mugs2000:

 

Typically, we use 350 to 400 units per month, with usage being relatively stable throughout the year as we use a wood burner.  Our electricity charge is $0.41c/unit. More, because Aurora in Otago has been slack with line maintenance the line usage charge looks like going out of control over the next few years, it may be time to go off-grid. Does anyone have any information as to whether one should go completely off-grid with large battery reserves, or use the method whereby you sell back unused power back to the supplier, or some combination of both methods?

 

PS we have an electric 8kWhr califont shower so we need periodic high usage power for 15 mins/day.

 

@mugs2000 Have a look at your power companies off peak controlled rates. They are likely to be far lower than what you are currently paying. You will need to replace the electric califont heater with a hot water cylinder, and have it heated via the night rate power. In effect using the cylinder like a battery in that it is storing energy in the form of heat.

Also check how much LPG via the 45kg bottles cost in your area. In Auckland it is around $100 per bottle, with a $100 per year fixed fee. So that translates to around 16.4c per unit. Change your hot water and cooking to gas. And as well as lower power usage, your peak power load will also be far lower. This means you can switch to the cheaper 8kVA connection size that Aurora offer. And change power companies to Flick Electric. As with gas cooking and hot water (Im assuming your wood fire provides 100% of your heating), You will have low peak time power usage. Therefore you will have above average savings with Flick Electric.

An offgrid system would cost you at least $15,000 And could easily go to over $20,000. You would still have to get gas installed to remove the cooking and hot water loads from the offgrid system. And almost certain you will need a diesel generator as well to get you through times when there is hardly any sun. And you would still need to allow for between $50 to $100 per month to cover system maintenance and eventual replacement of parts (especially batteries).

About the only time an offgrid system makes sense is when you are doing a new build, and the power company has quoted you a massive price to get power connected to the property. The other thing to consider is that you would be on a low user plan due to only using max 400 units per month. This means that the lines company is only allowed to bill you 15c per day max in fixed fees. (Rest of the fixed fees goes to the power retailer). No way would that even come close to covering the fixed costs in providing power to your house. So Aurora is forced to add a really high per unit surcharge onto the power that you use. And not surprisingly due to the really high per unit costs, people spend lots of money on things to reduce power usage. So less total power used per house divided by the exact same fixed costs = the lines company being forced to keep on raising their prices.

And since you have an electric califont water heater, your peak load would be the same if not more than 2 houses. So other Aurora customers are actually subsidising your usage.