Hanson Utility Scale PV

8/6/2019 Hanson Utility Scale PV

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The Promise of Utility Scale Solar

Photovoltaic (PV) Distributed Generation

Thomas N. HansenTucson Electric Power

Presented at: POWER-GEN International 2003December 10, 2003

Introduction:

The long term commercialization of utility based solar PV electric generationrequires the development of safe, reliable, affordable components and systems that meetutility expectations of performance and life cycle cost per kWh production goals, whileallowing for full integration of time variant intermittent renewable generation resourcesin the utility generation portfolio.

The higher cost of PV generation as compared to the price of traditionally fueled

grid supplied energy is the primary barrier to widespread commercialization of PVsystems. Cost reductions available through design, material specification andconstruction techniques developed by the power industry in response to the need forlower cost traditional generating stations can effect significant cost savings when appliedto PV generation systems. As part of its program to meet the Arizona CorporationCommission (ACC) mandated Environmental Portfolio Standard (EPS) annual solarenergy generation percentage goals, Tucson Electric Power (TEP) has developed a cookiecutter approach to the design and installation of large utility scale PV systems. Thisapproach has resulted in a 3,780 kW DC at STC rated PV system located on the propertyof the coal fired Springerville Generating Station in eastern Arizona.

In 2001 the ACC passed an EPS setting a goal that all ACC jurisdictional utilitiesshall derive from renewable energy resources an increasing amount of electricity sold atretail. The EPS requires that 1.1% of retail electricity sold will come from renewableresources in 2007 through 2012 and that 60% of that must be from solar electricgeneration sources. Various multiplying factors can be applied to reduce the actualamount of electricity produced. These factors provide incentives for in-state location of the renewable generators, early installation, net metering, green pricing programs, in-statemanufacturing of renewable generation components and distributed generation.



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Although TEP already produces sufficient electricity from landfill gas to meet thenon-solar renewable portion of the EPS goals, the EPS requires the installation of justover 10 MW of solar electric generation by 2007. In recognition that the funding for theEPS is not sufficient to meet the goal in the time required, the EPS currently has nopenalty provision. Review of the EPS program results in 2003 demonstrated that the EPS

has to date been very successful and while no jurisdictional utility has yet met its fullrenewable energy percentage goals, the EPS has resulted in installation of over 7,000 kWDC at STC of new PV in Arizona in less than three years. For a complete review of thecosts and benefits associated with development of renewable resources under the EPS,please see the Cost Evaluation Working Group report at http://www.cc.state.az.us



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Program Planning:

TEP chose two PV based solar generation development programs to meet its EPSgoals. Although one large solar thermal generation plant could have met the EPS solargoals, such a project would have done nothing toward developing cost effective customerbased solar generation, a long term goal of TEP’s energy supply strategy. The SunSharePV hardware buydown program provides financial and maintenance support incentivesfor customers to install their own PV system. To date the SunShare and other customerpartnering programs have over 40 customers with more than 120 kW of installed PV.However, given that meeting the EPS goal requires installation of more than 10,000 kWof PV in seven years, TEP also determined that the solar portfolio must include non-customer sited solar generation. Therefore, TEP started developing large distributedgeneration PV systems to meet the portion of the EPS goal not expected to be met bySunShare, initially 90% of the EPS solar goal.

As in real estate, siting a solar generator is location, location, location. TEP had

been performing solar and wind resource survey work for 5 years prior to the start of theEPS. This survey and data gathering and analysis work had been performed at many TEPowned sites as well as some customer owned sites. The high elevation desert region nearthe Springerville Generating Station (SGS) in eastern Arizona was found to have betterannual average and peak solar insolation levels, cooler annual average temperatures andhigher average winds during daylight hours - all factors positively affecting PV solargeneration - than any other location surveyed. Cloud cover percentage at SGS wasgreater than at Tucson, but the net annual effect of all factors resulted in an expectedimprovement of about 3% net annual AC energy production at SGS over Tucson. Inaddition, the property tax rates at SGS are less than half of those in Tucson whichprovides a significant economic benefit for a highly capital intensive project like solar

PV.

