Review of energy system flexibility measures to enable high levels of variable renewable electricity

The paper reviews different approaches, technologies, and strategies to manage large-scale schemes of variable renewable electricity such as solar and wind power. We consider both supply and demand side measures. In addition to presenting energy system flexibility measures, their importance to renewable electricity is discussed. The flexibility measures available range from traditional ones such as grid extension or pumped hydro storage to more advanced strategies such as demand side management and demand side linked approaches, e.g. the use of electric vehicles for storing excess electricity, but also providing grid support services. Advanced batteries may offer new solutions in the future, though the high costs associated with batteries may restrict their use to smaller scale applications. Different “P2Y”-type of strategies, where P stands for surplus renewable power and Y for the energy form or energy service to which this excess in converted to, e.g. thermal energy, hydrogen, gas or mobility are receiving much attention as potential flexibility solutions, making use of the energy system as a whole. To “functionalize” or to assess the value of the various energy system flexibility measures, these need often be put into an electricity/energy market or utility service context. Summarizing, the outlook for managing large amounts of RE power in terms of options available seems to be promising.Peer reviewe

Meeting Global Cooling Demand with Photovoltaics during the 21st Century

Space conditioning, and cooling in particular, is a key factor in human productivity and well-being across the globe. During the 21st century, global cooling demand is expected to grow significantly due to the increase in wealth and population in sunny nations across the globe and the advance of global warming. The same locations that see high demand for cooling are also ideal for electricity generation via photovoltaics (PV). Despite the apparent synergy between cooling demand and PV generation, the potential of the cooling sector to sustain PV generation has not been assessed on a global scale. Here, we perform a global assessment of increased PV electricity adoption enabled by the residential cooling sector during the 21st century. Already today, utilizing PV production for cooling could facilitate an additional installed PV capacity of approximately 540 GW, more than the global PV capacity of today. Using established scenarios of population and income growth, as well as accounting for future global warming, we further project that the global residential cooling sector could sustain an added PV capacity between 20-200 GW each year for most of the 21st century, on par with the current global manufacturing capacity of 100 GW. Furthermore, we find that without storage, PV could directly power approximately 50% of cooling demand, and that this fraction is set to increase from 49% to 56% during the 21st century, as cooling demand grows in locations where PV and cooling have a higher synergy. With this geographic shift in demand, the potential of distributed storage also grows. We simulate that with a 1 m$^3$ water-based latent thermal storage per household, the fraction of cooling demand met with PV would increase from 55% to 70% during the century. These results show that the synergy between cooling and PV is notable and could significantly accelerate the growth of the global PV industry

Meeting Global Cooling Demand with Photovoltaics during the 21st Century

Space conditioning, and cooling in particular, is a key factor in human productivity and well-being across the globe. During the 21st century, global cooling demand is expected to grow significantly due to the increase in wealth and population in sunny nations across the globe and the advance of global warming. The same locations that see high demand for cooling are also ideal for electricity generation via photovoltaics (PV). Despite the apparent synergy between cooling demand and PV generation, the potential of the cooling sector to sustain PV generation has not been assessed on a global scale. Here, we perform a global assessment of increased PV electricity adoption enabled by the residential cooling sector during the 21st century. Already today, utilizing PV production for cooling could facilitate an additional installed PV capacity of approximately 540 GW, more than the global PV capacity of today. Using established scenarios of population and income growth, as well as accounting for future global warming, we further project that the global residential cooling sector could sustain an added PV capacity between 20-200 GW each year for most of the 21st century, on par with the current global manufacturing capacity of 100 GW. Furthermore, we find that without storage, PV could directly power approximately 50% of cooling demand, and that this fraction is set to increase from 49% to 56% during the 21st century, as cooling demand grows in locations where PV and cooling have a higher synergy. With this geographic shift in demand, the potential of distributed storage also grows. We simulate that with a 1 m$^3$ water-based latent thermal storage per household, the fraction of cooling demand met with PV would increase from 55% to 70% during the century. These results show that the synergy between cooling and PV is notable and could significantly accelerate the growth of the global PV industry

A carbon gel catalyst layer for the roll-to-roll production of dye solar cells

Carbon gel catalyst layers were used in dye solar cells. These layers were prepared on flexible plastic substrates at low temperatures (130 °C). The carbon gel, demonstrated excellent flexibility which is an important feature for roll-to-roll production and special applications of dye solar cells. The use of these low cost and highly flexible catalyst layers resulted in good photovoltaic performance; only 10% lower than dye solar cells with rigid glass-based counter electrodes prepared with thermal platinization at ∼400 °C temperature.Peer reviewe

