1. Net Zero Elizabethton, Tenn
Photovoltaic System

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

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

4. 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

5. Average Daily Sun Hour Approach

7. 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 = MW

8. 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 = MW

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

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

11. 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

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

14. 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

15. String Sizing

16. String Sizing Module Voc = 37.78
Record cold multiplier = x 1.25 = C

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

18. 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

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

20. Racking http://www.schletter.us/fs-system.html
Schletter is a good brand in Charlotte

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

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

24. 3 times the height
3 x 40” = 120”
120/12 = 10’

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

26. 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