Smart power farm: wind, solar and hydrogen fuel (a case study)
Clean Power Solutions Ltd (CPSL) developed a trial site that is designed to work on a co-generational installation that uses micro generators to produce renewable energy, but instead of exporting surplus green energy to the grid, the site is designed to store energy as hydrogen using rainwater as a source.
Author(s): Dr Marc Stanton
The co-generational system uses renewable energy from a 48 kWp solar PV array and a 20 kW wind turbine. CPSL are using an Acta Spa electrolyser on the trial site in Cheshire; the electrolyser is producing hydrogen which in turn powers a Giacomini catalytic burner providing heat and domestic hot water. However CPSL are now able to further use this co-generational system to store greater amounts of hydrogen which enables them to use the hydrogen in a hybrid diesel vehicle. Using this information CPSL have created a design that ULEMCo Ltd in Liverpool are collaborating on to provide a whole system energy approach to hydrogen vehicles. The project entails creating a techno-commercial model for assessing the value of balancing the storage of onsite renewably generated hydrogen, located within the curtilage of a commercial building, with integrated storage and then used as fuel for light commercial vehicles.
A large number of wind turbines have completed planning approvals but following this restriction of the G83/G59 connection, cannot be installed. It had become necessary for a system using batteries and a thermal store to be developed but it soon became apparent this would be inadequate due to the large amount of production the wind turbines generate and the limitations of simply providing endless hot water. It was realised that a use for this additional energy was required. The present hydrogen system evolved from this initial work and is now balanced perfectly and provides grid connection facility where the export is directly from the bi-directional inverter and restricted to 16 A per phase as provided for in the Engineering Recommendation G83/2 .
For many locations, there will be more than one form of renewable energy generation such as wind turbines and solar panels or hydro water generation. This is known as co-generation. What was needed was a trial site that was designed to work on a co-generational installation that used micro-generators to produce renewable energy, but instead of exporting surplus green energy to the grid, designed to store energy as hydrogen using rainwater as a source. The co-generational system chosen for the trial site uses renewable energy from a 48 kWp solar photovoltaic (PV) array and a 20 kW wind turbine (Fig 1).
Fig 1: Co-generational system chosen for the trial site
The test site uses an Acta Spa electrolyser on the trial site in Cheshire; the electrolyser is producing hydrogen which in turn powers a Giacomini catalytic burner providing heat and domestic hot water (Fig 2).
Fig 2: Acta Spa electrolyser
The test site has been further developed and now able to further use this co-generational system to store greater amounts of hydrogen which enables them to use the hydrogen in a hybrid diesel vehicle. In Fig 3, Revolve Technologies (R&D partner for ULEMCo Ltd) have illustrated the performance of hydrogen vehicles.
Fig 3: Performance of hydrogen vehicles
Using this information Clean Power Solutions Ltd (CPSL) have created a design that ULEMCo Ltd in Liverpool are collaborating on to provide a whole system energy approach to hydrogen vehicles. The project entails creating a techno-commercial model for assessing the value of balancing the storage of onsite renewably generated hydrogen, located within the curtilage of a commercial building, with integrated storage and then used as fuel for light commercial vehicles (Fig 4).
Fig 4: Techno-commercial model for assessing the value of balancing the storage of onsite renewably generated hydrogen
NB: Revolve have recently advised, based on averages and for illustration purposes only, that the easiest estimate to convert H 2 into a diesel equivalent, would be 1 kg of H2=4 L diesel. So, however far you can travel on 4 L of diesel is how far you will travel on a kg of H2 . This is with a diesel/hydrogen hybrid vehicle, a pure hydrogen fuel cell vehicle will exceed this.
The Cheshire test site was originally designed to enhance the performance of micro, co-generation of the available renewable energy production. The site was designed to substantially reduce the cost of grid connection and ease the current demands on the high-voltage grid network. This can be important during times of high production and low demand, due to the growth in embedded generation from grid tied renewable sources.
Concentrating on the renewable sector of 15–250 kW production, commonly found in agricultural and commercial single applications, the system will work equally well in single, split and three-phase installations.
A 48 kWp PV system and a 20 kW wind turbine were installed at a location with a 6.0 m/s average wind speed. The power generated is often not at the times of demand and so surplus green energy would ordinarily be exported to the grid at a greatly reduced income, whilst when required on demand there may be little generated renewable energy available and so the site would be paying the peak tariff. The trial site provides energy to small industrial units as well as a farm house and a bed and breakfast annex.
The test site took the approach to first examine the annual use of the site in both electricity and heat demand and match the production accordingly. This negated the need for a grid upgrade as there would be no export above 16 A per phase, which is currently allowed under engineering recommendation G83/2 .
A 20 kW wind turbine installed at a location with a 6.5 m/s average wind speed will produce ∼72,000 kW of generated power per annum . So the design had to incorporate a system to provisionally store excess energy prior to sending it to the electrolyser. However, one of the main reasons for choosing the Acta Spa electrolyser was due to the fact that it could deal with the ‘spikes’ of renewably generated energy from a wind turbine.
Principle of design
Production is measured by the energy management system (EMMA) along with the demand from the batteries at any time by the two current transducers located in the circuit. The site electricity demand is met from the renewables and supported by batteries via a synthetic grid. The voltage transducer records the battery condition and signals EMMA. When the batteries reach a 90% charge, export at 16 A begins via a G83/2 certificated inverter and remains until the batteries drop to 80%.
If the batteries drop below 20% (in times of low wind or lack of sunlight for more than a day), power is drawn from the grid to recharge the batteries back to 50% capacity.
