Green Solar Energy

Passive Solar Heating

Technology Snapshot & Benefits:

Easy economic savings accrue from designing and building features that effectively trap heat from the sun during the day and release that heat slowly throughout the nighttime. The effect is similar to living near a large body of water where the thermal mass of the water lessens temperature extremes. That means reduced heating and cooling load for a building, and that saves you money.

You may easily incorporate thermal mass into a building for passive solar heating by using materials such as concrete, stone floor slabs, or masonry partitions that hold, then slowly release heat. Orienting your building so that the longest walls run from east to west, and using large south-facing windows, allows the sun to help heat the home in winter. Properly designed roof overhangs shield the building interior from the summer sun. Passive solar designs use natural methods to stabilize the internal temperature of a building without the need for active mechanical devices such as pumps or fans, although these may be used to supplement performance. Passive solar designs also include natural ventilation for cooling. An obvious method is simply locating windows in the building strategically so that when opened, a natural breeze may be easily accelerated in the interior. Openings and passages designed into ceilings will promote the escape of hot air from the interior of the building through the roof or upper windows.

Estimated Cost Savings:

Passive solar designs can reduce heating bills as much as 50 percent. For a monthly heating bill of $200 dollars, you may expect savings of $80-$120 per month. If passive solar features are included at the time of initial construction, or as part of an overall remodeling effort, the effective net cost of improvements will be much lower. However, you will benefit immediately in your monthly cash-flow.

Passive solar designs are easiest to implement at the planning and design stages of a new home. However, existing buildings may be quite easy to retrofit with passive solar improvements. Virtually all occupants of passive-solar homes report enjoying design features, improved efficiency, and an enhanced sense of “connectedness” to the natural world.

Solar Orientation Issues

Technology Snapshot & Benefits:

When building a new home, orienting it to take advantage of passive solar heat can help save a great deal of money off of your annual heating and cooling bills. In the northern hemisphere, it is recommended that you orient your home so that it is elongated in an east-west direction (with the widest side of the home facing south) helps maximize the amount of solar energy used to heat your home. This longest side should face anywhere from direct south to 10 degrees east of south to take advantage of the sun’s angle throughout the day.

Installing large windows on the south side of your home will further help take advantage of the sun’s heat as windows allow more heat through than solid walls. The total size of the south-facing windows should be between five and twelve percent of the total square footage of your home. For example, if you live in a 2000 square foot home, all of the windows on the south side of your home should total between 100 and 240 square feet. Having too many windows can overheat the rooms and having too few can block some of the passive solar from entering your home. Install enough windows on the north, east, and west sides of your home to allow for balanced light, natural cooling, and any available views. Installing too many windows on these other sides can drain the heat provided by the southern-facing ones and decrease the efficiency of your passive solar

Estimated Cost Savings:

If proper solar orientation is integrated into the design of your home, it will cost little more than simply building your home without the right orientation. Because passive solar utilizes large amounts of south-facing windows, there will be an initial expense to purchase and energy efficient windows install them. This cost will be slightly higher if you choose to go with to further maximize your home’s efficiency. Modifying your home through additions to take advantage of passive solar can be expensive, but will help save you money off of your annual energy bills and add value to your home. Proper orientation and adequate amounts of south-facing glass can help provide 20-80% of the heat needed in the colder seasons, saving a significant amount of money off of your annual heating and cooling bills.


Designing your home for maximum passive solar works best when constructing a new home, completely rebuilding on an existing property, or making additions to the south side of your home. Because solar orientation require the home to sit at a certain angle to the sun, it is difficult to retrofit an existing home without disrupting the foundation and completely moving the entire building. However, if your home is oriented in an east-west manner with a good portion of the exterior walls facing south, it is possible to add new windows to help enhance its solar efficiency. If you are selecting a home to purchase, solar orientation can be added to the features you are seeking.

Installing large windows on the south side of your home helps heat the home during the winter, but can often overheat the home in the hotter months. To avoid this, install overhangs over windows to block the sun at its higher summer angle. Consider planting

shade trees near the south side of your home. These will help block the sun in the summer when it is at its hottest and the trees are in full bloom. In the winter, when the trees lose their leaves, they will allow more sunlight through to penetrate the windows and heat the indoor space.

