Lesson 1
Energy Use in the Home

Introduction

Energy from the sun can be tapped to provide a clean source of home energy. This lesson will introduce you to the ways we use energy in the home, and how solar energy can be used to meet some, or all, of a home’s energy needs. It will also address safety, codes and covenants, and permits for Pennsylvania.

End Uses of Energy in the Home

Energy is used in many ways in the home, including space heating and cooling, water heating, refrigeration, appliances, lighting, televisions, computers, stereos, and more.

Residential energy use follows a typical pattern. Normally, people get up in the morning and get ready for work, and as they get ready for work, they shower, and fix breakfast. The activities surrounding getting ready for work in the morning makes a peak in home energy use, generally from about 6:00 a.m. to about 8:00 a.m. When people are away from the home during the day, the home’s energy use is low, but when they arrive home from work in the evening, energy use in the home goes up again. Preparation of the evening meal, domestic chores, and leisure activities make a larger peak in home energy use in the evenings. Energy use is lowest at night when people are sleeping.

typical energy consumption pattern graph

This graph illustrates a typical energy consumption pattern in homes.
Source: National Center for Appropriate Technology.

According to DOE’s Energy Information Administration, almost half of the average home's energy consumption is used for heating. Another 17 percent is used for water heating, 6 percent for cooling rooms, and 5 percent for refrigeration.

This chart illustrates how energy is used in homes. Due to rounding, percentages may not add to exactly 100 percent.
Source: DOE Energy Information Administration.

Source: Alliance to Save Energy
www.ase.org

Fossil fuels account for the nearly all residential energy use. Displacing fossil fuel use with renewable energy resources such as solar can make a significant contribution to reducing harmful emissions that contribute to global warming. Using renewable energy resources like solar also can reduce dependence on the utility grid, and reduce energy costs.

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Energy Efficiency First

Installing energy-efficient systems in a home is more cost-effective than meeting the energy needs of less-efficient equipment with solar energy. Reducing electricity use is the best and least expensive way to save energy and money. A homeowner interested in solar energy should be made aware that solar energy systems will provide a much higher fraction of the total energy used in the home if energy-efficiency measures are taken first. Although some efficiency measures amount to installing and using more energy-efficient equipment, some efficiency measures relate to energy-use habits.

Decreasing hot water requirements or electric requirements of the home will decrease the size of the solar water- heating system or solar electric system and, therefore, will reduce the cost of the solar systems to be installed. Decreasing the hot water requirements of the home from 20 gallons of hot water per person per day to 15 gallons per day will reduce the solar water system cost by about 20%.

Every kilowatt-hour you trim off your projected annual use in a PV-based system will reduce your initial setup cost by $10-$12. Being smart about the appliances and lights you choose will allow you all the convenience of a typical home while consuming far less energy. That can shave thousands of dollars off the initial solar energy system cost.

The homeowner should consider these energy-efficiency strategies:

Energy Star Logo
Replace appliances, lighting, heating and cooling equipment, and other products that are more than 10 years old with an ENERGY STAR® model. ENERGY STAR labeled products meet strict energy use guidelines, using about 30 percent less energy than their conventional counterparts. Choosing ENERGY-STAR products can save families about a third on their energy bill with similar savings of greenhouse gas emissions, without sacrificing features, style or comfort.

To find ENERGY STAR product lists, go to www.energystar.gov/.


Switch electric space heating, water heaters and clothes dryers to natural gas or propane.


Replace older full-size fluorescent lamps with newer, more efficient models. Most common full-sized fluorescent lighting fixtures are equipped with T-12 (1-1/2 inch diameter tubes) lamps and magnetic ballasts. This technology started to make its way into American homes in the 1940s. Many of these older fluorescent fixtures are still in use today. Although this lighting technology is much more efficient than incandescent lighting, new full-sized fluorescent technologies are available today that are even more efficient. The new lamps, T-8 (1-inch diameter tubes) and T-5 (5/8-inch diameter tubes) produce much better quality light because of better coatings on the inside of the tube and higher frequency ballasts. The new lamps are more efficient because of their smaller diameter and higher operating frequency. T-8 and T-5 lamps use ballasts specifically made for them; do not use the new lamps on the old T-12 ballasts.


various lightbulbs
Image: NREL/PIX 07737
Replace incandescent lights with compact fluorescent lamps. The most common lighting in the home is incandescent. This technology basically uses heat to create light. Incandescent lighting is inefficient, converting about 90% of the electric energy to heat, only 10% to light. Most incandescent fixtures can use compact fluorescent lamps (CFLs). CFLs are small fluorescent lamps that have the ballast built into the base. Early CFLs (manufactured in the 1990s) used magnetic ballasts and were heavy, relatively large, and flickered when they were turned on. Modern CFLs use electronic ballasts, are smaller, lighter, and come on instantly. CFLs use about one-third as much electric energy to produce the same light as an incandescent lamp. Most CFLs cannot be used with dimming, and CFLs in general do not like enclosed fixtures, where they can get too hot.


