5kW, the first 12 months.

What's happened so far..

The beginning of March marks the completion of a full 12 month's operation of the total 5kW system, and my most recent bill finally resolved to an overall, substantial, credit.
Analysis of my data reflect the following key conclusions:

1. A total saving of almost $1,800 in my electricity costs in that period.
2. Annual solar production in excess of my actual consumption
   (6800kWh v 6613kWh).
3. Average export of 63% of my total solar production.
4. An opportunity to save more by retaining more of my solar production.

The following graph shows our current trend:

By adopting strategic use of my appliances during daylight (solar) hours the benefit is apparent in the increased gap between the yellow (Total Solar) and green (Exported) lines. This, in turn, is reflected in the increased gap between the blue (Total Consumption) and red (Charged Consumption) lines. Any reduction to the export %, i.e. consume more of my generated solar rather than export it, is the key to further savings.

How can I improve this?

I've determined from observation and measurement that my typical daily consumption profile suggests 87% of my consumption of grid electricity is occurring at night (non solar). My typical energy load at this time consists of the following appliances:

1. Air Conditioning
2. Refrigeration
3. Entertainment

Of these three the last two are fairly constant and predictable energy consumers, while air conditioning is a fluctuating, seasonal consumer. My measurements of the latter two groups suggests consistent, daily consumption in the order of 2-3kWh. I also have another fridge that uses another 2kWh/day. As these devices are in relatively close proximity I am able to easily connect them to a 3.5kW inverter/charger which in turn is supplied by both mains A/C and battery storage. When the mains A/C is available it powers the refrigerators and entertainment centre (via the inverter circuitry but not actually using the inverter) , while also recharging the battery, if necessary. When the mains A/C is removed, supply to the attached appliances is maintained by the battery powered inverter.

By restricting the mains A/C supply (initially with a timer switch) to only be available during (solar) daylight hours, i.e. switching the A/C mains OFF at night, the batteries can be used to collect available solar for later use at night, when I would otherwise be purchasing (expensive) electricity from the grid. In this way I can reduce my exported solar, which, as I mentioned in the previous section, is the key to further savings.

In fact, over the course of a whole year, a collection of just 2kWh daily represents a 730kWh (2x365 days) redirection of my (cheaper) solar to night time consumption. In terms of electricity bill savings this equates to $93 p.a**. If the daily figure is greater, then the savings would increase as well. Once we go past September 2016, the feed-in tariff will drop to a mere 5.3c/kWh instead of the currently subsidised 23.6c/kWh, which will then represent an annual saving of $230. So this approach will initially return a small saving, but once the subsidy ceases I've protected myself quite effectively.

This setup is also advantageous as it provides "autonomy" in the event of a mains grid power loss or interruption. This incidental benefit has massive value, as most people would list "power outages" as one of their biggest inconveniences and stressors. Depending on the capacity of the batteries I use, this can provide protection for a number of days, if necessary. Furthermore, as this is connected as an appliance inside my home it escapes the prima facie restrictions and consequences of incorporating "grid connected" storage. The regulators can only go so far....inside my home is out of bounds.

** 750kWh at 36c/kWh costs $270

If that bought electricity is replaced by my solar (via storage) currently worth 23.6c/kWh, that means a loss of $177 feed-in credit against the full cost of $270, a saving of $270-$177=$93.

That sum changes to $270-$39.75=$230.25 saving when the feed-in subsidy is reduced to 5.3c/kWh