Regional Issues:

The orientation of your home, size of overhangs, and amount of heat retained from passive solar depends on your latitude and climate. It is important to understand the

solar angle at your location to maximize the savings that passive solar design can provide. In hot climates, sun-tempered homes (homes with south-facing windows that measure 5-7% of the total square footage of the home) provide the most solar benefit. For colder climates, it is recommended that your south-facing windows are sized to 7-12% of total square footage to take advantage of extra heating in the cold winters

Installation (Getting It Done):

If you are designing or redesigning your home, make sure your architect and contractor have experience with solar home building. Tell them you are interested in passive solar heat and ask them to design the building with the proper orientation to provide for maximum heat and energy efficiency. Place the most commonly used rooms along the south side of the house, leaving those that are rarely used (storage spaces, extra bedrooms, etc.) on the north side. This will help heat the rooms you spend the most time in and avoid wasting heat on empty rooms.

After orienting your home for maximum passive solar heat, it is important to reinforce it with thermal mass and proper insulation. Thermal mass is defined as materials that retain heat and then slowly emit it as the surroundings cool. Common types of thermal mass include brick, concrete, and wood, among other materials. Installing thermal mass around the south-facing windows in your home can help retain the heat from the sun and emit is slowly to warm the room after the sun has gone down


Solar Photovoltaic Panels

Technology Snapshot & Benefits:

Solar photovoltaic (PV) panels make use of photovoltaic technology to convert sunlight into usable electrical energy. Each panel is made of a collection of photovoltaic cells that each produce between 1 and 2 watts of energy. A typical cell consists of a glass layer on top of an antireflective surface (to prevent the sunlight from reflecting back into the atmosphere) and two semiconductor layers (typically made of silicon) surrounded by metallic grids or electrical contacts. When the sun’s light hits the semiconductor layers of the panel, it knocks electrons loose. Because of the electrical field on the panel, these free electrons are moved to the top of the grid where the electrical contacts gather them into a direct current. With the use of an attached inverter, the direct current is converted into alternating current (the form of energy used in electrical outlets). PV systems are used for “off-the-grid” applications (homes, cabins, and water pumping on farms) as well as federal government applications (traffic warning lights and emergency call boxes near highways).

Solar panels serve an important function by creating an alternative source of electricity and reducing dependence on coal. Because they generate electricity without any moving parts, require little maintenance, and emit no harmful gases or chemicals, they are becoming one of the best ways to reduce the carbon footprint and help the environment. Also, the more energy-efficient your home is, the fewer panels are needed to power it. Consider implementing smaller green renovations (CFLs, better insulation, energy-efficient appliances and windows, etc.) before installing solar panels. This will minimize your upfront costs by reducing the number of panels you need as well as decreasing your monthly energy expenses.

Estimated Cost Savings:

While solar systems are still relatively expensive, the price has come down significantly since they were first produced. Currently, a typical solar system can cost anywhere between $5,000 and $100,000 depending on how much energy you wish to produce and how large of a space you are powering. Starter kits, which usually consist of one panel, a battery, an inverter, and the necessary cables, start as low as $500-$1,000, but only generate a limited amount of energy. Individual solar panels cost anywhere from $50 to $1000 depending on how much energy they produce and the material they are composed of. The lower-range models are typically used for recharging electronics batteries (phones, iPods, etc.), but will not produce nearly enough energy to power a house. In addition to the panel itself, initial expenses include balance-of-system costs such as batteries, charge controllers, inverters, support structures, sensors, installation, and insurance fees. Solar energy currently costs between $3 and $4 per watt (15-25 cents per kWh), creating a 10-20 year return on investment.

Solar panels are ideal for remote locations where it is more expensive to connect to the power grid as the monthly monetary savings will be more dramatic. For a truly “off the grid” installation, the avoided cost of bringing in power lines from the utility offsets some or all of the PV installation cost. An off the grid installation uses batteries to store electricity for use at night and whenever sunlight cannot provide enough for the home.

Check for financial incentives offered in your state by consulting the

Database of State Incentives for Renewable Energy.


Because solar panels need sunlight to function properly, their efficiency depends on weather conditions, obstructions, and their position and angle relative to the sun. To maximize efficiency, remove any branches, trees, or other obstructions that shade the panels. If possible, place the panels on a south-facing roof at the

reecommended angle for your latitude. Dynamic mounts are available that alter the angle of the panels throughout the day to follow the sun, allowing for the greatest amount of direct light possible.

