We recently completed our net-zero farmhouse project. The house has a contemporary design and feel, but the exterior pays tribute to the classic farmhouse designs found throughout the Shenandoah Valley.

Some highlights of the project:

- 0.46 ACH50 final blower door test
- Exterior mineral wool insulation (Roxul Rockboard 80)
- Fiber cement siding (HardiePlank) and double-locked standing seam roof
- 5.6 kW PV system, with islandable capability
- Hearthstone Craftsbury woodstove with outside air intake
- Fujitsu slim duct high efficiency heat pumps
- Renewaire EV90P Energy Recovery Ventilator

This project combined energy efficiency with resilient design. Genesis Home and Energy installed an islandable PV system (discussed in a previous blog). Key electrical circuits will be maintained during a power outage: lighting, wall outlets, well pump, refrigerator and freezer, microwave, etc.

Although we were somewhat hesitant to install a woodstove in a tight house, the client wanted the ability to heat with locally harvested wood (ambiance, resiliency, radiant heat for comfort). No woodstove is airtight, so there were some risks:

- Backdrafting
- Depressurization of the house
- Lower indoor air quality

We mitigated these risks by making the house all-electric, and eliminating exhaust appliances. The range hood is recirculating. The dryer is a condensing, ventless model. We were also careful about specifying a woodstove with an outside air kit--and positioning the inlet and chimney to provide excellent draft.

John Semmelhack of Think Little fame completed several tests to determine if the woodstove would negatively affect the house. He found that the woodstove had a negligible effect on the house pressure (within the noise of precision). This measurement held when the woodstove was cold AND when it was operating.  He determined that the stove pulled between 10 - 15 CFM (cubic feet / minute) when operating. With the outside air intake the majority of that air is supplied from the exterior.

Armory Lovins, a physicist and the founder of the Rocky Mountain Institute, was the first to really define the cheapest watt. He coined the word negawatt---which is kind of the opposite of a megawatt. Actually, it is the exact same amount of energy as a megawatt, it is just that a negawatt is theoretical. It represents energy that has NOT been consumed, or energy that has been saved.

The negawatt is what energy efficiency and conservation is all about.
 
The idea becomes very important when we start to talk about energy production. To illustrate the idea, I’ll use photovoltaic power as an example. Let’s say that you are interested in PV panels, and you are thinking about installing a PV array at your home or business. The first step is to evaluate the cost of saving energy VERSUS the cost of producing that same amount of energy.
 
Let’s use your entertainment center as an example. You have a TV (Energy
Star® rated), a DVD player, audio amplifier, and maybe even an old VHS player.
Each and every one of these devices is drawing power, even when they are turned OFF (they are designed like that for a variety of reasons). In geek speak, this is known as a phantom load.
 
Using a watt meter, we find that together, these devices are drawing (18) continuous watts. It is energy that is being consumed, but not really put to any good use. How much energy does the entertainment center consume per day? 
                 
     18 watts x 24 hours / day = 432 watt hours / day

This system uses 432 watt hours / day. Over the course of a full year, it will consume almost 158 kilowatt hours. At the going rate of electricity, that will only cost about $16 per year. No big deal, right?

To produce an equivalent amount of power with a PV system, we would need to figure out the solar insolation value for the area. The solar insolation value is how much sunlight hits an unshaded part of the earth on the average day---at maximum power. We call this “peak sun hours.” We can find the value here, on the NREL (National Renewable Energy Laboratory) website. For our area, it is approximately 5 peak sun hours / day. Here’s the math for figuring this out: 
                 
     432 watt hours per day / 5 hours per day of sunshine = 86.4 watts
 
Of course, no system is 100% efficient. Most PV systems are “derated” by 15% -20%. Let’s avoid getting too detailed here. We’ll just call it a 100 watts.
 
PV systems are currently being installed for $3 - $5 / watt. That means we’ll need to spend $300 - $500 in order to generate the same amount of electricity that is being consumed by the entertainment center.

That energy is not so cheap anymore . . .
 
What is the cost of saving that same amount of energy? Well, if the entertainment center is plugged into a switched outlet, it wouldn’t cost anything; you would simply have to turn OFF the system at the wall switch, just like you turn OFF a light.

If it’s not on a switched outlet, you could install a power strip and turn it OFF there. Power strips are pretty cheap, usually < $10 each. Most people would find that too cumbersome; they would probably want to install a “smart” power strip like this one. It automatically turns OFF these devices when you power down the TV, eliminating most of that phantom load. These sell for ~ $30.
 
So . . . you can see that the negawatt is the cheapest solution. In this example, it ranges in cost from $0 - $30, compared to $16 for the annual cost of electricity, or the $300 - $500 cost of producing the same amount of energy using a renewable energy (PV) system.

How many negawatts have you produced lately?!