Dispelling the Solar Myth - Evacuated Tube versus
Flat Plate Panels
W illiam Comerford
Sales Manager Ireland
Kingspan Renewables Ltd.
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The Kingspan Group
Energy independent buildings for a sustainable future
Kingspan Renewables Product Areas
Kingspan
Renewables
Division
Kingspan Solar
Kingspan HWS
Kingspan Heat
Pumps
Kingspan Climate
What is Solar Energy
Solar energy is radiant energy produced by
the sun from a process called nuclear
fusion
The energy from the sun acting on the
earth’s surface, over a 15 minute period, is
more then the earth’s total energy
requirement for a year. The amount of
yearly global radiation on a horizontal
surface may reach over 2,200 kWh/m2 in
sunny regions.
In Northern Europe, the values are
943kWh/m2 in London and 990 kWh/m2
in Rosslare, Ireland.
The supply of solar radiation in UK and
Ireland differs by a factor of 10 between
summer and winter, e.g. Rosslare: 6.36
kWh/m2/day in June; 0.64 kWh/m2/day in
December
What is Solar Energy
Global radiation comprises direct and diffuse radiation.
As sunlight passes through the atmosphere, some of it is
absorbed, reflected and scattered by air molecules, clouds
and dust particles, this is known as diffuse radiation.
The portion of radiation that hits the earth’s surface without any
change in direction is known as direct radiation.
In Ireland and UK,
diffused radiation makes
up between 40%
(May) to 80% (December)
of the total solar energy
available in a year.
Why Use Solar Energy?
Solar energy enjoys many environmental and economic
advantages over other forms of energy currently used.
These include:
Environmentally Friendly
•Non-polluting: Solar hot water generation
produces no emissions
• Non-consumptive: The suns radiation is a limitless
resource
• Going ‘Green’ for commercial projects has now become a PR
advantage
Economically Beneficial
•Cost effective: Free energy source
•Immediate and permanent savings
•Technological advancements: Improvement in solar
technologies offer reduced costs and greater efficiency
The amount of Co2 emissions produced to generate the equivalent of 1,836 kWh:
– 0, Natural Gas:180g/kWh, Oil: 238g/kWh, Electricity 459g/kWh
So
W hy Use Solar Energy?
What Factors Effect a Solar Thermal
System?
Orientation (azimuth)
collector
50%
Slope (Inclination)
Collector Area
Storage Volume
DHW Demand
The difference between a collector facing south and a
facing west = circa 20%, a collector facing north produces
less energy
A collector mounted at 90º will collect 20% less energy then a
collector at an angle of 35º
The larger the area the more solar energy available to be
collected. Care should be taken not to oversize the system
The larger the cylinder volume, the larger the thermal store
The larger the demand the higher the solar energy
consumption
What Factors Effect A Solar Thermal System?
•
•
•
•
Is solar a viable energy source in UK and Ireland?
YES!
Ireland’s daily solar irradiation is circa 3 kWh/m2
Equivalent to approx 130 litres of oil per m2 per year
Zone
Average solar radiation on
collector surface (kWh/
M²day
1
2.4 to 3.4
2
3.4 to 4.4
3
4.4 to 5.4
The Hard Facts
Domestic Hot Water (DHW) =
Approx 21% of our Domestic Energy Consumption
As building standards improve and space heating demands reduce, DHW demand will not change
Collector Types
There are 2 main types of solar collectors
•
Flat Plate (Left)
•
Vacuum Tube (Right)
Collector Types - Flat Panel Collectors
Riser
System
Serpentine
System
Collector Types - Flat Panel Collectors
•
What is the effect of cold weather, wind and rain on a Flat Panel Collector?
Hot
Surface
Cold
Surface
Conduction
&
Convection
Losses
Cold Weather, Wind &
Rain has an ADVERSE
effect on
performance on a Flat
Plate collector
Gas
Significant
Thermal
Losses to
The
Environment
Collector Types – Evacuated Tube Collectors
Collector Types – Evacuated Tube Collectors
Hot Surface
Cold Surface
Radiation Losses
Minimal Thermal
Losses to The
Environment via
Thermal Losses :
Cold Weather,
Wind & Rain
DOES NOT
effect
performance on
a vacuum tube
collector
Evacuated Tube
Collector: Pressure < 1 x
10-6 mbar
To
Provide Thermal
Insulation
Vacuum is THE best insulator
available
- Minimises Thermal Losses
Collector Types – Advantages/Disadvantages
Vacuum Tubes
Advantages
•
Higher solar yield than flat plate collectors with the same absorber area.
•
30% more effective
•
Little thermal loss (only through some radiation)
•
As the tube is sealed, dirt or moisture cannot get into the collector
•
Works in cold, windy and humid conditions
•
Individual tubes can be rotated to optimise ideal orientation
•
High temperatures can be achieved
•
Some people like the aesthetics of tubes
Disadvantages
•
Cost !
•
Not easily integrated into the fabric of the building (e.g. roof or facade
integrated)
•
Some people do not like the aesthetics of the tubes
Collector Types – Advantages/Disadvantages
Flat Plates
Advantages
•
Lower cost
•
Can be more easily integrated with the fabric of the building (roof integrated /
facade integrated)
Disadvantages
•
Lower performance through conduction, convection and radiation therefore you
need more surface area of collector
•
Higher wind load requirements (they act like a sail and catch the wind)
•
Glass and absorber can get dirty and effect performance
•
Needs more maintenance
•
Higher volume content equated to larger component sizes. i.e. expansion vessel
•
Isn't as efficient in lower light
Product Selection
Most applications operate at tm-ta = 50degC
Basic Tube Design
Vacuum Tubes – Durability
Always look for the Hail Impact Test Report EN12975
The test is to fire a 25mm ice ball at 50mph at the tubes to ensure durability
System Simulation Comparisons
2m2 Evacuated Tube System
System Simulation Comparisons
2m2 Flat Plate Panel System
Stagnation
The occurrence of stagnation in a solar system should be avoided.
Continuous temperatures in excess of 170°C will cause the degrading of the Tyfocor solar
solution and degrade its inhibitor properties, this is evident by the solution turning a brown
colour (see solution on left in picture below).
The solution on the right is the delivered state of the Tyfocor solution, the beaker on the left
contains a solution that has been in stagnation for long periods above 170°C.
The solution should be tested annually using a refractometer and ph test paper.
Stagnation in a solar system can be caused by a number of reasons such as:
• Oversized systems – correct sizing methods have been addressed
in previous chapters
• Undersized expansion vessel – correct sizing methods have been
addressed in previous chapters
• Air locks or leaks in the system
• Prolonged periods of low hot water demand.
Commercial Solar Applications
System Solutions – Swimming Pools
One of the best applications for solar thermal due to low demand temps.
High solar fractions achievable on pools in Ireland circa 65-70%
Large System Solutions
Large System Solutions
Process Applications
System Solutions – Hospitals
System Solutions – Tourism & Agriculture
System Solutions – Alternative Uses
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