Chapter 2: A Primer on Energy and Energy Efficiency

In my classes on solar and wind energy at The Evergreen Institute, I continually remind my students of the virtues of energy efficiency and conservation — measures that reduce household energy use. In fact, like other solar advocates, I consider reductions in energy demand as a prerequisite to renewable energy. Accordingly, I encourage my students to make their homes (or, in the case of future solar- or wind-system installers, their clients’ homes) more energy efficient before they even think about installing a renewable energy system. I give the same advice to my readers, you included.

This chapter explores the rationale behind my push for efficiency first, advice I hope you will take before you retrofit your home with any of the solar home heating options discussed in this book. This chapter also presents key energy concepts and the terminology that you need to know when studying your options and making decisions on what is appropriate for your home or business.

Energy Conservation and Energy Efficiency

Reductions in energy consumption can be achieved in two ways: by employing energy conservation measures and by employing efficiency measures.

In home heating, energy conservation refers to the simplest measures one can use to cut down on energy use — for example, turning down the thermostat in winter when you leave the house for work each morning. Energy conservation measures typically include changes in behavior, such as turning off lights or wearing a sweater, insulated underwear, and heavy socks on cold winter days. It might include something as simple as donning one of those quirky Snuggies while reading or watching TV, or switching on a ceiling fan to force hot air down from the ceiling to the occupant level. I group all similar efforts within the broad category of energy conservation.

While energy conservation often entails behavioral changes, energy efficiency relies principally on technology to trim demand. Energy-efficient technologies are those that provide services with the least amount of energy.

Energy efficiency is a measure of energy in to energy out — that is, how much energy a device uses to provide a service, such as lighting or heating, compared to the amount of service we receive. A 100-watt incandescent light bulb, for instance, requires 100 watts of electricity, but delivers only about 5 to 10 watts of light energy. So, it is only 5% to 10% efficient. The remainder of the energy consumed by the light bulb is emitted as heat.

The more efficient a device is, the greater the conversion of energy into some useful end product. Substituting an energy-efficient LED floodlight to illuminate your front steps and walkway, for instance, can reduce the wattage of an outdoor light from 150 to 10 watts (Figure 2-1). You still receive the light you need to safely navigate the toy-littered front steps at night, but you do so with a lot less energy. The LED light produces proportionally more light per unit of energy it consumes than the incandescent lights that have been in use for many years. As another example, an energy-efficient furnace delivers more heat per unit of the natural gas or propane it burns than its less-efficient counterpart. You stay warm with less fuel and save heaps of money in the process. So why spend time talking about efficiency in a book on solar home heating solutions?

Fig. 2-1: This light consumes 10 watts but produces as much light as a 150-watt conventional floodlight.

The answer is simple. It costs less to save energy than to buy energy — a lot less. For example, it is much cheaper to don a comfortable wool sweater, or to wrap up in a blanket as you read or watch TV, than it is to crank up the thermostat four degrees. Yet they both have the same effect.

Study after study shows that it is much more economical to seal up the leaks in the walls, foundations, and roofs — known as the building envelope — with a few $5 tubes of caulk than it is to crank up the heat or even to generate heat from a renewable energy technology such as a solar hot water system.

Short-Term and Long-Term Benefits of Efficiency and Conservation

Efforts to reduce energy consumption can save you a fortune — and reduce your carbon footprint. In the short term, energy efficiency and conservation measures can save money by substantially reducing the size of the renewable energy system you’d need to install to meet your needs. Such measures often save enormous amounts of money. So remember, slashing energy use dramatically reduces the size and initial cost of renewable energy systems.

The way it works is simple: by lowering household energy demand, efficiency and conservation measures reduce the amount of energy your renewable energy system will need to supply to maintain comfort in your home. That means you’ll be able to install a smaller system to meet your needs. The smaller the system, the lower the initial cost. Investing a few thousand dollars in energy-efficiency measures to cut overall heating demand by 25% could reduce the cost of that $20,000 solar hot water heating system you were contemplating by as much as $5,000.

Measures to reduce energy consumption save in the long-term as well — by reducing your monthly fuel bills. If, for instance, you install a solar hot water system, you’ll still need to use your furnace once in a while — say, during long, cold, cloudy periods when there’s just not enough sunlight to provide space heat. The more efficient your home is, however, the shorter the run time, and the less fuel you’ll need. The less fuel you need for backup heat, the more you’ll save.

