Advanced

Utvärdering av solfönster, en integration av solhybrider och solskydd

Johansson, Tobias (2005) In EBD-R--05/8
Abstract
Solar energy is a renewable energy source which in the long term is important to develop

because the usage does not effect the environment in a negative way.

Increased energy exchange and cheaper production costs for solar collectors and solar cells

are main factors in making the solar energy commercially successful in the future.

Small scale solar collector systems are most common today because the heat storage time is

very limited. The heat is mostly stored in short time storage in an accumulator tank.

Large scale solar collector systems usually deliver the heat directly to the district heating net,

but there are also attempts to store solar heat in season storage.

... (More)
Solar energy is a renewable energy source which in the long term is important to develop

because the usage does not effect the environment in a negative way.

Increased energy exchange and cheaper production costs for solar collectors and solar cells

are main factors in making the solar energy commercially successful in the future.

Small scale solar collector systems are most common today because the heat storage time is

very limited. The heat is mostly stored in short time storage in an accumulator tank.

Large scale solar collector systems usually deliver the heat directly to the district heating net,

but there are also attempts to store solar heat in season storage.

The project EEBIS, energy efficiency constructed in society, is run by Lund Institute of

Technology and some construction and installation companies.

The result of this project is the building “Solgården” in Älvkarleby Sweden, a house

constructed to use the sun heat in the best possible way. One part of this project is the “solar

window” and the intention is to install 18 m2 solar windows at Solgården. To be able to

evaluate the performance of the solar window a solar window prototype was constructed.

The main purpose of this diploma work is to evaluate the heat insulating abilities but also to

evaluate the solar energy exchange of the solar window prototype.

The solar window is a new way of integrating solar energy in buildings combining solar

collectors, solar cells and sun shield in a window. The solar window has got movable

reflectors and solid solar hybrids mounted inside a double glass.

The reflectors concentrate the sunlight on the solar hybrids to make the expensive solar

collectors and solar cell areas smaller.

The reflectors are supposed to be closed on hot days (sun radiation > 300 W/m2) to reflect the

sunlight on the solar hybrids and then generate electricity and heat and at the same time work

as a sun shield to the large solar window area. On cold days (sun radiation < 50 W/m2) the

closed reflectors are used as an insulating wall. That is why the solar window construction has

to be well insulated, to avoid the heat in the house getting lost through the solar window.

In other cases the solar windows are supposed to be open to give passive sun heat to the

house. When the heat exchange, from the solar collectors, is low it can be complemented with

a pellet pan.

The construction is unique because it functions as a solar hybrid and a sun shield at the same

time it is installed in a window. This is based on the glass quality.

The glass, which is the most important component in a solar collector, has got the unique

quality to let the suns short wave ultraviolet radiation through and to close in the long wave

infrared radiation.

The solar window can be controlled automatically, through a light sensor, or manually.

The manual control is important in case they are installed in houses but the automatic control

is preferable because it optimizes the solar energy exchange.

The heat insulated abilities increased radically when the reflectors were closed.

The U-value decreased from 2,4 W/m²K, with open reflectors, to 1,3 W/m²K, with closed

reflectors. We hoped to reach the U-value of an insulated wall with an approximated U-value

of 0,5 W/m²K, this of course depending on the insulation and thickness of the wall.

6

The heat insulating parts of the solar window are the double glass and the five reflectors

insulated with four centimetres of polystyrene. Thicker insulation in the reflectors was not

interesting because then the aesthetic look was not pleasant. This, however, might be

interesting if the solar windows are installed in other places than houses, which was the

purpose from the beginning. One way to increase the heat insulating abilities of the solar

window is to install a double glass with better insulation as long as the sunlight transmission

does not decrease. These double glasses are probably much more expensive. The possibilities

to decrease the U-value by insulating the solar window in other ways are fairly low because of

the movable parts in the construction.

A solar window can yearly contribute 360 kWh/m² of solar energy, including both active and

passive solar energy, and will approximately cost SEK 2500 per m² with industrial

production. The solar energy will cost SEK 0.69 per kWh calculated to be paid over a ten year

period. The life time of the solar window is longer than ten years, probably up to thirty years.

The running costs that are normally approximated to 10 % of the investment cost will be

added.

A normal two glass window heading south yearly transmits 609 kWh/m² and the sun window

yearly transmits 368 kWh/m² given that the reflectors are closed to work as sun shields when

the sun radiation exceeds 300 W/m². This means that the solar window decreases the sun light

in pouring by yearly shading away 241 kWh/m² in comparison with a two glass window.

