Updated Dec 1, 2022
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A comprehensive guide to the concept of Zero Net Energy, and its application in residential homes.
Zero Net Energy (ZNE) is a very simple idea. It refers to a process in which the energy produced is the same as, or greater than, the energy consumed. When speaking in terms of residential homes, Zero Net Energy would require the installation of one or more renewable energy arrays in order to produce enough energy to meet all residential consumption, using renewable sources alone. Where renewable energy is used to generate electricity during low-use times, in order to offset the energy consumption of that home during peak-use hours, we refer to this as ‘net metering‘.
Zero Net Energy (ZNE) residential homes are homes which offset their entire energy consumption by producing an equal (or greater) amount of energy from renewable sources. Transitioning to ZNE as a standard requirement for residential homes is a necessary step in the global effort to combat the climate crisis.
Aiming to create a Zero Net Energy home is not only beneficial to the climate and our world, helping us to move toward a world which operates on a 24/7, 100% clean energy grid, it is also a means of minimalizing or eliminating utility bills completely, whilst providing a safe, reliable energy alternative for use during grid blackouts. In fact, in some states (such as California, which began their ZNE Action Plan in 2007), it is the law that all new builds should be fitted with solar panels.
One of the most crucial features of a ZNE home is its design and construction. In other words, the most important step in building a ZNE home takes place before the first brick is laid. A Zero Net Energy house is designed to require fewer building resources from the outset, to use available modern technologies to its fullest advantage, and to utilize the weather and land on which it is to be built. As such, designs for a ZNE house can vary greatly depending on location. For example, a home designed to withstand the hot and humid climate of the southern USA is going to have very different energy demands than a house built in Chicago. Nonetheless, there are certain elements in the design of ZNE houses which enjoy universal application. These include the careful placement of windows to maximize natural light (thus minimalizing artificial light use and energy consumption), considerate insulation (to minimize the need for artificial heating), and efficient space utilization (to keep carbon footprints at a minimum, without sacrificing necessary living space and, to some degree, comfort).
Another major element to ZNE design is a willingness to step away from traditional norms. Instead of large bay windows, which let in lots of light and heat, a clerestory with reflective shelves will maximize light during the evening, but prevent harsh light entering the room in the morning. Instead of using timber in construction, building a concrete wall on a southern exposure will keep the house cool during the day, and then release the heat it has slowly been storing during sunlight hours to keep you warm at night. Of course, design techniques and methods are constantly evolving, so the world of Net Zero Energy is constantly changing to maximise its design efficiency.
Once the design has been carefully planned out, it’s up to the construction companies to make sure the best, most energy-efficient practices are put in place during construction. These practices include: making the house as airtight as possible, to maximise insulation efficiency, and using modern techniques and materials to maximize the intended effects of the design. Using 2×6 walls which are 2ft on center, for instance, doubles the amount of high-value insulation over a traditional 2×4, 16″ on center framing. Construction of ZNE residential homes also requires that the builders are educated on the processes involved, such as knowing which way low energy glass needs to face, and what the acceptable tolerances for roofing insulation are.
Water heaters, furnaces, air conditioners, and residential lighting all consume a lot of electricity. By implementing new technology and adhering to standards like those set out by enterprises like Energy Star, a ZNE house will only use a small fraction of the energy an older house with older appliances does. LED lighting, tankless water heaters, and tier 3 washers and dryers are all necessary components of a high-efficiency Zero Net Energy residential home.
As the smart home industry expands, its products are having a direct impact on our ability to realise our goal of building fully-ZNE residential homes. One of the best investments you can make when outfitting your home with smart technology is to purchase and install a smart thermostat. Smart thermostats reduce energy use in a home dramatically, by pre-cooling and pre-heating water, reducing or increasing temperature when you are not home, managing the temperature when you are sleeping, and much more.
All of this regulation can drastically reduce your home’s energy consumption, especially when you consider that HVAC (heating, ventilation, and air conditioning) units are some of the biggest, hungriest appliances in any home. If you need any more convincing, you should know that almost all power utilities provide bill rebates of up to $100 off when you purchase a smart thermostat. Make sure to check your local utility website for details.
Other must-have smart home products include sensors to activate/deactivate lights as you come in and out of rooms, and automated outdoor lights. Small reductions in energy usage can have seriously important long-term benefits to our global energy consumption, and thus to our climate.
The final step in the creation of a Zero Net Energy residential home – after the design has been worked out, and the house has been constructed and outfitted as efficiently as possible – is to install or connect to renewable energy sources, which will produce all of the power the home will need throughout the year.
Oftentimes, ZNE homes need far fewer solar panels than traditional homes, thanks to their pre-planned energy efficiency; a fact which can help to keep solar installation costs down, thus maximizing the design potential of the whole house.
Whilst what we have discussed so far enables new constructions to achieve ZNE status, where does that leave those of us who already own their own home? How can you work toward achieving Zero Net Energy efficiency when living in an old building, or a building built without ZNE in mind? Whilst it may not always be possible to turn an old house into a modern, Zero Net Energy residential home, there are thousands of things you can do to drastically lower your energy consumption and maximise your home’s energy efficiency.
This is without a doubt the easiest, most affordable thing you can do to improve your home’s energy efficiency. Incandescent bulbs consume five times the power LED bulbs do, just to produce the same intensity of light. Appliances such as refrigerators (which are rarely replaced or updated) are the second biggest consumer of home electricity, behind HVAC units. Fridges made before 2001 are wildly inefficient and power hungry, whilst even those from pre-2010 may be consuming around 600kWh of electricity per year. In contrast, a new, high-efficiency fridge only uses about 450kWh. As a guide, that means that whilst you’d need 2 or more solar panels just to power an old fridge, you’d only need 1 to power a modern one.
