KWP vs. Inverter capacity

chamelion

Hi folks,

I've spoken to a number of installers now with a range of prices. I had a couple of questions for this group if you don't mind!

1) Is solaredge worth it? I have an East-West facing roof, no tree cover or things causing shade. If anything, I expect our neighbours on the east side will cast a BIT of shade first thing in the morning, but otherwise I should be clear the rest of the day. I think the improved efficiency and the smart monitoring are things I'd appreciate - but would love to hear your views.

2) Does it make sense to get, for e.g., a 6KWP array of panels despite having a 3.68KW inverter? I don't want to go down the planning route (just yet, at least), and I've heard from a few installers that maximising the panels would mean that I likely generate more into the inverter, and still get paid for what I generate - so for e.g. if I hit 4.2KW generation, the feed in applies to the 4.2, but I only get 3.68 into the house (Which is more than enough to be fair).

I've received a quote for approx £7400 for a 5.7KWP SolarEdge installation using eternity 285 panels, which also includes scaffolding on both sides of the house. Can also get Peimar 300 watt panels for about the same price, although that would be 6KWP, also solaredge.

Are these figures about right, or outrageous?

Thanks!

Martyn1981

chamelion wrote: »

Hi folks,

I've spoken to a number of installers now with a range of prices. I had a couple of questions for this group if you don't mind!

1) Is solaredge worth it? I have an East-West facing roof, no tree cover or things causing shade. If anything, I expect our neighbours on the east side will cast a BIT of shade first thing in the morning, but otherwise I should be clear the rest of the day. I think the improved efficiency and the smart monitoring are things I'd appreciate - but would love to hear your views.

It's a tricky call, perhaps 50/50. The main concern is if something goes wrong, but I had a PO (power optimiser) fail this year, and SolarEdge sent me a new one and the guys who were upgrading my non Solaredge system to a SolarEdge system, were one of their approved installers for repairs. The PO arrived in the post the day after they were round, but they popped in when next passing (a week later) and fitted it.

For 'a bit' of shading, not essential, but two rooves, some shading and great kit, with a 20yr warranty (I expect thrown in) ...... ahhhhhh 50/50, I can't call it.

chamelion wrote: »

2) Does it make sense to get, for e.g., a 6KWP array of panels despite having a 3.68KW inverter? I don't want to go down the planning route (just yet, at least), and I've heard from a few installers that maximising the panels would mean that I likely generate more into the inverter, and still get paid for what I generate - so for e.g. if I hit 4.2KW generation, the feed in applies to the 4.2, but I only get 3.68 into the house (Which is more than enough to be fair).

If it was me, I'd go 6kWp and have the inverter capped at 3.68kW if you can't go bigger. My system tops out at about 4.2kW (brief spikes to 4.9kW), so ratio wise 6kWp might be 4.5kW, but that's only 3 months of the year when the sun can hit both rooves at the same time, so about 6 weeks either side of Summer equinox.

But (again) that's only on the very best days, so poor and medium days it'll be lower, and it holds that from about 11am to 3pm, so 2hrs either side of solar noon. Certainly not the end of the world.

The FiT is paid on actual generation. So it has to go through the inverter, come out as AC and then run through the TGM (total generation meter), so if the inverter is capping gen at 3.68kW, then the TGM will only see 3.68kW.

chamelion wrote: »

I've received a quote for approx £7400 for a 5.7KWP SolarEdge installation using eternity 285 panels, which also includes scaffolding on both sides of the house. Can also get Peimar 300 watt panels for about the same price, although that would be 6KWP, also solaredge.

Are these figures about right, or outrageous?

Thanks!

I don't think that's too bad at all, pro-rata that's £5.2k for 4kWp, but as costs go down as you go bigger, perhaps fairer to say about £5.5k for 4kWp, then an extra £1.9k for the extra 1.7kWp ...... not sure what I'm waffling on about now, so I'll shut up.

All the best.

Crowmann

Be aware most 3.68Kw inverters can handle a max input of around 4.5kw.

