Energy efficient windows can make a big difference. They not only reduce heating and cooling bills, but also create a healthier and more comfortable living space.

Below we'll explore how energy efficient windows work, a few rating measures you should know, and how to choose the right windows for your situation.

What are energy efficient windows?

how energy efficient windows work
Efficient windows use gas-filled double glazing, Low E coatings, and non heat conducting spacers.

In simple terms these are windows which maintain a comfortable temperature in a room or building.

For colder locations, energy efficient windows keep out drafts and prevent cold air from penetrating indoors, while keeping warm air inside.

Tropical climates and warmer regions benefit from windows which allow adequate ventilation, reducing the need for air conditioning.

How Are Windows Rated?

Energy efficient windows are rated according to their insulating properties. Before buying windows, it is good to understand how these ratings work:

The U-Value of Windows

The U-value (or U-factor) indicates the rate of non-solar heat flow through a window or skylight.

Lower U-values indicate a higher insulating value.

The U.S. Department of Energy recommends selecting a window with a U-value of between 0.25 – 1.25, but for maximum energy efficiency, choose a window with a U-value of less than 0.5 [1].

R-Value of Windows

The R-value is the opposite of the U-value. It measures the ability of a window or skylight to resist heat flow, with a higher R-value indicating higher insulating properties.

Leakage Rating of Windows

The air leakage rating measures air-tightness of a window.

In some countries energy efficient windows carry the Energy Star label, indicating that they have been approved as a genuinely energy-efficient product meeting standards set by the U.S. Department of Energy and the U.S. Environmental Protection Agency.

How the "Energy Star" Rating Works

Energy Star approved windows can reduce household electricity consumption by as much as 15 percent, and are an environmentally friendly alternative, as they reduce the need to burn fossil fuels that add to global warming [2].

Window Technology - Improved Double Glazing, Minimizing Leakage, and Low-E Windows

Energy efficient windows use seals to prevent air leaks, and may also use other technologies to enhance their insulating capabilities.

retrofitting energy efficient windows
Energy efficiency isn't only for new builds. Efficient replacement windows can be retrofitted in any home.

Double glazing works by trapping an insulating layer of air between the glass panes.

In cold climates installing double glazed windows is the first step to prevent heat from escaping from your home.

To further increase the insulation properties of a window, double-glazed units can have the air space between the glazing filled with a gas such as argon, krypton, sulphur hexafluoride or carbon dioxide. These all have better insulation properties than air.

The gas is sealed into the pocket between the glass to prevent it from readily escaping [3].

Efficiency measures are most easily implemented when building a new home, however installing energy efficient replacement windows is generally straight-forward if you’re renovating.

When purchasing double glazed windows look for windows that have thermally improved edge spacers separating the glass panes. While aluminum is typically used as a spacer, it is a good conductor of heat, and therefore heat can be lost through the edges more readily than if a less conductive material, such as stainless steel, is used.

New technologies utilize a single-tape element consisting of a spacer, sealer, and a desiccant, or butyl tape, silicone foam and aluminum spacers with thermal breaks [3].

Low Emittance Windows (Low-E Windows) have a very thin metal or metallic oxide coating that is applied to one or more glazing surfaces that face an air space in a multi-glazed window, or to a thin plastic sheet that is inserted between the panes.

The low-E coating increases the insulating properties of a window, as it reflects heat back into the room during cold spells, and back outdoors during warmer spells. Low-E windows offer good insulation, and have a low U-factor [1].

Tips for buying new windows

Before purchasing windows with low U-factors make sure to ask the manufacturer if the U-factor specification listed applies to the glazing only, or to the whole unit.

If it only applies to the glazing, the U-factor is likely to be higher, since the frame and spacer effects are not taken into account.

It is also advisable to avoid aluminum-framed windows without thermal breaks, as these can present condensation problems during hot weather.

The best materials for window frames are fiberglass, vinyl, and wood, which have great insulating capabilities [2].

Shading devices, such as awnings, drapes, roller blinds and venetian blinds, can be used in combination with energy efficient windows for controlling heat and providing shade.

