Effectively interconnecting high-level penetration of 

photovoltaic (PV) systems requires careful technical 

attention to ensuring compatibility with electric 

power systems. Standards, codes, and implementation have been cited as major impediments to widespread use of PV within electric power systems. 

On May 20, 2010, in Denver, Colorado, the National 

Renewable Energy Laboratory, in conjunction with 

the U.S. Department of Energy (DOE) Office of Energy 

Efficiency and Renewable Energy (EERE), held a workshop to examine the key technical issues and barriers 

associated with high PV penetration levels with an 

emphasis on codes and standards. 

There was significant focus on future inverters that 

would be capable of staying online during grid 

anomalies while maintaining grid safety and reliability. Discussions included multiple definitions of high 

penetration, enhanced monitoring and control opportunities, and the new IEEE P1547.8 (Expanded Use 

of IEEE Standard 1547) that will focus on resolution of 

many concerns of high-penetration PV deployment. 

Presented at the 4th International Conference on the Integration of Renewable andDistributed Energy Resources, 6-10 December 2010, Albuquerque, New Mexico.

This work was supported by the U.S. Department of Energy under Contract No. DOE-AC36-08GO28308 with the National Renewable Energy Laboratory. The authors 

XJTIUPBDLOPXMFEHFUIFDPOUSJCVUJPOTPG,FWJO-ZOOBOE+FOOJGFS%F$FTBSPPGUIF64%0&4PMBS&OFSHZ5FDIOPMPHJFT1SPHSBN/3&-10t%FDFNCFS

t Minimum Load to Generation Ratio: this is the annual 

minimum load on the relevant power system section 

divided by the aggregate DG capacity on the power 

system section

t Stiffness Factor: the available utility fault current divided by DG rated output current in the affected area 

t Fault Ratio Factor: available utility fault current divided by DG fault contribution in the affected area 

t Ground Source Impedance Ratio: ratio of zero sequence impedance of DG ground source relative to 

utility ground source impedance)

DEFINING HIGH PENETRATION

DYNAMIC CONTROL OF INVERTERS

TECHNICAL CHALLENGES

t .PTUPGUIFDIBOHFTDBO

be done in software

t .JOPSIBSEXBSFDIBOHFT

- Additional Sensors

- UPS for LVRT

- Minimal additional cost 

t *OWFSUFSXJMMPQFSBUFBU

higher current levels when 

off of unity power factor 

than at unity

- Impacts efficiency 

and reliability

DYNAMIC CONTROL

t $PNNVOJDBUJPOTUP17JOWFSUFST

to control operational setpoints

- Real Power Limit

t$VSUBJMQSPEVDUJPO

t3BNQSBUFT

- Reactive Power Level

t7"3T

t1PXFS'BDUPS

t7PMUBHFDPOUSPM

- Trip levels

t0WFS6OEFS7PMUBHF

t0WFS6OEFS'SFRVFODZ

t 0QFSBUFMJLFUSBEJUJPOBMQPXFSQMBOUT

GRIDINTEGRATED SMART INVERTERS

t $POOFDU%JTDPOOFDUGSPN(SJE

t 0VUQVU1PXFS.BOBHFNFOU

t *OUFMMJHFOU7PMU7BS$POUSPM

t 4UPSBHF.BOBHFNFOU

t &WFOU)JTUPSZ-PHHJOH

t 4UBUVT3FQPSUJOH3FBEJOH

t 5JNFTZOD

NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency and Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

EVALUATING FUTURE STANDARDS AND CODES WITH A FOCUS 

ON HIGH PENETRATION PHOTOVOLTAIC (HPPV) SYSTEM DEPLOYMENT

Michael Coddington, 

Benjamin Kroposki, 

Tom Basso, and Kevin Lynn (DOE)

Michael.Coddington@nrel.gov

Advanced Volt-Var Control Effect on Service Voltage

VARs Generated

Capacitive

Inductive

System

Voltage

System

Voltage

V1

V1

V2

V2

V3

V4

Q1

Q4

Q2 Q3

Q2

Q1

7PMU7BS

Mode 1:

Normal

Regulation

7PMU7BS

Mode 2:

Transmission

VAR Support

VARs Generated

Capacitive

Inductive

Simple

Broadcast

0.9

0.95

1

1.05

1.1

Voltage (PU)

Hour

0 4 8 12 16 20

Baseline - No PV

Inverter Volt-Var

Control

20% PV Penetration

Bulk Generation

System Bulk

Generation

Bulk

Generation

Bulk

Generation

Bulk

Generation

Bulk Transmission System 

Subtransmission System 

Dedicated

Secondary 

Distribution

Substation & 

"EKBDFOU'FFEFST

Adjacent Distribution Substations

Shared

Secondary 

Customer A Customer B Customer 

PV PV 

1SJNBSZ'FFEFS Recloser

Alternate

'FFET

Type of Ratio

What is it useful for?

Note: these ratios are intended for distribution and subtransmission system impacts of DG listed below, and not necessarily the 

overall bulk system stability impact

Suggested Penetration Level Ratios

Very Low Penetration Very low probability 

of any issues

Moderate Penetration Low to minor probability 

of issues

)igher Penetration

Increased probability 

of serious issues. 

Minimum Load to 

Generation Ratio

tGround fault overvoltage analysis 

tIslanding analysis (use ratios 2/3 of those shown)

> 10 Synchronous Gen. 10 to 5 Synchronous Gen. Less than 5 

Synchronous Gen. 

> 6 

Inverters

6 to 3 

Inverters 

Less than 3 

Inverters 

'ault Ratio 'actor 

(ISCUtilityI

SCDG)

tOvercurrent device coordination 

tOvercurrent device ratings >100 100 to 20 Less than 20

(IUitliltySCI

RatedDG)

tVoltage Regulation 

need to check for current reversal at upstream regulator devices.)

>100 

PV/Wind

100 to 50 

PV/Wind

Less than 50 PV/Wind

> 50 Steady Source50 to 25 

Steady Source

Less than 25 

Steady Source

Ground Source 

Impedance Ratio

tGround fault desensitization 

tOvercurrent device coordination and ratings >100 100 to 20 Less than 20

Prism Solar PV Inverter

Manufactured by Satcon

Voltage Ride-Through 

Requirements

Point of Interconnection - Voltage (PU)

Time (seconds)

1.4

1.3

1.2

1.1

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

0.1

No Trip

Zone

High Voltage

Duration

Low Voltage

Duration

Return to between .95 and 1.05 PU

dependant on automatic or

manual changes to the system

1 10 100

'SFRVFODZ3JEF5ISPVHI

Requirements

Time (seconds)

62.5

62.0

61.5

61.0

 60.5

60.0

59.5

59.0

58.5

58.0

57.5

0.1 1 10 100 1000 10,000