Maybe you’ve heard the word “microgrid” tossed around the office break room or at happy hour— or maybe that’s just at Aquion.
You’ve certainly run across the term elsewhere on our blog. Microgrids are increasingly challenging the hegemony of the traditional, centralized power grid, which fires up massive power plants, shoots high-voltage electricity hundreds of miles, and squeezes it through tangled webs of sub-stations, transformers, and utility poles and finally into your blender so you can have a delicious smoothie.
So what is a microgrid? And what about those nanogrids? Read on.
Microgrid? Size matters not.
When it comes down to it, microgrids have two defining characteristics, which are not necessarily linked to physical footprint or electrical capacity.
- Microgrids are locally controlled.
Microgrids rely on distributed energy resources (DER), rather than centralized power plants. They’re called distributed because the diesel generators, solar panels, wind turbines, and geothermal plants are distributed among the blenders they power. Utilities don’t necessarily control when these resources turn on or off or how they distribute electricity. Whoever runs the microgrid does.
- Microgrids can work with or without the grid.
A microgrid can be grid-tied or off-grid. Grid-tied microgrids are often used to replace a portion of grid energy, either to stabilize costs against fluctuating retail electricity prices or to offset the carbon footprint of fossil-fuel power plants. Many power utilities pay microgrid operators for any excess renewable energy they feed into the grid.
Energy storage can increase the flexibility and independence of microgrids. A microgrid operator could, for example, stuff excess renewable energy into a battery instead of feeding it into the grid, if the feed-in incentives are low. Or, the microgrid could store renewable energy for a rainy day (or just a cloudy or calm one) or for use at night. That excess power then becomes dispatchable, or usable on demand, such as when you need a smoothie, like, right now.
Plus, if the grid goes down, distributed energy resources and batteries can keep microgrids chugging right along, an ability known as islanding.
Off-grid microgrids are always islanded. They have no grid connection to keep the blenders spinning when the sun’s not out or the wind’s not blowing, so they either curtail energy use or use stored energy. Diesel fuel is a common but ecologically dirty--and sometimes expensive--way to store energy. In more and more off-grid microgrids, diesel generators are themselves becoming the backup to banks of batteries. Typically, the batteries charge off of solar PV panels or wind turbines and discharge when those power sources aren’t available.
So, what's a nanogrid?
Nanogrids also generate, deliver, and often store electricity, but for a single building or a limited set of co-located loads. The collective definition is still a little doughy in the center, but some say a nanogrid is any power-load system smaller than 100 kW if grid-tied, 5 kW if not. A tiny house, for example, is a small nanogrid.
Nanogrids can give single, critical facilities--such as hospitals, police stations, and blender factories--controllable, flexible, and grid-independent energy. They can also be tied together to form a microgrid.
Remote telecommunications towers are a good example of an off-grid nanogrid. Typically, diesel generators and renewable resources, tied to batteries, serve all the loads at the tower. Advocates of so-called tower power propose connecting nearby, off-grid villages to telecom tower nanogrids, effectively turning them into community microgrids.
What's the future of integrated nanogrids, microgrids, and power grids?
Behold: The "PowMicroNanInteGrid."
The Mies campus of the Illinois Institute of Technology actually has one of these. Though they don’t call it that.
Keating Sports Center nanogrid: Has dedicated solar panels and batteries. The system serves only the loads at the spo
rts center and can run the facility independently, but it can feed
excess solar power to the…
IIT campus microgrid: Has several solar panel arrays, wind turbines, and energy storage installations distributed throughout campus. They power all the campus facilities (except the Keating Sports Center nanogrid!). The IIT microgrid can also run as an energy island, but it can give power to and receive power from the…
Regional utility power grid: Your basic centralized power grid.
(Right) The Illinois Institute of Technology "PowMicroNanInteGrid"
Or maybe the future is entirely off-grid, as at the Loisaba Conservancy wildlife research center and ecotourism destination in Kenya.
Solar panels and Aquion batteries at the Loisaba Conservancy off-grid microgrid.
Nanogrids give us the greatest degree of local control and energy independence. Microgrids scale up those benefits to multiple facilities or communities. For the foreseeable future, traditional grids will still play an important role. But as we humans wean ourselves from fossil fuels, distributed energy will have to come in many sizes and flavors. Here’s hoping for a tall strawberry-banana-spinach.
To learn more about our off-grid microgrid project in Kenya, download our project spotlight.