A microgrid can be defined in simple terms as a miniature power grid with its own energy resources, often interconnected with a utility-scale power grid, but capable of disconnection and independent operation.
Organisations that deploy microgrids can become self-sufficient in terms of energy needs, using the utility grid as a complementary power source only when it is more convenient or cheaper than relying on internal resources. However, a clear snapshot of energy consumption is necessary to deploy a microgrid, since it allows generation and storage resources to be optimised. In other words, the first step in a successful microgrid project is energy monitoring infrastructure.
Logic Energy monitoring solutions provide smart data aggregation and are capable of integrating with any system that generates, stores or consumes energy. Thus, they can be very powerful tools for any facility where a microgrid will be deployed.
Important Questions to Answer Before Deploying a Microgrid
Microgrids typically involve several kilometers of privately-owned transmission lines and multiple buildings with very different energy consumption profiles. For example, a large university campus may involve residential loads such as dormitories, commercial loads such as cafeterias and classroom buildings, and industrial loads such as engineering laboratories.
Ideally, energy generation resources should be located as close as possible to the buildings that consume the most energy, since that minimises transmission distance and losses, as well as voltage drop. If a microgrid is being considered for a facility, monitoring can answer some key questions:
Which are the buildings that consume the most energy?
What is the energy consumption profile for each building, and for the entire facility?
What is the peak demand?
Energy monitoring allows facility managers to determine how much energy must be generated to make the microgrid self-sufficient, and how its consumption is distributed throughout the day.
Optimising Generation Resource Location
As previously stated, a long transmission distance increases power losses and voltage drop, forcing generation resources to produce additional energy. Therefore, microgrids work best when generation is located where it can serve the largest possible number of high-consumption buildings with the minimal transmission losses.
Of course, there are cases where it may make sense to locate power generation equipment away from buildings, if the benefit of doing so outweighs the extra losses. For example, if there is a favorable site for a wind turbine that increases output by 10% while only increasing transmission losses by 2% due to distance, it makes sense to relocate the unit.
Solar power is also sensitive to location. For example, installing a photovoltaic array in a remote site with zero shading is better than installing it on a rooftop with many shades from adjacent trees and buildings. In this case, the rooftop array has very low transmission losses, but its output is drastically reduced by shadows.
Logic Energy monitoring systems can be configured not only for energy consumption measurement, but also for renewable energy site assessment. For example, weather stations by our WINDLogger business division or WINDCRANE for H&S can be used to measure metrics such as wind speed, wind direction, temperature and solar radiation. They provide the most cost-effective solution in the market when carrying out feasibility analysis for small- and medium-scale solar and wind power systems, such as those used in microgrids.
Our monitoring systems can also be used to assess the performance of the microgrid distribution network, by measuring operating temperatures & currents at multiple points. This way it is possible to create heat map that displays which parts of grid infrastructure are experiencing the highest transmission load. Keep in mind that transmission losses are proportional to current squared, so microgrid hot spots should be minimised.
Managing Building Demand
The demand profile on a microgrid is not very different from that experienced by a utility-scale power grid. Peaks in demand are expensive to meet because they require generation resources on standby, and peaks in variable generation can cause instability because it is necessary to ramp down production from dispatchable generation sources.
However, if the energy consumption profile of each building is known, it is possible to deploy demand-side management measures more effectively. For example, non-critical loads can be shifted away from peak demand hours, and battery storage can be used to trim consumption peaks that can’t be displaced. Battery storage tends to be more cost-effective when it trims short-duration peaks than when it provides an energy output over several hours.
Energy storage is generally more valuable when located at the point of consumption, since transmission losses only occur once, and demand peaks can be trimmed more effectively. When energy storage and buildings are physically separated, the power grid is still burdened by demand peaks even if generation is ramped down – energy must still travel between storage and the point of consumption.
Managing Total Demand on the Microgrid
This is where smart monitoring provides the most value, reducing the total generation capacity required for a microgrid to operate independently:
If complemented with smart data aggregation and control features, the monitoring system can be used to aggregate distributed storage resources and trim peaks in demand. The individual demand of all buildings is constantly measured, ensuring that the total stays below a specified value.
The monitoring and control system can also be granted access to loads that are flexible in terms of schedule, allowing it to disconnect them as needed to keep total demand low.
Capital expenditures have a direct relationship with generation capacity. Each time the total required capacity is reduced by one kilowatt, the project becomes cheaper by several hundred or even thousands of Euros.
In other words, a monitoring and control system can ensure that total energy consumption is spread over the longest timeframe possible while keeping demand stable. When there are generation peaks from solar or wind power systems, the control system can decide between consuming the energy right away or storing it.
Key Elements of a Microgrid
Microgrids are composed of many elements that work together to provide energy independence. The concept is possible thanks to the complementary functions they perform:
Power distribution infrastructure: This is what gives the microgrid its name. For the concept to be possible, it is necessary to have a network capable of receiving energy from generation resources and delivering it to buildings for consumption, or to energy storage systems for later use and demand optimisation.
Variable Renewable Energy (VRE) sources: Although wind and solar power are not mandatory for a microgrid, they are highly beneficial. After the upfront investment, both types of generation systems operate with a free resource and only require maintenance.
Dispatchable Generation: The main weakness of VREs is uncontrollable generation, so they must be complemented with dispatchable sources to make a microgrid independent and stable. Some of the most common dispatchable generation technologies in microgrid applications are diesel generators and small-scale gas turbines. Biomass and biogas may be feasible if the facility has access to large amounts of organic waste, and hydroelectric microturbines are also feasible when the property has a creek or river flowing through it.
Energy Storage: Dispatchable generation is generally cheaper than batteries when providing a stable energy output over an extended period of time. However, batteries can be competitive for short-term and high-current applications such as demand peak trimming. Batteries can also be used to help start large motors in cases where the inrush current can destabilise the microgrid.
Monitoring and Control System: This can be considered the glue that holds a microgrid together. Generation and storage resources cannot operate as a microgrid without a system telling them when to generate and when to store energy. The monitoring and control system can also aggregate and manage demand across the microgrid to minimise the total cost of meeting that demand.
The utility company’s power grid can be considered another energy resource for the microgrid, and monitoring is key to optimise its use. In general, purchasing energy from the utility makes sense when the cost of doing so is lower than supplying it with internal resources. There is a common misconception that going 100% off-grid is always beneficial, but there are many advantages of remaining connected to the electric utility:
It provides a backup power supply when key generation systems inside the microgrid must be serviced.
Off-peak energy from the grid has a very low cost. If there is spare storage capacity that can’t be filled up with internal generation resources, it makes sense to store cheap energy from the grid during off-peak hours.
In short, optimal operation of a microgrid depends on the availability and running cost of different energy resources, and these metrics often change by the hour. Only a monitoring system can keep track of key variables in real time to decide the best course of action.
Barnsley Metropolitan Borough Council
There are so many different systems on the market that connect to a particular renewable energy installation and no other and the benefit of the Logic Energy system is that it can connect to them all and we can then view all our information in one place. The system has had a positive impact on the school, it’s brilliant!
Richard Waterhouse Principal Officer AMP/Capital Programme