Learnings
Outcomes
Internal UKPN Engineering Technical Specification for Mobile Hybrid Generation has been drafted and is due to be updated to include lessons learned from the outcomes of the Cleaner Engines Project.
Specific technical specifications were drafted for the three different types of hybrid generators:
• Key Technical Requirements and Statement of Conformance for HVO hybrid generation
• Key Technical Requirements and Statement of Conformance for glycerine hybrid generation
• Key Technical Requirements and Statement of Conformance for LPG hybrid generation
Technical designs and operational procedures were completed by the suppliers for the HVO and LPG alternatively fuelled hybrid generators. The technical designs and operational procedures for the glycerine generator at the time of writing this report are going through the process of being finalised and signed off.
The environmental performance of each of the generators was compared by means of an emissions test conducted by Imperial College London’s centre for low emissions construction.
Storage and handling procedures were reviewed, and solutions were put in place to allow for the testing of the three generators produced by this project.
A high-level CBA shows that despite the higher capital cost the lifetime cost of operating alternative fuelled HVO hybrids is economic.
Two hybrid generators running on HVO fuel were designed, constructed, emissions tested and deployed in the field.
Two hybrid generators running on LPG fuel were designed and constructed and emissions tested. Practical operational considerations led to these units not being tested in the field.
Two hybrid generators running on glycerine fuel were designed, constructed, and emissions tested. These units have not yet been deployed on the network due to ongoing improvement works including optimised fuel efficiency and enhanced reliability but there are plans to evaluate their use in the field post the closure of this innovation project.
Outcomes:
· Of the three alternative fuel sources HVO was identified as the most suitable alternative fuel to replace diesel fuel currently used in temporary power generation.
· A comprehensive set of lessons learned has been developed and detailed in Section 6 of this document which will help inform other DNOs on their transition away from standard diesel temporary generation.
· The benefits of hybrid generators over traditional generators have been evidenced and include the following:
o Quiet operation overnight on battery supply
o Reduced noise output as the generator runs intermittently to recharge the battery pack as required
o Reduced emissions as when the generators are run they operate at close to 100% load and charge the battery pack which offers improved emissions performance when compared to operation at lower load points.
o CO2 emissions (g/kWh) from a diesel generator were tested and were shown to drop by 18% when the unit was run at 25% and 100% load comparatively.
o NOx emissions (g/kWh) from a diesel generator were tested and were shown to drop by 19.2% when the unit was run at 25% and 100% load comparatively.
o Reduced generator run time as a result of hybrid operation means regular services are required less frequently.
Lessons Learnt
Overall lessons learned:
· Reduced noise during operation of the generators especially overnight due to running form the battery pack has been well received by customers.
· Silent operation of the hybrid units when operating via battery supply meant operational warning lights were required to be installed to notify operatives that the unit was supplying electricity even without making noise.
· Key operated emergency stop buttons were installed on the HVO and glycerine generator units which stopped the operation of both the generator and the battery inverter. The idea behind the key operated emergency stop ensured only a qualified operative would be able to restart the unit following the emergency stop button being pressed.
· An online video-based familiarisation package was created to inform users of the hybrid generators about safe operation and considerations in addition to the operation standard non-hybrid generators. Confirmation of the completion of this familiarisation package can be shared with the operator’s manager. This was well received by those who completed the familiarisation package.
· Use of an online portal to remotely check the operating status, GPS location and state of fuel levels in the hybrid generators has been shown to be a very useful addition.
· Settings such as at what state of charge the hybrid battery will be recharged and times to charge the batteries to full capacity, e.g., in the evening before operation overnight, can be adjusted as required from the online portal.
· Use of a hybrid battery and generator in parallel set up allows for the unit to handle large inrush currents on startup allowing for a much smaller generator output to be specified. Historically diesel generators have had to be over sized in their power output to handle this large inrush current.
· Trailer certification is an important step in the acceptance of any mobile generator. It is important that future projects consider the early input of the relevant transport departments to approve the use of the trailers used.
Lessons learned LPG generator:
· The LPG cylinders used were found to freeze over during use meaning the unit would cease operation after a short period of time. An attempt to rectify this issue was made by reducing the power output of the generator however this still resulted in this issue occurring. The conclusion being that the 4.7kg LPG cylinders used were not capable of outputting sufficient power to the generator. The initially proposed 13kg cylinder size (gross weight in excess of 25kg) were flagged by the Health and Safety team as not being suitable for use as the weight of the cylinder and the gas stored within would exceed the safe workplace lifting limit.
