Our New Electric Mower

on June 28th, 2008 by

We finally did it! We bought an electric mower.

Keep in mind, we did need a new mower. We are very aware of the fact that buying something “green” when you do not need to replace a product you already own does not pay off fiscally. In this case, our old gasoline mower is on its last wheel. My father-in-law has already repaired the thing several times (it’s something he really likes to do). In fact, he will be taking the old mower for parts on his next visit.

Did It Cost More than a Gasoline Mower?

Yes.

I compared the feature set of the new electric mower to the features of gasoline mowers until I found a functionally equivalent product that I would have bought were it not for the electric mower calling to me. The equivalent gasoline mower was about $400. I know that you can buy a mower for $150, but “you get what you pay for” resounds in my head. The old gasoline mower was originally purchased for $350 in 2001, so I feel confident that the $400 is an accurate price for a solid comparison. The new electric mower cost $474 (shipping was free).

Naturally, I felt compelled to calculate the return on investment (ROI) for the new mower. I sat down the other night with a spreadsheet open and began my research and calculations. The research involved finding out the tank size of the gasoline mower. I used our current mower for that and the amount of gasoline used to cut our yard. The funny thing is, you simply cannot easily find the tank size for a walk behind mower anywhere! We scoured the Internet for any reference and for any mower to no avail. I had to resort to my math background to estimate the tank size based on measurements and the shape of the tank.

Another very interesting bit of research involved finding out how much electricity is used to charge a battery. I know how to calculate kilowatt-hours from the rated wattage and amp-hours of a battery, etc., etc. However, I never thought about charging a battery…until now. I’ve been interested in getting a meter that sits between an item and a wall outlet, but we did not buy one just yet. Instead, I found an obscure post from an energy expert about how to estimate the amount used to charge a battery to capacity. He claims that you can multiply the rated watt-hours of the battery by a factor of 1.6 to arrive at the total watt-hours necessary to charge fully.

Note: When we actually purchase a meter, I’ll update my calculations and this post.

The Necessary Calculations

So, our battery’s watts * amp-hours = 360 Wh * 1.6 = 576 Wh to charge the battery to capacity. The tank volume of our gasoline mower * 0.5 (I use about 50% of the 0.80 gal tank to cut our yard) = 0.40 gal used per cut of our yard. Now, for the fun.

I have calculated the cost of gasoline and electricity on June 27, 2008. Gasoline was $3.9590/gal at the station we frequent, and electricity was about $0.1580/kWh. I also looked at my history of cutting grass here. I cut the grass once a week for about 25 weeks each year.

I am looking for the time it will take to catch up, fiscally, with the alternative purchase we could have made; a gasoline mower. The price difference of the two mowers was a flat $74. All I needed to do was to divide that difference by the difference in cost per cut of our yard.

Break-even Analysis

Here are the numbers for the break-even analysis.

Gasoline Mower Electric Mower
Cost per Cut (Jun 27, 2008) $1.5638 $0.0910
Weeks to Break Even n/a 50.24
Seasons/Years to Break Even n/a 2.01

Well, it looks like it will take about 2 years to break-even. That, of course, carries quite a few assumptions. The main unreasonable assumption is that the price of gasoline and electricity will remain the same as they are now for the next 2 years. Reasonable assumptions are as follows.

  • We would have purchased a new gasoline mower for around $400 had we not been interested in an electric mower.
  • The cost of maintenance on a gasoline mower is roughly equivalent to the cost of maintenance on an electric mower (e.g. replace the carburetor on the gas mower vs. replace the battery on the electric mower).

Conclusion

I am quite happy with our purchase of an electric mower instead of a gasoline mower. It is drastically lighter and easier to push. It is about 75% quieter than our old gasoline mower (I can actually listen to my iPod without having to deafen myself with the volume). I don’t inhale all those fumes that irritate my sinuses and increase my allergy symptoms.

Finally, I feel better that I am not contributing to the pollution statistics. Did you know that 5% of the nation’s pollution comes from traditional gasoline-powered mowers? In fact, they produce as much pollution in a single hour as a modern car driven 95 miles!

In future posts, I will expand upon these fiscal calculations in an attempt to achieve more accuracy.

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