Energy Advantages of Passive Solar Heating

Introduction

Fig. 1: This illustration demonstrates the architecture of overhangs, large windows, and thermal mass. Each is designed to reduce reliance on fossil fuels for heating and cooling needs. (Courtesy of the DOE. Source: Wikimedia Commons)

Homeowners and renters alike are often willing and excited to invest some amount of time and money into saving energy to reduce energy bills. Typical suggestions include throwing on a sweater and lowering the thermostat, buying energy-star rated appliances, or switching out those incandescent light bulbs. [1,2] However, focusing on the architectural design of a house could drive down energy costs better than any retrofitted or replaced component of a house.

Passive solar design, or passive solar heating, refers to the use of the sun's energy to heat and cool indoor spaces. The architectural approach artfully combines intentional design, natural energy characteristics, and construction materials so the building itself becomes largely responsible for heating and cooling throughout the seasons.

A Few Components of Passive Solar Heating

The house in Fig. 1 is designed to reduce the annual cost of energy. How? In the winter months, the sun is low enough in the sky to penetrate through the south-facing windows and heat the space. In addition, the large amount of thermal mass within the floor allows the heat to be absorbed and stored, keeping the house warm throughout the day. On the contrary, in the summer months the overhang prevents the sun, which is higher in the sky during this time of year, from heating the space. This also allows the coolness from the night before that was absorbed by the thermal mass to be slowly released throughout the day to keep the house cool. [3]

There are also several other components of creating efficient homes that are tangentially related to passive solar design. Sun tubes and sky lights help illuminate spaces during the day without switching on a light. Choosing material such as straw bales to build a home can help decrease reliance on fossil fuels for heating and cooling because it is super insulating. [3] Last but not least, many energy-conscious architects include a PV- system (photovoltaic) in order to create a net-zero home given the energy generated by the solar panels.

Energy Saved from South-Facing Windows

Total Energy Consumption in the Residential sector accounted for 19,969 trillion Btu in 2017 (total energy consumption: primary energy consumption, electricity retail sales, and electrical system energy losses). If we assume the 2018 U.S. population to be 315 million, and if we assume households average 2.5 people, that gives us roughly 126 million US households.

Let's assume an average family decides to completely renovate their house so that it has all the elements of a passive solar heating. Depending on where in the United States the family lives, their heating and cooling costs could vary widely. However, if passive solar design reduced even just a quarter of their energy use, you would save a lot of money. In 2017, the real price (1984 dollars adjusted for inflation) of natural gas was $4.29 per million Btu. [4] This gives us:

In a 30-year lifespan, this looks like $5100 of possible savings. However, the price of fuel in real dollars (inflation-adjusted) is rising. This means that over a 30-year lifespan, even with an average fuel cost rise of only 5% a year, savings could be as much as $11,000 over that same 30-year period.

Conclusion

As people continue to seek more and more knowledge about ways to whittle their energy bill in order to save money and the planet, passive solar design architecture could become extremely popular. After the initial investment in the structure of the house, the house does most the work for you in terms of lighting, heating, and cooling.

© Michaela Crunkleton Wilson. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] A. Carrns, "Finding the Best Ways to Cut Utility Costs," New York Times, 21 Oct 14.

[2] J. Romano, "Ways to Whittle Your Energy Bill," New York Times, 13 Jan 08.

[3] R. Harris, "First Things First: An Efficient Abode," New York Times, 8 Nov 12.

[4] "Monthly Energy Review, November 2018," U.S. Energy Information Administration, DOE/EIA-0035(2018/11), November 2018.