Spain to tax sunlight
Home power fed to the grid can be taxed a lot, before break-even with an off-grid system is reached. Grid tied inverters have an efficiency around 97%. Battery systems about 50%. Partly this has to do with the very inefficient absorbtion charge part of the batteries. And when the pack is topped off, solar power is cut and wind power dumped, so lost too. Batteries do not live long enough to have them repayed, even if you baby them carefully. An off-grid system makes you independent? Independent of what? Yes, when one considers power suppliers. No, on behalf of suppliers of hardware like inverters and batteries.
In the Netherlands, a grid tied solar system has a payback time of 7-10 years. Same power, but kept indoors by means of a battery pack: no packback time, because batteries do not live long enough. Note that if you keep the grid connection intact, but do not use it, no costs are charged by the supplier. In fact you get some tax return, because you use so less….
When grid power is available, adding a battery based off-grid system can be considered as an expensive insurance. Or an expensive hobby…..
I'm Dutch too, living in Denmark. You are absolutely right that, in Holland, home power fed into the grid can be taxed a lot before it becomes economically unjustified. But that's in Holland and maybe still in some other places. Denmark and Germany had also very lucrative government deals, which produced high incentives for private people to purchase PV grid-tied systems. However, since 2011, 2012 in Germany and here in Denmark 2013, all those lucrative deals have been greatly reversed. Till last year, it made in Denmark a lot of sense to purchase a PV-system; the grid could be used, Free Of Charge, as a "storage". Excess production went into the grid and could be pulled out, FOC, at a later date. That's all gone. Now you sell it to the grid for 1.3 DKK / kWh (price in 2013, but progressively less in 2014, 2015 etc till 0 kroner in 2020) and if you can not use your own power within 1 hr, you have to buy it back at the current electricity price of 2.3 DKK / kWh (0.31 euro / kWh, 0.42 US$ / kWh). You also only allowed to produce a certain amount; above that threshold you get heavily taxed. If you happen to be without work and on a benefit, the money your PV system generates (the 1.3 DKK/kWh) is seen as an income and taxed accordingly. Doing your math now shows a complete different picture as in the "good old days", pre-2013, and PV is now economically a dead horse. Lots of new companies, who thought PV was the future and invested in it, are going bankrupt now, thanks to the new rules.
There was a very good documentary on YouTube, from the German television ZDF "Energiewende Rückwärts", detailing the corruption, the influence of lobbyist in Bonn and the horrendous impact which the change of rules in Germany had on the PV- & windmill-energy sector. Needless to say, that documentary has been removed. You may want to look at this http://en.wikipedia.org/wiki/Hermann_Scheer and his cause of death (no point intended). These Big Boys seem not to tolerate competition. Reading this blog, the EU PV-noose is tightening in Spain as well. I hope for you that in Holland the rules stay the same!?
Like you said, and I agree, in whichever way the calculations are done, it seems that a battery based system is indeed, or at least here in Europe and at the current prices, economically unjustified. That the EU clearly doesn't want cheap (and btw mostly very high quality) Chinese PV-modules for its citizen, or make PV as unattractive as possible, I like to refer to this article: http://www.bloomberg.com/news/2013-07-27/european-union-china-agree-on-solar-panel-shipment-deal.html.
They may "talk the green talk" but certainly don't "walk the green walk".
Maybe it is still an idea to invest in PV grid-tied as long as the rules are still favorable, but there seems to be a trend going……..