Tired of pumping energy into the grid

[mcart117]

Thanks for the link to "your story" @wattmatters . I'll enjoy reading that.

 

[mcart117]

I am continuing the story in a new thread in the Show and Tell forum.

 

[mcart117]

You need to talk with some who knows Australian Law. We can tell you how but I have heard it’s no joke to mess with that stuff there.

This reply is a bit late and out of sync with my other posts, but I'm learning as I go here.

I'd like to use the inverter offgrid, so I don't think the law will be a problem, but it was orginally used with 8 36 volt panels connected in series, producing a total of 288v. I want to use it with a 24 volt battery. So even if I could get it to work offgrid, which it is not designed to do, would it work with such a low input voltage?

 

[Nobodybusiness]

This reply is a bit late and out of sync with my other posts, but I'm learning as I go here.

I'd like to use the inverter offgrid, so I don't think the law will be a problem, but it was orginally used with 8 36 volt panels connected in series, producing a total of 288v. I want to use it with a 24 volt battery. So even if I could get it to work offgrid, which it is not designed to do, would it work with such a low input voltage?

Don’t known the inverter but it’s doubtful.

Most are designed for 12,24,48 or higher Voltages but have never seen one that will do 12- 400 before input wise.

Might be one but I’m not familiar with it.

It sounds just like solar only input for use or sell back.

Post the inverter Manufacture and Model#.

 

[wattmatters]

I'd like to use the inverter offgrid

If you mean the Fronius Primo inverter then it cannot operate on its own as an off-grid inverter. It is a grid following inverter only, IOW it needs a grid power signal to operate.

You can use it in an off-grid set up but you would need a grid forming inverter to control it. Something like a Selectronic which is designed precisely to do that. But frankly you may as well just get an inverter designed for off-grid use and find someone to sell the Primo to who might for one reason or another need one. Victron are one of the usual suspects in this space.

As you will see, the better quality inverters like the Selectronics and Victrons are not cheap. If you are looking for cheap(er), then something like a Growatt or other Voltronic-like PIP inverters (like the MPP units you see referenced on this forum, but models suitable for Australia).

 

[mcart117]

If you mean the Fronius Primo inverter then it cannot operate on its own as an off-grid inverter. It is a grid following inverter only, IOW it needs a grid power signal to operate.

Thanks for the reply. I was pretty well resigned to an answer like that.

But on a smaller scale, do most brands let you adjust the input voltage?

I'd like to start out building a 12v battery, and if all goes well buy more cells and upgrade to 24v. Do I have to lock in the input voltage of the inverter when I place the order? In other words if I buy one for the 12v battery, am I stuck with a 12v input or can I simply rotate a dial to make it accept 24v?

I've been looking at reviews on the XIJIA SwiPower 3kW Inverter, and it certainly looks as if the input voltage is fixed. Any thoughts?

 

[wattmatters]

But on a smaller scale, do most brands let you adjust the input voltage?

Not that I'm aware of. Normally you buy a 12, 24 or 48 V system.

I've been looking at reviews on the XIJIA SwiPower 3kW Inverter, and it certainly looks as if the input voltage is fixed. Any thoughts?

I've no experience with such inverters. But I would expect most will have a fixed DC input voltage. There will be variable voltage inverters but at what cost?

One of the reasons is they are designed for different outage power ranges. The more power output you need, the higher the battery DC voltage you'll want to work with. It keeps cabling, terminals and peripheral safety system costs down.

I would be starting with a power and energy audit. That will guide you on the inverter and battery voltage requirement.

 

[12VoltInstalls]

This thread is a reason why two, separated power systems make sense to me

 

[mcart117]

Not that I'm aware of. Normally you buy a 12, 24 or 48 V system.

I would be starting with a power and energy audit. That will guide you on the inverter and battery voltage requirement.

Thanks again.

I have been recording my energy consumption on a weekly basis for 3 years, and it is on that basis that I have decided to invest in some storage capacity.


Under my current supplier contract, On Peak means 3pm to 9 pm and Off Peak means 9 pm to 7 am. So a 12v 302 ah battery would get me through the expensive on peak period most evenings. And the On Peak Max of 7kwh includes an anomoly when the timer on my hot water system was running 6 hours late, after a power cut. So the 3kwh average is closer to typical usage.