If you choose not to pursue a solar home heating option, efficiency and conservation will by themselves save you a lot of money over the long haul. The weather stripping you install around leaky double-hung windows or leaky doors, the caulk you apply at the base of your walls, and the host of other measures discussed in the next two chapters can save you huge amounts of money and make your home much more energy efficient — reducing the waste of expensive energy. So take these steps, at the very least.

Efficiency isn’t Sexy, but it Really Works

Over the years, as I’ve been extolling the virtues of energy conservation and efficiency, several students in my classes have responded that these measures just “aren’t as sexy as renewable energy.” It’s hard to deny. A brand new solar hot water system or PV module is an exciting addition to a home and will gain a lot of attention — even accolades. Not many people will remark favorably (or at all) on your new caulk and weather stripping.

Without a doubt, modern humans are enamored of shiny gadgets, which are a lot sexier than a bead of caulk or some lowly weather stripping applied around doors and windows to seal up heat-robbing air leaks. However, all the sex appeal of a renewable energy system quickly fades when you compare the price of achieving the same energy reductions with efficiency measures. I learned this lesson many years ago after moving into a passive solar home in Colorado. Although the house was heated by the Sun and was pretty efficient, it was all-electric. It had an electric water heater, an electric stove, and electric baseboard heaters for backup space heat. The previous owner had not installed an energy-efficient refrigerator or any energy-efficient lighting. To power the home with solar electricity, I would have needed a $50,000 system. A couple of years later, I built a new home of similar size, but this one was designed and constructed to be as energy efficient as humanly possible. To power that home, I was able to meet my demands for electricity with a $16,000 solar electric system, all thanks to careful attention to energy conservation and energy efficiency and just a few thousand dollars additional investment. I got my solar system at a much lower initial cost thanks to the more affordable efficiency measures that trimmed demand.

Conservation and efficiency may not be sexy, but they work really well, and they save lots of money. Besides reducing initial costs, these two measures continue to save me money every year. From 1996 until 2010, for example, I saved approximately $20,000 on heating and cooling costs for my home in Evergreen, Colorado in the foothills of the Rocky Mountains. My savings have paid for the slightly higher cost of building an airtight, superinsulated, earth-sheltered passive solar home ($1,000 to 2,000) and the solar electric system ($16,000), which generated about $4,000 worth of electricity during that period.

Energy conservation and energy efficiency offer the best of both worlds. They save money initially by reducing the cost of renewable energy systems, and they save a ton of money in the long-term. It couldn’t get much better.

Energy Efficiency and Conservation are Renewable Resources

Energy efficiency and conservation are renewable “sources” of energy, too. That new energy-efficient compact fluorescent light bulb or that new Energy Star refrigerator you install, for example, will continue to save energy year after year after year. And remember, every bit of energy you save through such efforts — now and in the future — is freed up for others to use. Saved energy is energy that doesn’t need to be extracted from the Earth’s declining supply of coal or natural gas.

If that doesn’t make sense, think of it this way: Imagine that a small city with 50,000 homes expands by 100 new homes a year. Suppose the homes are heated by natural gas. To heat these new homes, additional natural gas deposits must be located, and natural gas must be extracted and piped to the new homes. Suppose, however, that the citizens of our hypothetical city embark on a citywide energy-efficiency and conservation effort. They enact various measures that reduce their natural gas demand by the same amount required to heat the 100 new homes. The net result is that the new homes are supplied by efficiency measures. And, there’s no need to extract more natural gas.

Conservation and efficiency are, in effect, the same as developing new energy resources. Annual savings go on year after year after year, too, creating an essentially renewable supply of energy. What is more, this strategy doesn’t increase the city’s carbon footprint. Per capita energy use and per capita carbon emissions actually decline.

Understanding Energy

Before you can save energy, it is important to first know what energy is and what the terms are that are used to describe it — specifically, the units of measurement.

What is Energy?

In simplest terms, energy is the “stuff” that allows us to do work. It helps us heat and cool our homes. It powers our lights and appliances. It powers electronic devices like cell phones, computers, fax machines, and stereos. It powers motors, busses, and even electric cars.

Most of the energy we use comes from the Sun. Coal, natural gas, and oil are nothing more than a mixture of organic materials that contain ancient solar energy. How so?

