We have G99 Lift Off!!!!

So what? we hear you say, big deal—what has a soft ice cream with a flake, or a multi-nation economic jamboree got to do with our Hydro?

Well, it is one of the most important of the approvals we need to obtain, (seems our whole lives have been driven by the projects various approval processes—Planning and Environment Agency Approvals—to get us up and running, OFGEM to ensure we qualify for the FIT’s (Feed in Tariff scheme) to name but a few).

G99 is a specification/standard issued by the Energy Networks Association (ENA) following the assimilation of the EU Commission regulation on harmonising network standards, known as Requirements for Generators (RfG), into UK Distribution and Grid Codes. It covers, in rigorous detail the requirements for connecting into the UK Power System. Without fully meeting the requirements of G99 we would not be able to connect into the Grid system, even though we are supplying our Power direct to Siemens, the Grid still “sees “our connection and we have to comply with all relevant standards. (And of course, then start to generate that crucial commodity called Income!!).

Before we look at the background to G99, what it requires and the approval process, did you know why an Ice Cream cone with a chocolate flake stuck in it is called a “99”.

Well, there are a number of theories, one of the most popular being that the name comes from Portobello, in Scotland, when Stefano Acari opened a shop at 99 Portobello High Street. Acari would break a large Flake in half and stick it in an ice cream, with the name then coming from the shop’s address (why the UK Ice cream market was dominated by Italians is a story for another day!!). Another claim, according to the Cadbury website is –In the days of the monarchy in Italy, the King had a specially chosen guard consisting of 99 men, and subsequently anything really special or first class was known as 99—and that is how the 99 Flake came by its name. (By the way much more interesting to write about ice-creams than G99!!!).

ice cream 99

National Grid Electricity Transmission owns and maintains the high voltage electricity transmission network in England and Wales. The national distribution system uses very high voltages (to reduce power losses) and as such National Grid does not connect directly to homes and businesses because of this high voltage. (The national grid network is very sophisticated and extensive, and more information can be found via What we do | National Grid Group )  National Grid connects to industrial properties and to DNO’s. The DNO (distribution network operator) is the company that owns and operates the powerlines and infrastructure that deliver electricity to homes and commercial properties through their own network of power lines and underground cables. The DNO for our area is Western Power Distribution (WPD) and it is their approval we have to obtain before being allowed to connect and transmit our power. Western Power Distribution – Our business

Up until approximately 20 years ago, electricity distribution was straightforward. In simple terms there was huge coal, gas or nuclear power stations, with maybe a couple of large pumped hydro storage schemes e.g. Dinorwig–Electric Mountain – Dinorwig Power Station, generating power which flowed through National Grid’s transmission network and then used in homes, offices and factories.

Over the last ten years, the major shift towards renewables and energy storage e.g., Wind farms, Solar and Hydroelectric, has placed far more generation at the distribution level (most often termed ‘distributed’ or ‘embedded’ generation). But this poses challenges for the network operators who need to ensure these distributed generators can stay connected safely, whilst supporting the energy system with correct attributes e.g., frequency and voltage. National Grid are gradually introducing a “Smart Grid system” to ensure our UK mix of large and embedded generation remains resilient. (Google smart grid and you will get rucks of info)

The large power stations which use synchronous generators, e.g., Drax, have supplied the whole electricity system with tremendous resilience, especially inertia and provided a very stable system, especially the crucially important nominal system frequency of 50hz. They are also usually very efficient as they can easily be accommodated to load power factor variables e.g., caused by long power lines etc.

The rapid expansion of lower-capacity generators e.g., solar, wind, small hydro can cause the grid to become less stable and this, risks damaging both the generator and the grid, essentially, they have very little inertia and can be easily “de-tuned”. This can be likened to a very large super tanker keeping a straight course largely unaffected by strong winds, whilst a small yacht can rapidly be blown off course. As a matter of interest, power generation in Scotland is dominated by wind. A major failure of some of the large wind generators could begin a ripple effect and cause large portions of the network to shut down. The core issue is switching back on, and the worry is that it will take some time for the system to be fully restored from such a “black start” without the inertia of a large power station in the system to provide the crucially important reference norms of frequency and voltage.

For those of you interested in where our power comes from on a daily basis (even hourly! and especially the demise of fossil fuels such as coal, the real time generation picture can be seen via  GB Fuel type power generation production (gridwatch.co.uk) or G. B. National Grid status (templar.co.uk)


 Back to Congleton Hydro— hopefully you are still awake and have not been bored by this all this background!

As mentioned earlier, before we can connect into the system, we have to demonstrate to our DNO i.e., WPD, that we meet the requirements of Specification G99 and if for any reason we should suffer some form of malfunction, we would automatically disconnect from the grid /enable WPD to disconnect us. Core to this approval, is the presence of and successful operation in our control system of a device called an Interface Protection Relay or as more commonly known a G99 Relay. Without such a Relay, Archie is essentially impotent!!


 G99 Interface Protection Relay

The G99 relay is an electronic monitoring device whose modules continuously monitor the quality and stability of our output power connection. It has been programmed to have certain fixed parameters dictated by WPD which includes voltage, frequency and Loss of Mains (LOM). The voltage and frequency elements make sure that the voltage and frequency are within defined statutory limits. To reduce the occurrence of nuisance tripping, there are 2 stages before the relay operates. The intention is that a small excursion outside the limits is permitted for a relatively long period before tripping, but a large excursion will result in a rapid trip. LOM is a general term associated with the automatic detection process that provides an ability to detect a change e.g., loss of one of the phases of the 3-phase supply.

