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Earthsong houses need considerably less energy than standard houses for heating, cooling and hot water, due to the passive solar design and solar hot water systems. We did, at the design stage, consider all the options to also generate our own power on site using renewable technologies, but weren't able to achieve it at the time.

Apart from storms there is only a trickle of running water on site through the wetter months, so hydro-electric generation was not an option. Wind-powered generation was considered, but although Ranui is close to the west coast famed for its powerful westerly winds, the Earthsong site in essentially in a wide valley sheltered by the Waitakere Ranges, and any wind generator would need considerable height to get above the turbulence of the surrounding built area. The generation of electricity through photovoltaic panels (PVs) is certainly possible, although the technology is still expensive.

Balancing the commitment to build leading-edge sustainable buildings with the equal commitment to keep the prices within reach of a diversity of people was a continual challenge, and this is one area where we felt the cost outweighed the environmental or financial benefits. In New Zealand, 80% of the mains-supplied electricity comes from renewable sources, mainly hydro and some geothermal power. The relative environmental benefits of on-site generation are therefore very different in New Zealand to countries where most of the mains power is generated using technologies such as nuclear or coal-fired generators.

We concentrated instead on energy efficiency, reducing our power use through passive solar design and solar water heating. We did make provision to simplify the future installation of photovoltaic panels by individual homeowners. 2 x 16mm cables have been built into the wall framing from the roof space to the electrical distribution board of every house, to allow easy retrofitting of the panels as funds allow.

Energy Efficiency

Mains power is supplied by the power company to a transformer on site. From there it is distributed around the site to houses, tank pumps and site lighting.

Minimising energy use was a key consideration of the design brief. All buildings use passive solar design to keep warm in winter and cool in summer. Features such as north-facing windows to admit winter sunlight, concrete floors and rammed earth walls to store the heat, pergolas on the north to shade the summer sun, and good insulation to conserve the heat, all contribute to homes that require considerably less heating in winter than they otherwise would.

All homes have solar water collectors with roof-mounted hot water tanks. 1 and 2 bedroom units have 180 litre systems, and 3 & 4 bedroom houses have 330 litre systems. A digital monitor inside each house gives a reading of the temperature of the water inside each tank, and includes a switch to turn on an electric booster element in each hot water tank if required. Power is only delivered to these boosters for 3 hours per day (1 hour in the afternoon and 2 x 1 hours through the night), so even if the switch is left on there is a maximum of 3 hours per day for boosting.

The cooktop in each house uses bottled gas instead of electricity, as an economic and very efficient energy source. Using gas directly for cooking rather than using it to generate electricity for cooking is a much more efficient use of the resource.

Power Charging System

There is a bulk meter near the transformer for the mains power that is delivered to the site, and this is paid by the Body Corporate. The Body Corporate then charges individual households according to their power use, measured by the check meters in each house, read quarterly for quarterly billing by the Body Corporate.

As for water, there is a two-stage tariff for power to encourage more careful use. The first 600 units per household per month are charged at a lower rate than subsequent power use per month. However this tariff step is set so high relative to average Earthsong use that only 2 or 3 households use more than 600 units per month even in winter.

Demand Management

One clear lesson from our experience is the importance of behaviour in reducing the environmental footprint. Designing buildings and neighbourhoods to be as sustainable as possible is an important first step, but the behaviour of the occupants is at least as significant when it comes to the overall impact (some studies show behaviour to have twice the impact of the built environment).

One example is with electricity use. The electricity use of individual Earthsong houses varies widely, even for identical houses with similar numbers and ages of inhabitants, because of the preferences and behaviour of the residents. Because high individual users to some extent determine the overall cost to everyone at Earthsong, (as the pricing plan from the supplier is determined by our overall use), we have debated this issue on all levels, from the underlying philosophy of pricing formulae to ways people can reduce their electricity use.

Earthsong residents are given information regularly about the power use of different appliances, and encouraged to limit their power use to around 3.5 kilowatts/household at any one time, for example by switching off the heater when using the oven. This is to reduce costs collectively by operating within small fuses at the transformer. Residents are also encouraged to buy energy-efficient appliances, including super-insulated fridges and compact fluorescent lighting.

A cooperative neighbourhood can facilitate behaviour change through information exchange and education, sharing ideas and tips about how to manage the systems more efficiently, internal pricing plans that reward low users and discourage high use, built-in information feedback mechanisms, and accountability through making information on individual house use available to all. All of these mechanisms are in place in some form at Earthsong, with the result that 32 homes and the common house are managing to function with an electricity supply of the size that usually supplies 6 houses in New Zealand.

These measures mean the average house at Earthsong uses only about half the electricity of an average house elsewhere, with some households who manage their solar water boosters efficiently paying only $30 - $40 per month for power even in winter.

HERS assessments (Home Energy Rating Scheme - an Energy Efficiency and Conservation Authority project) on a range of Earthsong house types in 2008 gave them an 8 rating, the highest energy ratings in New Zealand to date.