Solar Systems

Off grid photovoltaic systems,

Grid connected photovoltaic systems,

System Evaluation
For an unusual systemit may be worthwhile to measure the detailed operation of the system in order to understand the functioning of its components in detail. This was frequently performed in the 1980s and 1990swhen systems were often grant funded, and the main purpose of building the system was to improve knowledge and understanding. The operation of PV power systems is now well documented, and the expense of full monitoring, and the evaluation of the data, cannot normally be justified. The European Commission used to require full monitoring of every project they supported [11,but now this level of details seems to have outlived its usefulness. Of course, these three types of monitoring are not mutually exclusive. A display for user feedback is also necessary in a large system being fully monitored, or a system where the output is being measured [2].
2 Equipment
2.7 Displays
Displays are the backbone of monitoring. The easiest to fit is a simple indication as part of the inverter. Most PV inverter manufacturers offer an optional display. However this can place severe constraints on the placing of the inverter, which would normally be in a roof void, electrical switch room, or some other secluded place. If the display is to be effective it must be in a place where it is visible in everyday activities. Remote displays are easier to site, and may be provided with data from the inverter itself,or by a meter in the cabling from inverter to distribution board. A significant cost to installing this is the routing of the cabling to the display, but there are instruments on the market that avoid this by utilising short-range radio transmission (seeFigure 2).
Figure 2
(Photo EETS.)
A domestic PV output display receiving radio-linked data from a sensor next to the inverter.

820 Practical Handbook of Photovoltaics: Fundamentals and Applications There are many different formats of data that can be displayed: the most popular are the instantaneous power being generated, and the total energy to date. However, large displays often include derived values that mean more to the public, such as numbers of lights that are being powered, or the amount of carbon production being offset (see Figure 3). A computer-based monitoring system can often embed that information within a touch screen driven information point, or to have it displayed on the website for the building. 2.2 Data Acquisition Systems The main system tends to fall into two types: loggers and computers. The advantage of a logger is its simplicity and robust construction, but its disadvantage is its inflexibility and cost. A computer system, in contrast, may be slower to set up and commission, but has the advantage of a wider choice of operational modes and custom settings, while the cost may be less for a system based on a desktop PC. The choice between the types may well be dictated by the type of monitoring strategy for the project: are the data to be viewed in real time? Are different types of data to be monitored at differing intervals and in differingways?
2.3 Sensors
There is no limitation to the inputs that may be monitored for a PV System, but most systems will need to measure the input and output energy, and some environmental and system variables. A list of the more usual variables is given in Table 1.
3 Calibration and Recalibration
The system should be set up and calibrated preferably in situ. The need for recalibration should be determined whilst considering the length of time for the I-
Figure 3 A pair of meters measuring import and export of electricity into n building and outputting pulse data to a monitoring system.

Portable solar power systems,

Solar lighting systems for home,