8 E LECTROLYSERS AND INTEGRATION OF LARGE SHARES OF INTERMITTENT RENEWABLE ENERGY
8.1 I NTRODUCTION
8 Electrolysers and integration of large shares of
energy systems in the coming years, as the European initiatives to promote CHP and re‐
newable energy are implemented.
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000
1987 1992 1997 2007 2012
MWe
Development in Danish generation capacity
Offshore wind
Onshore wind
Private producers
Decentral CHP
Central PP/CHP
Fig. 29, Capacities of technologies in the Danish energy system from 1987 until 2007 and in the anticipated scenario in 2012.
The seven integration technologies analysed here are electric boilers (EB), heat pumps (HPs), electrolysers with local CHP (ELT/CHP), electrolysers with micro FC‐CHP (ELT/micro), hydrogen fuel cell vehicles (HFCV), battery electric vehicles (BEV), and flexible electricity demand (5%FLEX). The different integration technologies are analysed and compared in terms of their ability to integrate intermittent renewable resources (RES) and their fuel effi‐
ciency. The analyses are conducted in the BAU 2030 energy system, in which the shares of RES vary from 0 to 100 per cent of the electricity demand. In the analyses, RES is repre‐
sented by wind power. Subsequently, the costs of the integration technologies are com‐
pared in terms of their ability to improve fuel efficiency.
The technical energy system analyses are conducted for a period of one year, taking into consideration demands and RES during all hours. The ability of the reference energy system to integrate fluctuating renewable energy is defined by applying two different regulation strategies: 1) the capability of the system to avoid excess electricity production, and 2) the ability of the system to reduce fuel consumption and thus improve fuel efficiency. Hour‐by‐
hour the electricity production from RES is prioritised as well as the production of electricity at CHP plants, industrial CHP or micro‐FC‐CHP. The remaining electricity demand is met by power plants and the remaining district heating demand is met by boilers. By utilising extra capacity at the CHP plants combined with heat storages, the production at the condensa‐
tion plants is minimised and replaced by CHP production. At times when the demand is lower than the production from CHP and renewable energy sources, the electricity produc‐
and demand by introducing electrolysers or other available flexible technologies, such as the ones analysed here.
The system analysed constitutes an open energy system in which the technologies are util‐
ised with the aim of supplying demands. The measures introduced to secure the balance between the supply from CHP and RES and the electricity demand described may NOT be sufficient to reduce electricity production, and thus forced electricity export will be the re‐
sult. This type of technical energy system analyses enables the investigation of the flexibil‐
ity of the seven integration technologies. The analyses focus directly on the effect on excess electricity production, i.e. regulation strategy 1) of the two types of energy system analy‐
ses. Such analysis is presented by showing the ability of the reference energy system to integrate fluctuating RES. In Fig. 30, the x axis illustrates the wind turbine production be‐
tween 0 and 50 TWh, equal to a variation from 0 to 100 per cent of the demand (49 TWh), in excess electricity diagrams in an open energy system [69]. The y axis illustrates the excess electricity production in TWh. The less ascending curve illustrates a better integration of RES. In Fig. 30, a situation without CHP plants regulating according to the electricity de‐
mand is illustrated. The purpose of this is to show that the first step which must be taken is to introduce CHP and boiler regulation with heat storages. This can significantly reduce ex‐
cess electricity production with low investments in thermal storages and also reduce the production at power plants by utilising the extra capacity of the CHP plants. In Fig. 30, a total of nine energy system analyses have been conducted hour‐by‐hour for a year for both types of CHP regulations. For each of the seven integration technologies, these nine energy system analyses are performed.
0 5 10 15 20 25 30 35
0 10 20 30 40 50
Excess production (TWh)
Wind power production (TWh)
Open energy system
Ref. CHP reg.
Ref. no CHP reg.
Fig. 30, Wind power production and excess electricity production in an open energy system analysis of the reference energy system with and without the regulation of CHP plants.
The second of the two types of energy system analyses, i.e. regulation strategy 2), builds on the first analyses. However, here any excess electricity production is converted or avoided;
first, by replacing CHP production by boilers in the district heating systems and, secondly, by stopping wind turbines. The import/export is of course zero, as it is a closed system. The entire primary energy supply (PES) excl. the RES of the system is presented.
The result of such analyses represents a closed energy system and is illustrated in Fig.
31.The x axis shows the wind production and the y axis illustrates the PES excl. the RES of the entire energy system. The less PES excl. the RES, the more flexible and fuel‐efficient is the energy system. In Fig. 31, the same two analysis systems with and without heat storage are presented. Again, it can be seen that the first step is to introduce heat storage in order to increase the production potential of CHP plants at times with a low share of RES, instead of using boilers to supply heat at times with a high RES share. The heat storage also in‐
creases the opportunity to replace the production at power plants with CHP if the capacity is available. Again, a total of nine energy system analyses have been conducted hour‐by‐
hour for a year for both types of CHP regulation. These nine energy system analyses have been performed for each of the seven integration technologies analysed in this chapter.
The advantage of presenting PES excl. RES instead of PES incl. RES is the fact that such re‐
sults can reveal the ability of a technology to utilise RES, such as wind power, to efficiently replace fuels in power plants, CHP, boilers and internal combustion engines.
235 240 245 250 255 260 265 270 275 280 285
0 10 20 30 40 50
PES excl. wind (TWh)
Wind power production (TWh)
Closed energy system
Ref. CHP reg.
Ref. no CHP reg.
Fig. 31, Primary energy supply (PES) in a closed energy system analysis of the reference energy system with and without the regulation of CHP plants.