Cogeneration heat and power (CHP) systems
Cogeneration heat and power (CHP), is the simultaneous production of electricity and heat from a
single fuel source, such as biomass/biogas. CHP provides:
Distributed generation of electrical power.
Waste-heat recovery for heating, cooling, or process applications.
Seamless system integration for a variety of technologies, thermal applications, and fuel types into
existing building infrastructure.
Advantages
1.
2.
High efficiency. The total efficiencies of 120 MWe biomass-fuelled CHP plants
constructed in Finland in the 2000s vary
around 90 %. The electric efficiency of
these plants ranges between 8 and 30 %
Modular design, simple plug-and-play
installation
Disadvantages
1.
High capital costs. They are highly dependent on
the size of the plant. The estimated investment
costs for CHP-plants with an electric capacity
under 700 kWe is about 5000 €/kWe (in 2012).
2.
The need for maintenance and repairs associated
with the many subsystems, particularly the solids
handling components and filters.
3.
Biomass fuel delivery is required
Cogeneration heat and power (CHP) systems
CHPs typically include a fuel processor (combustion or gasification), necessary intermediate
fuel cleanup, an electric generator, and heat recovery from both the power generation and
energy conversion sections. An automatic fuel storage and delivery system must be added for a
complete operating system.
Gasification Systems
High Electric Efficiency (EE)
more than 20 %
Thermal flexibility: heat can
be make available at different
temperatures (from 80 °C of
the engine cooling to 500°C
of the exhaust gas)
Combustion Systems
EE is about 8-12 % with
thermal to electrical output
ratio of 6:1 or greater
Most of today’s biomass
power plants are
combustion (direct-fired)
systems
Problems with the presence
of tars and heavy metals in
the produced syngas, hence
gas clean up system is the
critical part (technically and
economically) of a
gasification plant.
Example Modular Biomass Gasification System
Hybrid Gasification/
Combustion Systems
Operate functionally like a
direct combustion system.
The difference is that the
combustion chamber is
actually a gasification
system that uses a twochamber gasifier approach.
The combination of these
features results in a cleanburning, fuel-efficient
system.
Underground Thermal Energy Storage (UTES)
Systems using natural underground sites for storing thermal energy are called underground thermal energy
storage (UTES) systems. UTES is one form of TES and it can keep a longer term and even seasonal thermal
energy storage. It has become one of the most frequently used storage technologies in North America and
Europe. Especially Northern European countries has good conditions in terms of climate, geology and
humidity for using UTES.
Ground temperature below a certain depth
remains relatively constant throughout the
year. The difference in temperature between the
outside air and the ground can be utilized as a
preheating in winter and precooling in summer
by operating a ground heat exchanger (GHE).
The basic types of underground thermal energy storage systems can be divided into two groups:
Systems where a technical fluid (water in most cases) is pumped through heat exchangers in the ground,
also called ‘‘closed’’ systems (borehole thermal energy storage, BTES).
Systems where groundwater is pumped out of the ground and injected into the ground by the use of wells
or in caverns, also known as ‘‘open’’ systems (aquifer thermal energy storage (ATES), cavern thermal
energy storage CTES).
Underground Thermal Energy Storage (UTES)
ATES uses natural water in a saturated and permeable underground layer called an aquifer
as the storage medium. Thermal energy is transferred by extracting groundwater from the
aquifer and by reinjecting it at a changed temperature at a separate well nearby.
Due to the high heat capacity of aquifer, ATES can achieve seasonal energy efficiency ratio
values of over 60 (ratio of electrical power input to thermal power output from a system).
Moreover ATES is the least expensive of all natural UTES options, but requires a suitable
aquifer.
ATES Winter Operation - Heating
ATES Summer Operation - Cooling
Underground Thermal Energy Storage (UTES)
BTES consists of vertical heat exchangers deeply inserted below the soil from 20 to
300 m deep, which ensures the transfer of thermal energy toward and from the
ground (clay, sand, roc, etc.).
BTES Winter Operation - Heating
BTES Summer Operation - Cooling
Underground Thermal Energy Storage (UTES)
Disadvantages
Advantages
1.
BTES systems are generally easier to construct
and operate, need limited maintenance, and have
extraordinary durability.
2.
BTES can achieve coefficient of performance
(COP) values from 4 to about 8, compared to
COP values of around 3.5 for a conventional
GSHP
3.
BTES systems usually require only simple
procedures for authority approvals.
Payback times are relatively long
compared to ATES systems, normally
6–10 years. This is due to expensive
borehole investments and the fact that
BTES systems normally need some
other sources to cover the peak load
situations.
Applications
Multitude of projects are about the storage of solar heat in
summer for space heating of houses or offices.
Ground heat exchangers are also frequently used in
combination with geothermal heat pumps, where the ground
heat exchanger extracts/transfers low temperature heat
from/to the soil.
The flexibility of this technology at almost any ground
conditions has made BTES systems one of the most popular
forms of UTES.
Ground Source Heat Pumps
Ground source heat pumps (GSHP) are common type of heat pumps in Finland. There
are two methods of inserting the ground pipes into the ground, vertical or horizontal piping.
In the horizontal type, the pipes are installed 1-2 meters below the surface in lining with the
surface. In the vertical type the pipes are installed into bore holes. The heat transfer
between the heat source and the piping is improved as the bore hole fills with water. GSHP
are usually used in larger than residential scales and requires investment about 1500020000 € / installation (approx. 50-500 kW)
Operation principle of Heat Pump
Example of GSHP
Suggested combination of solar collectors, GSHP
and BTES
BTES with two independent networks of
U-tube. One U-tube is dedicated to a solar
charging network and the other to the
house heating system through a
discharging unit.
A) BTES can be kept at a high enough
temperature in order to supply the
entire house heating and minimize the
use of an auxiliary heating. Large solar
collector area is required
B) small solar charging network can
be used to keep the BTES at a low
temperature level suitable for use
with heat pump. This variant can be
suitable for existing 10 kW solar heat
system.
Heating system (Chapuis & Bernier, 2009)
Photovoltaic system
Technologies
Polycrystalline silicon (p-Si)
Monocrystalline silicon (m-Si)
Efficiency about 18%
Efficiency about 16%
Thick wafers (about 200 m)
Thick wafers (about 200 m)
Efficiency strongly dependent on
temperature
Efficiency strongly dependent on
temperature
Electrical losses due to
interconnections
Electrical losses due to
interconnections
Price about 0.55 €/Wp
Price about 0.45 €/Wp
Installation type
Rooftop: most feasible solution in
case enough roof area is available
Ground-mounted: free open space
required; 1 or 2 axis tracking system
feasibility study must be conducted
Rechargeable Batteries
Low-self discharged NiMH Batteries
relatively low cost
lifetime is 1000-1500 cycles
large current can be produced
specific Energy 75 Wh/kg
low self-discharge (less than 10% per year)
environmentally friendly, nickel content
makes recycling profitable
Ni-MH Battery of Toyota Prius
Li-Ion Batteries
widely used in portable electronics,
most promising technology for larger
scales
specific energy up to 150 Wh/kg
preferred to keep level of 40% from
capacity
the highest cost (approx. 600$/kWh)
lower self-discharge
low capacity loss on low temperatures
large current can be produced
high durability, lifetime is up to 3500
cycles
low maintenance
Li-ion battery for renewable applications
Suggested System Configurations
Basic configuration. Operation of system in winter
Electricity
Heat
Cold
Suggested System Configurations
Basic configuration. Operation of system in summer
Electricity
Heat
Cold