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Annually $41 should provide heat and hot water to New Zealand's highest-rated energy efficient home.
Add LED lights, extra insulation and a modest size, and total electricity bills should be about $20 a month.
The Energy Efficiency and Conservation Authority has given the Golden Bay holiday home nine out of 10 for energy efficiency - the highest score it has given out.
Owner Lawrence McIntyre hopes people will visit the house, his "little greenie", and see they could build one themselves.
"The difference between insulating a house the way I have and the way another house is, is probably only $3000 to $4000 and the insulation value is more than double," he said.
"People are quite happy to put flash stereos in their cars or spend $20,000 to $30,000 on a kitchen but they'll scrimp on 20ml of insulation."
"(If) you take one ensuite out you can build the flashest solar hot water system that you can buy."
Mr McIntyre said the main thing was to keep the heat in by having as few joins as possible and plugging every tiny gap.
There are no fancy design features on the simple rectangular home, which is at the north end of Abel Tasman National Park, so every extra dollar could go into materials.
The $20,000 solar system will provide most of the heating and hot water, topped up by electricity from elsewhere.
A composting toilet sucks fresh air from a vent above the shower each time the toilet is used, so there is no smell and a flow of new air is maintained into the house.
"The toilet basically controls the air in the house. We've had quite a few people who hadn't realised there was a compost toilet come and stay and they couldn't believe how good it was.
"They probably would not have come and stayed had they known."
Mr McIntyre said he copied the design from German low-energy houses.
"In Europe it's not a new concept ... when you go to a trade show in Germany they show you photographs of how temperatures move through walls and windows."
High quality double-glazed windows stop heat escaping, along with wool insulation and a polystyrene break to stop the concrete floor touching the ground. Sun-warmed air is directed into the walls for storage and to release heat.
The authority said about 1000 homes had been rated for its Home Energy Rating Scheme and this was the best score yet. Homes were rated from 0 to 10 based on how well the design, materials, construction and orientation keep a comfortable temperature, as well as the efficiency of heating and hot water.
The authority worked out it would cost less than $50 for hot water and to heat the house to about 20C all year. The need for heating was about 85 per cent lower than an average new house, and about 97 per cent lower than an uninsulated house.
Mr McIntyre said the extra features would more than pay for themselves over their lifetime. "Really we need to move away from this (idea we should have a) pay-back period of five or seven years because the health benefits (of warm houses) ... are huge."
For more information, go to goldenbayhideaway.co.nz and eeca.govt.nz