A Report into the use of switching technology to facilitate Eday Renewable Energy's Microgrid For general distribution
25 March 2015 Eday Renewable Energy Limited
Supported with kind assistance from:
Part 1: The business case for a microgrid Introduction:
The Grid environment
Eday Renewable Energy's (ERE's) turbine is exporting less electricity than it is capable of due to Orkney's largely closed loop grid being at full capacity on a regular basis.
When this happens the grid company has the contractual right to balance supply against demand by trimming or completely stopping wind generators. This is known as curtailment and is carried out remotely via a tele-switching system called "Active Network Management".
A certain amount of curtailment was indicated in our grid agreement and budgeted for. However actual curtailment levels have been around 3 -4 times higher. Consequently, reduced exports against budget, have meant reduced incomes.
ERE's Goal
ERE's primary strategic goal is to maximise revenues for the holding company Eday Partnership (EP). However, it must do this sustainably by firstly ensuring that there are sufficient funds for working capital, mandatory bank reserves, contingent reserves etc.
Due to excessive curtailment, income has been ringfenced for normal operational expenditure and reserves, leaving insufficient surpluses to make gift aid donations (except for a small donation made in December 2014).
ERE is not meeting it's primary strategic goal.
To address this, ERE will need to use best endeavours to apply revenue assurance to restore income to its original budgeted levels for future operating periods.
Revenue Assurance
Revenue assurance is a term most commonly used in telecoms businesses, as a practical response to issues with operational under performance, most commonly relating to collection of revenue.
The most common metaphor is that of leaking water from a pipe, where water stands in place of revenues or cash flows, and the leaks represent waste. The value of revenue assurance is hence determined by the size of the leaks "plugged". The value added also includes the recovery of "lost" revenues or costs
In our case, the term revenue assurance is a good fit for our business because the operational under performance of our turbine due to congestion on the grid causing a reduction in revenue.
The leaks are the "lost" electricity that we could have generated had we not been so badly curtailed.
In figure 1, lost output is represented as an iceberg under the water. Like underwater icebergs, its size is significant and is not immediately apparent from the surface. Eday Turbine's situation is similar: the lost output is significant, but is not immediately visible; the lost opportunity cannot be seen or measured by the naked eye.
So how does Eday determine its lost output?
From our wind reading devices on the turbine we can record average ten minute wind speeds. The Scada system also records actual average output. By downloading this information onto a spreadsheet, and mapping wind speed against our turbine manufacturer's power curve, we are able to ascertain uncurtailed output each ten minutes. We deduct the actual output from the uncurtailed output to deduce lost output. We add up the lost outputs from each ten minute segment in the measured period (in our case once monthly) to determine total lost output.
The strategic case for change
Grid Legacy
ERE's curtailment appears to be improving by 10% for the periods where we can may like for like comparisons.
At the end of October 2013, our monthly curtailment improved slightly.
We are not sure why this is.
Our turbine is in Zone 1 and other generators in Zone 1 seems to have a marginally improved outlook.
Conversely, generators in Zone 2 have experienced a worsening in curtailment from roughly the same time.
It is likely that the ANM system, which is a pilot project, has had some modification to its programming where the priorities of zone 1 and zone 2 generators have altered favourably and adversely, respectively.
Further modification to the Active Network Management system could result in further changes to our curtailment percentages, adversely or favourably. This uncertainty does make the business vulnerable, in that it cannot plan properly for the future, with any degree of confidence.
This is rather like having an employee having the threat of redundancy hanging over their heads but not knowing for certain how it will "pan out". Future Grid prospects
As new generators are expected to come on line, grid congestion is increased and the existing legacy generators are forced to re-jostle for position on the adjusted grid. What generators are due to be coming on line in the near future?
One tidal developer is expected to be installing a 2MW turbine in early 2015, which is not expected to be curtailed and may impact adversely on other generators in Zone 1, including ERE.
There also appears to be a planned wind farm development in Zone 2 (with an estimated capacity of circa 7MW). It is not clear when this will be installed, or it's position in the grid "queue". Nevertheless, it's very presence will add to the supply to the grid "pool" and, potentially, worsen our curtailment position.
