Integration

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

Matching Electricity Supply To Short-term 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 Targets- The 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

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