The SGS is operated on 21 square miles land with very little growth of more thannative grasses. Consequently, land space was not a concern. A square mile that is verynearly flat with only eight bushes and a bisecting 35 kV transmission line was selected asthe location of the solar system. An aerial view of the site taken in late 2002 is shownbelow for reference. The 35 kV line provides power to the well field pumps that provideraw cooling water for the 760 MW coal fired generating station. The PV system wasdesigned for a completed maximum size of 10 MW AC peak to provide distributedgeneration support for the pump load, and will be built in phases to reach that size in2010. TEP was committed to using at least three different types of PV technology at the

solar system. The design needed to flexibly accommodate different types of PV modules.The use of different PV technology types in a side by side comparison would providecost and performance data beneficial to making improvements in future PV technology.



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Springerville Generating Station Solar System Vital Statistics:

Present DC Rating in KW at STC: 3,780 KW

Present AC Rating in KW at PTC: 2,824 KW

Present Peak AC 15 Minute Production in KW: 3,720 KW

Present Number of PV Modules – ASE: 9,000 Modules

Present Number of Modules – First Solar: 11,280 Modules

Present Number of Modules – BP Solarex: 12,000 Modules

Present Number of Modules – Total: 32,280 Modules

Present Acres of Ground In Use by Solar Field: 38 Acres

Completed Acres of Ground In Use by Solar Field: 80 Acres

Present Number of Xantrex PV150 Inverters: 28

Completed Number of Xantrex PV150 Inverters: 64Expected Annual Net AC Energy Production in 2004: 6,540 MWh

Expected Annual Net AC Energy Production in 2012: 15,000 MWh

Average Annual Temperature: 49 Degrees F.

Total Annual Solar Insolation: >2,100 KWH/M2

Average Annual Wind Speed During Sunlight: 13+ MPH

Site Elevation Feet Above Mean Sea Level: 6,600 Feet



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System Design and Construction:

The implementation of a multi-year, pay as you build style funded EnvironmentalPortfolio Standard (EPS) allows for development of cookie cutter PV system designs in asize optimized to take advantage of partnering opportunities with the manufacturers of

the major components of PV systems to optimize Balance of System (BOS) costs throughboth material and installation labor cost reductions. This funding method eliminatesfinance charges which dramatically reduces the life cycle cost of high capital, lowoperating cost generation such as solar PV.

Electrical costs can represent a significant portion of the BOS costs of a PVsystem. Development of cookie cutter PV system designs in a size optimized to takeadvantage of standard sizes of electric equipment can maximize the amount of connectedPV capacity per electrical connection point, and reduce electrical costs per DC watt.

TEP developed some small pilot PV systems of up to 22 kW using four different

PV technologies. These systems were designed, built and operated in 1999 and 2000leading to optimization of a cookie cutter design approach for the larger PV installation atSGS. The design process was started by optimizing the AC interconnection equipment.This allowed for optimal use of standard, readily available electrical components. Somedesign criteria used in the process:

• Two stages of transformation were selected – 35 kV Delta to 480 Wye and 480Wye to 208 Delta. The use of double isolation was needed to prevent resonanceissues if single phasing occurred on the 35 kV line.

• A 200 amp 480 volt disconnect was chosen matched to a 200 amp revenue meterand a Xantrex PV 150 inverter. The rated inverter output current is a near perfect

match to the NEC code requirement of a maximum of 80% of disconnect currentrating.

• A 150 kVA, 98.9% efficient 208 to 480 air cooled transformer was specified.

• Four inverters were connected to each 500 kVA 99.2% efficient oil/air cooled 480to 35 KV transformer. PV output is higher when ambient air temperatures arelower, taking advantage of the higher transformer capacity at lower ambient airtemperatures.

• Ground surface prep was economically determined to be set at +/- one inchvertical in 10 feet horizontal. This gives the array a somewhat jagged look inclose up, but annual energy performance is degraded by no more than 0.5%, andscarce funds are minimally spent on ground preparation.

• A high density ground grid of 250 MCM copper was installed in the ground forlightning protection of electrical components. This included a full perimeterground grid at the fence. PV array lightning protection was designed into thesupport structure system as a large scale metal grid to diffuse lightning currentsover large areas where they entered the earth.

• High efficiency PV module array block size was set at 300 feet north-south by140 feet east-west for the overall system layout.



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• Low efficiency PV module array block size was set at 300 feet north-south by 250feet east-west for the overall system layout.

• All intermodule DC connections are to be made by MC connectors. Significanttraining must be given to the installers to ensure proper seating of the connectorsby the installers.