Tips for Efficiently Shading Windows

Curtains and shutters can be used to both keep heat in, and to keep heat out. By opening or closing drapes and blinds in the daytime, one can control whether the warmth of the sun penetrates the room or not.

Drapes also provide a layer of insulation, and closing drapes when the sun goes down can provide an effective measure to retain heat in a room at night.

Exterior shading devices, such as awnings, are efficient at blocking radiation, and are effective for keeping a room cool.

Cost of Efficient Windows

The number one detractor that puts many homeowners off installing energy efficient windows is the cost involved.

While energy efficient windows are more expensive than most standard types of windows, and the initial financial outlay may be high, money will be saved in the long run. The household's annual electricity consumption will be reduced, allowing the homeowner to recoup this initial capital outlay.

Article References

[1] U.S. Department of Energy. Selecting Windows for Energy Efficiency: What’s New in Building Energy Efficiency.

[2] Energy Star. Residential Windows, Doors, and Skylights.

[3] U.S. Department of Energy. Energy-Efficient Windows.


As the focus on clean energy continues to grow, the wind energy industry has received heavy support from governmental bodies all over.

Below we'll look at the top countries harnessing wind energy today.

One country stands out above the rest, China. While still being considered a developing country [4], China has accomplished a feat sought after by many developed nations.

wind energy china
Wind Turbines cover the horizon along a highway in Xinjiang, China

China has exhibited one of the biggest growth trends in the development of wind energy projects by doubling its installed capacity from 25,810 MW in December 2009 to 52,800 MW in June 2011 [5]. This boost has enabled China to take the title of top wind energy producing country in the world.

Likewise, the European Union has chosen wind energy to be its frontrunner as it heads towards its sustainability targets [1].

Several countries that have exhibited growth in the industry such as Germany and the UK have attributed their recent progress to dynamic policies such as the Feed in Tariff and Green Energy Certificate [3].

The United States of America has also been surging forward with wind energy developments, issuing governmental policies, subsidies and other financial incentives such as tax cuts [2].

How Has China Become A Leading Wind Energy Country?

china pollution from manufacturing
China's wind energy industry growth has been driven partially by an enormous population and urgent pollution problems.

China’s progress with renewable energy was largely driven by the poor state of China’s environment.

With the help of policies to support renewables, China has has become a production giant.

As a result, two of the top three wind energy manufacturing companies in the world are Chinese; these are Sinovel and Xinjiang Goldwind respectively alongside the famous Danish Company Vestas [6].

China’s dynamic growth can be attributed to a few factors unique to the country when compared to other leading wind energy countries.

Unlike most of the top ten wind energy countries, China’s large population and extremely large manufacturing industry mean it needs a consistent energy supply. The boom can also be partially attributed to China’s urgent need to counter the pollution caused by the country’s coal powered electricity plants [6].

Besides support from the government and local banks, China’s manufacturing industry is supported by a large home market and low labour costs which is absent in smaller European countries.

The size of this nation in terms of both territory and population simply enables any significant growth to take place in massive proportions.

In Beijing, 8% of the energy is produced by non-fossil fuel methods – including solar and hydroelectric – with a target of 15% by 2020 [6].

It is worth noting that China’s solar energy industry is also huge with seven Chinese manufacturing companies in the top ten solar companies internationally.

The growth of the Chinese market has also benefitted a lot of other countries that were looking to develop their wind energy industries.

The drop in wind turbine price to about one third of what the cost was in 2007 has been attributed to the competition posed by Chinese products.

Low labour costs and availability of raw materials as well as a market for the products have made turbines and blades available more cheaply [6].
List of top Ten Wind Energy Countries and Their Installed Capacity [5]:

1. China – 52,800 MW6. Italy – 6,200 MW
2. USA – 42,432 MW7. France – 6,060 MW
3. Germany – 27,981 MW8. United Kingdom – 5,707 MW
4. Spain – 21,150 MW9. Canada – 4,611 MW
5. India – 14,550 MW10. Portugal – 3,960 MW
 11. Rest of The World – 29,500 MW

Article References

[1] Lords European Union Committee 27th Report of Session 2007 – 2008: The EU’s Target for Renewable Energy: 20% by 2020 Potential Energy Mix; Volume 1 Report - Page 20.

