Can you have grid-tied solar without export?

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Pete101

10 posts

Wannabe Geek

#310756 19-Nov-2023 14:32

Hi, I've tried searching this question but can seem to find an answer.

I'll looking into solar and thinking of installing some panels and battery storage, this is partly to save on my power bill and to have backup during power outages. The complication is my property has a 3 phase connection to a farm shed about 200m away from the house, I hardly use the 3 phase, but I don't want to lose it either as it's not costing me anything extra....low user rate of 60cents/day. The house only has a single phase connection which is metered as part of the 3 phase supply to the shed.

If I put in a solar system and want to export electricity (which I don't want to), I need a new export meter and being 3 phase this is an added complication I don't want to deal with. I want the solar at my house as it gets much more sun than the shed, and I don't want the unit 200m away from my wi-fi....so this would end up being a single phase supply back to a 3 phase export meter.

My question is, is it easy/common to have grid-tied solar with battery storage and no export to the grid, and which units allow you to do this?

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#3161189 19-Nov-2023 14:44

You do not have to export anything back to the grid if you do not want to in a grid tied Solar PV system. You can stop this with your PV energy meter. All brands' inverters come with energy meter options to monitor home consumption.

Do whatever you want to do man.

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Pete101

10 posts

Wannabe Geek

#3161194 19-Nov-2023 15:27

billgates:

You do not have to export anything back to the grid if you do not want to in a grid tied Solar PV system. You can stop this with your PV energy meter. All brands' inverters come with energy meter options to monitor home consumption.

Ok, thanks for the reply. I remember calling Harrisons a while back and asking, and their reply was "we only do grid-tied systems, we can pay for the export meter", which wasn't much help. I'm assuming most people want to export excess power so never ask the question, where as I want to store it in the battery for later use....if I generate more than I can use and store so it goes to waste, so be it.

mrdrifter

522 posts

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#3161265 19-Nov-2023 18:53

As billgates said, it's a software selection the installer can specify at time of setup, no different to them setting export limits for different lines company limits typically 5kw. The system would simply clip the additional generation and work to balance with your usage/load.

SomeoneSomewhere

1125 posts

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#3161281 19-Nov-2023 21:09

Getting a three phase smart meter for the shed should be fairly trivial? I'd be surprised it's not been done already.

The inverter doesn't necessarily need to know how much is being imported/exported at the garage; it can just dump power into the mains and let the retailer sort out the billing.

raytaylor

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#3161342 19-Nov-2023 23:24

I cant imagine why you would want to charge/discharge a battery when surely selling and buying from the grid would be cheaper than the amortised cost through wear and tear on a battery? Even if you sold more to the grid to compensate for anything you bought back later?

I'd much rather just stick up an extra 2 or 4 panels and sell more to the grid than cycle a battery.

A quick napkin calculation - At a loss of 10c per kwh by selling to the grid and buying back later would take 100,000kwh to make up $10k.

If a battery costs $10k and lasts ~7 years thats 39kwh per day you have to put into the battery and take back out to break even on a $10k spend. If the battery could even handle that while still lasting 7 years.

I would therefore think selling to the grid and buying back later at a loss of 10c per kwh will cost you less for the temporary storage of that energy.

If Onslow goes ahead, there would quite probably be a buyer that will happily purchase your excess solar power so offpeak sell prices during the day can be higher, while onslow would also supply a glut of power at night during the peak times so it would cost you less to buy back the power. Onslow efficiency would be around the 75-90% mark.

Regarding energy independence - during the week long power cut in Napier after cyclone gabrielle, we were quite happy using a couple of cheap deep cycle SLA batteries and a few of our solar panels switched to a low voltage DC system to keep them charged up for running our laptops, router fridge and some lights.

Ray Taylor

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SomeoneSomewhere

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#3161344 20-Nov-2023 00:37

National is in; Onslow is almost certainly dead.

Batteries are indeed expensive. Standard plans with small differences day/night or peak/shoulder/off-peak aren't likely to be enough to make batteries worthwhile. It's only if you're exposed to spot prices that they become financially viable (and even then, depends on market conditions). That's partly because the payout for midday residential PV generation is often above spot price, and that difference is only going to get bigger with more PV entering the market depressing midday prices.

In terms of the best place to spend another $1k, more panels is almost always the answer - even if it means you have so much panel that your inverter will be capping out. The inverter limits power only during the peak of the day when you probably have plenty; more panels produces more power at all other times including when sunlight is lower.

raytaylor

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#3161345 20-Nov-2023 01:22

Thats unfortunate.
Onslow would perfectly meet the definition of Think Big

Ray Taylor

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SomeoneSomewhere

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#3161346 20-Nov-2023 04:42

It would help a lot with dry years, although it's plausible solar will somewhat offset that on an annual energy basis.

