# data[].attributes.body
1.       a)
-   not centrally planned by the utility

-  not centrally despatched
-   normally smaller than 50 MW
-   usually connected to the distribution network

1.       b)

Environmental:

-  reduction in CO2 emissions by reducing reliance on fossil fuel burning for energy generation.

Political:

- support from European Union towards use of renewable energy sources

- Green Paper opened debates on important measures relating to renewable energy (12% of inland energy consumption must come from renewable sources)

- White Paper concluded a list of priority measures for promoting use of renewable energy

Technological:

- advances in PV and wind technologies give rise to more development of DG

- embedded generations, micro power and free piston Stirling technology have potential growth for DG

1.    c)
Power flow problems when power injected from a DG affects other transmission lines differently

Voltage control at high voltage levels

Fault current comes from DG units, making detection of fault more complicated (bidirectional)

Instable voltage levels due to integration of DG

1.    d)

# data[].attributes.body
a) Max efficiency = Betz limit  * Generator * Electrical system
= O.417 * 0.7 * 0.9
= 0.26271 (26.27%)

b) (i) Choice of Generators
SCIG (Direct-drive)
-well-known, robust, cheap for mass production
-Speed not controllable
-Machine always consume reactive power
-Increase acoustic noise

DFIG (Indiect)
-Variable Blade Speed
-Stator reactive control
-Rotor converter which provides voltage support
-Cost of power electronics
-Slip rings required
-Fragility of power electronics

b(ii)Turbine design and speed control

b(iii) Power electronics interface
Direct connection
-TBC

# data[].attributes.body
A. - wholesale electricity market
- ancillary service
- renewable obligation certificate
- levy exemption certificate
- EU Emmision Trading Scheme

B.  The NETA involved forward contracts between buyers and sellers of electricity up to one year in advance of actual generation

NETA is settled every 30 minutes and buyers and sellers are allowed to sign bilateral contracts. The System Operator then determines whether supply and the demand that the companies have forecast matches their demand forecast and it asks for bids from generators to supply additional power or reduce output in the so-called Balancing Market. The System Operator buys any difference between expected and actual sales by generators to wholesalers, and between wholesalers and their consumers for the companies in the Balancing Market.

NETA has a unique dual price system with:
- a system buy price (SBP)
- a system sell price (SSP)
the system operator balances the system and if renewable generation from a power plant is either over or below what is said it would generate in a half hour it has to pay penalty to 'balance' it's output. There is a cost differential between the SBP and  the SSP. In effect, it costs more to buy if you are out of balance as a result of under-generating. It is possible to have price spikes, although it is much less likely now than it was when NETA came into operation in April 2001. At those times, the cost of balancing can be onerous. As a result of this, suppliers are concerned at the additional risk of buying intermittent generation

C. The RO is legislated obligation on licensed electricity suppliers to buy a certain percentage of their supply in each one-year compliance period,
Starting 3% in 2002-2003
Rising to 10.4% for the period 2010-2011
Is intended to stay at the 10.4% level until 2027

D. DG delivers electricity directly to (large/small) consumers or via the electricity market to these consumers. DG operator may also gain access to the balancing and ancillary services market. The function of the distribution network will change , because the flows through the network may reverse.

The full access of DG to electricity markets, including markets for balancing and ancillary services, may help in creating an equal position for DG compared to centralised generation, in other words, creating a level playing field. We can say that to create a level playing field and hence a possible change towards a more decentralised electrical system, has to be valued in economic terms in order to consider the benefits and costs of DG.

G.
(i) bilateral power purchase agreements are the backbone of the trading arrangements between large producers ad supplier. Most UK electricity is traded through these arrangements some of which may last for several years

(ii) the spot market is for much shorter term power sales/purchases. They cover only a few hours ahead and will tend to be used when a supplier's or generator's short term forecasting shows that they have too much or too little generation. A generator who has significant wind

# data[].attributes.body
4. a. Modern distribution systems were designed to accept bulk power from the transmission network and to distribute it to customers. the flow of both real power (P) and reactive power (Q) was always from the higher to the lower voltage levels. However, with significant penetration of embedded generation the power flows may become reversed. The distribution network is no longer a passive circuit supplying loads but an active system. Power flows and voltages determined by the generation as well as the loads.

- the CHP generation scheme with a synchronous generator (S) will export real power when the electrical load of the premises falls below the output of the generator but may absorb or export reactive power depending on the setting of the excitation system of the generator.

- The wind turbine will export real power but is likely to absorb reactive power as its induction (sometimes known as asynchronous) generator (A) requires a source of reactive power to operate. •

- The voltage source converter of the photovoltaic (PV) system will allow export of real power at a set power factor but may introduce harmonic currents.

- Thus, the power flows through the circuits may be in either direction depending on the relative magnitudes of the real and reactive network loads compared to the generator outputs and any losses in the network.

b. i. Power flow will be 2 ways, DG1 and power plant. Power plant supply lesser real power to the grid.