Renewable energy technologies

Electricity and CHP I Wind farms

Three large private wind farms exist within and just outside the city boundary (Fig. 38) and others are planned. The 37 MW Phase 1 of the Tararua wind farm, located 12 kms to the west of the city on the plains, was completed in 1999. It has since been extended to over 140 MW as the site on the Tararua Ranges has an exceptional mean annual wind speed of over 10 m/s and a 45% capacity factor is typical for each turbine. No government subsidies are available in New Zealand, but carbon credits, sold to the Dutch government even before the Kyoto Protocol came into force by at least one of these wind farm developers, help the revenue stream. The total electricity demand of Palmerston North city in 2008 (560 GWh /yr), plus the neighbouring districts (240 GWh /yr), was exceeded by all the local wind farms when over 850 GWh was generated in the region that same year. Power from the first Tararua wind farm constructed in 1999 enters directly to the city distribution system, whereas power from the wind farms constructed afterwards is exported to the grid.

Figure 38 • The 1.5 MW turbines of the 120 MW Te Apiti wind farm under construction (left)

and in the foreground (right) are just outside of the Palmerston North city boundary (delineated by the Manawatu Gorge shown by the rising mist). Within the boundary are the original 660 kW turbines of the Tararua wind farm and the 31 recently added 3 MW turbines (seen on the plateau across the gorge). The urban city centre is located 12 km away to the right of the photo, down on the plains

Figure 38 • The 1.5 MW turbines of the 120 MW Te Apiti wind farm under construction (left)

and in the foreground (right) are just outside of the Palmerston North city boundary (delineated by the Manawatu Gorge shown by the rising mist). Within the boundary are the original 660 kW turbines of the Tararua wind farm and the 31 recently added 3 MW turbines (seen on the plateau across the gorge). The urban city centre is located 12 km away to the right of the photo, down on the plains

Photo credits: Ralph Sims (left); Phil Murray (right).


Due to the concentration of wind turbines on the hills overlooking the city, there has been growing resistance to further developments. The City Council, based on local experience, made a submission in 2008 to the government's proposed "National Policy Statement for Renewable Electricity Generation". Of the several points made, those most relevant to the city's policies were as follows.

• The benefits of renewable energy are evident. It is the potential, cumulative and actual effects of the development of renewable projects that causes the most debate at the local level.

• Consideration needs to be given to changing the construction of wind masts to monitor local wind conditions as a permitted activity or keeping it as a restricted discretionary activity to be judged on a case-by-case basis.

• In terms of small-scale wind turbines likely to become more popular in the future, it is very difficult to enable or provide for such activities within local planning documents without having a fundamental understanding of how they might actually eventuate and what their real effects on the surrounding environment might be.

Having gained experience from observations of wind farm developments in the region, the city is now undertaking its own development of a 360 MW wind farm in partnership with the state-owned power generation utility, Mighty River Power. To be constructed partly on city-owned reserve land that is covered with native forest and within the water catchment area, the Turitea wind farm proposal has become somewhat controversial. Some of the proposed 122 turbines, each up to 125 m tall and 3.5 MW capacity, will be clearly visible on the hills just 10 km from the city centre. If the project proceeds, city residents will benefit from the revenue earned from leasing the land and would gain access to the "Ecopark" reserve for recreational purposes that is currently prohibited. Some neighbouring landowners are keen to see the wind farm expanded outside of the reserve land boundaries and others are agreeable to grant access over their land for roads and power lines. If this wind farm is granted approval, then virtually all of the 20 km of plateau land running along the tops of the Tararua ranges that is within the city boundary will have received a wind farm consent.

