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A breakdown of the main system components required to build a stand-alone power system and their costs is given in Table 11-1. The renewable energy generators had been previously installed and their cost is from the time of their installation. This has been a developmental project requiring bespoke and non-standard components, some of which have been expensive.

Item Cost (£’000) Percentage cost

Wind turbines 50 5.2%

Solar PV 60 6.2%

Hydro turbines 67 7.0%

TOTEM CHP unit 5 0.5%

Hydrogen storage system

Electrolyser 140 14.5%

Hydrogen store*rental at £4k per quarter 50 5.2%

Pipe work (including compressor) 70 7.3%

Fuel cells*One unit rental for 2yrs, one unit bought 50 5.2%

Building 260 27.0%

Electrical interconnection system

Inverter drives 60 6.2%

DC-DC converters* 7 x 2kW units 35 3.6%

Zebra battery 18 1.9%

DAQ and control system 5 0.5%

Total 960 100%

Table 11-1. Project costs.

11.2.1 Comparison with current stand-alone solutions

At present, the majority of stand-alone power systems in use around the world are based upon diesel generators. Due to their mass production and standardisation, they are very low cost, in the region of £200 to £500 per kW [116]. The total cost of the diesel fuel and its transportation varies greatly depending upon the location and is a major factor in any economic comparison, as this cost is likely to rise in the future.

A system based upon a 30kW diesel generator supplying an average load of 2.5kW for twenty years would have a capital cost in the region of £15,000 to £20,000 and fuel costs of approximately £40,000 at £1 per litre [64] assuming no price increases. Obviously, this is much lower than the total system cost of this project, at

approximately £960,000, although it is important to note the likely rise in diesel fuel cost and the considerable room for cost reduction. Other factors to take into account are environmental benefits of reducing diesel consumption and the maintenance requirements, although the maintenance may be similar with both systems due to the complexity. The building is a large percentage of the system cost and this could be greatly reduced if an existing or more basic building was used.

11.2.2 Comparison with AC system

The DC electrical integration components constituted 19% of the overall costs and specialist DC connection equipment, such as 750V DC rated breakers and

contactors, were required. Within the electrical integration components, the cost of this equipment is proportionally high. The cost of the DC-DC converters is relatively high as these units were bespoke units.

An AC interconnection system, as presented in section 4.1.1, would still require the majority of the system components required for this DC system, with differences including:

• The solar and fuel cell converters would be DC to AC inverters, although with similar costs to the converters presented here.

• The electrolyser was supplied ready to connect to an AC grid and would require no additional converter.

• Some of the AC loads would require power electronics to perform a soft-start, such as the heat pump, so a number of drives may still be required.

• The hydro system was supplied to connect to a 120V DC battery bank and would therefore require some additional power conversion.

• The AC system would not require the Zebra battery, the majority of the drives nor the DC interconnection equipment.

• Some form of additional dump load or flywheel storage may also be required. AC equipment is standard and, although a similar amount of equipment is required, it is estimated, at present, a similar system based upon an AC interconnection would be less expensive. However, such a system may have power quality problems, and some form of fast acting storage or back-up generation is likely to be required.

11.2.3 Comparison of storage systems

Table 11-2 shows a comparison between the two storage technologies used and the lead acid battery, which is typically used for energy storage at present. The cost of a 4.5 MWh storage system, the same size to that installed at West Beacon Farm, is given for comparison. The incremental cost of adding additional storage capacity is also given. This is lower in the case of the hydrogen system, as the bulk of the system is installed and only additional gas tanks must be purchased. These figures are approximate and based upon the system costs for this developmental project, so are likely to be higher than longer-term predictions.

Technology Approximate system cost

(£/kWh)

Capital cost for 4.5MWh storage (£) Incremental storage capacity cost (£/kWh) Lead-acid battery 40 180000 40 Zebra battery 900 4050000 900

Hydrogen storage system 70 315000 11

Table 11-2. Storage cost comparison.

It is difficult to make comparisons of storage technologies, the main problem being that the storage time is not taken into account, as discussed in section 2.2.3. Even though a lead-acid battery bank may have a lower capital cost for the same size store as a hydrogen system, it would suffer from self-discharge and would not be able to store energy inter-seasonally.

Due to the low incremental cost of hydrogen storage systems, a hydrogen store becomes more economic than using lead-acid batteries at a certain size, which ought to decrease as the technology is developed.

The Zebra battery figure is very high, as the unit was specially commissioned and cost approximately twice that of a standard ‘off the shelf’ Zebra battery. There is significant room for cost reduction with the Zebra battery technology.

11.2.4 Summary of economic analysis

This is a developmental system and, to a certain extent, the cost of the equipment has been a less critical factor. When compared to a fossil fuel based system it is not economic, but in the long-term, it is highly probable that this will change. Now the system has been installed, the main areas for cost reduction can be investigated, including:

• Electrolysers • Fuel cells

• DC-DC step-up converters • DC contactors and breakers • Battery technology

It is expected that, with mass production and standardisation, there is great potential for cost reduction within these areas.