Poll

Do you keep records of your solar production

No I dont have solar
29 (58%)
No I don't care
4 (8%)
I look at the GTI LCD occasionally
5 (10%)
I look at the GTI display often
4 (8%)
I look at the GTI display even after dark
4 (8%)
I have solar, no GTI and I keep records (like Mike)
4 (8%)

Total Members Voted: 50

Author Topic: UK solar doldrums  (Read 21941 times)

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Offline tggzzz

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Re: UK solar doldrums
« Reply #25 on: January 13, 2018, 03:47:41 am »
Yes I'm sure they do but we are talking about a standardised thing using standard off the shelf kit, I'd be very surprised if anyone inverter stated anything different for "KW" than KWh, most people don't even understand the concept of instantaneous energy at which point you end up talking joules and coulombs just for it to make sense in your head.

Any inverter that has a spec in kWh is simply and grossly wrong.

"Instantaneous energy" has a simpler name: energy.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline Simon

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Re: UK solar doldrums
« Reply #26 on: January 13, 2018, 03:58:14 am »
well no inverters tend to tell you how much KWh the power they are delivering is equivalent to. Obviously this figure fluctuates, no inverter tells you in Ws or any other arbitrary unit. Watts by its very definition is a time related definition so we do standardize on KWh or the amount of KWh the current level of power is equivalent to if sustained for an hour. If you want to talk instantaneous power you either still have to narrow it down to a time frame however small and ridiculous or move to a unit that describes a quantity of energy in joules. The same goes for amps, what is an amp? it's 1 coulomb per second or 3600 coulombs per hour, you can't refer to amps without inferring a time frame.
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Offline metrologist

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Re: UK solar doldrums
« Reply #27 on: January 13, 2018, 04:13:31 am »
I installed a DC meter that displays volts, amps, W, and Whr. I think I can change it to display Ah as well. Since my panel is 100W, I like the W reading also indicates the % output from the panel.
 

Offline Simon

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Re: UK solar doldrums
« Reply #28 on: January 13, 2018, 04:18:42 am »
but your Wh presumably is simply an accumulation of instantaneous measurements that if maintained for an hour will give you the same in W as in Wh, as I have just explained watts is a time based definition so when you say "instant watts" what you really mean is a level of power that if maintained for an hour will give this W as Wh. as a solar panel output varies you can't measure the power delivered now in equivalent Wh and assume it will last for an hour. so multiple instantaneous levels are given that are integrated to give your actual Wh.
« Last Edit: January 13, 2018, 04:37:19 am by Simon »
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Offline metrologist

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Re: UK solar doldrums
« Reply #29 on: January 13, 2018, 04:41:33 am »
It did not seem the math was that complex. The W display is the instantaneous output. The Wh accumulates over time, and I suspect the algorithm is probably very linear. I'm sure it just takes a sample of VxA at periods and adds the normalized value.
 

Offline Simon

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Re: UK solar doldrums
« Reply #30 on: January 13, 2018, 04:45:31 am »
Yes you are measuring the volts and amps now and assume they remain the same until the next sample, divide the results by the amount of samples per hour and add them together. For example if you take a sample every second you calculate the current watts (Wh) and divide the result by 3600 and then keep doing that every second and add the results together. After 1 hour you will have the average Wh delivered.
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Offline stj

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Re: UK solar doldrums
« Reply #31 on: January 13, 2018, 05:04:08 am »
i would be very suspicious of meters that show Ah or Wh,
they probably take one sample and do some math on it.
using the assumption that supply/usage is stable.
highly unlikely that most meters actually use bulk sampling unless they activly advertise a logging or graphing function.
 

Offline tggzzz

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Re: UK solar doldrums
« Reply #32 on: January 13, 2018, 05:46:58 am »
well no inverters tend to tell you how much KWh the power they are delivering is equivalent to.

Of course they don't! That would be as non-sensical as equating "miles" with "miles per hour".

It would be entirely reasonable for them to state "you are currently generating x kW, and over the last day you have delivered y kWh", or "you are currently going at x mph and over the past day you have travelled y miles".
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline tggzzz

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Re: UK solar doldrums
« Reply #33 on: January 13, 2018, 05:55:58 am »
Watts by its very definition is a time related definition

Power is not a "time related" concept per se.

Quote
If you want to talk instantaneous power you either still have to narrow it down to a time frame however small and ridiculous or move to a unit that describes a quantity of energy in joules.

Er no. That's what calculus is all about.

Energy is the integral of power over time.

Quote
you can't refer to amps without inferring a time frame.

Er no. I have a current of 5 amps flowing. There is no need for any timeframe.

