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Living off Grid

The reason for putting this wiki together, is out of interest and possibly we may buy a property off the main grid system. There are several components required to living off grid, the first is why: In purely economic terms going off grid is much more expensive than connecting to the normal electrical system, but your property may be a long way from the road and a normal mains connection could be $50K plus, at this point off grid systems start to look attractive, a typical Photo Voltaic package being about $35K.

Work in Progress

Rough calculated cost for an on grid supply

Estimated costs for an on grid connection are $100 per metre (11,000 volts) or $60 per metre (240 volts). The next question is of course “why do I need 11,000 volt supply”, well you do not want 11,000 volts connected to your house, only 240, but it is not practical to run long distance at 240 volts because of volts drop, the more current you draw the more the voltage will drop across the length of cable. This is why electricity is distributed at 11,000 volts through towns up to to the point of use and then reduced down by a transformer to 240.

Rural living far from the normal systems, almost certainly means using rainwater for all sanitary purposes, including drinking water plus processors for dealing with sewer waste. This is quite normal for rural areas of NZ and not a problem.

The house must be designed and built for reduced energy use, extra insulation at build time is a minimal cost and included solar water heating (essential) is only about an extra $4000. Consensus of opinion advises an indoor storage tank not an on roof one, seems the on roof versions are poorly insulated compared to the indoor variety


The one component all systems need are batteries (the most expensive one) and an inverter, even if your primary power is a generator, batteries are stilled required, as it is terribly inefficient to run a generator for long periods on low load and power is usually required 24/7 for fridges and freezers, going to the loo at 3.00a.m.

Inverters convert the 12 or 24 d.c. volt battery voltage to 240 a.c. Yes it is possible to run on extra low voltage, but a real pain

How much battery capacity do you require and how much will it cost?

Starting point, electricity usage per day. Well its not practical to have electric heating, or cooking, but a microwave is essential nowadays. (Also heating water should be by solar and supplemented by a wood burner or LPG or possibly a heat pump, more on this later). We all “need” fridges, freezers, electric kettles, toasters and washing machines, but not a tumble dryer. The fridge / freezer and the washing machine are the greatest loads (prolonged). A hot fill washing machine would certainly reduce the electrical load.

Summarizing: to keep battery costs reasonable your load should be between 5 and 10 KWH's per day (average kiwi family uses approx. 28 KWH per day) with at least 5 days capacity, equating to 25 / 50 KWH capacity.

The reason for the 5 day battery capacity is that occasionally the wind or the sun output will be well below par, or the generator will act up, but more importantly is that batteries do not like being drained and their life will be greatly reduced by constant deep discharges

Battery Cost for 40 KWH storage (8 KWH per day * 5) approx. $9500

Working out the capital cost of batteries per KWH over a 10 year period based on 8 KWH per day: 32.5 cents per KWH

There must be a trade in value for old batteries, to reduce the above cost, but I am still looking

This is not working out for the good, electricity on grid costs at present 22 cents per KWH and the capital cost of batteries alone are 32.5 per KWH. ( I realise electricity will go up but I am not calculating in the potential interest on th capital sum). The capital cost of PV cells and inverters will cost approx. $20,000 which may last 20 years, but the economics look lousy unless the installation of on grid get overs $50,000.

Inverter / Charger

To get from your 12 / 24 d.c. battery voltage to 240 a.c. an inverter is required, and to keep the system as simple as possible it makes sense to have the battery charger combined. This unit is fundamental and should not be skimped. The inverter must deliver a pure sine wave a.c. voltage especially for powering computers, TV's etc and should be 90% plus efficient, you cannot afford to waste your expensive battery capacity. The price of a 3000 watt output inverter combined with a charger is around $4200 in NZ.

Wind Turbines

The main alternative to pv cells are wind turbines. Wind turbines really cannot be used in isolation without an alternative (unless you live in Wellington), the wind is just not that reliable. The output voltage of wind turbines is usually 24 or 48 volts. d.c. and so they still need batteries and inverters. Turbines are mechanical and so require maintenance and this is generally inversely proportional to their cost. Reading off grid forums the consensus seems to be “if there is enough wind to power a turbine, why do you want to live there”, also they are a real pain as compared to pv cells. For guidance some wind speeds and km/h and m/s.

100km/h = 30m/s
50km/h = 15m/s
10km/h = 3m/s

20 m/s seems to be the lower end of manufacturers ratings

This is all theoretical, as I have no real experience of living off grid, but here is a link to the journal of a family that live off grid near Christchurch. (Read from the bottom up)

Solar Water heating

Solar water heating is essential for off grid electrical supplies but are usually economic for an on grid house. Solar water heating can be installed in any house so long as you have a north facing section of roof. If you are considering building a new house, you really would be stupid not to have solar water heating as part of the project. Retro-fit costs are in the $4000 to $6000 price range and the pay back time is obviously dependent on your water usage, if you have teenagers and like baths its much more economic.

Remember: Auckland is on latitude 36 compared to London on 52, sun hours average 2200 compared to 1500

I have investigated this several times and even with the government grant of $1000, I cannot make an economic case for retro-fitting, the reason being we are only two adults that take showers (short ones), the washing machine and dishwasher are cold fill, so our hot water usage is small.

Have been given some tips to use more solar heated water. Use hot water for the dishwasher, it will not mind, also fit a mixing valve on the washers inlet pipe and set the temp to at least 30 degrees, higher if doing a hot wash, I know your rinses will use warm water, but if its free!

The spa pool costs $25 to $30 per month and so might be a case for a DIY installation.

Have a look at the bottom of this page, or:

Looks like we may be building a new house in a field, so brushing of all of my solar notes. SEE Buying land (section) and planning a house

Update Oct 2011

After much faffing around we eventually bought a house in Miranda and have sold some shares to buy 3 Kw of grid tied solar. The company we used was The entire package including resource consent and a new meter was slightly under $16,000.

Fuel cells

New technology are fuel cells, British Gas in the UK are testing out 37,500 Ceres fuel cells on customers hoping they will generate most of the household electricity cheaper than buying from the grid. These cells use natural gas where as LPG is the main fuel bottled in NZ, but look at this article:

DIY Solar Panel

Tempted to have a go at this for the spa pool

Suns Angle

The suns angle during the year comparing London and Auckland

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