• The DC wiring design was for 0.5% maximum voltage drop from the furthestpoint of the array to the inverter. A balance of voltage drop design and conduitfill derating required by the NEC was used to determine main DC conductor sizeas a #4 AWG.

• The AC wiring and physical layout of the transformers, disconnects, meter andinverter for all systems is cookie cutter identical with the exception of the numberof fuses in the DC interconnection cabinet, called the marshalling box. Thisallowed for very simple replication for different types of PV modules.

• The National Electrical Code allows electric power to be distributed at a voltageup to 600 volts without need for special voltage equipment or wiring, thus use of 480 volt AC equipment can maximize the capacity per dollar ratio.

• Availability and price of DC wiring components is much more favorable when theDC design is kept below a working voltage of 600 volts.

• Due to the SGS site conditions favoring solar generation, the DC array powerrating was designed to be no more than 90% of the AC rating of the inverter.Cloud enhancement can at times drive insolation levels over 1500 watts persquare meter for 15 minute intervals, demanding that the inverter have someavailable power capacity to adjust for the onset of this effect. This design pointalso allows the inverters to spend most of their operating time in the “sweet spot”of their efficiency curve.

When large numbers of similar systems are to be installed, extra care can be taken

using these and other design concepts in the design phase to reduce the cost of both theDC and AC wiring systems. With certain types of PV modules, a single DC electricaltrunk connection can be made for more than 5 kW DC at STC of PV modules. Thisdramatically reduces the cost of the DC electrical trunk system. Proper design of theelectrical system and proper construction staging can reduce the installed cost of theelectrical portion of a utility scale PV system using skilled union labor to less than $0.30per DC watt of PV capacity.

Likewise, design optimization of the PV array support structure must beperformed and the support structure should fill other functions such as lightningprotection and erosion control to minimize the cost of the support. Given that utility

scale PV systems will likely be installed where there is more land area than is required,advantage can be taken of the extra land. Design can be simple and maximize thenumber of watts of PV capacity installed per support. It can also take advantage of thestrength of the frame already designed into many PV modules or provide a simplisticassembly method for unframed modules. Support structure design can also be optimizedto make maximum use of raw material, coating systems available for the dry Arizonaclimate, existing construction components and simplicity of design to allow use of lowcost assembly crews. Supports can be designed to be matched to a particular PV moduleto take advantage of the PV module frame rigidity. Development of long term



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commitments with PV module makers takes advantage of partnering opportunities onstructure development. Support structure installed cost after a year of experience indeveloping construction staging methods can be as low as $0.15 per DC watt of PVcapacity.

Developing relations with inverter makers is essential to standardize large utilityscale inverters, their support software and infrastructure and thus the cost of inverters andinverter installation support components and tooling. Utility scale PV inverters with99+% reliability, 96+% conversion efficiency and sophisticated service features can nowbe purchased for less than half of their small PV inverter counterparts on a cost per wattbasis. Installed costs of inverters and support systems are now less than $0.40 per DCwatt of PV capacity.

Ground preparation and grid connection work for a utility scale PV system can bedone in sections, allowing for modular construction planning and associated efficienciesof construction. Preparation for the initial phase of the SGS Solar System included

blocks for the interconnection of 24 systems, each of 150 kVA AC size, for a total of 3,600 kVA AC rated capacity. The ground prep and grid connection work wascompleted at a cost of less than $450,000. Assuming that each block will have a DCcapacity of 135 KW, the installed cost is $0.14 per DC watt. This includes all surfacepreparation, underground conduit, concrete foundations, high voltage wiring, highvoltage disconnects, soil stabilizer, transformers and grounding to a power plantspecification. Even better, the second phase includes blocks for 20 more 150 kVA ACunits and cost less than $210,000, for a cost of $0.08 per DC watt.

The need for continuous data collection to a standard similar to conventionalpower plants was recognized as essential to solar system performance tracking anddevelopment of preventative maintenance algorithms. The data collection system wasdesigned to interface directly with the inverters and the revenue meter. Data is collectedon 10 second intervals and averaged for one minute intervals for archive. The data serveris accessible from the Internet. Even remote sites such as the SGS can now be linked viainexpensive satellite ISPs to the Internet. Data collection systems, metering andconnection to the Internet, again optimized for utility scale systems, have an installed costof less than $1,000 for a 150 kVA system. This is less than $0.01 per DC watt.

