One of the correct paths to achieve houses completely autonomous from an energy point of view is to initially evaluate the monthly energy consumption by differentiating the electric ones from thermal.
In most cases one will find the following situation: about 80% of consumption will be of the thermal type (25% for the production of sanitary hot water – ACS – and 56% for space heating) and 19% electric type.
This percentage may vary according to the lifestyle of the inhabitants and the geographical location of the building, but describes an average power consumption of a residential building; for this purpose were conducted about 600 energy analysis during the research project ‘Country of the Sun’.
The energy consumption is the main one for the heating and is about 2 or 3 times greater than the heat required for the ACS. Currently the average consumption in the home is about 20 MWh per year; in this situation a solar thermal plant type combi can contribute with 8 MWh per year. In contrast, in a home with low emissions, where annual consumption is only 8 MWh, solar thermal can cover almost any requirements.
In Germany this housing has already been built by time and manages to have a coverage of annual requirements from solar energy that val from 50 up to 100%. In the picture a type of houses built right in Germany where it is located on the roof a solar thermal system (on both sides, about 64 square meters) and one photovoltaic (center). Inside the building is located a highly insulated tank and with a layering system for the accumulation of weekly heat produced by the solar thermal field.
The house is energy and can, only with the help of this heat, to meet the needs of heating, of course, the house is equipped with an air exchange system with heat recovery.
In this case it is achieved the goal of a home autonomous from an energy point of view through the integration of the following technologies: a heat-insulated casing, a system for heat recovery for air exchange, a solar thermal plant and a photovoltaic system connected to the grid.
In a house with low consumption the incidence of the heating system is relative. However, usually, it prefers a radiant floor or wall. Reducing consumption through thermal insulation is also a priority to increase the capacity of solar systems to cover the entire energy needs.
In fact, if we look at the chart below we can see that in a house to which we applied an external insulation and reduced by half the energy consumption for heating, the items of consumption are almost equivalent: Heating: 36%, ACS: 36%, electricity : 28%; in this way the problems of overheating of the solar thermal system are greatly reduced and can be reached so a coverage of requirements ranging from 50 up to 100%.
In the case of a system that does not reach the entire roof of the heating load only with solar energy, you can use a biomass boiler. The boiler allows to cover the periods with less solar energy. You can also get the result of the complete coverage of the need to act without first sul’isolamento thermal envelope, but we will never achieve the same results. First of all we should use more biomass resulting in higher operating costs and increased local pollution: even if CO2 emissions are offset by the cycle of biomass, are not all other issues. We also do not exploit the most of the solar thermal plant that does not cover most of consumption and will not do so with the same thermal efficiency of the system, BOSth, and, moreover, we also consider that the boiler output will be greater.
The implementation of “good practices” certainly provides some variability with respect to the different situations, but we can say that the results of this research provide excellent general design principles for the majority of cases. Let us recall that the whole work is based on the analysis of hundreds of cases located in different geographical areas of Italy and with different types of housing. It is important to work and promote these principles and to avoid confusion in this market of energy saving and renewable technologies is to increase the efficiency of investment, public or private, in this area.