When the cost of photovoltaics fell from $100 a watt to $20 a watt in the early 1970s it opened photovoltaics up to entirely new markets, from the ecofreak neighbor that didn’t much like baths to remote ocean buoys or to the off-grid cabin dweller.

Since then the technology, in fits and starts, has been gaining traction with homeowners across the world. But now solar is reaching a point where enough average people are adopting it that today you’re likely to know a friend, neighbor or colleague down the street that’s either installed or planning to install solar on their roof.

It’s a major accomplishment for a technology that, in terms of commercialization, is moving into its early teen years.

When photovoltaics were first produced, they were prohibitively expensive. Early photovoltaics were used on the Naval Research Laboratory’s Vanguard 1 satellite launched in 1958. Bell Laboratories launched the first telecommunications satellite with photovoltaics, the 14-watt Telstar satellite, in 1962.

The first photovoltaic-powered houses actually didn’t come about until around 1973. That’s when the University of Delaware’s Institute of Energy Conversion and Delmarva Power and Light built SOLAR ONE, one of the world’s first photovoltaic homes.

The house was built to test the feasibility of photovoltaic-powered residences, included solar thermal phase-change materials and was net-metered, according to the institute.

It started to make sense for people without easy access to the electric grid to look to solar as an alternative source of energy. It was a way to free a home from the tethers of fossil fuel- or nuclear-powered electricity for those who were so inclined or those that wanted to make their home secure from cold war fallout in the 1970s and 1980s. Beyond that, residential solar adoption was rather slow through the 1990s and into the 2000s.

Times have changed.

Now solar is everywhere.

Three things have really helped with the spread of residential solar: more manufacturers, module price drops and government support. Taken together, these have spurred a number of developments, like feed-in tariffs (internationally), solar-financing options and third-party ownership agreements that make having a solar system on a home more affordable than ever.

Since 1998, the earliest period the Lawrence Berkeley National Laboratory has residential solar figures for, the cost of installed residential solar has fallen from $11 per watt to $6.2 per installed watt in 2010. According to LBL’s “Tracking the Sun IV” The largest cost reductions occurred over the past few years.

The costs of solar are expected to continue to decline in the near future and utility prices are expected to go up.

Incentives may dry up, which means the out-of-pocket cost of solar could be more for a while. But right now, in ever more states, it’s becoming cheaper.

What that means, ultimately, is that you’re likely to keep seeing solar popping up in your neighborhood, and soon, if you don’t install it on your home, you might be falling behind the Joneses.

But, more importantly, you’ll be paying more for electricity than they are.