Weather conditions may also affect the efficiency of your solar system. However, even on cloudy days, there is still enough indirect light to generate limited amounts of power. The panels will continue to generate energy throughout the winter as they rely on light not heat. However, because the days are shorter during wintertime, they will generate proportionally less energy due to a shortened exposure to sunlight.

Water damage is one of the biggest problems regarding solar panels as it causes the panels to decrease in efficiency or completely malfunction. To avoid this problem, do not mount your panels horizontally as this will cause water to collect and may cause serious damage. Also, make sure there is a sufficient air gap between the panels to allow for drainage and ventilation.

It is possible to connect your solar system to a battery to ensure your home is powered through the night and any power outages. Batteries can store the extra electricity generated throughout the day and keep it on reserve for later use.

Installation (Getting It Done):

Some solar panels can be installed yourself, but many manufacturers suggest professional assistance to ensure it is placed in the best possible location. When installing, remember that solar panels use light to produce energy, so it is important to place them in a location that receives direct sunlight throughout the day. A south-facing roof is usually the best option, but an east-west roof can work as well. If you have a large ground area without obstruction, a ground-mounted system may work for you. Be sure to remove and obstructions when installing to ensure your solar panels are able to work at their maximum capacity.

Remember that a 1 kW solar panel requires between 80 and 360 sq. ft. of space to install and a typical home system requires between 50 and 1000 sq. ft.

There are a few types of mounts for solar panels including pole mounts, roof/ground mounts, and flush mounts. These make it possible to mount your system on a pole or roof, as a free-standing system, or even on the top of an RV. Dynamic mounts can also help provide maximum energy capture by following the position of the sun throughout the day.

If you are installing solar panels on an older roof, it is recommended that you replace your shingles before installation to help provide better support for the mounting equipment.


Passive Solar: Roof OverhangsTechnology Snapshot & Benefits:

Roof overhangs are extensions off of your roof that help shade windows and walls. These help control the amount of sunlight hitting the surfaces of your home for maximum heating and cooling efficiency in both the winter and summer. Overhangs come in a variety of forms, from solid to louvered to vegetation-supporting, each with advantages in different areas. There are three main types of overhangs: fixed, adjustable, and removable. Fixed overhangs require the least maintenance and have the greatest longevity, but cannot be adjusted or removed to better suit changing sun conditions like the latter two can. Adjustable overhangs can be expanded or condensed depending on the sun’s angle, offering a great deal of flexibility and control. Removable overhangs can easily be uninstalled and reinstalled according to your preferences, making it easier to make alterations or additions to your home.

Overhangs operate on the basic principles of solar angles. In the summer when the sun is high in the sky, the overhang casts a long shadow over the side of your home while in the winter, when the sun is much lower in the sky, the shadow is much shorter. This prevents the hot sun from penetrating your windows and walls in the summer and allows it to help warm your living spaces in the cold of winter. Shutters, eaves, and awnings operate in similar ways.

Estimated Cost Savings:

Roof overhangs can be somewhat expensive to install. The cost of install depends on the size of the structure, the location, and whether the overhang is an addition to an existing roof or a part of a new roof. Roofs installed as additions to existing roofs tend to be more expensive because of the extra labor and materials needed to properly attach it.

Installing an overhang can help save on your cooling bills in the summer and heating bills in the winter. Decreasing windows’ exposure to direct summer sun can help keep your house cool without the energy expenses associated with HVAC systems. The opposite applies during winter when the sun is able to help heat your home without turning on your heating system or lighting a fire. This can help save a significant amount of money off of your annual heating and cooling bill.

For a less expensive alternative, consider installing shutters or an awning. While these are not always as effective or permanent as properly installed overhangs, they provide a more affordable way to help use the sun’s angle to your advantage.

Regional Issues:

Roof overhangs do not comply with all regional building codes and zoning ordinances. Check with your local zoning committee to find out if you can add overhangs to your home.

It is important to make sure the width of your solar overhang will provide adequate shade for your latitude. There is no hard and fast rule for calculating the angle necessary for your home, but properly trained contractors can help you determine the proper width. Overhangs are the most effective in areas close to the equator because of the extremely high angle of the sun creating a large shadow during hot summer months.

Installation (Getting It Done):

Solar overhangs work best when installed on the south side of your home (in the Northern hemisphere). If they are placed on roofs that face more than 30 degrees east or west of south, they are much less effective. The greatest heating and cooling savings will occur around midday when the sun is at its peak in the sky.

If you are putting a new roof on your house, consider adding overhangs. It is much easier and less expensive to bundle them into a new roofing project than to go back later and add them as additions to an existing roof.


