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Ensuring Reliable Electricity Supplies Using Distributed Generation. Gregory Tress Carnegie Mellon University. Overview. Introduction The Power Grid Power Disruptions Infrastructure Issues Distributed Generation Solutions. Introduction. What is distributed generation? EPA definition:

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Ensuring reliable electricity supplies using distributed generation

Ensuring Reliable Electricity Supplies Using Distributed Generation

Gregory Tress

Carnegie Mellon University

Overview Generation

  • Introduction

  • The Power Grid

  • Power Disruptions

  • Infrastructure Issues

  • Distributed Generation

  • Solutions

Introduction Generation

  • What is distributed generation?

    • EPA definition:

      “Small, modular, decentralized, grid-connected or off-grid energy systems located in or near the place where energy is used.”

  • Goals for electricity generation and delivery

    • Reliable

    • Affordable

    • Efficient

    • Environmentally friendly


What is the problem? Generation

We are addicted to electricity


  • We can consume any amount of power at any time

  • In most cases, this is not a problem

  • Under the right circumstances, it can be a big problem

Introduction Generation

  • What is the problem?

    • Northeast Blackout, 14 Aug 2003

    • 50 million people affected



The power grid

Generation Generation



The Power Grid




The power grid1
The Power Grid Generation

The classic model


High power flow

in transmission lines




The power grid2
The Power Grid Generation

What can distributed generation do?







Power disruptions
Power Disruptions Generation

  • Classification

    • Power shortages

      • Blackout: complete loss of power

      • Rolling blackout: intentional, temporary shutoff

      • Brownout: voltage reduction, may be intentional

    • Power quality issues

      • Voltage and frequency fluctuations

Power disruptions1
Power Disruptions Generation

  • Commercial and Industrial Impact

    • U.S. economy is losing over $100 billion / year

Power disruptions2
Power Disruptions Generation

  • Commercial and Industrial Impact

    • Critical economic sectors are at risk

      • Data storage, retrieval, processing

      • Research and development operations

      • Telecommunications

      • Financial operations

      • Precision and general manufacturing

      • Transportation

      • Utilities (e.g. water, natural gas)

Power disruptions3
Power Disruptions Generation

  • Residential consumer impact

    • Power-sensitive high-tech devices

      • Possible equipment damage

      • Expensive to replace or repair

      • Possible irreversible data loss

    • Essential devices

      • Refrigeration

      • Heating and cooling

      • Medical

Infrastructure issues
Infrastructure Issues Generation

  • Why isn’t the system reliable now?

    • High peak demand

    • Delivery bottlenecks

    • Grid fragility

    • Power Loss

Infrastructure issues1
Infrastructure Issues Generation

  • The demand pattern

    • Higher during the day, lower at night

    • Higher in the summer, lower in the winter

    • Result: highest during the day in the summer

  • Why does this matter?

    • We don’t know how much higher it will be

Infrastructure issues2

0 Generation






Infrastructure Issues

  • The demand pattern

    • Sample residential area: winter vs. summer day

Maximum transmission capacity

Infrastructure issues3
Infrastructure Issues Generation

  • The bottleneck

    • “Inadequate investment in transmission infrastructure... costs consumers tens of billions of dollars a year in higher energy costs and lost productivity”

      -- National Commission on Energy Policy

Infrastructure issues4
Infrastructure Issues Generation

  • The bottleneck

    • Transmission loading relief events (TLRs) recorded when lines reach full capacity

    • Quantitative indicator of transmission congestion

Infrastructure issues5
Infrastructure Issues Generation

  • The fragile grid

    • Equipment limitations

      • Safety systems (e.g. circuit breakers) are designed to prevent dangerously high power flow

      • Customers don’t know how high total demand is

    • Cascading failure

      • A single equipment failure can cause a chain reaction

      • Lack of redundancy increases risk and severity

Infrastructure issues6
Infrastructure Issues Generation

  • Power loss

    • Transmission loss 6-8% during peak demand

    • Heat released into atmosphere

Distributed generation
Distributed Generation Generation

  • Classification

    • Dispatchable

      • Turned on and off when necessary

      • Fossil fuel, biofuel powered

    • Intermittent

      • Not precisely controllable or predictable

      • Solar, wind

Distributed generation1
Distributed Generation Generation

Clean power

… but at what cost?

Distributed generation2
Distributed Generation Generation

  • The impact of intermittent generation

    • Reliability decrease

      • Maximum generation doesn’t necessarily match up with maximum demand

    • Transmission increase

      • Wind and solar have specific geographic requirements. Delivering this power to other areas will add to existing transmission congestion.

Distributed generation3
Distributed Generation Generation

  • Dispatchable generators: the solution?

    • Can satisfy peak demand

    • Not susceptible to transmission bottlenecks

    • Increase grid stability and redundancy

    • Reduce atmospheric power losses

Distributed generation4
Distributed Generation Generation

  • Dispatchable generators: the solution?

    • High efficiency

      • Up to 90% for combined heat and power generation

    • Works well with intermittent generation

      • Operates when wind and solar can’t

    • Flexible local fuel sources

      • Can use existing natural gas lines or locally-produced biomass/biofuels.

    • National energy security

Distributed generation5
Distributed Generation Generation

  • Dispatchable generators: the downside

    • Environmental impact

    • Public opposition

    • Additional points of failure

    • Capital cost

      • $500-$1000 per kW to install typical generator unit

      • Average residence uses 1-2kW; more during peak

      • $500-$4000 or more per household over lifetime of the generator, plus land, upkeep, etc

Solutions Generation

  • Combination of factors is at fault

    • Each problem can be fixed independently

    • Distributed generation can solve most at once

  • Reliability is limited

    • Impossible to reach 100%

Solutions Generation

  • Standards already exist

    • FERC Order 888 & 889 (1996)

      • Opens transmission lines to competition

    • FERC Order 2006

      • Small generator interconnection agreements and procedures

    • IEEE Standard 1547

      • Standard for interconnecting distributed resources with electric power systems

Solutions Generation

  • Government has spoken

    • Energy Policy Act 2005

      • $800 million for distributed projects and research

      • Includes focus on reliability, efficiency, emergency supply, effect on rates, advanced metering, residential grid connectivity, grid design and planning

    • Environmental Regulations

      • EPA Clean Air rules in effect

      • National preference for clean, “green” power

Solutions Generation

  • A question of value

    • High cost for non-obvious increase in reliability

    • Desire for cheap power vs. desire for reliability

    • Some customers are already installing their own systems (or backup supplies)

    • Should we force all customers to pay for distributed generation?

Solutions Generation

  • Do we need distributed generation?

  • Other options:

    • Add transmission capacity

    • Reduce consumption

    • Implement variable-rate billing

    • Deploy electricity storage units

    • Sell smart appliances

    • Do nothing

Conclusion Generation

  • There’s no clear winner

    • Distributed generation (both intermittent and dispatchable) is already being adopted without much government intervention

    • Many consumers may not want distributed resources or care about reliability (this must be assessed before making policy decisions)

    • Environmental impact can still be significant, even with high efficiency and limited operating time

Conclusion Generation

  • Incentives can still be helpful

    • Potential market in individuals, groups, or businesses for whom distributed resources would be cost-effective

    • Directed incentives or financial assistance would enable adoption for specific economic sectors

    • It may not be for everyone.

Thank you

Thank you Generation