We are nearing the completion of the big energy requalification project started before the summer.
The panels are already installed and so is the inverter, awaiting the connection to the grid; this week the new heating / cooling system units will be installed in all the rooms, and so will the thermostatic valves on the (now backup) gas powered heating system radiators.
The total cost of the full system is around EUR50k; this excludes the masonry work to embed the hot/cold air circulation in the walls, as this was done at the time of the renovation. The investment is financed through a 7.1% fixed rate 10 years loan, and I qualify for an annual tax credit of 5% for the same 10 years as part of the italian Government green energy incentive program.
I expect to save about 65% of my energy bill from now on.
The above chart represents (to the best of my still theoretical calculations) my energy inflows and outflows. The red bars (above) represent the energy I generate, with the lighter section being the portion I consume right away, while the darker portion is “set aside” in my “energy account” held in the grid.
The blue bars (below) represent the sources from which I draw the energy I consume: the lightest section is the same as the light red section, i.e. are the energy I consume on the spot. The mid-dark section is the energy I pull out of my “energy account”, while the darkest section is the energy I buy altogether from the grid.
You may notice that the energy I pull from the energy account is LESS than the energy I put in, and this is because the unit rate is much lower (€0.14 vs. €0.29).
The root of this problem is of course that the majority of consumption happens at a time that does not coincide with the majority of generation; the situation would improve significantly with the use of accumulators for energy storage: their use means the KWh I generate (but not use) can be stored for later consumption without “discounting” it. From a technical standpoint, using accumulators and increasing my generating power to 20KW (the maximum allowed for an individual installation) I could achieve a near independence:
As you can see, the dark blue bar has almost disappeared. In the above chart I am assuming no limitation on storage capacity (which peaks at around 10,500 KWh – black line – in mid-october.
This may or may not be realistic: in fact accumulators are still prohibitely expensive, and incentives may not exist at the time they will have come down in price, requiring a round of financials cost-benefit analysis to decide if this next step makes economic sense.
All the calculations have been performed with the help of this little template you are welcome to use for your own calculations.