Off Grid Shop Power?

[jeffpNC]

Anybody here have a wood shop powered by an off-grid solar panel based power system?

In particular I'm thinking along the lines of a system built around Outback, Magnum, or similar pure-sine units for the power invertors.

I'm just wondering how well the listed specs translate to a practical system when one is talking about 120V and 240V heavy machinery such as table saws and dust collectors, etc.

I have the needed skills to design such a system based on the specs...but I've also lived long enough to be acquainted with the reality that things don't always follow the numbers in the real world.  Hoping somebody here has some real-world experience with this atypical use of off-grid power systems.

[wtnhighlander]

No direct experience, but a lot of research. Unless you live in the desert, have acres of land to devote to panels and batteries, and enjoy running your saw at about a 2% duty cycle, I'd forget about solar.

Here in Western TN, we have an industrial pilot project, sponsored by the city. There is a warehouse of around 10k square feet, and the lighting is all supplied from solar. Takes over 5 acres of panels.

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[wareaglewoodworker]

Diesel generators are a better bet unless you're just determined to be "green".  Though if you had a water source running through your property you could build a millpond and one of those belt drive mills.   

[drzaius]

This topic comes up from time to time on various forums. I have no experience myself, but the consensus seems to be that unless you are primarily a hand tool user, it isn't practical to have an off grid, green shop

[jeffpNC]

Thanks for all the replies.  Since the technology and price of these systems is in such rapid flux, direct experience, and even recent direct experience is really key to relevance here.

So far, it seems, my question isn't finding such folks here (so far).

One thing I should clarify here...not talking about a production shop.  Not talking about running 6HP DC all day and big 240V saws and jointers and planers all day.  Just a hobby type shop.

The property in question has acres of nice woods...and also acres of a power transmission corridor that prohibits use for almost every conceivable use...but there seems to be a notable exception for placement of solar panels.  Still need to verify that.

Also should mention that the crux of my question is not "can I make enough power", but rather, does "spinning machinery" seem to be a particularly gnarly type of load for inverters which requires that part of the system to be horrendously over-built?

And, given the mention of the power transmission corridor above, I should also mention that power is not unavailable here...they just don't give it away for free.

[Tom Cancelleri]

Define your hobby shop. My hobby shop has 2 x 5hp tools, and several 3 HP tools. Some hobby shops are running small tools, some run large tools. I think that will make a difference.

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[jeffpNC]

Biggest current draw would likely be 2HP DC together with just one other large tool at a time, like TS, future purchase of a 2 or 3 HP large jointer, or a medium sized planer.  Definitely not a "pro shop" used for hobby use.

(but not a hand-tools-only shop either)

[wtnhighlander]

To answer at least one question directly, yes, electric motors do provide a 'gnarly' load that will require overbuilding the inverter system. This is much more evident in applications where the load is switched on and off more frequently, such as the tablesaw in a typical hobby woodworking shop. If utility power is available at all, it is pretty hard to justify the startup costs to go solar. Solar is quite variable, according to where you live, and not very efficient anywhere. If there is a stream on this property, a hydro-electric system would provide a more stable source, be less costly to maintain, and no more expensive to start up. You might even avoid the need for batteries & inverters completely.

[jeffpNC]

There is a stream, but seems too small.  Wild guess...maybe 50 to 100 gallons per minute.

[Tom Cancelleri]

You could always go solar and offset utility cost, or sell back to the power company

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[mat60]

It just doesnt seem like a good idea to me..The cost alone is a joke..

[drzaius]

To power a saw & DC together takes a lot of power. The solar doesn't HAVE to be able to supply that amount of power if you have sufficient storage & inverter capacity. But storage is super expensive too. I can't see this working unless you just want to do it for the sake of doing it & you have very, very deep pockets.

[wtnhighlander]

There is a stream, but seems too small.  Wild guess...maybe 50 to 100 gallons per minute.

Time to dig a mill pond! ?

[jeffpNC]

On June 17, 2016 at 11:14 PM, wtnhighlander said:

Time to dig a mill pond! ?

I did a little research on the water thing...seems that there is very little energy available in a simple flowing stream...you need what that industry calls "head", which is water moving from up high to down low.

On the property in question, a very small stream just trickles across it from one side to the other with barely any elevation change.

Looks like wind and solar (and Duke Energy) are my only available sources.

[andrew-in-austin]

The VFD (and inverter) industry is so mature that I don't think you will have a problem finding the right inverter.  Most VFD have to take ac, then convert to dc, then to ac again. You might be one step ahead by having a bank of dc already.  Just research the inverters heavily and I bet you'll find something adequate. All of the should be able to provide specs on Kw and duty cycle. 

[jeffpNC]

Just throwing this out there in case somebody finds it with a search....

I have done some more googling and researching and have come up with what I believe will be a successful formula for such a system. There are way too many variables to talk numbers here for sizing this sort of thing in a forum where everyone will have different needs.  The important points for this topic are:

1) heavy-duty modern pure-sine inverters such as those from Magnum and Outback can deal with the startup current needed by typical shop motors in the 1 to 5 HP range (size accordingly) when the wiring and storage systems are done well.

