ECE 566: Grid Integration of Wind Energy Systems S. Suryanarayanan - - PowerPoint PPT Presentation

Introduction Value of wind power Market value of wind power References

ECE 566: Grid Integration of Wind Energy Systems

• S. Suryanarayanan

Associate Professor ECE Dept.

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Value of a power plant

Value of a power plant [1]

A power plant‘s objective is to provide electricity to the load with the following characteristics:

Cheap Reliable Clean, where applicable and mandated by law

Depending upon the types of fuel and control system, different plants may have different characteristics General notion: The value of a new power plant is equal to the marginal value of the plant in the existing power system

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Value of a power plant

Parts of a power plant‘s value [1]

Operating cost value Capacity credit Control value Loss reduction value Grid investment value

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Value of a power plant

Parts of a power plant‘s value [1]

Operating cost value This is defined as the new power plant to decrease the

• perating costs in the existing power system

If a new plant is connected to the grid, it will have a finite amount of power that it can supply This implies that the production from the existing (rest of the) plants in the system/grid will decrease As a consequence, the operating costs of the existing plants will decrease (as these costs are tied to the output)

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Value of a power plant

Parts of a power plant‘s value [1]

Capacity credit This is defined as the ability of a new power plant to increase the reliability in the existing power system In the existing system, there is the risk of a capacity shortfall This shortfall is measured using the metric loss of load probability (LOLP) LOLP is defined as the probability of the electricity supply not meeting the demand in the grid This metric is grid-specific and when this value is high, loads have to be disconnected to keep the grid stable By adding new power plants to the existing grid, this metric can be lowered

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Value of a power plant

Parts of a power plant‘s value [1]

Control value This is defined as the ability of a new power plant to follow the load with some fidelity Loads and variable sourced generation change over time with different time signatures If a new plant added to the grid lowers supply-demand imbalance in the system, then its control value is considered positive If a new plant added to the grid increases supply-demand imbalance in the system, then its control value is considered negative

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Value of a power plant

Parts of a power plant‘s value [1]

Loss reduction value This is defined as the ability of a new power plant to lower the overall losses in the existing T&D system Proximity of the new plant to the load center plays a significant role This means that the new plant, which is located geographically/electrically closer to the customers, than existing plants, possesses a positive value in reducing delivery losses If the new plant increases the losses in delivery, then this value is negative

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Value of a power plant

Parts of a power plant‘s value [1]

Grid investment value This is defined as the ability of a new power plant to decrease the need for future grid investments Also known as capacity deferral A new plant located in proximity to a load center with high projected growth has a positive grid investment value, since the proximity decreases the need for investments in delivery infrastructure And, vice versa

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Operating cost value of wind power [1]

Refers to the capability of wind power to decrease

• perating costs of the other sources in the system

This value corresponds to the value of 1kWh produced from WECS which replaces that exact quantity of energy from another source Typically, wind power replaces fuel-based thermal power plants either directly or via a storage step In thermal plants, the lowest cost units are fired first. So, wind power normally replaces the highest cost units when storage is applied. This reduces the overall operating cost

• f the system.

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Capacity credit of wind power [1]

Refers to the capability of WECS to increase system reliability or the capability of WECS to replace other power sources while maintain the same levels of security and reliability [2] To understand capacity credit, we must define Loss of Load Probability (LOLP) [3] LOLP is the probability that the equivalent load E (i.e.,sum

• f physical load D and all outages in the system Otot)

exceeds the available generation ˆ Gtot P

• D > ˆ

Gtot

• = P
• E > ˆ

Gtot

• (1)

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Capacity credit of wind power [1], [3]

• Acc. to [3], capacity credit may be defined in 3 ways:

1

Equivalent firm capacity: of a generating unit g is the capacity of a fictitious 100% reliable unit which results in the same LOLP decrease as the unit g

2

Load carrying capacity: of a generating unit g is the ability of that new unit to allow the system to increase its loadability without compromising adequacy of generation

3

Equivalent conventional power plant: of a generating unit g is the same as the Equivalent firm capacity, except that in this case the unit g does not have a 100% reliability, but has that of a conventional power plant

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Capacity credit of wind power [1]. Figure from [1]

Let us look at an example from [1] Real hourly load for the week of Jan 2, 2003 from W. Denmark Available capacity is set to 3250MW Without wind in the system, the total deficit duration for that week is 40 hours

