Electricity is different from other forms of energy because it merely delivers the energy harnessed from other materials, the primary energy source, at the generating facility.
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Electricity flows from generating facilities through a network of power lines, transformers, and routing centers called the electrical grid. Electricity from all sources is mixed together or pooled on the grid for transport to our homes. During this process, resistance in the lines causes about 6% of the electricity to be lost (line loss) as heat between the generating station and the customer.1
1www.eia.gov/tools/faqs/faq.php?id=105&t=3 (accessed March 16, 2017).
More on the electric grid:
www.eia.gov/energyexplained/index.cfm?page=electricity_delivery (accessed March 16, 2017).
More on storage options:
www.eia.gov/todayinenergy/detail.php?id=6910# (accessed March 16, 2017).
Instant Energy from the Grid
Electricity (also known as electrical energy) is a flow of charges or charged particles (electrons) traveling about 186,000 miles per second (light speed). It must be used as soon as it is generated. That means that at every moment, electricity supply has to match the amount of electricity being used.
Matching Electricity Generation to Demand
Because of electricity’s instantaneous nature, generating just the right amount to meet demand is a guessing game. Grid managers estimate the minimum daily electricity demand (called base load) and the maximum extra demand (when customers are likely to use more electricity, called peak load). Using banks of computer screens connected to remote sensors throughout the grid, they monitor and actively manage electricity generation at baseload and peaking plants. Baseload plants meet the consistent and predictable demands for electricity. Peaking plants can quickly come online to meet the extra demand during higher-use periods. This is part of load management.
Power companies use other management strategies to meet peak demand such as working with commercial customers to reduce demand during peak times and having voluntary programs for regulating electricity to residential consumers. At times of very high demand, utilities even make requests to the public to reduce electricity use.
Two examples are off-peak and interruptible-power programs. Off-peak refers to times when demand for electricity is low (typically late evening through early morning). Electric water and space heaters on an off-peak program use electricity during off-peak hours to generate enough hot water and stored space heat for an entire day. This can be accomplished with either high storage capacity or dual-fuel systems (backup heating source).
In an interruptible-power program, the electric supplier places an electric control device in the home for the specific appliance(s). During peak demand periods, the electric provider sends a signal to the control device to shut the appliance(s) off for a period of time. Example of such appliances include central air conditioners, water heaters, and electric boilers or baseboard heaters. Customers might be compensated for the possibility of inconvenience by receiving a rebate or paying a lower rate on their monthly electricity bill.
How do intermittent supplies fit into the grid?
The intermittent availability of wind and solar increase the complexity of the electricity grid’s load balancing act. Grid controllers must continually make adjustments to the system in order to accept the electricity from intermittent power sources like wind and solar. This includes reducing electricity generation from existing baseload plants. Reengineering the grid will be a critical step in order to achieve a shift to diversified electricity sources like wind and solar.
Line loss happens because of the resistance to electron flow inherent in the metal wire. Silver has the least resistance, followed by copper, but both are too expensive to string across the continent. In addition, these lines must endure temperature extremes, wind, storms, and the weight of ice. As a result, transmission lines are generally steel or aluminum. Research into other materials to reduce line loss is under way. At very large voltage, direct current, or DC, lines experience less line loss than alternating current, or AC, lines, which offsets the cost of additional equipment needed to convert between AC and DC at both ends of the line. Two large DC lines carry electricity generated by North Dakota power plants into eastern Minnesota.
The ability to store electricity would help balance supply and demand on the grid and to accommodate the electricity from intermittent sources like solar and wind.
Unfortunately, we have a long way to go before stored electricity makes a significant contribution to the electric grid. Electricity “storage” options represent about 2% of the total generating capacity of our system, and nearly all of it involves hydropower.
For example: During periods of low demand, power producers use electricity to pump water uphill to fill reservoirs at hydro plants and then use the flow of water to generate electricity at times of higher demand. Other technologies being tested or investigated include compressed air, thermal storage, and batteries.
Developed for the North Dakota Department of Commerce Division of Community Services with funding from the U.S. Department of Energy