ME 432 Fundamentals of Modern Photovoltaics

Discussion 40: The Grid and 2 December 2020 Why Do We Need Energy Storage?

• To cope with the variability of wind and solar generation. • Need to accommodate variability in demand over the course of the day. Without storage, there is a need to match supply to demand. • Today, in our grid supply and demand must be balanced at all times to avoid blackouts, cascades, etc. – The moment that is created, it is used.

Typical Burning Plant

http://www.worldcoal.org/coal/uses-of-coal/coal-electricity/

Typical efficiencies for conversion of chemical energy into electricity are around 35%, with the best new plants achieving close to 40%. (US EIA, Annual Energy Review 2019) Power Plant Turbine

• https://www.youtube.com/watch?v=RaRc0oH Bk5M&t=75s • (1:25 s) Improvements to Efficiency

• Typical efficiencies in coal burning plants that use a steam engine are around 35%. But how much better could we do in principle? • As an estimate, let’s calculate the Carnot efficiency for a heat engine,

operating between a high temperature reservoir Th = 550C = 823K (reasonable guess for the boiler temperature) and a cold temperature reservoir Tc = 27C = 300K (a nearby lake or river). T 1− C = 0.64 TH • Improvements? – Combined cycle plants, in which the exhaust of one heat engine (say a engine) is used as a heat source for another. Efficiencies can be around 50% (or more). Typical example: Brayton cycle combined with . – Co-generation plants: the waste heat is fed through steam tunnels and used to heat buildings and residences. Efficiencies around 60%. & Distribution

Four Corners Power Plant, near Farminton, NM.

- 5 coal-fueled generating units - 2 GW plant - Electricity is supplied through transmission lines to Los Angeles, at a distance of ~500 miles The Power Distribution Grid 1000s of V 100,000s of V coming out of through long the power distance station (300-500 mi) transmission lines ~10 kV for local distribution

“Distribution bus” or splitter

240 V The Electric Power Grid

• This entire system of generating stations, substations, transmission lines is called the “electric power grid”. • Most of the electric power companies of the US and Canada are integrated into a single grid for reasons of economy, availability of backup power, ability to trade electric energy. • In North America, as of 2018 we have 850 electric utilities, 3000 power plants, and over 200,000 miles of high voltage transmission lines.

How Supply and Demand Are Balanced Today • Grid operators: constantly monitor and manage the demand, supply, reserve margins, and power mix to ensure that you have immediate access to power in your home or business. – reserve margin: a specified backup generation capacity that can compensate for potential forecasting errors, unexpected power plant shutdowns or weather events. • The grid operator uses a three-phase planning process to ensure that power plants produce the right amount of electricity to meet electric demand at any given time. • Electricity supply must balance demand at all times in order to avoid a blackout or other cascading problem. The production of electricity is adjusted in 15 minute intervals to account for demand changes throughout the day. For this reason, there are three main types of power plants: baseload, load-following, and peakers. How Supply and Demand Are Balanced Today • Baseload power plants meet the minimal power needed by the grid and are designed to be on most of the time. Their , or percent of time operational, is above 80%. They are only shut down or curtailed when performing maintenance or repair. Baseload power is the cheapest type of generation and usually supplied by coal fired and plants because they can provide large amounts of power (up to 1.6 GW). • Load-following plants, also known as intermediate load plants, are typically combined-cycled gas fired power plants, which have a high thermal efficiency of up to 58%. They have a gas turbine and a waste heat recovery system to capture the gas turbine’s exhaust to drive a steam turbine that produces additional electricity. Generation from load- following plants can be ramped up and down as needed. Their capacity factor is usually less than 30% of the time. But they are more complex to maintain and more expensive to operate. • The power plant of “last resort” are peaker plants. They are turned on for even shorter periods of time to meet extremely high high demands, for example, when air conditioning is used during hot days. Due to their low capacity factor, which could be as low as a few hours for the entire year, they the most expensive type of generation.

• Generation, Regional Flow, and Dispatch • https://www.youtube.com/watch?v=28- QU8AyISA&t=63s

• Grid energy storage (also called large-scale energy storage) is a collection of methods used to store electrical energy on a large scale within an electrical power grid. Electrical energy is stored during times when production (especially from intermittent power plants such as renewable electricity sources such as , , ) exceeds consumption, and returned to the grid when production falls below consumption. • As of 2017, the largest form of grid energy storage is dammed , with both conventional hydroelectric generation as well as pumped storage hydroelectricity. • Developments in battery storage have enabled commercially viable projects to store energy during peak production and release during . • Two alternatives to grid storage are the use of peaking power plants to fill in supply gaps and to shift load to other times. Common Approaches

• Pumped Hydro • Utility Scale Flywheel Systems • Compressed Air Energy Storage • Electrochemical Batteries

• Superconducting Magnetic Energy Storage • Electrochemical Capacitors Pumped Hydro

• Already used by electric power systems for load balancing; to balance baseload generation • Stores energy in the form of gravitational potential energy; excess electricity used to pump water uphill – During periods of high demand, the water is released back downhill through turbines • Losses of the pumping process make pumped hydro itself an energy consumer overall, but costs area recovered when electricity can be sold back at high cost during time of peak demand • 181 GW total capacity worldwide in 2020; 95% of all storage installations worldwide • Round trip efficiencies of 70-80% • Key advantage: cheap. • Key limitation: requires a special geography and water availability. • Also low storage density: need a large Bath County, VA: the "largest battery in the world",[2] with a maximum generation capacity reservoir capacity of 3,003 MW,[3] an average of 2,772 MW,[2] and a total storage capacity of 24,000 MWh.[2] Flywheels (‘Mechanical Battery’)

