Alternative to microinverters

[mikeselectricstuff]

Thanks everyone for the clarifications.
Yes, power optimizers look like a solution, and probably it would be the best one in my case.

But in general, would not it better to have isolated DCDC converters? Parallel connection, with every PV panel having a converter, stepping up the voltage to >320V and then a central inverter.

Why isolated ? Conventional series systems have HVDC on the cabling, so no real safety advantage, and added cost. Just isolate at the inverter.

[Someone]

In my opinion micro-inverters make no sense at all.

Until a single solar panel malfunctions, you get 0 output and you have to go up to the roof to replace it or let a company replace it and you are directly break even on the costs of the company replacing a single panel. 

It makes perfect sense, there is not a single point of failure anymore and you can wait till a couple panels have broken down.

But more hardware ( microinverters) means more potential failure points.
How often do panels go bad ?

How often does a panel and its integrated bypass diodes go bad at the same time? Either could fail and you'd still not get 0 output from the string (as the linked video shows).

[Marco]

But in general, would not it better to have isolated DCDC converters? Parallel connection, with every PV panel having a converter, stepping up the voltage to >320V and then a central inverter.

As I said, optimizers are optional. In a parallel system they would be mandatory, the small advantages probably don't justify an entirely separate product line.

It would minimize leakage currents and simplify the inverter, still not worth it.

[tszaboo]

Chasing the last few percent is usually uneconomic:

You get piece of mind, and a higher efficiency system.
It's well known that the marketing claims by Enphase or Solaredge are not true. They are made by marketing after all.
When I was buying my system, I paid 1:3 for the panels to the optimizers. More realistically, if you include the racking and the installer's cost (they base it on the number of panels). Plus as I said, the Solaredge inverters are cheaper compared to SMA or Fronius. Not compared to the bottom shelf inverters. So the extra cost in the end is that much.
Now this ratio is closer to 1.5:1, I wouldn't install this system.
And if you are only about the ROI, there are used systems on the market for next to nothing (here).
For example a 16x270W system with a 4KW inverter is for sale for 500 EUR. The ROI of that is probably less than a year.

Tigo also makes optimizers that work with regular inverters, and as I understand you can just place it on some of the panels.

[Kjelt]

So why are not cars equipped ..l..
".....
 that would reduce efficiency, add cost, and tire failures are rare enough

Microinverters do not reduce efficiency, esp in a three phase setup.
Add cost yes as said more expensive but gives additional benefits.

Rare yes but very unpleasant when occurs as any modern car driver will ackknowledge when he stands beside the road and the spare wheel was replaced by a shitty foam can or even nothing.

For companies, cost matter but reliability should also matter, depending on the cost / benefit you can make your decision.
My panels are unreachable at 12m height on a tilted roof for normal persons and require special equipment or human acrobats with life insurance to service. One of the reasons I choose the microinverters.
If someone else has a flat roof and is EE they might make another choice.
Another benefit of microinverters is that you can add panels if you want, no need for a bigger inverter.

[Kjelt]

It doesn't have to be.

Indeed depending on the circumstances of the installation and the skills of the owner, different choices might be made.
For teliability I get 25 years warranty on my microinverters but only 15 on the panel which also degrades over time.
Indeed weather and accidents out of the equation you still would think the microinverter would die before the panel however that is also guaranteed incl workmanship just as a weather event. Although I already saw insurance policies where solar installations are excluded for certain events.

[Kjelt]

Yeah, and this is not just like idle talk. Surprisingly good reliability of PV panels is well known, and so is the fact that microinverters do fail and are harder to replace than the string inverter.

Then why do my microinverters have a almostvtwice longer guarantee than any normal inverter?
Could it perhaps be that in countraey to normal inverters they do not use electrolytic capacitors which are known to degrade and are one of the first components to die in any electronic circuit? Could it be it only has to take care of a few hundreds Watts max and mostly less, while the normal inverter has to handle kWs?

Lets see how it plays out, I will post back in 8 years when the first ten years have passed and in 18 years. In the mean time my two neighbours have the same company install their systems with normal inverters , not statiscally relevant but still interesting to see who gets the first problems.

[nctnico]

Yeah, and this is not just like idle talk. Surprisingly good reliability of PV panels is well known, and so is the fact that microinverters do fail and are harder to replace than the string inverter.

