Computing - PV power

Previously disregarded due to the long payback periods associated with the technology, the application of pvs is becoming more attractive. Falling costs, hence shorter payback periods, are making the systems increasingly viable as an alternative source of heat and electricity.

With these developments in mind, a computer program, PV*Sol, for designing, planning and simulation of pv systems has been released in the UK by Construction Resources.

The software
Two versions of PV*Sol are available. First PV*Sol 2.1 which can be used to design stand-alone and grid-connected systems, and second PV*Sol-N which is solely for grid-connected systems.

The Windows-based program has both drop-down menus and an easy to use picture button menu. There is also an on-line help facility, accessible at any point by selecting the F1 key, that explains the program's less obvious functions.

Quick design function
The 'quick design' option is the simplest way to carry out a simulation of a pv system. This option is offered when a grid-connected or stand-alone system (the first choice on the program) has been selected.

In a single sub-screen a series of choices is given. For a grid-connected system the user must select each choice in turn, starting with weather location and moving onto pv module then inverter type; for each of these a drop-down list will show the available options for the design. The output required, orientation and tilt angle of the units (usually the roof angle) must then be entered.

If incompatible components are selected a helpful notice appears on-screen allowing reselection. This function removes the need to trawl through manufacturer's data to ensure compatibility, thereby saving design time.

From this information the program will automatically calculate the actual output, number of pv modules and inverters required, the surface area of the pv array and the number of modules per string. Simulation of the system is possible directly from this point and a summary results page is automatically produced.

For stand-alone systems, the quick design function allows a choice for each item separately.

If a more detailed and accurate analysis of a system design is required, the quick design option should be foregone. By working through the buttons on the left-hand side of the initial screen, the user is taken step-by-step through the detailed inputting of system information.

Initial choices are weather data and electricity tariffs. The user must then define the load of each individual electrical appliance in the building.

Inputting of holiday periods enables more accurate annual consumption figures. With this information a graphic display of each load can be viewed for hourly, daily, monthly and annual periods. Figures are also available in tabular form for printing out.

Results
The final results of the simulation are presented on a single page in an easy to follow and compare format. A diagrammatic representation of the system (including the actual unit choices) is shown above a listing of the most important values for the design, such as the percentage system efficiency and performance ratio, and the basic design information such as location and pv surface area (see illustration above).

Also offered is an economic efficiency calculation, which provides electricity production and annual and pv costs. It also gives the lifespan of the system and shows the percentage split of capital investment between the various system components. Increases in fuel and running costs are estimated.

An annual energy balance is also available in addition to the project summary report and the graphical results.

As a design tool, it appears that PV*Sol should prove valuable in ensuring that pv systems are not unduly over or undersized and a suitable mix of components is chosen so maximum efficiency can be gained from any system installed. The wide range of applications and components included make the program even more useful.