If, OTOH, you want to discuss how many coulombs have passed when a 5 amp current is flowing, then you have to state a time interval - since charge is the integral of current over time.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline Avacee

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Re: UK solar doldrums
« Reply #34 on: January 13, 2018, 06:36:59 am »
As an example of how overcast its been here in North-West England; pretty much all the solar-powered road signs weren't working when I was driving this lunchtime/afternoon.
E.g. the happy/sad faces you get as speed reminders ..

Does anyone know how much battery capacity those types of signs typically have?

 

Offline metrologist

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Re: UK solar doldrums
« Reply #35 on: January 13, 2018, 07:02:37 am »
i would be very suspicious of meters that show Ah or Wh,
they probably take one sample and do some math on it.
using the assumption that supply/usage is stable.
highly unlikely that most meters actually use bulk sampling unless they activly advertise a logging or graphing function.

probably. it's on the order of one of those USB power monitor things, which I have a couple. They show me volts, amps, amp hours, and watt hours. looks like they update about once per second, so that is probably a reasonable enough calculation.
 

Offline fourtytwo42

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Re: UK solar doldrums
« Reply #36 on: January 13, 2018, 07:06:49 am »
that's 200 watts for the day I think I have seen it peak at 150W instant. Oh you have a threshold of 100W? you didn't design the powervault did you ? ;)
Umm no I didnt design the powervault does it have a threshold ?
Well the reason I have one is I am in it for the long term so every hour write the accumalated watt/hours to an EEPROM but being mean squash it into one byte, so thats one place a comprimise is made and then the other is the display, I only use a 2x40 char LCD with lots of stuff on it so various energy readings get displayed as 10ths of Kwh. Primative I admit but then I dont want a PC running 24/7 and economics preclude something like a raspi for me anyway :) I should explain I personally don't rely upon a GTI display as the GTI only get's fired up when the water tank is >64degC and that is where most of the power is used, water heating :) Actually saves a significent amount of Oil especially in summer :)
I loved the to and fro here about instantanious power vs energy over time, can be confusing at times (inadvertant pun alert)!
Hey I got 700Wh (0.7Kwh) today, the clag is lifting a little, maybe I dont have to move to Bristol :)
« Last Edit: January 13, 2018, 07:17:52 am by fourtytwo42 »
 

Offline fourtytwo42

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Re: UK solar doldrums
« Reply #37 on: January 13, 2018, 07:14:56 am »
If, OTOH, you want to discuss how many coulombs have passed
Thats naughty introducing yet another confusing measure  :-// :)
Ohh I apologise I see Simon started it  :-\
« Last Edit: January 13, 2018, 07:19:08 am by fourtytwo42 »
 

Offline Simon

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Re: UK solar doldrums
« Reply #38 on: January 13, 2018, 07:22:12 am »
well no inverters tend to tell you how much KWh the power they are delivering is equivalent to.

Of course they don't! That would be as non-sensical as equating "miles" with "miles per hour".

It would be entirely reasonable for them to state "you are currently generating x kW, and over the last day you have delivered y kWh", or "you are currently going at x mph and over the past day you have travelled y miles".

erm yes it is exactly like that, miles per hour describes the distance you travel in an hour, again time related, just because you are doing 60mph now does not mean that you will travel 60 miles in one hour unless you keep at that speed, your speed may vary, if you look once at your speedo and it says 60 and you never look at it again and assume you will travel 60 miles in one hour you will find yourself quite wrong.

you cannot say that you will produce 200Wh just because your power meter says that you are making the equivalent of 200Wh in that instant no more than you can say that you will travel 60 miles just because now you are traveling at a speed that will take you 60 miles in one hour. if your power output varies and say for 1/2 hour you produce nothing and for 1/2 hour you produce 200W you will produce 100Wh over the hour but not the 200Wh that was shown as the instant equivalent when you happened to look at the meter.

even if they say you are generating x KW it is still a figure of equivalence to x KWh if you sustain that KWh over the period of one hour. I'll check what mine says tomorrow.
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Offline Simon

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Re: UK solar doldrums
« Reply #39 on: January 13, 2018, 07:25:29 am »
If, OTOH, you want to discuss how many coulombs have passed
Thats naughty introducing yet another confusing measure  :-// :)
Ohh I apologise I see Simon started it  :-\

W = J*s,
A = C*s

There is always a reference to time, if you want to take time out of it you will talk in units of C not A and units of J not W, any measurement of W or A is an assumption over time and can be only taken as an equivalent or verified after 1 hour if it is to be Ah or Wh, we could equally use minutes or seconds but for general transmission, storage and generation we use the hour as the unit of time
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Offline metrologist

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Re: UK solar doldrums
« Reply #40 on: January 13, 2018, 07:33:43 am »
Well, yeah, but I am using a 60 watt light bulb, and it was drawing 5 amps.
 