Should any of these areas go outside the pre-programmed limits, then the G99 Relay must cause an emergency stop and the main circuit breaker to open, thereby instantly disconnecting Congleton Hydro from Siemens and hence the wider grid.

Testing our system against the requirements of G99 is quite a long and complex operation. To satisfy ourselves that we would be able to meet the requirements, an extensive “commissioning schedule” was prepared and used for basic testing. However, to prove compliance with the details of G99 requires specialist test equipment and operator competence. To enable this, we contracted the services of a specialist Engineer from Industrial Power Systems G99 Testing (indps.co.uk) .After a very long day of setting up the equipment and performing the tests we were confident our system would pass muster. Now for the retesting witnessed by a WPD Engineer. Such is the growing demand of distributed network connections that DNO Engineer availability is somewhat sparse, and we were fortunate to get a WPD Engineer “slot” for 6pm. So, a long day—no food, no coffee or tea—we have yet to own even a kettle, let alone a microwave!! 

Anyway, all hard work and no play in this case paid dividends. By 8pm last Wednesday evening we had a WPD signed connection agreement. The WPD Engineer even asked if he could bring his family to look at the scheme and wished he had known about it so he could have invested!!  So —-to where this newsletter started, we have G99 Lift Off.

We now have two more pre-approvals to implement and please, please a drop of rain to give us some decent generating water! As mentioned in an earlier newsletter we have pre-qualified for the OFGEM FITs (Feed in Tariff). We are now awaiting OFGEM’s acceptance of this info i.e., Date of commissioning, Signed DNO acceptance, schedule of commissioning tests and statement that we believe we are ready to operate and evidence that the plant can operate at maximum power. Fingers crossed OFEGM will respond promptly to this information.

Finally, as mentioned last month we are awaiting the Environment Agency (EA) acceptance that we have met the conditions of their prior approval. Hopefully and again fingers crossed we will get a speditious positive response. One of the EA requirements is the installation of an EA “Approved” river level gauge fitted in a visible and prominent position. This gauge to be calibrated such that “0” equates to zero water flow over the Weir. You will hopefully recall from last month’s newsletter that the dominant input to our control system is the output from the sensor that monitors the Weir water level. It is an EA approval condition that we cannot abstract water if the Weir crest falls below 5cm.

So, we have duly fitted an approved board at the mouth of our water intake and adjusted its position so ensure that “0” equates to zero flow over the weir and also zero from our control system sensor.

Water level gage

You will notice from the above photographs that we are starting to replace temporary fencing/barriers with permanent structures. Now that we have basically got the core system “ready to go” we can start to turn our attentions to the site infrastructure and overall tidying up activities.

A key activity previously mentioned is the “re-wilding” of the site (not sure if re-wilding is the best term—but if it is good enough for The Archers, it is good enough for us!!). If left alone, nature itself will attempt to return the site to some degree of its former glory. We are however going to give nature a helping hand to accelerate the process of “greening up” some of our structures and the upheaval caused by the construction process. It will take some time, but we will make a start this autumn with the advice from the likes of the Cheshire Wildlife Trust and The Trees for Congleton project. An illustrated article is attached that gives you some information of what we are planning—additional suggestions most welcome.


A major event this last month has been the painting of the powerhouse floor. The past six years of the design, planning, construction, installation, testing etc processes have been chicken feed compared to getting agreement on the colour of the floor. We just could not agree—blue, green, red (and the various subset shades) have all been thrown into the ring. In the end Screwfix decided for us –the only floor paint they had in stock was Slate Grey!! (primed before hand with a 1:4 mix of PVA to seal the concrete) —it looks quite smart –we are determined to keep it clean!

Congleton Hydro is attracting worldwide attention—well from Geordie land anyway!! We were just leaving site this afternoon and we met a large family (four adults and three children strolling down the boardwalk—we had forgotten to secure the access fence!!). They were from Newcastle on Tyne and were on their way to a holiday in Cornwall and had decided to take a break in Congleton and took the opportunity to have a look at the Hydro Project. A bit bemused by this, we chatted further and found that one of the adults had actually lived in the former Havannah Village many years ago and was just visiting old haunts!!!—-still, they thought the hydro was fantastic! Actually, on this note of the former Havannah Village, an article has been written for us by somebody who was born and brought up in one of the old cottages (still remaining). We will feature the article in a future newsletter—great reading as she remembers the old industrial mills that once “graced” the site.

We hope you have found this newsletter, despite its somewhat technical content and minimal photos (but without G99 approval we would have no scheme!!) readable and informative. We would welcome your comments and feedback—please contact us via info@congletonhydro.co.uk


Whilst the COVID situation, thankfully down to the vaccine and our ongoing observance of suitable precautions, does seem to be improving, please continue to Take Care and Stay Safe.

We trust you manage to enjoy some form of Summer Holidays, but we would ask you to this time, cross your fingers and pray for some rain—we need it to get some decent generation under way!!!

With best wishes from The Congleton Hydro Team