Sizing of Energy Storage Systems for Photovoltaic–Wind Power Plants

As the share of highly volatile photovoltaic (PV) and wind power generation increases in power grids, there is an increasing need to level their power fluctuations. The power fluctuations from PV and wind power plants can be extremely rapid, and the stability of the power grid is endangered. To prevent these problems, some countries have set ramp rate (RR) limits that the output powers of power plants must not exceed. One solution to mitigate the power fluctuations of a power plant is to equip the power plant with an energy storage system (ESS). The topic of this thesis is to investigate the power fluctuations of PV–wind power plants and to discover the required sizes for the ESSs that are coupled with the power plants. The goal of this thesis was to investigate how the size of the centralized ESS for the PV–wind power plant differs from the sizes of the ESSs for the separate PV and wind power plants. This investigation was done for the small- and large-scale PV–wind power plants. It was also investigated that how the different levels of nominal PV and wind power affect the required size of the centralized ESS. The ESSs of this thesis were virtual and the output powers of the power plants were modeled based on climatic measurements done at Tampere University Solar PV Power Station Research Plant in Finland. The measured quantities were irradiance, PV module backside temperature, wind speed and ambient temperature. The modeled PV and wind powers seemed to match the literature well. It was found that the required size of the ESS for the PV power plant is larger than for the wind power plant in the small- and large-scale investigations. It was also found that on general, the relative size of the centralized ESS of the PV–wind power plant is smaller than the relative sizes of the separate ESSs of the PV and wind power plants. When the nominal PV power was scaled in contrast to the nominal wind power, it was found that the required relative energy and power capacities of the centralized ESS are the smallest when the scaling coefficients for the nominal PV power were 0.45 and 0.35, respectively

Effects of Ramp Rate Limit on Sizing of Energy Storage Systems for PV, Wind and PV–Wind Power Plants

As the share of highly variable photovoltaic (PV) and wind power production increases, there is a growing need to smooth their fast power fluctuations. Some countries have set power ramp rate (RR) limits that the output powers of power plants may not exceed. In this study, the effects of RR limit on the sizing of energy storage systems (ESS) for PV, wind, and PV–wind power plants are examined. These effects have been studied prior for PV power plants. However, for the wind and PV–wind power plants, the effects of the RR limit are studied comprehensively for the first time. In addition, the effects of the size of the power plant are considered. The study is based on climatic measurements carried out with a sampling frequency of 10 Hz for a period of 153 days. The modeling of the PV and wind powers and the simulation of the RR-based control algorithm of the ESS were completed using MATLAB. The results show that as the applied RR limit increased from 1%/min to 20%/min, the required relative energy capacities of the ESSs of the PV, wind, and PV–wind power plants decreased roughly 88%, 89%, and 89%, respectively. The required relative power capacities of the ESSs of the PV, wind, and PV–wind power plants decreased roughly 15%, 12%, and 20%, respectively. The utilization of the ESSs was found to decrease as the applied RR limit increased and as the size of the power plant grew.publishedVersionPeer reviewe

Effects of Ramp Rate Limit on Sizing of Energy Storage System for PV-Wind Power System

The power produced by variable renewable energy power plants (VREPP) can fluctuate heavily and cause issues in the power grid. To prevent the power quality issues in the grid, some countries have set a ramp-rate limit (RR) that the generated output power of power plants may not exceed. The power fluctuations of VREPPs are often mitigated by an energy storage system (ESS) and a power smoothing method. This paper presents how the RR limit value affects the size of an ESS needed for a photovoltaic (PV)-wind power system. Also, the size of the power plant is considered, and how it affects the size of the ESS. The generated power of the PV-wind power system was simulated using measured irradiance, temperature and ind speed. An RR-based control algorithm was used to operate the virtual ESS. It was found that the increase in the RR limit greatly decreases the size of the ESS. The size of the power plant also significantly affects the size of the ESS.Peer reviewe

