4.6 Simulation results
4.6.3 Complementary PV production
In this section, the benefits of adding photovoltaic panels on the available roof area are studied. In order to do so, and for both previous cases (0.2 and 0.1 roof m2 per heated m2), the following is assumed:
For the air, lake, river, groundwater and geothermal HP systems, the available roof area is considered to be fully used for PV production.
For the solar HP system, only the area that is not used by the solar collectors is available for PV production.
PV production is based on 12 % efficiency applied directly to the global horizontal solar irradiation, which leads to an annual electricity production of 150 kWh per m2 of PV.
Regarding the heat production system, building types and HP system components are exactly the same as in the pre-vious section (section 4.6.2). The interaction of the HP and PV systems and their relation with the electric grid are represented in Figure 4:14.
Figure 4:14 Simplified diagram of the heating system’s electricity flows.
Electricity production from the PV panels Epv is used in priority in the form of self-consumption Eself, to partake in the HP system electricity demand Esys (which includes electricity for the heat pump and for auxiliary direct electric heat-ing). This self-consumption is calculated by taking into account the daily match between Epv and Esys. The excess PV production Einject is injected in the grid. Similarly, the HP system final electricity consumption not covered by PV is pur-chased from the grid Efinal. These electricity flows obey the following relations:
𝐸𝑠𝑒𝑙𝑓 = 𝑀𝐼𝑁(𝐸𝑠𝑦𝑠, 𝐸𝑝𝑣)|∆𝑡=24ℎ (24)
𝐸𝑓𝑖𝑛𝑎𝑙 = 𝐸𝑠𝑦𝑠− 𝐸𝑠𝑒𝑙𝑓 (25)
𝐸𝑖𝑛𝑗𝑒𝑐𝑡= 𝐸𝑝𝑣 − 𝐸𝑠𝑒𝑙𝑓 (26)
𝐸𝑛𝑒𝑡 = 𝐸𝑠𝑦𝑠− 𝐸𝑝𝑣 = 𝐸𝑓𝑖𝑛𝑎𝑙− 𝐸𝑖𝑛𝑗𝑒𝑐𝑡 (27)
Furthermore, we define the performance factor of the combined HP & PV system SPFfinal: 𝑆𝑃𝐹𝑓𝑖𝑛𝑎𝑙 =𝐸𝑄𝑑𝑒𝑚
𝑓𝑖𝑛𝑎𝑙 (28)
Potential and constraints of available heat sources in relation to various building demands.
Note that the match between Epv and Esys is calculated on daily production and consumption values. Within this study, we do not calculate the match in hourly time step because:
a. for SH, the hourly load model is given by a linear function of the outdoor temperature, which does not properly account for finer day/night or hourly dynamics, as discussed in Chapter 3;
b. when upscaling the results at regional level (see further down), the sum of hourly load peaks would not rep-resent reality because each building will have different dynamics and the load peaks will not be at the exact same hour;
Furthermore, the choice of working with daily integrated values can be justified by the possibility of handling the ac-tual hourly miss-match with thermal and/or electric storage.
Finally, the above defined electricity balance only takes into account the electricity consumed by the heating system (heat pump and auxiliary direct electric heating), but no other electricity usages in the building.
The results related to the added PV are presented in terms of the eletricity flows defined above, as well as SPFfinal. Results for a low-rise building are presented in Figure 4:15, Figure 4:16 and Figure 4:19 while high-rise building results are in Figure 4:17, Figure 4:18 and Figure 4:20.
Figure 4:15 and Figure 4:17 can be interpreted as follows:
Solid bars (positive values) represent the total electricity consumption Esys of the HP system;
Faded solid bars (negative values) represent the total electricity production Epv of the PV system;
The dots represent the annual balance between total electricity consumption and production Enet. Figure 4:16 and Figure 4:18 can be interpreted as follows:
Hashed bars are the self-consumed electricity Eself (daily match between Epv and Esys).
Solid bars (positive values) represent the final purchased electricity from the grid Efinal (difference between Esys and Eself );
Faded solid bars (negative values) represent the electricity injected into the grid Einject (difference between Epv
and Eself );
The dots represent the annual balance between final purchased electricity and electricity injected into the grid Enet.
Figure 4:19 and Figure 4:20 are representations of SPFfinal in function of the building demand.
As a complement to these figures, separate graphs for the different electricity flows (Ehp, Edir, Esys, Epv, Eself, Efinal, Einject) are given in Annex K.
Potential and constraints of available heat sources in relation to various building demands.
Air Geo Lake River GW Solar
Air Geo Lake River GW Solar
Air Geo Lake River GW Solar
Ai r Geothermal La ke Ri ver Groundwater Sol ar Esys
Air Geo Lake River GW Solar
Air Geo Lake River GW Solar
Air Geo Lake River GW Solar
Air Geo Lake River GW Solar
Ai r Geothermal La ke Ri ver Groundwater Sol ar Efinal
Einject
Eself Enet
Potential and constraints of available heat sources in relation to various building demands.
Figure 4:17 System performance (Esys, Epv and Enet) of a HP and PV system in a high-rise building
(limited roof/ground area of 0.1 m2 per m2 of heated area).