Optimizing the BOS design and installation, resulted in BOS costs of less than$1.00 per DC watt of installed PV capacity in 2003, only the third year of the EPS. Thiscost level meets a long term goal of many federal government grant opportunities. Thisbenefit would not have been possible with a year to year type of EPS.

Time and motion construction reviews provided insight into placement of materialand kitting of parts to reduce lost motion in the field. This study was essential toreducing the costs of construction labor.



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The ground preparation, underground conduit and concrete foundation work wasperformed by an earthwork contractor local to the SGS area, M&S Construction. Theelectrical grid interconnection work was performed by either TEP or a high voltageelectrical contractor located in Tucson, Southwest Energy Solutions. The PV systemarray, inverter and electrical installation work was managed by Global Solar of Tucson.

All units have been successfully completed on schedule and within budget. TEP isresponsible for all design work.



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Operating Results:

Installation of 28 large utility scale distributed generation PV systems is completein Springerville. These systems use PV array building blocks of about 135 kW DC insize. Different PV module technologies have been used, including crystalline silicon,

Cad-Tel and amorphous silicon. Testing of new module technologies is supported byTEP. The results of daily energy production performance are shared with interestedmanufacturers. These systems are heavily instrumented and results are reviewed daily toensure proper operation of the systems. Effective availability of these systems in 2002was 99.43%, a very high “on line” operational record for any generating system. ThesePV systems have proven to be reasonably cost effective installations using theopportunity provided by the EPS program to eliminate financing charges. Financecharges are a considerable portion of total costs in high capital, low operational costprojects such as PV. Elimination of finance charges to reduce life cycle ownership costsusing the “pay as you go” up front funding concept inherent in the EPS mechanismadopted by the ACC has made a significant reduction in life cycle cost of energy

generated with PV. Evaluation of life cycle costs given limited experience with longterm operating costs of large scale PV indicate that large utility scale distributed PVgeneration systems should produce electricity at a simple cost basis of less than $0.11 perkWh at 2003 PV prices. Operating costs are expected to be $0.004 per kWh of thatamount.

PV module Degradation: One partnering PV module manufacturer recentlyretested PV modules which had been in service in Tucson for 28 months to test for dirtand time related output degradation. Modules were tested first without cleaning and thenafter cleaning. Results indicated soiling effect was less than 1% output degradation frommodules which had not been cleaned in two years and overall time related degradation of clean modules much less than that expected. 9,000 of these modules are used in the SGS

solar system. SGS modules have historically been cleaner than Tucson located modulesdue to no oily deposits and the ability of snow to very effectively remove solid depositslike bird droppings.

The units at Springerville experienced three failures of the electrical grid during2002. In all three cases all inverters met their IEEE-929 island detection requirements,even with 18 inverters in parallel on the line and some inductive pump motor load, anddisconnected nearly instantaneously. As additional inverters are added and the installedcapacity of PV approaches the installed load of the pumps and other loads on the radialline, it will be instructive to monitor the transient response of line faults as verification of correct IEEE-929 compliance. The same has been true of all 2003 transmission line

power failures with up to 24 inverters connected and operating.While the TEP fleet of large scale PV systems had a very high percentage of

effective availability in 2002, there are challenges remaining in maintenance of PVsystems. There were 15 separate incidents in 2002 requiring some level of humanresponse to restore the large system to full operation. These incidents were onlyidentified because of the instrumentation and communications that is economically viableon large scale systems.



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The following technical Qualitative PV Module Evaluation is based on 10 monthsof one minute interval data taken from operation of the Springerville solar units. UnitsU-1 through U-12 are each composed of 450 ASE 300DG-50 modules, connected with 9in series. Units U-33 and U-34 are each composed of 2,688 First Solar FS-50 modules,connected 6 in series. Units U-37 through U-40 are each composed of 3,000 BP Solarex

MST-43 modules, connected 5 in series. All modules are facing due south at an angle of 34 degrees from horizontal, which is latitude angle. The ASE and BP Solarex modules,with the exception of those in C-12 are commercial products, not test or preproductionmodules. However, the First Solar modules are a preproduction module, purchased fortesting purposes and were not expected to perform like production modules. Anyinterpretations of First Solar module data or comparisons with other systems atSpringerville or elsewhere must reflect that the First Solar modules are a preproductionversion.

