Saturday 28 March 2020

Living off the Grid


It has now been twelve months since we moved into our house and began living off the grid.
For us interesting has been a year of learning …

But first what is OFF THE GRID?

For us it means we are not connected to the National electrical power supply network, so we don’t draw our power from the Dams, Gas, Geothermal or Coal fired power stations. In effect we are our own power station. (just about).

We are still connected to the Town water supply, storm water and sewer system.

Why?
Mainly to reduce of carbon emissions footprint and have some control on the power prices. Ever noticed how power prices keep going up?

What makes up our system?

We have 12 photovoltaic panels on our roof (each 270 W, totals 3.24 kW), these convert sunlight to electricity in our case on average they will produce between 5 and 7 Kilowatt hours (kwh) per day.

These face directly North, and are set at a tilt angle of 51° to maximise the sun during winter hours when the day is shorter. see picture below from the NIWA Solarview website



These are feed into an inverter which does two things, if we are drawing power within the house at the time it converts the electricity from DC to AC and sends it to the house. Any surplus stays as DC and goes into the battery bank to use at a later time. Then it goes back through the inverter and converts it to AC. Simple!

The battery bank is made up of 24 batteries (600 amp hours (Ahr)) which gives 3 to 4 days of power storage. If we have to weather of storm longer than that we have 6 kilovolt (kV) petrol generator, that we can charge the batteries up with, this I have been told would take approximately one hour.

Battery bank in the garage with the Inverter next to it (redbox)

Our hot water cylinder (250 litres) is heated by 20 solar evacuated tubes, these very good at heating the hot water at around 90 to 95% efficient. Whereas a PV panel is only between 20 to 25% efficient at converting sun to power. The cylinder can be boosted with gas. It has also been wired for electrical supply, if we ever expand our number of PV panels.


Evacuated solar tubes at rear and the PV panels at the front

Nearly everything in the house is electrical, with the exception of the following we have (as mentioned) gas boost to the hot water and a gas hob and oven.

The house looks like any other on the street inside or outside.

Did it work? How has it gone?

In the short answer yes and well.

In some detail …
Hot water was boosted on 51 days, that means 314 days of fee hot water.

From the 6th of May when I started to record power use to yesterday (27th March) we have used 1450.24 kWh or 4.44 per day. This is within the plan production of power from our system.

Generator use has been limited to giving it a service run every three months to make sure it starts and its battery sis still charged. On two occasion, as we have used when using larger machinery, once was a concrete mixer and the second while using a large sander and vaccum at the same time. This demonstrates how small our system is.

Our smallest power use day has been 1.7 kWh, this was while we were on holiday and did not have anyone staying in the house so was basically just running the fridge/freezer and inverter, and our largest has been 7.42 kWh.

Nine of the twelve PV panels visible, there is another row of three sitting behind the row of six


What did we have to change to make this work?

This was the interesting part, it was a matter of changing habits more than anything
  •         Turning lights off as you leave a room
  •          Turning appliances off at the wall when you have finished using them
  •          Not using the dishwasher and washing machine at the same time.
  •          In summer we can use the washing machine and dishwasher on the same day but needs to be alternative days in winter
  •          Using the dishwasher and or washing machine mid-morning in winter as that time for the power storage to be built back up in the afternoon.
  •          Sometimes having to leave the dishes or washing to be done on the next sunny day (generally a storm cycle in Nelson is about three days).
  •          We use a slow cooker on sunny days when we want a casserole or roast
  •          Up until December we did not have a toaster or electrical kettle, since buying them power consumption has gone up between 0.75 and 1 kwh a day. We may be able to use them for 8 to 9 months of the year, reverting to using gas for these tasks.

How did it effect our emissions footprint?

Comparing the 12 months previous it looks like this

2018-2019
2019-2020
Power
185.1
0
Gas
57.9
206.5
Petrol Genie
0
12.5
Total kgCO2e
243
219


A 10% reduction, the key to further reductions will be using less gas … there is always something to work on and this is a start.

How much did it cost to run the house for the last twelve months?
Gas          $138.00
Petrol       $  10.00

Now if we can just get that gas volume down!

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