Remote Area Power Systems in New Zealand David MacKay New Zealand lies in the south west corner of the Pacific Ocean and is situated between 35¡ and 45¡ South latitude. The sub-tropical land, about the size of California, with 3 million people, has a significant proportion of remote areas. Despite the extensive mains power development in New Zealand there is a considerable need for independent power systems in isolated areas. With favorable climate conditions, the development of wind technology for Remote Area Power Systems in New Zealand is well advanced. A wealth of experience has been obtained in system design and installation for home power including the use of solar, photovoltaics, batteries, inverters, microhydro, and low energy lighting. Discussed here are just a few of the things that have been happening in New Zealand. When a place is a little bit out of the main stream, development and innovation can sometimes go off on a tangent from industry norm. There are not so many guidelines to work from and integrity can take its own undirected path and often come up with some exciting stuff. HYBRID WIND SOLAR SYSTEMS The ability to provide continuity of power is an important objective in the design of Remote Area Power Systems (RAPS). This is not easy when relying on natural elements which are variable and at times fickle. Wind power is subject to calm spells which, even in a windy area, may last several weeks, while reasonably cost effective storage batteries provide only 4-5 days supply at low consumption. Similarly solar power is subject to low output for considerable periods, particularly in winter. A GOOD PAIR Wind and solar energy inherently go together. It is the warming of the earths surface by the sun that creates the wind in the first place. A combination of wind and solar energy is effective in providing the sought after continuity of power supply in RAPS applications. FILLING IN THE GAPS In a hybrid Wind/Solar system, the large gaps in supply from a given source are offset by output from the other source. Reliance is spread between the two elements. In particular, wind systems have a high output producing large amounts of power but suffer from long gaps, while solar output, though more costly per peak watt than wind, has more even production which tends to be higher in calm weather. The overall supply of a hybrid system relates nicely to the variable nature of demand, allowing for high peak use, but maintaining reliability for lower continual use. For example, in a domestic situation uses tend to be spread between intermittent heavy ones - such as domestic appliances, vacuum cleaners and power tools - and continuous lighter uses - such as lighting, refrigeration, television, and stereo. Large power inputs from wind can be drawn upon for heavy loads while the smaller more even solar production improves supply for the lighter loads. QUESTIONS To what extent does the availability of power actually improve with a hybrid system? What are the economics of a wind/solar hybrid system? ANSWERS FROM THE UNIVERSITY OF AUCKLAND These questions have been discussed in a study carried out by C.C. King, University of Auckland in 1984/85. A Soma 300 watt wind generator, a solar tracking device incorporating two Solar Wind 24 watt panels, and Lucas 12 Volt, 80 Ampere-hour deep hour cycle batteries were used. Various combinations of solar input and battery size were evaluated. A detailed computer simulation was undertaken to test the cost efficiency of the system. Hourly records of sunlight and windspeed/direction were obtained from the Auckland Meterological office, covering the entire year from April 1984 to March 1985. These were then processed to simulate the actual site of the system (a more exposed site with a hill obstructing the south). A further simulation was made of charging characteristics of various sizes of battery banks under various combinations of wind and solar output (wind alone, wind and 1 or 2 solar tracking devices). These simulations were made at different continuous demand levels. The combined solar/wind system had only one complete charge-discharge cycle while wind alone had nine. Since battery replacement is a significant maintenance cost factor, reduced battery wear is an important advantage. An estimate was made of the days lost in the year for four systems (wind and wind/solar were tested with both 160 and 480 amp hours storage). The wind/solar system out performed the system using larger battery storage alone. A cost effectiveness study was then undertaken by taking the costs of components and dividing them by the maximum sustained drain without loss of days. The sustained drain was measured both over the whole year and over periods of higher output. Component costs, system performance and cost effectiveness are shown in the graph below. These values indicate that a balanced wind/solar system with good storage actually doubles the cost-efficiency of production. Although the initial expense is higher, a hybrid system provides greater continuity of power supply at a lower cost per watt hour. INSERT TABLE AND CHART The Soma Wind Generator New Zealand's connection with California isn't one of size alone. For 12 years a native of Santa Barbara, CA has been building wind generators here in New Zealand. Harold Ward sailed his 40 foot yacht across the Pacific to New Zealand in the years 1975-1977. Locals were soon to see the merits of the prototype wind generator he had built for his yacht and, one thing leading to another, "Wardy" began commercially building the machines in 1978. Soma Power Ltd. is now a well established company in Auckland manufacturing wind generators. The demand for wind generators through the early years was only just enough to keep one man in business, though it provided the experience to make the wind generator. As a result many 12 year old units are out there, testing the durability of the designs. Development has been centered around the original alternator configuration