Off Peak Vs Time of Use.

[Caban]

Some musings here for those interested in the economy of their systems.

In days of yore I had two analogue meters. One was Main power and the other one was Off Peak power. On the Off Peak I had the Solar HWS Booster and the Pool Pump supplied. This would save money as those loads would be active when that power was available, late at night and weekends.

When my system was updated with Solar Panels and a Battery (late 2013) there was a digital Time of Use meter fitted the old Off Peak meter remained, though the pool had stopped operating it still supplied the HSW Booster. I would only require the booster on less than 10 days a year so it was unused most of the time.

When I assessed my usage in order to find the best package I made a spreadsheet which would estimate to cost tailored to my own energy usage. Having a battery it became evident that the most significant figures were the daily charges and the Feed In Tariff.

The daily charge for the Off Peak had to be weighed against the slightly lower cost of the supplied power. If my memory serves me I was using about 6kWh per quarter it was costing me 12c a day. I was saving only 2c a kWh ver the TOU rate. My off peak usage would need to be huge to make that viable. I requested that the circuits on the Off Peak meter be shifted to the general meter. I switch the HWS Booster on only when required.

The point I am making is that too often we can get fixated on the charge per unit of power or the feed in tariff but neglect the daily charge. A simple spreadsheet can unlock the best path.

[Lester]

Seems like I might as well ask for removal of my CL TOU meter, and put a timer on the HWS.

We might go down the battery route still, once we have analysed past our first (just over) 3 months on solar, into winter a little more, so we can get a true picture of what we need year round.

For much of the year we could have it set to just solar production hours, but even in winter and those shoulder periods of the year, if we set a HWS timer for Night Saver EV period 6 hours of early morning, and take advantage of that very low rate, it would make some difference to having a CL TOU come on anytime, inc normal peak CL times.

Must look at the spreadsheet more to see where it is actually coming on mostly.

We do have the CL day / night switch in the kitchen, and that is turned to night now . . . so that would normally keep that to 7 hrs overnight in off peak 2330 - 0630, but off peak is dearer than daytime shoulder, or of course on the EV plan 0000 - 0600 on the very cheap rate.

We should be getting that 2330 - 1359 1/2 hour at peak TOU charge though, and that's probably when the HWS would kick in now.

We send a lot to the grid though, so a no brainer during daylight hours, just set for say 1000 - 1500 and get that free with solar on the regular TOU meter.

[Caban]

@Lester 

If you are exporting a lot of power during the day then that would be a good time turn on the HWS. The Feed In Tariff fees you miss out on will most likely be cheaper power than anything you buy from the grid.

In may case I have the SHWS (Solar Hot Water Service). There was one fitted originally in the late 70's and I have updated that about 15 years ago. There was also a Solar Clothes Dryer installed with the original build that still operates perfectly well. The only downside is that the SHWS takes a fair bit of Roof Space and once the water is hot that area is not productive. If that space was dedicated to more PV's then they could supply power to heating the water and continue to supply power when that role is finished.

BTW - What is CL?

[Lester]

@Caban 

Absolutely, and I think all but say 2-3 months of the year would be great to use the excess solar, much cheaper (even than the 8c EV rate in the wee hours) over any other tariff.

I am certainly being realistic about winter drop in solar output though, it's already going south in power generated quite a bit at times, today was probably the 3rd worst day for solar so far . . . although I have a couple of shading trees to get taken care of in the next month or so, they are going to take way too much winter light.

CL - controlled load.

We always have 2 meters with the HWS on CL off peak single rate, which was a pre solar saving worth the original effort (mid 80'2 build).

But CL TOU is really not as good, with 3 tariffs similar to normal digital meter, peak, shoulder, off peak, same operating hours, not that much of a drop in tariff charges for each period.