Edistyneen plasmonisiin ja eristenanorakenteisiin perustuvan valonhallinnan kehitystä ohutkalvo- ja kiteisen piin aurinkokennoihin

In this thesis, light scattering plasmonic nanostructures were studied as light management techniques in silicon solar cells with an experiment and a literature review, and solar cell designs was developed for future research on plasmonic and dielectric nanostructures. The broad literature review on the state of the art of plasmonic scatterers revealed that such nanostructures on the front side of Si solar cells have been shown to be superior to flat cells with an optimized anti-reflection coating, but the use of texturing has not been outperformed. Plasmonic nanostructures at the back, combined with Mie scatterers at the front side, have been shown to outperform the Asahi U texture for ultra-thin film a-Si solar cells. The effect of computationally optimized arrays of Ag and Al nanoparticles on the front surface of thin-film a-Si:H solar cells on the photovoltaic performance of the device was studied experimentally. The nanostructures enhanced EQE at long wavelengths, and decreased at short. The Ag structure enhanced JSC by 4.6 % compared to the best measured flat cell structure with an anti-reflection coating, and the Al structure by 3.4 %. To the best of the author's knowledge, an experimental demonstration of performance enhancement with an Al nanostructure has not been presented thus far in the literature. Crystalline Si solar cell designs were developed for experiments with metallic and dielectric photonic nanostructures. The designs are based on the IBC Si-HJ architecture and processed on mirror-polished FZ mono-Si wafers, with surface passivation implemented with SiNx for the cells with metallic nanoparticles and a-Si:H for the cells with dielectric nanoparticles.Tässä diplomityössä tutkittiin valoa sirottavia plasmonisia nanorakenteita piiaurinkokennojen valonhallintamenetelminä kokeellisesti ja kirjallisuusselvityksellä, ja suunniteltiin sopivat aurinkokennot metallisilla ja eristenanohiukkasrakenteilla tapahtuvaa tulevaa tutkimusta varten. Valoa sirottavien plasmonisten nanorakenteiden tekniikan nykytila selvitettiin laajalla kirjallisuuskatsauksella. On osoitettu, että tällaiset nanorakenteet yhdistettynä antiheijastuspinnoitteeseen piiaurinkokennon etupinnalla ovat parempi valonhallintamenetelmä kuin tasainen kenno, jossa on pelkkä optimoitu antiheijastuspinnoite. Teksturointia paremmin toimivaa kennon etupinnalla olevaa plasmonista nanorakennetta ei ole pystytty esittämään. Kennon takapinnalla olevan plasmonisen nanorakenteen, yhdistettynä Mie-sirottajaan kennon etupinnalla on osoitettu toimivan teollisuudessa käytettyä Asahi U -tekstuuria paremmin ultraohuissa amorfisen piin aurinkokennoissa. Laskennallisesti optimoitujen, a-Si:H-ohutkalvoaurinkokennojen etupinnalle valmistettujen Ag- ja Al- nanohiukkashilojen vaikutusta laitteen toimintaan tutkittiin kokeellisesti. Nanorakenteet paransivat laitteen ulkoista kvanttihyötysuhdetta pitkillä aallonpituuksilla ja heikensivät sitä lyhyillä. Hopeananohiukkasrakenne paransi oikosulkuvirtaa 4,6 % verrattuna parhaaseen mitattuun tasaiseen pelkällä antiheijastuspinnoitteella varustettuun kennoon, alumiininanohiukkasrakenne 3,4 %. Kirjallisuudesta ei löytynyt viitettä kokeellisesti osoitetusta aurinkokennon oikosulkuvirran paranemisesta alumiininanohiukkasrakenteella. Kiteisen piin aurinkokennot suunniteltiin metallisilla ja eristenanohiukkasrakenteilla tapahtuvaa tulevaa tutkimusta varten. Kennot perustuvat IBC-heteroliitosarkkitehtuuriin, ne prosessoidaan mekaanis-kemiallisesti kiillotetuille FZ-yksikiteisille piikiekoille, ja niiden pintapassivointi toteutetaan piinitridillä metallisten nanohiukkasten tapauksessa ja amorfisella piillä eristenanohiukkasten tapauksessa

