Thermal Energy Storage 03
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Energy Storage
Transcript of Thermal Energy Storage 03
TES CHALLENGES FOR SOLAR
APPLICATIONS
TES subsystem must be large enough to permit
the system to operate over periods of inadequate
sunshine.
The second major complication imposed by TES
is that the primary collecting system must be
sufficiently large to build the supply of stored
energy during periods of adequate insolation.
Thus, additional collecting area (and its
additional capital cost) is needed.
TES TYPES AND SOLAR ENERGY SYSTEMS
In solar energy applications, TES can provide savings in systems involving either simultaneous heating and cooling, or heating and cooling at different times of the year.
Most solar energy systems use diurnal storage, where energy is stored for at most a day or two. Diurnal storage offers a number of advantages, such as
capital investments for storage and energy loss are usually low;
devices are smaller and can easily be manufactured offsite; and
sizing of daily storage for an application is not as critical as sizing for larger annual storages.
A variety of active and passive systems for
storage have been developed for the effective
utilization of solar energy. Passive systems,
which do not need pumps are often suitable for
small scale domestic applications, and are widely
used throughout Europe and the United States.
The five main types of such passive systems are:
direct heat gain,
heat collection and storage,
sun space,
roof-top heat storage,
thermosyphon.
BUILDING APPLICATIONS OF TES AND
SOLAR ENERGY
The ability to store thermal energy is important
for effective use of solar energy in buildings.
Today, much interest is focused on passive
systems for space heating and active systems for
water heating.
For building heating, conventional passive TES
materials include water, rocks, masonry, and
concrete.
To perform well, these storage materials must be
massive because their allowable temperature
swings are limited by comfort conditions that
must be maintained inside the building.
DUAL MEDIUM STORAGE SYSTEMS
PHASE CHANGING MATERIAL
IN SOLAR THERMAL ENERGY
STORAGE
CONTENTS
Introduction
Benefits and Drawbacks of PCM
PCM Options
Encapsulation
Increasing Thermal Conductivity
Conclusion
INTRODUCTION
Most systems have a disconnect
between supply and demand
Intermittent solar energy supply
can be maximized with a heat
storage system
Thermal energy can be
stored both as sensible
and latent heat
Continued efforts to find a phase changing material is currently underway
BENEFITS AND DRAWBACKS OF PCM
Benefits:
Higher storage density than sensible heat
Smaller volume
Smaller temperature change between storing and releasing energy
Drawbacks:
High cost
Corrosiveness
Density change
Low thermal conductivity
Phase separation
Incongruent melting
PCM OPTIONS
PCM OPTIONS Inorganic
Glauber’s salt, calcium chloride hexahydrate, sodium thiosulfate penthydrate, sodium carbonate decahydrate
Benefits:
Low cost and readily available
High volumetric storage density
Relatively high thermal conductivity
Drawbacks:
Corrosive
Decomposition
Incongruent melting
Supercooling
PCM OPTIONS Organic
Paraffin waxes and fatty acids
Benefits:
Melts congruently
Chemically and physically stable
High heat of fusion
Drawbacks:
More expensive and flammable
Low thermal conductivity in solid state
Lower heat storage capacity per volume
PCM OPTIONS
ENCAPSULATION Prevents reactivity towards environment
Compatible with stainless steel, polypropylene, and
polyolefin
Controls volume as phases change
Prevents large drops in heat transfer rates
INCREASING THERMAL CONDUCTIVITY Metallic fillers
Metal matrix structures
Finned tubes
Aluminum filling with VSP 25 and VSP 50
PCM-Graphite Matrix Finned Tubes
The VSP25 filling provided the highest thermal
conductivity of 1W/(mK), which is about six
times that of pure paraffin
Total solidification time of PCM is shorter
with fins and lessing rings, but the total
quantity of stored heat is slightly smaller
CONCLUSION
Thermal energy storage is imperative to make
solar energy more reliable and competitive
Further research in phase changing material can
improve the efficiency of energy storage
Design of the system is also important in
optimizing energy storage
OTHER APPLICATIONS
Cooling of heat and electrical engines
Cooling: use of off-peak rates
Cooling: food, wine, milk products (absorbing peaks in demand), greenhouses
Heating and hot water: using off-peak rates
Medical applications: transportation of blood, operating tables, hot–cold therapies
Passive storage in bio-climatic building/architecture (HDPE, paraffin)
Safety: temperature level maintenance in rooms with computers or electrical/electronic appliances
Smoothing exothermic temperature peaks in chemical reactions
Solar power plants
Spacecraft thermal systems
Thermal comfort in vehicles
Thermal protection of electronic devices (integrated in the appliance)
Thermal protection of food: transport, hotel trade, ice-cream, etc.
Thermal storage of solar energy