I Landfill gas

Although the original city landfill site is now closed, it continues to produce methane gas. This has been collected for the past four years for heat and power generation. The site has since been transformed into a track for mountain bikers and an industrial recycling centre (opened by the Prime Minister in 2007) aiming to increase the waste recycling rate from 30% to 50%. At present the Awapuni Landfill Gas-to-Electricity Project has 17 active gas wells drilled to collect the methane, which is then combusted in an engine driving a generating set to power the wastewater treatment plant and the operations of the Awapuni Resource Recovery Centre on the former landfill. Any additional electricity is sold to the national grid. If test wells prove that sufficient methane is present, eight further wells will be drilled and connected to a new gas engine/generator to be co-located alongside the existing 1 MW generator. This should virtually double the present generation capacity. The Council budgeted around USD 80 000 for the generator, well drilling, pipe installation and the electrical work. To achieve a financial return from the second generator, the Council also intends to offer carbon credits for sale.

Currently, when running at full capacity, around 35 000 carbon credits per year are produced (one credit equating to 1 t CO , , emissions avoided). The credits were awarded to the council no 2 equivalent '

by the New Zealand Government Climate Control Office following auditing and verification by an internationally certified authority. They can then be sold on national or international markets. As this is outside of a planned national emissions trading scheme, (under review by the new government), initial sales of 149 000 carbon credits were made by the city through the Chicago Climate Exchange to the Austrian Government in 2006 for around EUR 600 000. Around 30% of the total was paid by the Austrian government initially, with the balance to be paid on delivery of the credits during the

first commitment period from 2008 until 2012. This agreement was made prior to the ratification of the Kyoto Protocol. A further 5 540 credits have been sold privately to Toyota New Zealand, whose head office is based in the city. Toyota's aim is to offset emissions from their business operations in order to become carbon neutral, with the revenue going towards the benefits of the local community. A carbon credit supply agreement is under negotiation for future years that could see Toyota help fund the landfill site development. The consultants Carbon Market Solutions and TBL Solutions assisted the council with the deal. One thousand credits have also been sold to the airline Virgin Blue and others sold over the internet on "Trade me".

■ Wastewater treatment plant biogas

For several years, the City Council has collected and then flared the methane gas produced from anaerobic digesters that are part of the process treatment at the wastewater treatment plant. In many similar plants the gas is used to generate electricity for use on-site. One proposal was to instead pipe the methane gas to the gas engine/generators at the landfill site nearby and, in return, receive hot water as a by-product to maintain the temperature of the digesters at the optimum 37oC needed for most efficient activity of the bacteria. However, it was finally decided to locate the second gas engine at the treatment plant instead of at the landfill alongside the first engine.

Gas feeder pipes have been laid to supply this second gas engine that will generate electricity using the biogas produced by the plant's sludge digesters. Since the existing landfill gas plant output will reduce over time as the site depletes, the electricity produced from the sludge feedstock used in the new system will eventually take its place. The gas digesters built at the treatment plant about 40 years ago will be extensively refurbished to maximise the gas production potential and will provide spare capacity to meet further growth of the population.

Heat from the engine will be recovered to maintain the digesters to an efficient 37oC. The power generated will be used locally with any excess exported to the local network. The total operational output of the two gas plants together will be able to meet about 75% of the council's in-house power demand. When fully operational, the project is expected to generate an initial surplus of around USD 50 000 annually, with a total revenue earned for the council of USD 4 million over a 20 year period. Plans are being made in association with Massey University researchers to significantly expand the biogas plant capacity and import more organic feedstocks from around the locality.

The Council's mini hydro station was initially proposed by a local Massey University student who realised the potential for using the twin dams at the city's water supply reservoir to also generate some power. She calculated how much power could be generated by the water passing through the dam outlet pipe. The cheapest design option was to use four pumps, acting in reverse, as motors to drive four 150 kW generators. The project was commissioned in 2002 and has since provided sufficient electricity to operate the nearby water treatment plant with any excess power being sold to the national grid to earn revenue. This has helped reduce the GHG emissions from the water treatment plant from around 95 tCO2 to 17 tCO2/yr. It is now proposed to install an additional dedicated turbine for USD 150 000 which will supplement the four existing motors and generate power using the water held behind the upper dam. The four motors will then be used to generate electricity from the excess water that currently spills over the dam in wet weather (Fig. 17, page 72). More effective utilisation of the hydro scheme should result and additional revenue made for the city through the sale of excess power.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

Get My Free Ebook

Post a comment