Challenging Common Energy Misconceptions – Part 5: Heating

When it comes to saving energy, there are a bunch mistaken assumptions that often mislead people and cost them more money. The very vexing thing about these energy misconceptions is that, at first glance, they make seem to sense — until you examine the facts.

Since it’s midsummer, let’s look at three less common things affecting your electric bill that have one thing in common: HEAT.

1) Wind energy works only for those who live in windy areas. Long transmission lines to carry the electricity to the major population areas result in large voltage drops that reduce the efficiency.

All transmission lines have some amount of line loss. 

When electricity is passed through a wire, the metal’s natural electrical resistance causes the wire to get warm. Increasing the resistance requires more current to send the same amount of electricity through, so higher voltages are used to reduce loss.

For example, a 100-mile long 345 kV line carrying 1,000 MW will lose around 330 volts (4.2%) in line loss. While a 765 kV line carrying 1,000 MW of power can have losses of about 700 volts, that’s only 1% of the total wattage being delivered — making it more efficient.

On a hot summer day, thick transmission lines get hot enough to expand and sag towards the ground. If that hot wire hits a tree and shorts out, a whole neighborhood or town loses power. All transmission lines have thermal limits affecting their capacity to carry power. Knowing the temperature of critical sections is important to despatching power to whole grid and prevent expensive black outs.

In January 2014, Texas completed the Competitive Renewable Energy Zone (CREZ) transmission projects. Not only does it bring west Texas wind power to Dallas-Ft. Worth, San Antonio, and even Houston more efficiently and cheaply, it also solves what has been a growing transmission congestion problem in Texas that costed consumers up to $27.8 million a year in congestion rent.

2) Coal is coal, and it’s cheaper to burn than natural gas.

Coal is actually pretty complex fuel. There are four types:

  • Anthracite (hard coal) has the highest carbon content (86% to 97%) and is the cleanest burning. It’s also rare in the US, mined only in northeastern Pennsylvania.
  • Bituminous (soft coal) has the widest range of carbon content (45% to 86%) and makes up 45% of the coal mined in the US with the Central Appalachian region leading production.
  • Subbituminous coal contains 35% to 45% carbon and is the second most plentiful coal in the US because it occurs in thick beds near the surface. Wyoming’s Powder River Basin produces most of the subbituminous coal.
  • Lignite (brown coal) has the lowest carbon content, 25% to 35%, with the lowest heat output and is mostly mined in Texas. Lignite can contain up to 70% water by weight.

For industry purposes, coal is divided into metallurgical (coking) coal and thermal coal. Hotter burning coal with high carbon content is used in blast furnaces for making steel – which makes it more expensive. Thermal coal is mostly subbituminous burned by powerplants. Subbituminous coal from Wyoming’s Powder River Basin has a less than average sulfur content and a moisture level of 20%-30%. It burns at roughly 8,580 Btu/lb.

Coal pricing is graded by heat output (Btu/pound) and sold by the short ton. Hotter burning, high-sulfur coal generally comes from expensive shaft mines. Open pit mines, like those in the Powder River Basin, are substantially cheaper to mine, but rising rail shipment costs add more to the delivered cost.

The annual average thermal coal price for power producers fell from $2.39/MMBtu in 2011 to an estimated $2.36/MMBtu in 2014. The EIA expects the delivered coal price to average $2.30/MMBtu in 2015 and $2.31/MMBtu in 2016. Natural gas, meanwhile, is selling at about $2.73/MMBtu.

But while coal still seems to be just a tad cheaper, an EIA levelized cost analysis of different utility generation types shows that coal is more expensive (due to capacity factor, capital costs, and operation/maintenance costs) than natural gas.

3) A radiant barrier in my attic will cut my air conditioning bills.

Not everywhere – just mostly if you live in the deep South, like Texas or Florida.

Radiant energy barrier looks like foil and bubble-wrap material. The recommended installation method is to staple it onto the underside of the roof deck to reflect radiant heat coming through the roof back out into space. Since summer sun is closer to a 90° angle in southern states, more heat gets absorbed into the roof. Generally, southern homes will have HVAC handlers and duct work located in the attic.

All that heat radiating through the roof will heat that stuff up and increase the home’s cooling load. So, a properly installed radiant barrier shields the attic contents from the radiating heat energy.

Radiant barriers have high reflectivity (usually 0.9, or 90%, or more) and low emittance (usually 0.1 or less), but they must face an open-air space to perform properly.The spacing is needed because if the reflective barrier is in contact with part of the building, the barrier will just conduct heat to that part.

There has been passionate debate on the effectiveness of radiant barriers in northern houses. Most of the published research concludes that due to the colder climate, insulation and air sealing in northern states provide far more cost-effective results. This is because insulation reduces conductive and convective heat transfer.

Radiant barriers have even less of an effect because HVAC systems and duct work are often located in the basements of northern homes. One suggested installation method is to cover the insulation and attic floor with radiant barrier. Unfortunately, without the spacing, the radiant barrier will lose its much of its reflective effectiveness and only have an R-value of about 1. There is also the potential problem the radiant barrier will prevent moisture from escaping the house and cause condensation problems.

Stay tuned for Part 6 of our Challenging Common Energy Misconceptions series next month.

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