Smart Heat Storage for solar heating systems Simon Furbo Department of Civil Engineering Technical University of Denmark Brovej – bygning 118 DK-2800 Kgs. Lyngby Denmark Email: [email protected]

Source:2 Common Vision for the Renewable Heating & Cooling sector in Europe European Technology Platform on Renewable Heating and Cooling

Renewables Potentials 3

Denmark 2050: All fossil fuels phased out - 2035: All heat and electricity from renewables

Wind energy: 2014, first 6 months: 41% of electricity consumption 2020: 50 % of increased electricity consumption (incl. transport, heat pumps, …) Solar heating: 2030: 15% of decreased heating demand 4 of decreased heating demand - 80% of this by solar heating plants & 20% individual systems 2050: 40%

Solar heating systems must have a good interplay with liberal electricity market Problem: As renewable electricity production increases: • mismatch of production and load will increase • dynamics of the elctricity price will increase Nord Pool Weekly 2012 70 60 EUR/MWh (DK)

Eur/MWh

50

EUR/MWh (NO)

40 30

Poly. (EUR/MWh (DK))

20

Poly. (EUR/MWh (NO))

10 0

0

20

40

Week No

5

60

Interplay with liberal electricity market Solution: Combined technologies and smart heat storage interacting with the electricity grid …

Heat Pum p

CHP gasmoto r Backup boiler on biomass

6

Load/usage

Benefits from combining technologies and using heat storage

H P

CH P Boile r

Load/us age

Solar:  Produce free heat Heat pump:  Produce cheap heat  Fast capacity regulation (load)  earn money  Reduce storage volume 7

CHP:  Produce valuable electricity  earn money  Fast capacity regulation (prod.)  earn money Smart heat storage:  Gives the flexibility  Makes the combinations of technologies possible

Danmark west, 2007 - from Nordpool

8

Solar heating plant - principle Heat exchanger

Forbrugere Consumers

Solfangerfelt Solar collector field

9

District heating boiler plant

Solar heating plants

Marstal 33365 m²

Ulsted 5012 m²

Dronninglund 37573 m²

Jægerspris 13405 m² 10

Total solar collector area of Danish solar heating plants

600000

Collector area, m²

500000

400000

300000

200000

100000

0

2005 11

2006

2007

2008

2009

Year

2010

2011

2012

2013

2014

Interaction with dynamic electricity production Simple solar heating plants with solar fractions of 5-25% are most common so far, collector areas about 10000 m² But it seems also to be cost effictive to go for higher solar fractions/long term heat storage due to: • Simple heat storage technologies • Large heat storages with small heat losses and low costs per volume • Interplay with liberal electricity market • Advantages by combining technologies 12

Cheap storage technology, water pond and borehole storage

No insulation to earth !

Heat capacity per volume: • Water: 4.1 MJ/Km3 • Soil: About 2.7 MJ/Km3

13

Marstal - seasonal heat storage - 75000 m3 water pond

14

15

Dronninglund - seasonal heat storage - 60000 m3 water pond

16

LARGE SYSTEMS  small storage losses & lower specific costs Surface area per volume

Cost per equivalent m3

(Cylinder, Radius = Height)

Investment cost per m³ water equivalent [€/m³]

1,20 1,00 0,80 0,60 0,40 0,20

450 400

Ilmenau

Crailsheim A if

Volume [m3]

1.2  0.1  Factor 12 on surface area/volume (heat loss/storage capacity( 17

100.000

10.000

1.000

-

realised study Tanks Pits BTES ATES

Rottweil Steinfurt (K/W)

350 300 250

Kettmannhausen Hanover Stuttgart Hamburg

200

Bielefeld

150 100

Eggenstein

Berlin-Biesdorf Munich

Chemnitz

Friedrichshafen (HW)

Neckarsulm (1. phase)

50

100

Area / volume [m²/m3]

500

0 100

Potsdam Rostock

1,000

Crailsheim f

10,000

Storage volume in water equivalent [m³]

100,000

Source: SOLITES

500  20  Factor 25 on costs/volume (cost/storage capacity)

•Water ponds under construction: • Vojens: 200000 m3 • Gram: 110000 m3

18

19000 m3 borehole storage in Brædstrup

19

Design and implementation, Brædstrup

20

Design and implementation, Brædstrup

21

Measurements Borehole storage, Brædstrup

Water pond storage, Marstal

Size

19000 m3 soil, corresponding to about 12000 m3 water

75000 m3 water

Prize

240000 euro, coprresponding to about 20 euro/m3 water

2400000 euro, corresponding to 32 euro/m3 water

Maximum storage temperature

50°C

90°C

Heat recovered from heat storage during first year, 2012-2013

44%

18%

38% Heat recovered from heat storage during second year, 2013-2014

65%

22

Individual solar/electric heating system for the future smart energy system Individual solar/electric heating systems with smart heat storages, which can be heated by solar collectors and by electricity in periods with low electricity prices

• Heat is produced by solar collectors and by electric heating elements or a heat pump • Electric heating elements/heat pump if possible only in operation in periods where solar heat can not fully cover heat demand and where the electricity price is low • System equipped with a smart heat storage (variable auxiliary volume) and a smart control system based on prognoses for: – heat demand – solar heat production – electricity price

23

Electricity price, DKK/MWh

24

Denmark west, November 3.-9., 2008

Smart solar tanks for solar heating systems Marketed Solar tank

Smart solar tank

TANK HEATED FROM THE TOP

25

INDIVIDUAL FLEXIBLE TIMER/ENERGY CONTROL SYSTEM

Solar heating systems with smart solar tanks Increased thermal performance by up to 35% due to:  Decreased tank heat loss  Increased solar heat production Further, also additional improved cost efficiency due to:  Use of low electricity price

26

Systems tested side by side

• 9 m² solar collector • 735 l smart solar tank. Auxiliary: One electric heating element, three electric heating elements, heat pump 27 control system - heat content in tank, weather forecast, coming heat demand, coming solar heat production, coming • Smart electricity prices from NORDPOOLSPOT

Solar collector loop & discharge loops

Inlet stratifier Inlet stratifier

Cold and hot water Auxiliary heating principles

3 kW 3 kW

PEX pipe Inlet stratifier

3 kW 28

9 kW HP

Measured results for spring 2013 • Electricity consumption of system with electric heating element(s) = 2.2 x electricity consumption of system with heat pump • Heat price for systems with electric heating element(s) = 2 x Heat price for system with heat pump

Theoretical calculations - results Home owner • Heat price for house: 100% • Heat price for house with 10 m² solar combi system: 70-80% Strongly influenced on policy on tax on electricity: • Heat price for house with 10 m² smart solar heating system with electric heating elements and variable electricity price: 65-75% • Heat price for house with 10 m² smart solar heating system with heat pump and variable electricity price: 35-40% Society • Socio-economic benefit of smart solar heating systems compared with a reference scenario with oil and gas boilers: The total benefit: 2200 - 6100 DKK per system per year

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Conclusions Centralised solar heating systems with smart long term heat stores • Water pond and borehole storages promising technologies for solar heating plants Individual solar heating systems with smart solar heat stores • Individual smart solar heating systems with electric heating elements/heat pump and variable electricity price are more cost-effective than traditional solar heating systems • Individual smart solar heating systems with electric heating elements/heat pump can help integrating wind power in the energy system and contribute to an increased share of renewable energy

Recommendations Increase research, development and demonstration efforts on: • Water ponds • Borehole storages • Individual smart solar/electric heating systems for low energy buildings • Individual smart solar/heat pump systems for normal houses 30

Thank you for your attention

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