Install lighting controls. Lighting equipment in the home is generally controlled by light switches. The biggest problem with light switches is that they can be left on when not in use. Lighting controls that can be installed include timers and occupancy sensors. Timers can be installed that will turn off the lights after a set time interval. Timers work well in places where the use is intermittent and the occupancy of the space is for short periods of time, such as stairways, hallways, and closets.

There are two basic types of occupancy sensors: Passive Infrared Radiation sensors, and Ultrasonic sensors. Both types have their strengths and weaknesses, and some more expensive occupancy sensors include both types. Occupancy sensors sense when a person is in the space controlled, and turn the lights on. As long as the sensor senses someone is in the room, the lights stay on. After the person leaves the space, the sensor turns off the lights after a pre-set time interval. Problems associated with occupancy sensors include false ons (caused by pets, mainly) and false offs (caused when the person in the room does not move enough to keep the lights on). Occupancy sensors work well in laundry rooms, workshop areas, and kitchens. If using occupancy sensors in bedrooms and bathrooms, an ultrasonic or dual-sensor type occupancy sensor is recommended.


Install low-flow shower heads and faucet aerators. Low-flow shower heads and faucet aerators can significantly reduce the amount of hot water used in the home. There are many different styles to choose from.


water heater
Image: NREL/PIX 03062
Insulate the current water heater, as well as any hot water pipes that you can get to.



Lower the water heater thermostat. If there is no dishwasher in the home—or if the dishwasher is equipped with its own automatic water heater—turn the water heater down to 120°F (49°C) to save energy and money.


Practice energy-efficient habits. If a family is accustomed to leaving lights and appliances on when they’re not in use, it will take a lot of dedication on the part of family members to change these energy-wasting habits. It’s a worthwhile effort, however, as considerable savings can be achieve simply by turning off lights and appliances when they are not in use.


a television
Image: Energy Star
Eliminate "phantom" loads. Phantom loads are caused by 120VAC to DC chargers such as cell phone chargers, and by appliances that still use power even though they are turned off, such as televisions, computers and audio equipment. These loads may seem small, but because they are on all of the time, they can add up. In fact, they can account for as much as 6% of a home’s energy use. To avoid this energy use, plug all of the related appliances (for example, all of the entertainment equipment) into a power strip that has a switch on it. When the appliances are not in use, switch off the power strip switch. Some homes have electric outlets that are switched with wall switches. These can also be used to turn off equipment that contributes to phantom loads.

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Using Solar Energy in the Home

a zero energy home
This Zero-energy home built by Habitat for Humanity features an integral collector storage system to provide hot water. Image: NREL/PIX 14164
Solar energy—energy from the sun—can provide the energy needed for many of these uses. In fact, solar energy can provide all the energy needs in a home. However, systems designed to meet all energy loads in a home are larger and thus expensive.

Zero-energy homes are both energy-efficient and capable of producing enough of their own electricity from solar and other renewable energy resources to offset the amount of energy purchased from the utility. The result is a net-zero annual energy bill.


Building Characteristics

Buildings must exhibit certain characteristics to be a good candidate for a solar energy system.

Exposure: The building should provide maximum southern exposure without any substantial shading from 9 a.m. to 3 p.m. Although an orientation of due south is best, a deviation of 30 degrees or less from true south is considered acceptable for most solar energy applications.

Slope: For roof-mounted systems, the preferred roof slope is equal to the latitude at the site, between 39 and 42 degrees in Pennsylvania. Roof slopes between 20 and 60 degrees (roughly 4/12 to 20/12 pitch) are acceptable.

This table shows orientation factors for various roof pitches.
Source: U.S. Department of Energy

Structure: Although most roofs can support the added weight of a solar energy system, you should check the condition of the rafters. The roof must be able to safely support the added dead load of the solar array and mounting rack and the temporary live load imposed by the installation crew. The solar array and mounting rack will add approximately 3 pounds per square foot of dead load to the roof. A structural engineer should be consulted if there is doubt that the roof can handle the additional load.

Access to wiring (solar electric) or plumbing (solar water heat): Ideally, the south-facing roof should be near the main electrical service entrance if you are installing a solar electric system. To minimize wiring runs, the breaker panel containing the building’s main disconnect switch and then household’s electrical end-use breakers should be easily accessible and relatively close to the solar array. The breaker panel should have space available for installing a 120/240V breaker; this is the solar system’s connection to the electrical grid. If you are installing a solar water- heating system, you will have to have access to the connections to the existing water heater, and there should be room near the existing water heater for the solar water storage tank.

The further a home is turned from south, the less its ability to collect solar energy in the winter.

Solar energy systems can be designed to heat water or living spaces, or to provide electricity. Solar electric systems can be connected to the existing utility grid or can be separate, stand-alone systems.

The following information summarizes common types of solar energy systems. Solar water-heating and solar electric systems will be addressed in more detail later in this course.


