These are some of the things that I'm working on at the moment.
This is just a pretty quick-and-dirty Java application that brings together some of the more basic PV specifications and requirements. The user puts in basic values for PV panels to supply power, how many of what size storage batteries, and identify some basic loads. From there the application will calculate a variety of parameters - how long to recharge storage, how long the home can operate without sunlight (recharging), and so on. The user also has the option of adjusting reserve capacity, preferred full-recharge time, and a few other things. Outputs are displayed as a table of numbers that can be printed or exported for inclusion in a spreadsheet or graphing program; all data values used in the calculations are output in printed copies. Parameters can be saved to, or loaded from, basic text files.
( 20090928) UPDATE! I've gotten the program written and ready to go, along with a brief user's manual. It's available for download as PVcalc.zip. It isn't pretty, but it works... Due to the fact that I'm just learning Java, and ran into enough OTHER issues with Java in the process, importing data isn't implemented. Maybe in the next version...
This one is a little more ambitious: an attempt to let the user specify the outside surfaces of a building, and then see what the heat loss/gain will be. Data requirements will be gross wall and ceiling/roof dimensions, insulation values, glazing type and dimensions, construction materials, external temperature ranges, and wind speed/direction. Again, output will be in a table format (until I can start doing graphs from within Java), printable or exportable to spreadsheet/graphing application. Data sets will also be through plain-text files.
A few months ago, I stumbled across something called Arduino. It's an inexpensive ($35) microcontroller board roughly the size of a credit card -- with 13 digital Input/Output pins (6 of which can be used as PWM outputs), 6 Analog inputs, bootstrap code, and USB interface. The circuit, development tools, and metric buttload of examples, applications, and other goodies are all free. I got one, and have been having a LOT of fun playing with it. I've even gone so far as to use the Arduino as the basis for a small 'bot that I'm developing; the 'bot is just a basic turn-loose-to-wander-around thing using a small Tonka tracked front-end loader toy as the platform.