The use of Distributed Energy Resources (DER) has been proposed as one of the possible solutions to today's energy and environmental challenges. The optimal integration of DER in distribution networks is essential to guarantee the best of resource, i.e. maximize their benefits, such as reduction of carbon emissions, reduction of network energy losses and to minimize the negative impacts, which can affect the network quality, cause network sterilization and increase investment and operation costs. Hence, DER planning is a multi-objective problem in which many objectives of interest, sometimes conflicting, need to be optimized simultaneously, and where a compromise for different perspectives (DER developer, Distribution System Operator, regulator) needs to be found. Appropriate multi-objective planning methods that consider technical, environmental and economic impacts of DER integration, and that are able to support a suitable model of stochastic DER and active networks, can provide a deep insight into the case specific and general advantages and drawbacks of DER. Consequently, the interest in multi-objective DER planning has increased in recent years, and a number of novel methods have been proposed in this area. This paper provides a timely review of the state-of-the-art in multi-objective DER planning, and discusses in detail the challenges, trends and latest developments in this field.
