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A Feasibility Study of Solar-Assisted District Heating in Torsång
Dalarna University, School of Technology and Business Studies, Energy Technology.
Dalarna University, School of Technology and Business Studies, Energy Technology.
2018 (English)Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

Nowadays, using renewable energy, especially solar, is an expanding trend in the Nordic

countries. In the past few years, the Europian Union has issued energy efficiency directives

[1] that obligated its member countries to involve 50 % of renewable energies in the

district heating (DH) networks. This opens the door for the integration of solar energy in

the existent heat generation plants.

Borlänge Energi AB, a municipal energy company, owns and operates a DH plant and

network in Torsång; a small-community village outside Borlänge, in Dalarna County,

Sweden. The plant generates the required heat using conventional energy boilers fueled by

wood pellets, grid electricity, and oil. The company suggested using the nearby empty land,

owned by the municipality, for installing a solar thermal collector field.

The thesis aims at doing a feasibility study of the possible integration of a solar thermal

collector field to the existent DH plant in Torsång. The goal is to replace the oil boilers

with solar energy and to estimate the amount of fuel and emissions that can be saved and

their effects on economics.

To achieve the appointed tasks, a planned strategy was developed. After visiting the site

and collecting all relevant data, the missing hourly load was calculated. Thumb rules were

used for system sizing. The Polysun simulation software is used to model and simulate the

proposed system. Two collector models from the same manufacturer were tested. The

effects of lowering the DH temperature and changing the pellet boiler shut-down period

were investigated. A sensitivity analysis of the solar fraction was conducted to provide

different sizing options. In the end, an economic evaluation of the proposed solutions was

made.

The results revealed that, for all cases, the oil boilers could be successfully replaced saving

0.6 m3 of diesel oil and 1.1 ton of CO2 emissions annually. A solar fraction of around 35 %

was achieved. Shutting down the pellet boiler in the three summer months was proposed

which reduced its operating time. Consequently, the pellet boiler energy production and

the fuel consumption reduced by around 36 %. While its CO2 emissions are mitigated by

26 %.

The project, from the economic perspective, is showing a competitive value of LCOH

(between 386 and 423 SEK/MWh) which is lower than the actual cost of the produced

heat by the plant (500 SEK/MWh). The payback period is quite reasonable with values

between 24 and 37 years, depending on the chosen solution. Governmental subsidies are

not taken into consideration in the economic analysis, so the proposed values represent an

upper boundary, which can be lowered whenever any incentive will be granted to the

project.

The proposed system makes room for two possible solutions: the first allows to shut-down

the pellet boiler for the whole summer, thus giving more flexibility for the maintenance of

it, benefits in terms of fuel and related emissions saved, but increasing the electricity

consumption. The second solution, instead, is offering a shorter shut-down time, but with

more monetary benefits.

Place, publisher, year, edition, pages
2018.
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:du-28197OAI: oai:DiVA.org:du-28197DiVA, id: diva2:1232960
Available from: 2018-07-13 Created: 2018-07-13

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CiteExportLink to record
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Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
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  • nn-NB
  • sv-SE
  • Other locale
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Output format
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  • asciidoc
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