Domestic solar PV quotes 2018

air · 27-08-2019 12:14PM

Looks fairly standard, so you'll be clipped at 11A input current, compare that with the MPP current on your data sheet.
They're probably around 7.5A max output so it should work fine. In practice you'll never have peak output on both arrays simultaneously.
I've about 6.75kW peak (panels) myself and never saw more than 5.5kW export.

thos · 27-08-2019 02:00PM

Excellent, thanks for your help!

29-08-2019 04:14AM

air wrote: »

You should put a series diode in line with both the 8 South facing ones and the 8 new ones.

Why not use opposing voltages instead?

air · 29-08-2019 04:40AM

Sir Liamalot wrote: »

air wrote: »

You should put a series diode in line with both the 8 South facing ones and the 8 new ones.

Why not use opposing voltages instead?

Primarily because I'm more focused on making useful practical suggestions than posting cryptic one liners.

jspuds · 29-08-2019 09:03AM

air wrote: »

Primarily because I'm more focused on making useful practical suggestions than posting cryptic one liners.

Please lets keep the thread on track

29-08-2019 12:20PM

There's no need for series diodes in unshaded panels. As long as there is ambient light the voltage of one string will oppose the other.
Diodes reduce efficiency.

29-08-2019 12:28PM

Yes and heat. Why add losses to the system? Diodes are not necessary.

air · 29-08-2019 12:35PM

Sir Liamalot wrote: »

There's no need for series diodes in unshaded panels. As long as there is ambient light the voltage of one string will oppose the other.
Diodes reduce efficiency.

The forward diode volt drop would cause a peak loss of efficiency of approximately 0.3% at full load in this application (assuming regular 60 cell panels) & cost next to nothing.

I think that's a fair compromise for protecting 8 panels from possible destruction in the (admittedly unlikely) event that one or all of the panels are shaded at some point in their 30 or so year installation lifetime.

A dark sheet or tarpaulin could be blown onto a string, one or more bypass diodes could fail shorted, a panel could be bypassed by cable rub etc.

There are myriad possible scenarios that are all protected against to at least some extent by a series diode.

If 0.3% is too much of an efficiency hit to live with, thos could also investigate ORing MOSFETs which have lower forward volt drop than a simple diode.

However 15A diodes are commonly available fitted to a pair of MC4 connectors which would make fitting them plug and play in this instance.

29-08-2019 12:40PM

Shaded panels get destroyed now? Panels work without bypass diodes..they just reverse bias and pull down the array.

air · 29-08-2019 01:17PM

Sir Liamalot wrote: »

Shaded panels get destroyed now? Panels work without bypass diodes..they just reverse bias and pull down the array.

If a panel is completely shaded it produces no voltage and will be reverse biased by the other string.

It becomes a big heater and given enough time/voltage/current will be irreparably destroyed.

Why don't you try connecting a panel to a battery without a controller and leave it overnight and report back to us how well the panel operates tomorrow.

Every inverter manufacturer that I'm aware of that provides multiple parallel inputs fits diodes for this very reason.

I think I've explained the reasons sufficiently at this stage and people are free to make an educated decision either way.

niallers1 · 29-08-2019 03:16PM

I think ye've just killed interest in this thread

Coltrane · 29-08-2019 03:43PM

Hoping to revive it!

I'm looking at installing more solar PV on the roof at home. My installer who seems very knowledgeable and helpful says that I won't qualify for the SEAI grant because I already have PV, even though that was not grant aided (it was installed before the current grant was introduced).

Any contrary experience? SEAI's terms and conditions state only that only one installation will be "supported" at each home, which I take to mean that they'll only grant-aid once.

unkel · 29-08-2019 04:11PM

Your installer is wrong. Whatever you have currently installed is irrelevant. I have PV and I got a quote for a battery only system and the grant of €1000 was applied on my quote

What's at play here is probably that the installer doesn't want to touch your current install. Which is understandable.

