Gas or electric efficiency

[QED]

Hi all, been a while since I was on the forum. I have an interesting question, half to do with brewing equipment but I suppose the other half is physics/thermodynamics!
I’m planning on scaling up the brewery just now however I am limited to the amount of current I can draw so the maximum electric power I use in the brewery is 3.5kw.
I’ve been looking at options of scaling up to between 120 - 150 litres however the heating at that volume becomes an issue so leaves me with a couple of choices; a propane system or an electric system with a generator.
This led me to wondering, if I had a 6kw propane burner heating a 100litre pot and a 6kw electric element driven by a propane generator heating the same pot, which one would be more efficient?
Also, anyone else out there use a gas system?
Thanks

 

[crowcrow]

There was a thread before that I believe showed electric was move cost effective for heating (in the UK), then gas (mains) then bottle gas last by a long way. But electricity from a generator was bit on that list!

Problem with gas if the amount of heat lost to the air and environment, especially when boiling outside. Electrical heating elements focus the heat where it is needed, and the losses are only through the walls of the vessel and air at the open top.

Anyway, what I'm trying to say is that I don't know - what country are you in, what is the price of gas, petrol and would buying a generator be an large additional cost, or do you already have access to one?

 

[The-Engineer-That-Brews]

I suspect that the energy loss due to inefficiencies in a propane powered generator would be considerably higher than the inefficiencies of heating directly with propane...
So if I were doing it then I’d go with a propane burner (but further down the line I’d seriously look into uprating the electrical supply to the brewery if possible)

 

[QED]

Thanks both, it’s a tricky one. Getting the mains supply upgraded is prohibitively expensive. 200m under a field, under an A road then 50m under our track. We already power 2 houses from a single supply helped with solar and battery storage. Long run would be more batteries and renewables so it’s a short to medium term option I’m looking for.
I don’t have a generator just now so weighing up options of diesel, petrol or lpg. Not sure on the laws with red diesel for powering a generator, that instantly half’s the cost.

 

[gyurmaember]

You're better off to upgrade the wiring to the place you brew, and go for electric. It'll cost fraction of the price of a generator.

 

[QED]

It's not the wiring to the place I brew, it's the SPEnergy Networks supply. Rough quote is £25-30k. I can get a 10kw diesel generator for £4k

 

[Northern_Brewer]

I’m planning on scaling up the brewery just now however I am limited to the amount of current I can draw so the maximum electric power I use in the brewery is 3.5kw.
I’ve been looking at options of scaling up to between 120 - 150 litres however the heating at that volume becomes an issue so leaves me with a couple of choices; a propane system or an electric system with a generator.

It's as much an insulation and patience problem as a heating problem - from memory PBC reckon you can go up to 4bbl (650 litres) on single phase. Even if you assume that's 30A, that's only 7.2kW. And eg if you have a dedicated HLT you can be putting heat into water during the mash.

And of course there's no reason why you can't have a 3.6kW electric immersion heater as well as heating by other means. Such as the old school method of rocks in a bonfire, then into the mash!

Yes you should be able to use red diesel, although they're generally tightening the rules and reducing the discount so one might speculate where it might go long term. I guess it's worth double-checking with your supplier though.

This led me to wondering, if I had a 6kw propane burner heating a 100litre pot and a 6kw electric element driven by a propane generator heating the same pot, which one would be more efficient?
Also, anyone else out there use a gas system?

My gut feel is that since electric-> water is near-as-dammit 100% efficient, then I'd guess that propane-electric in the enclosed, controlled environment of a generator is more efficient than propane->water in a burner, but I don't know.

Gas burners are the norm across the pond thanks to the weediness of their mains electricity, so you might be better off on one of the US forums for specifics.

As an aside, I see PBC now do nano systems - 110l copper, 80l in the fermenter - for £2.5k +VAT for a full 3-vessel system, an alternative to Chinese/German shiny from one of the main suppliers of small commercial breweries in this country :
https://www.pbcbrewerysolutions.com/nano-breweries/

 

[QED]

Amazing reply @Northern_Brewer thanks for that. I currently have a 70l all in one running at 3kw so was kind of basing everything on doubling that capacity. I haven't seen those PBC systems before however I have looked at the Powell set up as that does offer a gas burner option at the 100l size. But both systems only really add 30l to the capacity I already have.
For electric I was looking at the Brewtools150 however that has a 6.6kw power requirement (hence looking at generators) and I possibly have the opportunity of importing a used Blichmann 1BBL gas pilot system currently in use in a mates brewery in Canada however i'm not sure about using gas systems inside without lots of ventilation implications to avoid the old CO poisoning which wouldn't be ideal!

