Energy from waste for houses
The hydrogen-generation (Hygen) market has to be with the early adopters who can see the value in producing energy from their on-site generated waste. This energy from waste systems use natural gas as a backup only to augment any waste shortfall.
The Plug Power front-end reformer can be way to get started, but buyers should be aware that huge increases in natural gas prices are likely within 3–4 years.
Figure 14.3 shows the front end of a small-scale steam reformer that converts waste into hydrogen-rich syngas.
Although the author has designed and built prototype commercial units for waste conversion, they are not yet available in the marketplace for residences. So fuel cells converting the energy in the hydrogen feedstream to heat and electrical energy should be noted.
With fuel cells of today, half the feedstock energy is used to drive the fuel cell to produce electricity at 50% efficiency, while the remaining 50% can generate heat.
A check on the waste quantity to supply a home’s energy needs can be done assuming 1 ton/person-year (Curlee, 1994)
Energy from waste for houses
The hydrogen-generation (Hygen) market has to be with the early adopters who can see the value in producing energy from their on-site generated waste. This energy from waste systems use natural gas as a backup only to augment any waste shortfall.
The Plug Power front-end reformer can be way to get started, but buyers should be aware that huge increases in natural gas prices are likely within 3–4 years.
Figure 14.3 shows the front end of a small-scale steam reformer that converts waste into hydrogen-rich syngas.
Although the author has designed and built prototype commercial units for waste conversion, they are not yet available in the marketplace for residences. So fuel cells converting the energy in the hydrogen feedstream to heat and electrical energy should be noted.
With fuel cells of today, half the feedstock energy is used to drive the fuel cell to produce electricity at 50% efficiency, while the remaining 50% can generate heat.
A check on the waste quantity to supply a home’s energy needs can be done assuming 1 ton/person-year (Curlee, 1994)
Figure 14.3 Residential prototype steam reforming of waste.
of general garbage including sewage solid waste plus about 5 tons/year per household for green yard waste. If 5 persons/ household were assumed, the total is 10 tons/year per household.
So it can be assumed that this makes 10 tons/year of syngas (see Glossary) or 4.8 kWh/kg (7500 Btu/lb at 300 Btu/dscf with a density of 0.04 lb/dscf) or 22 MWh/year
(75,000 MBtu/yr). (A sanity check for municipal solid waste (MSW) shows its heating value as 3.9 kWh/kg (6000 Btu/lb) in an inefficient furnace).
With 50% electricity by the fuel cell and 50% heat for the building, the electricity would be 11,000 kWh/year and the thermal energy would be the same number. This is more than the most inefficient houses consume.
For example, the Berkeley house with a pool uses only 2400 kWh/year electricity.
A check can be made also on space heating requirements of a house. An efficient European house needs 15–30 kWh/m2-yr. So a 150m2 house in Europe will consume 2250–4500 kW/year (7–15,000 MBtu/yr). Therefore, in this energy from waste scheme, it is possible to generate more thermal energy than is used in an efficient house for space heating.
Now consider using this extra thermal energy to steam reform the waste to produce hydrogen for vehicles. Assuming they are driving 8000 km/year (5000 miles/yr at 20 mpg gasoline base) that is 950 L of petrol/year (250 gal of gasoline/yr).
With gasoline at 9.63 kWh/L (125,000 Btu/gal), this is 9.6 MWh/year (33,000 MBtu/yr) – comparable to the number calculated above at 11,000 kWh/year (75,000 MBtu/yr) as the extra heat available from waste.
This generates enough hydrogen providing the same amount of energy to the vehicle as gasoline, which shows that the concept can work to use the extra heat to steam reform waste into hydrogen on-site. So in conclusion, this is really a pretty good match all around. So why aren’t we considering local energy from waste more seriously?
The price could be worked out by going backward and assuming that the system has to pay for itself through savings over, say, 15 years. The fuel cell qualifies for $4500/kWh rebate or 50% of the capital cost of the equipment, which ever is less, through the California Energy Commission Buy-down program.
