Title: Review of energy system flexibility measures to enable high levels of variable renewable electricity Article Type: Review Article Keywords: energy system flexibility; DSM; energy storage; ancillary service; electricity market; smart grid Abstract: 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. AbstractThe 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 avai...

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 the yearly 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.Keywords: photovoltaics, intelligent building, demand side management, prosumer, energy storage, system control Highlights:• A new model of a heat pump with storage, a battery and shiftable appliances.• Both fixed and variable condensing modes of the heat pump.• A case study with a Finnish low-energy house.• Cost-optimal control decreased cost by 13-25% and grid feed-in by 8-88%.• Heat pump with storage and a battery were more effective than shiftable appliances. Nomenclature

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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. 3 IntroductionNanostructured dye solar cells (DSC) [1] represent a potentially cheap photovoltaics option due to simple manufacturing methods and cheap materials. Traditionally DSC have been prepared on glass substrates equipped with transparent conducting oxide (TCO). Although glass is a good option in terms of performance and stability [2,3], its high cost [4] and preparation limited to batch production motivate to find alternatives. A key issue in the commercialization of the DSC is to use roll-to-roll mass production methods to enable cost-effective solutions. Firstly, flexible substrates such as plastics are needed for roll-to-roll production. Secondly, flexibility of the electrode on top of the substrate is required. For instance Miyasaka et al. have demonstrated flexible photoelectrodes that give good cell efficiency (5.8 %) [5].In this work the focus is on counter electrodes. The main task of a counter electrode is to efficiently return the charge from the counter electrode back to electrolyte. Low charge transfer resistances are reached with Pt catalyst layers which are commonly prepared with a high temperature treatment at 400 °C [6]. To lower the cost, the use of carbon has been introduced [7]. The structures of DSC with Pt and porous carbon catalyst layers are show in Figure 1. To compensate the high charge transfer resistance of carbon, the carbon film is thick, usually around 10-20 μm, in order to have large surface area for the catalyst reaction [7]. To create good bonding between the particles which is needed to get high conductivity in the catalyst film, the layer is normally sintered is heat treated at high temperatures (~450 °C) [7].When flexible plastic substrates are used, low temperature methods (<150 °C) are required. Instead of sintering, low temperature pressing has been employed to get good connection between the particles [8,9]. These low temperature layers have provided low charge transfer resistance 0.5-2Ωcm 2 [9]. There have, however, been problems with the flaking of the catalyst layer and the related 4 poor flexibility [9]. Good flexibility of the counter electrode catalyst layer is, however, essential for roll to roll mass production and also important for special applications.In this work we gelatinize carbon paste and combined it to the previously developed pressing method to produce good adhesion between the particles and achieve sufficient flexibility for roll-toroll production. The inspiration for this work came from our previous stud...

Space conditioning, and cooling in particular, is a key factor in human productivity and well-being across the globe. During the 21 st 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 21 st 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 21 st 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.