All units use a Xantrex PV-150 150 KVA inverter proven in operation to becapable of intermittent operation at output levels as high as 157 KVA AC. The 208 volt

three phase output of the inverter is stepped up to 480 volt 3 phase at which point it ismetered for reporting purposes and then transformed to transmission voltage of 34.5 kV.The site is at 6,600 foot elevation, in eastern Arizona. ASE modules were installed in2001, 2002 and 2003, all BP modules, except replacement modules, were installed in2001, and First Solar modules were installed in 2001, 2002 and 2003.

Unit 10 on 10/3/2002

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Qualitative PV Technology Evaluation:

The crystalline silicon modules from ASE are the best overall performers in termsof reliability and predictability of output. After the initial month of operation duringwhich all module types at SGS experienced some degree of infant mortality, as of

February 1, 2003 we have experienced no ASE module failures. DC bus voltage rangesfrom 450 volts in the winter to 380 volts in the summer, exhibiting a normal pattern of sag as the time approaches noon and the voltage rises again after noon. The modulesexhibit expected voltage changes with temperature, lower in summer and higher in winterand power output follows the rule as well. The inverters follow maximum power pointwith great accuracy. Minimal tuning of inverter constants to accommodate closefollowing of cloud enhancement was needed.

The First Solar Cad-Tel modules experienced a level of cracked modules that todate has been less than expected, but has resulted in some loss of energy production. Ourexperience with the more recent preproduction module additions in 2002 indicates a

significant reduction in modules which later develop cracks. It needs to be noted that thedevelopment of a crack does not necessarily mean a reduction in module performance aswell over 70% of cracked modules were still performing properly a year after the crack developed. There have also been some module output failures that do not exhibit cracks.Designing to match the maximum power point tracking window of thin film modules to asite which in 15 months has experienced ambient temperatures from -22 deg F to +102deg F, insolation over 1500 w/M2 for 15 minutes and wind speeds in excess of 100 mphis a challenge with thin films. The initial installation of First Solar modules with 6 inseries did have difficulty matching a minimum inverter DC bus voltage level of 300 voltsin the summer months. However, the second installation of First Solar modules has nothad that problem. The modules exhibit expected voltage changes with temperature,

lower in summer and higher in winter and power output follows the expected rule as well.The First Solar units also exhibit much higher voltage earlier in the morning under partiallight conditions and can start the inverter earlier than either the ASE or BP modules, andunder partial light conditions some days have outperformed the ASE systems. The U-34inverter follows maximum power point with great accuracy, but the U-33 inverter is onlyable to track max power point about half of the time in a year, since the array max powerpoint is below the 300 volt floor of the inverter the other half of the time. Changes madeto the array configuration in 2003 resolved this issue. The second generation First Solarmodules installed in 2003 are producing energy well above expectations during the first 4months of operation. Some tuning of inverter constants to accommodate close followingof cloud enhancement was needed on all First Solar inverters.

The BP Solarex a-si modules have been challenging. The first delivery of modules appears to have been made from different production runs with different modulevoltage ratings although the label shows no difference, but individual module voltagelevel readings show differences. These modules are in U-37 which has been a relativelypoor performer from day one and exhibits open circuit voltage about 20 volts below theother three BP units. After the initial degradation period expected of a-si, which took about one week in the summer of 2001, the other three BP units have generally also notbeen able to reach the 300 volt voltage floor of the inverter. During summer of 2002 and



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2003 the max power point was about 280 to 290 volts, so power loss was minimal, giventhe flat IV curve of a-si. As winter 2002 approached and temperatures dropped, the unitsexhibited a rise in DC voltage and a rise in power output, just like the ASE and FirstSolar units, and U-38, U-39 and U-40 started to exhibit DC bus voltages slightly above300 volts in the early morning and the afternoon. However, toward the end of October

2002, the max power point DC bus voltage never climbed above 300 volts on any BPunits, and worse, a downward trend in power output started, sometimes as much as 20%below the daily energy output of the ASE units. This effect did reverse in mid July 2003,but it took record high temperatures to promote the self annealing which reverses the lossof energy production performance. Less than 1% of modules had cracked or failed afterone year of service and all failed modules were replaced under warranty by September2002. During the second year of operation the failure rate fell to 30 modules out of 12,000 or 0.25%, a very good record. U-38 exhibits much higher instantaneous outputduring cloud enhancements than the other BP units. It is as yet not clear if the effect isdue to the array or the inverter. U-38, U-39 & U-40 exhibit open circuit voltages within1 volt of each other during start up and shutdown. They seem to be very similar in

voltage characteristics. TEP has generally been satisfied with the performance of the BPsystems, with the exception of U-37 and the concern over lost production in cold weather.The inverters are seldom able to follow maximum power point since the units generallyhave a max power point below the 300 volt floor of the inverter. Significant tuning of inverter constants to prevent inverter trip during cloud enhancement was needed.