 

[The-Engineer-That-Brews]

I'd guess that propane-electric in the enclosed, controlled environment of a generator is more efficient than propane->water in a burner

I see where you're coming from!

Unfortunately however there are many (significant) losses in the process of generating electricity in a propane generator... chiefly, mechanical friction in the piston(s) and bearings, and electrical resistance in the alternator windings. I'd be surprised if the overall efficiency was more than 10-20%

OK... #engineer...

 

[QED]

I'm going to end up hiring or borrowing a propane genny and trying this out

 

[The-Engineer-That-Brews]

I'm going to end up hiring or borrowing a propane genny and trying this out

Heh... the whole process of converting burning gas expansion into rotary motion by a reciprocating piston, coupled to a few whirling magnets to induce current in kilometres of thin metal wires wound in coils, is what my Dad would refer to a "a triumph of engineering over common sense".... it's a miracle it even works at all ;-)

 

[Northern_Brewer]

i'm not sure about using gas systems inside without lots of ventilation implications to avoid the old CO poisoning which wouldn't be ideal!

Brewing in front of the garage seems to be the norm Stateside - I can appreciate that may not be ideal in Cupar, even with the help of a gazebo or similar to help keep the rain off.

It may be worth poking around eg the SIBA classifieds to see if you can find kit - round us there seemed to be a lot of semi-commercial garage nanobrewers that set up in 2016 but by 2018/19 had decided that it's far less fun than it seems, you may be able to find someone who's given up.

Unfortunately however there are many (significant) losses in the process of generating electricity in a propane generator... chiefly, mechanical friction in the piston(s) and bearings, and electrical resistance in the alternator windings. I'd be surprised if the overall efficiency was more than 10-20%

But open flames aren't that efficient either. eg I came across this which suggests 28% is typical for a saucepan on a gas cooker - and that's presumably in a nice wind-proof lab, and not outside on the east coast of Scotland. Any kind of wind will really hit that efficency.

I prefer numbers to theory. A random Google turns up this site which suggests a 3kW propane generator uses 1.35l/hour at 75% load. So that's 1kWh (= 3.6MJ) from 0.6 litres of propane. Which has an energy content of 0.6*22.8=13.7MJ. That's an efficiency of 26.3% - not knowing what to expect, I'm quite impressed that a random Google has ended up so close!

Obviously a brewpot on a propane burner in somewhere-sufficiently-ventilated-to-deal-with-CO is not going to have exactly the same efficiency as a saucepan on a methane hob in a lab, but I think we can at least say that it and the genny are in the same ballpark of efficiency - and the genny's efficiency should be more robust wrt wind etc.

But just to give a hint of the importance of heat loss - this random blog suggests putting a lid on your saucepan will halve the energy required, a lot of energy disappears in steam.

 

[The-Engineer-That-Brews]

just to give a hint of the importance of heat loss - this random blog suggests putting a lid on your saucepan will halve the energy required, a lot of energy disappears in steam.

That's not heat loss, that's due to the latent heat of vaporisation - but do please feel free to do some experiments and report back

 

[The-Engineer-That-Brews]

That's not heat loss, that's due to the latent heat of vaporisation - but do please feel free to do some experiments and report back

Sorry - didn't mean to sound like an ar$e... if you do get some concrete figures, I'll be genuinely interested :-)

 

[CD]

Due to the expense of getting the mains brought here, I ran on a 4½ KVa Lister Start-o-matic for nearly 10 years, so when I was building my 1 bbl brewery it had to be gas-fired. This is the 80,000 Btu/hr propane burner from the Copper (which is just to the left of it).

I would imagine you’d need a good three-phase supply of electricity to do the same job, but why bother.

 

[QED]

This is the 80,000 Btu/hr propane burner from the Copper (which is just to the left of it).

Is your setup inside a well ventilated garage or workshop?

 

[CD]

Is your setup inside a well ventilated garage or workshop?

Yes it is.

 

[CD]

If it is of interest, a 47Kg propane bottle does 9 Gyles, each producing about 30 gallons of beer. This works out at about 3p a pint.

 

[QED]

If it is of interest

Very much of interest, thanks!