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.
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
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
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.
Monthly Average Radiation (k Wh/m2/day)
in Sacramento monthly average radiation (k Wh/m2/day) in sacramento
Tilted at 23°,
2 Axis Tracking
Jan Feb Mar Apr May Jun July Aug Sept Oct Nov Dec