better?

This system is integrated with domestic heating requirements. If you run the system enough to heat the house and provide hot water, then any electricity it makes is effectively at 100% efficiency. This can easily make a lot of sense in cold places.

Commercial natural gas electrical generation facilities are about 35% efficient. It is probably inappropriate to consider transmission losses since natural gas power plants tend to be located in areas of high consumption, but that 35% only goes down on the way to the end user. Remember, it doesn't have to beat the utilities for it to make sense.

Consider a house with a $200/month natural gas bill for heating. At $1/therm that is 200 therms of gas. Let's just guess at around 10% efficient for these cells, 220 therms of gas would give us our 200 therms of heat plus 20 therms of electricity which we convert to kilowatt hours, about 600 kilowatt hours. At $0.12 per kwHr that gets us about $72 of electricity for $20 in gas. Let's just say for every $3 we currently spend on gas we can get $1 of 100% efficiently generated electricity (1/3 the carbon footprint).

At 37°N, in December it would cover half of my electricity for a free standing house (but remember I made up their efficiency. At 20% it would cover all of my electricity. Googling about shows a record high around 60% and some press releases around 50%. I have no idea what these are, but it is probably several times the 10% number I used.)

During summer when I'm using nearly twice the electricity my gas bill is so close to zero as to not matter.

Re: The Fuel Cell For Home

#16

Post by Zigurd »

The article seems to claim direct conversion from methane. That sounds unlikely. If they are not direct methane fuel cells, how do these systems create hydrogen?

Re: The Fuel Cell For Home

#17

Post by paulyg »

jws wrote: post #15
marvin wrote: post #2

Does anyone know what makes this more compelling than static power generation over the electric grid? Gas-fired power plants are pretty efficient. Is this significantly better?

This system is integrated with domestic heating requirements. If you run the system enough to heat the house and provide hot water, then any electricity it makes is effectively at 100% efficiency. This can easily make a lot of sense in cold places. Commercial natural gas electrical generation facilities are about 35% efficient. It is probably inappropriate to consider transmission losses since natural gas power plant…

Gas turbines are around 35% efficient in simple cycle but combined cycle plants are pushing 60% efficiency.

Re: The Fuel Cell For Home

#18

Post by gnoway »

This is a solid oxide fuel cell, right? What makes this one better than the bloom energy devices?

Speaking of which, what happened to the bloom boxes? Are the big customers still customers?

Re: The Fuel Cell For Home

#19

Post by hatbert »

jgamman wrote: post #14
marvin wrote: post #2

Does anyone know what makes this more compelling than static power generation over the electric grid? Gas-fired power plants are pretty efficient. Is this significantly better?

FCs don't operate via the carnot cycle so in theory can be 90+% efficient in electricity generation. in practice, 35-50% electrical efficiency is possible (although this isn't a ceiling, just a current tech benchmark). coal fired is 25-30% and gas fired 30-40% ish - i think the carnot efficiency maxes out somwhere 40-50% so no matter what you do (and we've been doing this for 100 years now) you aren't going to get 60…

> FCs don't operate via the carnot cycle so in theory can be 90+% efficient in electricity generation.

Sorry, this is wrong.

FCs are not heat engines, so the thermodynamic limitations of heat engines are not relevant to fuel cells. That said, thermodynamic limitations do set an upper bound on the efficiency of fuel cells. For hydrogen fuel cells, the theoretical upper bound is 83% [1]. That's for just the process of turning hydrogen into electricity, and that does not include the process for producing hydrogen in the first place. "90+%" efficiency is strictly impossible in theory or practice.

> i think the carnot efficiency maxes out somwhere 40-50% so no matter what you do (and we've been doing this for 100 years now)

It must be noted that 50% thermal efficiency is a practical upper bound for a real electrical power plant, not a theoretical one. Some combined-cycle gas turbines do exceed 50% efficiency under some operating conditions.

[1] http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/electrol.h...

Re: The Fuel Cell For Home

#20

Post by jws »

paulyg wrote: post #17
jws wrote: post #15

Earlier quoted context omitted.

This system is integrated with domestic heating requirements. If you run the system enough to heat the house and provide hot water, then any electricity it makes is effectively at 100% efficiency. This can easily make a lot of sense in cold places. Commercial natural gas electrical generation facilities are about 35% efficient. It is probably inappropriate to consider transmission losses since natural gas power plant…

Gas turbines are around 35% efficient in simple cycle but combined cycle plants are pushing 60% efficiency.

The EPA report shows combined cycle plants at about 52% efficiency in 2012. With respect to the above numbers, it means only 1/2 the carbon footprint, not 1/3. It doesn't play in the cost numbers since I worked from the sale price of the electricity rather than its input costs.
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