Monthly operating summaries are posted at GreenWatts.com During 2002, over3,100 MWh of solar energy was produced at the SGS Solar System. It is expected thatover 4,800 MWh of solar energy will be produced by solar energy at SGS in 2003,despite some downtime from a lightning storm that delivered nearly two years of groundstrokes to the area of the SGS Solar System in the first 11 minutes of the storm. The highrate of annual energy production from PV at this location is due to the high level of solarinsolation, cool temperatures and wind that generally blows during daylight hours.

The lightning storm while apparently striking the PV system in at least fourlocations, did no external physical damage to the arrays, inverters or transformers. Thedamage found was associated with the data collection system between the 480 voltrevenue meter, the inverter control and communications computer and the network switches. All three items are grounded at one location, but the location of the ground isnot the same in all cases and the lightning current followed the path between the groundreferences to cause some damage on almost half of the systems. One previouslyweakened inverter matrix was also damaged, a contactor coil winding and a single dataCat 5 cable. All damage was repaired within 30 days at a cost of less than 0.1% of theinitial cost of the PV system. Addition of surge protection and isolation devices wasmade to the data collection systems at a cost of less than $200 per inverter that isexpected to fully prevent damage from occurring in the future from lightning.

Additional operating and performance data is available at www.GreenWatts.com



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Renewable Generation Capacity Support Analysis:

Utility control area operation with significant amounts of intermittent generationenergy sources such as solar or wind provide challenges to stable utility system operation.The following discussion demonstrates some general system operating results of energy

and effective capacity based on actual hourly data from Springerville and Tucson basedPV generating resources extrapolated to a size appropriate for meeting a 10% nationalrenewable portfolio standard with Arizona’s most abundant renewable resource, the sun,applied to hourly native load data in the TEP service territory.

The location and grid node interconnection scheme allow for future testing andtuning of the interaction of the boiler, turbine, generator (BTG) controls with theintermittency of solar generation as the PV array approaches its planned size of 10,000kW ACp.

TEP has analyzed a number of possible options of renewable generation resources

available to meet the implementation of a 10% renewable energy portfolio standard. Thescenarios assume that all new renewable generation would be pure, that is not a mix of different resources. The scenarios are based on the actual 2002 hourly retail loads in theTEP service territory, actual 2002 hourly wholesale electric prices at Palo Verde, actualhourly solar electric generation at Springerville and Tucson sites and hourly windresources at an Apache County, Arizona monitoring site applied to a Vestas wind turbine.For comparison, the average wholesale electric price at Palo Verde in 2002 was $26.42per MWh. The results of the pure Wind and pure Solar PV cases are summarized in thetable on the next page below:



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Hypothetical Renewable Resource Generation Scenarios

All FueledGeneration

ApacheCounty WindGeneration

SpringervilleSolar

Generation

Tucson SolarGeneration

Installed Renewable EnergyCapacity in MW

0 509 495 495

Installed Renewable Cost at2002 Prices in $M

$0 $509 $2,846 $2,846

Maximum RenewableGeneration Capacityin AC MW

0 509 457 441

Annual Renewable Energyin MWh

0 862,414 861,143 842,588

Wholesale Energy Value - $ $0 $24,504,757 $26,568,065 $26,348,908

Average Renewable EnergyValue in $/MWh

$0 $28.41 $30.85 $31.27

Annual TEP System LoadMinimum Demand in MW 570 70 276 269

Annual TEP System LoadMaximum Demand in MW

1,868 1,859 1,822 1,741

Effective System CapacitySupport from RenewableGeneration in MW

0 9 46 127

Percent of Annual SystemEnergy from RenewableResources

0% 10.01% 10.00% 9.78%



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Below is a graph of the TEP 2002 hourly native retail load, the hourly energy producedby 495 MW of hypothetical solar generation located at the Springerville GeneratingStation and the effect on fueled generation demand reduction – 46 MW – from theapplication of 495 MW of solar capacity. The 495 MW of solar capacity was chosen as

the level needed to produce 10% of the TEP annual retail energy sold from newrenewable generation sources in 2002, the proposed national renewable portfoliostandard. The distance the red points are spaced above the yellow points represents theamount of load the renewable resource supports. Capacity support is only provided inhours ending 08:00 through 17:00. At the typical time of peak system loads at hourending 16:00, the solar generation resource is providing only 46 MW of capacity support.