In the Spring you might see over this number which will cause the inverter to shut down.

Martyn1981

Crowmann wrote: »

Be aware most 3.68Kw inverters can handle a max input of around 4.5kw.

In the Spring you might see over this number which will cause the inverter to shut down.

But we're not talking 3.68kW inverters, we're talking inverters capped at 3.68kW. So it could be a 5kW, 6kW etc inverter.

Also the new Solaredge HD wave inverters, as well as being tiny (my new one is about 8kg and replaced two inverters totaling over 50kg), and 99% efficient, are also able to handle very high loads.

My 3.5kW inverter is capped at 3.68kW, but can handle 5.4kW DC.

The SE4000H model can handle 6.2kW DC side, the SE6000H can handle 9.3kW.

Additional HD-Wave Feature Highlights:

- Small lightweight and easy to install at <10kg
- 99% weighted efficiency (33%-50% less losses than the market standard)
- Superb reliability due to lower heat dissipation and film capacitors instead of electrolytic capacitors
- Up to 155% oversizing allowed
- Backward compatible with existing SolarEdge systems

chamelion

Martyn1981 wrote: »

The FiT is paid on actual generation. So it has to go through the inverter, come out as AC and then run through the TGM (total generation meter), so if the inverter is capping gen at 3.68kW, then the TGM will only see 3.68kW.

Hmm - this comment is what I believed true but it was just directly contradicted by a MCS certified installer.

I asked him about this explicitly and he said, with no hesitation, that FiT was based on generation capacity, not on inverter capacity. So, if I had a 6KWP system generating 5KW, even with an inverter capped at 3.68KW my FiT payments would be based on 5KW.

I'm guessing this isn't right!

Martyn1981

chamelion wrote: »

Hmm - this comment is what I believed true but it was just directly contradicted by a MCS certified installer.

I asked him about this explicitly and he said, with no hesitation, that FiT was based on generation capacity, not on inverter capacity. So, if I had a 6KWP system generating 5KW, even with an inverter capped at 3.68KW my FiT payments would be based on 5KW.

I'm guessing this isn't right!

Possibly, in his defence he's talking about FiT rates. There used to be an upto 4kWp rate, and an over 4kWp rate, and the legislation seemed to suggest that a system limited to 4kW was eleigible for the upto rate, but the ruling was that the FiT rate was based on kWp of panels not kW of inverter.

So playing devil's advocate the statement as you've typed it up, is correct

FiT was based on generation capacity, not on inverter capacity. So, if I had a 6KWP system generating 5KW, even with an inverter capped at 3.68KW my FiT payments would be based on 5KW.

but might be an answer to a different question, answering FiT rates, not FiT income IYSWIM. Or he's talking carp!

Edit - Oops, I missed the 5kWp and 6kW difference, so if capped at 3.68kW the FiT rate would be based on 6kWp, which would have previously taken you into the 4-10kWp FiT banding, but it's now 0-10kWp. Sorry. M.

Martyn1981

chamelion wrote: »

Hmm - this comment is what I believed true but it was just directly contradicted by a MCS certified installer.

I asked him about this explicitly and he said, with no hesitation, that FiT was based on generation capacity, not on inverter capacity. So, if I had a 6KWP system generating 5KW, even with an inverter capped at 3.68KW my FiT payments would be based on 5KW.

I'm guessing this isn't right!

I've made this overcomplicated.

To earn money you have to generate leccy.

If the inverter is capped at 3.68kW, then at that level over an hour, your system will generate 3.68kWh's and your TGM will record 3.68kWhs.

Your FiT and export payments will be based on the TGM reading.

QED they will be based on 3.68kWhs.

chamelion

Martyn1981 wrote: »

I've made this overcomplicated.

To earn money you have to generate leccy.

If the inverter is capped at 3.68kW, then at that level over an hour, your system will generate 3.68kWh's and your TGM will record 3.68kWhs.

Your FiT and export payments will be based on the TGM reading.

