Methods recommended for the evaluation of the environmental impact of dispersed generation

WG C3.05 ‘Environmental impact of dispersed generation’ 

Dispersed Generation, based both on fossil sources and renewables, is a growing source of generation in power systems but the issue of its impact on the environment is still open. WG C3.05 ‘Environmental impact of dispersed generation’ has prepared the recently published Technical Brochure (TB 679) on defined procedures and methods to evaluate the environmental impacts of Dispersed Generation (DG) in distribution networks. The work includes a collection and analysis of practical experience and a synthesis and benchmarking of different methods and experiences.  As Australia is a world leader in the use of rooftop solar, this work should be of broad interest. 

DG is defined as:

• not centrally dispatched
• connected to the distribution network (MV, LV);
• smaller than 50 MW;
• based on co-generation units (heat and electricity), renewable energies, conventional sources or electrical storage devices. 

Examples include micro turbines, internal combustion engines, wind turbines, photovoltaic converters, mini hydropower systems, biomass and waste material power systems, fuel cells, etc. 

The Working Group noted that there is no universal answer to the question of whether DG is better or worse from an environmental point of view, as this depends on the specific case and particular conditions.  It also recommended that when following the procedures explained in the report on environmental impact assessment for DG, the following main aspects should be taken into account: 

• Fossil based DG produces pollutant emissions in densely populated areas, while centralised power stations can be located away from cities and other residential zones;
• Fossil based DG needs “cleaner” fuels than centralized generation, because it is more difficult to apply sophisticated flue gas treatment systems;
• DG brings power generation closer to consumption points, with potential reduction of transmission and distribution losses and reduces the need for network reinforcements;
• Integration of DG with Combined Heat and Power is ideal for tertiary and residential customers (i.e., near load centres), as it will lead to higher energy efficiency levels (with environmental benefits);
• DG fits very well with renewable energy sources. However, it not only provides environmental benefits (reduction of pollutant emissions, liquid discharges, wastes…), but also creates problems like visual impact, land occupation, and noise;
• Many Life Cycle Assessment (LCA) report results are available at the component level of DG but they have to be reviewed at the system level during an assessment as defined in the final report of this WG;
• Integration of a LCA assessment of DG in the planning phase is necessary to find an overall environmental best fit solution;
• LCA results for DG in distribution networks have to be adapted to local conditions i.e. results are valid only if they are applied to local circumstances;
• Site and network boundaries are important and might influence the best solution. 

DG could play a key role in lowering the environmental impacts when compared to a power system that only has a fossil based energy supply system. The WG notes that their recommended LCA approach is only one among several approaches and does not address economic considerations and network constraints. 

New solutions and technologies such as Smart Grid Components, electrical storage devices (including electrical cars), voltage regulated distribution transformers, new ICT Solutions for demand side management, virtual power plants and new process automation solutions may also reduce emissions in distribution networks. The size of their impact can be measured by using the system model defined in the WG report. In order to promote environmentally friendly solutions in future distribution networks, the results of the environmental impact assessment of DG in distribution networks could be used to create incentive systems for using environmentally optimal technologies.

Technical Brochure 679 is available free to members through the e-cigre document site, non member can buy it for 130€.

The abstract and purchase info can be downloaded here