Solar Thermal Energy The University of New South Wales The production of packaged solar water heaters has developed into a significant industry in Australia. Domestic and commercial solar hot water collector production in 2004 is likely to exceed 160,000 m 2 and the annual conventional energy displaced by the cumulative installation is greater than 1000 GWh/year. The cumulative area installed up to 2003 is of the order of 1.2M m 2 . Local sales of solar water heaters showed a significant dip in the early 1990’s but have recently expanded significantly partially as a result of the renewable energy credit program. Detailed performance analysis of every solar water heater is now published by The Office of the Renewable Energy Regulator. The impact of this public information has had a significant effect on competition between manufacturers and the requirement that all products in the Renewable Energy Credit program meet AS2712 design requirements has had a significant impact on the quality of solar water heater products. As a result there has been a substantial increase in the range and quality of products now available. This paper reviews design concepts for domestic solar water heaters and summarises new product developments for passive and active solar water heating including •High efficiency flat plate solar collectors •Evacuated tubular collectors •Seasonally biased collectors •Low cost plastic integral solar pre-heaters •Low flow rate system design •Solar preheating with gas boosting •Heat pump water heaters, solar boosted and air source •Freeze protection (required in most parts of Australia) •Photovoltaic water heaters Solar Water Heater Innovations Presented at Enviro – 04 Sydney March 2004
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Solar Thermal Energy The University of New South Wales
The production of packaged solar water heaters has developed into a significant industry in Australia. Domestic and commercial solar hot water collector production in 2004 is likely to exceed 160,000 m2 and the annual conventional energy displaced by the cumulative installation is greater than 1000 GWh/year. The cumulative area installed up to 2003 is of the order of 1.2M m2. Local sales of solar water heaters showed a significant dip in the early 1990’s but have recently expanded significantly partially as a result of the renewable energy credit program. Detailed performance analysis of every solar water heater is now published by The Office of the Renewable Energy Regulator. The impact of this public information has had a significant effect on competition between manufacturers and the requirement that all products in the Renewable Energy Credit program meet AS2712 design requirements has had a significant impact on the quality of solar water heater products. As a result there has been a substantial increase in the range and quality of products now available. This paper reviews design concepts for domestic solar water heaters and summarises new product developments for passive and active solar water heating including •High efficiency flat plate solar collectors•Evacuated tubular collectors •Seasonally biased collectors•Low cost plastic integral solar pre-heaters•Low flow rate system design•Solar preheating with gas boosting•Heat pump water heaters, solar boosted and air source•Freeze protection (required in most parts of Australia)•Photovoltaic water heaters
Solar Water Heater InnovationsPresented at Enviro – 04 Sydney March 2004
Solar Thermal Energy The University of New South Wales
SOLAR WATER HEATER INNOVATIONS
Graham MorrisonSchool of Mechanical Engineering
University of New South Wales
Solar Thermal Energy The University of New South Wales
CONVENTIONAL SOLAR WATER HEATER DESIGNS
• Thermosyphon
Flat-plate collectors with direct connection to a horizontal tank
Solar Thermal Energy The University of New South Wales
CONVENTIONAL SOLAR WATER HEATER DESIGNS
• Thermosyphon
Flat-plate collectors with connection to a horizontal tank through a heat exchanger for freeze protection
Solar Thermal Energy The University of New South Wales
CONVENTIONAL SOLAR WATER HEATER DESIGNS
• Pumped circulation
Frees placement of collectorand tank
Pump controller
Solar Thermal Energy The University of New South Wales
PUMPED CIRCULATION SOLAR WATER HEATERS
Pump controller
Pumped circulation
With freeze protection
Solar Thermal Energy The University of New South Wales
SOLAR BOOSTED HEAT PUMPS
Small refrigerant compressorused to move heat from low temperature solar collector (heat pump evaporator) to high temperature water tank.
