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How to power an off-grid shop? Generator, solar, and/or battery 'wall'.

Lil'John

Lil'John

Former #278
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Walking to the Rubicon
Title basically states the topic.

In my case, it doesn't have to do with issues hooking up to the house. Already trenched/conduited from house to area. My issue is the fact that PGE screws customers badly; just having a house puts it into their level 2 rates:rolleyes::mad3: I think in under a year I could easily make up the cost of a generator and fuel.

For my specific case, I'll say the shop has standard "small" fabrication equipment; 220v welder, 220v plasma, 220v air compressor, numerous 110v smaller tools. No high power lathes, mills, etc. Maybe a car lift.

I'm not sold on solar being able to do it without a "backup" for overcast days.

So I'm leaning toward a generator. So I've got a few questions:
1) How big of a generator should I eyeball? Is 10kW good enough?
2) Propane or diesel? I get propane dropped off at my house so having another tank to fill doesn't make a difference. How is longevity of fuel for storage? How is diesel in colder weather(10F worst I've seen)? Do diesel engines always require water cooling? Which would do better in terms of hours per gallon?
3) Is it worth looking at the welder/generator type units?

The more I think about generators, the more I think about having a battery backup. The thought being a generator is going to be running whether it is loaded with 1W or 5000W so why not run the generator a "short" time to charge a battery backup. Is this barking down the wrong path?
 
My standard issue answer 6-8000watt diesel light plant. Mine has been running for the last 5 days straight pumping water out of a pit. Awesome on fuel.
 
What about a hybrid solution - Solar for lights, hand tools, easy stuff and a generator or welder/gen for the big items.

When I look at my shop time about 10% of it is running stuff that requires the power. Tons of time spent measuring, designing, basic cuts, etc. It would be nice to not burn a generator when all you need is some lights. With modern batteries I find myself reaching for battery grinder, sawzall and jigsaw more often just to not deal with cords. Batteries are easier to charge and deal with on a solar setup than spike load devices.
 
I looked at this long and hard, did a bunch of math and all sorts of shit.

basically, it came down to a generator costing about $0.80/kwh. looking at diesel 8-16k gensets, no real significant difference in operating cost. some, but not enough to really matter.

You'll want a 8k min and probably closer to a 10k to run welders and saws and other typical everything off of. it will tolerate the startup power requirements much better and not react as slowly. i wouldn't use a 3-5k unless i "had" to, like a service truck on the trail situation. not something to shoot for at home.

If you add a battery to a generator, there is just enough system loss in converting in and out of the battery that it is marginally worse than running the generator at idle in between use unless you are looking at long time between use and very low draw during those times. You'd about be better off switching to cordless tools at that point and just firing up the generator when you want to use something big though, honestly.

then you add in the cost of buying batteries and shit and it quickly becomes a not-worthwhile option. Using a big battery bank and a small generator is more wasteful than buying a gen that you can run at a decent load (near 100%) at the max battery charge rate. but again, something running a generally or fairly steady load will do much better straight off the gen and without the batteries, they are just trash.


the hobart gen/welder above or a comparable used one would 100% be the thing to buy, use and enjoy. nothing else really required.

if you find yourself wanting to use lower power things fairly often, or want a different way to charge up your cordless tools, at that point consider a couple hundred watts of solar panels to tie into a rather small battery bank
 
also, diesel for the gen.

always diesel for a standalone. cheaper to operate, lower rpms, easier to maintain, cooler to run long term, better build quality in general than propane units

you want water cooling
 
oil lamps for around the place, or install enough electric lights that you feel justified in letting the gen run while you are out there, but again, is PG&E really charging you more than $0.80 per KWH? the utility might be expensive, but generator isn't cheap
 
Diesel genset with on/off controls mounted near every point of use. Use solar for lights and a few outlets with ability to charge the battery bank with genset while it's running. This way genset only runs for big stuff and charges battery without penalty, and solar keeps the lights/ outlets on for non heavy power tool use.
 
Dethmachinefab said:
Diesel genset with on/off controls mounted near every point of use. Use solar for lights and a few outlets with ability to charge the battery bank with genset while it's running. This way genset only runs for big stuff and charges battery without penalty, and solar keeps the lights/ outlets on for non heavy power tool use.
Click to expand...

This.

I'd even be tempted to run most of the 120v stuff off the genset or at least set it up with some type of transfer switch. Most small hand tools will run fine off solar. Same for things like a computer or radio. You don't want to fire up the generator just to run the grinder for 30 seconds.


Also, generator should probably be sized for the compressor + the biggest load. The compressor and plasma will almost always be running at the same time and unless you want to have to rely on remember to shut the compressor off all the time, there's a good chance it'll fire up at the most importuned time while you're using the welder.