30-08-2019 12:08AM

Dear Air,

I am not trying to get into a peeing competition here, I have no antipathy for you I would like to address the postings of what I consider to be contentious advice. It is nothing personal I am addressing your comments as impartial and with scientific merit. I'm happy to agree or disagree with you til the cows come home based on my own experience. Nor am I trying to divert this thread, nor reduce the tone. May I attempt to resolve the controvertial series (blocking) diode issue? We are all learning so if I may...

air wrote: »

If a panel is completely shaded it produces no voltage and will be reverse biased by the other string.

If a cell is reverse baised in a cell string it will become a heater by the other cells in that string. If a cell string is reverse biased in a panel the rest of the panels and cell strings do not heat the shaded cell string they use the bypass diodes. Limited heat, overhead built into panel. If a panel is reverse biased within a panel string it will reduce the voltage of that string by not contributing Vmp to the rest of the array using the parallel bypass diodes in the offending panel.

Easiest path to ground rules apply.

I am of course talking about pitch black, not shadow but absence of light only created by a poor siting of a panel, say under a willow tree, in a cellar etc...

If there is any diffused ambient light on the panel string it will produce Vmp at zero current and oppose current from the other string as the connected load is an easier path to ground.

In the unlikely event, a panel string is reverse-biased the lit panel string will power the load and the entirely shaded panel string as a potential divider.

Sure that's a problem, diodes aren't the solution better siting is the answer.

air wrote: »

It becomes a big heater and given enough time/voltage/current will be irreparably destroyed.

Emphasis on time (years), shading recurrence over the same cells and poor installation location choice.

air wrote: »

Why don't you try connecting a panel to a battery without a controller and leave it overnight and report back to us how well the panel operates tomorrow.

Have you tried this?

I can attest I have and it works very well.
What does a charge controller do? Reduce voltage seen at the panel to battery nominal!

If I get a 60 cell 31 Voc panel and connect it to a flooded lead acid 24V nominal meat and spuds battery with a 29.8V + temperature compensation absorption setpoint why do I need a charge controller? Opposing voltages will normalise and regulate the current. It works great, I've been doing it for years.

Now consider using a series diode in this system..
Lets say it's 1kWp on a 45A charge controller
45A x 0.7Vf = 30W peak heat devolving from that diode. I assure you the nighttime losses through the panel are less than this, and the heating effect at night is offset by the ambient temperature reduction and lack of irradiance.

Series diodes are poor practice and a high-risk failure point imo.

air wrote: »

Every inverter manufacturer that I'm aware of that provides multiple parallel inputs fits diodes for this very reason.

Is this not for isolation for more effective power point tracking?

Sure prevention of losing the array to a string failure is a rare side-benefit. I fit panel meters. If there's no output; open the offending string disconnect.

Blocking diodes are a lot like taking a 2wd off-road to me.

Here's a peer review all about it.

30-08-2019 12:26AM

unkel wrote: »

What's at play here is probably that the installer doesn't want to touch your current install. Which is understandable.

I've emailed 50 installers and 4 made the short list. Either I upset them too much or vice versa.

I don't think it's understandable that some installers only want the high profit easy no questions asked jobs...

The amount of installers I've had to quote their own installation guide to is ridiculous. Quite a lot of crowbarring out there.
"Oh you can't use lead acid..."
First one to show me a B-type RCD on a high frequency inverter and a DC disconnect rated for full load rupture current gets a commendation..so far I have zero.
Hence I've designed my system for them. :rolleyes:

air · 30-08-2019 07:18AM

I suggest you start a new thread Sir Liam, totally OT here.

garo · 01-09-2019 02:49PM

It breaks my heart to see 3+kW being exported for free. As consolation I tell myself I am doing my bit for the environment.

gally74 · 01-09-2019 02:57PM

garo wrote: »

It breaks my heart to see 3+kW being exported for free. As consolation I tell myself I am doing my bit for the environment.

