Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE credits
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.
2018.