SOLAR THERMAL SYSTEMS

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RENEWABLE ENERGY SYSTEMS

SOLAR ENERGY (3)

SOLAR THERMAL SYSTEMS

Prof. Ibrahim El-moher Prof. Ahmed Anas

Lec. 4

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 Photovoltaic (PV)

 Solar cell

 Solar thermal energy

 Solar water heater

 Solar cooling

 Solar water pumping

 Concentrated Solar Power

Application of Solar Energy

Types of Solar Energy Applications

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Solar Water Heating Collectors Global Capacity, 2000–2013

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Solar Water Heating Collectors Global

Capacity, Shares of Top 10 Countries, 2012

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Solar Water Heating Collector Additions, Top 10 Countries for Capacity Added, 2012

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Concentrating Solar Thermal Power Global Capacity, by Country or Region, 2004–2013

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Solar Thermal Energy Systems

How to use solar thermal energy Types of solar collectors

Solar water heating Solar thermal cooling

Solar water pumping

Concentrated Solar Power (CSP)

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How to Use Solar Thermal Energy

Solar Thermal Energy

working fluid

thermal energy

Solar Radiation Solar Thermal Energy

Solar collector Working fluid

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Types of Solar Collectors

 Collectors and working temperature

Low temperature

Medium temperature

High temperature



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Flat-plate collector

 Use both beam and diffuse solar radiation, do not

require tracking of the sun, and are low-maintenance, inexpensive and mechanically simple.

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Flat-plate collector

 Glazed collector ^ Unglazed collector

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Flat-plate collector

 Main losses of a basic flat-plate collector during angular operation

Weiss, Werner, and Matthias Rommel. Process Heat Collectors. Vol. 33, 2008.

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Evacuated tube collector

 A collector consists of a row of parallel glass tubes.

 A vacuum inside every single tube extremely reduces conduction losses and eliminates convection losses.

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Parabolic trough collector

 Consist of parallel rows of mirrors (reflectors) curved in one dimension to focus the sun’s rays.

 All parabolic trough plants currently in commercial

operation rely on synthetic oil as the fluid that transfers heat from collector pipes to heat exchangers.

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Linear Fresnel reflector

 Approximate the parabolic trough systems but by using long rows of flat or slightly curved mirrors to reflect the sun’s rays onto a downward- facing linear, fixed receiver.

 Simple design of flexibly bent mirrors and fixed receivers

requires lower investment costs and facilitates direct steam

generation.

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Parabolic dish reflector

 Concentrate the sun’s rays at a focal point propped above the centre of the dish. The entire apparatus tracks the sun, with the dish and receiver moving in tandem.

 Most dishes have an

independent engine/generator (such as a Stirling machine or a micro-turbine) at the focal point.

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Heliostat field collector

 A heliostat is a device that includes a plane mirror

which turns so as to keep reflecting sunlight toward a predetermined target.

 Heliostat field use hundreds or thousands of small

reflectors to concentrate the sun’s rays on a central

receiver placed atop a fixed tower.

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Solar Water Heater

 Most popular and well developed application of solar thermal energy so far

 Low temperature applications

(Mainly using flat plate collector or evacuate tube collector)

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Solar Water Heater

Direct (open loop) Indirect (close loop)

Passive

Active

User

(Thermosyphon)

User User

Heat exchanger

User 19

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“Solar Thermal Action Plan for Europe”, ESTIF, 2007

Solar Water Heater

 Residential hot water system

 Hot water production

 House warming

 Large-scale system

 Dormitory hot water

 Swimming pool

 Industrial process heating

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Solar Water Heater

 Industrial process heating

 In EU, 2/3 of the industrial energy demand consists of heat rather than electrical energy.

 About 50% of the industrial heat demand is located at temperatures up to 250°C.

