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Net metering

Net metering is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Net metering rather than just read about it. In short: Net metering (or net energy metering, NEM) is an electricity billing mechanism that allows consumers who generate some or all of their own electricity to use that electricity anytime, instead of when it is generated. This is particularly important with renewable energy sources like wind and solar, which are non-dispatchable (when not coupled to storage).

Net metering — main illustration
Net metering — illustration

Key takeaways

  • Net metering belongs to physics; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Net metering to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Net metering from memory before moving on to harder problems.

Reference excerpt

Net metering (or net energy metering, NEM) is an electricity billing mechanism that allows consumers who generate some or all of their own electricity to use that electricity anytime, instead of when it is generated. This is particularly important with renewable energy sources like wind and solar, which are non-dispatchable (when not coupled to storage). Monthly net metering allows consumers to use solar power generated during the day at night, or wind from a windy day later in the month. Annual net metering rolls over a net kilowatt-hour (kWh) credit to the following month, allowing solar power that was generated in July to be used in December, or wind power from March in August. Net metering policies can vary significantly by country and by state or province: if net metering is available, if and how long banked credits can be retained, and how much the credits are worth (retail/wholesale). Most net metering laws involve monthly rollover of kWh credits, a small monthly connection fee, require a monthly payment of deficits (i.e. normal electric bill), and annual settlement of any residual credit. Net metering uses a single, bi-directional meter and can measure the current flowing in two directions. Net metering can be implemented solely as an accounting procedure, and requires no special metering, or even any prior arrangement or notification. Net metering is an enabling policy designed to foster private investment in renewable energy.

History Net metering originated in the United States, where small wind turbines and solar panels were connected to the electrical grid, and consumers wanted to be able to use the electricity generated at a different time or date from when it was generated. The first two projects to use net metering were an apartment complex and a solar test house in Massachusetts in 1979. Minnesota is commonly cited as passing the first net metering law, in 1983, and allowed anyone generating less than 40 kW to either roll over any credit to the next month, or be paid for the excess. In 2000 this was amended to compensation "at the average retail utility energy rate". This is the simplest and most general interpretation of net metering, and in addition allows small producers to sell electricity at the retail rate. Utilities in Idaho adopted net metering in 1980, and in Arizona in 1981. Massachusetts adopted net metering in 1982. By 1998, 22 states or utilities therein had adopted net metering. Two California utilities initially adopted a monthly "net metering" charge, which included a "standby charge", until the Public Utilities Commission (PUC) banned such charges. In 2005, all U.S. utilities were required to consider adopting rules offering net metering "upon request" by the Energy Policy Act of 2005. Excess generation is not addressed. As of 2013, 43 U.S. states have adopted net metering, as well as utilities in 3 of the remaining states, leaving only 4 states without any established procedures for implementing net metering. However, a 2017 study showed that only 3% of U.S. utilities offer full retail compensation for net metering with the remainder offering less than retail rates, having credit expire annually, or some form of indefinite rollover. Net metering was slow to be adopted in Europe, especially in the United Kingdom, because of confusion over how to address the value added tax (VAT). Only one utility company in Great Britain offers net metering. The United Kingdom government is reluctant to introduce the net metering principle because of complications in paying and refunding the value added tax that is payable on electricity, but pilot projects are underway in some areas. In Canada, some provinces have net metering programs. In the Philippines, Net Metering scheme is governed by Republic Act 9513 (Renewable Energy Act of 2008) and its implementing rules and regulation (IRR). The implementing body is the Energy Regulatory Commission (ERC) in consultation with the National Renewable Energy Board (NREB). Unfortunately, the scheme is not a true net metering scheme but in reality a net billing scheme. As the Dept of Energy's Net Metering guidelines say, "Net-metering allows customers of Distribution Utilities (DUs) to install an on-site Renewable Energy (RE) facility not exceeding 100 kilowatts (kW) in capacity so they can generate electricity for their own use. Any electricity generated that is not consumed by the customer is automatically exported to the DU's distribution system. The DU then gives a peso credit for the excess electricity received equivalent to the DU’s blended generation cost, excluding other generation adjustments, and deducts the credits earned to the customer’s electric bill." Thus Philippine consumers who generate their own electricity and sell their surplus to the utility are paid what is called the "generation cost" which is often less than 50% of the retail price of electricity.

Controversy Net metering is controversial as it affects different interests on the grid. A report prepared by Peter Kind of Energy Infrastructure Advocates for the trade association Edison Electric Institute stated that distributed generation systems, like rooftop solar, present unique challenges to the future of electric utilities. Utilities in the United States have led a largely unsuccessful campaign to eliminate net metering.

… excerpt ends here. Continue reading the full article.

Illustrations

Net metering illustration
Net metering: Net metering, unlike a feed-in tariff, requires only one meter, but it must be bi-directional.
Net metering, unlike a feed-in tariff, requires only one meter, but it must be bi-directional.
Net metering: Growth of net metering in the United States
Growth of net metering in the United States

Worked examples

Example 1 — a first encounter with Net metering

Start with the simplest possible case. Write down what Net metering claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Net metering before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Net metering ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Net metering

In research
Net metering appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Net metering in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Net metering is common in secondary-school and first-year university syllabi. It links to neighbouring topics Energy storage, Pricing, Renewable energy economics, so understanding it makes those chapters shorter.
In everyday life
Look for Net metering outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Net metering in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Net metering means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Net metering out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Net metering in simple terms?

Net metering (or net energy metering, NEM) is an electricity billing mechanism that allows consumers who generate some or all of their own electricity to use that electricity anytime, instead of when it is generated. This is particularly important with renewable energy sources like wind and solar…

Why does Net metering matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Net metering?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Net metering.

Tags

  • Energy storage
  • Pricing
  • Renewable energy economics
  • Renewable energy policy

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