The simulation in Minsun was used to approximate the active solar energy supply for every

hour over a year for Stockholm city. The simulation shows that the sun window yearly

contributes with 234 kWh/m² active solar energy, where 79 kWh/m² is sun electricity and 155

kWh/m² is sun heat. In the real case approximately 180 kWh/m2 active solar energy will be

contributed, where 60 kWh/m2 is solar electricity and 120 kWh/m2 is sun heat.

Simulation in ParaSol was used to approximate the passive sun heat contributed through open

reflectors and losses through closed reflectors. The total passive sun heat contribution is

yearly approximated to 210 kWh/m². Where approximately 180 kWh/m2 yearly contributes to

the house in the real case.

18 m2 solar windows at Solgården in Älvkarleby approximately give 6500 kWh/year, which

gives 26 % coverage of the total energy need at Solgården. Provided that the total energy need

is 25000 kWh/year. At Solgården the remaining heat will come from an already installed

pellet pan and because the solar cells do not cover the electricity need electricity will also be

installed.

Enlargement of the solar window area will in this case not be meaningful because the solar

windows give 100 % coverage during the summer months which the dimension is based on.

Enlargement of the solar window area means that you risk to get a lot of surplus heat during

the summertime and only a small enlargement of the total heat need coverage. (Less)
Please use this url to cite or link to this publication:
author
publishing date
type
Book/Report
publication status
published
subject
in
EBD-R--05/8
pages
48 pages
publisher
[Publisher information missing]
ISBN
91-85147-09-5
language
Swedish
LU publication?
no
id
04098d17-4116-4c31-b9f7-8c03b8c288b2 (old id 1027957)
alternative location
http://www.ebd.lth.se/fileadmin/energi_byggnadsdesign/images/Publikationer/Exjobb_Tobias_J.pdf
date added to LUP
2008-05-13 12:05:21
date last changed
2016-06-29 09:05:40
@misc{04098d17-4116-4c31-b9f7-8c03b8c288b2,
  abstract     = {Solar energy is a renewable energy source which in the long term is important to develop<br/><br>
because the usage does not effect the environment in a negative way.<br/><br>
Increased energy exchange and cheaper production costs for solar collectors and solar cells<br/><br>
are main factors in making the solar energy commercially successful in the future.<br/><br>
Small scale solar collector systems are most common today because the heat storage time is<br/><br>
very limited. The heat is mostly stored in short time storage in an accumulator tank.<br/><br>
Large scale solar collector systems usually deliver the heat directly to the district heating net,<br/><br>
but there are also attempts to store solar heat in season storage.<br/><br>
The project EEBIS, energy efficiency constructed in society, is run by Lund Institute of<br/><br>
Technology and some construction and installation companies.<br/><br>
The result of this project is the building “Solgården” in Älvkarleby Sweden, a house<br/><br>
constructed to use the sun heat in the best possible way. One part of this project is the “solar<br/><br>
window” and the intention is to install 18 m2 solar windows at Solgården. To be able to<br/><br>
evaluate the performance of the solar window a solar window prototype was constructed.<br/><br>
The main purpose of this diploma work is to evaluate the heat insulating abilities but also to<br/><br>
evaluate the solar energy exchange of the solar window prototype.<br/><br>
The solar window is a new way of integrating solar energy in buildings combining solar<br/><br>
collectors, solar cells and sun shield in a window. The solar window has got movable<br/><br>
reflectors and solid solar hybrids mounted inside a double glass.<br/><br>
The reflectors concentrate the sunlight on the solar hybrids to make the expensive solar<br/><br>
collectors and solar cell areas smaller.<br/><br>
The reflectors are supposed to be closed on hot days (sun radiation &gt; 300 W/m2) to reflect the<br/><br>
sunlight on the solar hybrids and then generate electricity and heat and at the same time work<br/><br>
as a sun shield to the large solar window area. On cold days (sun radiation &lt; 50 W/m2) the<br/><br>
closed reflectors are used as an insulating wall. That is why the solar window construction has<br/><br>
to be well insulated, to avoid the heat in the house getting lost through the solar window.<br/><br>
In other cases the solar windows are supposed to be open to give passive sun heat to the<br/><br>
house. When the heat exchange, from the solar collectors, is low it can be complemented with<br/><br>
a pellet pan.<br/><br>