Offline Simon

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Re: UK solar doldrums
« Reply #41 on: January 13, 2018, 07:37:43 am »
yes and if you run your 60 "watt" lightbulb for 1 hour it will use 60Wh, you could say it uses 1Wm (W') or 1/60W" ;)
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Offline fourtytwo42

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Re: UK solar doldrums
« Reply #42 on: January 13, 2018, 07:43:11 am »
any measurement of W or A is an assumption over time and can be only taken as an equivalent or verified after 1 hour if it is to be Ah or Wh, we could equally use minutes or seconds but for general transmission, storage and generation we use the hour as the unit of time
I think the word equivalent is important and it need not be verified, for example if 300W is measured for 30 minutes it is correct to quantify it as 600Wh because that is the equivalent hourly energy production. I have some Kwh displays that update every minute (for example how much energy have I consumed today), its just a ratiometric progression.

BTW I see we have added miles into the mix now :)
 

Offline fourtytwo42

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Re: UK solar doldrums
« Reply #43 on: January 13, 2018, 07:45:03 am »
Well, yeah, but I am using a 60 watt light bulb, and it was drawing 5 amps.
Then it's a 12V bulb right and every hour it will use 60Wh of energy :)
 

Offline GeorgeOfTheJungle

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Re: UK solar doldrums
« Reply #44 on: January 13, 2018, 07:53:01 am »
if 300W is measured for 30 minutes it is correct to quantify it as 600Wh because that is the equivalent hourly energy production.

300W * 1/2h = 150 Wh
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Offline GeorgeOfTheJungle

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Re: UK solar doldrums
« Reply #45 on: January 13, 2018, 08:08:59 am »
yes and if you run your 60 "watt" lightbulb for 1 hour it will use 60Wh, you could say it uses 1Wm (W') or 1/60W" ;)

Watt the... ?? No.
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Offline Simon

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Re: UK solar doldrums
« Reply #46 on: January 13, 2018, 08:14:01 am »
yes and if you run your 60 "watt" lightbulb for 1 hour it will use 60Wh, you could say it uses 1Wm (W') or 1/60W" ;)

Watt the... ?? No.

Why ? when we say 60W we are implying 60 watts over 1 hour period or 60Wh or 216'00 Joules in one hour.

Where people can be justified for being pedantic is in defining battery storage where Wh is really a good precisation to make, but in ongoing energy use/generation/flow watts is generally meant in one hour period unless otherwise specified.
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Offline ahbushnell

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Re: UK solar doldrums
« Reply #47 on: January 13, 2018, 08:34:54 am »
If, OTOH, you want to discuss how many coulombs have passed
Thats naughty introducing yet another confusing measure  :-// :)
Ohh I apologise I see Simon started it  :-\

W = J*s,
A = C*s

There is always a reference to time, if you want to take time out of it you will talk in units of C not A and units of J not W, any measurement of W or A is an assumption over time and can be only taken as an equivalent or verified after 1 hour if it is to be Ah or Wh, we could equally use minutes or seconds but for general transmission, storage and generation we use the hour as the unit of time

watts are joules per second not times seconds.  So
W=Joule/second
Amps are coulombs per second
A=coul/second.




 

Offline GeorgeOfTheJungle

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Re: UK solar doldrums
« Reply #48 on: January 13, 2018, 08:36:21 am »
yes and if you run your 60 "watt" lightbulb for 1 hour it will use 60Wh, you could say it uses 1Wm (W') or 1/60W" ;)

Watt the... ?? No.

Why ? when we say 60W we are implying 60 watts over 1 hour period or 60Wh or 216'00 Joules in one hour.

Where people can be justified for being pedantic is in defining battery storage where Wh is really a good precisation to make, but in ongoing energy use/generation/flow watts is generally meant in one hour period unless otherwise specified.

No, "watts is generally meant in one hour period" is wrong. Look, the analogy is as tggzzz has told you before, above, this:

power (Watts) = speed (kilometers/hour)
energy (joules) = distance (kilometers)

So if you travel at a speed of 100 km/h for half an hour you have moved 100 km/h * 1/2 h = 50km

In the same vein if you consume energy at a "speed" (power) of 100W for half an hour you have consumed 100 watts * 1/2 h = 50 Wh

Why would you say that 100 km/h "is generally meant in one hour period"? It makes no sense.
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Offline Simon

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Re: UK solar doldrums
« Reply #49 on: January 13, 2018, 08:37:03 am »
erm yes sorry

W = J/s
A = C/s
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