question: Why is it so difficult to store renewable energy?
comment: Because energy storage sucks. Anytime you convert energy from one kind to another there are losses. You can only convert so much energy at a time, the storage only works for a limited time versus something like a generator that keeps going if you add more fuel. Batteries - expensive, limited lifetime, take up room, typically are more efficient when discharged or charged slowly. Heat or extreme cold makes them less efficient. Not light. Pumped storage - requires land for pond or dam, hydroelectric turbine, water evaporates leading to losses, etc.
passages: Storage of electrical energy results in some lost energy because storage and retrieval are not perfectly efficient. Storage may also require substantial capital investment and space for storage facilities.
  
  Section::::Compensating for variability.:Geographic diversity.
   Many renewable energy sources (notably solar and wind) produce variable power. Storage systems can level out the imbalances between supply and demand that this causes. Electricity must be used as it is generated or converted immediately into storable forms.
   For most ESaaS services, energy is stored during night time, off-peak hours when energy production is created from non-carbon emitting sources. The energy is then used to offset the required carbon emitting production during peak-times. The load shifting capability provided by ESaaS displaces heavy emitting generation requirements.
  
  Section::::Pricing.
   To provide household electricity in remote areas (that is areas which are not connected to the mains electricity grid), energy storage is required for use with renewable energy. Energy generation and consumption systems used in the latter case are usually stand-alone power systems.
  
  Energy from renewable sources can also be stored as heat or cold, through thermal energy storage technologies. For instance, summer heat can be stored for winter heating, or winter cold can be stored for summer air conditioning.
  
  Section::::Non-renewable energy sources.
   Renewable energy production from some sources such as wind and solar is more variable and more geographically spread than technology based on fossil fuels and nuclear. While integrating it into the wider energy system is feasible, it does lead to some additional challenges. In order for the energy system to remain stable, a set of measurements can be taken. Implementation of energy storage, using a wide variety of renewable energy technologies, and implementing a smart grid in which energy is automatically used at the moment it is produced can reduce risks and costs of renewable energy implementation.
   Section::::Integration into the energy system.:Electrical energy storage.
  
  Electrical energy storage is a collection of methods used to store electrical energy. 
  
  Electrical energy is stored during times when production (especially from intermittent sources such as wind power, tidal power, solar power) exceeds consumption, and returned to the grid when production falls below consumption. Pumped-storage hydroelectricity accounts for more than 90% of all grid power storage. Costs of lithium-ion batteries are dropping rapidly, and are increasingly being deployed grid ancillary services and for domestic storage.
  
  Section::::Market and industry trends.
   The largest source and the greatest store of renewable energy is provided by hydroelectric dams. A large reservoir behind a dam can store enough water to average the annual flow of a river between dry and wet seasons. A very large reservoir can store enough water to average the flow of a river between dry and wet years. While a hydroelectric dam does not directly store energy from intermittent sources, it does balance the grid by lowering its output and retaining its water when power is generated by solar or wind. If wind or solar generation exceeds the regions hydroelectric capacity, then some additional source of energy will be needed.
   The first study using DIETER examines the power storage requirements for renewables uptake ranging from 60% to 100%. Under the baseline scenario of 80% (the lower bound German government target for 2050), grid storage requirements remain moderate and other options on both the supply side and demand side offer flexibility at low cost. Nonetheless storage plays an important role in the provision of reserves. Storage becomes more pronounced under higher shares of renewables, but strongly depends on the costs and availability of other flexibility options, particularly biomass availability.
  
  Section::::Open electricity sector models.:Dispa-SET.
   All managed grids already have existing operational and "spinning" reserve to compensate for existing uncertainties in the power grid. The addition of intermittent resources such as wind does not require 100% "back-up" because operating reserves and balancing requirements are calculated on a system-wide basis, and not dedicated to a specific generating plant.
   The capacity of a reliable renewable power supply, can be fulfilled by the use of backup or extra infrastructure and technology, using mixed renewables to produce electricity above the intermittent average, which may be used to meet regular and unanticipated supply demands. Additionally, the storage of energy to fill the shortfall intermittency or for emergencies can be part of a reliable power supply.
  
  Section::::Compensating for variability.:Operational reserve.
   The French consulting firm Yole Développement estimates the “stationary storage” market could be a $13.5 billion opportunity by 2023, compared with less than $1 billion in 2015.
  
  Section::::Benefits of storage and managing peak load.:Demand side management and grid storage.
  
  The demand side can also store electricity from the grid, for example charging a battery electric vehicle stores energy for a vehicle and storage heaters, district heating storage or ice storage provide thermal storage for buildings. At present this storage serves only to shift consumption to the off-peak time of day, no electricity is returned to the grid.
   Storing wind or solar energy using thermal energy storage though less flexible, is considerably less expensive than batteries. A simple 52-gallon electric water heater can store roughly 12 kWh of energy for supplementing hot water or space heating.
  
  For purely financial purposes in areas where net metering is available, home generated electricity may be sold to the grid through a grid-tie inverter without the use of batteries for storage.
  
  Section::::Applications.:Grid electricity and power stations.
  
  Section::::Applications.:Grid electricity and power stations.:Renewable energy storage.
   Compressed-air energy storage (CAES) plants can bridge the gap between production volatility and load. CAES storage addresses the energy needs of consumers by effectively providing readily available energy to meet demand. Renewable energy sources like wind and solar energy have variable resources. As a result, the supplement of other forms of energy is necessary to meet energy demand during periods of decreased resource availability. Compressed-air energy storage plants are capable of taking in the surplus energy output of renewable energy sources during times of energy over-production. This stored energy can be used at a later time when demand for electricity increases or energy resource availability decreases.
   The most popular technique is ice storage, which requires less space than water and is less costly than fuel cells or flywheels. In this application, a standard chiller runs at night to produce an ice pile. Water then circulates through the pile during the day to chill water that would normally be the chiller's daytime output.
   The economics of Energy Storage strictly depends on the reserve service requested, and several uncertainty factors affect the profitability of Energy Storage. Therefore, not every Energy Storage is technically and economically suitable for the storage of several MWh, and the optimal size of the Energy Storage is market and location dependent.
  