Old houses are especially prone to gaps around windows and doors, and spaces behind trim may have no insulation at all. Depending on the age of your building, you may not even have roofing insulation. In each of these situations, you are essentially throwing energy away, and will require massive amounts more heat energy to sustain a liveable indoor temperature than you would if your house was properly insulated.
Small lifestyle changes can have a truly positive impact on your home’s energy efficiency. Turn off lights when you leave a room, use natural light in place of artificial light as much as you can, use only the water you need (in other words, don’t leave taps running unless you are using them), and try using blankets, warm clothing, heavy curtains and the like to keep warm in winter, rather than always resorting to heating. Similarly, do what you can to cool your house without resorting to air conditioning in summer.
Solar power is the most accessible green energy solution, and usually the most affordable, too. With government rebates, state incentives, and the ever-decreasing price per watt, it is now easier than ever to invest in domestic solar setups.
Remember that, by installing solar, not only do you get cost and energy savings, but you are also eligible for Investment Tax Credits (ITC) up until 2023. ITC is a federal tax credit which reduces the upfront capital costs of solar installation. Additionally, many US states also offer state tax incentives for investors in solar power.
The most obvious incentive for making your house a Zero Net Energy home is money. A ZNE home is much cheaper to run than a traditional home, and may even save you money on tax, or make you money, depending on the government and utility incentives available. Combining supremely low utility costs with high-efficiency products which are less prone to failure, means that within the first decade after construction, a net-zero home will have more than payed for itself.
The Federal Income Tax Credit for Energy Efficiency is one of the largest rebates available to those who choose to install solar and other renewable energy arrays in their home. With this incentive, you can recoup up to 26% of the construction costs as tax credits.
Currently, 17 US states offer net metering, through which surplus power generated by a residential home’s solar panels is sold back to the grid. The less energy a home uses, the more power it can sell back to the grid, and in some cases, where ZNE and lifestyle permit, a home can actually become ‘Net Positive’, meaning that residents actually make money through renewable energy production.
As it stands, laws surrounding tax breaks and renewable energy incentives are changing very quickly, location to location. So, if you’re looking to go down the ZNE route, we say it’s best to check with your local government for specific incentives, and to make sure that they will cover you for the duration of your build/renovation. As of 2019, however, 17 states have passed legislation offering large tax breaks for builders who practice net-zero construction. New York, Los Angeles and Phoenix go even further, by creating special opportunity zones which are intended only for high-efficiency buildings.
The rebates and incentives can be incredibly specific too, so it pays to do your research. In California, for example, there are specific credits for such innovations as using waste to power heat technologies, and new energy storage systems.
Yes, lots! California and Massachusetts lead the way, with mandates to achieve green standards going into effect in 2020. New Jersey, Missouri, Connecticut, Colorado, and South Dakota are also working hard to cap greenhouse emissions and decrease their reliance on fossil fuels, in which high-efficiency construction will play a very large part.
California is the first major state to enforce the transition toward ZNE homes, following plans set in motion back in 2007. All new buildings in California must now have solar panels, with the goal being to ensure that these homes were Zero Net Energy by 2020.
California has been working closely with various stakeholders, including California Public Utilities Commission (CPUC), California Energy Commission (CEC), and business throughout the state, to successfully lead the charge on ZNE.
At Semprius, our energy experts are keeping tabs on the progress and impact of California’s ZNE Action Plan. Stay tuned!
The transition to a Zero Net Energy (ZNE) world is not only possible, affordable in the long-term, and relatively simple, it is absolutely necessary to the fight against the ongoing climate crisis, and for the survival of humanity. Building new ZNE homes requires careful planning, construction using new, modern materials and methods, the furnishing of the home with smart technologies, and a renewable energy source from which the home can take all of the energy it needs. However, it is equally possible to renovate an existing home in order to push it toward the ZNE status. Simple changes you can make to your current home include replacing old bulbs and technologies with new, high-efficiency ones, properly insulating your space, and making small lifestyle changes. Federal and State Governments, as well as utilities, often offer tax breaks and cash incentives to help make the transition as affordable and accessible as possible.
What does Zero Net Energy mean?
Zero Net Energy (ZNE) refers to any building, community, or country which produces an equal (or greater) amount of the energy it consumes through renewable means (i.e. with solar, wind, and/or hydro power).
How can new residential homes be built to meet Zero Net Energy requirements?
The most important factors which go into making a new build of ZNE status are: careful design, considerate construction, the inclusion of smart technologies within the home, and the installation and/or connection to one or more renewable energy sources.
How can I make my current home achieve Zero Net Energy status?
Whilst not always possible to achieve full ZNE status with an old building, there is plenty you can do to drastically improve your home’s energy efficiency, and reduce its energy consumption. These include: properly insulating your home, replacing old lighting and appliances with new, high-efficiency ones, and making small lifestyle changes such as wrapping up warmer in winter, and turning lights off when you leave a room.
Which US States are leading the transition to a Zero Net Energy society?
There are lots of states making impressive strides toward a ZNE society, though much still needs to be done, and many attitudes still require changing. However, those states at the vanguard of the renewable energy revolution include California, Massachusetts, New Jersey, Missouri, Connecticut, Colorado, and South Dakota.
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