Lake Onslow's position in the far south means it's not much use as peaking to replace the likes of Huntly and Marsden Point; you still need to upgrade the lines north to get more capacity into Auckland. The proposed battery going in at Bream Bay/Marsden Point will help with that somewhat. Dispatchable battery has the benefit of being able to act as reserve while almost never actually doing anything. By being ready to supply power to cover a failure elsewhere, you can operate the remaining equipment closer to capacity.

It's a pity that residential demand response (ripple and similar) seems to be fading away here. Peak shaving and rapid demand response can significantly reduce the need for grid upgrades and reduce the need for the costlier (and more polluting) end of the generation mix.

JimmyH

2820 posts

Uber Geek

#3161369 20-Nov-2023 08:45

raytaylor:

Thats unfortunate.
Onslow would perfectly meet the definition of Think Big

If you mean technically brilliant but utterly economically unviable and unlikely to ever even recover its cost of capital (like most of Think Big), let alone generate economic value, then it shouldn't go ahead.

From what I have seen Onslow would work and work well. But the engineering isn't the problem, the financials are. A $16 billion cost (assuming it comes in on budget) is an enormous sum. At a 9% cost of capital it would have to turn a profit of $1.4 billion a year to even cover its cost of capital, let alone be a positive for the investor. And an assumed 9% is a very low cost of capital for a commercially risky venture of this type, investors would be likely to require more. I just can't see it doing that. And the fact that the reporting I have seen says that it isn't viable without government money confirms that it looks like an investment dog. If it made sense commercially it wouldn't require government money, there are lots of long-term investors (think giant pension funds like CALPERS) willing to invest in long-term infrastructure that makes sense economically; maybe just some help with regulatory approvals etc. Taxpayers shouldn't back gargantuan feel-good risky money losers, we are too poor for that.

I'm happy to support Onslow, and maybe even invest in it personally, if they issued a prospectus that made financial sense to raise money. But the numbers have to work. And from what I have seen, they don't.

boosacnoodle

653 posts

Ultimate Geek

#3161529 20-Nov-2023 12:49

You're either going to need a three-phase smart meter or an home use meter for your solar inverter. There's no issue exporting on a single phase with three phase power from what I understand either.

richms

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#3161538 20-Nov-2023 13:30

It would need current transformers at the shed end to know whats going on so that it can stop exporting.

You will not be permitted to connect an inverter without the appropriate metering installed. No sparky will do a solar install unpermitted from the lines company, and its not something that comes in the DIY exemptions for own work.

Richard rich.ms

SomeoneSomewhere

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#3161646 20-Nov-2023 16:56

I think OP is suggesting setting the solar up on the house with a CT on the feed into the house, and the inverter set up so that it can't ever export from the house back to the garage, let alone to the grid. This would still constitute mains parallel generation requiring lines compliant and inspector signoff, but they might not need a new meter. Seems like a lot of lost revenue and hassle to save a simple meter swap.

There's no inherent need to have CTs on an inverter; plenty are installed without them and simply dump everything into the grid regardless of what other loads are doing.

Pete101

10 posts

Wannabe Geek

#3161719 20-Nov-2023 18:01

boosacnoodle:

You're either going to need a three-phase smart meter or an home use meter for your solar inverter. There's no issue exporting on a single phase with three phase power from what I understand either.

I read the following from my supplier (Genesis)

I guess I need to ask a sparky who knows the local setup, what the story is?

Pete101

10 posts

Wannabe Geek

#3161721 20-Nov-2023 18:15

raytaylor:

I cant imagine why you would want to charge/discharge a battery when surely selling and buying from the grid would be cheaper than the amortised cost through wear and tear on a battery? Even if you sold more to the grid to compensate for anything you bought back later?

I'd much rather just stick up an extra 2 or 4 panels and sell more to the grid than cycle a battery.

Yeah, I know a battery doesn't make economic sense. Yet I see it as a form of insurance against natural disasters, being able to use electricity when the panels aren't producing any/enough...just on that, it seems a grid-tied only system will shut down when the power is out anyway. I would assume there is some way to keep using the solar during a blackout, I just haven't seen the solution yet.

boosacnoodle

653 posts

Ultimate Geek

#3161766 20-Nov-2023 21:55

What are you looking to actually achieve here?

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