2) Unless you are only using the shop at noon in the summer time, storage is the expensive part of such a system.  Sadly, unless you have some sort of "special" free energy situation on your property (like either near-constant high winds or a waterfall), you will need to store a lot of energy to make this practical.  The sun is a good source, but obviously doesn't work very well at night or on cloudy days (or weeks).  My "back of a napkin" math and some various sources around the net suggest that alternative storage methodologies (i.e. anything other than batteries - like hydrogen, pumped water, flywheels, etc.) are all fraught with issues of cost, maintenance, storage density, and various other practicality issues.  Batteries are expensive.  Nickel-Iron batteries (Edison cells) appear to be the best long-term value in battery storage, but still very expensive even over time.

3) Given the very high start-up currents associated with electric motors, supplementation of the battery system with a significant set of super-caps right next to the inverter is a very good idea.  The caps handle the high surge current needed by the inverter as a motor is starting up.

4) A generator should be factored into the system not just as a "backup", but as a way to limit the long-tail of trying to deal with higher than normal usage and/or long periods of low solar output.  Thinking of it as only a "backup" makes the price of the system boundless and impractical.

5) Because the system will include heavy-duty inverter/battery, the generator can be surprisingly downsized, as it doesn't need to supply the peak power needed, only the average.  This makes the generator less expensive, and also more efficient on fuel and quieter.  A big generator, running at a low idle, is less efficient and noisier than a smallish one running at a medium clip.  A case could actually be made for having both a "small, occasional use" generator as above, and also a larger generator that is primarily used as a backup and set up to power things directly without the inverter/battery system.

[BobInAustin]

A capacitor bank tuned for each motor would help the power factor.  Typically we don't care in our houses because we don't use enough power to worry about the crappy power factor but you will see this a lot more in industrial shops were the load is heavy and is nearly all inductive because of the motors.  

Figuring out the power factor of each tool would be a challenge though.

[jeffpNC]

1 hour ago, BobInAustin said:

A capacitor bank tuned for each motor would help the power factor.  Typically we don't care in our houses because we don't use enough power to worry about the crappy power factor but you will see this a lot more in industrial shops were the load is heavy and is nearly all inductive because of the motors.  

Figuring out the power factor of each tool would be a challenge though.

Easy enough...just hook up my o'scope and try a few sizes until the voltage and current wave-forms line up.

In my first job as a EE, there was one guy who always insisted on doing pages of calculations to figure out the value of a resistor (this was back in the olden days before Spice was readily available) .  The rest of us just threw in a pot and adjusted it until we saw what we wanted on the scope...then take it off and measure it and write down the "calculated value".  I like to think of this method as using an "analog computer".

[BobInAustin]

A watt meter and amp meter will do it also.  You can also do it with a DMM but I wouldn't do it with mains because you'd have to insert a resistor in series with the load.  Problem with an oscope is you'd need an amp probe, right?

I wonder if it would make much difference in a home shop.  I rather spend more money on planes and saws than a reactive power compensation bank.  

[andrew-in-austin]

Have you looked in to the Telsa PowerWall battery?  Not quite available yet, but should hopefully make the energy storage cheaper and take less space.  Looks like a single unit can do 350-450 volts and 9.5 amps.  Converted to 220v AC, hopefully that's ~20 amps.  Maybe two of the units would be enough.

[jeffpNC]

1 hour ago, andrew-in-austin said:

Have you looked in to the Telsa PowerWall battery?  Not quite available yet, but should hopefully make the energy storage cheaper and take less space.  Looks like a single unit can do 350-450 volts and 9.5 amps.  Converted to 220v AC, hopefully that's ~20 amps.  Maybe two of the units would be enough.

The Tesla power wall is just an assemblage of the same lithium ion cells they use in their cars.  Lithium ion cells are not very cost effective.  Their best use is in situations where weight/size are a big factor, where they blow away everything else for "watts per pound" or "watts per cubic foot".

For a non-mobile off-grid solution, frankly, they suck.  About twice the initial cost of Edison batteries or lead acid, and about one third of the life expectancy of Edison (Nickel Iron).

One point in favor of lithium in the case of an off-grid shop would be its ability to provide a faster discharge rate.  Something like lead acid or Edison would be best with super-caps to supply inrush current.  Probably not needed with lithium ion.

That one plus point is substantially outweighed by the (comparatively) low cost and long life of Nickel Iron.

[drzaius]

Jeff, how well do Edison batteries do with deep discharge. That's something that lead acid aren't great at.

[jeffpNC]

4 minutes ago, drzaius said:

Jeff, how well do Edison batteries do with deep discharge. That's something that lead acid aren't great at.

I have no personal experience with them yet, but the marketing hype on all the related sites claims they can handle repeated deep discharge without damage.

[drzaius]

Using them in conjunction with the super caps is intriguing. I'll have to do me some reading. My only experience with them is when they're used in lieu of batteries for backup on circuit boards. 

[wtnhighlander]

Supercaps are used in some automotive applications where brief surges of high current are required.

I say forget solar: http://climateerinvest.blogspot.com/2012/05/surviving-in-your-doomsday-bunker-with.html?m=1