I believe that most of the fundamental building blocks to tackle climate change already exist. We know how to generate energy from renewable resources, how to store it, and how to reduce consumption. Now, the challenge is to put them together, making them suitable for complex and diverse environments and scaling them to become a viable alternative for traditional fuel-based technologies.
I am interested in complete energy systems, that is, microgrids or bottom-up grids that make the most out of renewable resources and that can become a viable alternative to traditional grids. This is especially crucial for one billion people still living without electricity. Could they be electrified via clean microgrids? If so, how to make them cheaper and faster to compete with conventional technologies?
This paper proposes an evaluation model to analyze the impact of microgrid topologies on self‐sufficiency for a given size of batteries and photovoltaic (PV) panels (resources). Three topologies are evaluated for a community of 19 houses: centralized resources (ideal case), stand‐alone resources, and a multi‐microgrid topology with autonomous exchange. Depending on the ratio of PV and battery size, the topology with stand‐alone resources has a clear disadvantage in terms of self‐sufficiency compared to the centralized, ideal topology. To counteract this, we propose a hybrid topology: households are interconnected so that they can exchange energy between each other based on an autonomous energy exchange algorithm we developed. We show that for a well‐chosen ratio of batteries and PV, the interconnected system can improve the stand‐alone design by up to 10% without requiring any additional resources. This topology can approach performance similar to that of a centralized microgrid but its design is more flexible and resilient to failures or accidents. The evaluation model computes the self‐sufficiency ratio (SSR) for the three topologies for 0–20 kWh batteries and 1–14 kWp PV sizes. Furthermore, seasonal differences in SSR per topology are analyzed for an actual community with real resources. We also calculate the savings in PV and battery due to the interconnected topology. Finally, the third topology’s feasibility is demonstrated on a full‐scale platform in Okinawa on which the autonomous energy exchange software was tested for over a year in a community of 19 houses. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
We propose and implement a dc microgrid with a fully decentralized control system, using the ICT concept of network overlays and peer-to-peer (P2P) networks. Decentralization not only concerns the physical systems and control logic but also the control structure which provides the network infrastructure on which Energy Management is carried out. In this study, we show how such decentralization can be achieved using P2P frameworks as underlying control structures and implemented a pure P2P to eliminate single points of failure. For this, a Direct Current Open Energy System (DC-OES) made of the interconnection of standalone dc nanogrids is used as underlying microgrid. The power ﬂows between nanogrids are controlled by a decentralized exchange strategy: each household can request or respond to energy deals with its neighbours without requiring system-wide knowledge or control. Using dc combined with a layered, modular software allows loose coupling which increases ﬂexibility and dependability. The system has been implemented and tested on a full-scale platform in Okinawa including 19 inhabited houses. Real data analysis as well as simulations demonstrate improvements in selfsufﬁciency compared to other types of systems. Resilience against utility blackouts is proven in practice.
In this study we examine microgrid topologies that combine solar panels and batteries for a community of 20 residential houses: In the first case we consider a system with centralized PV panels and batteries that distributes the energy to the 20 homes. In the second case we consider 20 standalone home systems with roof-top PV panels and batteries. Using real electricity consumption and solar irradiation data we simulated the overall demand energy that could replaced by solar energy for both topologies. The centralized-resources approach achieves better performance but it requires extended planning and high initial investments, while the distributed approach can be gradually built bottom-up. We analyze the additional resource investment needed to reach the same electricity savings as for the centralized topology. Finally, we compare it to a hybrid approach named Open Energy Systems (OES), a 2-layered microgrid made of interconnected nanogrids and show that it improves the solar replacement ratio by autonomously exchanging energy with neighbors.
We describe the general concept and practical feasibility of a dc-based open energy system (OES) that proposes an alternative way of exchanging intermittent energy between houses in a local community. Each house is equipped with a dc nanogrid, including photovoltaic panels and batteries. We extend these nanogrids with a bidirectional dc–dc converter and a network controller so that power can be exchanged between houses over an external dc power bus. In this way, demand-response ﬂuctuations are absorbed not only by the local battery, but can be spread over all batteries in the system. By using a combination of voltage and current controlled units, we implemented a higher-level control software independent from the physical process. A further software layer for autonomous control handles power exchange based on a distributed multiagent system, using a peer-to-peer like architecture. In parallel to the software, we made a physical model of a four-node OES on which different power exchange strategies can be simulated and compared. First results show an improved solar replacement ratio, and thus a reduction of ac grid consumption thanks to power interchange. The concept’s feasibility has been demonstrated on the ﬁrst three houses of a full-scale OES platform in Okinawa.
We propose a recursively scalable DC infrastructure starting off from simple DC nanogrids (subsystem) that are interconnected via a DC power bus line to form a cluster. We have conceived a non-droop based procedure to exchange power from one subsystem to another in order to balance demand/generation fluctuations within the community without requiring any central monitoring or control. To scale the procedure to higher layers we further propose three approaches that could be used for managing power ex-changes between clusters. The approaches are compared using analogies with the internet architecture i.e. circuit-switching,packet-switching and virtual switching. Each approach is analyzed in its ability to provide decoupling between analog and digital-centric goals as well as between infrastructures. Furthermore, we discuss whether the approaches could verify the four ground rules of the internet. The 2-layer architecture and the procedure for DC power exchange has been validated in practice on a full-scale 19DC nanogrids installed in inhabited houses in Okinawa. The evaluation of the multi-layer exchange procedure is still ongoing.