Generating energy at home

This Issue This is a part of the Energy feature

By - , Build 107

Residential energy generation is an emerging field in New Zealand. We look at the micro-scale technologies available and what the future holds.

Micro-wind turbines typically come in sizes from 0.3 to 20 kW or more. A 2–3 kW unit (4 m diameter rotor) might be used for a home and a 20 kW unit (12 m diameter rotor) on a farm. The tower would be up to 12 m or more tall.
The hill-top test site of a new type of local energy system being developed by Industrial Research Limited. This uses both electricity and hydrogen as energy carriers. Hydrogen is used to transport the wind-generated energy via a 2 km plastic pipe. It can be converted on demand to electricity in a fuel cell or used directly for water heating.

Residential energy generation involves complex technology and will require market change for its growth. Not many technologies are yet competitive with network retail prices, but this is likely to change as grid electricity prices continue to rise. New technologies will also enter the market as they become competitive due to fuel prices skyrocketing.

Technologies and costs

Distributed electricity generation (DG) refers to a wide range of technologies and power ratings up to 30 MW or more (30 MW will supply the average electricity demand of about 30,000 New Zealand homes).

Only micro-scale DG technologies – that are connected within residential premises and are smaller than 10 kW capacity – are covered here. At 100% capacity (continuous full power operation), this is still enough energy to power around 10 homes.

Nominal capacity factors for some common micro-scale technologies are:

  • micro-hydro and engine generators: 100% with year-round water and plentiful fuel
  • micro-wind turbine: 20–30% in a reasonably windy location
  • solar photovoltaic arrays: 10–20% depending on latitude and cloud conditions at the site.

As you move down this list, the energy costs increase for the renewable technologies. Unfortunately, the resource availability in residential areas is in the reverse order.

A good micro-hydro site is competitive with network retail prices now, but photovoltaic energy currently costs two to three times more. As production volumes ramp up (over 30% compound growth per year has occurred for the past decade), photovoltaics will become the clear winner in the near future. Massive uptake of rooftop systems (surface mounted and building integrated) can be expected, but specific orientation and clear view of the sun between at least 9 am and 4 pm is essential for adequate performance.

Micro-wind turbines typically come in sizes from 0.3 to 20 kW or more. A 2–3 kW unit (4 m diameter rotor) might be used for a home and a 20 kW unit (12 m diameter rotor) on a farm. The tower would be up to 12 m or more tall.

The benefit of fuel-based generation is that power can be provided when it is needed, not just when the wind blows or the sun shines. Fuel is now a substantial cost, so efficiency becomes ever more important – particularly where the focus is on energy savings, rather than time of availability. To this end, fuel cell microCHP (combined heat and power) systems are being developed and trialled in a number of countries. These refrigerator-sized appliances are being designed for external locations, like the outside unit of a heat pump, but will eventually be fitted within the building envelope.

Off-grid systems

Most activity in New Zealand at present is in the installation of SAPS (stand-alone power systems). This is mainly though need, rather than choice. If you live more than a few hundred metres from an existing distribution circuit, own-generation may be the most cost-effective option – but it may not be the most convenient. To provide a supply capacity that is taken for granted from the network (say 15–20 kW peak), a relatively large, expensive local generation system costing up to $100,000 could be required, plus there is the ongoing cost of fuel.

There are an increasing number of suppliers with the design, build and installation expertise to provide these solutions. Hybrid systems are now the norm, involving a diesel genset for supply reliability and renewable solar photovoltaics or wind generation with a battery bank for energy storage. An inverter is necessary to produce standard 230 V ac from the dc battery voltage.

As for any engineered system, there are no cheap shortcuts. Reliable solutions need good design and quality products. Codes and standards are available and must be followed.

More information is on the EECA and Sustainable Electricity Association of New Zealand websites ( www.eeca.govt.nz and www.seanz.org.nz).

On-grid systems

Micro-scale distributed generation is in its infancy in New Zealand. The attraction of distributed generation is that no battery is needed – the network replaces this storage function. In practice, electricity storage is not involved, as power injected into the network by local generation travels no further than to a near neighbour. The central power plant is simply required to generate a little less.

Distributed generation uses the same local generation sources and conversion technologies as off-grid, but connection to a public distribution system imposes another stringent set of requirements. A grid interactive power electronic inverter complying with specific standards is required for converting the dc sources to compatible ac.

