Ask Natural Life:
Can We Save Money by Going Solar?
by Wendy Priesnitz
Photo © Markus Gann/Shutterstock |
Q: Due to the high cost of energy, my husband and I would like to consider converting to solar. Could you please give us an overview of how it works, how much it costs, and whether it’s feasible?
A: There are two main ways to use the power of the sun to reduce energy costs in your home. You can use the heat from the sun’s rays to heat your home or your domestic hot water, or to produce electricity to power lights and appliances.
Other people have written some very good books about using solar energy in both renovations and new construction of homes. (See the list at the end of this article for some good ones.) So in the small amount of space available here, we’ll give you the very basics as well as some things to think about.
Rather than spreading energy payments over a long period of time, as with natural gas or electricity, a solar system places all the costs up front. However, once the system is paid for, the sun doesn’t charge for its energy, so the payback begins.
The initial costs (and, hence, the payback timeline) will depend on the purpose, type, and size of the solar system you choose. And that will depend on your budget, as well as the size of your family, your lifestyle, your geographic location, and the way your house is situated. However, an increasing number of governments are offering financial incentives to encourage homeowners to switch to solar, so you’ll need to research what’s available in your area.
Heating Hot Water
You are probably looking at a relatively high initial cost to retrofit your home with a thermal space heating system. But just about anyone whose house or yard is exposed to continuous sunlight can preheat their hot water using solar energy, so that might be a good place to begin your solar adventure. The initial cost is not as high as other solar projects and the payback won’t take too many years.
In 2006, the solar industry reported that the average price of a solar domestic hot water system in Canada was around $6000. Estimated payback periods for a solar water heater range from six to 13 years for water originally heated by electricity, and 12 to 20 years for natural gas heating. That system will easily cut your water heating bill in half and could save up to two metric tonnes of greenhouse gas emissions annually.
Solar water heating systems include solar collectors and storage tanks. Two main types of solar collectors are used for residential purposes in cold climates. They are flat plate collectors and evacuated tube collectors. Glazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or polymer covers. Unglazed flat-plate collectors—typically used for solar pool heating—have a dark absorber plate, made of metal or polymer, without a cover or enclosure. Evacuated-tube solar collectors feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin’s coating absorbs solar energy but inhibits heat loss.
In climates where temperatures rarely dip below freezing, a direct circulation system can be used, where pumps circulate household water through the collectors and into the home. In colder climates, an indirect circulation system is used, with pumps circulating a non-freezing, heat-transfer fluid through the collectors and a heat exchanger.
There are also passive solar water heating systems. A thermosyphon system works on the principle that warm water rises as cooler water sinks. The collector is installed below the storage tank so that warm water will rise into the tank, typically situated on a roof.
Most solar water heaters require a well-insulated storage tank. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank.
A typical family of four in North America is estimated to use about 80 US gallons of hot water per day. One gallon of hot water requires one square foot of collector area. A family of four will probably require two four-foot by ten-foot solar collectors and a tank with a 100-gallon capacity.
Hot water can also be used to heat your whole home. In that scenario, solar hot water is used for in-floor radiant heating or even to circulate through conventional radiators.
But that will not keep your house warm when the sun isn’t shining and hardly seems worth the effort or cost if a conventional heating system was also still required. So you would need to add a large bank of batteries or a serious amount of thermal mass to the equation, perhaps in the form of thermal mass interior walls, which would be warmed by the solar heated water, and retain and radiate that heat for longer. However, that sort of experimentation is not easily accomplished in a retrofit situation.
Photovoltaics
Conventional solar electric technology uses photovoltaic (PV) cells, which are semiconductor devices, usually made of silicon. Photons in sunlight are absorbed by the silicon and electrons are knocked loose from their atoms, allowing them to flow through the silicon to produce electricity. Because they contain no liquids, corrosive chemicals, or moving parts, PV cells require very little maintenance, don’t pollute (once they are manufactured), and operate silently.
Individual PV cells are used for powering small devices such as electronic calculators. To provide larger amounts of energy, the cells are bundled together into modules or what we know as “solar panels” to produce higher voltages and increased power. These panels have a sheet of glass on the front, allowing light to pass while protecting the cells from the elements. Panels can be linked together in arrays.
