Solar Energy

I will bet on more than 10 years. Although research in the solar energy field is rapidly increasing. Efficiencies are still low (Max about 38%) and prices are high. I also think that solar energy alone can't replace all other sources, but it will be a worthy supplement.

There is a definite positive payback now depending on your local electricity rates and the effective cost of financing a PV system.

In Calif we have available a time of use energy tariff from PG&E which charges more for electricity during peak usage hours when the least efficient generators are brought into production. 

There is a surge of investment by financial institutions partnering with energy companies for funding School system power with PV
http://money.aol.com/news/articles/qp/pr/_a/milpitas-unified-school-district/rfid116092540

 Electric power rates to the consumer are rising at 5 - 6%/year and a grid tied PV system will cost basically te loan charges and the occassional panel cleaning.  Panels are guaranteed to deliver at least 80% of rated output after 20 years.  Check out the E-1 standard tariff against the E-6 time of use tariff at PG&E or the equivalent at your local energy supplier.
http://www.pge.com/tariffs/ERS.SHTML#ERS

The daily Electricity consumption cycle can exceed a 2:1 Peak to baseline power ratio, so the peak correlated output from PV systems really helps power companies supply this cycle without overloading the distribution and generation system.  In Northern Calif this cycle can be monitored in real time at
http://www.caiso.com/outlook/outlook.html

 We recently installed a 3 KW PV system (with 22% efficiency panels) after refinancing at below 6% and we are currently recouping twice the system finance cost each month.  We expect the payback to payoff the investment in about 8 years.  After that our minimal PG&E bill will be without additional cost.

The main tradeoff is between system cost / watt and financing costs.  If you have plenty of available area then less expenive PV panels can be used.

Checkout the magazine homepower at http://www.homepower.com/home/

and download the free trial issue.

Also check out PV suppliers such as Wind-sun.com at
http://www.wind-sun.com/

A great series of down-loadable talks (Videos with slides) is referenced at http://modular-e.com/education.htm

I think it will happen only when the world oil reserves are finished. No one is really into moving towards cleaner energy everything is ruled by the big corporations. People in this world don't get it yet.... It's really sad but I wish it would happen sooner then 10 years the minute the US will set an example to the world like it should then maybe things in this world will change. The technology already exists the government need to fund such a program therefore it's all in the politics.

The worlds oil reserves will not be "totally" depleted in the forseeable future -- BUT THE RATE of access (daily pumping volume) of existing reserves will continue to diminish.  Meanwhile China and India are increasing their petroleum demands by adding cars and developing industries so as to cause demand to exceed supply.

This will result in a bidding war that will continue to increase petroleum prices and make previously un-economical oil deposits profitable to exploit.

Renewable energy sources are not susceptable to these increases, however a shortage of high purity poly-silicon has kept photo-voltaic panel prices at about $5 / Watt in consumer quantities.  Several Calif school systems have teamed up with Chevron and Bank of America to Finance multi-million dollar installations with paybacks afrom current and projected future energy price increases.

The venture capital community is investing heavily in "Cleantech" which includes renewable / sustainable energy.

http://venturebeat.com/2008/02/29/cleantech-investment-in-2007-up-43-percent-tops-3-billion/

A worthwhile video clip

http://www.pickensp lan.com/

Soon, allthough it's costly to set up I'ts already possible to make your home almost solar dependant.  I live in Israel where almost everybody has solar water heaters, and that's already been around for years here.  In the southern dessert they are building entire community's dependant on solar energy and a japanese and french auto maker are each developing a country wide system of solar charged battery powered cars

More on Solar energy