energy efficient patio doors
Patio doors can’t be truly energy-efficient. Glass is a bad insulator, and a door based on glass can’t ever be energy-efficient. There are some less bad options, or reasonable options, but never exactly truly energy-efficient patio doors.
If patio doors are in close connection with your living space, you can easily have a serious thermal-conduction problem. Patio doors can be a blessing in some weather conditions, but also a curse in many other situations.
Many of these doors are affordable and they look very nice but their low insulation value soon will be unveiled… 
Sliding patio glass doors
Sliding patio doors are between the worse options in what concerns energy-efficiency and patio doors. Their design may enlarge views and be very un-obstructive but it is also a bad option to keep heat inside home (in cold weather) or out of home (in hot weather).
The weatherstripping of sliding doors doesn't ever stop all the air leaking, but after some time of use it will increase sharply...
If possible, avoid sliding patio doors - stationary patio doors, or hinged patio doors are much more effective in blocking air-leakage - unless keeping heat inside or outside your home isn’t a concern.
Keep in mind: if you have or if want to have patio doors, and if the issue of energy-efficiency and heat loss and gain is a concern, pay attention to some important “details” to minimize the negative impacts of glass doors. Namely: 1) the type of glass, 2) thermal breaks and 3) the design of the doors (avoid sliding patio doors)… These elements can add make the doors more expensive, but you will be paid back many times over in energy efficiency.
The type of glass of the patio doors
The type of glass (and the number of panes) of patio doors is extremely important. It determines the insulation value (measured by its U-value) of the door, or its capacity to resist overheating (measured by its SHGC or Solar Heat Gain Coefficient).
The best U-Value and SHGC coefficients vary with climates. Having a low U-value is crucial in cold climates (the lower the U-value, the better the insulating value of the patio door glass), while high SHGC coefficient glass doors are important in hotter climates (the higher the SHGC the better the door glass is at blocking the heat).
These coefficients are also determined by the number of panes of glass (two or three pane glasses are very important for energy efficiency), low-E coatings, inert gas fills and low-conductivity spacers or thin sheets of special films. See for more information on these issues: Types of window glass.
The assessment of the efficiency of a patio door is – for obvious reasons – very similar to that of windows. And like windows, when assessing patio doors, consider their AL (Air Leakage) and their Condensation Resistance (CR) coefficients.
The efficiency of the frame of the patio doors
It’s common to define a patio door by the type of material of its frames: wood, vinyl, aluminum, fiberglass… And the exact type od material is obviously important for energy efficiency. Aluminum is known by its high thermal conductivity, and wood is not a very good insulator either…
Some disadvantages can be largely overcome by using thermal breaks (in the case of aluminum and other metal patio doors) or by combining wood with other materials. But pay attention to it...
Assessing the insulation value and the air sealing capacity of a patio door requires the assessment of the whole unit: the glass but also the frames, and the elements associated to each part.
Look for the patio door label to know the insulation value, air leakage, or heat and condensation resistance of a patio door: like windows, patio doors can also be assessed by their rating labels...
So, if shopping, look for the The National Fenestration Rating Council (NFRC) label, or the Energy Star rating, or the BFRC/British Fenestration Rating Council label, or the Australia Windows & Doors Labeling: Australian GreenHouse Office… and compare.
See also: