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Cutting your energy bill.??. Don't try this at home, kids.

PostPosted: Thu Sep 22, 2011 7:31 am
by Tracker
Well, it was an interesting experiment, but I can't say that it was productive.

Buy a bank of batteries and a Charge/Inverter, of the type that is used in BIG boats.. You know, where you plug into Shore-Power and charge batteries and then go to sea and run your fridge from the batteries or a generator.

The idea was to charge the batteries in OFF-PEAK hours at 8c and then run some refrigerators for the rest of the day.
Well the initial figures are in... :oops:

To run the fridges direct from house power, used 2.97Kwh and with an estimated cost of 61c.
To run the fridges from Battery system, used 8.1Kwh and with a real cost of 65c.

Whilst I will be experimenting more, it is clear that as far as cost is concerned - it's break even (excluding capital costs), and that using the battery system , involved dramatic inefficiency.. ie 8kwH to give back 3KwH.
I must say that I was expecting about 70>80% efficiency in the charge/invert process.

I think that the real issue is the efficiency of the "Chinese Inverter/Charger".. eg. Floating the batteries required .25KwH, and this quickly adds up. Unsurprisingly, the Inverter Manufacturer gave no figures for Charge and Invert efficiency.

My next phase will be to try and secure a recognised brand device, and see how it's efficiency pans out.
ie either an integrated 48V Charger/Inverter, or separate components.

Anyone in Sydney got a 48V charger for loan..?
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Re: Cutting you energy bill.??. Don't try this at home, kids.

PostPosted: Thu Sep 22, 2011 2:51 pm
by Sonnig
Interesting experiment.

For those on NET metering with a PFIT there is an additional saving to be considered.

Using a typical figure of 3kWh, you could estimate that approximately 1 kWh of extra power would be exported to the grid as the fridges are isolated from the grid during this peak time coinciding with solar generation. With gross metering this is not a factor since there is already a 100% financial benefit from the solar power generated.

Using my circumstances, my 500L upright fridge/freezer used 9.2kWh over a whole week measured with a single power point plug-in device so the potential savings are obviously less for those with lower usage devices effectively being moved periodically off grid. Never-the-less potentially more devices could be connected to the inverter assuming the capacity is there.

I don't have any battery charging experience. No doubt those who have power off grid can elaborate on this, including inverter/charger/battery efficiencies.

I have seen references in these forums to floating batteries as well as deep cycling batteries and the impact on lifespan. I’ll be trawling through previous posts to see what I can find. Does anyone know of a good “Charging & Battery Usage 101” source of info?

When you recharge your batteries during the off peak period, I guess that once the batteries are recharged you enter this float period that consumes 0.25kW/h. I wonder how much, if any float period is needed. If operating off a timer could you have multiple charging cycles during off peak or would the total energy consumed be similar. I was thinking of something like recharging the batteries at the start of the off peak period then letting them discharge and giving them a final charge just prior to the peak period kicking off again.

Re: Cutting you energy bill.??. Don't try this at home, kids.

PostPosted: Thu Sep 22, 2011 4:52 pm
by Tracker
Using timers would be my next process..
The first experiment was to determine how much power I delivered from the batteries (AC KwH) and then how much it took to get the batteries back to float.. (Not scientific - Just read the AC KwH at the start of the next day.

The real plan was/is to only use the batteries during the PEAK period, rather than ALL day.
The real issue is the constant power drain by the system, just maintaining FLOAT for most of the day, awaiting the PEAK drain and then recharge.

PS - Your idea of taking the load to allow NETT power to flow free, would be a good idea.. You could do it (say) from 10 to 2, so that it's at peak solar capacity..
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Re: Cutting you energy bill.??. Don't try this at home, kids.

PostPosted: Fri Sep 23, 2011 7:43 am
by Gordon-Loomberah
Using 250W just to maintain the float voltage indicates that the inverter-charger is very inefficient! I'd just turn it off to save wasting power when it's not being used for powering something or charging the batteries... or get a better inverter-charger or separate units to better suit the task size.
I started a thread about how much usable AC you get in a DC battery system last year, which has some info for my system with old batteries. I think the result was about 65% from memory, and although I haven't updated the thread recently, with new batteries it seems to be running at close to 73%. Those efficiencies include significant float and EQ time- a normal part of an off-grid system's operations.