Then why do my microinverters have a almostvtwice longer guarantee than any normal inverter?
Could it perhaps be that in countraey to normal inverters they do not use electrolytic capacitors which are known to degrade and are one of the first components to die in any electronic circuit? Could it be it only has to take care of a few hundreds Watts max and mostly less, while the normal inverter has to handle kWs?

Lets see how it plays out, I will post back in 8 years when the first ten years have passed and in 18 years. In the mean time my two neighbours have the same company install their systems with normal inverters , not statiscally relevant but still interesting to see who gets the first problems.

Actually the lifespan of an inverter doesn't really matter. 10 years is good enough. If you want to add batteries for example, then you'll need to either pay for an extra inverter for the batteries OR replace the existing inverter with a hybrid one. With micro-inverters you'll always need to invest in an extra inverter for batteries with the additional efficiency reduction as you'll need to convert between AC and DC twice. And with micro-inverters you are stuck with old technology long before the solar panels are due for a replacement.

The shop I bought my solar installation from less than 2 years ago only sells the hybrid version for the inverter I have nowadays. And they are cheaper compared to the inverter I have as well. Either way, by the time an inverter needs to be replaced due to a failure, you likely want to upgrade anyway.

[Kjelt]

Batteries is aagain a new parameter to the equation. The economic justification for those in our country makes 0 sense even if you build them yourself from server batteries, in which case the bms and charger/ inverter are probably also from the same brand.
But then you can also charge the batteries from mains in combination with a dynamic energy contract making it even more versatile than charging from your own solar. (Again a new parameter which does not help the discussion).

[tszaboo]

Batteries is aagain a new parameter to the equation. The economic justification for those in our country makes 0 sense even if you build them yourself from server batteries, in which case the bms and charger/ inverter are probably also from the same brand.
But then you can also charge the batteries from mains in combination with a dynamic energy contract making it even more versatile than charging from your own solar. (Again a new parameter which does not help the discussion).

I was calculating that a battery system at home makes electricity more expensive than not having it. Because of the charging-discharging efficiency loss, you use more electricity. And gain nothing.
These new cartel made extra solar charges are that stupid.

[Siwastaja]

Then why do my microinverters have a almostvtwice longer guarantee than any normal inverter?

Exactly because the guarantee is the only way for the manufacturers to manage the reputation hit from earlier reliability problems that are too widely known. It doesn't even matter if the problems are that widespread, but people know about them so they have to offer guarantee.

The cost of the microinverter itself being negligible, the key question is, does the guarantee of the inverter cover the replacement work? Or does the installer or sales company need to provide such extra guarantee with their own risk?

Could it perhaps be that in countraey to normal inverters they do not use electrolytic capacitors which are known to degrade and are one of the first components to die in any electronic circuit? Could it be it only has to take care of a few hundreds Watts max and mostly less, while the normal inverter has to handle kWs?

This is totally absurd. You have no idea what you are talking about.

[Siwastaja]

I was calculating that a battery system at home makes electricity more expensive than not having it. Because of the charging-discharging efficiency loss, you use more electricity. And gain nothing.

Of course you can gain savings, but return of investment is still nearly impossible. Exact details depend on country and types of contracts available, but usually self-storage of generated solar makes money because for selling PV out to grid, price you get from it is much worse compared to when you buy the electricity back in the evening/night/morning. For example, here you can buy for spot price plus transmission plus taxes, but sell for only the spot price minus margin. E.g. buy at 15 cents/kWh, sell at 8 cents/kWh.

Further money can be made in spot markets / hourly pricing. Buy when cheap, self-use when more expensive. In extreme cases, sell to grid.

But all this requires careful optimization, and even if you do it right you can make say 200, maybe 300 EUR/year with a 10000EUR investment with a guarantee of 8 years.

And yet, this is what people want. Battery business is growing hugely and now more than 50% of our new customers are buying our box because it does said battery optimization. We would like to see our box bought primarily to control those hot water boilers, EVs and so on, it makes roughly the same 200-300 EUR/year for one fifth of the investment. Luckily, many of our battery customers also have something else to control.

[Kjelt]

This is totally absurd. You have no idea what you are talking about.

Indeed I have to take that back it was in my memory that they did not use electrolytics. But by reviewing some teardowns they do indeed, although only four pieces.

