Solar energy has been growing in leaps and bounds over the last decade; it seems that the logical goal of capturing and storing unlimited, free, clean solar energy (as opposed to harvesting limited and hard-to-get-to crude oil and natural gas, which also create a host of problematic gases when burned), has become more widespread. Not only can we set up giant solar arrays to act as next-gen power plants, but individual buildings and homes can generate all or some of their own energy. 

But when it comes to solar panels on buildings and homes, there have been a couple of stumbling blocks. First is the not-so-pretty aesthetic impact of solar panels, which many businesses and homeowners who want to reap solar's benefits end up having to hide or "put 'round back." A second, related issue is that solar cells mounted on panels are usually put on roofs, where they share space with HVAC systems, emergency exits, and other maintenance equipment, and while it's a sensible place to put panels, it also means that a roof area (valuable real-estate in urban areas) can't be used for decks with a view, or a place to grow plants or a garden. When thinking holistically about greening a smaller residential building, some owners have had to choose between offering an outside green area/garden and solar panels. When thinking of ways to make urban areas healthier and greener, we want to encourage — not discourage — using roofs for green areas or growing food and recreation, but not at the expense of creating clean, low-cost energy.  

But what if another part of a building could be used to make solar power? Say, a big glassy facade, or even just your living room's bay window, or your bedroom's picture window? New solar cells that are embedded in glass solve the limiting aesthetic placement problems by allowing solar cells to exist wherever a window does. They also allow and even support greater window use per-square-foot in a new building, which has the extra benefit of allowing/utilizing natural daylighting (and in the winter, passive solar heating), which cuts down on electricity use — a double fossil fuel-savings whammy. And larger, multiple windows are more popular in new buildings than ever. 

And the cost savings could be significant. Instead of paying to buy and install separate solar panels, window solar cells would be installed just as conventional windows are, with a small additional cost for the solar windows versus typical windows. Since solar panels are tied to the availability of silicon, solar windows can also save money since they are not reliant on silicon, but can be made from various types of inexpensive plastics. Cost return on investment is estimated to be three to five years (about half the time it takes for solar panels to earn their cost back in energy savings). 

So how have engineers turned windows into solar panels? 

Thin films are sprayed onto glass, and within those films, tiny functional organic solar cells (they are about one-fourth the size of a grain of rice) collect light — from the sun and from light bulbs — which is then converted into electricity. There are a number of different films, some of which concentrate light energy near the frame of the window (which has resulted in efficiency gains) and some with lower efficiency but that can be used over larger surface areas.

Currently, efficiency is low compared to panels, but since costs and surface-area are large, it could be less important — though engineers are looking to increase efficiencies. 

Sphelar solar cells can be attached to either polycarbonate (plastic) or glass, and absorb light from any direction, which is ideal for large window expanses on buildings, and could have applications for cars. The tiny globes are formed via an interesting process wherein the molten silicon is allowed to fall freely; it naturally forms spheres — and this system has the additional bonus of generating minimal waste. Because they are spherical, the company claims these globes produce more energy than flat cells, since they can absorb energy from more than one direction. While they are not totally clear, they do let plenty of light through (it seems they are like privacy glass) and can be flexible, so they could be used in applications where bended glass is needed, like specific types of architecture (a curved glass window). See video below to see how Sphelar solar cells work.

Even stained-glass can be made to harness solar energy, though in a slightly lower-tech way than the methods mentioned above. Sarah Hall, an artist who specializes in large-scale art glass with solar components has sandwiched solar cells between colored glass in a number of projects (they are not obviously visible), including a church in Saskatoon, an elementary school in Washington state, and the Solar Decathlon House in Washington, D.C. Each of Hall's creations harnesses the power of the sun to both create color and generate electricity, including sending some of it back to the grid. 

It looks like the future of solar power is as clear as a window, so that we can enjoy the sun's light on our faces, and harness its energy to run our computers at the same time. 

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