Passive Solar Energy Systems

Passive solar designs are those that collect the sun’s energy using no moving parts. Passive systems can provide over half the space heating energy by using windows to allow more sun into the home in the wintertime, increased levels of insulation to help to keep the house warm, and added thermal mass—such as concrete, tile, or brick.

the interior of a house
In passive solar designs, the majority of windows are placed on the south elevation, as shown here. Image: NREL/PIX 02778
Windows also are an important component of passive solar designs. Effective passive solar designs for most U.S. climates, including Pennsylvania, use windows to maximize solar heat gain in winter and minimize it in summer.

In heating-dominated climates like Pennsylvania, most windows should generally face south to collect solar heat during the winter when the sun is low in the sky. In the summer, when the sun is high overhead, overhangs or other shading devices, such as awnings, prevent excessive heat gain.

Windows on east-, west-, and north-facing walls are reduced in heating climates, while still allowing for adequate daylight.

a trombe wall
In passive solar designs, the majority of windows are placed on the south elevation, as shown here. Image: NREL/PIX 02778
An indirect-gain system has its thermal storage between the south-facing windows and the living spaces. Using a Trombe wall is the most common indirect-gain approach. The wall consists of an 8–16 inch-thick masonry wall on the south side of a house. A single or double layer of glass is mounted about 1 inch or less in front of the wall's surface. Solar heat is absorbed by the wall's dark-colored outside surface and stored in the wall's mass, where it radiates into the living space.

In direct gain passive design, the sunlight is allowed to enter the living space directly. Concrete walls and floor, along with tile, and sometimes water storage features are used to absorb the solar heat gain in the daytime, and these building elements re-radiate the warmth at night.


Solar Water-Heating Systems

Solar water-heating systems can reduce the cost to heat domestic water by as much as half. The challenge in northern climates such as Pennsylvania is freeze protection, but there are a number of systems on the market that provide freeze protection.

Solar water heating is addressed in detail later in this course.


Solar Electric Systems

Solar electric systems—also called photovoltaic (PV) systems—generate electricity directly from the sun.

A grid-connected—or net-metered—PV system is connected to the utility grid through a special meter than turns backwards when the house produces more electricity than it needs. The utility grid serves as storage, eliminating the need for batteries. Grid connected PV systems are covered later in this course.

Off-grid—or remote—systems are those that are completely independent of the utility grid. They require batteries to storage the energy they collect during sunny times for use at night or when the sun isn’t shining. Since off-grid systems generally provide electricity for the entire home, they require storage batteries and usually have some kind of backup generator. This course covers only the installation of grid-connected solar electric systems without batteries.

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Pennsylvania’s Solar Resource

Most residential solar collectors are flat panels that can be mounted on a roof or on the ground. Called flat-plate collectors, these are typically fixed in a tilted position correlated to the latitude of the location. This allows the collector to best capture the sun. These collectors can use both the direct rays from the sun and reflected light that comes through a cloud or off the ground. Because they use all available sunlight, flat-plate collectors are the best choice for many northern states.

PVWatts (www.pvwatts.org) is a useful on-line calculator that helps to understand the solar resource at a given location. The table below shows summer, winter, and annual solar resources for Wilkes-Barre, Pennsylvania. PVWatts can help you determine the solar resource available at your specific site, and also help you estimate the size of solar system needed to provide the necessary solar energy for either solar water-heating or solar electric systems. (Tip: To convert from Kilowatt-hours to Btu, multiply by 3413. To convert square meters to square feet, multiply by 10.76).

 

Average Daily Solar Radiation
for the months of January and July and yearly for various tilts and azimuth angles in Wilkes Barre, PA (kWh/m2/day)
Source: PV Watts Website
www.pvwatts.org

Tilt Angle Azimuth Angle January July Yearly
25 180 2.50 5.58 4.19
25 210 2.40 5.81 4.12
25 270 1.72 5.52 3.59
40 180 2.81 5.47 4.19
40 210 2.66 5.45 4.09
40 270 1.69 5.08 3.37
55 180 2.89 4.82 3.98
55 210 2.79 4.85 3.88
55 270 1.62 4.55 3.09

 

Codes, Permits and Covenants

Different communities have different restrictions and requirements in place regarding the installation of solar energy systems. Before installing any solar energy system, contact your local building code officials to learn about required permits, as well as codes and covenants that could affect where and how you install a solar energy system.

Grid-tied PV systems should be interconnected by a licensed electrician in compliance with the National Electrical Code (NEC). Hot water systems should be installed by a licensed plumber in compliance with the National Standard Plumbing Code. In fact, some municipalities issue permits for such work only to licensed contractors, and others might require approval of the system by a committee.

It is wise to investigate all requirements prior to beginning your project to ensure that installation is fully in compliance.

Lesson 1 Questions

  1. What’s the most important step to ensuring that a PV system provides the highest fraction of total energy used in a home?


  2. What is a "phantom" load?


  3. What building characteristics must be present in a home in order to be a good candidate for a solar energy system?


  4. What is direct gain passive design?


  5. Describe a Trombe wall.


  6. What is a grid-connected PV system?

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Answers