Dumb question - is the 240/120v side of the generator affected when the welding side is in use?
 
bgaidan said:
Dumb question - is the 240/120v side of the generator affected when the welding side is in use?
Click to expand...

Yes. It should have a chart of how much genset amperage you have leftover for a given welding amperage somewhere on it.
 
Good info.

I was thinking about pulling maybe 30amp of service to handle lights. But a small solar panel setup plus small battery bank is interesting.

A few more questions.
1) Is there an issue firing up the generator at time of use vs just leaving it running for 2-3 hours at a time?
2) How long is max recommended storage length with diesel?
3) At what temp will diesel become a problem? The lowest I've seen at my house is upper teens about 2-3 years ago. Usually lowest is mid to upper 20s for a couple of days. I also get snow... usually in the 2-3 feet per storm with an accumulation of 3 to 4 feet.
 
Just like a car, driving a car for a few minutes then shutting it off is bad for the engine over time. Condensate will build up in the crank case, cause premature oil degradation, and cause exhaust components to rot out. It's best to run it at least long enough to come up to operating temp.

Diesel's cetane level is low enough that it won't degrade in storage over a few years like gasoline will. It will grow algae if the conditions are right, which is a problem, but if your system is kept clean, then usually not an issue.

Normal (summer) diesel will start to gel around 30*, winter diesel i've read is closer to 10*. Diesel fuel distributors will modify the chemistry of the fuel seasonally in regions where it gets cold to reduce the gelling temperature, which is part of why fuel economy is lower in the winter. If you live in a real cold area, and keep a tank of summer diesel around till winter, it will most likely gel sooner than a tank of winter diesel stored in the same spot. You can add something like this to un-gel fuel, and/or prevent gelling, in your tank:

https://powerservice.com/psp_product/diesel-911/
 
Shouldn't be an issue, as long as it gets to warm up fully every so often.

Diesel can be stored for years, or go bad in a week depending on if it has anything growing in it. My untreated fuel will sit for a year and be fine, but I don't run anything modern with very low micron filters.

Temps in the 20°s will not be an issue. Days below 10° it can begin to gel, but there are ways to minimize it so I wouldn't worry.
 
Maybe I'm not totally following, are you currently at .80kw? Or going to get a rate jump if you tie in the shop? 2 different rates for house and shop?
 
Projectjunkie said:
Maybe I'm not totally following, are you currently at .80kw? Or going to get a rate jump if you tie in the shop? 2 different rates for house and shop?
Click to expand...

PGE in my location does power usage in tiers. The rate in those tiers jumps. Going from tier one to tier two is almost guaranteed by living:homer: I forget how quickly tier three sneaks up.

As for tying in the shop, I only have one option: subpanel from the house. I forget the metric PGE had for pulling a new service but it was way more than my 100' from the house.
 
Dumb question- could you do a little sneaky 20-30 Amp run from the house to the shop? Just one breaker for lights, stereo, maybe a couple of outlets. Then have the generator (or solar) for compressor, welder, and all the other shit.

Everyone is different with shop use, but I can tell you 90% of my time is lights on, music, and a single 110v tool.
 
45acp said:
Dumb question- could you do a little sneaky 20-30 Amp run from the house to the shop? Just one breaker for lights, stereo, maybe a couple of outlets. Then have the generator (or solar) for compressor, welder, and all the other shit.

Everyone is different with shop use, but I can tell you 90% of my time is lights on, music, and a single 110v tool.
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This is what most people who build their own shops around here do. I recommend doing two wires just so that lights, ventilation, tunes and compressor (assuming 120) can be on their own circuit leaving the other one for getting things done.
 
I looked at doing truly “off grid” on a piece of vacant property to save the cost of running service for awhile. That Hobart Champion elite is definitely what I’d go with, as it’s industrial duty, would make a badass backup house generator, and you get a portable welder for no more $ than a standalone generator. Downside was the fuel cost for me, it would be like $30/day just to keep the lights on. I do finish carpentry so I typically use a miter saw about every 2-5 minutes all day long. If you factor in solar or a battery bank and 12v lights for something that will eventually be wired anyways, if wasn’t worth it.

For you though, having the ability to run 120v for some lights and battery chargers, it wouldn’t be a big deal to fire up the generator for a particular project.

However, if the whole purpose is to lower your electric bill, I can help but wonder if you’d be better off investing that money on solar for your house that will lower your bill all day long, and just wiring the shop with a sub panel for everything. I put a 100 amp breaker in the main panel at my current shop, then I have eight 20A 120V circuits, and a 50A 240V circuit. I have two 50A plugs so welders can be left plugged in, and then a third one for the air compressor.
 
