Distributed Generation &

Renewable Energy
Technologies

By
Mohammed A.
Cogeneration
 A cogeneration system is the sequential or
simultaneous generation of multiple forms
of useful energy (usually mechanical and
thermal) in a single, integrated system.

 Combined Electricity& Heat Production(CHP)

systems are a cogeneration consisting of a
number of individual components: prime
mover, generator, heat recovery, and
electrical interconnection configured into an
integrated whole.
Cont,d
 Prime movers for CHP systems include
reciprocating engines, combustion or gas
turbines, steam turbines, micro-turbines,
and fuel cells.
 These prime movers are capable of burning
a variety of fuels to produce shaft power or
mechanical energy.
 Although mechanical energy from the prime
mover is most often used to drive a
generator to produce electricity, it can also
be used to drive rotating equipment such as
compressors, pumps, and fans.
 Cogeneration
 Thermal energy from the • Improves energy
system can be used in direct efficiency
process applications or
• Conserves natural
indirectly to produce steam,
resources (fossil fuels)
hot water, hot air for drying,
or chilled water for process • Lower emissions
cooling. (including CO2)
 simultaneous production of • Lower energy costs
power and heat, with a view • If heat fits demand,
to the practical application of cheapest way of electricity
both products. production
• Improves security of
supply
• Reduces transmission
and distribution losses
• Enhances competition
 Power Quality Issues
 A major issue related to interconnection of
distributed resources onto the power grid is
the potential impacts on the quality of power
provided to other customers connected to the
grid.
 Voltage Regulation: Over-voltages due to
reverse power flow.
◦ If the downstream DG output exceeds the
downstream feeder load, there is an increase in
feeder voltage with increasing distance.
◦ If the substation end voltage is held to near the
maximum allowable value, voltages downstream on
the feeder can exceed the acceptable range.
Cont,d
DG Grounding Issue:
 A grid-connected DG, whether directly or
through a transformer, should provide an
effective ground to prevent un-faulted
phases from over-voltage during a single-
phase to ground fault.
 Proper grounding analysis of DG will ensure
compatibility with grounding for both the
primary and secondary power systems.
Cont,d

 Harmonic Distortion:
◦ Voltage harmonics are virtually always present
on the utility grid.
◦ Nonlinear loads, power electronic loads effects
of the harmonics include:
 Overheating and equipment failure,
 Faulty operation of protective devices,
 Nuisance tripping of a sensitive load and
 Interference with communication circuits‟
Cont,d
 Islanding:
“Islanding” occurs when a small region of
the power grid is isolated by broken lines,
etc., and yet local sources provide enough
power to keep the voltages up
In case the DG in the distribution system is
capable to meet the load demand, DG can
be operated in the island mode and
continue to from utilizing the distribution
system.
Cont,d
Direct use of Distributed Generation
 Photovoltaic (PV), wind, micro-combined
heat & power (CHP) and many others
produce power locally for direct use,
reducing the need for transporting the
energy across transmission and distribution
grids.
MicroGrid
 Micro-grid definition
 the definition from the EU research
projects is used:
 Micro-grids comprise LV distribution systems
with distributed energy resources (DER) (micro-
turbines, fuel cells, PV, etc.) together with
storage devices (flywheels, energy capacitors
and batteries) and flexible loads.
 Such systems can be operated in a non-
autonomous way, if interconnected to the grid,
or in an autonomous way, if disconnected from
the main grid.
 The operation of micro-sources in the network
can provide distinct benefits to the overall
system -performance, if managed and
coordinated efficiently.
 Cont,d

 Microgrid is an integration platform for supply-

side (microgeneration), storage units and
demand resources (controllable loads) located in
a local distribution grid.
 A microgrid should be capable of handling both
normal state (grid-connected) and emergency
state (islanded) operation.
 The difference between a microgrid and a
passive grid penetrated by microsources lies
mainly in terms of management and
coordination of available resources.
Microgrid definition

Microgrid Power grid

Distributed energy resources Power grids are larger
and loads that can be conventional and spread out
operated in a controlled, grids with high voltage power
coordinated way either transmission capabilities.
connected to the main power
grid or in “islanded”* mode. Microgrid technology can be
applied to weak grids making
Microgrids are low or medium the network more robust.
voltage grids without power
transmission capabilities and
are typically not
geographically spread out.

Nanogrid
Low voltage grids that
typically serve a single
building.
Islanded mode: ability to provide
power independently from the
main power grid
 Microgrid segments and main drivers
Main drivers
Environmen
Social Economic Operational
tal
Fuel
Segments Typical customers Access to Fuel & cost Reduce CO2 independen Uninterrupt
electricity savings footprint ce ed supply

Island
utilities
(Local) utility, IPP*    ()

(Local) utility, IPP,

Remote
Off-grid

communities
Governmental development   
institution, development bank
Mining company, IPP, Oil &
Weak grid

Industrial
Gas company, Datacenter, 
and
Hotels & resorts, Food &  () 
commercial
Beverage
Grid-connected

Governmental defense 
Defense
institution () () 

Urban
communities
(Local) utility, IPP () 

Institutions Private education institution,

and IPP, Government education () ()
campuses institution
 : Main driver
IPP: Independent : Secondary
()Power
driver
Producer
 Microgrid: generation at the point of
consumption and always available