[2] Using Financial Incentives To Encourage Wind Power Project Development by Sasha Kemmet WISE Intern Iowa State University – The Institute of Electrical and Electronics Engineers IEEE, August 2006:

[3] EWEA – EU Will Exceed Renewable Energy Goal of 20% By 2020:

[4] International Trade Centre – Trade Map, List of Developing Countries 2007 – 2011:

[5] Clean Technica – Wind Power Growth Rebounds 15% in H1 2011, Capacity Rises ~ 23% (June 2011):

[6] Financial Times – China’s Rush Into Renewables: The Way The World Turns (28 November 2011):

A home energy audit can reduce bills, create a healthier environment, and reduce your carbon footprint.

The goal is to reduce unnecessary energy use and improve comfort in the home.

This page looks at what an audit can acheive, information about DIY and professional energy audits.

Below you'll also find a home energy audit checklist.

DIY Energy Audit

You can do a DIY energy audit to assess your situation. If problems are mild, you can take steps towards DIY solutions.

Make a list of things you need to check and take note pad and pen in hand as you conduct the audit. Take notes of all the things you can fix yourself, and the things for which you’ll need to call for professional help.

Home Energy Audit Checklist

What kind of problems should you be looking for? Start with the most obvious and glaring faults that might be wasting electricity.

1. Air Leaks

Air leaks will cost you when it comes to both heating and cooling. Check windows, doors, electrical outlets, attic hatches, air conditioners, and baseboards, for leaks.

If you can see sunlight around a window, there is a leak. Caulk in whatever gaps you can.

2. Insulation

If your home is inadequately insulated, you could lose a lot of heat through the walls and ceiling, which results in excessive energy required for artificial heating in winter.

Similarly, your home may get very hot in summer, requiring mechanical cooling measures, which consume high levels of electricity.

Check the attic, and if possible also the exterior walls to determine if your home is sufficiently insulated. While inspecting the attic, also check for air leaks that may need to be caulked or weather stripped.

3. Lighting

Check the wattage of the bulbs at use in your home.

If they are of high wattage (such as 100 watts), they can be replaced with lower wattage bulbs.

Softer light will suffice in areas where you relax, while you may need stronger light for study areas.

Fluorescent bulbs help save energy in places where you spend most of your time and lights are kept on for hours at a time.

4. Heating and Cooling

Check and clean the filters of your forced-air furnace every month. A professional cleaner should be called annually.

If your equipment is older than fifteen years, a newer model is likely to provide greater efficiency, and decrease energy consumption.

A short term investment could lead to long term returns as newer models are far more energy efficient than older versions. Also check the ducts of heating and cooling units for leaks.

5. Windows

Windows can make a huge difference in the energy efficiency of your home. They reduce heating and cooling costs, add value, and create a healthier environment.

Double glazing is the most common modern option.

Click here to learn more about energy efficient windows.

Get a Professional Energy Assessment

If you want a more thorough assessment, complete with recommendations, you could call a professional home energy auditor.

Professional energy auditors utilize the help of specialized technical equipment, such as blower doors and infrared cameras, to conduct the audit in order to get more specific results.

This will give you the most accurate assessment of where the problem areas lie, and what you can do to improve the overall energy efficiency of your home.

Why Do A Home Energy Audit?

Your home may have been built with flaws, or it may have developed flaws over time, which can cause energy consumption to be higher than it need be.

By identifying problem areas you will gain insight as to what you need to do to improve, so that less energy is used in the home. Less energy use means greater efficiency, which means you get to live just as comfortably, while paying less money on your monthly electricity bill.

This not only reduces the drain on your wallet, but also goes a long way to reducing the drain on non-renewable energy resources, and the consequent carbon emissions that these are responsible for.

Many wind energy companies are taking big steps forward in making electricity more efficient, affordable, and generally more accessible for individuals, energy companies, and governments.

This page looks at some of today's top wind energy companies and their recent projects.

