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“Supercharging” an electric lawnmower

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What you see here is a bank of 12 AGM batteries connected to 1,500 watts of solar panels. They’re configured as a 48v pack with 3 parallel sets of 4 batteries in series. Total capacity is 9kWh.

The zero turn mower has 7 Nissan Leaf cells connected in series making a 48v nominal pack. Capacity is 3kWh

The lead acid batteries store up the solar power. They can hold around 2 days of good sun. When the zero turn is depleted it can be dump charged extremely quickly.  If the AGMs are full and the leaf cells empty peak currents are quite high, over 120 amps. That is about 2C into the lithiums, or a full charge in about half an hour. This is much faster than just charging the zero turn directly from the solar panels, which would take 4 hours. And it allows the use of solar power even when dark or cloudy.

The economics of electric mower operation

Let’s break down the cost of operation for an electric mower vs. the gas counterpart.

From some quick googling it seems the cub cadet zero turn uses 1.8 gallons of fuel per hour.  Let’s round this down to 1.5GPH. Fuel cost in this area is $3.50/gallon, so

1.5GPH x $3.50 = $5.25/hour

Our electrified zero turn mows for approximately 1 hour on a 4KWH battery pack. The electricity price in this area is $.13/KWH, so

4KWH x $.13 = $.52/hour

But the electric zero turn costs more upfront than the gas version. The total part cost breakdown is as follows

3x Enerdel ME330-049 Energy @$480/ea = $1460

ME-1004 Double brush 48v motor = $525

Soliton Jr. Motor controller = $1750

PMP-450 pump, radiator, tubing = $250

——-Grand total——-  $3985 dollars

So the operational cost difference is $5.25 – $.52 = $4.73/hour

And the payback time for the conversion based purely on fuel cost savings is…..

$3985 / $4.73 = 842.49 hours of operation