Your comment ....."The only efficient solution is to be fully self-supplying, means energy storage (batteries) generating with a mix of wind (because of less sun during the winter) and solar".
Renewable energy creation equipment has never been cheaper at this time, but to be honest, having any sustainability/energy creation installed by so called professionals, is a no brainer as the figures do not add up. It is possible for a professional company 'to make a living' but in my experience they are generally OTT when it comes to profit margins.
Have a look at our creations in Normandy, (not for profit) http://www.echorenovate.com
It is possible to store energy and we have 65kW (1300ah at 50vdc) of battery storage, but ours are GEL type and they are recycled from UPS system's in Banks etc, but I have to select each 40kg battery very carefully. Even so I loose about 1/3rd of my power generated when charging the batteries, inverter etc.
A good friend came up with these up todate real prices for a self install PV 10kW system. see http://www.navitron.org.uk/forum/index.php/topic,21925.0.html
PV 10 kw "SunClass - SC 100-AS " 2700 Euro
INVERSOR/CARGADOR VICTRON 48/5000-70-50 1800 Euro
Chargecontroler and Gridtie inverter 1300 Euro
40 kwh PzS Battery ca 3000 cycles at 50 % DOD 2600 Euro (or refurbished 1600 Euro ) both minus 600 Euro lead value
Mounting frame ?? up to you ! mine under 1000 Euro
Cable , connection etc .............................. 1000 Euro ?
Planning is key. We convert our buildings to a passive huase standard, and we insulate, insulate, insulate and more insulate. This means are energy use is minimal.
We have 3off 3.7m diameter Hugh Piggott design Wind Turbines that are Home built, they are very efficient, simple, cost effective and robust. We also have Our own design of PV trackers, (New book, so you can make your own) which eventually will take us to 10kW of panels.
It is possible to be energy independent but its no FREE LUNCH, and to get the costs down so it all makes financial sense, means a fast learning curve and plenty of that PLANNING.
For Realistic sustainability information in Europe..... http://www.navitron.org.uk/forum/index.php