· There was no suitable method found to accurately measure the state of fuel levels in the LPG generator leading field teams to be unsure about deploying the unit on customer faults without being notified of when gas would need to be refuelled.
· The LPG cylinders carry a greater risk in their operation due to the highly flammable nature of the fuel source.
· Feedback from field staff was that due to separate generator and inverter systems operation is complex and there is a need for an easy to use interface to ensure adoption into BAU.
Lessons learned glycerine generator:
· Glycerine is a denser liquid than diesel, 1.26 kg/litre vs. 0.838 kg/litre. Glycerine also has a much higher viscosity than diesel especially at low ambient temperatures. Over the course of the project, it was found that a high-pressure pump would need to be used in order to allow for the generators to be refuelled.
· Supply chains for glycerine are not well established and it was decided that the most suitable purchasing solution at the time of the project was to buy Intermediate bulk containers (IBC) of Glycerine which have a volume of 1,000 litres or five full refuelling cycles of the glycerine generator (tank size is 200 litres).
· The operation of the glycerine generator as built for the project requires the use of three separate liquids which adds an additional operational and refuelling consideration. The liquids required are HVO, for the start up of the generator, AdBlue to reduce NOx emissions of exhaust gases, as well as glycerine for the main operation of the generator itself.
· Additional lessons learned relating to the glycerine hybrid generator following a demonstration of the unit to operational staff, area managers, transport, and safety representatives were implemented as follows:
o Wiring from rooftop solar panels boxed in to avoid catching tree branches
o Denser mesh fitted to air intake grill to prevent birds nesting
o CCTV security monitoring camera installed
o Updated warning labelling and clearer instructions for operatives
o Warning lights installed to indicate when unit was feeding live electricity and warning labelling to the same effect.
o Installation of key operated emergency stop button to shut down the generator and inverter output.
o Location of earth connection point in accessible location on trailer frame.
o Weighbridge results showing even weight distribution across both axles and total unit weigh below maximum limit.
o Removal of rear trailer bed plate to allow for easier routing of cables from the generator to the customer to be connected.
o Addition of labels to the unit to not stand on the trailer
o Main output breaker moved to more accessible location on rear control panel to allow for easier resetting of the unit in the event of a trip
Lessons Learned HVO generator:
· The conversion of an existing diesel generator to run on HVO has been proved to be possible, however fuel filters were found to need to be replaced repeatedly at the start of operation of the unit as the HVO was found to strip carbon deposits built up inside the engine.
· The diesel generators selected for conversion to run on HVO were small and have a low power output and difficulty in manoeuvring as they were on non-road towable. This needs to be considered in detail for BAU adoption.
· Tailpipe emissions testing between HVO and diesel in the same generator set showed small emissions improvements, depending on the source of the HVO the net lifetime emissions can be shown to be lower due to offsets in reproposing waste oils for example. It should be noted that care must be taken in order to ensure that the HVO supply chain can be verified and does not contain palm oil for example. Suitable suppliers must be selected with transparency over their supply chain.
· If the HVO fuel tank is filled with diesel by mistake the generator will still operate as the two fuels are fully miscible. There is no requirement to clean or discharge the fuel prior to refilling with HVO.
· Significant price variability of HVO observed during the course of the project has been a cause for some concern over the cost benefits offered by HVO. The price of HVO increased as a result of the recent energy crisis and appear to be returning to a reasonably stable level at the time of closure of this project.
· A dedicated cable storage box was added to the HVO generator to safely and securely store cables required for connecting the generator to supply homes during outages. This was found to be of great benefit to field staff.
Other lessons learned to inform future projects:
· Interlocked electrical output connections should be used as an additional safety measure for operators.
· A list of required warning and instructional labelling has been developed and is recommended for use in other projects.
· Storage boxes to house and safely store connections leads should be included in generator scopes.
· From the emissions testing it can be observed that operation of generators to EU nonroad emissions standard Stage V will have a dramatic effect when compared to older Stage III-A generators. Updated emissions standards require exhaust gas aftertreatment.
