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Stylized Text: Data Monitoring - For Photovoltaics.

Example 1

An electric utility company is interested in providing a grid-connected photovoltaic-power service option to their residential customers.  Having heard about the roof-top grid-connected residential PV systems installed in Lakeland, Florida, they are interested in how comparable systems would perform at their location.  Following are questions that this utility may have that can be answered by the information from FSEC's Photovoltaic Systems Data Network.

Question:

How much south-facing roof surface area is required for a similar installation using a 4 kWp STC-rated PV array?

Answer:

Referring to any of the monthly reports for any of the Lakeland PV Residences, the array power density rating is listed as 8.44 m2/kWp.  This means that 8.44 m2 of surface area is required for a PV array with 1 kWp STC-rated output.  For a 4 kWp STC-rated PV array, the surface area required would be 8.44 x 4 = 33.8 m2 or 363 ft2.

Question:

How much AC energy would a similar system with a 4 kWp STC-rated array produce in a different location?

Answer:

Referring to the monthly reports for Lakeland PV Residence #2, the AC energy production normalized with respect to solar insolation and the array STC rating is 0.75 kWh/kWp/kWh/m2.  Using solar radiation data available from the National Renewable Energy Laboratory, you determine for your location that the annual average daily solar insolation for a south-facing latitude-tilt surface is 5 kWh/m2/day.  This means that a system using similar hardware, operating in a similar thermal environment, using a 4 kWp STC-rated PV array would produce approximately 0.75 x 4 x 5 = 15 kWh of AC energy on an average daily basis at this location.

Question:

How does the output of the PV system compare to typical residential electrical load profiles?

Answer:

That depends on a number of issues, including the type of building, appliances, habits of the occupants and the weather.  This information is shown on the daily and monthly plots for the three Lakeland PV Residences where the PV system output, the house load and power supplied by the utility are plotted versus time of day.   Note that Lakeland PV Residence #1 is a super energy-efficient home, and has a larger PV array than Residences #2 and #3.   Referring to these charts, the amount of PV energy delivered to the load and that required from the utility varies considerably between these three homes.  For example, in February 1999, the 2 kWp system for Lakeland PV Residence #2 delivered about 58% of its energy to the house loads, satisfying about 25% of the load requirement, while the 4 kWp system for Lakeland PV Residence #1 delivered about 54% of its energy to the load, satisfying nearly 50% of the total load requirement.

Example 2:

The manufacturer of the inverter used in the Lakeland PV Residences is interested in how their product performs with the associated array technology and in the hot-humid Florida climate.  Following are questions this manufacturer may have that can be addressed by information on FSEC's Photovoltaic Systems Data Network.

Question:

What is the DC to AC power conversion efficiency of this inverter as a function of power level and on a daily basis?

Answer:

Referring to the data for the three Lakeland PV Residences, the peak inverter efficiencies are about 90%, and the daily efficiencies are about 85%.

Question:

How well does the inverter track the PV array maximum power point?

Answer:

Referring to the March 28, 1999 daily plots for Lakeland PV Residence #2 (a cloudless day), the plot of PV array DC voltage and current versus time of day shows a reduction in the array operating voltage of 8-10 volts for periods of one hour or more when the solar irradiance level is around 500 W/m2 in the morning and afternoon.   This data suggest some inconsistencies with the inverter maximum power point tracking of the array.  
 

Example 3

The manufacturer of the PV modules used in the array for the Lakeland PV Residences is interested in how their modules perform in the given design and under typical operating conditions.

Question:

How close to the STC-rated output does the PV array operate in this application?

Answer:

Referring to any of the monthly plots or reports for the three Lakeland PV Residences, the array DC energy normalized with respect to solar insolation and array STC rating varies between 0.77 and 0.83 kWh/kWp/kWh/m2.  This means that the arrays are producing between 77 and 83% of their peak-rated STC output.

Question:

How hot do the module operate in using a typical stand-off mounting technique?

Answer:

The temperature rise coefficients for the arrays are reported daily and on the monthly plots and reports.  These values range from 25 to 30 oC/kW/m2, meaning the arrays operate between 25 and 30 degrees C warmer than ambient temperature at a solar irradiance level of 1 kW/m2.
 

Example 4

Energy managers at Interface Flooring have installed a 15 kWp grid-connected PV system to offset part of the day time peak electrical load for a weaving loom.  They are using FSEC's Photovoltaic Systems Data Network to collect, process and archive information from this installation.

Question:

How much of the loom electrical load is satisfied by the PV system, both on a time of day basis and for the entire day?

Answer:

This information is provided on the daily and monthly plots and reports in the Interface Flooring PV Systems database.  
 

Example 5

A systems integrator is designing and packaging a stand-alone PV lighting system.  They require information about the performance and ratings for this system, and the system is installed under test at FSEC.   Following are questions that the integrator may have that can be addressed with information from FSEC's Photovoltaic Systems Data Network.

Question:

What is the maximum load that this system can operate under different solar insolation?

Answer:

This information is provided in monthly data reports in terms of normalized PV to Load energy ratios.  For example, if the test results for the system indicate a normalized PV to Load energy ratio of 1.3 under 5 kWh/m2 solar insolation, and the integrator want to maintain this minimum ratio under an insolation level of 4 kWh/m2, the load should be reduced by approximately 20%.

Question:

Considering type of shielding used to protect the back of the array from damage, how hot do the arrays operate, and what is the effect on module lifetime?

Answer:

The array operating temperatures and temperature rise coefficients are given on the daily plots for the Photovoltaic Area Lighting Systems database.  For example, the temperature rise coefficient for PV Area Lighting System #9 (one with a completely enclosed array back surface) approaches 40 oC/kW/m2, meaning the array operates 40 degrees C warmer than ambient temperature.  Module lifetimes in this configuration should be expected to be about one-half that for arrays having free air circulation and operating 10 degrees C cooler. 
 

Example 6

A systems integrator and or PV module manufacturer wants better information on PV module energy performance for use in system sizing and design calculations.  Following are questions that these entities may have that can be answered by the information from FSEC's Photovoltaic Systems Data Network.

Question:

How much energy (amp-hours and watt-hours) will a given module produce operating at peak power?

Answer:

This information is provided on the daily and monthly reports for FSEC's PV Module Test Facility, both in absolute terms and normalized with respect to insolation.

Question:

What is the module operating current and power under actual operating conditions and as a function or solar irradiance?

Answer:

The relationships between current, power and solar irradiance are available on the daily and monthly plots for modules installed in FSEC's PV Module Test Facility.