Although NRES currently form only a relatively small part of the world’s electricity generation, their use is expanding and they have a contribution to make to the future diversity of energy mix. As a global trend, government’s central energy policy objective is to ensure secure, diverse and sustainable supplies of energy at competitive prices. One of these studies goes on to suggest that, an available resource from renewables of up to about half of current United Kingdom electricity consumption at prices below 3p/kWh is achievable in the longer term, assuming a development program can be successfully carried out.[4] The study of this case goes on to state that, scenario studies show that in the period up to 2010 and 2025 wastes, wind and energy could make the dominant contributions with modest contributions from landfill gas and hydro resources. In the longer
term, non-fossil sources may form an increasingly large proportion of electricity and energy systems and those of expanding economies, at competitive prices. Moreover, the cost of generative electricity from renewables has almost halved since 1990 and the more mature technologies now generate electricity at prices not far above the wholesale market price. The NRES are, on present projections, amongst the lowest cost ways of providing alternative options to gas fired generation.[5]

DG is a concept of installing and operating small electric generators, typically less than 20 MW, at or near an electrical load. The premise of DG is to provide electricity to a customer at a reduced cost and more efficiently with reduced losses than the traditional utility central generating plant with transmission and distribution wires. Other benefits that DG could potentially provide, depending on the technology, include reduced emissions, utilization of waste heat, improved power quality and reliability. New technologies like small-scale co­generation, gas engines, PV, wind turbines and fuel cells enable an increasing flexibility in energy distribution systems. One of the technologies for DG is the natural gas distributed generators. It is a powerful tool for commercial, institutional, and industrial customers needing a higher level of power supply security. Whether the issue is life safety, securing data processing information, or ensuring plant productivity, natural gas onsite power systems offer the potential for enhancing reliability. For over two decades, stationary natural gas turbines and gas engines used in power generation and combined heat and power (cogeneration) applications have shown a high level of reliability and availability. Another technology, Phosphoric Acid Fuel Cells (PAFC) have recently been introduced into the market and showing these same strong performance characteristics. Compared with the well-established conventional energy systems, most technologies being developed for DG applications are currently costly. However, it is anticipated that with advances in the technologies and a greater demand for DG, costs will be reduced and more installations will take place.[6,7]

HES combine different power generation devices or two or more fuels for the same device. When integrated, these systems overcome limitations inherent in either one. HES may feature lower fossil fuel emissions, as well as continuous power generation for times when intermittent renewable resources, such as wind and solar, are unavailable. Potential hybrid combinations include generators (e. g., fuel cells that use hydrogen; and natural gas — powered turbines, micro-turbines, and reciprocating engines) that work in conjunction with NRES. The cost and environmental advantages of these advanced power generation technologies can be improved by using "opportunity” fuels, such as bio-generated gases and biomass, to supplement or replace conventional natural gas. As applications fields, HES can be used in commercial power parks, industrial plants, renewable energy — integrated buildings and remote (off-grid) power sites.[8]

Based upon the above mentioned advantages of the three alternatives, combining them as a Hybrid Distributed Generation (HDG) can provide electricity grid support and stabilization, achieving higher reliability measures, improve the quality and availability of power. Nevertheless, the concept of HDG should not be taken as a grant; each time this concept is questioned to be added to existing power system, the performance of the modified system should be tested concerning well-known probable problems. This will lead to a scientific assessment behind adding HDG and to what penetration level. Therefore, this paper discusses one of the common problems in power systems; voltage collapse problem, and the effect that can be detected by introducing Dg to an existing power system.