With real world numbers averaging ~90+% of stated efficiency over 25 years.
1W solar produces ~8-10 wh/day * 365 days * 25 years /1000 kw per w = 65.7+ kwh over 25 years. 2.04 / 65.7 = 3.1 cents per kwh worst case. Panels don't instantly die at 25 years. So, actual lifetime output is guaranteed to be higher so costs are lower. But there are vary low maintenance costs and occasional physical damage so that's a reasonable estimate on average.
The time value of money is only meaningful if you want to compare your returns with other options over the long term there is no point in including inflation etc. As it's not like 1kwh will magically turn into more than that just by time passing.
Let's suppose you your buying a large scale solar system with actual money right now.
Utility system prices are $2.04/W in Q3 2013. http://www.seia.org/research-resources/solar-market-insight-... it's less now but that's close enough.
Standard warranties offered in the market offer 90% rated power output for 10 years and an 80% rated power output for 25 years http://www.solarenergyhome.co.uk/performance.php
With real world numbers averaging ~90+% of stated efficiency over 25 years.
1W solar produces ~8-10 wh/day * 365 days * 25 years /1000 kw per w = 65.7+ kwh over 25 years. 2.04 / 65.7 = 3.1 cents per kwh worst case. Panels don't instantly die at 25 years. So, actual lifetime output is guaranteed to be higher so costs are lower. But there are vary low maintenance costs and occasional physical damage so that's a reasonable estimate on average.
The time value of money is only meaningful if you want to compare your returns with other options over the long term there is no point in including inflation etc. As it's not like 1kwh will magically turn into more than that just by time passing.