One page descriptions of a technique or action for a given designer, planner, engineer or project manager to take.
Photovoltaic Design Basics
What Is It?
How To
There are 2 ways to base the design of your photovoltaic (PV) design:
- Determine a photovoltaic
(PV) target in kW-hrs
Example: Client would like to aim for 2.5% of our energy consumption to be derived from renewable sources)
- Determine a photovoltaic
(PV) target based on installed watts of
photovoltaics
Example: Client would like to install a 50kW rated system.
The examples below will provide you on how to realize both of these goals.
Select the size (normally 175 - 200W) of the photovoltaic panel for your design.
Panel Manufacturer's: http://www.ecobusinesslinks.com/solar_energy_solar_power_panels.htm
PV -1 Example
Step 2: The project decides to use a Kyocera KD210GX-LP 210
Watt PV Panel. Data sheet indicates the following electrical
characteristics:
Watts = 210W
Amps = 7.90A
Voltage = 26.6V
PV-1 Step 3:
Determine the Insolation Data for your installation geography. The National Renewable Energy Laboratory (NREL) website link below provides insolation data for your location. http://rredc.nrel.gov/solar/pubs/redbook/
The website is broken down by State and each corresponding link has different cities within that state.
NREL Data Sheet for Boston, MA
The data is broken between a flat-plat collector, single axis tracking and dual-axis tracking. Data is provided for each month and averaged for a typical year. Please note, if you are planning on having a system that needs to be fully operational only in the winter, use the monthly averages for the months that you need.
Flat Plate Collector are the non-moving arrays that face south at a specific tilt. The table provides data for different tilts:
- Flat (0� or no-tilt) array - shown as an annual average of 3.9
kW-hr/m2/day
- Vertical (90�) array - shown as a an annual average of 3.2
kW-hr/m2/day
- Latitude (42.37� tilt for Boston) array - shown as an annual
average of 4.6 kW-hr/m2/day
- Latitude -15� (27.37� tilt for Boston) array - shown as an annual average of 4.5 kW-hr/m2/day
- Latitude +15� (57.37� tilt for Boston) array - shown as an annual average of 4.4 kW-hr/m2/day
As you can see, the difference between a 42.37� tilt and a 27.37� tilt is negligible. Additionally, when looking at shadows cast between adjacent panels, the 27.37� tilt allows for closer spacing. (each grey square is 1 foot).
Single-Axis Tracking is a PV array that is installed at a fixed tilt and tracks the sun from East (rising sun) to West (falling sun) over the course of a day to have a higher insolation rating and thus produce more electricity. The table provides data for different tilts:
- Flat (0� or no-tilt) array - shown as an annual average of 5.2
kW-hr/m2/day
+ 33% more than the flat plat collector - Latitude (42.37� tilt for Boston) array - shown as an annual
average of 5.7 kW-hr/m2/day
+ 26% more than the flat plat collector - Latitude -15� (27.37� tilt for Boston) array - shown as an annual
average of 5.7 kW-hr/m2/day
+ 23% more than the flat plat collector - Latitude +15� (57.37� tilt for Boston) array - shown as an annual
average of 5.6 kW-hr/m2/day
+ 27% more than the flat plat collector
Single-Axis Tracking is a PV array that is installed at a variable tilt (flatter in the summer and vertical in the winter and tracks the sun from East (rising sun) to West (falling sun) over the course of day to have a higher insolation rating and thus produce more electricity.
- 2-Axis Tracking - shown as an annual average of 5.9 kW-hr/m2/day
- + 3% more than the single-axi tracking at tilt = latitude and 28% greater than flat plat collector at latitude.
As you can see with each system there are benefits and ideally you want to capture as much sun as possible. Some installations will shy away from ‘tracking' type systems due to the maintenance aspect. Therefore, to continue our PV-1 Example, I will assume we are using a flat plate collector type system installed at 27.37o providing 4.5 kW-hr/m2/day
PV-1 Example
Step 3: Determine the insolation data for the system you are
installing. Here we are installing a flat-plate collector system at a
tilt of 27.37� providing 4.5 kW-hr/m2/day.
PV-1 Step 4: Perform the following Calculation: Insolation Data (from Step 3) x Panel Rating (from Step 2) x De-Rating Factor* (Use 0.73) to determine annual energy production (kW-hrs) from a single panel for a day. Then multiply by 365 to determine annual energy production.
PV-1 Example
Step #4: PV Energy kW-hrs/day
= Insolation Data x Rating of PV Panel (Watts) x De-Rating Factor
= 4.5 kW-hr/m2/day x 210 Watts x 0.73 = 689.85 Watt-hrs/day or 0.690 kW-hrs/day
PV Energy kW-hrs/yr
= PV Energy kW-hrs/day x 365 days/yr
= 0.690 kW-hrs/day x 365 = 251.85 kW-hrs/yr
Therefore, a single 210 Watt Kyocera PV panel in Boston at a tilt of 27.37� will produce (on average) 344.925 kW-hrs/yr.
* De-Rating Factor accounts for module mismatch, wiring losses, dirt accumulation, etc..
PV-1 Step 5: Perform the following Calculation: PV Target kW-hrs/year (from Step 1) / PV Energy kW-hrs/yr (from Step 4) to determine the total number of panels required to meet the PV Target as set in Step 1.
PB Project Experience:
- Conrac Facility, Logan Airport, Parking Deck Photovoltaic Design
New Jersey Cherokee NE Bergen Transit Line Station
Sustainable Design Webinar
Series: Solar PV 101 with Sean O'Rourke [*very large file - 48MB]
Related External Resources:
PVWATTS v.1 - A
Performance Calculator for Grid-Connected PV Systems
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