Air Geo Lake River GW Solar
Air Geo Lake River GW Solar
Air Geo Lake River GW Solar
Ai r Geothermal La ke Ri ver Groundwater Sol ar Esys
Air Geo Lake River GW Solar
Air Geo Lake River GW Solar
Ai r Geothermal La ke Ri ver Groundwater Sol ar Efinal
Einject
Potential and constraints of available heat sources in relation to various building demands.
Figure 4:19 System performance (SPFfinal) of a HP and PV system in a low-rise building.
Figure 4:20 System performance (SPFfinal) of a HP and PV system in a high-rise building
For the low-rise building (Figure 4:15), the 0.2 m2/m2 available roof area allows for a PV production Epv of 29.7 kWh/m2 (related to heated floor area), except for buildings with a solar HP system, in which case the remaining available roof area allows for a PV production of 0 – 18.2 kWh/m2, depending on the heat demand and associated solar collector area.
The self-consumed PV production (Eself, Figure 4:16) amounts to around 10 kWh/m2, except for solar HP systems, where it varies between 0 – 5.3 kWh/m2.
The impact of the PV production on the annual balance of final purchased / injected electricity (Enet) is as follows:
Except for solar HP systems, and in all cases except for No-retrofit, the system produces more electricity than it consumes (Einject ≥ Efinal or Epv ≥ Esys), so that Enet is inferior to zero. No-retrofit is the only building type with an Enet superior to 0 (Einject ≤ Efinal or Epv ≤ Esys).
For solar HP systems, the lowest building demand New low DHW is the only one with Epv higher than Esys.
0 5 10 15 20 25
New New
low DHW
Retrofit best case
Retrofit intermediate
Retrofit reference
No-retrofit SPFfinal
Air Geothermal Lake River Groundwater Solar
0 5 10 15 20 25
New New
low DHW
Retrofit best case
Retrofit intermediate
Retrofit reference
No-retrofit SPFfinal
Air Geothermal Lake River Groundwater Solar
Potential and constraints of available heat sources in relation to various building demands.
Even when Epv compensates for Esys (Enet ≤ 0), Efinal and Einject can reach important values. As an example, the Retrofit reference building with an air source HP is close to a net-zero energy heating system, but Efinal amounts to 17.0 kWh/m2/yr and Einject to 18.9 kWh/m2/yr. This points out the seasonal mismatch between PV production and heating demand.
Regarding the final purchased electricity from the grid Efinal, it is in the range of 2.1 – 12.1 kWh/m2 for the three low energy buildings (New, New low DHW, Retrofit best case). For the No-retrofit building, it is essentially above 20 kWh/m2, reaching up to 39.0 kWh/m2 in the case of solar HP. The Retrofit intermediate and Retrofit reference build-ings are in between, with values below 15 kWh/m2 except for air and solar HPs.
These Efinal values lead to fairly high SPFfinal (Figure 4:19). In the case of the three low energy buildings, SPFfinal is always above 5 and, in the case of groundwater, reaches values of 17.2 for New, 21.9 for New low DHW and 12.7 for Retrofit best case. The No-retrofit building has the lowest values (3.2 - 6.5, depending on the heat source), while Retrofit in-termediate and Retrofit reference have inin-termediate values (4 – 9.7 and 4 – 7.8).
Overall, for all the buildings, groundwater has the lowest Efinal /highest SPFfinal value, followed by river, deep lake, geo-thermal, air and solar. Even though the SPFfinal values may suggest otherwise, this classification is not so important for low energy buildings, because their Efinal is quite low (no matter what heat source is chosen), whereas it is a key issue for higher demands due to their high Efinal.
For the high-rise building (Figure 4:17), and except for the solar HP systems, the 0.1 m2/m2 available roof area allows for a PV production (Epv) of 14.8 kWh/m2 (half the value of the low-rise building). This reduction of the PV production has a limited effect on Eself (Figure 4:18), which amounts to around 8 kWh/m2, and mainly impacts Einject. All in all, the annual PV production does not cover the HP system electricity consumption (Esys > Epv or Efinal > Einject), except for the New low DHW building.
In the case of a solar HP, New low DHW is also the only building with a remaining available roof area, limited to 0.02 m2/m2, allowing for an Epv of 3.4 kWh/m2, however largely below the Esys of 11.0 kWh/m2. For all other buildings Epv is null, hence Efinal is equal to Esys.
As for Efinal values, the same structure as for low-rise buildings is observed: i) Efinal less or close to 10 kWh/m2 for low energy buildings (New, New low DHW, Retrofit best case) and for all heat sources, except for solar HP; ii) Efinal above 20 kWh/m2 for No-retrofit and for all resources; iii) intermediate values for Retrofit intermediate and Retrofit refer-ence, except for air (intrinsically linked to the heat source), solar (linked to absence of PV production) and geothermal (combined effect of limited ground area and limited roof area for PV production).
The same structure as for low-rise buildings is also observed for SPFfinal (Figure 4:20) but with lower values due to the slightly higher values of Efinal. The highest range of SPFfinal is 5.1 – 12.6 for New low DHW and the lowest is 2.5 – 5.5 for No-retrofit.
Potential and constraints of available heat sources in relation to various building demands.