The Rise of the DC Microgrid

Microgrids come in all shapes and sizes.  Some can be measured on the kilowatt scale, others on the megawatt scale. Some include storage, some do not.

The U.S. Department of Energy defines a microgrid as “a group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid. A microgrid can connect and disconnect from the grid to enable it to operate in both grid-connected or island-mode” Or, in other words, a localized source where energy is both generated and consumed, independent of the larger energy grid. A microgrid can be as small as a single residence, to a commercial building all the way up to an entire industrial park or even an entire community or municipality.

How the various sources of energy and consumers of energy (also known as loads) are connected inside a microgrid is subject to engineering interpretation. Also, in most cases, while microgrids are designed to be self-contained they do need to connect to the outside world, i.e. the broader energy grid.

At its core, there are two ways to connect the various power generating and consuming elements of a microgrid – via an AC connection or a DC connection.  The choice as to which approach to use gets back to the age-old debate between Edison and Tesla (quick reminder: Edison was an advocate of DC power, Tesla AC. Long story short, Tesla won, Edison lost.)

But let’s remember why Tesla won.  Tesla won, because AC makes more sense for long distance transmission.  Clearly, in a microgrid, long distance transmission isn’t the issue. However, the legacy of AC remains and many microgrids today rely on so called “AC coupling”, or integrating on the AC side, because such topologies have been more common place and in many cases are still more “bankable” (a fancy way of saying more people are used to it, so it’s easier to get banks to pay for it, even if it is an inherently inferior solution.) 

That trend is now changing as systems designers, owners and financiers recognize the benefits of DC-based microgrids. Today, new DC-based microgrids are popping up everywhere.  The DC microgrid makes sense on so many levels, particularly when powered by a DC source like solar.  Additionally, when storage (i.e. batteries) is incorporated, the DC argument only gets stronger.  Batteries are of course inherently DC driven devices, whether they are acting as a source or a load. Click here to learn about the benefits DC-coupling solar and storage.

When solar and storage are brought into the picture, DC microgrids are inherently simpler and require less power electronics switch gear. This of course means less equipment in the form of rectifiers and inverters, which saves money, and less conversion losses, which of course increases energy efficiency.

At the heart of the DC driven microgrid powered from PV is the DC-DC optimizer.  Here at Alencon, we are seeing the movement toward DC microgrids unfolding before our eyes everyday.  Our DC-DC optimizer, the SPOT, provides the point of entry of PV into a DC microgrid by taking the variable voltage harvested from PV and providing a fixed voltage to a DC bus or other DC devices at their preferred voltage. The Alencon SPOT, thanks to its unique Galvanic Isolation, can be configured to meet any voltage input and output requirements. This is a vital feature because it makes it load agnostic as well as chemistry agnostic so that any storage technology can be incorporated. To help promote these benefits, we’ve partnered with a number of leaders in DC microgrids like ARDA Power and thought leaders such as the Emerge Alliance.

The spate of natural disasters we’ve seen of late, most prominently the devastation wrought by Hurricane Maria in Puerto Rico, is putting microgrids front and center in our collective consciousness with titans like Jigar Shah and Elon Musk weighing in on the importance in bringing the island back to life. Hopefully, as we do so, system designers and financiers alike will recognize the benefits of the DC microgrid in terms of higher efficiency, lower cost and improved resiliency.