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Capacity credit of wind power [1]. Figure from [1]

Available capacity increases when 1994MW of wind is added to the system Mean wind power during the week of Jan 2, 2003 is 392MW; and mean weekly production for that area was 396MW (i.e., selected week is representative) With wind in the system, the total deficit duration for that week is 27 hours, thus increasing reliability

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Capacity credit of wind power [1]. Figure from [1]

If load increases by 300MW each hour in that week, the total deficit duration will increase to 40 hours This means, the load carrying capacity is 300MW, i.e., the capacity credit is 300MW

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Capacity credit of wind power [1]

Capacity credit when there are situations with no wind In the previous example, for an installed capacity of 1194MW, the capacity credit is 300MW, i.e., 15% of installed capacity Like with other power sources, there is a finite probability that the plant may be unavailable (i.e., wind will not blow as expected) during some peak times The example showed the drop in total deficit duration (by 13 hours) but not to 0 hours with increases in wind power No matter the installed wind power capacity, when the wind is not blowing the capacity credit is 0 Larger window lengths of time are required for drawing credible conclusions on capacity credit

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Capacity credit of wind power [1]

What about the capacity credit when there are situations with no wind? Mean weekly production in the example was 392MW Annual power production: 396MW×365 × 24hours = 3469GWh If a thermal plant with capacity factor of 92% (because it is taken out of service for 4 weeks in a year for maintenance), then its rating to produce the same amount of energy as the wind plant is: 3469 × 100

92 × 1 8760 = 429MW

The capacity credit for this thermal plant is 429MW The capacity credit for the wind plant was 300MW, i.e. 70%

• f that of the thermal plant

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Control value of wind power [1]

Refers to the capability of wind power to participate in balancing supply and demand The balancing is done differently depending on the time frame:

1

Primary control: seconds up to 1 minute

2

Secondary and tertiary controls: from end of primary control time frame up to 1 hour

3

Daily and weekly controls

4

Seasonal control

5

Multi-year control

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Control value of wind power [1]

Primary control Typically, most generators in the interconnected system are synchronous machines where the rotational speed is closely tied with the electrical frequency When not enough power is produced, the frequency decreases due to the fact that momentarily the extra power needed is extracted from the rotating masses When this is exhausted, the machine slows down and decreases the frequency In some cases, the frequency is measured and primary controls are used to balance the supply with demand and reduce the error

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Control value of wind power [1]

Primary control Generators must be capable of fast ramp-up and ramp-down for such primary control Generator fuel supply must be deterministic and predictable Wind power plants are highly variable and have very low margins in their production units Wind units normally produce at their max output depending

• n wind speed ν

Having wind units increases the need for primary control in the system

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Control value of wind power [1]

Primary control Wind speed variations are of 2 types

1

When νcut−in ≤ ν ≤ νrated: second-to-second variations in different wind units will require the use of a pre-determined amount of reserve margins for primary control

2

When ν is affected by gusts and thunderstorms, wind units cut-out. When sufficiently large number of units do so, the need for reserve margins may be elevated. However, since the loss of supply from several 100s of units at the same time is a low probability event, large reserves may not be needed.

Conclusion: primary control value of wind is negative, but small

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Control value of wind power [1]

Secondary & tertiary control Secondary and tertiary controls keep the balance between supply and demand after primary controls are done and up to 1 hour Deployment of primary control means f = frated & reserve margins are used Some units have to be used for secondary controls if f ⇓ Secondary control also plays a role in Automatic Generation Control (AGC) When secondary reserves are used up, tertiary reserves are called in

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Control value of wind power [1]

Secondary & tertiary control Wind power does not contribute to secondary controls Wind power units have hourly variations which increase the need for secondary controls Conclusion: secondary control value of wind is negative, but more significant than primary control value This is because hourly variations in wind are more significant than second-to-second ones

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Control value of wind power [1]

Daily, seasonal, & multi-year control Daily control value of wind power is negative and is a function of diurnal variations Seasonal control is needed when there are hydro reservoirs in the system for storing energy After careful seasonal planning ans scheduling and coordinating with the wind unit productions in an area If the seasonal load pattern matches the seasonal wind variation patterns, then the control value is positive A similar approach to seasonal may be handled for multi-year control; but, hydro inflow is different for different years which may complicate the process

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Loss reduction value of wind power [1]. Figure from [1]