Astonishingly, the energy released when fossil fuels are burned is ancient solar energy. That’s because fossil fuels are made from plant matter (in the case of coal and natural gas) and photosynthetic algae (in the case of oil). Plants and algae get their energy from the Sun. During photosynthesis, this energy is used to make organic molecules that make up the bodies of plants and algae. When these organisms die, they are covered by sediment. Over time, heat and pressure convert the organic matter into fossil fuels. When we burn these fuels, we release the ancient solar energy.

Unfortunately, utilizing this form of solar energy also releases billions of tons of carbon dioxide and other pollutants. They, in turn, have made quite a mess of the Earth’s atmosphere, the air we and all the rest of Earth’s creatures breathe. Carbon dioxide, of course, is also responsible for mucking up the planet’s climate. As most readers already know, carbon dioxide is a greenhouse gas that traps heat in the Earth’s oceans and atmosphere. This extra heat wreaks havoc on the climate.

We can, however, tap directly into solar energy without all the garbage carbon. That’s what this book is all about: finding ways to heat our homes from carbon free sunlight beaming down from the sky (Figure 2-2).

Fig. 2-2: The south-facing windows in this passive solar home in the Northern Hemisphere (Carbondale, Colorado) allow the low-angled winter sun to enter, providing heat during the cold winter months.

Putting Energy to Good Use

Energy comes in many different forms. There’s sunlight energy, electrical energy, heat, light, and even coal, oil, and natural gas. These last three are considered raw energy. All forms of energy have one thing in common: they permit us to do work. However, most forms of raw energy are pretty useless to humankind. A lump of coal or a gallon of gas, by itself, is hardly worth the money we pay for it.

Raw forms of energy become useful (allow us to perform work) when we convert them into other, more useful forms. When coal is burned in a power plant to produce heat, for instance, the heat is used to boil water. Steam from the super-heated water is used to drive a turbine that is attached to a generator that then produces electricity. Sunlight by itself isn’t that useful either. However, Sun streaming into the south-facing windows of a home is converted into heat that can warm our living spaces, making life more bearable. Sunlight bombarding a solar electric module, on the other hand, causes electrons to move, creating an electrical current that can power lights, appliances, electronics, and even electric cars. All this is to say that it is the conversion of raw energy into useful energy that matters to us the most.

Over the years, humans have devised many amazingly ingenious technologies to convert “raw” solar energy into useful forms. This book is about three of them: passive solar homes, solar hot air systems, and solar thermal systems (also called “solar hot water” systems). Each system requires a device to collect and then convert solar energy into a more useful form of energy — heat.

One thing to remember, though, is that solar energy is a low density form of energy. That is, it doesn’t contain a lot of energy per unit volume compared to coal or oil or even natural gas. Another fact to keep in mind when working with energy is that each time we convert one form of energy to another, we lose some energy — often, a lot of energy. Put another way, no energy conversion is 100% efficient. Far from it. Your car, for instance, only converts about 20% to 30% of the energy it consumes into forward motion. Diesel engines convert a bit more (about 40%) of the energy they consume into forward motion. During the conversion of these fuels into mechanical energy, there’s obviously a huge amount lost. Energy is lost as heat, which simply radiates out into outer space.

Because of the diffuse nature of solar energy and the loss of energy during conversions, to make the most of solar energy, we must do everything within our power to retain the useful energy we obtain from the Sun and to use it efficiently.

As you will see, all of the solar home heating technologies discussed in this book are designed to gather up diffuse solar energy and then convert that energy into a more directly useful form, specifically, heat. Like all other technologies, solar heating equipment doesn’t convert 100% of the solar energy it captures into useful energy. But if we are smart about it, we can keep our homes warm and cozy in the winter, all thanks to conservation, efficiency, and the Sun.

To make the most of the heat we gain in these systems, we need to be sure that we retain that heat where it belongs, so we can enjoy its benefits. To do that, we need to seal up our homes and offices as tightly as possible while maintaining a fresh air supply. We also need to insulate the daylights out of our buildings. My mantra is this: Insulate, Insulate, Insulate!

Weatherization, air sealing and insulation, are keys to making solar heating systems work.

Period.

Attempting to use solar heating without weatherization is like trying to fill a leaky bucket with water.