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Solar Water Heater

 Market potential of industrial process heating

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Solar (Thermal) Cooling

 Active cooling

 Use PV panel to generate electricity for driving a conventional air conditioner

 Use solar thermal collectors to provide thermal energy for driving a thermally driven chiller

 Passive cooling

 Solar thermal ventilation

Solar thermal cooling

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Solar Thermal Cooling

International Journal of Refrigeration 3I(2008) 3-15

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Solar Thermal Cooling

 Solar cooling benefits from a better time match between supply and demand of cooling load

1 "Renewable Energy Essentials: Solar Heating and Cooling," International Energy Agency, 2009.

2 B.W. Koldehoff and D. Görisried, "Solar Thermal & Solar Cooling in Germany," Management.

2

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Solar Thermal Cooling

 Active cooling

 Use solar thermal collectors to provide thermal energy for driving thermally driven chillers.

Heat source

Cooling distribution Cooling tower

Chiller

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Solar Thermal Cooling

 Basic type of solar thermal chiller

 Absorption cooling－LiBr+H₂O

 Adsorption cooling－silica gel+H₂O

 DEC, Desiccant Evaporative Cooling

Open cycle Closed cycle

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"Solar Assisted Cooling – State of the Art –,“ESTIF, 2006.

Solar Thermal Cooling

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Solar Thermal Cooling

A. Napolitano, "Review on existing solar assisted heating and cooling installations," 28.04.2010 – Workshop Århus, Denmark ABSORPTION, 2010.

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Solar Thermal Cooling

D. Mugnier, "Refrigeration Workshop Market analysis Market actors Systems costs Politics : incentives & lobbying Conclusion Introduction,"

28.04.2010 – Workshop Århus, Denmark ABSORPTION, 2010.

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Solar Thermal Cooling

D. Mugnier, "Refrigeration Workshop Market analysis Market actors Systems costs Politics : incentives & lobbying Conclusion Introduction,"

28.04.2010 – Workshop Århus, Denmark ABSORPTION, 2010.

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Solar Thermal Cooling

 Passive Cooling (solar ventilation, solar chimney)

 A way of improving the natural ventilation of buildings by using convection of air heated by passive solar

energy.

 Direct gain warms air inside the chimney causing it to rise out the top and drawing air in from the bottom.

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Solar Water Pumping



Energy for Water Pumping



Photovoltaic Pumping Systems



System Design Example

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Energy for Water Pumping



The starting point for any assessment of water pumping is the relationship between energy and water

requirements.



The pumping (or hydraulic) energy required to deliver a volume of water is given by the formula;

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E =  g V h Joule

Where:

E is the required hydraulic energy in Joules

V is the required volume of water in cubic meters (m³) h is the total head in meters (m)

 is the density of water (1000 kg/m³)

g is the gravitational acceleration (9.81 m/s)

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With (V) in cubic meters and (h) in meters the pumping energy is

E = (9.81 V h) / 1000 ^MJ

For example: To lift 60 m³ through a head of 10 meters requires (9.81 x 60 x 10 / 1000) = 5.89 MJ (1.64 kWh) of hydraulic energy.

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Schematic of a pumping system

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Required Power for Water Pumping



The power required to lift a given quantity of water depends on the length of time that the pump is used.



Power is the rate of energy supply, so the formula for hydraulic power is extracted from the formula for energy by replacing water volume (V) with water flow rate (Q), in cubic meters per second.

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P =  g Q h Watt

 If the flow rate (Q) is in liters per second then the hydraulic power is:

P = 9.8 Q h Watt

 For example, the average hydraulic power required to lift 60 m³ of water through a 5m head in a period of 8 hours, (i.e. an average flow rate of 2.08 liters per second) would be 9.81 x 2.08 x 5 = 102 Watts.

 With a typical pump efficiency of 60% the mechanical power required would be 102 / 0.6 = 170 watts.

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Photovoltaic Pumping Systems

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System Design Example

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Design Result Details

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Solar Thermal Applications

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Facade integration (roof)

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Conventional installation way in Taiwan

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Conventional installation way in Taiwan

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Roof integrated flat-plate collectors on house in Denmark (Source: VELUX)

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Facade integration (balcony)

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Contribution of solar thermal to EU heat demand by sector

Summary, Executive, Werner Weiss, and Peter Biermayr. Potential of Solar Thermal in Europe - Executive Summary, 2009.

