Panel Area And Efficiency

= Introduction =

Understanding Solar Panel efficiencies and calculating outputs is a more complicated subject than it first appears. The obvious approach is to multiply the panel area by the solar insolation level and panel efficiency to get a power output. However there are various areas (Gross, Aperture, Absorber) quoted for each panel, the effective area also changes as the angle relative to the sun changes, and insolation levels vary during the day and year).

= Test houses =

Solar test houses pysically test panels and provide data on how they perform which is generally deemed to be definitive. To interpret this data properly requires an understanding of how it is calculated and what the various sorts of area are.

There are two I am aware of:

 * Institut für Solartechnik SPF in Rapperswil Switzerland http://solarenergy.ch/
 * Fraunhofer-Institute for Solar Energy Systems ISE in Freiburg http://www.kollektortest.de/

= Panel Areas =

These are the Fraunhofer ISE definitions for vacuum panels:

 * Gross area is the simplest to understand - it is just the external dimensions of the panel, and thus includes the manifold on vacuum panels.
 * Aperture area is the projected area of the inside diameter of the outer tube
 * Absorber area is the proejcted area of the outside diamter of the inner tube

These are the SPF definitions:

 * 
 * The aperture area is the surface of the collector, through which non-concentrated sunlight enters. (tubular collectors without reflector: inner tubular diameter x length x number of tubes, with reflector: largest projected area of the collector).
 * 

The different areas are defined for different purposes. Gross area tell you how much space it takes up when mounted. Aperture area tells you how much area is exposed to the sun.

These areas are easier to understand for flat-panel collectors.

The apricus website has an excellent explanation of Incident Angle Modifier so rather than me write something worse I suggest you just read that: http://www.apricus.com/html/solar_collector_efficiency_iam.htm , bearing in mind that the actual IAM numbers for the Navitron Panels are given in the SPF test report, with a maximum of 1.25 at about 60 degrees, putting it between the 'Leading ET' panel and the 'Apricus' panel on the graph on that page.

The Apricus collector is very similar in construction to the Navitron panels so simialar considerations apply.