Examples: • A flywheel-storage power system uses a flywheel for energy storage, • In Stephentown, New York, Beacon (see Flywheel energy storage) and can Power operates a flywheel storage be a comparatively small storage power plant with 200 flywheels of 25 kWh capacity and 100 kW of power. facility with a peak power of up to 20 Together this gives 5 MWh capacity and MW. 20 MW of power. • Excess electricity is used to drive a • peak speed at 15,000 rpm. motor that spins a flywheel; when the stored energy is being recovered the • rotor flywheel consists of wound CFRP fibers which are filled motor acts as a generator to convert with resin. the spinning motion back to electricity • sold to the New York power grid. • 85-95% roundtrip efficiencies • Fresno, CAA: running flywheel storage power plants to store solar energy, which is produced in excess quantity in the daytime, for consumption at night. • electricity to compress air, which is usually stored in an old mine or some other kind of geological feature. When electricity demand is high, the compressed air is heated with a small amount of and then goes through turboexpanders t o generate electricity. • RTE 60 - 90% • Two types: – constant Volume Storage (Solution mined caverns, aboveground vessels, aquifers, automotive applications, etc.) – constant Pressure Storage (Underwater pressure vessels, Compressed Air Hybrid Pumped Hydro - Compressed Air Energy Storage (CAES) Storage) Lithium Batteries ion (Electrochemical)

• Lots of types: – Lithium ion (sodium ion – sodium more abundant and cheaper), molten salt batteries, flow batteries (better for scale up) • 80% to 90% efficient for new lithium ion devices. • Cost per power or energy unit is crucial, and currently expensive. – relevant metrics is the $/Wh (or $/W) rather than the Wh/kg (or W/kg). – Growth of electric vehicle induced a fast decrease in the production costs of batteries below $300/kWh. – By optimizing the production chain, major industrials aim to reach $150/kWh by the end of 2020. – Technologies optimized for the grid should focus on low cost and low density. • As of 2019, the maximum power of battery storage power plants is an order of magnitude less than pumped storage power plants, the most common form of grid energy storage. In terms of storage capacity, the largest Flow battery – tanks with liquid battery power plants are about two orders of magnitude less than pumped hydro plants. Emerging

• Hydrogen • Superconducting magnetic energy. • Thermal Energy Storage

https://www.vox.com/energy-and-environment/2019/8/9/20767886/renewable-energy- storage-cost-electricity • Can we achieve a fully 100% grid? • Common answers: – Yes – No, there will always be a need for some amount of alternatives (nuclear, natural gas, , CCS) due to variable nature of wind and solar. • This is really a question about energy storage. If energy storage becomes cheap enough, then yes, we can. • A better question: how cheap does storage have to get for us to be able to achieve 100% renewable grid? Wind & solar: - variable sources - not dispatchable

Grid that relies heavily on non-dispatchable sources requires flexibility to smooth out and balance the fluctuations.

Storage is one way to achieve this flexibility.

If storage gets cheap enough, we can simply add as much storage capacity as needed to achieve 100% renewable grid. • This study analyzes 20 years of hourly history for wind and solar at four locations in the US, • Asks the question: how cheap does storage have to get, for the grid to be able to meet demand 100% of the time for the last 20 years, and have the LCOSE be competitive with conventional electricity production? (100% of the time = ‘100% Equivalent Availability Factor’) • Answer: $20/kWh of stored energy. This is about a 90% reduction from current costs! (It may happen, eventually … but not by 2030). • Assume a cost of: • $1500/kW wind • $1000/kW solar • Storage at • $1000/kW power capacity • $20/kWh energy capacity • Like pumped hydro (Tech I); this is cheap • We have to tune baseload, intermediate, and peaker production so that supply equals demand 100% of the time for the last 20 years (100% Energy Availability Factor, EAF) • Solve for the combination of baseload, intermediate, and peaker and the wind/solar mix that minimizes the LCOSE

What happens if the cost of storage is different from our original assumption?

Answer: The cheaper it is, the more of it we use and the less solar/wind we need to install. The more expensive it is, it is cheaper overall to have more on-demand wind/solar production capacity. At most locations, if we want the LCOSE to be competitive with natural gas, we need storage energy capacity costs to drop to $20 kWh. That is far from where we are today!!

At most locations, if we want the LCOSE to be competitive with natural gas, we need storage energy capacity costs to drop to $20 kWh. That is far from where we are today!!

But wait, this is based on requiring that supply = demand for 100% of the time over the last 20 years. Role of rare events. What if we reduce the required EAF from 100% to 95%? • What if we relax our requirement to a 95% EAF? That would require less storage, and thus reduce the LCOSE. • Afterall, 100% over 20 years is a stringent requirement. Our current grid is not that reliable (black outs and brown outs) • If we relax the EAF requirement to 95%, then the cost of storage at which our renewable grid is feasible now can be as high as $150/kWh. Much more feasible than $20/kWh. – Li-ion batteries projected at $145-$480 / kWh by 2030 – Flow batteries projected at $108 - $576 / kWh by 2030 • Why the big difference between 100% EAF and 95% EAF? – Rare events. The last few % of EAF are exponentially more expensive. Lesson

• Having the US grid run on renewables 95% of the time, with flexibility coming from energy storage, is not that out of reach – Other 5% could come from load flexibility, enhanced long distance transmission, dispatchable renewables like hydro • In fact, its much more in reach than most conventional wisdom would suggest.