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PV System Design and Installation LO 7 – PV System Sizing RPS SOLAR SOLUTIONS

PV System Sizing (12% of test questions) Task/Skill 7. 1. Illustrate interaction of typical loads with IV curve (battery, MPPT, dc motor) 7. 2. Analyze load demand for stand-alone and grid interactive service 7. 3. Identify typical system electrical output derating factors 7. 4. Calculate estimated peak power output (dc and ac) 7. 5. Calculate array and inverter size for grid-connected system 7. 6. Calculate estimated monthly and annual energy output of grid-connected system 7. 7. Explain relationship between array and battery size for stand-alone systems 7. 8. Calculate array, battery and inverter size for stand-alone system

Steps in Grid Tied PV System Sizing 1. Determine type of mounting system (Roof, Ground Mount or Pole) 2. Determine available roof area and orientation 3. Check for shading problems 4. Check roof structure 5. Check existing main load center 6. Check electrical service 7. Determine location for inverter and disconnects 8. Review customer electricity bills 9. Discuss PV system costs with customer 10. Determine approximate PV system size based on customer budget and electricity demand 11. Determine different combinations of PV modules and inverters to provide appropriate PV system 12. Cost out PV system

Site Assessment Tools Shading Issues http: //www. google. sketchup. com http: //www. solarpathfinder. com http: //earth. google. com http: //www. nysgis. state. ny. us System Production 12 to 15 Watt DC per Square Foot of PV array For every PV Array k. W DC power will provide approximately 100 k. Wh AC energy per month. Clean Power Estimator http: //www. powernaturally. org

Energy Production adjustments for orientation and tilt angle

1. Loss due to tilt angle and orientation

3. Loss associated with system inefficiencies Overall PV System Efficiencies PV Array Input (DC) = 70 to 80% AC Output (AC) Reference 2

Class Exercise Ranch House in Capital Region Owner wanted to produce as much of their electricity as possible. Roof is asphalt shingle with rafters at 24 inches on center

House Orientation

Roof tilt and area 5: 12 roof slope

One solution, get rid of trees

Practical Concerns Check main load center Check roof structure

Determine existing electricity usage

Chose PV modules

Choose inverter

Equipment Loads and IV Curves PV Array IV Curve Reference 3 Reference 6

More on Maximum Power Point Tracking (MPPT) MPPT devices include DC-DC converters. Convert PV array DC output to DC input requirements of IV curves of equipment loads Reference 6

Maximum Power Point Tracking (MPPT) and Inverters Reference 3

PV Array IV Curve overlay on Inverter IV Curve Best Condition Reference 3

PV Array Vmp Too Low Vmp can drop below MPPT range due to shading or excessive heating Reference 3 Inverter keeps operating but not at MPPT. Hence, lower power from the array

Array Pmax Too High Array Power exceeds maximum power limit of the inverter. Reference 3 Can happen due to poor design or temporarily due to reflection off snow, water, building surfaces, etc. Inverter keeps operating, however at not at MPPT. Results in lower power output from the inverter.

Importance of Good Grid Power for Inverter Performance Inverters are designed to operate between ANSI Range A and B voltages If grid voltage out of inverter operating range, inverter will shut down Can happen if utility company voltage too high (heat wave boosts) or if there is too high a resistance between the inverter and utility point of connection (voltage too low). Reference 3