What drives grid congestion(curtailment)?
There are three drivers: 1) Demand: An end user's electricity needs (factories, schools, houses etc) 2) Supply: The capacity of generators to meet an end user's electricity needs. 3) Distribution: The capacity of the cable to "transport" the electricity from the generator to the end user. If there is an imbalance it can be detrimental.
For example, . if there were not enough supply to meet demand, there would be power cuts, as evidenced in England. . if there were too much supply, the excess of supply over demand would be dissipated as heat causing stress on the cable . if the cable wasn't robust enough to transport all of the generators electricity, the grid system would only be able to transport some, but not all, of the electricity generated
So what would be a dream system? The supply should always be more than demand, and the cables need to sufficiently thick and robust to cover all eventualities. But, if the supply is too much more than demand, then the generators will be losing money through under utilisation.
What is our situation, in these terms? ERE's supply is more than demand and we are losing money through under utilisation.
What would change this?
If demand were to increase across the grid by new end users, housing estates, factories, hospitals etc, there would be a better fit between supply and demand. However, this assumes an increase in net demand (i.e. new loads, rather than new for old), and generators would still need to jostle for position to meet new demand according to their stacking order. Whilst there are plans to build a new hospital in Kirkwall, this is to replace an existing hospital so it remains to be seen whether an additional load will be created on the grid.
If supply was to increase, yet further, with no increase in demand, then there would be a worse fit between supply and demand and cause increased curtailment.
If demand were to increase locally, (i.e. a near to site micro grid), then ERE's supply would fit hand in glove with this new demand and would not be shared with any other generators.
Bearing this in mind, the use of a microgrid would appear to be the best fit for our curtailment issues by being reclaim some of lost income and floating more of the iceberg above sea level. Using a Microgrid to capture an increase in local demand
What is it?
A microgrid is a group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid and that connects and disconnects from such grid to enable it to operate in both grid-connected or “island” mode.
In establishing whether Eday exhibits the behaviour of a microgrid
Eday's loads are: the hydrogen electrolyser which is interconnected between a feed from both ERE's wind turbine, and a feed from EMEC's developers' tidal turbines. the horticultural project which is interconnected to just ERE's wind turbine.
Part 2: How the switching would be an integral and necessary part of the microgrid
Microgrids work using boundaries where loads (including the grid) can be connected or disconnected. Because Eday's wind will work in grid connected mode, or island mode, or both it therefore will exhibit the typical characteristics of a Microgrid.
Boundaries are enforced by using robust high voltage switching. In the "off-state", switching protects loads from overheating, and controls the effective use of those loads. In the "on-state" switching allows a controlled diversion of electricity according to logic controller protocols such that local demand is matched with local supply.
Without having boundaries using switching it would be impossible to control the loads on the microgrid.
It would be rather like a house with all the lights turned on, all the cookers rings turned on, the immersion heater turned on, the shower turned on. It would be impossible to control. With houses we "reclaim control" by having a system of switches which as their default disconnect the main supply to the individual loads and zones unless we instruct otherwise via manual switching or semi automated controls such thermostats (for heating), photo conductors (for light), timers or cloud based teleswitching.
For Eday's the principle is very similar. The default is that where there is demand on the grid in excess of supply, the grid will be switched on. Where supply exceeds demand, the grid operator will partially or fully switch off the grid (i.e. curtail). Eday "reclaim control" by activating a switch or switches to allow the curtailed electricity to supply alternative loads.
Part 3: How does the switching work?
A controller at ERE's turbine monitors for a curtailment signal.
Currently, where there is curtailment, the active network management system will instruct the turbines via an electrical signal to trim its output and so potential electrical generation will be lost.
With a microgrid, however, there will be additional electrical loads available to it.
