Hackney’s wind turbine: a Mega what?

Artist's impression of the proposed wind turbine on Hackney Marshes

Hackney Council’s latest projection for the amount of electricity that could potentially be generated by Hackney’s east marsh wind turbine does not appear credible.

Council freesheet Hackney Today recently announced (7 June 2010) that  the amount of power that could be generated by the wind turbine planned for East Marsh was estimated to be “… enough electricity to power two thirds of Hackney’s street lights”.

The turbine in question has a theoretical maximum output of 2MW, but engineers interviewed by the Hackney Marsh User (HMUG) group on 16 March this year are reported to have said that the “assumed actual power of each turbine (the ‘load factor’) is 22.8 per cent of the potential maximum of 2MW.”

According to my calculations, this means that the wind turbine on East Marsh could provide just 28.7 per cent of the power requirement of all of Hackney’s street lights – less than half  of the amount that the Council claim.

What’s going on here? Well, Hackney Council’s “two thirds of street lights” claim means it believes the wind turbine could generate just over one megawatt nearly continuously.  That’s 50 per cent of the wind turbine’s theoretical maximum output.

When I asked Hackney Council, “For how many days per year is the turbine predicted to be producing 50 per cent of its maximum output?” the reply was that the Council did not “…hold information in relation to [my questions.] … The background work undertaken for the Eton Manor turbine project has helped inform consideration of delivering a turbine of a similar specification at East Marsh.”

The Eton Manor turbine is now out of the picture, but the fact remains that Hackney Council couldn’t answer my question on how often 50 per cent output was predicted to be achievable.  Odd, then, that it now makes a claim for the wind turbine’s power output that depends on exactly this 50 per cent figure being taken for granted.

Here’s how the figures cited above have been worked out:

The turbine’s 22.8 per cent ‘load factor’ (source: engineer talking to HMUG) is 0.228 x 2,000,000 Watts = 456,000 KW (Kilowatts) = 456 thousand Watts.

There are 11,091 street lights in Hackney, and their total annual power consumption is 6,493,900 KWh (source: Hackney Council).

So, the power consumed by all the lights is 6,493,900 KWh divided by the number of hours they are on.  This is 4,087 hours per year (source: Hackney Council), so that’s 6,493,900 KWh/4,087 hours = approximately 1,589 Kilowatts = 1.589 Megawatts. That means Hackney’s lights need a source of power that can provide 1.589 Megawatts to have them on all at once.

Two thirds of 1.589 Megawatts is about 1 Megawatt.  But as we saw earlier, the single remaining turbine is projected to be capable of delivering 456 Kilowatts when it’s in situ.  That’s less than half a Megawatt, and not even one third of the power needed by Hackney’s street lights (in fact it’s 456/1,589 *100 = approx. 28.7 per cent of the required power.

Related stories:

Hackney Marsh User Group speak out over wind turbine

Hackney Marshes plans on course as Olympics wind turbine scrapped