Calculating Energy Consumption
and Understanding Energy Efficiency

Read on and learn how we rank products, calculate energy consumption and understand energy efficiency. There's no super-easy way to explain it all, but we'll do our best to make things as straightforward and clear as possible.

Our focus is on pretty much anything with a power plug - Products that consume meaningful amounts of electricity. Our first task: Find you the best purchase price. To do that, we check the inventory of virtually every major online retailer in the USA. The shopping data we use is updated constantly, so you get the very latest deals, always.

Our next task: Figure out how much electricity it will cost you to run your product over a certain period of time (you nominate how long). Some sites show you an "average" electricity cost for a product. Not us. We don’t do averages. Why? Well, take LCD TVs for example. The difference in electricity cost for one TV compared to another can be huge. That difference depends not just on the product itself, but also on who your power company is. Electricity costs vary, they're lower or higher (up to five times) depending on where you live. A TV that’s Energy Star rated could cost you as little as $23 in electricity over 5 years, but a TV that isn’t could cost you up to $800, over the exact same period. It all adds up. And so we avoid using averages whenever possible.

It's great to see the electricity cost of a specific product but how can you tell if that number is good or bad. To help with that we are calculating the energy efficiency of a product by looking at it's electricity in combination with the product attribute that influences the consumption the most. An example of this would be the screen size for TVs or the volume in cubic inches for freezers. Then we identify what the average energy efficiency is for each product category. With that done we can then tell you for each product if it has a higher or lower than average energy efficiency - so you can compare products easily.

Our final task: Calculate how much CO₂ the product will produce over a given period of time. So you can see the cost to the planet.

That’s the basics covered. For the nitty gritty, keep reading.

Calculating Energy Consumption

Say you’re buying an LCD TV set. To figure out the TV's energy consumption for a year, we take the number of Watts the TV uses multiply this with the hours per day your TV is on and then multiply that with 365 days for the year. Well, it's a bit more complicated because we also add the consumption the TV is on in standby mode - as this uses power too. The total of the two then gives us the annual electricity consumption.

Once we have a result, we multiply the energy consumption with the residential rate your power provider charges for electricity (selected by you/based on your zip code). You select the number of years that you think you will own the product, and based on all this data we can show you the specific electricity usage costs for this product. We go through all of that, because we really don't like averages :)

Here’s the math:

E_{energy consumption} × P_{power company charges for electricity} × Y_{number of years you think you will use the product} = C _{specific electricity usage costs for the TV}

How we work out what it costs the planet

It’s great to know how much the electricity that runs your new TV will cost you but to make a green decision, you may want to consider the cost of CO₂ emissions to our planet.

We work out these CO₂ emissions with help from our partner CARMA.org. We take the usage costs of the TV (based on it’s annual power consumption as well as the power company you use) and make a prediction of how much CO₂ (Carbon Dioxide) your power company has to produce for the amount of electricity the product will require.

CO₂ is measured in pounds. And although it sounds impressive that a TV can produce 1.5 tons of CO₂ over 5 years - it really doesn't mean all that much to most of us. So, to make this number more meaningful, we do two things:

A. We tell you how many cylinders of gas you would have to use with your barbecue or alternatively how many gallons of fuel you have to run through your car to produce the same amount of CO₂.

B. We identify a cost for this amount of CO₂. Not a cost you pay personally, but a cost to us all. In our search for an "official" cost for CO₂ emissions, we found a market for carbon credits. Specifically we use Certified Emission Reductions (CERs) which are issued by the Clean Development Mechanism (CDM) Executive Board and verified under the rules of the Kyoto Protocol. CER carbon credits are used by countries and companies to comply with their emission limits. They are traded on an emissions market which is much like a stock market, and therefore they have a daily price (carbon credits are traded in units of one ton). We get the latest Carbon Credit price from ICE Futures Europe - the leading global marketplace for trading carbon dioxide emissions. And that’s how we can tell you just how much your CO₂ emissions cost us, and the earth.

There. We’re pretty much done. Thanks for sticking with us. We hope you found the information we’ve provided clear and simple to follow. And that it helps you to make better decisions and save money and energy.

See a list of our Partners, Service and Data Providers here...