When the batteries are at 90% and exporting, power is sent, via SSR’s in 5 kW bytes to the electrolyser. The electrolyser produces, from rainwater using 5 kW of generated power, 2.1 kg of hydrogen per day, this is stored in the hydrogen tank at 30 bar pressure for use in a Giacomini hydrogen catalytic burner when required (Fig 5). The data in Fig 5 are from test site showing current profile.
Fig 5: Data from test site showing current profile
By adopting this system, the site demands are fully met in terms of electricity and heat by the renewable generation, and the hydrogen, when used, is a carbon-free heating solution. The number of electrolysers and hydrogen storage facility can be multiplied up as required, with each using maximum 5 kW when available.
The lessons learned during this trial may be scaled up for systems larger than 50 kW. To further enhance the developments of the system, a South Wales Company has been instructed to begin development of a combined heat and power unit using a carbon-free hydrogen powered three cylinder internal combustion engine to drive a generator. The system cost will often be met or significantly contributed towards by the saving in grid connection upgrades whilst the consumer has no requirement for imported power or heat to their site and places no additional strain on the UK high-voltage network.
Hybrid grid tied/off grid hydrogen system can be used with new or existing embedded generators.
On the Cheshire site, the engineers considered a 20 kW wind turbine in a 6.5 m/s wind speed area will produce ∼72,000 kW (total production) of electricity per annum .
The site will consume the same amount over the year, but as a mix of heating and electricity requirement, then much of the electricity will be exported. Additionally, as the wind is a constant variable, much of the electricity will be produced at times of low site demand.
Assuming the wind blows for 70% of the time when there is demand and for 30% of the time there is no production, but the demand remains (Table 1).
site demand electricity per annum
export = total production − consumption
import = consumption − low production
Table 1: Production, consumption and export data
Total renewable energy production consumed on site = 14.5% of production with all heating requirements met by imported oil, propane or natural gas.
The original trial design aimed to meet all the heat and electricity demands of the site utilising the total renewable power produced, by storing as hydrogen and electricity, whilst exporting the maximum allowable without a grid upgrade when the storage facilities are full. The process of hydrogen production is completely carbon free, and the process of heat production via a fuel cell boiler is also carbon free.
This would result in a carbon saving from burning fossil fuels to produce 57,000 kW heat:
- Oil – 14.49 t of carbon per year,
- Propane gas – 12.15 t of carbon per year,
- Natural gas – 11.65 t of carbon per year.
Additionally, it is assumed that the electricity stored and used, rather than drawn from the grid, say over a 12-month period = 4500 kWh.
Then an additional 2.37 t of carbon can be saved.
So to compare the difference between a 20 kW wind turbine used as a standalone unit without a storage system, the annual carbon saving will be 5.51 t.
The same wind turbine with a carbon-free storage system, replacing natural gas for heating and providing all the electricity demand of the site, then the saving will be:11.65 + 2.37 + 5.51 = 19.53 t.
The demands of the property will be met in a sustainable way, with continuity and security of supply for the lifetime of the renewable energy production unit, e.g. 20 years, saving a total over that period of 390.60 t of carbon .
Client savings are derived from Table 2.
electricity 15,000 kWh
at 120p = £1800.00/annum
57,000 kWh at 0.045p = £2565.00/annum
£15,000.00 one off average cost
Table 2: Financial equivalence
Total saving over 20-year period = £102300.00 (no allowance for RPI).
After many months of research and discussion with manufacturers and suppliers, the correct balanced technologies and components for the system has been achieved, with a number of component parts being bespoke designed from existing devices used in other applications. We are confident there are no other comparable technologies being used today that have achieved the same results using an alkaline electrolyser and a catalytic burner. Due to the installation design and management of both the electrolyser and the catalytic burner, the commissioning of pure hydrogen powered combined heat and power plant is also unique to the system. The electrolyser is designed to work with variable power inputs, such as found from renewable sources.
NB: The example relates only to 20 kW of renewable production. The carbon-free storage system can be ‘up-scaled’ to any size of generation to meet on site demand.
The hydrogen produced from rainwater, using this method, is 99.997% pure, suitable for the use in hydrogen vehicles, if stored at greater compression, thus providing carbon-free transport. Following monitoring of output over the 12-month period, the trial has been fully operational; results from the test site can confirm the electrolyser produces 200 L of hydrogen per kW of electrical energy used. This is produced consistently across all inputs varying between 1 and 5 kW. The Giacomini boiler consumes 1.67 m 3 hydrogen per hour to provide an output of 5.01 kWt.
The further development and installation of renewable energy will have an effect on the ability of the district network operator’s to accept any connections to the grid in excess of G83 parameters. This will have a concomitant effect on the development of small-scale renewable energy in this country and around the world. The system that has been developed by the CPSL Group have shown that these problems can be overcome and the excess energy; that otherwise would present a problem to the local network can be converted into a more valuable fuel source. The cost of the energy storage and conversion system in many places will be uneconomic. However, a partial installation of just the energy storage system will make financial viability a possibility in more and more locations where grid connection is either refused or the upgrade cost is prohibitive.
Further research though is required into battery technology. Lead acid batteries are not suitable for this type of energy storage, lithium ion batteries are too expensive and the benefits of weight and size are not required in this instance. NiCad batteries are more suitable and there is some interesting development available with salt and flow batteries.
- www.ofgem.gov.uk/sites/default/files/docs/2012/08/er-g83-2-_v5--the-master-09-07-12-inc-ofgem-comments---clean-version_0.pdf, accessed June 2016.
- http://www.afdc.energy.gov/fuels/fuel_comparison_chart.pdf, accessed June 2016.
- http://www.cfgreenenergy.com/cf-20/, accessed June 2016.
- www.forestcredits.org.uk, accessed June 2016.