On the face of it, solar power is about as green as it gets as far as power production is concerned. However, the overall picture is not so clear.
The end Products
Once installed, your solar power system should produce electrical power for a large number of years with practically no further inputs to damage its green credentials, bar perhaps the occasional use of water to clean the modules, maintaining their efficiency.
But this is only part of the story, it is necessary to look at the bigger picture and consider energy cost of manufacturing the solar power equipment and any other environmental issues resulting from the manufacturing process.
Modern PV modules (produced after the year 2000) should have a useable life (generally considered to be while they still produce 80% of their original output) of at least 25 years, and will probably still be producing power after 40 years.
Other electronic components however Inverters and controllers) may have a shorter lifetime of 10 to 15 years as the high operating temperatures and the electrical loads they handle take their toll.
An off grid system will have batteries which also have a shorter life. Lead acid batteries which are sufficiently large enough for the system and treated with reasonable care (not discharged too low or fast, or left in a discharged state) are likely to need replacing after 10 to 15 years. This may drop to 5 years if the batteries are worked too hard.
Energy Requirements for the Manufacture of Solar Power Systems
It is of course very difficult to measure the overall energy input into the manufacturing process of solar power systems in general, though many people have made judgements in the past. That judgement may have been along the lines of "Solar Power systems use more energy in their manufacture than they produce in their lifetime".
A report by Michael Dale and Sally M. Benson, both of Stanford University, United States, suggest that that the energy put into solar power system manufacturing should have been equal to the power produced around 2010. However, this was simply looking at the power produced so far by solar power sustems that were likely to have many more years of life in them. After 2012, they said, the solar power industry was a "net electricity provider".
A further factor (until we get to the point where all electricity is produced by renewable sources) here, is how green is the energy used in the manufacturing processes. Much of this production now comes from China, which was reported to produce 25% of its electricity from renewable sources in 2015, comparing favourable with many other industrialised countries, according to the Enerdata Statistical Yearbook. By coparison, the USA is reported to produce 14% of its electricity from renewables.
Factors in the Solar Cell and Module Manufacturing Process
The majority of solar cells are made from silicon (over 90% in 2014) which is the second most abundant element in the earths crust after oxygen. It is not in short supply and is non-hazardous but other hazardous chemicals uare used in the process including hydrochloric acid, hydroflouric acid, and sodium hydroxide. These hazardous chemicals can be handled safely but this has not always been the case.
Other types of solar panels (non-silicon) use rare or precious elements including silver, tellurium or indium, together with carcinogenic cadmium in some cases.
The good news is that work is being carried out to develop thin film solar cells which do not use toxic chemicals, whilst texic chemicals are being reduced in other processes.
Factors in the Battery Manufacturing Process
The lead acid battery principally contains suphuric acid and lead. Lead is well known as a powerfull neurotoxin and very dangerous at low levels in the blood, with children being most vulnerable. This has been a particular concern in China where lead acid battery manufacturing (and the batteries use) has seen a sharp expansion in recent years.
Cadnium in nickel cadnium batteries is also highly toxic and can be absorbed through the skin on contact. Lithium-ion batteries are much less toxic however.
Recycling Solar Power Systems
All such equipment can and should be recycled. There are not many module recycling plants yet as currently, there are not many modules coming to the end of their life.
Recycling of lead acid batteries is a well developed industry as they have been used in motor vehicles for many years. All other batteries can and should be recycled though the process required can be complex due to the elements involved.