Units of Measurement

Now that you understand a little about energy and the importance of energy efficiency and energy conservation, let’s take a look at some common units of measurement. You’ll very likely encounter these units in discussions with energy auditors or installers.

In the heating and cooling arena, the most important unit of measurement is the British Thermal Unit, or BTU. A BTU is the amount of energy it takes to raise the temperature of one gallon of water one degree Fahrenheit (specifically from 59° to 60° at one atmosphere of pressure).

BTUs are used to measure the heat content of fuel. Each type of fuel contains a certain number of BTUs per gallon or cubic foot or pound. A gallon of gasoline, for instance, releases 115,000 BTUs when it is burned; a gallon of diesel fuel contains 130,500 BTUs. A cord of firewood cut from a pine tree contains 17 million BTUs of heat that can be liberated during combustion. A hardwood tree like an oak would contain nearly twice as much energy.

BTUs are also used to describe the heat output of appliances such as water heaters or furnaces. A 60,000-BTU heater, for instance, produces 60,000 BTUs per hour when running at full speed. Obviously, the higher a furnace’s or boiler’s BTU rating, the more heat it will produce.

If your home is heated with natural gas, you’ll note that your fuel charge is based not on BTUs, but on another unit of measurement, the therm. A therm is 100,000 BTUs.

In this book, I’ll primarily be concerned with BTUs, since my focus is on home heating. I should mention, however, that BTUs are also used to measure heat extracted from a building. This is known as cooling capacity. A 10,000-BTU air conditioner removes 10,000 BTUs of heat from a building per hour. The higher the BTU rating, the greater the cooling capacity.

Cooling capacity is also expressed in tons. This term refers to the cooling capacity of a ton of ice. An air conditioner with a one-ton cooling capacity, for example, removes 12,000 BTUs/hour. In other words, a one-ton air conditioning unit is the same as a 12,000-BTU unit.

Just as BTUs can be converted to therms, BTUs can also be converted to another common unit of measurement: kilowatt-hours. To understand what a kilowatt-hour is, we can begin with a more familiar measurement: watts. All of us have purchased light bulbs and other electrical devices, such as microwave ovens and hair dryers, by their wattage. A 100-watt light bulb, for instance, is so rated because it consumes 100 watts of electricity continuously when turned on. A 1,000-watt microwave oven consumes 1,000 watts of electricity continuously, when operating. A 1,200-watt hair dryer, consumes 1,200 watts of electricity.

Watts can be confusing to newcomers to electricity. Bear in mind that it is not a measure of quantity, like pounds or liters. It is a rate. More specifically, it is the instantaneous rate of power consumption. It’s a lot like the speed of a car. If you are traveling at 50 miles per hour on a highway, that is a rate of movement. It doesn’t say a thing about how far you will travel. It just tells you at that instant, you are traveling at 50 miles per hour. If you kept that speed up for an hour, you would travel 50 miles.

Utility companies aren’t concerned with instantaneous power consumption of your home, however. They’re interested in how much power you consume over time — specifically, the monthly billing period. Power consumption over time is measured in kilowatt-hours. The following example illustrates what a kilowatt-hour is:

If a 100-watt light bulb runs for 1 hour, it consumes 100 watts. This is expressed as 100 watt-hours of electricity.

If that bulb is left running for 10 hours, it consumes 1,000 watt-hours (100 watts x 10 hours = 1,000 watt-hours). If that bulb is left running for 20 hours, it consumes 2,000 watt-hours.

Because a kilo is equal to one thousand, 1,000 watt-hours can also be referred to as a kilowatt-hour. A kilowatt-hour is abbreviated kWh.

Two thousand watt-hours is 2 kilowatt-hours or 2 kWh. Twelve thousand watt-hours is 12 kilowatt-hours or 12 kWh. It is kilowatt-hours that utility meters track and what utility companies charge you for each month.

Kilowatt-hours is the unit of measurement typically used to assess electrical consumption. Interestingly, as noted above, kilowatt-hours can also be converted to BTUs and vice versa. We most often convert BTUs to kilowatt-hours. A kilowatt-hour of electricity is 3,412 BTUs.

Conclusion

Energy conservation measures like sealing up the leaks are key to successful and economical solar heating. Energy conservation and efficiency are to solar what walking is to running. Ignore these important steps, and you’re bound to fall. You’ll have to oversize your system to create heat, the vast majority of which will just leak out into the bitter cold winter air.