SOLAR TODAY - May 2010

here is an example of a system with severely reduced power output due to solar resource obstruction (in this case, birds and their droppings). unless the system is cleaned regularly, it will not reach its maximum power production capability.

ItRon InC.

by checking a system’s panels for dirt and other solar irradiance obstructions and cleaning them when necessary, the system owner can reduce the likelihood of these types of power reductions. monitoring helps indicate when such maintenance is necessary.

For Monitoring solar heating systems, the options Are Limited

Because solar water-heating (SWH) systems continue to be outnumbered by PV systems in the United States, and because monitoring heat recovery is more complicated, fewer options for SWH sensing and monitoring services are currently available. However, you will gain the same benefit from monitoring your SWH system as you would for a PV system, and you will need to ask yourself the same questions regarding what you want in a monitoring system.

At the most basic level you will want to monitor the heat recovery rate of your SWH system. Sensors are required for this, including a flow meter and two temperature sensors. Many different flow meters are available, with varying levels of accuracy and data outputs. They can range in complexity from mechanical inline flow meters to digital ultrasonic flow meters. The latter type is typically more expensive, but it requires less installation labor if you already have an SWH system in place.

For more information, contact your SWH manufacturer or installer.

a PV system’s tilt is described in degrees from the horizon. a PV system’s azimuth describes the direction that a tilted PV module faces and is often described based on compass direction. The tilt and the azimuth of a fixed PV system allow the maximum solar resource to be available at only one given moment in time. a PV system’s installation height is the distance from the object on which it is installed to the underside of the PV panels. Installation height affects air circulation under the panels, for cooling of the panels. Shading of a PV system by external objects such as trees can block available solar irradiance. Debris that builds up over time, called soiling, can also block available solar irradiance.

Figure 2 (page 50) compares the annual average PV output divided by the maximum output for different climate zones in California, the tilts and azimuths, and the associated solar resource for the given climate zone. (The energy produced by PV modules is direct current, or DC, which is converted to alternating current, aC, by the inverter, to be usable in the utility grid and in your home. The power losses associated with this conversion are typically identified by the inverter efficiency. In the simplest sense, a PV system’s maximum expected output is the sum of the PV module output multiplied by the associated inverter efficiency.) The solar resource is designated here as full sun-hours, where one full sun-hour is the energy produced by the peak noon sunlight intensity in the middle of summer over one hour. This figure shows

FIgurE 1.

radiation available to a photovoltaic system Based on time, mounting
the average radiation available to a pV system varies depending on the time of day
and year and depending on how the panel is mounted.