Micropower and CHP

There is an increasing climate of opinion in favour of 'distributed' or decentralized power generation. This is especially the case in rural locations or where stability of supply is essential, such as for banks, hospitals research facilities etc. Micropower or small-scale generation is the key to this trend.

There are several advantages to this alternative to the large-scale grid system served by a few large thermal power plants:

• Small-scale power can be closer to the point of use, overcoming the inefficiency of long distribution lines.

• It can be scaled to meet the exact requirements of the consumer. For example, in the USA domestic consumers use an average rate of 1.5 kW

• In most of its versions it has a relatively high efficiency by producing both electricity and heat.

• There are considerable environmental cost avoidance benefits.

• In some cases it is modular, meaning that it can be scaled up or down to meet changing needs.

Summary of expected break-even points for different scenarios.

2005 2010 2015 2020 2025 2030 2035 2040 2045 2050

Summary of expected break-even points for different scenarios.

2005 2010 2015 2020 2025 2030 2035 2040 2045 2050

Domestic

o_^ Long term, PV requires EEE for break-even

Domestic •-^

Small wind requires EEE for break-even

LU

Micro Hydro 0.7 kW

Micro hydro requires EEE for break-even

Solar Water Heating (with elec.)

Solar water heating requires significant price reductions for breaks-even

HEAT

Biomass Heating (with elec.)

Biomass heating can currently be cost effective

Pump (with elec.)

In 2005, GSHP is on the verge of break-even

Stirling CHP

^M Stirling CHP breaks even under all

1 kW (33% electricity export) * ^

■ 1 kW SOFC CHP breaks even under all scenarios

3 kW (72% electricity export) •-►

3 kW SOFC CHP requires EEE for break-even due to large quantity of electricity exported

2005 2010 2015 2020 2025 2030 2035 2040 2045 2050

Scenario (EEE: Energy Export Equivalence - Placing a higher value on mlcrogen electricity exported to the grid) Not cost effective

Earliest break even (with EEE for elec. technologies) Median break even (with EEE for elec. technologies) Median break even (with no EEE for elec. technologies)

2005 2010 2015 2020 2025 2030 2035 2040 2045 2050

Scenario (EEE: Energy Export Equivalence - Placing a higher value on mlcrogen electricity exported to the grid) Not cost effective

Earliest break even (with EEE for elec. technologies) Median break even (with EEE for elec. technologies) Median break even (with no EEE for elec. technologies)

Figure 9.1 Current, medium and long-term prospects for microgeneration technologies (courtesy of the Energy Saving Trust)

• Small-scale power has a short lead time and can be planned, built and commissioned in a much shorter time than is the case with larger plants.

• It can obviate the need for new large-scale power plants often subject to public enquiry. This is especially important in the case of new nuclear installations.

• Micropower is capable of running on a variety of fuels emitting rates of particulates, sulphur dioxide, nitrogen oxides and carbon dioxide which are significantly lower than larger plants. In the case of direct hydrogen, this means zero emissions.

• It is largely immune to the price volatility of fossil fuels distributed by the large utilities, a fact that will be increasingly advantageous as oil and gas prices reflect diminishing reserves or political tensions.

• There can be community control and choice of the technology. This can trigger local initiatives like a plant for the treatment of sewage through anaerobic digestion to produce biogas for the energy system.

The shift to distributed or embedded generation is part of a trend which was first witnessed in computers. Mainframe and minicomputers were all but vanquished by the personal computer, just as the fixed telephone has been severely challenged by the mobile phone and email.

The virtue of a distributed system is endorsed by the Washington Worldwatch Institute, which states: 'An electricity grid with many small generators is inherently more stable than a grid serviced by only a few large plants. So-called intelligent grids which can receive as well as distribute electricity at every node are already emerging.' Seth Dunn of the Washington Worldwatch Institute believes that micropower is the shape of the future for energy: 'It is not inconceivable that, in the long run, most of society's power will come from small-scale local systems, with the rest coming from large wind farms and solar plants making centralized thermal plants no longer necessary'.1

Microturbines

This is the technology which looks set to penetrate the US market at a phenomenal rate. Microturbines are a spin-off from the jet engine industry. Heat released by combustion at high-speed drives turbine blades that, in turn, spin a high speed generator. Their power output ranges from 15 to 300 kW. If their waste heat is usefully employed they are highly efficient.

Having only two moving parts, they are straightforward to manufacture and consequently relatively cheap. Maintenance is kept to a minimum since no lubricants or coolants are required. Their life expectancy is about 40,000 hours.

Another benefit is that turbines can use a variety of fuels, for example, natural gas, propane, kerosene, diesel fuel and biogas. The last is of particular interest since anaerobic digestion processing of biological waste to produce biogas may become increasingly popular.

It is a technology that is especially suitable for the domestic and small business market. Groups of homes needing between 25 kW and 300 kW of power will be obvious candidates for microturbines, especially with their CHP/cogeneration potential.

The US producer of microturbines, Capstone, predicted that by ~2007 this will be a $1 billion industry. Assuming the economy of scale of at least 100,000 units per year, a 30 kW turbine would cost $400/kW. Ultimately a 100 kW unit could cost as little as $200/kW, which is less than half that of the most economic conventional power plants.

There are reservations about microturbines for individual homes. They can be scaled down appropriately but the main problem is that they require a pressurized gas supply which raises safety concerns within homes. A small leak could lead to an explosion.

Fuel cells

As indicated on p. 83 and Fig. 7.5, an innovative UK fuel cell company, Ceres Power, is focusing on mini-fuel cells from 1 to 10 kW output. The company has linked up with British Gas to provide a 1 kW fuel cell to heat a domestic boiler and provide electricity simultaneously. It is a solid oxide fuel cell operating at about 600°C. Because of its high operating temperature the cell is able to run directly off natural gas, hence the interest shown by British Gas. It takes some time to reach its operating temperature but this should not be a problem in a static situation. A fuel cell in this range of output could be destined to revolutionize the domestic energy market, especially as homes become more efficient at retaining warmth. The long-term value of this system lies in the fact that this type of fuel cell will still be appropriate as and when the full-blown hydrogen economy becomes established. It should be market-ready by 2007.

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