We envisage that our microgrid would comprise: load 1: a hydrogen electrolyser (upto 500KW) load 2: the horticultural project (upto 200KW)
The controller will continually monitor the additional loads available. Where there is a curtailed event, and additional loads available, the controller will activate a switch relay which will divert curtailed electricity to those loads according to a priority protocol as follows:
grid, then hydrogen production, then horticultural heating
The design comprises two single line diagrams detailed in Appendix 1 and 2:
1. CURRENT INSTALLATION
The single line diagram (Appendix 1) reflects straightforward export of all production to the boundary with SSE's equipment. Metering takes place on SSE's side, as export and production are tied together. A single step-up transformer is needed to achieve export at 11kV. Note that no control systems are shown on this SLD, as they are not connected to power equipment that is ERE's responsibility. At the turbine, there is an ANM signal input to the Enercon SCADA, which governs the allowed export.
2. MICROGRID INSTALLATION
The revised SLD (Appendix 2) shows much of the equipment illustrated in the previous SLD, plus significant extra items.
• METERING
Metering of generation will be needed in addition to grid export. This is achieved with a new FiT meter, shown at [B5]. The existing export meter (located on SSE's side) will continue to provide that function.
• POWER DIVERSION TO MICROGRID
The right hand side of the SLD shows the proposed switchable power supply to the grow project and other future uses.
In order to make best use of power across a range of wind speeds and grid export limits, multiple circuits each of between 50-100kVA are proposed. There are manual controls and automated switching shown [E6-E8]. A step-down transformer is needed [D6] to drop from 11kV to 415V. There is no practical way to get significant power from the turbine at below 11kV.
A similar setup is envisaged for connection to the prospective hydrogen electrolyser [B8], but this was not specified in the IIF project, nor in the tender brief to the design contractor, and is not therefore shown in detail.
• MONITORING AND CONTROL
The microgrid system assumes responsibility for keeping grid export within the ANM limit. Export monitoring is installed to ensure this [B3].
Further systems, connected via a Controller at the hub [E3], allow variable diversion of power to the microgrid as well as signalling to the turbine its output limit – the sum of export allowance and actual microgrid power demand.
The switching designer describes it as follows:
“The single line diagram (Appendix 2) depicts the entire essence of the switching system and how energy will be diverted from flowing to the grid, to flowing to the on site horticultural loads. At present, the wind turbine is simply connected to the grid connection. In the above single diagram, "Point B" (the wind turbine), is simply connected to "Point A" (the grid connection). All other elements on the proposed single line diagram do not yet exists. At present, all energy produced by the wind turbine has no choice but to flow to the grid (Point B to Point A and onto the grid)
The proposed single diagram introduces some new 11 kV switchgear, transformer, low voltage (400 volt) loads and a switching system to provide an alternative route for the energy from the wind turbine.
The principle functions of the main components are as follows; 11 kV switchgear - Provides a "tapping off point" for power between the turbine and the grid connection. As both the turbine and the grid connection operate at 11 kV, then any tap off also needs to operate at 11 kV. Due to the power levels involved, it is not feasible to tap off power at the low voltage side of the turbine transformer. 11 kV to 400V transformer - This steps the power being tapped off down to 400 V which can then be readily switched and used by standard industrial heating and lighting equipment in the horticultural project. Low voltage distribution and switching equipment (The 800A Panelboard) - Standard industrial distribution equipment that allows for the safe distribution of LV supplies to the horticultural loads Control system - Represented by the dashed lines on the single line diagram - Measures power flow at several key points and operates the low voltage horticultural loads to pick up the turbine energy at times of grid curtailment. Feed in tariff metering - At present, the FiT metering is combined with the export metering at the grid connection point. This metering is owned and operated by the sites meter operator. The single line diagram shows new FiT metering at the turbine output point, where power flows into the 11 kV switchgear. This metering is connected at 11 kV, hence the requirement for the Voltage Transformers (VT's) and Current Transformer (CT's) to safely step down the 11 kV to be metered. The final component shown on the single line diagram is within the clouded area, and this shows a potential future 11 kV circuit breaker to feed potential other future supplies. A hydrogen generator has been briefly mention, but is outwith the scope of this project. The single line diagram and the design acknowledge this potential for future expansion by utilising "extensible" 11 kV switchgear. In essence, this means that the switchgear can be expanded in the future if required, by bolting on additional components to create additional 11 kV circuits. By comparison "non- extensible" switchgear is fixed and cannot be added to.
