2.5 2.0 1.5 1.0 0.5 o.o E. Texas emissions limit (2005) 0.064 kg NO,!MWh The case of carbon dioxide emissions is similar. Emissions rates for DG are generally lower than those for coal plants, but not as low as those for new combined cycles. lf, however, DG is used in a CHP mode, there can be signifıcant emissions savings, even compared to combined cycle power plants. Measures should be designed that encourage distributed generators to reduce their emissions. The use of economic instruments (such as carbon emissions trading) would encourage DG operators to design and operate their facilities in ways that minimize emissions of greenhouse gases. Energy security The energy security considerations affecting distributed power take two forms: fırst, its impact on the diversifıcation of primary energy supplies, and second, its impact on the reliability of electricity supplies. The impact on primary fuels depends on the underlying technology. Photovoltaic systems help diversify supply away from fossil fuels. Most of the other technologies rely directly or indirectly on natural gas. Since much of the new investment in DG is for natural gas, the effect on increasing diversity in the power system is therefore quite limited. in the case of CHP, higher fuel efficiency would mean lower overall fuel consumption and therefore would be favorable to energy security. The reliability of electric power systems can be enhanced by DG. The availability of standby generators in the US electricity markets in the summer of 2001 helped reduce the risk of blackouts. Betler integration of standby resources into system operations would further enhance security of supply. Furthermore, the use of distributed generators at selected locations helps distributors overcome local bottlenecks. MAKALE/ ARTICLE lncreasing DG could reduce the demand for transmission, thereby increasing margins on transmission lines. Ultimately, a power system based on a large number of reliable small generators can operate with the same reliability and with a lower capacity margin than a system with equally reliable large generators. The main negative impact from DG would be in reducing a network's ability to supply primary reserve power if DG technologies are not capable of responding to load changes. This would be the case if most of the DG capacity were nondispatchable because of natural variability (wind and PV) or because of their operating characteristics (CHP where power output is matched to heat demand). The operators of the Nordel system have identifıed the expansion of wind and CHP as a design concern and are studying how best to address it. They have suggested that 'distributed network regulation', where sub-areas of Nordel each have their own system operator, may be needed. DG iN THE WORLD ENERGY OUTLOOK The IEA's latest World Energy Outlook2 has incorporated DG explicitly into its ' reference scenario' for the first time. The key methodological step was to assume that demand for DG occupies a unique and growing niche in the demand for electricity, given the strong growth of DG over the past decade, policies in some countries that favor development of CHP, and the increasing need for greater power reliability. Reliability concerns are especially pertinent to developing countries such as lndia where large consumers have turneci to DG to displace requirements for grid. The reference scenario assumes that global DG will grow by 4.2% annually between 2000 and 2030. New DG, excluding photovoltaic systems, will amount to 521 GW in 2030, roughly 11 % of new generating capacity. This includes about 1 00 GW of fuel cells - see Figure 4. While DG might remain of secondary importance at the global level over the 30-year period (additional DG produces about 1800 TWh of electricity in 2030, versus global production of over 31,000 TWh), its role is greater inside the OECD, particularly during the last decade of the outlook period. in fact, the Outlook results suggest that over half of the net increase in generation between 2020 and 2030 in the OECD will come from either DG or renewable sources. ENERJi & KOJENERASYON DÜNYASI 55
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