The construction is unique because it functions as a solar hybrid and a sun shield at the same<br/><br>
time it is installed in a window. This is based on the glass quality.<br/><br>
The glass, which is the most important component in a solar collector, has got the unique<br/><br>
quality to let the suns short wave ultraviolet radiation through and to close in the long wave<br/><br>
infrared radiation.<br/><br>
The solar window can be controlled automatically, through a light sensor, or manually.<br/><br>
The manual control is important in case they are installed in houses but the automatic control<br/><br>
is preferable because it optimizes the solar energy exchange.<br/><br>
The heat insulated abilities increased radically when the reflectors were closed.<br/><br>
The U-value decreased from 2,4 W/m²K, with open reflectors, to 1,3 W/m²K, with closed<br/><br>
reflectors. We hoped to reach the U-value of an insulated wall with an approximated U-value<br/><br>
of 0,5 W/m²K, this of course depending on the insulation and thickness of the wall.<br/><br>
6<br/><br>
The heat insulating parts of the solar window are the double glass and the five reflectors<br/><br>
insulated with four centimetres of polystyrene. Thicker insulation in the reflectors was not<br/><br>
interesting because then the aesthetic look was not pleasant. This, however, might be<br/><br>
interesting if the solar windows are installed in other places than houses, which was the<br/><br>
purpose from the beginning. One way to increase the heat insulating abilities of the solar<br/><br>
window is to install a double glass with better insulation as long as the sunlight transmission<br/><br>
does not decrease. These double glasses are probably much more expensive. The possibilities<br/><br>
to decrease the U-value by insulating the solar window in other ways are fairly low because of<br/><br>
the movable parts in the construction.<br/><br>
A solar window can yearly contribute 360 kWh/m² of solar energy, including both active and<br/><br>
passive solar energy, and will approximately cost SEK 2500 per m² with industrial<br/><br>
production. The solar energy will cost SEK 0.69 per kWh calculated to be paid over a ten year<br/><br>
period. The life time of the solar window is longer than ten years, probably up to thirty years.<br/><br>
The running costs that are normally approximated to 10 % of the investment cost will be<br/><br>
added.<br/><br>
A normal two glass window heading south yearly transmits 609 kWh/m² and the sun window<br/><br>
yearly transmits 368 kWh/m² given that the reflectors are closed to work as sun shields when<br/><br>
the sun radiation exceeds 300 W/m². This means that the solar window decreases the sun light<br/><br>
in pouring by yearly shading away 241 kWh/m² in comparison with a two glass window.<br/><br>
The simulation in Minsun was used to approximate the active solar energy supply for every<br/><br>
hour over a year for Stockholm city. The simulation shows that the sun window yearly<br/><br>
contributes with 234 kWh/m² active solar energy, where 79 kWh/m² is sun electricity and 155<br/><br>
kWh/m² is sun heat. In the real case approximately 180 kWh/m2 active solar energy will be<br/><br>
contributed, where 60 kWh/m2 is solar electricity and 120 kWh/m2 is sun heat.<br/><br>
Simulation in ParaSol was used to approximate the passive sun heat contributed through open<br/><br>
reflectors and losses through closed reflectors. The total passive sun heat contribution is<br/><br>
yearly approximated to 210 kWh/m². Where approximately 180 kWh/m2 yearly contributes to<br/><br>
the house in the real case.<br/><br>
18 m2 solar windows at Solgården in Älvkarleby approximately give 6500 kWh/year, which<br/><br>
gives 26 % coverage of the total energy need at Solgården. Provided that the total energy need<br/><br>
is 25000 kWh/year. At Solgården the remaining heat will come from an already installed<br/><br>
pellet pan and because the solar cells do not cover the electricity need electricity will also be<br/><br>
installed.<br/><br>
Enlargement of the solar window area will in this case not be meaningful because the solar<br/><br>
windows give 100 % coverage during the summer months which the dimension is based on.<br/><br>
Enlargement of the solar window area means that you risk to get a lot of surplus heat during<br/><br>
the summertime and only a small enlargement of the total heat need coverage.},
  author       = {Johansson, Tobias},
  isbn         = {91-85147-09-5},
  language     = {swe},
  pages        = {48},
  publisher    = {ARRAY(0xb92cc98)},
  series       = {EBD-R--05/8},
  title        = {Utvärdering av solfönster, en integration av solhybrider och solskydd},
  year         = {2005},
}