Only fuel cells that use renewable fuel qualify for this rebate. There is also a Federal Tax credit for fuel cells used in homes. Though the author has not developed a detailed design for costing, it is crudely guessed that $50,000 budget would work for a 2.5kWe fuel cell – steam reformer system.
So the rebate is $11,250 and assuming the IRS tax credit to be 25% or $12,500, the balance of $26,250 is amortized over 15 years or $3500/year interest plus principal. The savings in electricity of 2.5 kWh/h is $2847/year at 13¢/kWh and in heating of 4.4 MWh/year (15,000 MBtu/yr at 60¢/therm) is $900/year, which totals to $3747/year. Garbage, plastics, paper, and yard waste bills are eliminated at about $300/year.
So there is a saving of about $4047/year, which would payback the initial investment plus interest in less than 15 years. So even the economics work out.
Now the question is, can this waste steam reformer be built for $50,000–60,000 retail price? Not sure precisely, but it is a great business goal for a future technology high volume business.
Figure 14.3 Residential prototype steam reforming of waste.
of general garbage including sewage solid waste plus about 5 tons/year per household for green yard waste. If 5 persons/ household were assumed, the total is 10 tons/year per household.
So it can be assumed that this makes 10 tons/year of syngas (see Glossary) or 4.8 kWh/kg (7500 Btu/lb at 300 Btu/dscf with a density of 0.04 lb/dscf) or 22 MWh/year
(75,000 MBtu/yr). (A sanity check for municipal solid waste (MSW) shows its heating value as 3.9 kWh/kg (6000 Btu/lb) in an inefficient furnace).
With 50% electricity by the fuel cell and 50% heat for the building, the electricity would be 11,000 kWh/year and the thermal energy would be the same number. This is more than the most inefficient houses consume.
For example, the Berkeley house with a pool uses only 2400 kWh/year electricity.
A check can be made also on space heating requirements of a house. An efficient European house needs 15–30 kWh/m2-yr. So a 150m2 house in Europe will consume 2250–4500 kW/year (7–15,000 MBtu/yr). Therefore, in this energy from waste scheme, it is possible to generate more thermal energy than is used in an efficient house for space heating.
Now consider using this extra thermal energy to steam reform the waste to produce hydrogen for vehicles. Assuming they are driving 8000 km/year (5000 miles/yr at 20 mpg gasoline base) that is 950 L of petrol/year (250 gal of gasoline/yr).
With gasoline at 9.63 kWh/L (125,000 Btu/gal), this is 9.6 MWh/year (33,000 MBtu/yr) – comparable to the number calculated above at 11,000 kWh/year (75,000 MBtu/yr) as the extra heat available from waste.
This generates enough hydrogen providing the same amount of energy to the vehicle as gasoline, which shows that the concept can work to use the extra heat to steam reform waste into hydrogen on-site. So in conclusion, this is really a pretty good match all around. So why aren’t we considering local energy from waste more seriously?
The price could be worked out by going backward and assuming that the system has to pay for itself through savings over, say, 15 years. The fuel cell qualifies for $4500/kWh rebate or 50% of the capital cost of the equipment, which ever is less, through the California Energy Commission Buy-down program.
Only fuel cells that use renewable fuel qualify for this rebate. There is also a Federal Tax credit for fuel cells used in homes. Though the author has not developed a detailed design for costing, it is crudely guessed that $50,000 budget would work for a 2.5kWe fuel cell – steam reformer system.
So the rebate is $11,250 and assuming the IRS tax credit to be 25% or $12,500, the balance of $26,250 is amortized over 15 years or $3500/year interest plus principal. The savings in electricity of 2.5 kWh/h is $2847/year at 13¢/kWh and in heating of 4.4 MWh/year (15,000 MBtu/yr at 60¢/therm) is $900/year, which totals to $3747/year. Garbage, plastics, paper, and yard waste bills are eliminated at about $300/year.
So there is a saving of about $4047/year, which would payback the initial investment plus interest in less than 15 years. So even the economics work out.
Now the question is, can this waste steam reformer be built for $50,000–60,000 retail price? Not sure precisely, but it is a great business goal for a future technology high volume business.
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