Notes from class 2 of Introduction to Solar Energy Systems. With introductions and other requisite class 1 dealings behind us, the class last Thursday (1/18) switched the course into a new gear and we covered ground focused on solar energy fundamentals and basic electricity.
When you start to think about solar energy, you have to think about units of measure, because you are ultimately trying to figure out how much power a system has the potential to produce. The class discussed radiant energy, irradiance and irradiation. Irradiance basically refers to the measure of the rate of solar radiation falling on an area. Measured in watts per square meter, this is - for lack of a better phrase - intensity of the sun. Irradiation is subtly different from irradiance, in that it measures the amount of solar energy impacting an area over time. This is measured in kilowatt hours per square meter.
There are, of course, different types of solar radiation. These include direct, diffused (through clouds, for example) and reflected (off water or snow). Further, there are a variety of factors that affect solar radiation, including the angle of incident, cloud cover, snow, rain, fog, air pollution, reflective materials and more.
When you begin to consider the amount of power a solar system will produce, you have to calculate the number of peak sun hours available in a day at a given location at a given time of the year. Because of earth's orbit, the sun is not always located at the same altitude year round. In summer, the sun is much higher above the horizon - around 70 degrees above horizon. In the winter, however, the sun is only around 30 degrees above horizon. The difference in altitude angle is important because a lower sun will often create more potential shading at the solar site. In addition, the height of the sun is important in order to properly pitch the solar panels and increase irradiance.
The instructors use a handy device called a solar pathfinder to analyze the sun's position and path at a site. The pathfinder helps to identify potential shading spots on the roof throughout the year.
We also discussed magnetic declination, which is somewhat confusing to a navigational newbie like myself. In short, the "true north" pole is not the same as the magnetic north pole (which a compass will point to). In order to properly align solar panels (they should ideally face due south), the solar installer must identify true south prior to using the solar pathfinder or reading charts. In Albany, true south is 14 degrees west of compass south.
I know next to nothing about electricity, so I was listening with rapt attention to this part of class 2. We discussed power, voltage, amps, current, resistance and Ohm's law.
I'll spare the gory details here, because I'm not 100% sure I would be telling the truth. For more info, just head to Wikipedia.
We also discussed parallel versus series circuits. We did some wiring of small solar panels to test changes in volts and amps. All in all, it was a good intro to basic electricity.
Notes on Class 1 available here