[nctnico]

Batteries is aagain a new parameter to the equation. The economic justification for those in our country makes 0 sense even if you build them yourself from server batteries,

That is true for today. But that may change completely a few years down the road. Building some flexibility into your energy system makes sure you can adapt and don't overspend at the start. That is also why I pinched every penny when doing my solar panel installation to make the sure the time until it has paid for itself is no longer than 4 years. Any longer just doesn't make sense due to all the economic uncertainties (including unforeseen breakdowns). And to be honest, I don't think I'm going to achieve break-even within 4 years due to tariff changes.

[Marco]

I think government should set some standards and protocols in time to let batteries be used collectively.

Otherwise people who got their batteries late are going to get screwed just like late adopters of PV, cost of power will inevitably shift from kWh to fixed connection costs. If the power companies can take a long term contract to take control over the home batteries, they can provide some ROI while needing to build less batteries of their own.

[nctnico]

At this moment I'm not sure domestic / home batteries will ever be viable. In the end you can't beat the economics of doing something on a large scale. Also the energy grid is still organised to go from large producers to many small consumers. A large scale storage system fits much better within the existing infrastructure compared to a decentralised, fragmented system.

In the Netherlands they are working on huge battery storage systems with capacities in the ballpark of 1 GWh -each-. Based on what I'v read in the news, these systems' storage cost are at little below 4 euro-cents per kWh and they get a major discount on transport costs. As a comparison: the cheapest 5kWh home-battery I found so far sits at 10 euro-cents per kWh stored. With my current electricity prices, I pay the utility company around 10 eurocents per kWh to use the grid as a battery (if I ignore the existing subsidies for a moment).

Ofcourse you could speculate on electricity prices going negative and try to make batteries pay for themselves that way but big companies are better at playing that game. Recently I got an offer to spend 5k euro on a 5kWh battery pack (which is twice the price compared to a battery pack I found elsewhere) and the seller says it pays for itself in 5 years but I don't see that happening. It is a massive gamble and very unlikely to break even. An investment fund will be more likely to deliver a positive ROI during the same time.

[tszaboo]

I think government should set some standards and protocols in time to let batteries be used collectively.

Otherwise people who got their batteries late are going to get screwed just like late adopters of PV, cost of power will inevitably shift from kWh to fixed connection costs. If the power companies can take a long term contract to take control over the home batteries, they can provide some ROI while needing to build less batteries of their own.

Sure sure, but then don't you already see that every single one of our governments are just puppets to the energy providers?
I mean Enexis makes a Billion EUR profit in 2022, and then increases the prices because the network capacity is insufficient.
They only serve 2.8 Million houses. So 360 EUR per household. For making sure that a bunch of wires don't break*. (euphemism)
Don't expect that you will get a good deal for home batteries. They have profit targets to reach.

[mikeselectricstuff]

The plummetting cost of panels makes microinverters seem excessively  expensive. I can buy a 400W panel for £60, an Enphase IQ8 (that can't even handle 400W) costs twice that.

[Kjelt]

The plummetting cost of panels makes microinverters seem excessively  expensive. I can buy a 400W panel for £60, an Enphase IQ8 (that can't even handle 400W) costs twice that.

True prices plummeted here because the rules were changed here. If you own solar panels you have to pay monthly to your energy provider, which was not the case before. Now nobody buys solar panels anymore and fourteen installer companies that I know of went bellyup.

[nctnico]

Sure sure, but then don't you already see that every single one of our governments are just puppets to the energy providers?
I mean Enexis makes a Billion EUR profit in 2022, and then increases the prices because the network capacity is insufficient.

This reasoning & ranting gets tiresome. You forget to mention Enexis made barely any profit in the years before and after. The billion euro profit is a one-time exception. Probably due to selling off something. And all of their shareholders are provinces and cities / villages. So all the money they make flows back into public funds.

[tszaboo]

The plummetting cost of panels makes microinverters seem excessively  expensive. I can buy a 400W panel for £60, an Enphase IQ8 (that can't even handle 400W) costs twice that.

True prices plummeted here because the rules were changed here. If you own solar panels you have to pay monthly to your energy provider, which was not the case before. Now nobody buys solar panels anymore and fourteen installer companies that I know of went bellyup.

