Hot Topics in Solar PVPresented at

Tech Advantage 2014by

Douglas Danley

Grid-Tied Photovoltaic (PV) power systems are being installed in ever increasing number, both at small residential levels and at larger commercial and utility-scales.

Design of a PV System

The goal for this presentation is to provide an overview some of the topics that are being discussed related to PV system design and integration, including:• System Design – the DC/AC ratio• Advanced Power Electronics• PV and Fire Safety• PV and Storage

Why pay attention?

• “US Passes 10 GW Installed Solar PV Capacity Milestone in 2013”

• Costs are dropping at the same time that there are increasing calls for more renewable energy.

What is causing this?

Topic 1 - The DC / AC Ratio and Clipping

Prototypical PV System

PV ArrayMeasured in Watts-DC

DC-AC InverterMeasured in

Watts-AC

Utility

• The DC rating of the array is always greater than the inverter capacity due to legacy methods for rating PV Modules.

• Traditionally, the ratio of DC to array was set so that no PV energy would be wasted under any circumstance. The ratio was typically 1.1 to 1.2.

• As modules got cheaper, engineers reevaluated this assumption and are now specifying DC to AC ratios between 1.3 and 1.5.

• This introduces a limited amount of wasted PV energy (“clipping”) which is not a physical problem, but merely one of economics.

• Since the PV array gradually degrades over its life, the losses actually get smaller over time.

Topic 1 - The DC / AC Ratio and Clipping

• Example 1 – Vermont DC/AC Ratio of 1.2

Topic 1 - The DC / AC Ratio and Clipping

• Example 2 – Vermont DC/AC Ratio of 1.4

Topic 1 - The DC / AC Ratio and Clipping

• Example 3 – SoCal DC/AC Ratio of 1.4

Topic 1 - The DC / AC Ratio and Clipping

Topic 1 - The DC / AC Ratio and Clipping

• Detail of daily performance

• Historically, PV system must follow IEEE 1547, which requires systems to get off line under specified disturbances (for safety reasons), and which prohibits localized voltage control.

• As penetration increases, utilities realized that PV systems might be able to provide additional benefits such as Volt/VAR management, ramping control, curtailment, low voltage ride through and low frequency ride-through. Experiences in Germany have helped to show the benefit of this approach.

• IEEE 1547.8 and IEEE 1547a are being developed to address these capabilities, which are being implemented in advanced power electronics, sometimes called “smart inverters”.

Topic 2 – Advanced Power Electronics and Integration

• Energized PV systems present unique challenges to firefighters, both because of the physical characteristics of the system (even when they are “turned off”, 600-1000 VDC may still be present), and because firefighters are not familiar with these systems.

• This is especially true for residential and commercial rooftop systems.

• There have been a number of changes to the NEC 2014 to address these issues, and there are additional anticipated changes to NEC 2017 being discussed.

• There are also a number of changes to the International Building Code (IBC) and International Fire Code (IFC) for the next cycle (2015) including new rules for clear access lanes.

Topic 3 – PV Systems and Fire Safety

• There are an increasing number of resources available to help understand the issues.

• Sources include NFPA, UL and CalFire

http://lms.ulknowledgeservices.com/catalog/display.resource.aspx?resourceid=406873

http://www.ul.com/global/documents/offerings/industries/buildingmaterials/fireservice/PV-FF_SafetyFinalReport.pdf

http://www.nfpa.org/~/media/Files/Research/Research%20Foundation/Research%20Foundation%20reports/For%20emergency%20responders/RFFirefighterTacticsSolarPowerRevised.pdf

http://calfire.ca.gov/serp.php?q=pv&cx=001779225245372747843%3Ableoj5gjmwq&cof=FORID%3A10&ie=UTF-8

http://osfm.fire.ca.gov/training/photovoltaics.php

http://www.youtube.com/watch?v=ldzJIf4j8do

http://content.learnshare.com/courses/73/352901/player.html

Topic 3 - PV Systems and Fire Safety

• The utility-scale storage industry is still in prototype / early commercial stage, but it seems clear that, as costs come down, storage will play an increasing role in helping utilities deal with intermittent DG such as PV systems.

Topic 4 – PV and Storage

• Don’t miss the “Utility Scale Energy Storage” sessions with Dale Bradshaw this afternoon.

For Questions:Doug Danley, NRECA240-462-6554Doug.Danley-contractor@nreca.coopDebra Roepke, NRECA703-907-5841Debra.Roepke@nreca.coop

SUNDA Project Goals

• Work with Rural Electric Co-ops to develop tools and processes to reduce barriers to implementation of utility-owned, utility-scale PV systems.

• Develop and streamline these “business products” through implementation of a minimum of 22 MW of PV at 15 co-ops.

• Produce training and outreach materials to reach balance of 900 co-ops plus other interested utilities.

SUNDA Project Strategy

• Standardized engineering designs to minimize design and engineering costs.

• Volume purchasing program through NRECA’s National Discounts Program

• Analysis of business plans and financing options through Cooperative Finance Corporation (CFC)

• Specifications for tailored insurance packages

• Reduced Labor Costs. Targeting a 25% reduction

• Extensive outreach and training

Participating Co-ops

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Co‐op LocationGreatRiverEnergy MNOneida‐MadisonElectricCooperative NYSussexRuralElectricCooperative NJNorthArkansasElectricCooperative ARAnzaElectricCooperative CABrunswickElectricMembershipCorporation NCCoServElectric TXGreenPowerEMC GAOwenElectricCooperative KYPedernalesElectricCooperative TXEauClaireEnergyCooperative WISandhillsUtilityServices NCTri‐StateGeneration&TransmissionAssn. CO/WY/NE/NM/UTVermontElectricCooperative VT

• National Rural Electric Cooperative Association – Management and Dissemination

• PowerSecure, Inc. – Technical Assistance/Engineering

• National Rural Utilities Cooperative Finance Corporation – Business Plans and Finance

• Federated Rural Electric Insurance Exchange – Risk Management and Insurance

• Co-op Utility Partners – Deployment and Implementation

SUNDA Partners

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Doug Danley,

Technical Liaison to CRN

doug.danley-contractor@nreca.coop

Thank You

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