G Duke wrote:My questions:
For people who realistically only have access to "dirty" power grid electricity, does using an electric saw really have greater net benefits over gas?
And what do you do if the electrical "engine" fails? Are these saws rebuildable in any sense?
How much energy is tied up in the production of those batteries, and how long are they expected to last?
I read that the batteries for my Husqvarna 536 Li XP
should last for at least 800 charge cycles. I put a sticker on each of the 3Ah batteries last year and started ticking off each time they were charged, but I quickly lost track. I am not a day-to-day user, but I would guess each one has been discharged and charged somewhere between 50-100 times now, and like most lithium batteries, there is no noticeable loss of capacity-- they aren't like the NiCd batteries that were used a decade or two ago in cordless drills and such.
I did some calculations when I bought my saw. Unfortunately, I did not write them down, but what I found was that given the then current prices of gas and electricity in Slovakia, the amount of electricity needed to charge, the amount of gas an equivalently sized gas chainsaw would use for the same actual use, etc. that if the batteries do indeed last 800 charge cycles, including the price of the battery and electricity to charge it, the cost would be half what gasoline would cost (and I did not factor in the additional cost of 2-cycle oil). The economics may work out differently in the US, where both gasoline and electricity are much cheaper.
From a pollution perspective, I believe the battery saws win. A 2 cycle gas chainsaw engine is not a very clean, pollution free power source, nor does it make very efficient use of the energy contained in the gasoline. A gas turbine or steam turbine generator at even a coal burning power plant is far more efficient at converting the heat energy from the burning coal to electricity. (The figure I could find is that an automobile engine has a thermal efficiency of 25% whereas a combined cycle generating plant has, in the real world, 54% thermal efficiency.) And remember that to refine crude oil into gasoline requires energy as well.
The motor on a battery saw is only running when you are pulling the trigger, unlike a gas saw which is idling between cuts. Most importantly to me-- I'm not breathing in uncatalyzed gasoline exhaust.
The manual for my saw suggests that the sprocket for the chain is user replaceable. Otherwise, it says to take the saw to service for any other problems. So, replacement parts don't seem to be available for mine for DIY service. It uses a brushless DC motor. Given the prices that I see on international trading sites for 36V BLDC motors, I would guess that if they saw has to be serviced, the motor is simply replaced with a new one. A BLDC motor should have one moving part-- a rotor supported by two bearings. The possible locations of failure would be either in the bearings or in the magnet wire windings. Since the windings are controlled by an intelligent controller circuit, my guess is that eventually the bearings will fail. Looking online though, I see that there are companies selling bearings for BLDC motors, so its quite possible that the bearings could be DIY-replaced. I would have to open my saw up to see the exact motor though, and as it has a two year warranty here, I am reluctant to poke around until next year when the warranty is over. The saw body is held together by regular allen-key type screws, so it looks like it is designed to be taken apart and serviced.
Husqvarna now sells two back-pack battery packs-- one with 14Ah capacity and the other with 26Ah capacity. Certainly the latter should last all day and probably the former as well, though the price I see online is $1100 and $2000 respectively (price for Great Britian, probably a bit less in the US as taxes are less). The back-packs weigh 7 and 8kg (15, 18lbs). The advantage of the backpack is that at the end of the day it is just one battery to be charged (taking 2 and 4 hours respectively to charge), instead of having to swap a bunch of individual battery packs that each take about 30 minutes to charge. The disadvantage is added weight an having a power cord connected to the saw.
As far as energy used to produce the batteries:
http://www.transportation.anl.gov/pdfs/B/855.PDF (this is for huge batteries for electric cars, but should give some idea.)
The main concern though is-- what are you cutting? My chainsaw has just a 14" bar (according to specs 13" "effective cut"). As long as the chain is sharp, it cuts faster than a comparable size gas saw. But a 14" bar is a 14" bar, and if the trees you are going to be cutting are ever over 26" diameter, then its not going to be possible to use such a saw! And even then, although its possible to cut in the 13"-26" range, I don't think that's very effective.
Bottom line:
for me the saw works great-- its always ready, I don't have to fool with mixing gas and oil for it, and don't have to worry if its sitting for a month without use that the gas-oil mix will go bad. My off-road transport is a walk-behind
tractor with a small trailer. If I want, I can fill that trailer with wood using two batteries for the saw. And more often I am just clearing a bit of brush to put portable electric fencing, and its very handy for that. I count as well that over several years of use the batteries will save money compared to gas, as well as reduced need to service the saw compared to a gas motor saw.