Dong Energy Opens World's Biggest Offshore Wind Farm

The world's largest offshore wind farm was recently completed off the coast of Cumbria.

The Walney wind farm project was completed in two phases, at a cost of £1.2 billion.

off shore wind farm Cumbria
The world's largest offshore wind farm, off the coast of Cumbria.

The wind farm, which consists of 102 wind turbines, is expected to generate enough power to provide electricity to 320,000 homes.

It has a total installed capacity of 367 megawatts.

Dong Energy, the Danish wind energy company operating the wind farm, completed the second phase of the project in record time, with huge financial savings compared to similar projects.

The project set a precedent as it is the first renewable energy project to be funded entirely by foreign pension funds [2].

TransAlta Conducts Research to Reduce Mortality of Migrating Bats

TransAlta, Canada's largest public traded renewable energy company, has funded a study to mitigate bat mortality from wind turbines, in an effort to make wind energy even more environmentally friendly.

Working closely with researchers from the University of Calgary, TransAlta representatives have been trying their best to get to the bottom of what causes bat mortality around wind turbines, and how it can be reduced or prevented.

Research conducted in the Pincher Creek area shows that a sudden drop in air pressure around the blades is the reason for the high rate of bat deaths.

The drop in pressure causes barotrauma – fatal injury to the lungs – in bats, who are not physiologically equipped to cope with the sudden drop in air pressure.

The research looked at ways to reduce bat mortalities, and deduced that bat activity is highest in low-wind conditions.

By slowing turbines down to virtually motionless during periods of low wind speeds, bat mortalities can be substantially reduced, without significantly affecting the amount of energy generated by the wind farm.

TransAlta has implemented these measures in wind farms, reducing bat mortality by up to 60% [1].

Japanese Researchers Design Wind Turbine that can Triple Energy Production

A team of researchers from the Kyushu University's Research Institute for Applied Mechanics (RIAM) have designed a super efficient wind turbine, called a 'wind lens' that is nearly three times more efficient than regular wind turbines.

By incorporating a diffuser shroud that encircles the outer circumference of the rotor blades, and an outer brim, strong vortices are created, which lowers the pressure behind the turbine, creating a wind suction effect that draws more air through the turbine.

The result is that wind power is magnified, significantly enhancing energy production [7].

Wind Powered Web Hosting

Web hosting company, HostGator, has taken the initiative to power its servers with green wind energy.

As hosts to over 4 million websites, HostGator's servers require a lot of power to keep them running, and to keep them cool.

After switching to energy efficient servers, they took a further step to reduce their carbon footprint by purchasing renewable energy certificates equivalent to 130% of their energy consumption.

This equates to enough energy to power 321 homes with green energy for a year.

Renewable energy certificates are used to fund the expansion of green energy projects in an effort to gradually switch from non-renewable energy to cleaner renewable energy sources [4].

Bringing Wind Energy to the Masses with Small Wind Turbines

Urban Green Energy has a major point of difference to other wind energy companies – their products take advantage of the energy generated by low wind speeds.

They believe that by providing an opportunity for more people to tap directly into wind power by distributing small scale wind turbines to the masses, they can contribute enormously to the clean energy revolution.

To this end they have designed a number of products that take advantage of low speed winds, to deliver wind power to homes and small businesses [5].

The units consist of an asymmetrical vertical turbine that can capture wind coming from all directions.

This allows the turbine to operate at much lower speeds than conventional fan-type wind turbines, reducing noise, and hazards to birds as a result of collisions.

The company produces a 600 watt, 1 kilowatt, and 4 kilowatt models, ranging in price from $4000 to $19,000 for the turbine [6]; they also provide additional products and services, such as installation, batteries, and monitoring tools that let you monitor both energy generated, and your energy consumption, remotely from anywhere in the world – how cool is that?

New Tech: Wind Energy Generation Using Kites


Article References

1. University of Calgary. Scientists Find Successful Way To Reduce Bat Deaths At Wind Turbines. ScienceDaily, 28 Sep. 2009.