Solar TubesTechnology Snapshot & Benefits:

Solar tubes are tubes that run from the ceiling of a room to the roof, where they collect light that is reflected down the tube and then diffused into the attached room. Solar tubes work like skylights but are less expensive, require less roof/ceiling space, and can be easily installed in almost all buildings. They can even work in the basement or the first floor of a two-story house if there is a closet, a chase, or any place to feed through the solar tube up to the roof. Solar tubes are made to look like ordinary ceiling lights and can easily blend into a home. They are carefully built to maximize the amount of light provided, and can light 100 to 600 square feet of space, depending on the depth and diameter of the tube. Short, wide solar tubes provide the most light. A 10-inch solar tube can produce 3,750 lumens of light, whereas a 60-watt incandescent bulb only produces 870 lumens. This means that one 10-inch solar tube can replace about four 60-watt incandescent bulbs! Solar tubes also produce roughly 68 percent less heat than the average light bulb.

Solar tubes require no electricity to run and produce no pollution. This can result in energy cost savings and contribute to a healthier planet. The natural light that solar tubes provide also has been shown to have numerous benefits for the people living in the home. According to the National Health and Environmental Effects Research Laboratory of the EPA, natural lighting can contribute to psychological and physical health by boosting energy and concentration levels. A study by the Florida Energy Conservation Assistance Program showed that natural lighting resulted in reduced eye fatigue and headaches by providing better light and matching the normal functional rhythms of the human body. Having access to natural light also helps the body produce vitamin D.

Solar tubes are also commonly referred to as tubular skylights or sun tubes. The leading providers of solar tubes are SolaTube and Velux.

Estimated Cost Savings:

Because solar tubes require no electricity to run, replacing lights with solar tubes will reduce monthly energy bills. The savings depends on the type of light bulbs the solar tubes are replacing (incandescent or CFL), the amount of time the electric lights were normally left on, and the number of electric lights replaced with solar tubes. Solatube, a leading manufacturer of solar tubes, reported that they saw an 86.1 percent reduction in daytime lighting costs and a 68.2 percent reduction in nighttime lighting costs when their headquarters incorporated 21-inch solar tubes. This is a very high number and, again, the reduction percentage depends on the amount of lights replaced, size of the solar tubes, and initial costs.

Installation of solar tubes usually costs between $500 and $800, depending on the size of the tube and the features installed (see “Issues” for more information on possible features). It also costs more if tube extensions are required to install the solar tube. This is less expensive than typical installation costs for regular skylights. Installation costs should be weighed against long-term savings for each particular case. Some investments will pay for themselves more quickly than others; in some cases, you might even be able to make a small profit by installing solar tubes. It is important to weigh the investment against the environmental, health, and light quality benefits of solar tubes.


When choosing a solar tube, several issues must be considered. First, look for the ENERGY STAR® label. This label indicates the solar tube truly works in the environmental-friendly fashion it should, and it could be used for federal or state tax credits. It’s also important that the solar tube has some kind of moisture control so that water does not leak into the home. There are several extra features available for solar tubes that may desirable, including an electric light add-on that can be installed in the tube and used at night, a daylight dimmer to control the amount of sunlight allowed in, and designer diffusers to maximize light diffusion. Some companies also offer a softening lens instead of a dimmer for very bright climates. The actual look of the light fixture attached to the solar tube can also be customized to suit the aesthetic desires of a homeowner or business.

Regional Issues:

Solar tubes are technologically advanced, using advanced optics to draw as much light from the sun as possible. As such, they can function even in cloudy regions, during low-light hours, and in winter, although it is possible to draw more light in sunnier climates during the day. Look into details on the efficiency of different manufacturers’ products in your specific climate before purchasing a solar tube.


Solar tubes are simple enough that, in many cases, they can be installed by the homeowner. This can cut costs by almost 50 percent. Instructions often come with solar tube kits; however, a simple installation instruction video, “How to Install Solar Light Tubes,” is available here. If the tube must be very long or must be bent through complex structures and is too difficult for the homeowner to install, professional contractors are available to install solar tubes.

Solar Water Heaters

Technology Snapshot & Benefits:

Solar water heating systems utilize the sun’s energy to heat water for use within a household or commercial property. Typically, solar water heaters are made up of a storage tank, a solar collector, and a series of tubes, valves, pumps and fluids that allow for water circulation. While certain systems may function at higher capacities in warmer locations with greater sun exposure, they do work in all climates. Different models are available for the home, pools, and commercial properties.