  Moreover, ESS are affected by several risks, e.g.:
  
  1) techno-economic risks, which are related to the specific technology;
  
  2) Market risks, which are the factors that affect the electricity supply system;
  
  3) Regulation and policy risks.
   In the twentieth century grid, electrical power was largely generated by burning fossil fuel. When less power was required, less fuel was burned. Concerns with air pollution, energy imports, and global warming have spawned the growth of renewable energy such as solar and wind power. Wind power is uncontrolled and may be generating at a time when no additional power is needed. Solar power varies with cloud cover and at best is only available during daylight hours, while demand often peaks after sunset ("see" duck curve). Interest in storing power from these intermittent sources grows as the renewable energy industry begins to generate a larger fraction of overall energy consumption.
   Transmission of electrical power from power stations to population centres is inherently inefficient, due to transmission losses in electrical grids, particularly within power-hungry dense conurbations where power stations are harder to site. By allowing a greater proportion of on-site generated electricity to be consumed on-site, rather than exported to the energy grid, home energy storage devices can reduce the inefficiencies of grid transport.
  
  Section::::Advantages.:Energy grid support.
  
  Home energy storage devices, when connected to a server via the internet, can theoretically be ordered to provide very short-term services to the energy grid:-
   Common examples of energy storage are the rechargeable battery, which stores chemical energy readily convertible to electricity to operate a mobile phone, the hydroelectric dam, which stores energy in a reservoir as gravitational potential energy, and ice storage tanks, which store ice frozen by cheaper energy at night to meet peak daytime demand for cooling.
  
  Fossil fuels such as coal and gasoline store ancient energy derived from sunlight by organisms that later died, became buried and over time were then converted into these fuels. 
   Demand for electricity from the world's various grids varies over the course of the day and from season to season. For the most part, variation in electric demand is met by varying the amount of electrical energy supplied from primary sources. Increasingly, however, operators are storing lower-cost energy produced at night, then releasing it to the grid during the peak periods of the day when it is more valuable. In areas where hydroelectric dams exist, release can be delayed until demand is greater; this form of storage is common and can make use of existing reservoirs. This is not storing "surplus" energy produced elsewhere, but the net effect is the same – although without the efficiency losses. Renewable supplies with variable production, like wind and solar power, tend to increase the net variation in electric load, increasing the opportunity for grid energy storage.
   As of 2019, the cost and logistics of energy storage for large population centres is a significant challenge, although the cost of battery systems has plunged dramatically. For instance, a 2019 study found that for solar and wind energy to meet energy demand for a week of extreme cold in the eastern and midwest United States, energy storage capacity would have to increase from the 11 GW currently in place to 277.9 GW. 
   Reducing greenhouse emissions, is being tackled at all scales, ranging from tracking the passage of carbon through the carbon cycle to the commercialization of renewable energy, developing less carbon-hungry technology and transport systems and attempts by individuals to lead carbon-neutral lifestyles by monitoring the fossil fuel use embodied in all the goods and services they use. Engineering of emerging technologies such as carbon-neutral fuel and energy storage systems such as power to gas, compressed air energy storage, and pumped-storage hydroelectricity are necessary to store power from transient renewable energy sources including emerging renewables such as airborne wind turbines.
   Renewable resources are available each year, unlike non-renewable resources, which are eventually depleted. A simple comparison is a coal mine and a forest. While the forest could be depleted, if it is managed it represents a continuous supply of energy, vs. the coal mine, which once has been exhausted is gone. Most of earth's available energy resources are renewable resources. Renewable resources account for more than 93 percent of total U.S. energy reserves. Annual renewable resources were multiplied times thirty years for comparison with non-renewable resources. In other words, if all non-renewable resources were uniformly exhausted in 30 years, they would only account for 7 percent of available resources each year, if all available renewable resources were developed.
   BULLET::::- In a close-to-100% wind scenario, surplus wind power can be allowed for by increasing the levels of the existing Reserve and Frequency Service schemes and by extending the scheme to domestic-sized loads. Energy can be stored by advancing deferrable domestic loads such as storage heaters, water heaters, fridge motors, or even hydrogen production, and load can be shed by turning such equipment off.
   BULLET::::- Some coal, gas, or hydro power plants are partially loaded and then controlled to change as demand changes or to replace rapidly lost generation. The ability to change as demand changes is termed "response". The ability to quickly replace lost generation, typically within timescales of 30 seconds to 30 minutes, is termed "spinning reserve".
  
  BULLET::::- Generally thermal plants running as peaking plants will be less efficient than if they were running as base load.
  
  BULLET::::- Hydroelectric facilities with storage capacity (such as the traditional dam configuration) may be operated as base load or peaking plants.
   Other sources of thermal energy for storage include heat or cold produced with heat pumps from off-peak, lower cost electric power, a practice called peak shaving; heat from combined heat and power (CHP) power plants; heat produced by renewable electrical energy that exceeds grid demand and waste heat from industrial processes. Heat storage, both seasonal and short term, is considered an important means for cheaply balancing high shares of variable renewable electricity production and integration of electricity and heating sectors in energy systems almost or completely fed by renewable energy.
  
  Section::::Solar energy storage.
  
raw_presuppositions: It's uniquely difficult to store renewable energy.
raw_corrections: It's difficult to convert and store any kind of energy.