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Optimal Control of a Dispatchable Energy Source for Wind Energy Management

  • Guglielmo D’Amico , Filippo Petroni EMAIL logo and Robert Adam Sobolewski
Published/Copyright: February 15, 2019
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Abstract

The major drawback of wind energy relies in its variability in time, which necessitates specific strategies to be settled. One such strategy can be the coordination of wind power production with a co-located power generation of dispatchable energy source (DES), e.g., thermal power station, combined heat and power plant, gas turbine or compressed air energy storage. In this paper, we consider an energy producer that generates power by means of a wind park and of a DES and sells the produced energy to an isolated grid. We determine the optimal quantity of energy produced by a DES, given the unit cost of this energy, that a power producer should buy and use to hedge against the risk inherent in the production of energy through wind turbines. We determine the optimal quantity by solving a static optimization problem taking into account the possible dependence between the amount of energy produced by wind turbines and electricity prices by using a copula function. Several particular cases are studied that allow the determination of the optimal solution in an analytical closed form. Finally, a numerical example concerning a real 48 MW wind farm located in Poland and Polish Power Exchange shows the possibility of implementing the model in real-life problems.

MSC 2010: 90B25

A Proofs

Proof of Lemma 2.1.

We have

=𝔼[χ{WeK-Pg}πeK]-𝔼[χ{WeK-Pg}πgPg]
+𝔼[χ{We<K-Pg}πe(We+Pg)]
-𝔼[χ{We<K-Pg}[πgPg+C(K-(We+Pg))]],

where

(A.1)

𝔼[χ{WeK-Pg}πeK]=KK-Pg+(-+xf(we,πe)(x,p)dx)dp,
𝔼[χ{WeK-Pg}πgPg]=K-Pg+πgPgfwe(x)dx=πgPgF¯we(K-Pg),
𝔼[χ{We<K-Pg}πe(We+Pg)]=0K-Pg-+x(p+Pg)f(we,πe)(x,p)dxdp,
𝔼[χ{We<K-Pg}[πgPg+C(K-(We+Pg))]]=0K-Pgf(we)(p)[πgPg+C(K-(p+Pg))]dp.

Now we calculate the first-order derivative of with respect to the variable Pg. In order to do this, we need to evaluate the derivatives of all the four addenda in formula (A.1). Let us start computing the derivative of the first addendum of (A.1):

KK-Pg+(-+xf(we,πe)(x,p)𝑑x)𝑑pPg=KlimL+PgK-PgL𝔼[πeWe=p]f(we)(p)dp.

The use of the Leibniz formula for differentiation under an integral sign gives

(A.2)KlimL+(0+𝔼[πeWe=K-Pg]f(we)(K-Pg)+0)=K𝔼[πeWe=K-Pg]f(we)(K-Pg).

The derivatives of the second addendum is

-PgπgPgF¯we(K-Pg)=-PgπgPglimL+K-PgLfwe(p)𝑑p.

Interchange the limit and the derivatives and apply Leibniz’s formula for differentiation under an integral sign to obtain

(A.3)-limL+(fwe(K-Pg)πgPg+(Fwe(L)-Fwe(K-Pg)πg))=-fwe(K-Pg)πgPg-F¯we(K-Pg)πg.

The derivatives of the third addendum is

Pg0K-Pg-+x(p+Pg)f(we,πe)(x,p)𝑑x𝑑p
=Pg[0K-Pgpf(we)(p)(-+xf(πewe)(xp)dx)dp+0K-PgPgf(we)(p)(-+xf(πewe)(xp)dx)dp]
=Pg[0K-Pgpf(we)(p)𝔼[πeWe=p]dp+0K-PgPgf(we)(p)𝔼[πeWe=p]dp].

Apply Leibniz’s formula for differentiation under an integral sign to obtain

(A.4)

Pg0K-Pg-+x(p+Pg)f(we,πe)(x,p)𝑑x𝑑p
=(K-Pg)fwe(K-Pg)𝔼[πeWe=K-Pg](-1)-fwe(K-Pg)Pg𝔼[πeWe=K-Pg]
+0K-Pgfwe(p)𝔼[πeWe=p]dp
=-Kfwe(K-Pg)𝔼[πeWe=K-Pg]+0K-Pgfwe(p)𝔼[πeWe=p]dp.

Now we have to calculate the derivatives of the fourth addendum:

(A.5)

-Pg0K-Pgfwe(p)[πgPg+C(K-(p+Pg))]𝑑p
-(fwe(K-Pg)[πgPg+C(K-(K-Pg+Pg))](-1)+0K-Pgfwe(p)(πg-C)𝑑p)
=fwe(K-Pg)πgPg-(πg-C)Fwe(K-Pg).

The summation of formulas (A.2), (A.3), (A.4) and (A.5) and some algebraic manipulations gives

(A.6)(Pg)Pg=-πg+CFwe(K-Pg)+0K-Pgfwe(p)𝔼[πeWe=p]dp.

To prove the concavity of (Pg), we proceed to compute the second-order derivative. The calculation makes use again of the Leibniz formula:

2(Pg)Pg2=Pg[-πg+CFwe(K-Pg)+0K-Pgfwe(p)𝔼[πeWe=p]dp]
=Cfwe(K-Pg)(-1)+fwe(K-Pg)𝔼[πeWe=K-Pg](-1)
=-fwe(K-Pg)[C+𝔼[πeWe=K-Pg]]<0,

where the latter inequality is due to Assumption 3. ∎

Proof of Lemma 3.1.

The objective is the computation of the integral

𝔼[πeFπe(πe)]=-+xfπe(x)Fπe(x)𝑑x,

where the random variable πe is normally distributed with mean μ and variance σ2. We have

𝔼[πeFπe(πe)]=-+x12πσ2e-(x-μ)22σ2-x12πσ2e-(t-μ)22σ2𝑑t𝑑x.

A change of variable (standardization) z=x-μσ gives

𝔼[πeFπe(πe)]=-+(zσ+μ)12πσ2e-z22Fπe(zσ+μ)σ𝑑z,

where

Fπe(zσ+μ)=-zσ+μ12πσ2e-(t-μ)22σ2𝑑t.

This latter integral can be calculated by introducing again a standardization, i.e. h=t-μσ by obtaining

Fπe(zσ+μ)=-zσ12πσ2e-h22𝑑h=Φ(z),

where Φ denotes the cdf of a standard Normal distribution. Therefore we have

𝔼[πeFπe(πe)]=-+(zσ+μ)ϕ(z)σΦ(z)σ𝑑z
=σ-+zϕ(z)Φ(z)𝑑z+μ-+ϕ(z)Φ(z)𝑑z,

where ϕ denotes the probability density function of a standard Normal distribution. The former integrals have been evaluated by [14] who established that

-+Φ(a+bx)ϕ(x)𝑑x=Φ(a1+b2)

and

-+xΦ(bx)ϕ(x)𝑑x=b2π(1+b2).

Then a simple substitution gives

𝔼[πeFπe(πe)]=σ12π(1+12)+μΦ(01+12)=σ2π+μ2=12(σπ+μ).

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Received: 2019-01-09
Accepted: 2019-01-29
Published Online: 2019-02-15
Published in Print: 2019-06-01

© 2019 Walter de Gruyter GmbH, Berlin/Boston

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