Thread: Solar Cells and Woodworking

I think it would be possable to charge battery tools but bandsaw and table saw would be a tough and expensive project. You would likley need DC motors on them and a large amount of battery storage. As an example the average caraven battery can be charged with solar panels but that battery will only run the fridge for a few hours on a charge. Perhaps some of the more electrically tallented members can chip in as I would be interested to see what is possable.
Regards
John

You cannot power the tools directly from the solar cells. You would have to use the PV cells to charge up a set of batteries (eg truck), and then power your tools via an inverter hooked to the batteries.

Thanks to both of you for your replies.

I've got to admit; sometimes I wonder if the benefits of solar power are way overstated.

It is winter. -20C. The snow out back is wind-packed. The lights flicker, flicker and go out.
It seems useful to be able to contuinue to heat my house, yes?
I grab a flashlight, go down stairs and push 1 button on the pure sine wave inverter to see 1.2kW x 120VAC available.
Unplug the compressed wood pellet stove from the dead mains and plug that into the inverter.
All 3 motors come back to life and I go back to bed.
In the morning, I have a dedicated line up to the kitchen.
I will turn on a light and plug in the coffee pot.

The value of a back up solar power system is vastly underrated. Maybe you have reliable electricity. I don't.
The real trick is the need for storage batteries. That's the charge volume that the inverter works from.
The PV panels (12VDC X 75W x $750 each) can't help diddly squat at night. The only thing better than 4 deep-cycle batteries would be 8 ($250 each).

Yes, you can run your power tools. No big deal but a big deal expense getting set up.
You must have a pure sinewave inverter with enough capacity (surge/inrush current)
for twice the operating load of the tool motor.

Originally Posted by Gassito

Thanks to both of you for your replies.

I've got to admit; sometimes I wonder if the benefits of solar power are way overstated.

Dont worry, the benefits of solar power are massively understated. The only problem we have now is storage.

You can bet a peaceful winter sleep or coffee in the morning.
I had no desire to do any "greenie" off the grid crap. I want my routine.
$2k before I needed it. The very first time I turned it on, as I have described,
paid for in ultimate convenience.
Power failures here? One day, the girls in the grocery store counted 60 then quit.
Fortunately, the store owner had dropped $4k on a back up system.
Even the local bank and gas station have gensets.

No, it isn't worth the capital investment to fool with your power tools like this,
even if the off-the-grid thing is exciting. Try armstrong power. Used to be all the rage 300 yrs ago.

My pellet stove is about 1/2 the cost of oil heat. So 3 winters paid for the capital cost of the stove.
That's usually 10,000lbs pellets per winter.
The next 2 winters paid for the capital cost of all my solar rigging.

Originally Posted by Robson Valley

No, it isn't worth the capital investment to fool with your power tools like this,

Depends. I wouldnt want to hook any tools up to solar power directly (or through an inverter) but I wouldnt have a problem using solar to charge a load of car batteries and then use that to charge some cordless stuff.

HI Robson Valley -- where is Robson Valley (the place, that is)?

He's probably sleeping soundly now DonIncognito snug in bed with his pellet heating.
He's next to Mt Robson in the beautiful Canadian Rockies.
Cheers, Ian

Re the original question, there are two ways to approach the question, and you have not really given a lead as to which way you are considering.

Option 1 Off grid, as discussed in many replies to date. Panels are used to charge a large battery bank that drives an inverter that powers your tools. Fairly expensive due to the cost of the battery bank involved. If you use Lead Acid technology batteries, you need to size your your bank to store about 10 times your typical usage, and your panels to supply about 1.5 times you daily usage.

Lead Acid banks have a very short life if repeatedly disharged by more than 15-20% of their storage capacity, and the deeper the discharge the shorter the lifespan. Banks that last thousands of cycles at 10% discharge max typically last a few hundred cycles at 50% discharge or 50 cycles at 80% discharge. So if you decided you needed 5KWh per day to power machinery via the batteries, you would be looking to a bank of 50KWh capacity if you want the bank to last for years. These banks would probably be based on 48V nominal, using 24 off 2V x 1000AH cells in series. More recent and expensive Lithium cell technology is more tolerant of deep discharge, and will tolerate regular 50% discharge without significantly compromising battery life. A lithium bank of 20KWh capacity would generally be able to match a 50KWh lead acid bank in usable supply capacity and life and would be similar in price to the lead acid.

Batteries do not store power with 100% efficiency, it is typically closer to 85%, so you need to supply more charge than you withdraw to recharge them, around 20% more is typical at the battery level, but there are inefficiencies in other parts of the system as well. Again, if you wanted to supply 5KWh per day, your panels would need to generate around 7.5KWh per day to supply the load and make up for system inefficiency. For Melbourne, a clear day in winter has a maximum 4hrs usable collector time in the day, so you would need to opt for arond 2KW of panels minimum. You would still get periods when there would be insufficient sun penetration for days on end and either have to provide a generator or severely limit consumption for these periods.

Inverter system would need to be sized to accomodate the start surge of you motors which is typically regarded as 6 times the rated power of the motor. Decent off grid inverters will normally have a surge capacity about 2-2.5 times their continuous rated capacity, so the inverter system would need to be rated at about 2.5 - 3 times the continuous (rated) motor power to ensure correct starting.

