Results - Folsom Labs
Practical Applications of DC Conductor Optimization! Paul Grana and Paul Gibbs / Folsom Labs / www.folsomlabs.com!
Background: !Frequently, system design choices are made based on rules of thumb rather than project-specific cost-benefit analyses. We leveraged modern design tools to determine the lowest-cost wiring design optimizing total cost of ownership, and show its application on a specific project. ! Methodology: !Using HelioScope, a design and performance modeling tool, we ran a comprehensive scenario analysis on the DC plant. HelioScope is component-based: it models an array based on the exact location and stringing of each module, also calculating distances for each conductor run from the string to the combiner and inverter. This detailed array information is used to simulate the energy production of the array, including the exact wire losses from each conductor (factoring in hourly current requirements). ! Analysis:
!We ran over 100 scenarios for a commercial solar array, varying key performance drivers, and measuring the impact on array energy production, as well as bill-of-material costs.! Modules per string!
Combiner box layout!
Performance Driver!
Minimum!
Maximum!
Modules per string!
10!
15!
#12 AWG!
#8 AWG!
Along racking!
Up & down racking!
Combiner box size!
12 strings!
24 string!
Home run conductors!
0/1 AWG!
4/0 AWG!
Scattered throughout array!
Grouped at inverter!
Source circuit conductors! Wiring direction!
Home run conductor!
Wiring direction!
Results:!
27%!
Source circuit conductor!
Combiner box layout!
Total electrical costs were calculated, including: ! • Wire quantity and cost (both source circuits and home runs)! • Combiner box quantity and cost! • Electricity value lost from wire resistance!
Combiner box size!
The design optimization showed that the system electrical costs could be reduced by over 25%. The optimization called for smaller wire for source circuits while using thicker wire for home runs, and modifying the stringing direction. !
Improvement in system electrical costs!
String length and source circuit conductors can have a 2 cent per watt impact on CAPEX!
The direction of the string wiring can reduce the source circuit wire by over 20%! 80%!
71%!
2.4!
2.5!
60%!
2.0! Wire along racking!
1.7! 1.5! 1.0!
1.0!
0.8! 0.4!
0.5!
0.5!
Change in wire content!
Impact on system cost (¢/Wp)!
3.0!
The lowest-cost design called for the most even balancing of costs!
Electrical wire loss (40%)!
40%!
Source circuit conductor cost (35%)!
20%!
0%!
Combiner box cost (15%)!
Home run conductor cost (10%)!
-20%! -21%! Wire up and down racking!
0.0!
-40%! Modules per string!
Source circuit conductor!
Wire direction!
Combiner size!
Home run conductor!
Combiner layout!
Source circuit!
Home run!
Implications: !Though DC wiring design is often overlooked, it can be an importance source of project profits. By rigorously optimizing the array’s design to jointly minimize CAPEX and wire losses, engineers can increase project profits by $0.01 - $0.03/Wp with minimal effort. ! www.folsomlabs.com!
The optimal design will change based on: ! ! Site irradiance! ! Electricity prices! ! Wire pricing!
Background: !Frequently, system design choices are made based on rules of thumb rather than project-specific cost-benefit analyses. We leveraged modern design tools to determine the lowest-cost wiring design optimizing total cost of ownership, and show its application on a specific project. ! Methodology: !Using HelioScope, a design and performance modeling tool, we ran a comprehensive scenario analysis on the DC plant. HelioScope is component-based: it models an array based on the exact location and stringing of each module, also calculating distances for each conductor run from the string to the combiner and inverter. This detailed array information is used to simulate the energy production of the array, including the exact wire losses from each conductor (factoring in hourly current requirements). ! Analysis:
!We ran over 100 scenarios for a commercial solar array, varying key performance drivers, and measuring the impact on array energy production, as well as bill-of-material costs.! Modules per string!
Combiner box layout!
Performance Driver!
Minimum!
Maximum!
Modules per string!
10!
15!
#12 AWG!
#8 AWG!
Along racking!
Up & down racking!
Combiner box size!
12 strings!
24 string!
Home run conductors!
0/1 AWG!
4/0 AWG!
Scattered throughout array!
Grouped at inverter!
Source circuit conductors! Wiring direction!
Home run conductor!
Wiring direction!
Results:!
27%!
Source circuit conductor!
Combiner box layout!
Total electrical costs were calculated, including: ! • Wire quantity and cost (both source circuits and home runs)! • Combiner box quantity and cost! • Electricity value lost from wire resistance!
Combiner box size!
The design optimization showed that the system electrical costs could be reduced by over 25%. The optimization called for smaller wire for source circuits while using thicker wire for home runs, and modifying the stringing direction. !
Improvement in system electrical costs!
String length and source circuit conductors can have a 2 cent per watt impact on CAPEX!
The direction of the string wiring can reduce the source circuit wire by over 20%! 80%!
71%!
2.4!
2.5!
60%!
2.0! Wire along racking!
1.7! 1.5! 1.0!
1.0!
0.8! 0.4!
0.5!
0.5!
Change in wire content!
Impact on system cost (¢/Wp)!
3.0!
The lowest-cost design called for the most even balancing of costs!
Electrical wire loss (40%)!
40%!
Source circuit conductor cost (35%)!
20%!
0%!
Combiner box cost (15%)!
Home run conductor cost (10%)!
-20%! -21%! Wire up and down racking!
0.0!
-40%! Modules per string!
Source circuit conductor!
Wire direction!
Combiner size!
Home run conductor!
Combiner layout!
Source circuit!
Home run!
Implications: !Though DC wiring design is often overlooked, it can be an importance source of project profits. By rigorously optimizing the array’s design to jointly minimize CAPEX and wire losses, engineers can increase project profits by $0.01 - $0.03/Wp with minimal effort. ! www.folsomlabs.com!
The optimal design will change based on: ! ! Site irradiance! ! Electricity prices! ! Wire pricing!
