One of our staff members, Rembrandt Koppelaar, made the following rough cost calculations of the return on investment for the Bloom Box, excluding the cost for grid connection. Based on his calculation, it takes 15 years to get back the investment cost. (The time would be longer, if the cost for grid connection were included.)
Conservative assumptions based on the video: (All amounts in US $).
- $800,000 for a Bloom Box that generates power for 100 American Households
- American household energy usage is 10,000 kWh per year (10,600 in 2001)
- Bloom Box hence generates 1 million kwh per year at an investment cost of $800,000
- Production costs US for electricity from natural gas for residential use is $ 0.10 per kwh (http://www.eia.doe.gov/cneaf/electricity/epm/table5_3.html)
- costs for 1000 cubic foot of natural gas for residential use is 12 dollars (http://tonto.eia.doe.gov/dnav/ng/ng_pri_sum_dcu_nus_m.htm)
- 1 cubic foot of natural gas has an energy content of 1,034 BTU
- 1 kWh is equivalent to 3413 BTU spent in an hour
- Bloom Box can turn natural gas into electricity at an 80% conversion efficiency
Calculation:
- Costs per year for 1 million kWh from natural gas from centralized power sources is $100,000.
- 1000 cubic foot of natural gas gives 1,034,000 BTU which can be converted at 80% efficiency, hence 827,200 BTU of power which is equivalent to 242 kWh, costing $12 for the fuel. So 12/242 = $ 0.05 per kWh incorporating fuel costs only. Which amounts to a total fuel cost of $50,000 for 1 million kWh.
At an investment cost of $800,000 dollars it would take approximately 15 years (800,000 / 50,000) to pay back investments, excluding the costs of connecting to the grid.
anz.theoildrum.com
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a comment
Libelle on February 24, 2010 - 10:09am
This device appears to be a gas reformer, using air and natural gas to make hydrogen, followed by a solid oxide fuel cell. It isn't a new idea.
Let's look at likely overall fuel energy to electrical energy efficiency.
Fuel cell - 50%
Reforming - An industrial-scale steam reforming setup might get 80% efficiency, but this a small-scale air-based one, so I think that 60% would be optimistic.
That would give an overall efficiency of 30%, but the calculation neglects electrical power consumed within the box. This can amount to a substantial portion of the output - 20% internal use would not surprise me.
The useful electricity production would in that case be 24% of the fuel energy in the gas.
See here for a thermodynamic analysis of what is possible for a combination of steam reforming with a PEM fuel cell. The authors give 40% as the attainable efficiency for this type of unit. The PEM fuel cell would be comparable in efficiency with a solid oxide one, but the air reformer would not be as good as the steam one.
I would expect the overall gas energy to electricity efficiency of the Bloom Box would be about 25%. I can see how it could be a little higher or lower, but I doubt very much that it would be over 30%.
Comparable efficiencies are attainable with normal reciprocating internal combustion engines, and it is not hard to set up a cogeneration system with this type of engine. IC engines have the advantages of being cheap, reliable, easy to maintain and very common indeed.
For comparison, big combined-cycle gas turbine installations achieve about 55% efficiency in the production of electricity from natural gas. |