of 12 or 24 poles of copper windings set around the central stationary aluminum stator housing. The appropriate number of ceramic ferrite magnets are set in an aluminum hub which rotates around the outside of the stator. Using this number of poles allows power output from the alternator at lower RPM than, say, a 4 pole automotive type alternator. As with all alternators there are no carbon brushes to wear out and replace. The alternator is directly driven and the 3 blades on the Soma windmill are in fact bolted on to the face of the alternator hub. This is an extremely secure method of attachment with the hub having been designed to both take the blades and contain the magnets. INSERT ALTERNATOR DIAGRAM The Real Advantage The real advantage of building the alternator from the ground up, in house, is that we can choose the materials for wind generator use and abuse. Corrosion resistant alloys are used for the stator and hub housings. The stator is completely encapsulated in high temperature epoxy resin. Copper windings can be varied in size to optimize output in relation to the blade characteristics and swept area. The blades and alternator are in effect "tuned" to go together. Earlier Days In the earlier days the blades feathered by way of centrifugal flyball type governor weights. It worked well and certainly looked very technological but was time consuming to produce and the number of parts involved added to the risk of mechanical failure. Now, by bolting the blades directly on to the face of the alternator hub, there is a robustness that is instinctively appealing. Regulation Regulation in high winds is now obtained by allowing the complete rotor to tilt upwards out of the wind reducing swept area presented to the wind. There is a gyration effect to consider with this type of regulation and the first prototypes would fly back or slam back down if a wind gust coincided with a change in wind direction. By placing a shock absorber on the tilt back mechanism the action is dampened and the windmill has a gentle tilting motion. Two weighted legs set at 45¡ to vertical enhance feathering through the first 45¡ of tilt and retard it through the reminder of the arc acting as counterbalance weights to bring the machine back to face the wind when the wind dies down. INSERT Wind machine foldback diagram Blades Soma windmills have always, since day one, had fiberglass blades. Although the exact laminations and concentrations of unidirectional fiber have changed, the process of manufacture remains the same. The blades are hollow molded with an outer fiberglass skin over a high proportion of unidirectional fibers running up the leading and trailing edges. Consistency in manufacturing for both shape and elasticity is an important advantage of fiberglass. The effect on performance of a blade that has warped is quite dramatic as is the effect of blades that twist or bend in a non-uniform manner while under load. Stainless steel tape protects the leading edge from long term erosion. The Soma 300 watt machine has 0.8 meter blades (1.7 meter diameter). INSERT Blade Art The alternator and blades are bolted to a galvanized steel swivel assembly which incorporates the tilt back mechanism and the tail vane. The swivel turns inside the top of a length of 3 inch galvanized pipe with "Ertalyte" self lubricating nylon bushings. This is a tough, low wearing material, especially effective for the low work rate experienced with windmill yaw. SEE PHOTO TOWERS The most common towers used with the Soma windmills are wooden telegraph poles. A 6 foot length of pipe is U-bolted to the 8 inch diameter top end of the pole. These towers are readily available in most places, are cheap, and provide the ideal medium for home built installations. Complete instructions for building this type of tower are included in the installation manual. Alternatively, 40 feet of the 3 inch galvanized pipe with guy wires makes a good tower. SAFETY Provision to shut the windmill down, and then to be able to restart it, from the ground, has been an important consideration for Soma. For safety reasons windmills must have a manual fail safe shut down mechanism (if you have ever seen a windmill out of control you'll know just how frightening it can be). The approach on the Soma machine is for the electrical cable running between the alternator and the ground to double as a shut down pull chord. The mechanically strengthened cable can be pulled from the ground causing the windmill rotor to tilt completely back to horizontal. It is then held in the "off" position by a spring tensioning device at ground level. The machine is turned back on simply by releasing the chord. ELECTRICALLY SPEAKING The 12 or 24 volt 3 phase ac current is rectified in the control panel near the batteries. The amount of charge going in to the batteries is regulated by the voltage sensitive circuitry in the control panel. An amp meter gives a visual indication of the charge rate and when the batteries are fully charged the current is directed into a wire wound resistor dummy load which absorbs the excess power and keeps the wind generator fully loaded. Rated at the recognized standard windspeed of 10 ms or 23 mph the Soma F.P. 300 will deliver 300 watts while charging begins at 8 mph and peak output is 320 watts at 30 mph. The comprehensive installation and maintenance manual provides all of the information necessary for easy installation by the user. A job that will take two people 2 days to complete including building the tower. One might say that Soma Power Ltd. has taken the "tractor" approach rather than the "sports car" approach in its design philosophy. The Soma F.P. 300 weighs in at 60 kg. This rugged toughness and durability has enabled the machine to survive whatever New Zealand winds can throw at it. One thing is for sure, it won't blow away in the wind. Access David MacKay, SOMA Power Ltd., 1/28 Parkway Drive, Mairangi Bay, Auckland, New Zealand. Telephone: (9) 479 1605 or FAX (9) 478 7197.