There are two types of solar water heating systems – active and passive. The former have circulating heat pumps while the latter do not. Active systems are either direct (circulates water directly from collectors to the home) or indirect (circulates

non-freezing heat transfer liquid from the collector through tubes in the storage tanks to heat the surrounding water). Passive systems, which are generally cheaper, but less efficient, are typically either integral-collector systems or thermosyphon systems. Integral-collector systems are best in warmer climates where temperatures rarely drop below 32 degrees. Thermosyphon systems use basic water principles for circulation by placing the outlet that goes to the home at the top and the outlet that goes to the solar collector at the bottom. This allows for the hot water (which rises) to go to the home and the cold water (which sinks) to be circulated through the solar heater.

Storage tanks should be well-insulated to prevent heat loss. There are two main types of storage tanks: two-tank systems and one-tank systems. Two-tank systems have an additional conventional water heater attached for back-up while one-tank systems have the conventional heater and solar heater integrated into the same tank. Both systems provide back-ups in case the solar heat is insufficient on any given day.

There are many different types of solar collectors and system set-ups. Consult a local specialist and the online resources listed at the bottom of this page to determine which type is right for you. For a basic overview of the different types,

click here.

Estimated Cost Savings:

While solar water heating systems are more expensive than conventional heating systems, they can save you up to 50-80% on your water heating bills. The amount of money you save depends on several factors, including the amount of water, geographic location, fuel costs, financing incentives available, and the system’s performance. Installation and maintenance costs create additional expenses, but these are still minimal when compared to overall savings.

To determine your estimated savings,

click here. For information on financial incentives in your state, visit theDatabase of State Incentive for Renewables and  Efficiency.

As solar heating systems rely on the sun’s energy to heat your household’s water, weather can sometimes create an issue by preventing adequate sunlight from reaching the collector. However, the storage tanks often store enough hot water to compensate for lapses in sunlight. Also, a conventional water heater is attached to most systems to provide back-up in case there is not enough solar heat.

These systems require a decent amount of maintenance to ensure they are working properly. Check annually for problems like obstructions shading the collector, failing pipe and storage tank insulation, and visual signs of wear or corrosion on pipes and tanks. Consult a technician for routine qualified inspections. For a complete list of recommended inspections,

click here.

Regional Issues:
It is important to take into account local temperatures when choosing a solar water heater. While the heaters generally work for any climate, certain types will not work in colder climates where temperatures frequently drop below freezing because the outdoor components may freeze. Dry climates may also require extra maintenance including cleaning the collector glazing as there is no natural rainwater to cleanse it.

As solar water heaters use the sun as a source of energy, items blocking direct sunlight may inhibit their proper function. Be sure to trim branches and trees that may block sunlight.

Check local codes and regulations before installing a solar water heater. Some areas require permits or special permissions before installation.


(Getting It Done):
Most solar water heaters require professional installation. For a list of solar water heater companies,

click here. If you decide to install your system yourself, for a series of articles to help guide you through the process.

Before installing a solar water heater, make sure there is enough sunlight to create noticeable energy savings. In the northern hemisphere, this typically means installing the solar collector on a south-facing roof. In some cases, they can be installed on roofs facing up to 90 degrees east or west and still provide adequate heat. Consult a professional to find out what type of solar water heater best suits your needs before purchasing. Also, remove any obstructions that could potentially block sunlight from reaching the collector. These include branches, satellites, tall trees, etc. Collectors should usually be installed flat on the roof or according to the guidance of your installation professional.

As a rule of thumb, solar collectors should be at least 20 square feet for each of the first two family members in the house. For any additional family members, add 8 square feet if you live in the Sunbelt region (south and southwest U.S.) and 12-14 square feet if you live in more northern regions. For example, if you live in the Sunbelt region and there are five people in your house, your solar collector should be at least 64 square feet (20 + 20 + 8 + 8 + 8) to ensure adequate hot water supplies.

The size of the storage tank also correlates to the number of people in the house.

Small – 1-2 people

Medium – 3-4 people

Large – 4-6 people

It is important to purchase the right size solar collector and storage tank for your system to properly heat enough water for every member of the household.

Many old hot water heaters can be retrofitted with new solar technology. Ask your solar technician or professional resource about retrofit kits when purchasing heater equipment.