Net Metering Guidelines

for LebanonIng. José Daniel Lara

Net Metering: a working definition

A system in which renewable energy generators (mostly solar panels) are connected to a public-utility power grid and surplus power is transferred onto the grid, allowing customers to offset the cost of power drawn from the utility.

The objective of electricity generation has no commercial purposes.

In the case of Lebanon the user may have interests in order to enhance local reliability.

A classical residential net metering

installation

1. Solar Panels

2. Inverter/Converter

3. Main Panel

4. Load

5. 2-way meter

6. Grid

Why do technical standards matter?

Guarantee safety for the users and

installations where the power

generation units are installed.

Protect the network (shared asset)

from undesired voltage or current

injections.

Protect the distribution system and

other users from undesired

operations. For example, islanding

or reconnect after electric fault.

Impacts of PV systems to the grid - 1

Inadequate inverters can cause power quality issues such as:

Harmonic distortion

Flicker

DC injection

Electromagnetic interference

Reverse Power (when installed in parallel with diesel generators)

Most of this issues are covered by manufacturing standards. The majority of suppliers comply with minimum power quality standards.

Two main standards groups depending on

the standardization organizations.

American UL: Safety standards from the

equipment perspective

UL 1741 Covers Power Conversion and Protection Equipment

IEEE: Interconnection standards, grid compatibility and many others

IEEE 1547 Standard Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems

NFPA: Safety standards from the installation perspective (mostly to avoid fires)

European (IEC)

IEC 61727:2004 Photovoltaic (PV) systems – Characteristics of the utility interface

IEC 62116:2008 Test procedure of islanding prevention measures for utility-interconnected photovoltaic inverters

IEC 60364-7-712: Electrical Installations of Buildings: Requirements for Special Installations or Locations – Solar Photovoltaic power supply systems

IEC 61683 (Power conditioners – Procedure for measuring efficiency

Some European countries have local version of ICE norms like GER and UK.

Impacts of PV systems to the grid - 2

Normally the timing between load

and solar power generation is not

coordinated.

This reality causes the distributed

units to inject power into the grid

during some hours of the day.

Even though the net daily energy

demand can be positive.

In order to manage this is

important for the utility to gather

data from the installation.

Components of a Distributed Generation

Installation

The Utility should gather information about all the devices in

the schematic and guarantee access to the Utility Disconnect

when performing maintenance on the grid.

Components of a Distributed Generation

Installation with storage

This installation

scheme is similar

to the previous

one.

The only

addition is the

battery system

installed right

before the

inverter.

Standards on utility disconnect to avoid

islanding.

This is a very important standard to take into account considering the

conditions in Lebanon.

On one hand, the system needs to disconnect when the grid shuts down and

avoid islanding. However, the system also needs to be resilient to voltage and

frequency variations typical in Lebanon's distribution grid.

Example of the American IEEE 1547 (60 Hz based):

Example of application to Lebanese system:

under voltage limit (level 1): 200 V

under voltage limit (level 2): 115 V

over voltage limit (level 1): 240 V

overvoltage limit (level 2): 310 V

lower frequency limit: 49 Hz

upper frequency limit: 51 Hz

loss of main detection limit: 300 ms

Any inverter compliant with IEC 62116 should be able to be configured with

these parameters.

Standards on utility disconnect to avoid

islanding.

Minimum required information for a Net

Metering project.

Energy source information

Main energy source: [Wind, Solar, Biomass]

Expected daily and annual energy output [kWh]

List of assets [Inverters, Batteries, Diesel Gen Sets]

Load information

Expected peak load (peak load when DG is not online) [kW]

Expected net peak load (peak load most of the time) [kW]

Expected daily and annual energy consumption [kWh]

Feasibility study performed (if available)

Using this information the decision process can be expedited. If the expected

daily energy produced is below 20% of the total daily energy consumed the

grid impacts will be minimal.

Minimum required information for a Net

Metering project.

If the total daily energy produced exceeds 50% of the total daily energy

demanded, it is likely that the system will require a deep interconnection

study that should include:

Power Flow analysis

Max and Min expected voltages

Short Circuit current analysis

Protection coordination with the utility.

Extremely important! GPS coordinates of the plant location [Lat, Long]

Required inverter information

Obtain pictures of the nameplate and datasheets to

corroborate that the inverter complies with

international standards.

All the certificates for the standards can be

obtained from the manufacturer. (See example)

IMPORTANT: If the inverter was custom

configured with regards to anti-islanding those

parameters need to be recorded.

Plant drawings as built displaying

protections and circuit breakers.

Example, Tahrir square.

General guidelines:

Make sure that the utility has access to the main circuit breaker to disconnect the

power plant if necessary.

The installation must contain ground fault protection in the schemes.

The opportunities of Net Metering with

PV panels.

Old System

GG G G

Tensión de generación

Tensión de Transmisión

Tensión de distribución

Carga GD GD GD

GG G G

Tensión de generación

Tensión de Transmisión

Tensión de distribución

Carga

New System