QED they will be based on 3.68kWhs.

Ah, think I got it. Banding was based on generation capacity, but FiT is based on actual generation post inverter - so best I can do without further applications is 3.68 for FiT.

What about people who say they get more than 3.68 - for e.g someone actually generates 4.1. Assuming FiT payment will be on 4.1 rather than 3.68, even though this is above the limit?

Martyn1981

chamelion wrote: »

Ah, think I got it. Banding was based on generation capacity, but FiT is based on actual generation post inverter - so best I can do without further applications is 3.68 for FiT.

What about people who say they get more than 3.68 - for e.g someone actually generates 4.1. Assuming FiT payment will be on 4.1 rather than 3.68, even though this is above the limit?

Hiya, the 3.68kW isn't really anything to do with FiT's it's simply the amount of export a micro-generation scheme can have when notifying the DNO after the install for registration. If the system is to have the potential for more export, then prior approval is needed from the DNO.

The DNO's do this so that they can monitor and manage the amount of export anywhere on their networks in case there is too much, or in case the households cabling can't cope.

So the 3.68kW rules apply regardless of any government schemes etc, you'd still need to follow them even if FiTs didn't exist, or after it ends in the future.

FiT and export payments are based on the TGM reading and this will 'grow' quickly or slowly depending on how much generation your system actually makes, just like your import meter clocks up more units when you run all your big items in the day, rather than slowly during the middle of the night.

So let's say you had 6kWp split E/W. On a nice morning the E might be generating 2kW and the W 0.4kW, and over an hour the TGM will clock up 2.4kWh, on which FiTs and export will be calculated.

Then around 11am, nice day the E generates 3kW and the W 0.5kW, so over an hour (again if it stayed steady, which it won't it'll rise and fall) you'd clock up 3.5kWh.

Now, let's say it's a really good day in the summer, around 1pm, so split nicely over both rooves. Whilst they might be able to generate 4.5kW in total, the inverter would cap at 3.68kW, so over an hour you'd clock up 3.68kWh on the TGM, not 4.5kWh.

Note, you didn't generate 4.5kWh as the inverter prevented that happening, so actual/real generation is 3.68kWh, and that's what the inverter will clock up during that hour.


Bit of guesswork here, but on a really good day my system can generate 30kWh+, I think my very best is 34kWh, but all 30kWh+ are rare for me. So let's scale that up for you and say (30/5.58) x 6 = 32.25kWh. Now let's assume that the system is capped from 4.5kW down to 3.68kW from 11am to 3pm, but the rest of the day doesn't exceed 3.68kW. So that's a 'loss' of 4hx 0.82kW = 3.28kWh.

So you'll get 32.25 - 3.28 = 29kWh on a very good day.

Earlier in the day, later in the day, poor weather days, and most of the rest of the year generation won't be impacted much, or at all.

But please be kind to me, and accept that this is real guesswork and gut feeling. I don't won't you looking at the monitoring, seeing 3.68kW output in April or September and grumbling about 'that git Mart'.

chamelion

Martyn1981 wrote: »

Hiya, the 3.68kW isn't really anything to do with FiT's it's simply the amount of export a micro-generation scheme can have when notifying the DNO after the install for registration. If the system is to have the potential for more export, then prior approval is needed from the DNO.

The DNO's do this so that they can monitor and manage the amount of export anywhere on their networks in case there is too much, or in case the households cabling can't cope.

So the 3.68kW rules apply regardless of any government schemes etc, you'd still need to follow them even if FiTs didn't exist, or after it ends in the future.

FiT and export payments are based on the TGM reading and this will 'grow' quickly or slowly depending on how much generation your system actually makes, just like your import meter clocks up more units when you run all your big items in the day, rather than slowly during the middle of the night.

So let's say you had 6kWp split E/W. On a nice morning the E might be generating 2kW and the W 0.4kW, and over an hour the TGM will clock up 2.4kWh, on which FiTs and export will be calculated.

