Grams per kWh instead of GPW

JMD

JMD

Well-Known Member
We all like to compare results and battle each other on a friendly level, but in order to do that, we need a measure of efficiency. The current grams per watt (GPW) is severely flawed.
The common problem when comparing efficiency of grows, is the fact that people veg and flower for very different lengths. This is further complicated by trying to compare regular strains to auto flowering strains. (18/4 and 12/12 vs. only 18/4).


Example:
I grew a Royal Dwarf (auto flower), which yielded 80 grams after 11 weeks. My lights consisted of 72W red/blue LED, 90W CW/red LED and 2x 20W CFL. I ran the lights at 18/4 throughout the entire period.
So that's 1386 hours drawing 0.202 kW, which equals to ~280 kWh. With a yield of 80 grams, that means that the efficiency was 0.29 grams per kWh.



By calculating the efficiency this way, it's possible to compare various grow techniques (bare bulb, perpetual, LED, SCROG etc.), since it doesn't matter how long you vegged or flowered for, or which light cycle you run!

Let me know what you guys think :mrgreen: Happy growing!
(I'm sorry if this idea has been posted before and I haven't noticed it)


Picture of the Royal Dwarf, because.. why not? We all love weed, right? :joint:
2013-11-17 23.01.32.jpg
 
vostok

vostok

Well-Known Member
Grams per lumen is my favorite, either way it don't make you a better grower, but is ideal for noobies to boast of volume, a totally unkind canna thing?
 
JMD

JMD

Well-Known Member
vostok said:
Grams per lumen is my favorite, either way it don't make you a better grower, but is ideal for noobies to boast of volume, a totally unkind canna thing?
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Don't get me wrong; it's not a race or competition to see who can grow the most. But we all have bills to pay, right? :)
Wouldn't it be great if you could start to compare different grow systems, and maybe little by little optimize your own grow and save money or increase your yield?

I love to optimize and improve designs, and I gather much information from other growers. But the massive spread on veg and flower duration and light cycles makes it close to impossible to see which works better than others.
 
C

churchhaze

Well-Known Member
I agree with you 100% on this. I think the problem is that even engineers suck with units. Since W is a measurement of instantaneous power (derivative of energy), it's impossible to know how much energy was used to get a given amount of grams unless a total time of lights on is also given.

I've seen people remedy this by calling it g/W/m, but W/m is not a measure of energy either. W*m is, and like you said, a month can mean 12/12 to some people, 18/6 to others, or a combination to people who start in veg and switch to 12/12. (some starting with 24/0, etc etc)

g/W*h would be a great unit of efficacy for a complete growop, but I doubt anyone will use it, or calculate it right.

JMD said:
We all like to compare results and battle each other on a friendly level, but in order to do that, we need a measure of efficiency. The current grams per watt (GPW) is severely flawed.
Click to expand...
 
cannaculturalist

cannaculturalist

Well-Known Member
I have thought this also, well said. I have calculated my entire power usage across different growth stages. I've worked out an automated calculating spreadsheet with all light sources, fans etc, their relevant kWh usage, with relevant power company info etc. It's really handy to dial in exactly what is being consumed. This sort of measure gives me a far better idea of what is going into the grow, rather than pure yield per flowering lamp wattage - which as you correctly say, doesn't actually say anything about the reported grow.

However I doubt a lot of others have their setup worked out to this degree. Some of the pro-growers probably have this in mind, but from what I read on many forum posts here, it'd be hopeful at best to get someone to conceive of this detail. Though even with a g/kWh calculation as you state, there are still variables to consider which this simple result doesn't entirely explain - which you've suggested, such as differences in veg/flower time, strain, auto, photoperiod etc. But it would still standardise things a lot more than they currently stand.

I'd vote that the cannabis grow scene would benefit greatly from using this terminology over what is currently used. But think the need to standardise the usage of EC measurements over PPM is much more important to get sorted sooner. I can't get that one - as a still recent hydro newcomer, it took ages to decipher all this PPM business - EC is far easier to understand/communicate with others. I guess it's all a slow improvement.
 
vostok

vostok

Well-Known Member
I prefer 'roundings' my 600w glows 12 hours per day. but every 12 hours the timer(20w estimated) turns the lights on by activating the ballast(250w initial activation?) after about 20 minutes the fan may go on(20w estimated) then off again as per my Whilly temp. controller(15w estimated).. the same sceneairo in my other vegging closet or any grow room in the country ...perhaps, best I can do is a rough equivalent or rounding
 
Ou8aCracker2

Ou8aCracker2

Well-Known Member
I will agree that GpKwh is a reading of true efficiency over GPW but high density (dangerously high plant count) is where you get the good GpKw/h numbers.