Apache County 2002 - Summe r Diurnal Power

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Below is a graph of the TEP 2002 hourly daily maximum and minimum native loadgeneration demand as if provided: 1. Maximum daily demand met by fueled generationonly, in red; 2. Maximum daily demand met by fueled generation as reduced by 495 MWof Springerville Generating Station located solar generation, in pink; and 3. Minimum

daily demand met by fueled generation as reduced by 495 MW of SGS located solargeneration, in blue. Increasing amounts of red showing behind the pink indicateincreasing amounts of fueled generation that could be displaced by solar generation.Increasing amounts of pink showing behind blue would represent reductions in minimumfueled generation requirements possibly requiring taking fueled units out of service whenrenewable generation was available. This does not appear to be a concern with solargeneration.

Fueled Generation Daily Range with SGS Solar

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Below is a graph of the TEP 2002 hourly native retail load, the hourly energy producedby 495 MW of hypothetical solar generation located at TEP’s Tucson located OperatingHeadquarters and the effect on fueled generation demand reduction – 127 MW – from theapplication of 495 MW of Tucson located solar capacity. The 495 MW of solar capacity

was chosen as the level needed to produce nearly 10% of the TEP annual retail energysold from new renewable generation sources in 2002, the proposed national renewableportfolio standard. The distance the red points are spaced above the yellow pointsrepresents the amount of load the renewable resource supports. Capacity support is onlyprovided in hours ending 08:00 through 17:00. At the typical time of peak system loadsat hour ending 16:00, the solar generation resource is providing 127 MW of capacitysupport.

Tucson 2002 - Summer Diurnal Power

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Below is a graph of the TEP 2002 hourly daily maximum and minimum native loadgeneration demand as if provided: 1. Maximum daily demand met by fueled generationonly, in red; 2. Maximum daily demand met by fueled generation as reduced by 495 MWof Tucson located solar generation, in pink; and 3. Minimum daily demand met by fueled

generation as reduced by 495 MW of Tucson located solar generation, in blue.Increasing amounts of red showing behind the pink indicate increasing amounts of fueledgeneration that could be displaced by solar generation. Increasing amounts of pink showing behind blue would represent reductions in minimum fueled generationrequirements possibly requiring taking fueled units out of service when renewablegeneration was available. This does not appear to be a concern with solar generation.

Fueled Generation Daily Range with Tucson Solar

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Below is a graph of the TEP 2002 hourly native retail load, the hourly energy producedby 509 MW of hypothetical wind generation located at the area of one of the TEPmonitor stations in Apache County and the effect on fueled generation demand reduction– 9 MW – from the application of 509 MW of wind capacity. The 509 MW of windcapacity was chosen as the level needed to produce 10% of the TEP annual retail energysold from new renewable generation sources in 2002, the proposed national renewableportfolio standard. The distance the red points are spaced above the yellow pointsrepresents the amount of load the renewable resource supports. Capacity support fromwind in Arizona is not coincident with loads at any great degree of confidence, although asignificant amount of the energy provided does occur during peak load hours.

Apache County Wind 2002 - Summ er Diurnal Power

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Below is a graph of the TEP 2002 hourly daily maximum and minimum native loadgeneration demand as if provided: 1. Maximum daily demand met by fueled generationonly, in red; 2. Maximum daily demand met by fueled generation as reduced by 509 MWof Apache County located wind generation, in pink; and 3. Minimum daily demand met

by fueled generation as reduced by 509 MW of Apache County located wind generation,in blue. Minimum daily loads are much more difficult to predict with a significantamount of wind generation as part of the generation resource base. Increasing amountsof red showing behind the pink indicate increasing amounts of fueled generation thatcould be displaced by wind generation. Increasing amounts of pink showing behind bluewould represent reductions in minimum fueled generation requirements possiblyrequiring taking fueled units out of service when renewable generation was available.This does appear to be a concern with wind generation.