Energian varastointi paineilmaan

Uusiutuvan energian käyttäminen sähköntuotantoon on haasteellista, sillä uusiutuvan energian tuottaminen on epäsäännöllistä. Yksi lupaava ratkaisu tähän ongelmaan on energian varastointi paineilmaan (engl. Compressed Air Energy Storage, CAES). Tässä työssä tutkitaan erilaisia paineilman tuotantomuotoja ja paineilmavarastoja, sekä niitä vertaillaan kirjallisuuden perusteella. Sähköntuotantoa pystytään säätelemään ja tasaamaan paineilmavaraston avulla. Paineilmaa tuotetaan sähköenergialla kompressorien avulla paineilmavarastoon, kun sähkön kysyntä ja hinta ovat alhaiset. Paineilmasta tuotetaan takaisin sähköenergiaa turbiinin ja generaattorin avulla, kun sähkön kysyntä ja hinta ovat taas korkealla. Paineilmaa tuotettaessa ilman puristusvaiheessa ilman lämpötila kohoaa korkeaksi. Esimerkiksi kun ilman painetta kasvatetaan puristuksessa 10 baaria, ilman lämpötila nousee tällöin noin 300 celsiusastetta. Paineilmasta pitää poistaa lämpöenergiaa, jotta paineilman lämpötila laskisi ja paineilman varastointi olisi mahdollista. Paineilman lämpöenergian käsittely on ratkaisevin tekijä jaoteltaessa eri paineilman tuotanto-muotoja. Tässä työssä käsitellään kolmea eri paineilman tuotantomuotoa: diabaattista, adia-baattista ja isotermistä tuotantomuotoa. Diabaattinen tuotantomuoto on tällä hetkellä ainoa käytössä oleva tuotantomuoto suurissa CAES-laitoksissa. Diabaattisessa tuotantomuodossa ei oteta talteen lämpöenergiaa, kun taas adiabaattisessa tuotantomuodossa lämpöenergia otetaan talteen, ja lämpöenergiaa käytetään ilman laajentumisvaiheessa hyödyksi. Isotermisessä tuotan-tomuodossa taas ilman lämpötilan muutos halutaan minimoida. Paineilmavarastoja on erilaisia sekä rakenteeltaan että toiminnaltaan. Paineilmavarastot ovat joko isobaarisia tai isokoorisia. Isokooriset paineilmavarastot ovat yksinkertaisempia toimin-naltaan kuin isobaariset varastot. Tällä hetkellä toimivissa CAES-laitoksissa on käytössä vain isokoorisia varastoja. Paineilmavarastona voidaan käyttää maanalaisia luolamuodostelmia tai rakennettuja säiliöitä. CAES-laitosten paineilmavarastoina pyritään hyödyntämään luola-muodostelmia, sillä niiden käyttöönottokustannukset ovat paljon matalammat kuin rakennetuilla säiliöillä. Kirjallisuuden mukaan adiabaattisella paineilman tuotantomuodolla on eniten potentiaalia yleistyä täysimittaiseen käyttöön. Isotermisellä tuotantomuodolla voidaan saavuttaa adiabaattista tuotantomuotoa korkeampi hyötysuhde, mutta isoterminen tuotantomuoto on kehityksessä vasta laboratorioasteella. CAES-laitoksen sijainti on tärkeä, sillä luolamuodostelmien käyttäminen paineilmavarastona laskee laitoksen hintaa huomattavasti

Effects of Ramp Rate Limit on Sizing of Energy Storage Systems for PV-Wind Power System

The power produced by variable renewable energy power plants (VREPP) can fluctuate heavily and cause issues in the power grid. To prevent the power quality issues in the grid, some countries have set a ramp-rate limit (RR) that the generated output power of power plants may not exceed. The power fluctuations of VREPPs are often mitigated by an energy storage system (ESS) and a power smoothing method. This paper presents how the RR limit value affects the size of an ESS needed for a photovoltaic (PV)-wind power system. Also, the size of the power plant is considered, and how it affects the size of the ESS. The generated power of the PV-wind power system was simulated using measured irradiance, temperature and ind speed. An RR-based control algorithm was used to operate the virtual ESS. It was found that the increase in the RR limit greatly decreases the size of the ESS. The size of the power plant also significantly affects the size of the ESS.Peer reviewe