The single line diagram shows how simple the system required is. Effectively, the load controller monitors power flow to the grid, along with power flow from the turbine. It also monitors the permitted generation signal from SSE's ANM system. If the ANM signal is "high" (900 kW, un restricted), then the load control system will allow all turbine energy to flow to the grid, by turning off all non essential horticultural loads. If the ANM signal is "low" (<900 kW, restricted or curtailed), the load controller will progressively turn on horticultural loads until the requirements of the curtailment are met. For example, if the curtailment signal is 450 kW, and the turbine is producing 600 kW, the load controller will turn on 150 kW of horticultural load to bring the export down to the required 450 kW. In the event that the required curtailment level can not be attained using all the available horticultural load, then the load controller will command the turbine to reduce its power output. Again, for example, the curtailment demand is 0 kW (no power to be produced to the grid), the turbine is producing 900 kW and the maximum available horticultural load is 400 kW, then the load controller will command the turbine to reduce its power output to 400 kW”. Bryan Rendall
Part 4: Technical Viability The switching designer comments on the viability of the switching design as follows: “The concept of load balancing is well established. Ever since the earliest days of power generation, there has been a requirement to match load and generation at any one point in time. Load balancing on the National Grid is a complex discussion topic, but a much simpler historical version was seen on the island of Foula in Shetland in the 1980's. There, an innovative off grid system was constructed comprising a 60 kW wind turbine, a 25 kW hydro turbine and centralised diesel generation, with a 3.3 kV distribution system to the properties on Foula. Being off grid, generation always had to meet demand, and this was accomplished in the case of the wind turbine, by sending signals around the system to turn on loads in the island properties. At the time, the primary "diversion" loads were storage heaters located in each property. If there was a surplus of energy, the load controller turned on the storage heaters in the properties. When the wind fell, and there was no longer a surplus of energy, the storage heaters were turned off.
Closer to home, and more recently, a number of community owned micro turbines in Orkney were installed in the early to mid 2000's where there were a number of grid constraints that prevented their output being exported to the rid. Even though these turbines may only have been of around 6 kW in power rating, the concept remained the same, and systems were designed and built that did the same as in Foula - When the wind increased, more energy was put into heating - When the wind died down again, less was put to heating. Some of these systems have been successfully operating for more than 10 years now.
On the ERE project, the philosophy is exactly the same as these examples. The only difference is that the numbers are bigger - The turbine can produce up to 900 kW, and the horticultural loads can consume up to 400 kW. The "maths" that the load controller has to do is exactly the same, and its simply controlling bigger loads.
The equipment required to effect the load diversion is based on completely standard industrial equipment. The load controller will be a standard industrial PLC (Programmable Logic Controller ) - Effectively a very simplified industrial computer that runs a very basic software (unlike Windows and other complex systems) for reliability, that carries out the monitoring, the decision making, and the commanding. It addition, it will provide data to the outside world for external monitoring purposes. The power equipment is similarly standard, and we have intentionally avoided over complexity in order to make the project as cost effective as possible, and also to ensure that maintainability is as simple as possible. Signalling between devices has been intentionally kept as a very traditional analogue current loop. This signalling protocol has been around for decades, and is extremely simple, effective and reliable.
In summary, both the concept of the load switching, and the hardware that will be used to do it are based on methods and equipment that have been around for decades”. Bryan Rendall
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A provision has been made in the revised single line diagram to allow for the potential for an additional feed to a hydrogen electrolyser. However, the scope of the switching design carried out is limited to the horticultural project. It is envisaged were the electrolyser to go ahead, that this will require an additional switching design at or near to the electrolyser site comprising multiple inputs (tidal generators and wind generators) and two grid systems. Eday Renewable Energy Board 27 March 2015
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Appendix 1: See attached file
Appendix 2: see attached file.