45acp said:
Dumb question- could you do a little sneaky 20-30 Amp run from the house to the shop? Just one breaker for lights, stereo, maybe a couple of outlets. Then have the generator (or solar) for compressor, welder, and all the other shit.

Everyone is different with shop use, but I can tell you 90% of my time is lights on, music, and a single 110v tool.
Click to expand...
I've already got conduit dropped for a full power run so no issue pulling only a "light" run.

Part of the issue I have with solar tied into the grid is the fact that from what I've read, power company(PGE) doesn't pay shit for overage. I'm not going to front capital for them.
 
While I haven't specced a full "off grid" shop setup, I have been making plans for backup and redundancy in my next shop.

I'm planning on all LED lighting and eventually an inexpensive solar/battery array for lighting and other DC charging. But the main unit will be a Miller Bobcat welder generator and I honestly want to run it on LPG. I'm planning on a propane tank for other uses so bumping it to a 500gal and keeping it at least half full will be easy and stable for long term storage. Aa opposed to storing a bunch of diesel that I don't currently use for anything else.
 
Lil'John said:
I've already got conduit dropped for a full power run so no issue pulling only a "light" run.

Part of the issue I have with solar tied into the grid is the fact that from what I've read, power company(PGE) doesn't pay shit for overage. I'm not going to front capital for them.
Click to expand...

Have you done the math on it? I understand not spending the money to get totally independent, but say the house bill is $300/month, and adding the shop would bump you up to $500/month. Rather than spending $5k on the generator, fuel storage, etc, you spend $5k on solar and end up paying them $150/month for both the house and shop.
 
i prefer propane generator because the fuel doesnt go bad and it burns cleaner so you dont have to change the oil as often, and you can use propane for your water heater and stove/oven in the home
 
Yotota said:
While I haven't specced a full "off grid" shop setup, I have been making plans for backup and redundancy in my next shop.

I'm planning on all LED lighting and eventually an inexpensive solar/battery array for lighting and other DC charging. But the main unit will be a Miller Bobcat welder generator and I honestly want to run it on LPG. I'm planning on a propane tank for other uses so bumping it to a 500gal and keeping it at least half full will be easy and stable for long term storage. Aa opposed to storing a bunch of diesel that I don't currently use for anything else.
Click to expand...
A propane generator/welder is appealing. The propane because I'm already running propane for the house.

Gatorgrizz27 said:
Have you done the math on it? I understand not spending the money to get totally independent, but say the house bill is $300/month, and adding the shop would bump you up to $500/month. Rather than spending $5k on the generator, fuel storage, etc, you spend $5k on solar and end up paying them $150/month for both the house and shop.
Click to expand...
Last time I priced out solar, it was closer to $25k than $5k.

I like the sound of a hybrid solution of LED lights, small solar panel with battery backup, and then a generator/welder for the big stuff.

rockyota83 said:
i prefer propane generator because the fuel doesnt go bad and it burns cleaner so you dont have to change the oil as often, and you can use propane for your water heater and stove/oven in the home
Click to expand...
Since I have propane for my house, this route looks most appealing.

But I'd love to hear all options.
 
Lil'John said:
I've already got conduit dropped for a full power run so no issue pulling only a "light" run.

Part of the issue I have with solar tied into the grid is the fact that from what I've read, power company(PGE) doesn't pay shit for overage. I'm not going to front capital for them.
Click to expand...

batteries/storeage are the most expensive and shortest life part of the whole thing. being grid tied has big value even without getting paid for overages.

alternative if the utility rates are very high and also dependent on the time of day would be to install batteries ONLY. charge them at night from the grid when/if power is significantly less expensive, then cut off the grid during the day and use the batteries to run everything until the price break time.

you would need 30-50% difference between day/night grid power costs for that to begin to make sense though due to conversion and storage efficiency drops
 
Lil'John said:
A propane generator/welder is appealing. The propane because I'm already running propane for the house.


Last time I priced out solar, it was closer to $25k than $5k.

I like the sound of a hybrid solution of LED lights, small solar panel with battery backup, and then a generator/welder for the big stuff.


Since I have propane for my house, this route looks most appealing.

But I'd love to hear all options.
Click to expand...

the hardest part about propane is finding a constant duty generator rather than one designed to run for 7 days a year

edit: and the fuel consumption per KWH difference between propane and diesel is significant, so the fuel cost savings per gallon up front doesn't always pencil out in the end
 
Provience said:
edit: and the fuel consumption per KWH difference between propane and diesel is significant, so the fuel cost savings per gallon up front doesn't always pencil out in the end
Click to expand...
you've gotta pencil it out in terms of BTUs, not gallons
propane's still generally cheaper than diesel in bulk
 
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