Option 2 Grid connect systems. A bank of panels on the roof generate a high DC voltage which is passed to an inverter producing a mains voltage locked to the available mains supply, and slightly higher in voltage. When the panels produce power from the sun, the inverter supplies about 95% of the panel output power as mains power to your meterbox. If you have sufficient load applied, the power you generate will be consumed first, and any shortfall will be drawn in from the grid. This is a good way to cope with startup surge currents etc as the grid covers them, rather than your panels and inverter. If the system produces more power than you are consuming, the excess is fed back to the grid and you are credited something for it. However, you have a electricity with fixed service fees, your consumption fees are generally higher per KWh than a non solar installation account, and the amount that you get for supplying you excess power to the electricity co. could be as little as 20% of what they are charging you for electricity. Again to cope with a daily consumpsion of 5KWh, you are looking at around a 1.5KW to 2KW nominal system in Melbourne.

Oh, Robson Valley is in Canada, see the top right corner of his posts for his location.

Malb, brilliant posting.

As an idea of the cost of going off grid and wishing to maintain an approximation of normal grid usage, albeit at the lower end of consumption, you will be looking at a fair swag of money.

A personal friend is now starting to build just that, he lives in rural Victoria on the northern side of the Great Dividing Range, so normally quite a lot of sun hours available.

His guestimation using lithium batteries, essentially mobile telephone battery type technology, is that the system as a whole, will be around $19,000. His original estimates were in the $14,000 to $15,000 range, but his budget blew out with the inclusion of micro inverters attached to each panel and an enlargement overall of the solar system.

His solar system is (at this stage) going to be 24 x 250W panels, with 4 facing east 8 facing west and 12 facing north. As each panel has a micro inverter attached, if any single panel goes into shade or starts to falter, whatever each and every other panel is catching will be fed into his system. There is no averaging of panel power whatsoever.

As panel technology either advances, or becomes cheaper (not too likely it would seem at this stage) he has the ability to add another 24 panels before he runs out of real estate to place the panels.

As an aside, and with regard to power costs and the power one feeds into the grid and receives money for, there are some interesting things we were unaware of until we actually hooked up a solar system and started feeding into the system.

We somehow are all told that in Victoria the rate you sell power to the power companies for is set in stone at $0.08 per kWh which is true, but there is a but. There is what is known as a "Fair Use Policy". Whatever you pay for your power, you receive the same for power you send into the grid. An example is the cost of power is $0.28402 kWh, which is what we pay, we receive $0.28402 for every kWh or part thereof we send into the grid. That is a GST inclusive price.

We had no idea of this, until we received our first quarterly bill last year. Then the missus after a fair bit of searching found out what power charge/sell system we were operating under. We have had our system up and running for 7 months today, projections at this stage, as of now, are that we will have paid for our system in 5.93 years, unless electricity prices go up; then the pay off time should be shorter.

We have micro inverters on each and every solar panel, as well!

Mick.

Originally Posted by malb

Option 2 Grid connect systems. A bank of panels on the roof generate a high DC voltage which is passed to an inverter producing a mains voltage locked to the available mains supply, and slightly higher in voltage. When the panels produce power from the sun, the inverter supplies about 95% of the panel output power as mains power to your meterbox. If you have sufficient load applied, the power you generate will be consumed first, and any shortfall will be drawn in from the grid. . . . . .

It's a minor point but this is not really correct in a physical sense - any load connected to such a system cannot discriminate between the potential (Volts) generated by a local PV system and the existing potential in the wires. Even the electrons in the wires in an AC circuit only travel back and forth a very short distance in the wires and are not used up or drained away preferentially to a local load.

A simple analogy of how these systems work is to think of electricity in terms of water pressure. Grid connected PV systems are not connected direct to appliances but simply add pressure to the grid. As local appliances draw on grid pressure to operate they cannot discriminate between the the specific water pressure generated by their local PV system or the grids existing water pressure. As local PVs increase the V levels in the grid the big generators back at the generating station sense the V is going too high and back off their input to the grid to balance the load.

One way I explained this to an elderly friend who was very anxious that she would get back all the power her system generate was to explain it in terms of money, so if she deposited $100 in notes into the bank one day and then went back and withdraw $100 it was unlikely that she would get the same notes back again. Then she wanted to know if she waited while before using the power would she get any interest!

Wow. Terrific, informative answers.

After looking at the tsunami of $$$ required to go off-grid, it looks like I won't be heading in that direction even if I had the money.

Sheeesh, when's the big breakthrough in cheap batteries gonna arrive!

Thanks again everybody.

Hey! I'm awake! Just -15C this AM, clear and sunny so that helps. No wind, that helps.

The village now has a cutoff if there's any damage to the grid more than 10km out of town.
We have 2 biodiesel gen sets, each the size of a 4,000HP mountain locomotive.
Most trains have 2x4k in the front and 2x4k in the middle (east is seriously uphill.)

By car on a good day (no avalanches), Mt Robson is about an hour east of me, just shy of
13,000'. Another hour east of that is Jasper National Park.
Nothing around my home more than 9,000', most about 7,000' or so.
But, the peaks are close enough that if you're standing in my living room/lounge,
you have to sit down to see the tops.

The Robson Valley is the name for the region of the upper drainage of the Fraser River.
Headwaters are up around Mt Robson itself.
This is where I live and play in the mountains.
The #1 snowmobile destination in all of North America.
I'd rather wake up in this village than in any city on earth.

If you snooped around with Google Earth, you'd get a fair look.
I can even see my garden shed!

Come to think of it, if you scroll down to about p5 in Woodworking Pics, you can find a thread called "Chasing the Wood."
My last big Trebuchet is in another nearby thread.