The concept of a microgrid has drawn the interest of research community in recent years. The most interesting aspects are the integration of renewable energy sources and energy storage systems at the consumption level, aiming to increase power quality, reliability and efficiency. On top of this, the increasing of DC-based loads has re-open the discussion of DC vs AC distribution systems. As a consequence a lot of research has been done on DC distribution systems and its potential for residential applications. This paper presents an overview of the LVDC distribution systems used in residential applications. Several publications that study the potential energy savings and overall advantages of the LVDC distribution systems are analysed. Different power architectures and topologies are discussed. The existing demonstration facilities where LVDC distribution systems have been implemented are also shown.

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An overview of low voltage DC distribution systems for residential applications

It is well established that access to energy is closely linked with socioeconomic development. India houses the largest share of the world's population deprived of electricity with about 237 million people lacking access (International Energy Agency). At the same time, in India, many households that do have access to electricity lack an uninterrupted and quality power supply. A recent study conducted by the Council for Energy, Environment, and Water (CEEW) across six states (Bihar, Jharkhand, Madhya Pradesh, Uttar Pradesh, West Bengal, and Odisha), found that about 50% of the households had no electricity despite having a grid connection. This indicates that there is an immediate need to address the quality, affordability, and reliability of the power supply in addition to extending the grid footprint.

Solar-dc Microgrid for Indian Homes: A Transforming Power Scenario

DC Microgrids (DC MG) present themselves as an obvious choice enabling integration of multiple renewable energy sources and distributed energy storage. This concept of DC electrification of homes in small communities is being explored in many parts of the world. Furthermore, typical household loads are increasingly becoming natively DC. In this paper, a community DC MG in an urban environment is analyzed. In combination with a community revitalization effort, up to 9 renovated dwellings (a mixture of apartments in a commercial property and houses) will be equipped with a smart DC power panel for loads such as LED lights, fans and air conditioning while a portion of loads will remain AC with an AC/DC converter interface between the loads. The smart DC power panel interfaces to the community DC MG. The effectiveness of driving down utility costs in a low-income household using this concept is compared to a home with conventional AC loads and AC loads with smart technologies. The efficacy of the DC MG to optimal installation and usage of solar energy and battery energy storage is determined and a notional smart energy management approach is presented.

Assessment of the feasibility of interconnected smart DC homes in a DC microgrid to reduce utility costs of low income households

A community DC microgrid is proposed that is embedded within an urban neighborhood in an underserved community in Milwaukee, Wisconsin. This community microgrid will be a proving ground for residential DC power distribution and sharing of renewable energy resources between homes. The system will be built into existing homes that have been vacated as a result of a long period of economic recession in the area in such a way that homes can be occupied while their energy usage is being monitored and managed with in a non-invasive way. Renovated homes will either operate off of the 380Vdc or from the utility. The detached home garage for each home will be equipped with solar PV and battery energy storage with a lead home acting as substation that connects the microgrid into the larger utility through a 240Vac gateway connection. The homes will also be outfitted with readily available DC appliances so that a large portion of the home load can be directly fed from DC. In this environment living laboratories will be created that will enable participation of community members and students from a local STEM high school to become stakeholders in the operation of the community microgrid. The community microgrid will also demonstrate safe power distribution between homes using both wide band gap solid state circuit breakers. This aspect of the community microgrid will be a developmental environment for a protective system design that undergirds the entire system.

System specification for a DC community microgrid and living laboratory embedded in an urban environment

Various statistics indicate that many of the parts of India, especially rural and island areas have either partial or no access to electricity. The main reason for this scenario is the immense expanse of which the power producing stations and the distribution hubs are located from these rural and distant areas. This emphasizes the significance of subsidiarity of power generation by means of renewable energy resources. Although in current energy production scenario electricity supply is principally by AC current, a large variety of the everyday utility devices like cell phone chargers, computers, laptop chargers etc. all work internally with DC power. The count of intermediate energy transfer steps are significantly abridged by providing DC power to mentioned devices. The paper also states other works that prove the increase in overall system efficiency and thereby cost reduction. With an abundance of solar power at disposal and major modification in the area of power electronic conversion devices, this article suggests a DC grid that can be used for a household in a distant or rural area to power the aforementioned, utilizing Solar PV. A system was designed for a household which is not connected to the main grid and was successfully simulated for several loads totaling to 250 W with the help of an isolated flyback converter at the front end and suitable power electronic conversion devices at each load points. Maximum abstraction of operational energy from renewable sources at a residential and commercial level is intended with the suggested direct current systems.

https://www.mdpi.com/1996-1073/12/11/2157/pdf

DC Grid for Domestic Electrification

India is a power deficit country and one third of its homes are off grid or near off grid. This paper presents an efficient and affordable Solar DC solution for powering such homes. Though several solutions have emerged in the past for powering these homes, those have been expensive and energy inefficient. These solutions rely on several DC to AC and AC to DC conversions, to feed the widely used AC home loads, thus, wasting a large chunk of the expensive power. The proposed Solar DC solution for off-grid homes (OGH) is developed to use the generated PV power efficiently. With this solution, the panel and battery size is reduced by 2 to 2.5 times and the cost to power a house is reduced to nearly half the cost of the existing solutions. The paper also presents a techno-economic comparison between the proposed OGH solution with some existing solar systems.

Sudeep Jain

Papers

Solar-DC deployment experience in off-grid and near off-grid homes: Economics, technology and policy analysis