I have a story in today’s Toronto Star about plans to build another three large solar farms in Ontario, adding to the four 10-megawatt projects that were announced last month by California-based OptiSolar Inc.

OptiSolar Farms Canada, the local subsidiary, is building another two 10-megawatt farms in Petrolia, Ontario, home of North America’s first commercial oil well. It’s about half an hour away from Sarnia, where the first four farms were announced. This brings OptiSolar’s announcements to 69 megawatts, and another 10-megawatt farm is planned for Sarnia and another at another location is being announced within the next month. OptiSolar hinted that total announced projects could reach 100 megawatts.

Meanwhile, SkyPower Corp. of Toronto and Balitmore-based SunEdison LLC announced the first of several solar farms planned for Ontario under their joint venture. A 9.12 megawatt farm is being built in Norfolk County in southwestern Ontario, and should be complete sometime in 2008. SkyPower has committed to building at least 50 megawatts of farms, possibly much more.

It’s quite amazing really that Ontario, a laggard in the solar market a year ago, is suddenly one of the fastest growing markets in the world. This is because of the provincial government’s standard offer program, which pays a premium of 42 cents per kilowatt-hour for solar power. Now, announcements are one thing — we’ll have to wait and see if these projects actually get built.

Curious, even at 42 cents the economics of these projects are bound to be tough. OptiSolar, which is manufacturing and installing the panels and operating/owning the solar farms has a vertical structure, so it saves costs down the supply chain. Plus, it’s betting it can manufacture its thin-film solar panels at much lower cost than rivals, and it sees Ontario as a showcase for its product. I’m less clear of the SkyPower/SunEdison model, but obviously these folks have crunched the numbers and are satisfied with the level of risk and return on investment.

As I’ve said before, interesting times.