K eene Housing’s Harper Acres rooftop solar project is a good example of how small-scale efforts toward energy efficiency and renewables can pay off.

The project, which goes online this week, involved putting panels atop nine of the 14 buildings in the complex at one end of Castle Street. Harper Acres, sometimes referred to as “the yellow buildings,” includes 112 units for elderly and low-income residents. The solar project was completed Friday, and is expected to generate a little over 100,000 kilowatt hours of energy — about 10 percent of what the complex uses.

Joshua Meehan, Keene Housing’s executive director, says the agency is expecting to save almost $500,000 in energy costs from the project, over its life. But Keene Housing is stepping beyond that savings. Meehan says the solar array is just part of a larger energy-efficiency project at Harper Acres that’s included installing LED lighting, new windows and more.

All of that should help save the agency money, but it helps in a larger sense as well. New England’s energy costs are the highest in the nation not only because of the cost of generating energy here — fossil fuels such as oil and natural gas have to be imported to power plants in the region, driving up production costs. Another big factor is the age of many buildings here.

As one of the earliest-settled areas of the country, New England has many older buildings; you know, the ones without adequate insulation and with drafty windows, doors and utility openings. That all helps drive up energy use, and therefore, costs.

Retrofitting older buildings with tighter, weather-stripped windows, new insulation and energy-savers such as LED lighting and automated thermostats reduces the overall energy demand in the region. On a wide scale, that ought to reduce prices.

Of course, there’s also the reduced demand that comes along with supplying your own power. Dropping the demand of Harper Acres by 10 percent has an effect.

Monadnock Food Co-op’s rooftop solar array, installed in 2016, produces about 50,000 kilowatt hours of electricity per year, covering about 8 to 10 percent of the power used by the business. (At least for now; we’d expect the power usage to rise when the organization’s major expansion is finished.) That matters, too. Every project does.

It doesn’t have to be solar, though that’s the renewable source in which technology has advanced quickly enough that individual users can easily implement it. Any self-produced power, from wind to hydro, lessens demand on the grid. Every kilowatt of power that can be removed — by reducing use or replacing the source — helps not only the individual user, but all of us.