A 24v 8kwh battery would get me through most nights as well. The 15kwh max would have been a few nights in winter when the kids had an reverse cycle air con system warming their room. They're older now, and don't really need that any more. So again 8kwh should fit the bill.

I'll never need the battery during the day, because my grid tied panels on the house cover that - unless there is a power cut, in which case I'll crank up the petrol generator.

Anyway, from what you say, it looks like I should dive straight in with the 24v 8kwh system.

 

[wattmatters]

Anyway, from what you say, it looks like I should dive straight in with the 24v 8kwh system.

That's the energy part of a power and energy audit.

What about the power side? 24V systems are typically rated max of 3 kW continuous. Is 3 kW going to cover your power demand at times?

You'll need enough power to cover whatever appliances you might choose to use at any one time. Whether that's an issue is going to depend on how the system is set up and what you expect to power.

If it's grid tied then there's no real issues as the system is supplemented by grid power as/when required (same as your grid-tied solar PV system is). The two power supplies (the battery system and the grid) operate in parallel, by that I means they can both supply power such that if the battery system supplying its maximum power but if that is not enough to cover the power demand, then the balance of power demand is supplied by the grid.

During outages you'll need to moderate what you use to the limit of the battery system but that's only during outages.

But a grid-tied battery in Australia is quite a different ball game to an off-grid scenario and it's not really a DIY project.

If you are talking about a separate off-grid scenario supplying power on a more permanent basis then you have two challenges:
i. you'll need a way to distribute that energy from the off-grid system which is isolated from the grid supply, and
ii. it will need to have sufficient power output capacity to manage whatever appliances you are wanting to power at any one time. There is no grid to add to the power the inverter can supply, the off-grid inverter sets the upper limit on how much power you can draw at any time.

e.g. at night you'll have some lights, a TV and/or computer perhaps, internet connection, fridge(s), and then you'll have high power appliances to consider. Electric kettle to boil water for tea, or a coffee maker. Toaster. Oven/stove? Any electrical heating or cooling appliance (e.g. aircon). You mentioned electric hot water, I'd imagine you'd be isolating that from an off-grid supply to be grid only.

I'm going through this mind wrestling with myself at present.

I would like to run my essential loads overnight via my off-grid system (I would supplement the existing bank with some LiFePO4 capacity to do that). But even the essential load circuits can add up. e.g. if both homes happen to put on an electric kettle at the same time then that would be enough to overload the system. Overnight I think it would be OK but during the day I can see too many situations where the load will exceed the off-grid inverter's capacity.

So to manage that I would need either:
i. a way to reliably change the essential loads supply between off-grid and grid supplies each morning and evening. Most "affordable" programmable ATS units are not really designed for a lot of switching cycles.
ii. a more powerful off-grid system (current one is 4 kW max)
Neither are cheap which kills any energy cost savings.

 

[Britguy]

Anyway, from what you say, it looks like I should dive straight in with the 24v 8kwh system.

I never understand why people in houses consider anything but 48V.
12V is for mobile homes/vans/campers.

 

[mcart117]

That's the energy part of a power and energy audit.

What about the power side? 24V systems are typically rated max of 3 kW continuous. Is 3 kW going to cover your power demand at times?

You are quite right and this has also been much on my mind when mulling over the inverter. My petrol generator is only 2.5kw so we have a strict regime during power cuts: no toasters, kettles or ovens allowed. A few months ago the generator was bouncing and juddering across the shed, and I ran around the house looking for the rogue appliance, only to find my wife had started a wash in the laundrey. On another occasion, I had forgorten to disconnnect the hot water system.

Our oven is 2.5kw, the kettle 2.2kw and the microwave 1.35kw. During breakfast we often use the microwave and the kettle at the same time. At night my wife sometimes uses the 2.3kw washing machine. All our lights are LED and we don't turn on the telly until after supper. The fridges are rated at 149kwh/yr or 400wh/day. I think the max power when starting the motors would be around 200w, momentarily pulling another 8 amps each.

