Net Zero Elizabethton, Tenn Photovoltaic System

Annual Energy Usage 4 million KWH/month 4 x 12 months = 48 Million KWH/year

Array Sizing General Rule of Thumb Average Daily Sun Hour Approach PV Watts

General Rule of Thumb for Array Sizing Each 1000 KWH desired requires approximately 1 KW 48,000,000 KWH / 1000 = 48,000 KW or 48 MW Assumes some shading, inverter inefficiency and other typical BOS losses

Average Daily Sun Hour Approach

Average Daily Sun Hour Approach (70% BOS efficiency) AEO = Rated Power x Average Daily Sun Hours x 365 x BOS efficiency (70 to 80%) Rated Power at 70% BOS eff = AEO / Average Daily Sun Hours x 365 x .70 Rated Power at 70% BOS eff = 48,000,000 KWH / 4.6 hrs/day x 365 x .70 Rated Power at 70% = 40,840 KW = 40.84 MW

Average Daily Sun Hour Approach (80% BOS efficiency) AEO = Rated Power x Average Daily Sun Hours x 365 x BOS efficiency (70 to 80%) Rated Power at 80% BOS eff = AEO / Average Daily Sun Hours x 365 x .80 Rated Power at 80% BOS eff = 48,000,000 KWH / 4.6 hrs/day x 365 x .80 Rated Power at 80% = 35,735 KW = 35.73 MW

PV Watts http://pvwatts.nrel.gov/ Polysun might be another option (in room 40)

Estimated Installed Costs 35,000,000 watts x $1.06/watt = $37,100,000

Land Required Each MW requires 5 – 10 acres 35 MW x 5 acres = 175 acres 35 MW x 10 acres = 350 acres Land should ideally be level with good solar access and close to grid connection

Number of Modules or Panels Required https://www.wholesalesolar.com/ Astronergy 260 watt modules for example 35 MW = 35,000,000 watts / 260 watts per module = 134,615 modules

Inverters SMA is a good brand (http://www.sma-america.com/ ) Array DC rating is often 25% larger than inverter rating to save money without significantly reducing AEO because modules don’t produce their rated power and inverters are not 100% efficient 35 MW / 1.25 = 28 MW of inverter SMA 2.75 MW Inverter with 1500 VDC maximum input 28 / 2.75 MW = 10 inverters

String Sizing

String Sizing Module Voc = 37.78 Record cold multiplier = 37.78 x 1.25 = 47.22 Voc @ -31 C

String Sizing 1500 volt maximum DC input voltage / 47.22 Voc = 31.7 = 31 modules per string is maximum 134,615 modules / 31 = 4342 strings or voltage units

Combiner Box Combines strings in parallel to increase amps, power and energy production while mainting maximum voltage Solar BOS is a good brand 1500 VDC and 36 input circuits 4342 strings / 36 = 121 combiner boxes 121 / 10 inverters = 12.1 combiner boxes/ inverter http://www.solarbos.com/Combiners

Summary of System Design 10 Inverters 12 combiner boxes per inverter 36 strings per combiner box 31 modules per string

Racking http://www.schletter.us/fs-system.html Schletter is a good brand in Charlotte http://www.schletter.us/fs-system.html https://www.youtube.com/watch?v=cB6KMAeyOCc

Trackers http://arraytechinc.com/commercial/duratrack-hz-comm 25% annual increase in KWH typical

Avoiding Shading with Multiple Rows of PV on Flat Roofs or Ground Mounts Need to avoid shading problems 3 times the height

3 times the height 3 x 40” = 120” 120/12 = 10’

Alternate Inter-row spacing 3 x Height of row or module 3 x 40” = 120”/12 = 10’

TRIG Method Example for south facing PV array: Distance between rows = H x cos azimuth angle tan altitude angle H = Vertical difference between top of module on one row to the bottom of module on the next row Target is typically 9 -3 on December 21st