Ability of wind power to reduce grid losses Tied to transmission line distances and voltage interconnection level PL = 3RI2 = R (P2+Q2)

U2

= R 1+tan2(φ)

U2

× P2 = kP2

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Loss reduction value of wind power [1]. Figure from [1]

PLO = kP2 & let local source reduce tr. to P1, and tr. losses to PL1 Assuming change in tr. is small and linearizing PL1 = PLO − dPL dP (PO − P1) = PLO − 2kPO(PO − P1)

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Loss reduction value of wind power [1]. Figure from [1]

if local production is ∆P = (PO − P1), that causes a tr. loss reduction ∆PL ∆PL = ∆PL

∆PL = (PLO−PL1) (PO−P1) = 2kPLO

Value depends on locations of load and wind unit

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Grid investment value of wind power [1]

Capacity of win power to decrease future grid investments (deferral) Studies on grid dimensionalities with and sans wind units are needed Drawing general conclusions are hard Must consider overall costs v. benefits

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Grid investment value of wind power [1]

Capacity of wind power to decrease future grid investments (deferral) Studies on grid dimensionalities with and sans wind units are needed Drawing general conclusions are hard Must consider overall costs v. benefits

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Market value of wind power [1]

Markets are usually organized to provide the owners of production sources payment commensurate to the value of the source In this section, we will look at:

1

Market operation cost value of wind power

2

Market capacity credit of wind power

3

Market control value of wind power

4

Market loss reduction value of wind power

5

Market grid investment value of wind power

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Market operation cost value of wind power [1]

This depends on the methods available for trading power

1

Bilateral sales to customers

2

Bilateral sales to traders

3

Pool pr central bidding

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Market operation cost value of wind power [1]

Bilateral sales to customers

This implies the need for a balancing entity responsible for balancing the wind power production and consumption Requires the consideration of power control value of wind Requires the involvement of trader

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Market operation cost value of wind power [1]

Bilateral sales to traders

A trader buys the wind power, along with power from other sources, for selling to other traders and/or customers The trader will usually enter the central or pooled bids market for this purpose

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Market operation cost value of wind power [1]

Pooled/central bidding markets

Sellers submit bids and buyers submit offers Market attains equilibrium at a price corresponding to the highest operational or marginal generator cost Implies that selling companies are paid the avoided cost of the most expensive units Bidding and allocating wind power in pool markets is challenging due to forecast accuracy, variability, and time-scales of market operation

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Market operation cost value of wind power [1]

Pooled/central bidding markets

Sellers submit bids and buyers submit offers Market attains equilibrium at a price corresponding to the highest operational or marginal generator cost Implies that selling companies are paid the avoided cost of the most expensive units Bidding and allocating wind power in pool markets is challenging due to forecast accuracy, variability, and time-scales of market operation

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in markets [4]

Wind power producers (WPP) aim to minimize forecasting errors over longer times for achieving better schedules System operators (SO) aim to maximize system security and minimizing operational cost

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in markets [4]

SO perspective

SO manages the combination of generation and demand variability while considering unit outages SO acquires adequate reserves in a control area for maintaining security

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in markets [4]

SO perspective

Large changes to forecast wind power in short periods of time is a major concern for SO Operational procedures are needed for such ramping events Challenge: how to handle the uncertainty and variability from wind power in a cost-efficient and reliable way?

1

By scheduling adequate reserve margins

2

New mechanisms for scheduling and market clearing

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in markets [4]

WPP perspective

Wind power is primarily sold under long-term contracts called power purchasing agreements (PPAs) PPAs lock in price of electricity Wind power is also sold directly in the market Important for market to reflect the variability in wind power to trade-off the risk versus return PPA buyers also need to factor the variability into their own scheduling strategy and its influence on their portfolio

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in markets [4]

WPP perspective

Forecast errors have an associated cost/penalty In a day-ahead (DA) market, WPP offer bids (Eb) on day D until a certain time t for every hour of the next day D + 1 for payment at the market clearing price ps If actual generation Eg > Eb, excess may be paid at a discounted price psurplus (can be -ve) If actual generation Eg < Eb, penalty may be applied at price pshortage pshortage is SO cost for compensating insufficient generation using the spot market

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in markets [4]

WPP perspective

The WPP income (I) for a given look-ahead time period t + k is:

It+k =

• ps

t+k · Eb t+k + psurplus t+k

· (Ep

t+k − Eb t+k)