Fit will come

CiaranIRE · 02-09-2019 11:24AM

Response for the ESB:

The smart meters upgrade programme is phased over the next 5 years. During that period services will be introduced in a phased manner beginning with “time-of-use” tariffs from 2021, with other services such as pay-as-you-go scheduled for 2023.

Initially we are focusing our meter replacement programme on 24 hour legacy meters and not day/night or pay-as-you-go meters as we don’t want customers to lose out on their current tariff or service until equivalent services are available.

We would therefore ask you at this stage to bear with us. Your meter replacement, which will be free of charge, will be scheduled at a point when Suppliers are able to offer a wider range of Smart Services.

With regard to the smart meter functionality, we confirm they do have the capability to record both import and export.

Sounds like they won't install a smart meter until they can offer the services you already have, beginning with day/night metering in 2021.

Even if a feed in tariff is announced soon, (reading between the lines) that service won't be available on the smart meter until at least after 2021 unless you install an export meter in the mean time at your own expense which likely wouldn't even pay for itself.

Hopefully they're just being a bit vague until a feed in tariff is officially announced.

04-09-2019 12:15AM

Solar PV is not worth it without a FIT, no need for battery with FIT, not worth the money, sell all the excess and buy back when needed.

reklamos · 04-09-2019 08:48AM

[Deleted User] wrote: »

Solar PV is not worth it without a FIT, no need for battery with FIT, not worth the money, sell all the excess and buy back when needed.

FIT will only work if it is fit for purpose. We do not know the details yet but the feed to grid charge could make FIT irrelevant for most people.

unkel · 04-09-2019 08:57AM

It might very well be only 5c / kWh. That means with a simple no battery south facing 4kwp array producing 4MWh per year, if three quarters goes to the grid, you will get €150 per year for that (3000 * 0.05) and you save 1MWh almost completely at the day rate for self consumption, that's 1000 * 0.18 = €180 per year. So €330 per year total

Let's say this system cost you €3k installed. That means a pay back period of 9 years. Really not bad at all. Who else gets 11% return on their investment tax free?

04-09-2019 09:24AM

Tax free , are you sure about that?

unkel · 04-09-2019 09:53AM

I would be confident that FIT income will not be taken account for income tax purposes. It would be too ridiculous to consider really. Like the free coffee you get in work.

The rest of the return is a saving you have, so not income.

antoinolachtnai · 04-09-2019 10:31AM

unkel wrote: »

It might very well be only 5c / kWh. That means with a simple no battery south facing 4kwp array producing 4MWh per year, if three quarters goes to the grid, you will get €150 per year for that (3000 * 0.05) and you save 1MWh almost completely at the day rate for self consumption, that's 1000 * 0.18 = €180 per year. So €330 per year total

Let's say this system cost you €3k installed. That means a pay back period of 9 years. Really not bad at all. Who else gets 11% return on their investment tax free?

5c would be a great price to get for PV. Sunnytime electricity is frequently under 3.5c wholesale. This is the time when you would be mostly exporting.

The price of sunny time electricity will fall still further when hundreds of MW of subsidised commercial PV hits the grid.

The smart meter will also give you the chance to access these cheaper prices when they are available.

So the benefit of home PV will be much smaller. On the other hand, the benefit of a home battery will be much bigger.

air · 04-09-2019 10:41AM

antoinolachtnai wrote: »

5c would be a great price to get for PV. Sunnytime electricity is frequently under 3.5c wholesale. This is the time when you would be mostly exporting.

The price of sunny time electricity will fall still further when hundreds of MW of subsidised commercial PV hits the grid.

The smart meter will also give you the chance to access these cheaper prices when they are available.

So the benefit of home PV will be much smaller. On the other hand, the benefit of a home battery will be much bigger.

