Demand side flexibility for solar and wind power integration

Jyri Salpakari

Research output: ThesisDoctoral ThesisCollection of Articles


A major increase in the use of solar and wind energy in electricity production is envisioned to limit CO2 emissions, along with other low-carbon energy sources, as well as energy efficiency and electrification of heating, cooling, and transportation. This requires increasing flexibility in power systems, warranting the searching for enhanced flexibility in all possible sources. Wind energy has already lowered electricity market prices, calling for flexibility in the short term.This dissertation investigates the technical and economic potential of demand side flexibility for managing the variability of solar and wind production. To this end, three new mathematical models capable of optimal control are presented. The first model considers a heat pump with thermal storage, batteries, and shiftable appliances in a building with photovoltaics (PV); the second looks at power-to-heat conversion with thermal storage in district heating and shiftable loads in a city with PV and wind; and the third model focuses on space heating with heat pumps and electric vehicles in houses with PV. A case study with the first model on a Finnish low-energy house showed a 13-25 % cost decrease and an 8-88 % grid feed-in decrease with cost-optimal control and hourly spot market-based pricing, compared to inflexible reference control with a constant price for bought electricity. The exact values depend on the PV capacity and chosen flexibility sources. Limiting grid feed-in to zero decreased the energy efficiency of the control. The heat pump with storage and batteries provided more flexibility than shiftable appliances. Helsinki, Finland was studied with the second model. For a VRE scheme providing circa 50 % of the electricity consumption of the city through self-consumption, power-to-heat with thermal storage could absorb all the surplus VRE production. Shiftable loads significantly reduced the net load magnitude. Cost-optimally controlled power-to-heat with heat pumps and thermal storage as well as load shifting with electric heating and commercial refrigeration were found to be profitable investments.Between 1 and 10 Swedish net zero energy houses were investigated with the third model, resulting in 8-33% annual electricity cost savings per household with various system configurations, along with significant increases in PV self-consumption. The cost of additional battery degradation significantly decreases the added value of bi-directional vehicle-to-grid compared to flexible smart charging only.The thesis shows that power-to-heat in district heating, distributed electric heating, commercial refrigeration, batteries, and electric vehicles are effective demand side flexibility sources. They should be considered for flexibility provision in power systems with solar and wind production.
Translated title of the contributionKysyntäjousto aurinko- ja tuulisähkön integroinnissa
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Lund, Peter, Supervising Professor
  • Lund, Peter, Thesis Advisor
Print ISBNs978-952-60-7326-2
Electronic ISBNs978-952-60-7325-5
Publication statusPublished - 2017
MoE publication typeG5 Doctoral dissertation (article)


  • variable renewable energy
  • demand side management
  • power-to-heat
  • energy system flexibility
  • optimal control


Dive into the research topics of 'Demand side flexibility for solar and wind power integration'. Together they form a unique fingerprint.

Cite this