Kysyntäjousto aurinko- ja tuulisähkön integroinnissa

A major increase in the use of solar and wind energy in electricity production is envisioned to limit CO2 emissions, along with other low-carbon energy sources, as well as energy efficiency and electrification of heating, cooling, and transportation. This requires increasing flexibility in power systems, warranting the searching for enhanced flexibility in all possible sources. Wind energy has already lowered electricity market prices, calling for flexibility in the short term. This dissertation investigates the technical and economic potential of demand side flexibility for managing the variability of solar and wind production. To this end, three new mathematical models capable of optimal control are presented. The first model considers a heat pump with thermal storage, batteries, and shiftable appliances in a building with photovoltaics (PV); the second looks at power-to-heat conversion with thermal storage in district heating and shiftable loads in a city with PV and wind; and the third model focuses on space heating with heat pumps and electric vehicles in houses with PV. A case study with the first model on a Finnish low-energy house showed a 13-25 % cost decrease and an 8-88 % grid feed-in decrease with cost-optimal control and hourly spot market-based pricing, compared to inflexible reference control with a constant price for bought electricity. The exact values depend on the PV capacity and chosen flexibility sources. Limiting grid feed-in to zero decreased the energy efficiency of the control. The heat pump with storage and batteries provided more flexibility than shiftable appliances. Helsinki, Finland was studied with the second model. For a VRE scheme providing circa 50 % of the electricity consumption of the city through self-consumption, power-to-heat with thermal storage could absorb all the surplus VRE production. Shiftable loads significantly reduced the net load magnitude. Cost-optimally controlled power-to-heat with heat pumps and thermal storage as well as load shifting with electric heating and commercial refrigeration were found to be profitable investments. Between 1 and 10 Swedish net zero energy houses were investigated with the third model, resulting in 8-33% annual electricity cost savings per household with various system configurations, along with significant increases in PV self-consumption. The cost of additional battery degradation significantly decreases the added value of bi-directional vehicle-to-grid compared to flexible smart charging only. The thesis shows that power-to-heat in district heating, distributed electric heating, commercial refrigeration, batteries, and electric vehicles are effective demand side flexibility sources. They should be considered for flexibility provision in power systems with solar and wind production.Aurinko- ja tuulisähkön huomattavaa lisäämistä suunnitellaan hiilidioksidipäästöjen rajoittamiseksi energiatehokkuuden, muun vähäpäästöisen energiantuotannon sekä lämmityksen, jäähdytyksen ja liikenteen sähköistämisen lisäksi. Tämä vaatii lisää joustavuutta sähköverkkoihin. Tuulivoima on jo laskenut sähkön markkinahintaa merkittävästi, mikä tekee eri joustolähteiden tutkimisen ajankohtaiseksi. Tässä väitöskirjassa tutkitaan sähkön kysyntäjouston teknistä ja taloudellista potentiaalia aurinko- ja tuulisähkön tuotannon vaihteluihin mukautumisessa kolmella uudella optimaalisen ohjauksen laskevalla matemaattisella mallilla. Ensimmäinen mallintaa lämpöpumpun ja lämpövaraston, akut ja joustavat sähkölaitteet rakennuksessa, jossa on aurinkosähköä. Toinen keskittyy sähkön muuntamiseen lämmöksi kaukolämmössä lämpövarastojen kanssa ja joustaviin sähkönkulutuksiin kaupungissa, jossa on aurinkosähköä ja tuulivoimaa. Kolmas mallintaa lämpöpumppulämmityksen ja sähköautot taloissa, joissa on aurinkosähköä. Ensimmäisellä mallilla tutkittiin suomalaista matalaenergiataloa. Kustannusoptimaalinen ohjaus sähkön markkinahintapohjaisella tuntihinnoittelulla tuotti 13-25 % kustannussäästöä verrattuna joustamattomaan ohjaukseen vakiohintaisella ostosähköllä. Sähkön syöttö verkkoon väheni myös 8-88 %. Tarkat arvot riippuvat aurinkosähkön mitoituksesta ja valituista joustolähteistä. Sähkön verkkoon syötön estäminen laski ohjauksen energiatehokkuutta. Lämpöpumppu ja lämpövarasto sekä akut tarjosivat enemmän joustoa kuin joustavat sähkölaitteet. Toisella mallilla tutkittiin Helsinkiä. Kun aurinko- ja tuulisähkö oli mitoitettu tuottamaan noin 50 % kaupungin sähköntarpeesta paikallisen kulutuksen kautta, sähköinen kaukolämmön tuotanto lämpövarastoilla pystyi ottamaan vastaan kaiken ylijäämäsähkön. Joustavat sähkökuormat pystyivät pienentämään sähkön nettokuormaa merkittävästi. Sähköinen kaukolämpö lämpöpumpuilla ja lämpövarastoilla sekä joustaminen sähkölämmityksellä ja kaupallisella jäähdytyksellä havaittiin kannattaviksi investoinneiksi. Kolmatta mallia sovellettiin 1-10 ruotsalaisen nettonollaenergiatalon tutkimiseen. Kustannusoptimaalinen ohjaus tuotti 8-33% säästöä taloa kohti eri tapauksissa ja lisäsi aurinkosähkön omaa kulutusta huomattavasti. Akkujen lisääntynyt kuluminen laski huomattavasti sähköautojen verkkoon purkamisen lisäarvoa verrattuna pelkkään joustavaan lataamiseen.Tutkimus osoittaa, että sähköinen kaukolämmön tuotanto, hajautettu sähkölämmitys, kaupallinen jäähdytys, akut ja sähköautot ovat vaikuttavia kysyntäjouston lähteitä. Niiden käyttöä tulisi harkita sähköverkkojen joustojen lisäämiseksi aurinko- ja tuulisähkön tuotannon osuuden kasvaessa