Consents for generation

For those contemplating installation of distributed generation, the process is not simple. At a technical process level, four consents must be obtained – two electrical and two related to the built environment.

BUILT ENVIRONMENT

Most structures associated with local residential generation will need approval from local councils for the building compliance and resource consent. Unfortunately, councils often don’t have much experience in addressing micro-energy system requirements and thus these vary around the country. The processes need to be simplified and more uniformity reached.

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ELECTRICAL CONNECTION

Both the electricity retailer and lines company must be involved. The lines company is responsible for approving the technical connection to the network. The retailer is responsible for the contractual transactions involving energy flows to and from the supply system. An agreement must be made with the retailer on purchase of energy flowing into the network before the lines company will agree to connection.

Most lines companies now have information kits and processes (albeit rather complex) in place, and they are generally helpful. The same cannot be said of the retailers, who still appear to be coming to grips with setting up contractual processes in what for them offers zero benefit.

DG connection regulations

A set of technical regulations to allow connection is now in place. These are the Electricity Governance (Connection of Distributed Generation) Regulations 2007.

The regulations are set out in two categories for:

  • DG with rated output of 10 kW or less
  • DG rated in excess of 10 kW.

Household scale distributed generation – such as a small solar photovoltaic array or a micro-wind turbine – will normally fall into the lower output category. There is usually no charge for connecting small generation to the system, but the government has accepted that the supply system operators have the right to recover some of the costs associated with the process.

The hill-top test site of a new type of local energy system being developed by Industrial Research Limited. This uses both electricity and hydrogen as energy carriers. Hydrogen is used to transport the wind-generated energy via a 2 km plastic pipe. It can be converted on demand to electricity in a fuel cell or used directly for water heating.

Apart from the customer’s distributed generation equipment needing to comply with certain technical standards, the main requirement is for metering of the energy exported from the site. A new meter must be fitted. This may be an import/export meter that will have two separate energy registers that can be read manually. An alternative is to install two simpler meters – one wired to read imported electricity, the other to read exported electricity.

These regulations are a great start but will need to be revised and improved if the full benefits of distributed generation are to be made available to the consumer and community at large. The key areas that need looking at are a more appropriate market structure for local generation, with pricing signals that incentivise network supportive behaviour, and a simpler process with lower transaction costs for connection of very small systems (<1 kW).

Smart metering

In many areas, manually read meters are being phased out and replaced by so-called smart meters, also known as advanced metering systems. These systems have a two-way communications capability, for example, via the mobile telephone network. This provides the ability to remotely read the meter, upgrade the meter’s internal programming on the fly and measure energy use in much shorter time intervals than the usual 2-monthly reads. The most likely time interval will be a half-hour period, as this fits in with the way that energy is traded in the wholesale electricity market in New Zealand.

Smart metering will allow time-of-use pricing schemes for residential customers that reflect the real-time cost of supply. The same pricing opportunity should also be applied to customer-generated distributed generation export power.

Jargon abounds in the power supply industry. Here are some common terms, though definitions are not universal.  
Local energy A generic term that includes CHP and other non-electric technologies.
Off-grid/SAPS/RAPS Independent, stand-alone or remote local power system that is not interconnected to any other user via an electricity supply network.
On-grid/grid interactive/DG/EG/micro-grid A local power generation system that is electrically connected with other users, usually via the public electricity distribution network. Distributed generation (DG) and embedded generation (EG) are interchangeable. A number of interconnected DG/EG systems form a micro-grid.
SSR Small scale renewable generation systems comprising hydro, wind or solar resources. Generally well below 100 kW in capacity.
SSR/DG Covers the field of small local systems and includes fossil-fuelled generators.
CHP/cogen Combined heat and power.

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For more

More detail is available from ‘Get smart, think small – Local energy systems in New Zealand’ (see www.pce.govt.nz). See also www.eeca.govt.nz and www.seanz.co.nz.

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Articles are correct at the time of publication but may have since become outdated.

Micro-wind turbines typically come in sizes from 0.3 to 20 kW or more. A 2–3 kW unit (4 m diameter rotor) might be used for a home and a 20 kW unit (12 m diameter rotor) on a farm. The tower would be up to 12 m or more tall.
The hill-top test site of a new type of local energy system being developed by Industrial Research Limited. This uses both electricity and hydrogen as energy carriers. Hydrogen is used to transport the wind-generated energy via a 2 km plastic pipe. It can be converted on demand to electricity in a fuel cell or used directly for water heating.

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