These panels generate direct current (DC), the kind of electricity produced by batteries. Most North American electrical devices require 120-volt alternating current (AC), which is what is supplied by local utilities. A device known as an inverter is used to convert the solar-generated DC to AC current for use in your home. Inverters vary in size and in the quality of electricity they supply. Less expensive inverters are suitable for simple loads, such as lights and water pumps, but high quality models are needed to power electronic devices such as TVs, stereos, microwave ovens, and computers.
Many PV systems are grid-tied, either ground-mounted or built into the roof or walls of a building. Off-grid PV systems generally use rechargeable batteries to store excess electricity.
Due to the increasing demand for solar energy, the manufacture of solar cells and PV arrays has been increasing rapidly. Technology has also been improving, decreasing the cost and making the cells smaller and more flexible.
Although prices vary, for a small scale PV system, you would probably pay around twice what you’d pay for a solar water heating system and the payback period would be approximately 15 to 25 years. Greater cost savings are usually realized through an economy of scale: The larger the solar energy system, the lower the cost of energy delivered for the money invested. In addition, some levels of government may provide rebates and other cost incentives when PV solar systems are installed by approved companies.
Passive Solar
If you have sat by a sunny, south-facing window on a cold day, you have felt the effects of passive solar energy. Passive solar uses walls, windows, floors, and roofs, in addition to exterior building elements and landscaping, to collect and store heat generated by solar radiation. Although it won’t provide all of the space heating necessary in a cold climate, passive solar can significantly lower your bill. Experts claim that, using building envelope upgrades alone, passive solar can supply 25 percent of a building’s heating requirement.
For effective passive solar heating, high performance windows are necessary, including insulated frames, multiple glazing, low-e coatings, insulating glass spacers, and inert gas fills. The most efficient window orientation for heat gain is due south, but any orientation within 30 degrees of due south will work. To let the sun in, a ratio of roughly eight percent window to floor area is recommended for south walls.
Once the heat is in, high levels of insulation and an air-tight building envelope help keep it there. With the heat contained, a simple ceiling fan or your furnace fan can distribute the heat.
The solar warmth can be maintained by using thermal mass in the walls and floors to absorb the sun’s heat and radiate it back into the room in the evening. Common thermal mass materials include stone, cement, and water.
A solar (or thermal) chimney is a passive solar ventilation system composed of a vertical shaft connecting the interior and exterior of a building. As the chimney warms, the air inside is heated causing an updraft that pulls air through the building.
Grid-Connected Solar
If/when your solar PV system produces more power than your family uses, you might be able to connect it to the utility grid and provide power to other customers of the utility. Net metering programs give these systems a credit for the electricity they deliver to the grid. This credit offsets electricity provided from the grid when the system cannot meet demand, effectively using the grid as a storage mechanism. So, you would receive a credit on your electricity bill for the difference between the value of the energy your system feeds back into the grid and the cost of the amount consumed. At times when the reverse is true, and the power generated by your solar system is less than what your family uses, you purchase the amount required from the grid.
No matter how you decide to harness the power of the sun in your home, you will be doing both your bank account and the planet a favor!
Learn More
Solar Water Heating: A Comprehensive Guide to Solar Water and Space Heating Systems by Bob Ramlow, Benjamin Nusz (New Society Publishers, 2006)
Passive Solar House by James Kachadorian (Chelsea Green Publishing Company, 2006)
The Renewable Energy Handbook: A Guide to Rural Energy Independence, Off-Grid and Sustainable Living by William H. Kemp (Aztext Press, 2006)
Photovoltaics: Design and Installation Manual by Solar Energy International (New Society Publishers, 2004)
The Solar House: Passive Heating and Cooling by Daniel D. Chiras (Chelsea Green Publishing Company, 2002)
Wendy Priesnitz is Natural Life Magazine's co-founder and editor. She is also a journalist with over 40 years of experience and the author of 13 books. This article was first published in 2008 and last updated in 2019.
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