Reduction of -40%

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Solar Thermal Power

 Conversion of sunlight into electricity

 Direct means : photovoltaics (PV),

 Indirect means : concentrated solar power (CSP).

 High temperature applications

(by means of sun-tracking, concentrated solar collectors)

Solar thermal power

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Solar Thermal Power

 Electrical power is generated when the concentrated light is converted to heat and, then, drives a heat

engine (usually a steam turbine) which is connected to an electrical power generator.

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Solar Thermal Power

 Types of solar thermal power plant

Technology roadmap concentrating solar power, IEA, 2010.

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

Combination of storage and solar energy in CSP plant

Solar Thermal Power

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Solar Thermal Power

PS10 and PS20 solar power tower (HFC) (Seville, Spain). 2007 and 2009

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Solar Thermal Power

Kimberlina solar thermal energy plant (LFR) (Bakersfield, CA), 2008.

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Solar Thermal Power

Calasparra solar power plant (LFR) (Murcia, Spain) 2009.

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Solar Thermal Power

Andasol solar power station (PTC) (Granada, Spain), 2009

Puertollano solar power station (PTC) (Ciudad real, Spain), 2009

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Restrictions in Using Solar Energy

 Geographical aspects

 Financial aspects

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 Low energy density

 Solar radiation has a low energy density relative to other common energy sources

 Unstable energy supply

 Solar Energy supply is restricted by time and geographical location

 Easily influenced by weather condition

Restrictions in Using Solar Energy

Geographical Aspects

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 Higher cost compared with traditional energy

 The capital cost in utilization of solar energy is generally higher than that of traditional ones, especially for PV.

 Solar water heater

 Most economically competitive technology by now

 The need of SWH is inversely proportional to local insolation

Restrictions in Using Solar Energy

Financial Aspects

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Examples

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Example 1

 A family with 5 members plans to install a solar water heater which is mainly used for bath. The hot-water temperature

required for bath is 50 ℃, while the annual average

temperature of cold water is 23 ℃. Assuming that each person needs 60 liters of hot water for taking bath a day. How much heat should be provided by the solar water heater to satisfy the family’s demand for bath?

(Note: water specific heat C_p is assumed to be 1 kcal/kg-℃, water density is 1 kg / l. )

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Answer 1

T C

M

Q   _p 

p

Q Heat Demand

M Hot Water Quantity

C specific heat capacity of water

ΔT temperature difference between hot and cold water



 

day kcal

C C C

kg person kcal

day person

kg

C C C

kg person kcal

day person

Q l

8100

23 50

1 5

60

23 50

1 5

60









 

 



 



 

 







 

 



 



 

 

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Example 2

 A solar water heater is equipped with an effective collect area of 1m², and the daily cumulative insolation onto the collector is 4 kWh/m²-day in February.

If the average efficiency of the solar water heater is 0.5, how many kilo-calories (kcal) of heat can be collected by this solar water heater during a day?

(Note: 1cal = 4.186J = 4.186 W × s).

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Answer 2





 H A Q_c

2

4 2 1 0.5

3600 1

4.186

2 2 7200 7200

1720

c

Q kWh m

m day

kJ s kcal

kWh s kJ

day day day day

kcal day

  



    



er water heat of solar

Efficiency η

area collector Effective

A

nsolation mulative i

Daily accu H

ollector ded from c

Heat provi Q_c



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Example 3

 The minimum heat demand is 8100 kcal/day, and there is a certain solar panel which can offer a heat supply of 1720

kcal/m² in a day. With the absence of auxiliary heating device, calculate the required installation area of the solar panel.

 If the effective arer of this solar panel is 0.8 m² /piece, how many pieces of solar panel should be installed to collect this heat demand?

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Answer 3

Qc

A  Q

area collector Effective

A

er m ollector p ded from c

Heat provi Q

t Demand Hea Q

c



2

2 2

764 . 4 1720

8100

m day

m kcal

kcalday

A 





pieces m

m 5.955 6 8

. 0

764 . 4

2

2  

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