Solar Thermal Energy The University of New South Wales
SOLAR BOOSTED HEAT PUMPSHeat pump circuit uses low cost unglazed solar collector (evaporator) and a double walled heat exchanger (condenser) in the water tank
Condenser coil
Cold water
Insulation
Water tank
Hot water
Accumulator
Compressor
Expansion valveEvaporator plates
Solar Thermal Energy The University of New South Wales
INNOVATIONS IN SOLAR WATER HEATER DESIGN
• High efficiency flat plate solar collectors• Evacuated tubular collectors • Seasonally biased collectors• Low flow rate system design• Intelligent control of electric boosting• Solar preheating with gas boosting• Low cost integral plastic solar water heaters• Heat pump water heaters; solar boosted and air source• Freeze protection (required in most parts of Australia)• Photovoltaic water heaters
Solar Thermal Energy The University of New South Wales
SOLAR COLLECTOR EFFICIENCYIMPROVEMENTS
• Improved selective surfaces (sputtering of wide absorber sheets)
• Laser welding of absorber and risers• Anti-reflection coatings of glass• Optimisation of flat plate cover spacing, insulation and
casing design
Solar Thermal Energy The University of New South Wales
SOLAR COLLECTOR EFFICIENCY current products
0.0
0.1
0.2
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0.5
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0.8
0.9
1.0
0 0.02 0.04 0.06 0.08 0.1(Tm-Ta)/G
Effic
ienc
y
G = 800 W/m2
Solar Thermal Energy The University of New South Wales
EVACUATED TUBE SOLAR ABSORBERS(China)
Solar Thermal Energy The University of New South Wales
LARGE SCALE USE OF EVACUATED TUBE SOLAR COLLECTORS
(China)
Large arrays of evacuated tubes for commercial heat systems Full utilization of high rise building roof for
evacuated tube solar water heaters
Solar Thermal Energy The University of New South Wales
U-TUBE HEAT REMOVAL IN EVACUATED TUBES
Fluid in pressurised pipes inserted into evacuated tubes
Solar Thermal Energy The University of New South Wales
EVACUATED TUBE WATER HEATER WITH AIR CIRCULATION
Prototype evacuated tubular collector solar water heater,using air circulation to eliminate stagnation and freezing problems.
Solar Thermal Energy The University of New South Wales
DYNAMIC SWITCHING OF ELECTRIC BOOSTING
• Variable auxiliary boost volume
• Electric booster thermostat setting reduced during periods of good solar input and at night
• User setting of electric boost to match usage patterns
Solar Thermal Energy The University of New South Wales
VARIABLE BOOST VOLUME
Controller
Temperature sensors
Auxiliary element
Auxiliary element
Solar loop connections
Solar loop connections
Fixed volume auxiliary boosting Variable auxiliary volume
Solar Thermal Energy The University of New South Wales
LOW FLOW RATE SYSTEM DESIGN
Component matching has a significant effect on performance
Major factor in both pumped and thermosyphon systems is the concept of “Low Flow” design to maximise thermal stratification in the storage tank.
Solar Thermal Energy The University of New South Wales
STATIONARY REFLECTORS FOR BOOSTING WINTER PERFORMANCE
Solar Thermal Energy The University of New South Wales
WINTER BIASED PERFORMANCE USING MIRRORS
Mirror booster to give winter biased peak performance for low slope installation.
Prototype solar water with stationary mirrors to give winter biased peak performance.
Solar Thermal Energy The University of New South Wales
PACKAGED SYSTEM WITH WINTER BIASED PERFORMANCE
Stationary concentratorsStationary concentrators
Solar Thermal Energy The University of New South Wales
AIR SOURCE HEAT PUMP WATER HEATERS
Solar Thermal Energy The University of New South Wales
FREEZE PROTECTION OPTIONS
Dump valve
Tapered riser tubesCollector loop heat exchanger
Solar Thermal Energy The University of New South Wales
PLASTIC INTEGRAL SOLAR WATER HEATERS
Insulated-tank integral system Fully integrated collector/ tank
Solar Thermal Energy The University of New South Wales
PHOTOVOLTAIC WATER HEATERno plumbing to the roof, no freeze problems
no bank balance!
Photovoltaic array
Auxiliary element
Radiation sensor
Peak power point control by element switching
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