You can read all about the history of Solar panels that make electricity on wikipedia. It was so simple Einstein had to explain it and win a Nobel prize. See the note at the bottom of this page for details.
COST- The cost of Solar panel is listed in dollars per watt. In 1954 it was over $1,000 a watt. In 2009 it's about $2.50 a watt. It keeps slowly falling. Panels become more efficient (22.5% sunpower) and have longer warranties (25 years standard). Similar pricing still in 2010. In 2012 the price is $1.50 per watt on many 200-300 watt panels. A few more US solar PV companies have failed after China started importing 50% of all panels at very low cost. There are still great solar PV companies in the USA like Solar World and Sunpower in Calfornia and Suntech and First Solar in Arizona.
The shortened notes version from the wikipedia link above that affects you is below.
Solar Panels that make electricity were first made and sold in the USA by Bell Laboratories. They make no pollution and use no water. They have been use in space for years. Yes, the Telephone Phone company Bell System Labs made the first commercial panels that were 5% efficient in 1954. In 2012 Sunpower now makes and sells panels that are 24+% efficient.
Solar panels make DC Direct Current similar to a battery voltage. The type of voltage we use in our homes is AC alternating Current. You can read the big debate about this on wikipedia too. It was between Thomas Edison DC and Westinghouse AC. A simple efficient inverter changes the DC into AC. A grid tied system needs no batteries.
Cost- The cost per watt has been coming down every year since they were invented. In 1954 it was over $1000 a watt. The efficiency has been going up each year. It was about 5% in 1954 and now is over 20% for SunPower moduals. In 2009 First Solar in Phoenix Arizona reported they now make solar panels at less than 1$ per watt. In 2009 most panels sell for about $2-4 a watt.
In 2012 many panels sell for about $1 a watt. This is about 1,000 times less than when they were first commercialized.
WARRANTY- Most solar panels have a warranty for 25 years. Inverters have 5-10 years. A few have 15 years..
Standard generally used in photovoltaic panels:
In 1922 Einstein was awarded the 1921 Nobel Prize in Physics, "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect". This refers to his 1905 paper on the photoelectric effect: "On a Heuristic Viewpoint Concerning the Production and Transformation of Light", which was well supported by the experimental evidence by that time. The presentation speech began by mentioning "his theory of relativity [which had] been the subject of lively debate in philosophical circles [and] also has astrophysical implications which are being rigorously examined at the present time." (Einstein 1923)
It was long reported that Einstein gave the Nobel prize money directly to his first wife, Mileva Marić, in compliance with their 1919 divorce settlement. However, personal correspondence made public in 2006 shows that he invested much of it in the United States, and saw much of it wiped out in the Depression.
Einstein traveled to New York City in the United States for the first time on 2 April 1921. When asked where he got his scientific ideas, Einstein explained that he believed scientific work best proceeds from an examination of physical reality and a search for underlying axioms, with consistent explanations that apply in all instances and avoid contradicting each other. He also recommended theories with visualizable results (Einstein 1954).
November 2014 Solar panels are less than $1 a watt. They continue to get more efficient and have longer warranties. Small Micro Inverters are becoming the standard on every panel.
December 2014 Prices are still less the $1 with some down to 50 cents a watt. BUT big utilities are fighting to keep Solar in their central locations and not your home where you own it.