# KWh or KWy

#### ericmark

This statement "A turbine this size should produce around 9,000 kWh per year which is a significant amount of power." seems to me a little odd. Is it kW per year or kW per hour?

"33 kWh per month" = "26% of its capacity" so 127 kWh must be full capacity. A month as unit of time = 28 days (does not refer to calendar month) which means 1655 kWh per year.

I think using kWh is rather confusing 1 watt = I Joule per second so 1 kW = 3600 kilojoules per hour so 1655 kWh = 5956 MJ so why use kWh rather than Joules?

"A turbine this size should produce around 422357 MJ per year which is a significant amount of power." make sense but how can you have per hour per year?

Also how can 1655 kWh = 9000 kWh? Is my maths really that bad?

Neither it's kilowatt hours per year.

1 kWH/Y = 0.00011408 W

But as with many things there are implications beyond the direct meaning of the unit. When people talk in kwh per year there is an implication they are talking about average production/consumption whereas when people talk in watts they are generally talking about peak production/consumption.

There is something weird in the article though certainly, I suspect it has something to do with the definition of "operating at n% of capacity" that whoever made the announcement used.

I think using kWh is rather confusing 1 watt = I Joule per second so 1 kW = 3600 kilojoules per hour so 1655 kWh = 5956 MJ so why use kWh rather than Joules?
I suspect because many years ago some engineer found it easier to think in hours than in seconds.

There is something weird in the article though certainly,
There will be. It is council wriggling.

A Welsh government spokesperson said: "We have an ambitious carbon management strategy for the whole of our estate which includes a wide range of activities aimed at reducing CO2 emissions.

"For example, the Welsh government office in Aberystwyth includes a biomass heating system, solar panels and a wind turbine designed to power a small number of workstations.

"As a result we have seen a 17% reduction in CO2 emissions over the past two years and are well on course to meet the overarching target of a 30% reduction by 2020."

In other words - it's not our money so it doesn't matter as long as the target is reached.
The CO2 will be emitted elsewhere.

i read it as kwh spread over the year as a predicted i assume average

"33 kWh per month" = "26% of its capacity" so 127 kWh must be full capacity. A month as unit of time = 28 days (does not refer to calendar month) which means 1655 kWh per year.

Also how can 1655 kWh = 9000 kWh? Is my maths really that bad?
Is the 9000 refering to what the turbine could output ideally and the 1655 its capacity in this unfavourable location?

I don't see anything odd about it. kWh (kW times hours, not 'kW per {i.e. divided by} hours) is simply a measure of energy, and one can add up amounts of energy over any period you want. If your immersion heater uses on average, say, 5kWh of energy each day, there's no reason why you can't multiply that by 365 to get the total energy used 'per year' of 1825 kWh. A 'kWy', on the other hand, would be an average power of 1kW continuously for one year - i.e. 8760 kWh.
"33 kWh per month" = "26% of its capacity" so 127 kWh must be full capacity. A month as unit of time = 28 days (does not refer to calendar month) which means 1655 kWh per year.
They do effectively refer to calender months. Their average figure of 33 kWh per month results from dividing 585 kWh by the corresponding 18 calendar month period (Jan 2012 - July 1013, I assume inclusive). The '100%' capacity they are implying would therefore be 1525 kWh per year, rather than your 1655 kWh.
I think using kWh is rather confusing 1 watt = I Joule per second so 1 kW = 3600 kilojoules per hour so 1655 kWh = 5956 MJ so why use kWh rather than Joules?
As you indicate, kWh and MJ are totally interchangeable units of energy - so you can use either you wish. KWh is probably more easily conceptualised by most people, since they have some understanding of both kW and hours, but most don't have a clue what a Joule is.
"A turbine this size should produce around 422357 MJ per year which is a significant amount of power." make sense but how can you have per hour per year?
As above, (a), whether one gives the figure in kWH or MJ is irrelevant (no different from quoting a distance in km rather than miles) and (b) it is not "per ('divided by') hour, per year" - is is "for ('times') hours, per year". As above, there's nothing wrong with adding up the total energy generation (in kWh or MJ) over a year (or any other period).
Also how can 1655 kWh = 9000 kWh? Is my maths really that bad?
As above, it should probably be 1525 kWh, not 1655 kWh. However, if I understand, I think that you have probably missed the whole point of the article. As far as I can see, they are saying that 'a turbine of this size' should, if appropriately located, be able to generate 9000 kWh per year, but that it has been so badly located that, even at 100% capacity, it would only produce about 1525 kWh per year.

