Microgrids

Question 1

Residential solar panel inverters shut down during a grid blackout, this feature is called ___.

Answer 1

Anti-islanding.

Question 2

What is the different between intentional and unintentional islanding?

Answer 2

Unintentional islanding occurs when distributed energy resources are isolated from the rest of the power system and continue to serve loads separate from the utility system. Intentional islanding is the intentional creation and planning of a microgrid that connects to the main grid at one location and adheres to IEEE standards.

Question 3

Vehicle to grid technology is the ability to both charge and discharge an electric vehicle battery to the grid.

Ture or False

Answer 3

True

Question 4

Which of the following is not a benefit of using an electric vehicle instead of a stationary battery storage unit in a residential microgrid?
	•	Built in AC to DC converter
	•	Multipurpose
	•	Increased storage capacity
	•	Always connected to the microgrid

Answer 4

Always connected to the microgrid.

Question 5

• Which of the following is not a benefit of microgrid battery storage in grid-connected operation?
  
  • Can reduce peak usage in the grid overall by storing excess solar energy produced during the day
  • Allows for grid electricity purchases during the cheapest times
  • Increases the amount of electricity sold to the grid
  • Prevents excess electricity from being sold to the grid at a low wholesale rate for certain utilities

Answer 5

Increases the amount of electricity sold to the grid

Question 6

Anti-islanding protects the safety of utility works by ensuring that there are not any energized power lines due to unintentional islanding during a power outage.
• True
• False

Answer 6

True

Question 7

How does the DOE define a microgrid?

Answer 7

A group of interconnected loads and distributed energy resources (DER) 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.

Question 8

What are the five main components of a microgrid architecture?

Answer 8

Existing assets

Hardware

Integration Services

Controls

Deployment Services

Question 9

Explain passive anti-islanding protection

Answer 9

• In the event of an island, the voltage and frequency setting of the equipment will trip first before the active anti-islanding trips.
• If the loads are not closely matched, but could quickly exceed their acceptable ratings, the settings that are programmed into the inverter will turn off all the inverters in their required times

Question 10

Explain active anti-islanding protection

Answer 10

For the active anti-islanding function, a technique called Slip Mode Frequency Shift is used. This varies the reactive power output of the inverter. The goal of this protection method is to destabilize an islanded feeder by trying to influence the frequency.

Question 11

What are the key points to be considered when designing a microgrid?

Answer 11

1. Determine what you want the microgrid to do?
2. Determine the power supply?
3. Bridge the gap between what you have and what you need
4. Locate the best place to build
5. Determine the microgrid’s boundaries
6. Line up financing, stakeholders and your team