Optimal and rule-based control strategies for energy flexibility in buildings with PV

PV installations in buildings can utilize different on-site flexibility resources to balance mismatch in electricity production and demand. This paper studies cost-optimal and rule-based control for buildings with PV, employing a heat pump, thermal and electrical storage and shiftable loads as flexibility sources to increase the value of PV for the prosumer. The cost-optimal control minimizes variable electricity cost employing market data on electricity price and optionally constrains grid feed-in to zero; the rule-based control aims at maximizing PV self-consumption. The flexibility strategies are combined into a simulation model to analyze different system configurations over a full year. The applicability of the new model is demonstrated with a case study with empirical data from a real low-energy house in Southern Finland. Compared to inflexible reference control with a constant price for bought electricity, cost-optimal control employing hourly market price of electricity achieved 13-25% savings in theyearly electricity bill. Moreover, 8-88% decrease in electricity fed into the grid was obtained. The exact values depend on PV capacity and the flexibility options chosen. Limiting grid feed-in to zero led to less energy efficient control. The most effective flexibility measures in this case turned out to be thermal storage with a heat pump and a battery, whereas shiftable appliances showed only a marginal effect. (C) 2015 Elsevier Ltd. All rights reserved.Peer reviewe

Review of energy system flexibility measures to enable high levels of variable renewable electricity

The paper reviews different approaches, technologies, and strategies to manage large-scale schemes of variable renewable electricity such as solar and wind power. We consider both supply and demand side measures. In addition to presenting energy system flexibility measures, their importance to renewable electricity is discussed. The flexibility measures available range from traditional ones such as grid extension or pumped hydro storage to more advanced strategies such as demand side management and demand side linked approaches, e.g. the use of electric vehicles for storing excess electricity, but also providing grid support services. Advanced batteries may offer new solutions in the future, though the high costs associated with batteries may restrict their use to smaller scale applications. Different “P2Y”-type of strategies, where P stands for surplus renewable power and Y for the energy form or energy service to which this excess in converted to, e.g. thermal energy, hydrogen, gas or mobility are receiving much attention as potential flexibility solutions, making use of the energy system as a whole. To “functionalize” or to assess the value of the various energy system flexibility measures, these need often be put into an electricity/energy market or utility service context. Summarizing, the outlook for managing large amounts of RE power in terms of options available seems to be promising.Peer reviewe

Improved flexibility with large-scale variable renewable power in cities through optimal demand side management and power-to-heat conversion

Solar and wind power are potential carbon-free energy solutions for urban areas, but they are also subject to large variability. At the same time, urban areas offer promising flexibility solutions for balancing variable renewable power. This paper presents models for optimal control of power-to-heat conversion to heating systems and shiftable loads in cities to incorporate large variable renewable power schemes. The power-to-heat systems comprise heat pumps, electric boilers, and thermal storage. The control strategies comprise optimal matching of load and production, and cost-optimal market participation with investment analysis. All analyses are based on hourly data. The models are applied to a case study in Helsinki, Finland. For a scheme providing ca. 50% of all electricity in the city through self-consumption of variable renewables, power-to-heat with thermal storage could absorb all the surplus production. A significant reduction in the net load magnitude was obtained with shiftable loads. Investments to both power-to-heat and load shifting with electric heating and commercial refrigeration have a positive net present value if the resources are controlled cost-optimally.Peer reviewe