Re: Cutting you energy bill.??. Don't try this at home, kids.

PostPosted: Fri Sep 23, 2011 7:49 pm
by Tracker
Gordon-Loomberah wrote:Using 250W just to maintain the float voltage indicates that the inverter-charger is very inefficient!


How right you are.. Thanks for the observations.. I do plan to (initially) continue with the experiment, with time clocks and a controller/relay..

A separate Charger would be a preference, so that I have the control on charging..

The other big issue for the "Casual" use of an inverter, is turning on the inversion process.. ie. it's not easy switching large DC currents.
At least the Inverter I have does have a "Power-Save mode", where is goes to sleep and pulses the output to detect a load.. (every 1 second)
It's actually the Inverter that draws the 1/4KwH, on idle, as in low-power mode, it goes to sleep and pulses the output, and then there is minimal A/C power drain.

I would be concerned for it's use with "Electronic" appliances.. ie. not sure of the full effect.

What "Standby" power would you normally see from your inverter.. ie the DC power drain, when NO a/c load..
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Re: Cutting you energy bill.??. Don't try this at home, kids.

PostPosted: Fri Sep 23, 2011 8:33 pm
by Gordon-Loomberah
Tracker wrote:I would be concerned for it's use with "Electronic" appliances.. ie. not sure of the full effect.

What "Standby" power would you normally see from your inverter.. ie the DC power drain, when NO a/c load..


I've used Selectronics and Latronics sine wave inverters in demand start/standby mode for years with no problems. Current draw in demand start mode depends on the size of the inverter, but typically is around 60-80mA... ie just a couple of watts, not 250!

Re: Cutting you energy bill.??. Don't try this at home, kids.

PostPosted: Sat Sep 24, 2011 11:50 am
by Tracker
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What I am concerned or Interested in is the power-technology of pulsing the 240V line, "Looking" for a load..
I'm just curious what such would do eg. to a microwave drawing a few watts, and not enuf to lock the inverter in.
This pulsing the load is obviously a cheap-skate way of minimising standby consumption. An efficient electronic inverter, should be able to produce 240Vac at neat zero load, and minimal input power.
In the least , it will sure create fun resetting clocks... :|
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Re: Cutting you energy bill.??. Don't try this at home, kids.

PostPosted: Sat Sep 24, 2011 3:36 pm
by Gordon-Loomberah
Tracker wrote:.
What I am concerned or Interested in is the power-technology of pulsing the 240V line, "Looking" for a load..
I'm just curious what such would do eg. to a microwave drawing a few watts, and not enuf to lock the inverter in.


I think the pulses are over 300V peak, and the demand start point is adjustable, but it didnt seem to bother any appliances I have.

This pulsing the load is obviously a cheap-skate way of minimising standby consumption.


It seems to be what they all do, at least the few I have experience with.

An efficient electronic inverter, should be able to produce 240Vac at neat zero load, and minimal input power.


Invent that and you'll make a million ;)

Re: Cutting you energy bill.??. Don't try this at home, kids.

PostPosted: Sun Sep 25, 2011 2:46 pm
by GeoffHammond
My VestFrost fridge (or at least the makers of it) reckon that powering it with a demand-start/standby inverter will void its warranty.

The way I've managed to clutter up my life means that I need my inverter on all the time to power electronic thermostats and the like, so I stopped investigating the why's/where's/etc.

Re: Cutting your energy bill.??. Don't try this at home, kids.

PostPosted: Sun Sep 25, 2011 9:57 pm
by Tracker
GeoffHammond wrote:My VestFrost fridge (or at least the makers of it) reckon that powering it with a demand-start/standby inverter will void its warranty.

I must say that I am "Concerned" for the practice.. (at the risk of repeating myself)
With my device, it pulses the load every second.. I could easily see an electronic device finding this unpalatable.

I've got a microwave the clags at temperature. - I might connect it up and see what it does.. but Gordon's experience suggests that there is no issue..
I WOULD hate to see a FingPaykel Washer on the line, or worse, a DishDraw - OUCH..!

BTW - Gordon, your comment about a 300V pulse concerns me because I have distributed suppression around the house and the MOV's are 275V.. Hmmmm? :oops:
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