2. Terry Macalister. Ed Davey throws weight behind green energy by opening giant UK windfarm. The Guardian, 9 Feb. 2012.

4. HostGator. HostGator Has Gone Green!


6. Scott Tharler. Small Wind Meets Smart Grid. Discovery News.

7. RIAM Kyushu University Division of Renewable Energy Dynamics. Development of Wind Energy and New Wind Turbine System.

"Hybrid" refers to something that combines different elements. Hybrid technology has advanced rapidly, giving birth to hybrid cars, groundbreaking communications tech, smart-houses, and eco homes.

Similarly, hybrid energy systems have been designed to generate electricity from different sources, such solar panels and wind turbines.

Hybrid energy systems often consist of a combination between fossil fuels and renewable energy sources, and are used in conjunction with energy storage equipment (batteries).

This is often done either to reduce the cost of generating electricity from fossil fuels or to provide back up for a renewable energy system, ensuring continuity of power supply when the renewable energy source fluctuates.

One of the biggest downfalls of renewable energy is that energy supply is not constant [3]; sources like solar and wind power fluctuate in intensity due to the weather and seasonal changes [3].

Therefore, a reliable backup system is necessary for renewable energy generating stations that are not connected to a national power grid.

These systems consist of a variety of power control methods and storage equipment which include battery banks and diesel generators among others.

The power systems that are connected to the national grid don’t have this problem because, in most cases, there are many different sources of power contributing to the national electricity supply.

Different Hybrid Power Technologies

There are several types of hybrid energy systems such as wind-solar hybrid, solar-diesel, wind-hydro and wind-diesel.

The design of a system or the choice of energy sources depends on several considerations.

The factors affecting the choice of hybrid power technology can also tell us why people use hybrids and some of the advantages. The main factors are cost and resources available.

The cost hybrid power technology greatly affects the choices people make, particularly in developing countries.

This also depends on the aim of the project. People who are planning to set up a hybrid energy project for their own use often focus on lowering the total investment and operational costs while those planning to generate electricity for sale focus on the long-term project revenue.

As such, systems that incorporate hydrogen storage and fuel cells [4] [5] are not very common with small scale projects. The viability of one hybrid energy system over another is usually pegged on the cost of generating each kilowatt.

The availability of the natural resources plays an enormous part when selecting the components of a hybrid energy system - the right power generation location and method must be chosen.

Often, a hybrid system is opted for because the existing power resource is not enough to generate the amount of power needed - which is often the case when using micro-hydro plants.

In some developing countries, such as parts of Ethiopia, a wind-solar hybrid power system, consisting of wind turbines and solar photovoltaics was found to be most viable. This was because the wind resource alone was not sufficient to meet the electric load. Solar P.V. cells were very expensive, so it wasn’t feasible for the project developers to use solar power alone [6].

Hybrid systems are most suitable for small grids and isolated or stand-alone systems as hybrid power generation is, by definition, a solution for getting around problems where one energy source isn’t sufficient.

The popularity of hybrid energy systems has grown so much that it is now a niche-industry in itself – with custom systems being engineered for specific functions. For instance, Enercon, a German wind power company, has come up with unique factory-designed hybrid power technology, including the world’s first hybrid wind-diesel powered ship, the E-Ship 1 [7].


Article References

[1] Oxford English Mini dictionary ISBN 0-19-860255-3

[2] Toyota – Prius V Specs:

[3] Zero emission Project – The Problem of Renewable Energy Fluctuation by Lorenzo Polidori, May 2010:

[4] U.S. Department of Energy – Fuel Cells Technologies Program:

[5] M. Khan, M. Iqbal; Pre-feasibility study of stand-alone hybrid energy systems for applications in Newfoundland – Memorial University of Newfoundland St. John’s Canada June 2004: Elsevier Renewable Energy Issue 30 (835 – 854).

[6] Feasibility for a standalone Solar-Wind-Based hybrid energy system for application in Ethiopia by Getachew Bekele and Bjorn Palm Department of Energy, KTH, Stockholm, Sweden; Elsevier - Applied Energy 87 (487-495) 2010.

[7] Got Powered – Enercon E-Ship 1: Wind-powered ship:

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