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Politics : Sioux Nation -- Ignore unavailable to you. Want to Upgrade?

To: T L Comiskey who wrote (74034)	7/24/2006 10:28:31 AM
From: Wharf Rat	Read Replies (1) \| Respond to of 361008

Yeah; it's expected. PTC (PVUSA Test Conditions) are defined as 45°C (113°F) cell temperature, 1000 W/m2 solar irradiance, and 1 m/s wind speed. This test was developed in an attempt to simulate what happens in a real-world outdoor installation. Usually, the PTC rating for a PV panel is between 70% and 85% of the STC rating. The reason that the PV panels produce less power under these conditions has to do with the material properties of the panels themselves. Most PV panels become less efficient as their temperature increases, and so they produce less power to the inverter. This property is roughly linear in the temperature range under which PV panels are usually exposed. Each manufacturer assigns a value to this characteristic, and it is usually expressed as a percentage change of the total power per °C. For example, if a panel has a temperature coefficient of power that is -0.50%/°C, the panel produces 0.5% less power for every 1°C increase in temperature. As you will notice, the difference between the STC temperature and the PTC temperature is 20°C. This equates to a 10% performance difference between the two conditions due to ambient temperature alone. The PTC rating (which is closer to most real-world conditions), will produce 10% less power than the power shown on the rating label of the PV panel. Any material that is exposed to sunlight will heat up as it absorbs the infrared radiation that the Sun produces. Dark colored surfaces tend to become warmer than light colored surfaces. PV panel are typically fairly dark colored, and tend to warm significantly due to the Sun's insolation. A PV panel mounted in direct sun with no wind blowing can be as hot as 70°C or 80°C. If we perform our calculations again, with the panel at 70°C, we arrive at a power output of 124W per panel, or 75% of the STC rating. This number must be multiplied by inverter efficiency to arrive at inverter output power. sma-america.com Solar dude told me the max efficiency would be when the sun pops out from behind a cloud around the equinoxes; equinoxii? Thought about putting a sprinkler behind them :>) Hmmm. Looks like somebody is trying that. esru.strath.ac.uk