Sizing Your Solar System

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How Much Power will Your Solar System Really Produce?

Power output depends on the microclimate that you live in, temperature, cloud cover, azimuth orientation, roof or ground mount pitch, and wind speed. Additionally, losses can be mitigated with good design techniques, proper wire sizing, and by proper string sizing. Choosing the right modules for hot climates is extremely important.

STC ratings are approximately 25% higher than real world output. Call one of our Technical Representatives for a Real World Estimate.

Electricity Production Estimates for Standard Crystaline Modules

Solar Energy Panels

The Solar Photovoltaic industry is relatively young and immature.Data from the California Energy Commission shows that 98% of all Solar installations in California occurred in the past 6 years. In fact, 71% of all installations occurred in the past 3 years. There are very few standards and it is quite common for Solar Companies to quote Standard Test Conditions (STC) which are very specific laboratory tests. Your system will not be in a laboratory. If you want to acquire a system that will perform to your expectations, you will need to reduce the STC rating by at least 23%-25%. After this, you will need to account for inclination, compass direction and shading. Call us for an honest Real World Estimate. One of our Technical Representatives can provide this information for you at no charge.

Sample 3000 watt System

For example, a 3,000 watt (3 kW) system (STC) would have the following more conservative ratings:

3,000 watts Standard Test Conditions (STC)
2714 watts PVUSA Test Conditions (PTC)
2578 watts California Energy Commission (CEC AC)
2315 watts including losses due to AC/DC/Diodes/Inverter mismatch

2315 watts is a real world estimate.

This system assumes no shading, 34 degree tilt and due South roof placement.

Predicted Monthly System Output
STC 3000/1000 watts/kw x 5.5 sun hours/day x 30 days = 495 kWhs
PTC 2714/1000 watts/kw x 5.5 sun hours/day x 30 days = 448 kWhs
CEC 2578/1000 watts/kw x 5.5 sun hours/day x 30 days = 425 kWhs
A real world estimate for most Crystaline Modules
—–2315/1000 watts/kw x 5.5 sun hours/day x 30 days = 382 kWhs

Although the example above is for a standard crystaline module, on a standard day on a standard month, system outputs can vary a great deal. Sanyo modules produce much higher output than standard crystaline modules due to their high temperature efficiency. Local microclimates and variation in installation techniques also have a significant effect on power output.

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