Monday, January 7, 2008

How much hydro does it take to "power Glasgow"?

Whenever a renewable power facility is described they always say how many 'homes' it will power. Today's news says The 100MW Glendoe Hydro Scheme will be able to power around 250,000 homes – equivalent to a city the size of Glasgow.

I think this 'homes' description is really misleading, because I bet people confuse 'powering all the homes in Glasgow' with 'powering all Glasgow's electricity' or even 'powering all Glasgow's energy'.

Let's do a simple calculation.

The average expected power from Glendoe is 180 GWh per year [source]. Now
if we take 180 GWh per year and share it between a Glasgow of people
(616,000 people), we get 0.8 kWh/d per person.

OK; what is the average electricity consumption per person (including all forms of electricity, not just domestic)? Answer: 16 kWh/d per person. So Glendoe actually provides 5% of the electricity consumption of Glasgow.

So if people get the impression from the press releases that Glendoe will power Glasgow, they have been misled by a factor of twenty!

This is a bigger factor than the normal factor by which people are usually misled. The statement
that Glendoe (180 GWh/y) would power 250,000 homes implies that each 'home' uses just 720 kWh per year. But the normal assumption in press releases about wind or tide is to assume the average home uses 4000 kWh/y or 4700 kWh/y. What's going on? The ratio between 720 kWh and 4000 kWh (18%) is suspiciously similar to the ratio between the average power production of Glendoe (180 GWh/y) and its capacity (100 MW is equivalent to 877 GWh/y). Methinks that someone at Scottish and Southern must have screwed up (or deliberately misled the public) by pretending that Glendoe will produce 100MW 100% of the the time, whereas in fact it will have an average load factor of 20%.

6 comments:

David MacKay said...

Whahey! The Scotsman published my letter

David MacKay said...

I see that (As of December 2008) Press releases are still perpetuating the twaddle that 'Glendoe could power Glasgow'.

Helen Highwater said...

I was happy to see that someone else noticed this vast discrepancy between what the media were persuaded to say and reality (the 5% of Glasgow figure is on Wikipedia too). I used to walk in that area pre-hydro and knew those small streams no way had the energy to power Glasgow. I obtained figures for the reservoir filling and emptying times and came up with it would need roughly 25 Glendoes to power Glasgow inc. non-domestic.
We had to wait years for actual results due to the tunnel collapse. The load factor achieved was only 16%. A very senior SSE employee inadvertently gave me their calculation method and you're right- they didn't factor in the fact that the water would soon run out and take much longer to refill the reservoir. In June they only ran it for 2 hours! The other cheat that they used was to use 3300kWh as the average domestic consumption. DECC give this figure as the average for STANDARD meters, and 4227kWh as the overall average, and 6600 kWh for houses having off peak meters. Instead of using the average, they cherry picked the lowest figure. At the time in 2006 the average was c. 4600kWh so 9 Glendoes would have been needed to provide the electric for the homes in a city the size of Glasgow. Conspiracy theorists would claim that renewable energy companies are deliberately misleading the politicians and public the generate support for ineffective schemes in the wrong places. Claims like "wind farm x provides the power for y,000 homes" should be ignored as totally inaccurate, irrelevant and meaningless.
And yes, the term "power" means all forms of energy; how many Glendoes would it need to replace all the gas central heating in Glasgow, which is what the govt. wants eventually. And what about the push for electric cars?

Helen Highwater said...

As you say above David, the media are still perpetuating the twaddle; in August there was a bit of film of Glendoe on the BBC news and they said "can keep the lights on in a city the size of Glasgow". Even if it never ran out of water, it is only 100 MW and the average instantaneous household consumption of that city is 127 MW.
Helen Highwater
Oh, I did the calculation, it would need approx. 32 Glendoes to power Glasgow (including non-household and gas).

Helen Highwater said...

I could fill this forum with stuff that the pro-renewables people don’t want you to know about, but their latest propaganda is so deceitful that it needs an immediate response. I was angered by the misleading figures which they released on the TV news and in various newspapers last Thursday. I beg that the reader take these figures with a pinch of salt because power from wind and water is as variable as the weather so such figures should never be looked at in isolation, only as part of the big picture or a calculation of long-term averages. These people are either being deceitful or need to study basic statistical analysis; I suspect the former.
Firstly, they say that wind output rose by 20% when one period this year is compared to the same period last year. This is just cherry-picking; did they announce in the summer that wind output FELL by 52% despite 3% more turbines being operational when comparing the second quarter of this year with the first?
Secondly, they say that hydro output rose by 50%. I will now show the truth here. In 2009 UK hydro output was 5240 GWh (gigawatt hours), it had an all-time record fall to 3575 GWh in 2010 due to low rainfall, then rose back to 5690 GWh in 2011 (in other words by 59%). But this rise is indicative of a bad situation (that so much output was lost the year before), not a good one. This is a similar situation to what happened with the hydro figure released last week. I wonder was there a press release in 2012 saying that “Hydro output rose by 59%”.
I know it is hard to believe, but UK hydro output has had no upward trend since 2002 despite 500 new hydro schemes, costing many, many hundreds of millions of pounds and paid for by you. This is due to new legislation that year giving new subsides which had the effect of hydro schemes being optimised for cash flow at the expense of electrical generation. All my data can be checked on the DECC statistics website; just Google:
Energy trends: September 2012 - Gov.uk
Go down to table 6.1
For other years obviously type a different year

Average annual UK hydro generation 1990-2002 =4726 GWh
Average annual UK hydro generation 2003-2013 =4753 GWh

So it has increased by less than 1%

It is not possible that the UK could see a permanent 50% increase in average hydro output because virtually all the good sites were developed by 1963. It is possible that we could see a permanent 50% increase in average wind production but only if they built 50% more wind turbines in 12 months.

A study commissioned by the Scottish Govt. identified 7000 potential hydro sites.
And for every wind turbine you see now, you will see 5 by 2020 judging by those which have planning permission but not yet built.
Helen

Helen Highwater said...

The Hoover Dam can electrically power Glasgow on an average year.