I question your figures.
You're excluding TUOS charges again, as well as VAT.
For a long time to come, domestic PV export will be resold immediately to neighbouring properties without PV so an export rate of 5c/kWh (Inc VAT) should be profitable for energy suppliers.
Commercial PV operators are currently negotiating unsubsidised deals at well over 5c/kWh ex VAT.

unkel · 04-09-2019 10:45AM

antoinolachtnai wrote: »

5c would be a great price to get for PV. Sunnytime electricity is frequently under 3.5c wholesale. This is the time when you would be mostly exporting.

Even at 3.5c it probably still gives you a better return than a battery system. Or immersion diversion.

In my example above a 3.5c fit still gives a return on investment of just a touch over 10 years. Not bad. And no investments (battery / immersion diverter) and no maintenance / replacement costs

reklamos · 04-09-2019 11:26AM

I think Irish government being very 'innovative', will just copy/past what UK is doing. For those interested you can read it here:
https://www.ofgem.gov.uk/environmental-programmes/fit/fit-tariff-rates

In less than to months I only exported 27kWh but I do have a battery and hot water diverter.
Once FIT comes in place, for me it could make sense to cut down on water diversion and push to grid more during sunny hours.Then at night time pull back at lower cost to charge the battery at early morning hours. This way I could feed back more to the grid the next day as the batteries would be full early on and have plenty juice for evening hours. I did not do the math if that is economically viable solution when installing new setup.

antoinolachtnai · 04-09-2019 03:23PM

air wrote: »

I question your figures.
You're excluding TUOS charges again, as well as VAT.
For a long time to come, domestic PV export will be resold immediately to neighbouring properties without PV so an export rate of 5c/kWh (Inc VAT) should be profitable for energy suppliers.
Commercial PV operators are currently negotiating unsubsidised deals at well over 5c/kWh ex VAT.

TUoS is only a cent a kWh. You have to pay the DUoS regardless of how little of the distribution network you use. The daytime DUoS will be reduced too and peak DUoS will increase. There is already a review planned under the climate action plan to review these rates.

If you can consume all the power on site, certainly a higher price per kWh makes sense. That is why that commercial stuff works. As you rightly say, at the moment you avoid the DUoS, though that benefit will diminish as DUoS rates change.

There is also a complicated issue about de minimis benefits for small generators.

There isn’t much benefit re VAT because an unregistered person can’t offset capital cost for VAT purposes where commercial operators can. There is something that could be done with VAT on the sale but it is not going to make that much difference even if the purchasers go to the bother of implementing the VAT break.

air · 04-09-2019 03:38PM

antoinolachtnai wrote: »

TUoS is only a cent a kWh. You have to pay the DUoS regardless of how little of the distribution network you use. The daytime DUoS will be reduced too and peak DUoS will increase. There is already a review planned under the climate action plan to review these rates.

If you can consume all the power on site, certainly a higher price per kWh makes sense. That is why that commercial stuff works. As you rightly say, at the moment you avoid the DUoS, though that benefit will diminish as DUoS rates change.

There is also a complicated issue about de minimis benefits for small generators.

There isn’t much benefit re VAT because an unregistered person can’t offset capital cost for VAT purposes where commercial operators can. There is something that could be done with VAT on the sale but it is not going to make that much difference even if the purchasers go to the bother of implementing the VAT break.

A cent a kWh is very significant in terms of a FIT of 5c!!!

Also VAT is relevant, as the supplier is a commercial operator and can offset the VAT paid.

The advertised FIT rate is likely to be inclusive of VAT - as is the FIT on the existing (closed 9c/kWh) scheme.

A FIT of 5c/kWh Inc VAT only costs the supplier 4.4c/kWh in real terms.
Subtract the 1c/kWh saving on TUOS and it's below your claimed daytime average wholesale rate of 3.5c/kWh

I didn't mention DUOS because it's unavoidable as you say.

All told I don't see any evidence why a domestic FIT of 5c should not be perfectly commercially viable in the current market.

Domestic solar PV quotes 2018

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