So I'm thinking I need a 5kw inverter, which is twice the price on a 3kw one, but the whole point of this exercise is not to stress when the oven is used in the evening. 4.8kw would pull 200 amps from a 24 volt battery. The max discharge rate on the EVE 3.2V 304Ah cells is 250 amps, but it should rarely happen. The kettle and the microwave would pull 150 amps, but only for a minute or two. The washing machine would pull 100 amps, but again, only while it is heating the water.

 

[mcart117]

I never understand why people in houses consider anything but 48V.
12V is for mobile homes/vans/campers.

In short, because this is all new to me and I don't want to sink too much money without getting a personal feel for how robust and long lasting these batteries are. I'm not powering the whole house 24/7. I just want to test the feasibility of going offgrid for a few hours each day during the peak rate period. If the economics don't work out for the peak rate period, it is a waste of money buying enough capacity for 24 hour cover.

 

[Britguy]

. I think the max power when starting the motors would be around 200w, momentarily pulling another 8 amps each.

My chest freezer pulls 1000W when the compressor starts, then drops to 100W.

 

[mcart117]

My chest freezer pulls 1000W when the compressor starts, then drops to 100W.

Good info, thanks. I'll need to monitor that.

 

[wattmatters]

I just want to test the feasibility of going offgrid for a few hours each day during the peak rate period.

Yeah that can be problematic.

It's a peak rate period for good reason as it corresponds with the time of day when people want to use peak power draw appliances such as cooking, heating/cooling systems and other stuff when they come home. As a result, attempting to cover that period using a grid isolated system without a lifestyle change = higher specification / more expensive system.

Things like laundry are usually much more discretionary with respect to time of day and day of week they can be used. That's just a modest habit change. But I'm not going tell the wife we can't boil the kettle for a cup of tea right after making dinner.

For me the possibility of my off-grid system running our essential loads most of the time is enticing.

From an energy supply POV it would be fine as it also has an AC input which is fed via grid supply (including out grid tied solar PV) should we need supplemental energy to what the off-grid system could provide. But from a power throughput POV the limit of the inverter is 4 kW and the off-grid supply infrastructure is designed for handling 20A @ 230V (4.6 kW).

For supply to essential loads during outages, it's perfect. We know not to do laundry or for my wife to use a hair drier.

But as a supply to run a home during normal operation, it's inadequate. I already have non-essential loads separated and they are not powered by the off-grid system during outages, things like ovens, stovetops, large aircons etc. But all GPOs and lights are covered, as are the two outbuildings.

 

[12VoltInstalls]

never understand why people in houses consider anything but 48V.
12V is for mobile homes/vans/campers.

Depends on the house depends on the locale depends on the person.
My lawyer’s been 12V solar going back 20 years. Her home is not mobil, isn’t a van, and is a wood framed house a couple miles from the nearest powerco pole. I guess she didn’t get the brief?

If the economics don't work out for the peak rate period, it is a waste of money buying enough capacity for 24 hour cover

Good logic. If it ROIs reasonably well it is worth it and a convenient backup system is in place.

Don’t judge it to harshly. Every year your electric bill goes up the solar system will just put out. Not a care!

 

[Britguy]

Depends on the house depends on the locale depends on the person.
My lawyer’s been 12V solar going back 20 years. Her home is not mobil, isn’t a van, and is a wood framed house a couple miles from the nearest powerco pole. I guess she didn’t get the brief?

Surprised she isn't still using gaslights.

 

[12VoltInstalls]

Surprised she isn't still using gaslights.

I think she has some for backup.

But I’m interpreting your comments as a bit snobby on the teacup tipping.
It’s fine to explain the relative practical advantages of 24V or 48V but you are making assumptions and thinking with jaded stereotypes.
But a blanket statement without context does nothing but communicate that you have an opinion.
There are many reasons people maintain 12V systems and those reasons don’t equate to people being ‘backwards’ and those reasons don’t explicitly make them ‘stupid’ or confused.

 

[Britguy]

But I’m interpreting your comments as a bit snobby on the teacup tipping.

More to do with me being cheap.
12V needs big expensive 'special' wires.
48V I can do everything with cheap 2.5mm twin used for normal house wiring (10cents/m).
I can even make the battery busbars out of 3 loops (6 thickness) of 2.5mm wire, no need to buy expensive 'special' copper bar.

The boss agrees with me .............