How To Use Real-time Data: Simple View

The information available in the Simple view breaks down as follows:

Last Data Update: At the top left corner of the Simple view you will see a date and time labeled "As of"; This should show today's date and approximately the current time. In the event the school's PV system is not sending data to the Internet, it will not be updating and this time or date would be earlier than now, so the live data may not be accurate. Also keep in mind that the system only updates the current conditions every few minutes, so on days where there are clouds passing in front of the sun the numbers may not be quite accurate for what is happening at this particular moment.

1. System Size

Across from the time of last update, there is a System Size number shown. This is the theoretical maximum power that the photovotaic (PV) system can produce. It comes from what the manufacturer of the PV panels claims they are capable of producing when pointed directly at the sun, at noon, while the sun is straight up in the sky. In reality, the system will produce less power than this most of the time, both because the sun is usually not that bright and not shining directly on the panels, and because the inverter is not 100% efficient, so it will put out less power than the PV panels generate. On sunny days in the summer, however, it will come close to this number at around noon.

2. Generating

This simply displays the amount of power that the system is producing right now. The bar to the right of the number shows visually how the current power output compares to the total power the system is capable of producing in theory, taken from System Size.

3. Current Weather Conditions

To the right of the Generating box is a display of the current outdoor conditions on the roof of the building, according to the instruments attached to the PV array. Ambient Temp and Wind speed show what you would expect, and Cell Temp shows the temperature of the PV panels themselves, which will almost always be higher than the Ambient Temp during the day, since they are absorbing sunlight.

Irradiance (also called insolation) is the most interesting number; It comes from a sensor that determines how much power is in the sunlight currently shining on the array. This takes into account both the amount of sunlight--affected by clouds and time of year--and the amount of sunlight that actually strikes the array, which is affected by the angle of the sun relative to the angle of the PV panels. At noon when the sun is straight up in the sky, this number would be about 1000 W/m² (also called "full sun").

It is also possible for the irradiance to exceed 1000W/m² occasionally; when there is a thin layer of clouds passing near the sun it acts something like a giant magnifying glass. This effect is called cloud focusing, and can cause irradiance to be significantly higher than would be possible on a perfectly clear day.

4. Historical

The next section of the Simple view shows how much cumulative power has been generated by the system over various periods of time. The length of time shown is changed by clicking on Today, Week, Month, etc across the top of the box. The number shows the cumulative total for the period selected (the bar next to it doesn't represent any useful information). The bar graph can be used to demonstrate seasonal variation in the amount of sun; looking at the Year or Lifetime graphs should show a relatively smooth curve corresponding to summer and winter cycles (assuming the array has been in operation long enough). Students could also use this to roughly calculate the ratio of power produced during winter months compared to summer months.

The Week and Month graphs could be used to compare power output with recent weather, and also possibly as a point of discussion for how significant daily variation averages out into the smoother curve shown over a longer period of time. The daily graph has very poor resolution, so is usually not of interest.

5. Greenhouse Gases Avoided

This section shows the total pounds of CO2 theoretically not produced due to power produced by the PV array. While this might be good to start a discussion on greenhouse gases, the numbers are only very rough estimates based on a number of generalized assumptions about the CO2 produced by conventional (coal) electricity production. The section showing the cumulative power production in terms of houses and TV hours is, similarly, quite generalized, though it could be used to illustrate how much electricity the average home uses as a starting point for a discussion on energy efficiency.