Earthblog

Micro-grid Opportunities

Today's buildings operate as islands of consumption on the electricity grid. There are few restraints on when and how much energy is consumed. The most common restraint is in the form of published utility tariffs, which provide a combination of price adjustments based on consumption (kWh) and demand (kW). Very few buildings are managed to respond to their respective tariff. Demand limiting (kW) is seldom implemented. Energy conservation (kWh) is usually weakly implemented as part of general conservation program. As alternative energy sources have moved up the priority list very few building owners are prepared to deal with these energy alternatives. Simply put they have neither the technical expertise nor the budget to manage this type of initiative.

The problem is even more complicated where a single building doesn't offer an opportunity to effectively leverage a solar installation or sizable generation capacity, regardless that it uses natural gas, landfill gas, or even pyrolysis gas. Clearly multiple buildings need to be linked into a cohesive operating arrangement with an electrical connection capable of sharing distributed renewable resources.

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The opportunity

Micro-grids provide the ability to link buildings into a working arrangement that leverages load management as well as energy sources. It's not enough to mount a solar array on the roof of a building and proclaim this building as "energy efficient because it uses renewable energy". It's equally important that buildings (loads) and generation (sources) be combined into an optimized "source-load management" system. Further, renewable energy source connections cannot be casually installed without significant attention to utility details that mandate certain operating provisions for personnel safety and grid reliability. What's needed is a micro-grid of inter-connected buildings operating as a single entity. It must be capable of managing internal building loads in such a manner that building environmental conditions are reasonably preserved. At the same time it must incrementally provide for load reduction in response to both on-site generation as well as grid generation. It needs to actively involve building participants who can contribute to load management within their personal space while understanding building energy usage needs in the context of available sources. This is not the equivalent of watching a power meter as daily energy usage changes. The most successful installations will keep participants informed but work within an "energy policy" that automatically manages sources and loads. The switch to renewable generation sources requires an approach that leverages technology, people, and creative methods to handle building energy requirements in the future.

Quick Summary

A quick look at the important features of a successful micro-grid involves geography, energy costs, building aggregation and system security.

Geography

Buildings may be located within a relatively close proximity or otherwise within a geographical area that inter-connects within the common utility energy distribution. In some instances several buildings within small regions, each drawing from 500 to 3,000 kW, could be linked together into a single micro-grid. Depending on building sites, alternative generation can be added at one or several buildings.

With buildings already connected to the primary grid, either a separate connection between the buildings is needed or the utility must be able to separate the buildings within the existing grid layout. To avoid service disruption, installation of suitable high voltage connections between nearby buildings may work better.

For micro-grids located in a larger geographical area, the primary grid is needed for local inter-building connections. Distributed energy sources can feed their respective buildings. Micro-grid management involves inter-building coordination in combination with the primary grid operator.

Security

Communications between distributed energy sources, building loads, and each building can be managed using secure Internet communications. Data packets are encoded as AES 256 protocol. Data traffic is socket-to-socket using IP Version 6.

In-building communications uses IP version 6 where available (i.e. wireless 6LoWPAN) or IP version4 to connect with building automation systems. Existing building IT systems may currently offer a VLAN for data isolation between standard communications and dedicated building micro-grid and load management communications. Metering devices can either be connected through the existing building automation system or separately to a dedicated network - wireless or wired.

Outside attack prevention uses a combination of VLANs, encrypted Internet communications, and suitable firewall protection with all web servers. Access to the local network within a building needs to be managed through physical means, such as a combination of RFID wireless devices along with appropriate login and password.

Electrical Costs

Alternative energy sources provide a more effective method for managing off-peak and on-peak energy sources. On-peak conditions typically require all available energy sources whether the tariff includes energy (kWh) price adjustments by time-of-day, dynamic pricing on 5 minute intervals, or uses separate demand (kW) charges. Peak loads for buildings are set by the demand for cooling in the form of extended compressor runtime or full output performance for chillers. Managing peak energy cost requires a combination of operating all energy sources while restricting air conditioning to the building for limited times or in accordance with pre-set environmental conditions (i.e. temperature, humidity, air flow, etc.) Environmental feedback is important to limiting restricted HVAC operations.

Base load energy usage contributes to both peak load and off-peak energy usage. Today's buildings are experiencing significant increases in plug load that often ranges from 30 to 50 percent of total building consumption. In many cases it's not possible to reduce plug loads much during building occupied hours. However, plug load energy management represents an important method for reducing CO2 from power plant emissions over the long term. Further, reducing unoccupied energy consumption also allows alternative energy sources to be shutdown while power is taken from the primary grid, especially during non-peak periods.

Air conditioning loads can be managed appropriately to minimize peak demand and the need for alternative energy sources. In many buildings it is possible to defer cooling during the 2 to 4 hour peak cooling demand such that building temperatures are not significantly impacted. Most chillers can be demand limited using a 4-20 ma signal. Air handler variable frequency drives also offer an important reduction opportunity. A 10% reduction in supply air reduces motor horsepower by approximately 25%.

Aggregating

In a simple micro-grid installation multiple buildings can be linked via the Internet to reduce loads with or without the use of alternative energy sources. This form of aggregating offers an opportunity to share loads as a function of outside air temperatures, internal building loads, and Demand Response signals.

Micro-grids equipped with alternative energy sources offer a better opportunity to manage energy through the appropriate sharing of energy sources. In some cases, such as linking large schools with commercial office buildings, significant reductions are possible with the installation of only a few shared alternative energy sources.

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