Ep

t+k > Eb t+k

ps

t+k · Eb t+k − pshortage t+k

· (Eb

t+k − Ep t+k)

Ep

t+k < Eb t+k

(2)

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in markets [4]

WPP perspective

Let us consider balancing costs: cdown−reg = ps − psurplus & cup−reg = pshortage − ps When WPP are assigned balance responsibility they have a financial responsibility for any imbalance First component of It+k is income with perfect forecasts; second comp. is the cost of balancing WPP will seek to minimize the second comp. by finding the

• ptimal bid for Eb

t+k

It+k =

• ps

t+k · Ep t+k − cdown−reg t+k

· (Ep

t+k − Eb t+k)

Ep

t+k > Eb t+k

ps

t+k · Ep t+k − cup−reg t+k

· (Eb

t+k − Ep t+k)

Ep

t+k < Eb t+k

(3)

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in markets [4]

WPP perspective

Finding such an optimal bid for Eb

t+k is complex & depends

• n very good forecasts of wind power output and price

Instead, an economic-oriented approach that penalizes acc. to balancing costs and the forecast error signs may be used

min

• jdown

wdown−reg | Pt+k − Pt+k | +

• jup

wup−reg | Pt+k − Pt+k | (4) I & II terms correspond to over and underestimation, resp. while wdown−reg & wup−reg are penalty factors

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in US electricity markets. Data from [4]

MISO NYISO PJM ERCOT Peak load (2006 MW) 116030 33939 144644 62339

• Tot. ins. cap (MW)

138000 38000 165000 80000 Wind cap. (2009 MW) 7600 1300 2500 9000 Market participation for wind

• DA: day-ahead; OH: operating hour; RT: real-time

RAC: reliability assessment commitment - a tool used by the SO to ensure sufficient resources are available and

• nline to meet forecast load [5]

SCED: security constrained economic dispatch

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in MISO [4]

If wind is a capacity resource, it must bid in DA market and RAC No penalties for deviation

11 AM: DA bids are due 4 PM: DA results 5 PM: DA re-bidding due OH-30 min: RT bids are due

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in NYISO [4]

Wind reqd. to bid in RT market; bidding in DA is optional SCED provides dispatch signals Over-generation penalties apply in constrained scenarios Under-generation has no penalties

5 AM: DA bids are due 11 AM: DA results OH-75 min: RT bids are due

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in PJM [4]

If wind is a capacity resource, it must bid in DA market Deviation penalties/charges apply Wind dispatch signals provided in constrained scenarios

12 PM: DA bids are due 4 PM: DA results 6 PM (DA): RT bids are due

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in ERCOT [4]

Bilateral market; imbalances settled at RT zonal energy price Penalty exemption for ±50% of scheduled gen. Ramping limits are in place

1/4 PM: DA bids are due (reserves only) 1:30/6 PM: DA results OH - 60 min: RT bids are due

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References Wind power in markets

Wind power in CAISO [4]

WPP‘s RT bid based on ISO forecast Deviations netted over one month at average price 10-min imbalance charges for non-participants in wind forecasting Wind is not dispatched

10 AM: DA bids are due 1 PM: DA results OH - 75 min: RT bids are due

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

• T. Ackermann. Wind Power in Power Systems. Wiley,
• 2012. ISBN: 9781119941835. URL: http:

//books.google.com/books?id=QM60LmgaeeQC. Capacity credit and fuel savings. Wikipedia. URL: http://goo.gl/HtPmL5 (visited on 10/27/2014).

• M. Amelin. “Comparison of Capacity Credit Calculation

Methods for Conventional Power Plants and Wind Power”. In: Power Systems, IEEE Transactions on 24.2 (2009),

• pp. 685–691. ISSN: 0885-8950. DOI:

10.1109/TPWRS.2009.2016493.

• A. Botterud et al. Use of wind power forecasting in
• perational decisions. Argonne National Laboratory

Decision and Information Sciences Division ANL/DIS-11-18. URL: http://goo.gl/ahDu4 (visited

• n 09/30/2011).

Suryanarayanan ECE 566 Lecture/Week 11

Introduction Value of wind power Market value of wind power References

Reliability assessment committement (RAC). White paper.

URL: http://goo.gl/5Svp48 (visited on 11/04/2014).

Suryanarayanan ECE 566 Lecture/Week 11