Kind Regards, John

Is the 9000 refering to what the turbine could output ideally and the 1655 its capacity in this unfavourable location?
Exactly - see the post I was typing whilst you posted this one. I think that is essentially the whole point of the article.

Kind Regards, John

i read it as kwh spread over the year as a predicted i assume average
It's just the total amount of energy totted up over a whole year. Just as you can add up the total number of litres of petrol, bags of coal or whatever you use over a year, so you can with kWh of electricity.

Kind Regards, John

Even at 9000 kWh with no interest on money considered it would take 33 years to pay off. If interest is considered then it would never pay for it's self.

I have said many times one can't run a firm with just accountants and there has to be other considerations but this is really OTT and if a government can't get it right what chance does a private guy have when considering what so called green measures to take.

i read it as kwh spread over the year as a predicted i assume average
It's just the total amount of energy totted up over a whole year. Just as you can add up the total number of litres of petrol, bags of coal or whatever you use over a year, so you can with kWh of electricity.

Kind Regards, John
yes thats what i meant but not put as eloquently as you

Even at 9000 kWh with no interest on money considered it would take 33 years to pay off. If interest is considered then it would never pay for it's self. ... I have said many times one can't run a firm with just accountants and there has to be other considerations but this is really OTT and if a government can't get it right what chance does a private guy have when considering what so called green measures to take.
That's all true, BUT, somewhat playing Devil's Advocate, I think we have to realise that "protecting the planet/environment/resources/whatever" might sometimes involve financial (and other) costs - i.e. some 'green measures' may never 'pay for themselves' and, indeed, may result in increased energy costs.

As an aside, the problem about this turbine they seem to be highlighting is that it was located in a valley, on quite a short tower and near to buildings. Once cannot help but wonder whether pressure from local residents (particularly if elections were in the offing!) might have resulted in the turbine being sited in this 'inconspicuous', but very ineffective. location? That, of course, relates to another sort of 'cost' (environmental, rather than financial).

Kind Regards, John

We had a guy trying to sell us solar panels who gave us an excel work sheet showing how it paid for it's self which included prospective increase in energy cost but excluded the interest lost due to not being invested.

Result I did not go for it as if he tried to hide costs which are easy to see what else is he hiding? Had he assumed energy prices would remain static I would say also not including interest lost also fair.

Case of having cake and eating it.

When in the Falklands I saw a boat which a wind turbine which drove the propellers one of Jacques Cousteau inventions called the "Calypso II" I have tried to find out more about her since my return to UK.

However all the info says it was never built so I wonder what I saw in Stanley harbour it had the sail as shown in the drawing
but it would seem these types of wind generators have to have a motor to start them?

Not far from the one reported by the BBC there is the alternative technology centre which seems to have some answers until you look carefully for example they sell a instruction set on how to make a wind charger from a bicycle hub dynamo but fails to work out how to connect up the dynamo without as the device rotates to face the wind stopping the supply wires being ripped off and also converting the AC supply to DC.

The water lift works well but it would seem far too politically motivated and one does wonder if they had a hand in the white elephant down the road?

"A turbine this size should produce around 9,000 kWh per year which is a significant amount of power.

A very poor return on the investment. But this is not uncommon when costing up wind turbine installations.

Also these omni-directional turbines are less efficient in converting wind energy into mechanical / electrical energy.

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