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How To Choose The Most Cost Effective Appliances For A Net-Zero Energy Home.

There’s this new thing for energy star appliances called the “energy star most efficient 2014”. This list is the all-star list of appliances. I wondered if any of these appliances would save enough energy to have an effect on the size of a renewable energy system for a net-zero energy home. In other words, would it be worth making the investment in the super efficient appliances or not?  I was surprised to find that though the improvements in efficiency aren’t dramatic, they do make enough of a difference to make them the right choice for your pocketbook.

Net-Zero Energy Homes

A net-zero energy home is one that makes as much energy as it uses over the course of a year.  In order to make this magic happen every net-zero home needs to have a source of renewable energy, like wind or sun power. Renewable energy systems provide a clean way to power your home. This is good. The downside is that they can be expensive. If you are like me and don’t want to spend an arm and a leg on a system, then reducing the amount of energy used is the key to spending less.  This is where the most efficient appliances can make a difference.

Washing Machines and Refrigerators

I looked at washing machines and refrigerators to get a feel for the impact that efficiency would have. The efficiency gains and cost differences between an energy star appliance and a “most efficient” appliance weren’t huge, but adding the cost of the PV made the “most efficient” appliance the best deal.   The charts below to show what I’m talking about.

Energy Star Most

Efficient 2014

Energy Star

Non-Energy Star






Model Number

WF6300 4.5 CF



Cost (MSRP)




Annual kWh

90 kWh

165 kWh

488 kWh

PV System Size 

.08 DC kW

.15 DC kW

.45 DC kW

Cost of PV System




Total Cost






Energy Star Most

Efficient 2014

Energy Star

Non-Energy Star






Model Number




Cost (MSRP)




Annual kWh

400 kWh

587 kWh

650 kWh

PV System Size

.37 DC kW

.54 DC kW

.59 DC kW

Cost Of PV System




Total Cost




The most striking difference was for the non-energy star $650 washing machine.  I was surprised that a washing machine at just over half the cost of the most efficient one would almost be double the price when PV was added.​

​Finding a less efficient refrigerator was difficult, this is good news because historically refrigerators have been one of the bigger energy users in  homes.

Even Better Appliances

In my search for information on appliances I found appliances that were even more efficient than the “most efficient” and that were less expensive than the models I reviewed. Generally they were less feature packed than the ones I looked at above.  I found it pays to do a little homework, because it can save big in the long run.

Sizing a PV System:

Part of the job of the PV installer is to run the numbers to size your system,  but If you are curious to run a few numbers to do your own comparisons the calculation is below.

How to Size a Photovoltaic Solar System

  • Annual kWh/365 days per year/solar hours per day/.75 derate factor = system size in kW

I used 4 solar hours per day in my calculations to be conservative. To give some perspective, this is what New York City gets per day.  Your actual solar hours per day will vary.  The way to find your average solar hours is by searching for solar insolation maps.

I assumed that the average cost of the PV system was $5/Watt or $5,000/kW.  This number is a moving target, so best to check with your local installer on costs.

Does It Really Matter?


According to the U.S. Energy Information Administration appliances, lighting and electronics account for about 34.6% of the overall energy use in home. That’s a clue that making reductions in this area is going to have a big impact.  Water heating accounts for 17.7%, another area to look for savings.

The other area to find BIG savings is in reducing the heating, ventilating and air conditioning (HVAC) loads by building a high performance home, because HVAC loads are 47.7% of home energy use.  ​

Yes, It Matters.

No matter what, using the most efficient appliances you can find is the best deal when adding solar. The cost of solar is getting more and more affordable, but it’s always going to be a big ticket item like a car.  Working to reduce the amount of energy used in a home is the best way to save on the upfront cost of a renewable energy system like solar PV.   All of those savings add up, and saving thousands of dollars, while still getting great performance is nothing to sneeze at.