Transcript Are renewable-energy supplies available when we want them?

Integration
• Are renewable-energy supplies available where we
want them?
• Are renewable-energy supplies available when we
want them?
Matching Electricity Supply To Shortterm Demand Fluctuations
• Electricity has to be generated on demand and the
voltage and frequency of the AC supply have to be
held within relatively tight limits. A range of
technologies is used to meet rapid and possibly
unexpected increases in demand:
• Pumped storage plants
• Gas turbine and diesel peaking plants
• Compressed air energy storage (CAES)
• Rechargeable batteries
Which Is Best
• Balancing the electricity grid of an entire country requires
large amounts of power and appreciable amounts of stored
energy.
• At present only pumped storage systems have power ratings of
over 1 GW and the capacity ot supply this for more than an
hour or so , but such systems require suitable sites in
mountainous regions.
• Peaking gas turbines can be installed almost anywhere, but
consume fossil fuel in a relatively inefficient manner.
• CAES systems can supply 100 MW or more, but require the
special geology suitable for underground high pressure air
storage.
• Rechargeable batteries can potentially be installed
anywhere, but at present are only available in ratings of
less than 50 MW and are typically only used to supply
that power for periods of an hour or less. They have the
advantage of very rapid response-fractions of seconds
rather than minutes. They are more likely to be used to
absorb short surges and to correct control instabilities
in local distribution systems. They may also act as
starting batteries to allow a power station to recover
from a grid failure and perform what is known as black
start.
Connecting The Renewables
• When do the renewables fit into all this? The answer
depends on the particular source and the extent to
which the timing and quantity of its output matches
demand.
Some System Solutions
• To a certain extent, there are some common solutions
to the where and when of deploying renewable
energy: stronger electricity grids, better demand
management, the use of embedded generation, and in
the longer term, the development of the hydrogen
economy.
Grid Strengthening
• The existing grid has grown up around the power
stations of the past. Connecting large amounts of
power from new renewable sources will undoubtedly
require strengthening the power grid. This will not
come cheaply.
Demand Management
PV, Micro-CHP And Emergency
Generators
• Large numbers (possibly millions ) of small embedded
generators (i.e. at the low voltage end of the grid)
could cut the need for large scale electricity grids and
provide backup for wind generators.
• Small-scale generators are designed to operate
completely automatically. They will connect and
disconnect from the grid in response to their local
energy needs or circumstances. The information
technology to allow remote scheduling of such devices
undoubtedly exists, but at present the operating
procedures that cover this only apply to larger
generators.
Hydrogen – The Fuel Of The Future
• Hydrogen has been widely advocated as an energy
carrier for the future. Its use as a fuel has many
advantages:
• It can act as a store of renewable energy from season
to season.
• It can provide a transport fuel not dependent on the
world’s declining reserves of oil.
• The only by-products of its combustion are water and
a very small amount of nitrogen oxides, and even the
emissions of these can be reduced to zero if fuel cells
are used.
Renewables And Conservation
Promoting Renewables
• Supporting research and development
• TargetsThe European Commission in its 1997 White Paper
(European Commission, 1997) asked for the
contribution from renewables to EU primary energy
consumption to be increased from 6% to 12% of EU
by2010.]
• Legislation and building regulations
•
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Financial incentives
Exemption from energy taxes
Capital Grants for renewable-energy schemes
Auctions of supply contracts for renewable energy as
used in the UK Non-Fossil Fuel Obligation (NFFO)
scheme
- Renewables Obligations – obligations on electricity
suppliers to purchase a specific proportion of
renewable energy
- Renewable Energy Feed-In Tariffs (REFIT) – fixed
premium prices for electricity from renewable
sources