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: sf@byg.dtu.dk

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

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Renewables Potentials

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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 2050: 40% of decreased heating demand - 80% of this by solar heating plants & 20% individual systems

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0

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60

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0 20 40 60

Eur/

MW

h Week No

Nord Pool Weekly 2012

EUR/MWh(DK)

EUR/MWh(NO)

Poly.(EUR/MWh(DK))

Poly.(EUR/MWh(NO))

Problem: As renewable electricity production increases: • mismatch of production and load will increase • dynamics of the elctricity price will increase

Solar heating systems must have a good interplay with liberal electricity market

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Interplay with liberal electricity market

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

Heat Pum

p CHP

gasmotor

Backup boiler on biomass

Load/usage

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Solar: Produce free heat

Heat pump: Produce cheap heat Fast capacity regulation

(load) earn money Reduce storage volume

CHP: Produce valuable

electricity earn money Fast capacity regulation

(prod.) earn money Smart heat storage: Gives the flexibility Makes the combinations

of technologies possible

Benefits from combining technologies and using heat storage

HP CH

P

Boiler

Load/usage

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Danmark west, 2007 - from Nordpool

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Solar heating plant - principle

Forbrugere Solfangerfelt Consumers

District heating boiler plant

Solar collector field

Heat exchanger

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Jægerspris 13405 m²

Ulsted 5012 m²

Dronninglund 37573 m²

Marstal 33365 m²

Solar heating plants

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Total solar collector area of Danish solar heating plants

0

100000

200000

300000

400000

500000

600000

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

Col

lect

or a

rea,

m²

Year

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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

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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

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Marstal - seasonal heat storage - 75000 m3 water pond

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Dronninglund - seasonal heat storage - 60000 m3 water pond

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0,20

0,40

0,60

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1,00

1,20

100

1.0

00

10.

000

100

.000

Are

a /

vol

um

e [m

²/m

3]

Volume [m3]

Surface area per volume (Cylinder, Radius = Height)

LARGE SYSTEMS small storage losses & lower specific costs

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

0

50

100

150

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250

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450

500

100 1,000 10,000 100,000

Inve

stm

ent c

ost p

er m

³ wat

er e

quiv

alen

t [€/

m³]

Storage volume in water equivalent [m³]

realisedstudyTanksPitsBTESATES

Neckarsulm(1. phase)

Rottweil

Stuttgart

Hamburg

Friedrichshafen (HW)

Berlin-Biesdorf

Potsdam

Chemnitz

Rostock

Steinfurt (K/W)

Bielefeld

Hanover

Ilmenau

Kettmann-hausen

Crailsheimf

Munich

CrailsheimA if

Eggenstein

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

Source: SOLITES

Cost per equivalent m3

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•Water ponds under construction:

• Vojens: 200000 m3

• Gram: 110000 m3

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19000 m3 borehole storage in Brædstrup

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Design and implementation, Brædstrup

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Design and implementation, Brædstrup

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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%

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

38% 65%

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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

Individual solar/electric heating system for the future smart energy system

• 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

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Electricity price, DKK/MWh Denmark west, November 3.-9., 2008

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Smart solar tanks for solar heating systems Marketed Solar tank Smart solar tank

TANK HEATED FROM THE TOP INDIVIDUAL FLEXIBLE TIMER/ENERGY CONTROL SYSTEM

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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

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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 • Smart control system - heat content in tank, weather forecast, coming heat demand, coming solar heat production, coming

electricity prices from NORDPOOLSPOT

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Inlet stratifier Inlet

stratifier

3 kW

3 kW

3 kW

Inlet stratifier

HP 9 kW

PEX pipe

Auxiliary heating principles

Solar collector loop & discharge loops

Cold and hot water

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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

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Thank you for your attention