Solar + BESS system with Genset Backup: How to efficiently manage microgrids

Kiesse Sita-Kengue

Welcome back to our four-part series on how to effectively manage microgrids to power Commercial and Industrial buildings.

In these four articles, we give you our best practices to control microgrids in different situations and configurations. If you missed our first article, click here to read and learn more about load shifting.

This second article will focus on a particular configuration encountered in many countries and territories that are connected to an unreliable grid: the hybridization of a backup Genset system with Solar PV and BESS.

But first, what is a microgrid?

Feel free to jump to the next section if you are already familiar with this concept.

 A microgrid is an energy distribution network that relies on local means of producing electricity. It is designed to operate independently or in synchronization with the national grid within a defined area.

It is necessary to ensure electricity production and distribution to enable areas or buildings to secure their economic activity and benefit from reliable energy. It is also an opportunity to profit from clean distributed and renewable energy. 

A microgrid can be typically composed of renewable energy sources, BESS, utility grid (when available), diesel generators, or gensets. 

If you want to dive deeper into the microgrid topics, here are two articles that might interest you:

“What is a solar hybrid microgrid?”

“What is a solar hybrid system?”

Microgrid controller operational mode

The democratization of hybrid systems is fueled by the value that Solar PV and BESS bring in C&I sites. That value can be presented in four main advantages to hybridization: 

  • Increasing renewable penetration: 

→ When PV > Load, the EMS can store the excess in the BESS reducing the curtailment of the PV.

→ When Genset Power < 30% the EMS can store a part of the PV produced in the BESS.

  • Limiting power outage impacts such as a decrease in productivity, the shutting off or malfunction of the machinery, the damage to equipment,…
  • Stabilizing the grid for reliable and stable power supply.
  • Keep fuel consumption to a minimum as Solar PV+Storage energy production is often cheaper than fuel. Adding storage enables using electricity during the night where the consumption is higher and not using the backup genset. It also allows being less reliant on diesel resupply.

In a microgrid with poor grid, solar PV, BESS, and genset(s) backup, there are two main operational modes:

  • Grid-Connected mode:  

The utility grid is available; therefore, the genset plant is offline. The grid forms the network while the PV and BESS are in grid following mode.

When the grid forms the network, it means that the PV and BESS follow the grid voltage and frequency.

  • Genset back-up mode:  

In this case, the utility grid is down, and consequently, the Genset plant is online. The genset forms the network, and the PV and Batteries are in grid following mode.

In this case, the genset sets the voltage magnitude and frequency of the islanded microgrid.


The controller will automatically control the use of the genset to improve the microgrid’s reliability and keep fuel consumption to the minimum. We advise using a microgrid controller like the ePowerControl MC and a monitoring platform such as ePowerMonitor to manage your microgrids efficiently. 

To optimize your microgrid use and maximize your system’s performance and profitability, request a call with one of our microgrid experts.

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What is the business case for this application of microgrid?

For years diesel generators have been the standard emergency backup power for commercial and industrial buildings. A few years ago, it was even the most economical option for most systems above 150kW. It used to be the first choice because of its simplicity and efficiency. But with an increased focus on low carbon solutions and a steep drop in the levelized cost of renewable energy and storage, the use of hybrid systems is democratizing.

With various power generation and energy storage options, buildings get the ability to be more resilient to power outages in the long term. PV + BESS can provide near-instantaneous backup power at a cheaper price than diesel while also giving the advantage of the separation between resource availability and exploitation of the solar energy.

This application’s best usability case is the hybridization of a grid-tied coupled to a diesel system as a back-up with solar PV and BESS. This type of microgrid is most suited for a bad grid that suffers many outages and where there is a concern about the electrical reliability. There are as many reasons to hybridize diesel with solar and battery storage that there are different projects. 

As an example, you can find below one of our projects which is a perfect representation of the use of a controller for a solar-diesel-BESS system tied to a weak grid. 

Use Case

Akyna MedPharm – Puerto Rico

  • PV – 2 x 60 kWp 
  • Gensets – 1 MW 
  • Storage – 170 kWh

This site is subject to hurricanes that may cause power outages. Connected to the network, it has backup gensets. Our controller, the ePowerControl MC, allows the integration of PV and BESS. In the case of grid and generator failure, the BESS and PV supply critical loads.

We will release the third article about off-grid Solar BESS Genset applications in the next few weeks. 

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