I'll stick to less plants,longer veg for a good GPW.
 
skunkd0c

skunkd0c

Well-Known Member
plant grew for 13 weeks total and yielded 435 grams (15.5 oz)


3 weeks veg under 1 x 250 mh for 16 hours per day = 84kwh
10 weeks flower under 1x 600w hps@ 12 hours per day = 504 kwh

total light power = 588 kwh (435g/588kwh = .74 g/kwh

this works out at a cost of £1 for 6 grams
once the power for fans and extraction and food are accounted for it would be more like £1 for 5 grams

not sure how this helps really unless electricity is the most important thing to a grower

personally i would consider yield/space/time to be a better judge of efficiency
electricity is not the most expensive thing in the world i do not mind using a little bit more power
if the result is more bud , its cost effective

peace
 
C

churchhaze

Well-Known Member
This is exactly what I mean when I say most people, even engineers, are bad with units. It's not g/kW/h, it's g/kWh.

It makes a big difference. Even if it was a typo, it'll be a frequently made "typo" that people don't put much thought into.

It's really important for people to actually follow convention when using units too. Grams is g, watts is W, and kilo is k. That's case sensitive. It's futile attempting to use more meaningful units when most people just use whatever symbols they feel like.

Ou8aCracker2 said:
...is where you get the good GpKw/h numbers....
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C

churchhaze

Well-Known Member
skunkd0c said:
total light power = 588 kwh (435g/588kwh = .74 g/kwh
Click to expand...
kWh is a unit of energy. kW is a measure of power


skunkd0c said:
personally i would consider yield/space/time to be a better judge of efficiency
Click to expand...
Efficiency is actually unitless. The units always cancel out with efficiency (like W/W. Watts out per watts in). 100% efficiency is 1W out per 1W in.

g/kWh technically isn't a measure of efficiency because it's not unitless. It only measures the effectiveness, or efficacy of the grow. (since grams isn't a measure of energy, it's not energy out vs energy in and thus the units don't cancel out)
 
skunkd0c

skunkd0c

Well-Known Member
You are correct that was a slip when i think of energy i tend to think of joules rather than kWh

your second point went way over my head
sorry

ok i get it now .. thanks for the clarification, i thought you was being a little bit difficult
but now i can see you are just being precise cos you are smart
are you a scientist ?
 
GrowByDesign

GrowByDesign

Member
cannaculturalist said:
I have thought this also, well said. I have calculated my entire power usage across different growth stages. I've worked out an automated calculating spreadsheet with all light sources, fans etc, their relevant kWh usage, with relevant power company info etc. It's really handy to dial in exactly what is being consumed. This sort of measure gives me a far better idea of what is going into the grow, rather than pure yield per flowering lamp wattage - which as you correctly say, doesn't actually say anything about the reported grow.

However I doubt a lot of others have their setup worked out to this degree. Some of the pro-growers probably have this in mind, but from what I read on many forum posts here, it'd be hopeful at best to get someone to conceive of this detail. Though even with a g/kWh calculation as you state, there are still variables to consider which this simple result doesn't entirely explain - which you've suggested, such as differences in veg/flower time, strain, auto, photoperiod etc. But it would still standardise things a lot more than they currently stand.
Click to expand...
i'm no pro grower but I've done basically the same as you....every piece of equip that draws power, w/ exception of my radio is calculated by kWh cost, per hour, daily & monthly. I also track water & soil costs to arrive at a cost per gram $ figure...I needed to know hehehe I've also broken it down to $/sqft and $/plant just for shits n giggles.

Lighting-watts-per-gram is a completely bogus measurement of costs and productivity. I imagine some Pro telling some newbie to "just figure a gram per watt" in response to the 10,00th "what can I expect.." question...and a standard was born!
 
racerboy71

racerboy71

bud bootlegger
i've said this in other threads, but gpw is about the most useless pos way to measure a grow imvho.. it doesn't take into account the time used to get to that number, which is what the op is talking about..
say for instance, someone grows three plants from seeds, they veg them for four months, they like trees, then flip them to flower and flower for another 10 weeks, and at the end, they get a pound a plant under a 1k bulb.. those numbers sound impressive, 3 pounds right?
now we have another guy, he's running sog from clones, 2 week veg, 10 week flowering time, 25 plants, and gets an ounce per, so that'd be 1 lb 9 oz, and looking under a 1000 watter as well.. going by gpw, you'd think the guy who got three pounds did better, but that doesn't take into account that he vegged for 4 months to get that.. the guy running sog could have two complete grows in the time it took the first guy to get his 3 pounds, meaning gpw is about useless imvho.. and in the end of the same amount of time, the guy who pulled smaller numbers in the sog setup would yield more then the guy whole ran trees, but vegged them forever..
 
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