Solar PV Wind Remote asset

power power management Commercial
plant plant and data loads
analytics

Conventional Distributed
power Residential
control system loads

Grid Advanced power Industrial

connection distribution and loads
protection

Modular scalable energy

storage and grid
stabilization
 Microgrid operational goals and power system
functions drive choice of technology
Power system functions –
Operational goals “8S”
– Access to electricity Renewable 1. Stabilizing
power
– Maximize reliability 2. Spinning reserve
– Uninterrupted supply 3. STATCOM (static synchronous
compensator)
– Reduce environmental impact Microgrid
control 4. Seamless transition between
– Maximize renewable energy system islanded and grid-connected
contribution states
– Fuel & cost savings 5. Standalone operation
– Fuel independence Energy storage
6. Smoothing
and grid
– Provide grid services stabilization 7. Shaving
8. Shifting
 Micro-grids and the grid interaction
• Micro-grids could have a grid interconnection to
improve system economics, improve operation and
improve availability

• With a suitable planning, grid planning can benefit

from having micro-grids by reducing conductor‟s
size, improving availability and improving stability

• Tools, strategies and techniques for an effective

integration of a micro-grid into the main grid:
• Net metering – bi-directional power flow.
• Peak shaving
• Advanced communications and controls
• Demand response
 Cont,d
• Interconnection practice / recommendation: IEEE
standard 1547
• Potential issues with microgrids integration to main
grid:
 Infrastructure long term planning / economics:
• There is no coordination in planning the grid and
microgrids.
• The grid is planned on a long term basis
considering traditional loads.
• Microgrids may “pop-up” afterwards “without
notice.”
• Grid‟s planning links economic (cost of grid‟s
electricity, future demand…..) and technical aspects
(line congestion….)
 Stability: microgrids are variable loads with
positive and negative impedance (they can act to
the grid as generators)
 Cont,d
• More potential issues with micro-grids integration
into the main grid:
• Safety: When there is a fault in the grid,
power from the micro-grid into the grid should
be interrupted (islanding)
• Availability: Micro-grids can trigger
protections (directional relays) upstream in the
grid and interrupt service to other loads

• Key issue: micro-grids are supposed to be

independently controlled cells within the main grid.
• How much independence micro-grids should
have?
• Does independence apply also to planning?
• How much interaction / communications
should be between the grid and the micro-
grid?
 Cont,d
• Example of microgrid development. Initial condition.
• Equipment and
financial planning is
done with all the load
in the figure in mind.
 Cont,d
• Example of microgrid development. Planning issues. A
microgrid is installed few years later.

Transformers
and
conductors
can now be
oversized

(remember
this aspect
for PEV and
PHEV
integration)

Microgrid’s
area
 Cont,d
Example of microgrid development. Initial normal
power flow direction

Directional
Relay
 Cont,d
• Example of microgrid operational issues. New power
flow with a microgrid.
• The
microgrid‟s
power trips open
the directional
relay
• Is it possible • What
to change the microgrid‟s
grid‟s state fast control action
enough to follows?
Directional
prevent voltage Relay • Can the
collapse due to microgrid stop
loss of stability injecting power
caused by the back into the
sudden load grid (i.e.
changes prevents
introduced by islanding)?
the microgrid? Microgrid’s
area
 Cont,d
• Example of microgrid operation. Islanding.
• If islanding occurs the
microgrid will continue
to provide power to a
portion of the grid
even though the grid
connection upstream
has been interrupted.
“Island”
• Potential issues:
• Utility crews safety.
• Power quality at
the energized
portion could be
poor. Loads could
be damaged. Microgrid’s
area
 Cont,d
• Grid interconnection might be different for dc or ac
microgrids
• For ac microgrids, grid interconnection can be done
directly, with a disconnect switch, and a transformer
only.
• For dc microgrids an inverter is necessary
• Examples:

CERTS microgrid (ac) NTT Facilities Sendai project

(ac and dc)
 Cont,d

• dc microgrids integration with the grid

• The interface may or may not allow for bidirectional

power flow. Bidirectional power flow can be needed for:
•`Energy storage
• dc loads
 Smart grids
• There are two similar but not equal approaches to the
smart grid concept.
• EU-led vision (customer and environmentally driven):
• Europe‟s electricity networks in 2020 & beyond will be:
• Flexible: Fulfilling customers‟ needs whilst
responding to the changes and challenges ahead;
• Accessible: Granting connection access to all
network users, particularly for renewable energy
sources and high efficiency local generation with
zero or low carbon emissions;
• Reliable: Assuring and improving security and
quality of supply, consistent with the demands of
the digital age;
• Economic: Providing best value through innovation,
efficient energy management and „level playing
field‟ competition and regulation.
• US led vision (security and consumer driven)
 The smart grid concept
• A smart grid is not a single concept but rather a
combination of technologies and methods intended to
modernize the existing grid in order to improve flexibility,
availability, energy efficiency, and costs.

• Smart Grid 1.0:

• Intelligent meters

• Smart Grid 2.0 (“Energy Internet”

enabler):
• advanced autonomous controls,
• distributed energy storage,
• distributed generation, and
• flexible power architectures.

• Distributed generation (DG), flexible power architectures,

autonomous controls and loads constitute local low-power
grids (micro-grids).
 Smart grid evolution: dull past/present

• Centralized
operation and
control

• Passive
transmission and
distribution.

• Lack of flexibility

• Vulnerable
 Smart grid evolution: present/immediate future
• Still primarily
centralized control.
• Limited active
distribution network
(distributed local
generation and storage).
Use of virtual storage
(demand-response)

• Addition of
communication systems
• More efficient loads

• Flexibility issues

• Somewhat more robust

 Smart grid evolution: Future
• Distributed operation
and control

• Active distribution
network (distributed
local generation and
storage).

• Integrated
communications
• Advanced more
efficient loads

• Flexible
• More robust