A fellow by the name of Kollector coined this thumbrule...
The installed cost of the photoelectric set should not exceed the ten year payout of the feed-in tariff.
Example: A set that delivers 850 kWh/kWp in its first year will deliver approximately 9700 kWhs/kWp over ten years of work. The following examples give a rough picture of how this thumb rule predicts installed costs will trend between now and the beginning of 2011.
--If the value of the feed in tariff is 39 cents/kWh (current FiT) the installed cost should not exceed 8275 kWhs x .39 cents/kWh = 3227 €/kWp.
--If the value of the tariff is 33 cents/kWh (FiT as of July 1st) the installed cost should not exceed 8275 kWhs x .33 cents/kWh = 2730 €/kWh.
--If the value of the tariff is 26.5 cents/kWh (projected FiT as of Jan 1st, 2011) the installed cost should not exceed 8275 kWhs x 26.5 cents/kWh = 2193 €/kW.
With Chinese panel cost falling under a euro per watt it looks possible to achieve installed prices in Germany of under 2200 €/kW. One interesting question to ponder goes something like: will sunnier markets outside of Germany start producing higher rates of return for PV investment such that Germany no longer drives the market clearing price of panels?
Another interesting question is, how will Germany transform the FiT structure once grid parity is reached (installed costs of 2200-ish €/kW). Will the self-consumption premium result in smaller PV sets compared to the oversized 10 kW+ sets that have become common? Will batteries come into common use? Hmmm... Neglecting the cost of input energy and assuming a daily charge/discharge cycle, what are the LCOE for batteries over their lifetimes? Something for the EV car guys to deal with.