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.

[profdraper]

Thanks for this, interesting.

We’ve had a ToU EV plan & smart meter here in Brisbane for a few years now. So far so good, tho’ the T33 CL charges for our small, retired family & electric HWS is simply outrageous.

We’re considering a new solar /battery bundle install in the near future, but have head some horror stories about AGL then immediately switching to the most expensive single Tariff arrangements; there seem to be mixed messages about this in this forum.

As per recent advice from most experts (see SolarQuotes etc), what we would aim for is:

- keep the existing ToU & EV Plan

- take the HWS off the T33 tariff & put on a timer

- then wonder about if we get a reasonable FiT? would seem that we could be punished for that by AGL with a very low 3c FiT unless we buy into their solar/battery bundle & their VPP ..

Anyone had any practical experience with this? My impressions right now it that it may well be best to switch to another provider with the solar install.

[Lester]

Taking out the option of investigating if the HWS is somehow not working right (if not already checked), and adding so badly to your bill . . .

Option 1. Get a assessment for solar system of good brand, if site suitable, little shading issues etc, and can afford it, go with a Powerwall3 battery, with its inbuilt in 10kw inverter, marry up with 10 kw or so of quality panels, and you have the ideal setup.

You shouldn't have to worry about a timer, if the system is only using say 6 - 8 kwh a day, just have it heat on main circuit (just leave CL metering, it will show zero in future), and at night use battery or EV rate if it happens to deplete, very unlikely (ours uses a few kwh a night early morning tops).

Option 2. Get a Tesla PW3 battery, and only use it as a battery (for now), get the HWS on a timer and time for HWS for EV rate, time the battery to charge during EV rate, this should allow daily usage between 0600 and 0000 to use the battery, and thereby you should get all your power for 8c/kwh, a bargain which should drop your bill by 2/3 ?

Get an assessment based on your kwh usage through the year, and work with it until you feel it right to add your panels, then you have the best of both worlds, and are protected against any supplier changes to plans etc (ie EV Night plan can be changed or deleted anytime).

[profdraper]

Thanks for this.

I hadn’t considered option 2). Interesting - assuming the small 160L HWS actually can do its job during 6am-12pm with only 6 hours of overnight power. Am a little dubious about this one, but sure, with a timer it ‘could’ be more flexible. BTW our sparkie advised that a timer on the HWS would not make much difference given that T33 *should be turned on and off at peak load times by AGL … but clearly something is not right here (still no response from AGL).

re. 1) If panels are not possible (given flat roof slope, shade etc), an addition to option 2) would be to install a heat pump HWS (often with its own timer) and perhaps also increase to size to 250L which would also make it eligible for T31.

Thanks again.

[Lester]

Considering you suggest your flat roof and shading might make solar less attractive, yes option 2 might be good to go for.

Flat roofs tend to gather more crud in the lower sections of panels, dust / making dirty where it pools, builds up, usually 22 degree pitch is fine for rain to clean them off, but flatter (like some of ours at 8 degrees) they need a clean now and then.

Shading, well if bad then trust me, solar not worth it, even with a system like SolarEdge with optimisers, or others with micro inverters, you just lose too much efficiency.

You won't need a PW3 then, as you don't need the inverter.

So, a battery like the PW2 would be great, BUT they are obsolete once sold out now that the PW3 is out.

I can't fathom why they don't want to keep the PW2 as a battery option, lots of people with suitable solar systems might still buy one when ready, but that is Teslas apparent choice.

You could get modular BYD batteries, stack to whatever capacity you like, or any of the commercial grid connected batteries would be fine I would think.

You'd have to check if an extra Gateway device is needed if blackout protection desired.

So yes get the existing HWS onto main circuit and a timer, they can be set to numerous on / off cycles, so you could have it come on 0000-0600, which I think would cover you . . . depends on shower habits, length of showers etc, but you would have full hot water every morning at 0600, that should do you if you have morning showers, and maybe a top off from the battery for a hour later in the afternoon (shoulder 1400-1500) ?

You can have your battery charge anytime, multiple times . . . it SHOULD last your full day usage, even with a little HW top off.

Ideally you want the peak hour usage covered in the early evening, through to whatever time you usually retire.

The heat pump HWS option would be ideal, especially if eventually you find your existing unit IS using abnormally high power.

That would use solar during the day, probably in conjunction with battery charging, and before anything is sent to the grid.

There are usually deals on heat pump HWS offered, but a quick google reveals no offers to QLD consumers at the moment.

Hopefully, you can consider option 2 and adapt on the fly once you know what you need with HW.

[Caban]

@profdraper 

Only thing I would add is that maybe consider avoiding Tesla or other battery systems with a relatively short life. Batteries designed for cars trade off longevity in favor of weight. Makes sense in a car but less on a house, which does not move. They do have a bit of a cost advantage as they have economy of scale, but you still have to spread their cost (and carbon penalty) over the estimated life of the product. So a slight increase of initial purchase price over 50+ Years is a better prospect than slight saving divided by 12 to 15 years.

[profdraper]

Sure, ok, which battery then?

otherwise, I’m pretty sure AGL or any energy company is going to pick up on this option 2 battery pattern quickly, then quickly shift the plan to something else that suits them better &  makes them more money.

no such thing as a free lunch & track record shows they absolutey cannot be trusted ..,

did I tell you about the time it took AGL three months to transfer our land line for my 94 yr old mother in law? Meanwhile, no OOO, overseas relatives, local doctors. She could never be left alone. Many many calls & escallations. Endless. Finally took our local Fed MP to intervene, fixed in 24 hrs. Arsehats.