Also, somehow every single supplier changed the rules, somehow the same time. And customer protection ACM just stands by, and shakes their head, "yeah, this is fine. Let's charge 2 million solar installation about 30 EUR a month". But there is no cartel and no interference according to nctnico.
/rant off.

[mikeselectricstuff]

The plummetting cost of panels makes microinverters seem excessively  expensive. I can buy a 400W panel for £60, an Enphase IQ8 (that can't even handle 400W) costs twice that.

True prices plummeted here because the rules were changed here. If you own solar panels you have to pay monthly to your energy provider, which was not the case before. Now nobody buys solar panels anymore and fourteen installer companies that I know of went bellyup.

If you own panels, or if only you export?

[nctnico]

The plummetting cost of panels makes microinverters seem excessively  expensive. I can buy a 400W panel for £60, an Enphase IQ8 (that can't even handle 400W) costs twice that.

True prices plummeted here because the rules were changed here. If you own solar panels you have to pay monthly to your energy provider, which was not the case before. Now nobody buys solar panels anymore and fourteen installer companies that I know of went bellyup.

If you own panels, or if only you export?

Only if you export and typically depending on how much you export. But this is supposed to stop when the subsidies stop. The energy companies basically found a loop-hole to recoup some of the money for the subsidies they have to contribute to. Another effect is that electricity prices have been made lower which is a double whammy for solar panel owners.

To add some numbers:
I used to pay 26ct/kWh and get 26ct/kWh for what I supply to the grid. So 4000kWh/year would make me 1040 euro/year (either by using directly or supplying to the grid). With the new tarif system, I pay (approx) 22ct per kWh and also get 22ct per kWh, so I would still make 880 euro/year. However, due to supplying around 2500kWh/year back to the grid, I need to pay a fee around 240 euro. So the 'profit' from the solar panels went from 1040 euro / year to 640 / year.

[nctnico]

It is not a sunny day but covering a few cells makes the output power for that string go down to 355W from 480W. I also see the DC voltage going up for that string. In this particular situation it means a reduction of around 25%. The inverter is less than 2 years old.

To get back to shading losses. On my Growatt inverter I see output drops to over 30% when only a few cells are shaded. According to the seller, Growatt inverters don't have any shading optimisation in them. The alternative is to add optimisers.

I also checked some other brands from the same seller but it seems shadow optimisation is not very standard in the inverter brands they are carrying.

[Siwastaja]

I used to pay 26ct/kWh and get 26ct/kWh for what I supply to the grid. So 4000kWh/year would make me 1040 euro/year (either by using directly or supplying to the grid). With the new tarif system, I pay (approx) 22ct per kWh and also get 22ct per kWh, so I would still make 880 euro/year. However, due to supplying around 2500kWh/year back to the grid, I need to pay a fee around 240 euro. So the 'profit' from the solar panels went from 1040 euro / year to 640 / year.

So did I understand correctly - for you, value of sell-to-grid is 640 / 4000 = 16 cents/kWh, and value of self-use is, as always, equivalent to buying price, that is 22 cents/kWh. So "having to sell" would lose 27% of the value compared to self-use.

This doesn't sound bad to me at all, just understandable and fair. Say you are a nuclear plant or a coal power operator. It's not like you get paid for the final customer price either; there is value added in the chain, producer always gets less.

Here we don't have such weird "first someone gives you too much credit for something then you have to return part of it" system, but the difference between buy/sell results in from having electricity bill consist of two different parts, paid to two different companies: energy itself which you can buy from multitude of providers, and transmission/grid fee which you have to pay to your local grid company. When you sell excess production to grid, you sell the energy to the energy company of your choice, hence get paid for energy, but you do not get the transmission fee; which is understandable, because transmission fee is meant to cover for the costs of maintaining the grid and distribution.

Here energy companies only accept to buy your excess production with spot price terms, which means that often the price you get from the excess is near zero. But many/most people find it somehow still feels like a fair system because it's all based on free market operating, on understandable terms. After all, if you need to sell for zero energy cost, you are also allowed to buy for zero! So this motivates people to (1) time the use of their energy, (2) increase self-use of PV, both very good things. At least much better than complaining about conspiracies as some others do.

But I understand that your NL case where you are first subsidized and then penalized feels stupid and wrong. Similar to our system where EVs are free from one type of car taxation, but then have another EV-specific extra tax so that the end result is close to normal ICE taxation. It feels stupid as hell.