Fueled Generation Daily Range with Wind

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Fuel Only Max Fuel - Wind Max Fuel - Wind Min



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Applicability of Utility Scale PV:

The SGS Solar System can be replicated outside Arizona. Care must be taken toidentify a site with at least a square mile of relatively flat land that has a cool climate withhigh average annual solar insolation, moderate winds while the sun is shining, easy

access to transmission with sufficient capacity and load to support the addition of the PVgeneration and relatively low property tax rates. An existing power plant, old landfill siteor an area that is used as a shallow storm runoff retention basin is an ideal location for aPV system improving the use of the land. It is recommended to obtain at least two yearsof weather data prior to committing to a site. Even then, a comparison to 20 years of historic values of a reference site in the area would be beneficial in performing acomprehensive site resource evaluation. The site should be free of bushes and trees,rocks and any archeological findings. Do not place the PV system over pipelines that useimpressed current cathodic protection as the PV field will adversely affect the cathodicprotection field. Do not site a PV system in an area known for strong hail storms ortornadoes.

Permitting a solar generating site is not a simple task and can take up to two yearsif near populated areas. Concerns primarily focus on glare, vegetation removal and stormwater runoff/erosion. However, inverters do produce some noise and access for servicepersonnel is necessary which produces increased traffic in a residential area.Construction activities will significantly increase traffic for short periods of time and mayneed to be addressed during permitting. Some locales require a rezoning to use the landfor electrical generation purposes. This may result in imposition of traditional powerplant infrastructure requirements such as water and sewer lines, which are not needed at asolar generating station. Always check with the local zoning authorities to determine therules and be prepared to work with them for a variance to remove those features not

needed for solar generation.

Take care to design the PV system to be installed by the type and quality of laboravailable in the area. A high tech tracking system that requires laser alignment skills cangenerally not be supported by local labor in a rural setting. Likewise, even the cost of general assembly labor in a large metropolitan area will be nearly as expensive as highlyskilled labor. Match the design sophistication to the expected skills of the area.

Once installed, the system must be monitored for proper performance andmaintained in a safe and efficient operating condition. While PV modules are inherentlysimple, experience has demonstrated they have many possible failure modes. Some of

which are not readily apparent. Likewise, inverters are highly sophisticatedmicroprocessor controlled devices which have the ability to mask a flaw in another pieceof interconnected equipment. Ensure the availability of the necessary test equipment andcontinuity of the trained personnel to use and interpret readings from the tests, as well ascontinued support from the vendors of the major PV system components. Test equipmentshould include a clamp on ammeter for DC and AC with a maximum range of 0 to 40amps and a separate clamp on ammeter for DC and AC with a range of 0 to 600 amps.At least one, preferably two, voltmeter with a DC and AC range to 600 volts and anintegral ohmmeter is essential. A frequency counter or frequency indicator and an



available dual trace oscilloscope with a range to 100 kHz is needed. A harmonic meterand a three phase power meter are helpful. In addition it will be beneficial to build amodule continuity tester that will test power output across a wide range of loads and solarinsolation to build a module IV curve. A thermometer and a calibrated solar insolationmeter are recommended tools for evaluating performance. A PC with Excel capability to

monitor trends of data is highly recommended.

Watts Next??:

Implementation of large utility scale, distributed PV solar generation systems isdeveloping a positive trend around the world. With the 2003 German installation of 4.0MW of PV near Hemau and the announced start in July 2003 of a 5.0 MW PV system inGermany, the installation of 2.0 MW of tracking and concentrating PV by Arizona PublicService near Prescott, Arizona in 2003 and the continuing expansion of the SpringervilleGenerating Station Solar System, there is developing a wealth of data on the design

criteria, installation practices, operational experience and production results of large PVinstallations and their accompanying costs. Total installed cost is less than $6.00 per DCwatt. By 2007 that is expected to be less than $5.00 per DC watt.

The experience gained from these large solar PV systems will provide dataneeded for improving prediction of supply from intermittent generation resources andsupport development of the tools needed to mitigate the effects of that intermittency ongrid regulation, as well as hour ahead and day ahead energy requirement forecasting.

While customer located PV systems are still needed to fully take advantage of thepotential of solar energy, large utility scale PV systems are starting to take their rightful

place under the sun. For utilities, the time is now right to harness the power of the sunfor the long term benefit of our customers. The promise of utility scale solar photovoltaicdistributed generation is within our reach today.

Hanson Utility Scale PV

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