Then around 11am, nice day the E generates 3kW and the W 0.5kW, so over an hour (again if it stayed steady, which it won't it'll rise and fall) you'd clock up 3.5kWh.

Now, let's say it's a really good day in the summer, around 1pm, so split nicely over both rooves. Whilst they might be able to generate 4.5kW in total, the inverter would cap at 3.68kW, so over an hour you'd clock up 3.68kWh on the TGM, not 4.5kWh.

Note, you didn't generate 4.5kWh as the inverter prevented that happening, so actual/real generation is 3.68kWh, and that's what the inverter will clock up during that hour.


Bit of guesswork here, but on a really good day my system can generate 30kWh+, I think my very best is 34kWh, but all 30kWh+ are rare for me. So let's scale that up for you and say (30/5.58) x 6 = 32.25kWh. Now let's assume that the system is capped from 4.5kW down to 3.68kW from 11am to 3pm, but the rest of the day doesn't exceed 3.68kW. So that's a 'loss' of 4hx 0.82kW = 3.28kWh.

So you'll get 32.25 - 3.28 = 29kWh on a very good day.

Earlier in the day, later in the day, poor weather days, and most of the rest of the year generation won't be impacted much, or at all.

But please be kind to me, and accept that this is real guesswork and gut feeling. I don't won't you looking at the monitoring, seeing 3.68kW output in April or September and grumbling about 'that git Mart'.

That's an amazing response, thanks

What about Crownmann's comment above at http://forums.moneysavingexpert.com/showpost.php?p=73456340&postcount=3

and your response to it - this suggests that if I do get 6KWP on my roof I'd need a 5-6 KWP inverter as my actual generation potential can be up to 4.4KWP based on the potential estimation utility. The 5.6 KWP inverter would be capped though at 3.68?

i.e. I can't get a 3.68KWP inverter as it would 'shut down' with anthing over 4.5KWP, which is a little too close to comfort to the potential?

Martyn1981

chamelion wrote: »

That's an amazing response, thanks

What about Crownmann's comment above at http://forums.moneysavingexpert.com/showpost.php?p=73456340&postcount=3

and your response to it - this suggests that if I do get 6KWP on my roof I'd need a 5-6 KWP inverter as my actual generation potential can be up to 4.4KWP based on the potential estimation utility. The 5.6 KWP inverter would be capped though at 3.68?

i.e. I can't get a 3.68KWP inverter as it would 'shut down' with anthing over 4.5KWP, which is a little too close to comfort to the potential?

This can all get a bit misleading. First consideration is an appropriately sized and wired inverter for the job. For instance, most normal 4kW inverters are designed to have two strings of panels. So let's say two strings of 8 panels.

What that does is double the amperage, but half the voltage v's a single string of 16 panels. So you could have a situation where the inverter is happy with 16 panels on 2 strings, but 1 string of 12 panels would exceed it's voltage max causing it to shutdown - but that would happen almost immediately it was turned on, and it's unlikely a decent installer would make such a mistake.

In the case of Solaredge, they run on a single string so the inverter has to be correctly sized for the whole string. You'll see from my earlier link that their latest inverters are able to cope with large amounts of oversizing, which makes sense if you think about it, as Solaredge is a specialist in 'odd' installs, where you have multiple orientations, shading, pitches etc, so you might have a lot of PV, but less output than say a nearby system that faces south and has no shading.

Looking again at the SE spec sheet, the 3.68kW inverter can cope with 5.7kW DC, and the 4kW model can cope with 6.2kW DC. I don't know what model the installers would recommend, they may even go bigger, such as the 5kW model, but their Solaredge modeling will tell them what can, can't be done, and suggest the best model too.

When they install it, they'll then need to set max output at 3.68kW during the configuration stage, and then they'll report the install to your DNO stating a max output of 3.68kW from your system.

Obviously most of this is theory, the important part is that the correct inverter will be chosen to cope with the number of panels and the sum of their voltage, and after that it will be set to cap as per the DNO rules.