There are two tools available on the internet to do modeling of renewable systems. These systems are useful for bloggers because they let you do quick and dirty simulations, and pop out some good numbers and (more importantly) some pretty pictures.
Natural Resources Canada's RETScreen
RETScreen is available in many different languages. It uses Microsoft Excel to perform analysis of renewable systems in a number of different configurations. It generally evaluates the performance of systems based on statistical monthly averages. RETScreen is largely a stand alone system -- it has a lot of geographical information built-in. The documentation of RETScreen is a strength. Many people will want to read the documentation simply because it helps to explain the issues involved in renewables. Economics modeling is the strength of RETScreen.
National Renewable Energy Laboratory's (of the USA) HOMER
HOMER is a stand alone program, and as such it can handle a much denser simulation. While RETScreen might split its model into monthly chunks, HOMER can handle fluctuations on an hourly basis. This makes HOMER useful for modeling the intermittancy of solar and wind power. HOMER is also capable of doing brute-force system optimization, given a number of variables. While HOMER is more powerful than RETScreen, it requires much more in the way of data inputs. As such, HOMER is better suited for the more advanced user. Personally, since I don't have access to actual utility power data, I tend to simulate data in MATLAB. HOMER's economic model is not comparible to that of RETScreen.
Hopefully some people who weren't aware of these FREE tools will find them useful.