Mowing the Lawn with Solar Renewable Energy

The mowing season of 2007 has seen my lawn being clipped by this setup.

• Cordless Mower, Black and Decker, CMM1000
• 45 Watt Solar Module Array, Harbor Freight
• Charge Controller, Morningstar, Pro-Star-15M

This has been a very workable setup. I Seem to average mowing the lawn every 10 days. I am estimateing I mowed the lawn about 20 times for the 2007 season. At a stretch I might be able to say I saved a whole 6-7 gallons of gasoline, 18-21 bucks?!. Not much, but it sure feels good. :)

I am accumulating data for the 2008 season with more detail.

I got the mower for free. Someone was throwing it out 'cause it was busted. I fixed it! The battery was low at around 10 volts. Not bad, but I put it on a battery desulfator I made and let it charge up with the solar array through the charge controller. Letting the battery set out in the sun like that soaking up the photons from the solar array for a week and it has been a great little battery since. The mower seems to have a low voltage disconnect (LVD) that keeps the battery from being fully discharged. The mower automatically shuts-off at 11.9-12.0 volts. 12.0 volts is about a 25% State of Charge for VRLA batteries. It takes me about 60-70 minutes to mow the entire lawn with pauses to empty about 4-5 bags of clippings. When the outside temp gets to 95+ degrees the battery discharges quicker while mowing and I hit the LVD shut-off with about 10-15 minutes to go in completing the entire lawn. If I mow in the morning at under 90 degrees I can consistently complete the 60-70 minute mow time. Fully discharging batteries and not immediately recharging them to a full State of Charge really kills batteries. It takes from three to four days to recharge the battery from the 45 watt solar array. I am estimating that this is the third year of life for this battery. The battery is actually two 12volt, 20ah batteries wired in series for operation as 24volts in the mower. The battery is pulled out of the mower and rewired in parallel as 12volts for the solar array and charge controller's voltage rating. If batteries are taken care of, they can last a long time. I owned a motorcycle and kept the battery watered and well charged, not just via the motorcycle's alternator. While all around me other motorcyclists were only getting a couple years out of their batteries. Mine lasted five.

See the Mowing with Solar Youtube Video of the recharge process where I explain expected and actual recharge times and amp-hour current math.

The Texas Commission on Environmental Quality states "The engines in gas-powered lawn equipment pollute more than car engines. One hour of lawn mowing with a gas-powered lawn mower produces as much pollution as driving your car for four hours."