Electricity generation and consumption in a Passivhaus

Passivhaus image

Electricity Consumption in a Passive House:

The Passivhaus Standard primary energy requirement has a limit of 120 kWh/(m2a), regardless of energy source, for all space and water heating, ventilation, electricity for fans and pumps, household appliances, and lighting energy requirements of the house. This limit means that in a passive house the efficiency of household appliances and all electrical systems is crucial to meet this challenging requirement. This is emphasised by the fact that the primary energy factor for electricity in the PHPP software (as well as in the DEAP, Dwelling Energy Assessment Procedure) is 2.7. This means that every 1kWh electricity used in a passive house accounts for 2.7kWh of primary energy consumption. In comparison, gas only has 1.1kWh of primary energy for every kWh used.

When designing a passive house, the PHPP (Passivhaus Planning Package) software is used to calculate the electricity balance. The first step is to calculate the electricity requirement in the house including all household appliances and lighting. In order to achieve the Passivhaus Standard it is necessary to specify refrigerators, freezers, cookers, artificial lighting, washing machines, tumble dryers, etc. with the highest energy efficiency available on the market (i.e. category ‘A’ energy rating or better). The second step is calculating the auxiliary electricity requirement, in which electricity consumption is specified for mechanical ventilation system fans and controls, DHW circulation pumps, and any other present in the dwelling. The calculation results are presented in primary energy kWh/(m2a) and included in the PHPP ‘Verification page’.

Electricity Generation

In order to reduce the impact of electricity demand, electricity can also be produced on site, e.g. through PV, CHP (Combined Heat and Power, i.e. a generator that also produces heat, or a boiler, that produces electricity), wind power or micro hydro power. Out of these, PV is the easiest and most common to be installed on an average dwelling. At the very least, the circulation pump of the solar thermal system (if you have one) should be driven by it; if there is enough sun for the thermal collectors to work, there is also enough to feed the PV panel(s) to drive the pump.

This example shows how much yield one can expect from a 1kWpeak PV installation in Edinburgh, facing due south (no shading), either fixed with the optimal inclination (for Edinburgh) of 38, or with a 2-axis tracking system. In this case you can see, that the elaborate tracking of the sun would only increase the yield by approx. a quarter; so it might not financially viable to go to the expense for such a device (rather add one more panel – this has also the benefit of less maintenance). Estimated system losses are 14%.

  Inclination 38º 2-axis tracking system
Month Production per month (kWh) Production per day (kWh) Production per month (kWh) Production per day (kWh)
 Jan  24  0.8  30  1.0
 Feb  40  1.4  49  1.7
 Mar  69  2.2  85  2.7
 Apr  91  3.0  118  3.9
 May  109  3.5  146  4.7
 Jun  103  3.4  138  4.6
 Jul  106  3.4  141  4.5
 Aug  92  3.0  115 3.7
 Sep  72  2.4  89  3.0
 Oct  47  1.5  57  1.8
 Nov  30  1.0  38  1.3
 Dec  16  0.5  20  0.6
 Yearly average  67  2.2  85  2.8
 Total yearly production (kWh)  801  1026

 Below is the result for the same installation in Aberdeen. Because it is situated further north, the ideal inclination is increased to 40º:

  Inclination 40º 2-axis tracking system
 Month Production per month (kWh) Production per day (kWh) Production per month (kWh) Production per day (kWh)
 Jan  25  0.8  31  1.0
 Feb  41  1.5  51  1.8
 Mar  75  2.4  93  3.0
 Apr  93  3.1  121  4.0
 May  111  3.6  152  4.9
 Jun  1.5  3.5  145  4.8
 Jul  1.6  3.4  142  4.6
 Aug  94  3.0  119  3.8
 Sep  75  2.5  94  3.1
 Oct  51  1.7  63  2.0
 Nov  29  1.0  36  1.2
 Dec  15  0.5  18  0.6
 Yearly average  68
  2.2
  89  2.9
 Total yearly production (kWh)  819  1065

 

Explanation of Primary Energy:

Primary energy, in kWh/year:
This includes delivered energy, plus an allowance for the energy “overhead” incurred in extracting, processing and transporting a fuel or other energy carrier to the dwelling. For example, in the case of electricity it takes account of generation efficiency at power stations.

Delivered energy, in kWh/year:
This corresponds to the energy consumption that would normally appear on the energy bills of the dwelling for the assumed standardised occupancy and end-uses considered.

Source: SEI, Dwelling Energy Assessment Procedure (DEAP), 2005 version 2, pp. 28.