THERMAL STORAGE ENABLING DISTRICT HEATING PLANTS TO SERVE AS FLEXIBILITY PROVIDERS IN THE ENERGY SYSTEM

Transcription

1 THERMAL STORAGE ENABLING DISTRICT HEATING PLANTS TO SERVE AS FLEXIBILITY PROVIDERS IN THE ENERGY SYSTEM Dr.ing. Monica Havskjold, Statkraft AS R&D Symposium District Heating Days, Fornebu, October 2014

2 Motivation Demand for system flexibility More intermittent power production Thermal power production reduced New electricity demand, e.g. electric vehicles Danish DH plants supply flexibility All district heating plants equipped with thermal storage El-boilers (400 MW) installed in district heating plants - Only allowed in plants with CHP (Combined heat and power) Flexibility - High el-price: Produce electricity - Low el-price: Consume electricity - Supply system services (primary reserve etc.) 2

3 Storage Why storage? System perspective: Enable more intermittent renewables in the energy system Wind power plant perspective: Decrease imbalance cost, more operating hours District heating perspective: improved operation of base load, new business Relevant options for storage Batteries: Mature, most suitable for short term storage (sec/min/hours) Thermal storage: Mature, low cost relative to other options, suitable for intermediate (hours/days) to long term (months) Chemical storage *) : Mature, most suited for constant operation, technologies rapidly developing *) E.g. production of hydrogen by electrolysis 3

4 Infrastructures enabling flexibility Enabling more renewable electricity Well known technologies, but not all widely deployed in Norway Power to heat (P2H): Heat pumps and el-boilers use surplus electricity Storages: Optimise heat production, including from heat pumps/el-boilers CHP: Producing electricity Heat pumps and el-boilers are well known in Norwegian district heating systems Few district heating plants with thermal storage Few CHP plants in Norwegian district heating Storages Heat Pumps El-boilers CHP 4

5 5

6 The analysed district heating plant Heat demand - 54 GWh/year - Load profiles based on actual plant - 23 MW peak demand Installations - 10 MW + 5 MW biomass boilers (wood chips) for base load (min. load 20%) - 2*10 MW natural gas boilers for peak load and backup 6

7 Modelling of storage Assumptions - Only heat from biomass boilers allowed to be stored - Temperature difference 40 K, maximum temperature below 100 C - Heat loss 10 % Analysis - What is the optimal storage size? - Varied from 500 m 3 (24 MWh) to 5000 m 3 (240 MWh). - Is it profitable to invest in new thermal storage? 7

8 Results, operation of production units No storage Availability of storage enables improved utilisation of base load units Very large storage: Demand for natural gas boilers almost eliminated 500 m 3 storage 5000 m 3 storage 8

9 Årlig varmeproduksjon (GWh/år) Brenselkostnader (MNOK/år) Thermal storage reduce use of natural gas Utilisation of biomass increases with storage size Fuel cost declines with storage size El-kjel Gasskjel 2 Gasskjel LPG Biomass Biokjel 5 MW Biokjel 10 MW Saving pr year Størrelse, lager (m3) Thermal storage volume (m3) A storage of 2000 m3 is ideal, not much extra to gain by increasing size 9

10 Cost of thermal storages not easily accessible Investment costs vary Published international cost data Choice of technology - Atmospheric - Pressurised In- and outlet temperatures in district heating net ( T) Size - Economy of scale Availability of sites m /m NOK/m Tot cost (MNOK)

11 MNOK Preliminary results indicate that thermal storage is profitable, further analyses required Cost savings (fuel) > yearly capital cost of storage Simple pay back time 2,5 years for optimal storage size Thermal storage volume (m3) Saving pr year Yearly capital cost Assumptions: WACC of 12%, life time of thermal storage 15 years, no operational cost included Year Thermal storage volume (m3) 11

12 12

13 Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov El demand (MWh/month) Spot price(nok/kwh) El demand (MWh/month) Spot price(nok/kwh)) El-demand (MWh/month) Spot price (NOK/MWh Flexible operation of el-boilers highly dependent on design of grid tariff PRELIMINARY RESULTS Grid fee 0 NOK/MWh 400 Grid fee 200 NOK/MWh Grid fee prop. with spot price Jan Mar May Jul Sep Nov 0 13

14 THANK YOU