-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Solar Panels UK - is it worth it?
- Thread starter jdwuk
- Start date
And at least in the Eastern region it's almost immediate up to 5kw.
phil4
Member
They're working to their interest... not your friends. G99 doesn't take long at all, and most defo is better this time of year to wait the few weeks it might take than clip away 3kW of power.
Funnily enough I've just had the same conversation with an installer. They weren't being pushy, just saying there could be a delay with the G99 app and I guess they're probably thinking most people want everything as fast as possible. I just think they want the faster turnover of the G98 application so they get paid quicker.
So for my piece of mind, for a 6.72kWp array, I absolutely want to be going for the 5kW inverter on offer rather than the 3.6kW? We have some early and late shading issues but the quote includes optimisers to deal with that. There is no advantage to the smaller inverter other than possibly getting it all approved a bit quicker, correct?
So for my piece of mind, for a 6.72kWp array, I absolutely want to be going for the 5kW inverter on offer rather than the 3.6kW? We have some early and late shading issues but the quote includes optimisers to deal with that. There is no advantage to the smaller inverter other than possibly getting it all approved a bit quicker, correct?
A smaller inverter has less overhead, and works a little more efficiently on days with poor production. But generally you'd use that as justification for a 5kw inverter on a 6-7kw set of panels.
3.6kw would significantly restrict production in the summer, and I think for a 6.7kWp it would be madness vs getting the G99 in and a 5 or 6kw inverter.
Smaller inverters also cost a *little* less, but it's nothing in the grand scheme of things
Thanks. The cost between the 3.6 and 5 is only £100 on the quotes I've had so I was always going to go for the 5kw, it just threw me a bit when they said about the delays. As you say I'd rather wait for the G99.
On the simulation from the installer it shows "Installed DC power: 6.72" for the array and then "Max achieved DC power: 5.60kW". This is 16 panels, 8 east and 8 west (almost dead on, 91 and 271 degrees) with a tilt of 23%. Is the "max achieved" reduced because of the positioning of the panels? If the 5.6kW is more accurate then a 5kW inverter is a 1.12 ratio which seems to be in the recommended range. The simulation shows just 0.01% of clipping but I don't know how reliable these simulations are.
East-West is a different case, since the sun is unlikely to shine directly on both sets of panels at the same time.
5kw would be ample, you could make an argument for 3.6kw in that scenario, although I'd probably want the 5kw if the installer isn't pushing 3.6kw or charging a huge amount extra
5kw would be ample, you could make an argument for 3.6kw in that scenario, although I'd probably want the 5kw if the installer isn't pushing 3.6kw or charging a huge amount extra
It's only £100 difference between the two inverters so not much of a saving consideration.
If I take the installers suggested "Max achieved DC power" for the array as 5.60kW, that gives a ratio of 1.12 for the 5kW inverter and 1.52 for the 3.68kW inverter, both Solaredge. I ran some scenarios on the PVWatts Calculator using these ratios which showed pretty much the same annual generation between the two.
The installers simulations are showing slightly more estimated annual generation with the 5kW (around 130kWh). They also show slightly higher clipping with the 3.68kW inverter (2% vs 0.01%).
The other consideration is that if the G99 application takes us in to next year I would miss out on the £350 Tesla rebate.
So it's very close between the two! Ideal scenario would be to go with the 5kW inverter and a fast turnaround on the G99 application.
Does the inverter restrict what the battery can discharge in to the house? With evening meal times seeing an electric cooker, induction hob, possibly microwave all potentially running at the same time, is that another reason to go for the 5kW inverter over the 3.68kW? Or are the differences going to be negligible (I understand the electric cooker/hob don't draw full power constantly)?
phil4
Member
phil4
Member
Being really specific, if you have a Powerwall, it powering the house and charging from grid is entirely independent of your solar and it's inverter. The DNO may still limit it, but with out that it can do it's full 5/7kW regardless of the solar inverter.
WannabeOwner
Well-Known Member
I haven't read / remembered your circumstances, so this may be irrelevant in terms of comparison two configuration proposals.
Rather than total generated p.a. I would be interested in amount generated at the start / end of the day. If your different scenarios would make more available at start / end of the day (in particular start-sooner and finish-later) that is likely when you would be at home and using it, whereas more at the peak of the day is likely to be "too much". It can charge a battery, provided not already full. Can export too - if you are getting a decent rate for that (and can arbitrage against night-time usage)
The benefit of early-start / late-finish is both the likelihood that you are home and can make use of it, and also it shortens the non-solar night, so battery has to cover for shorter night duration - which becomes more important in the shoulder months
I’m not sure the start or end of day production has a bearing on which size inverter to go for in my case? Or does it?
I’m looking at 2 identical arrays, one east one west. Each array would be 3.36 kW so for some of the time a 3.68kW inverter would be fine.
Although presumably at some point in the summer the sun will be high enough to hit both arrays at the same time and potentially produce anything up to the maximum of 6.72kW at which point I would be better off with 5kW inverter.
I don’t know how to work out how much time the arrays could be producing more than 3.68kW at a time.
I keep thinking I’ve made a decision and then start doubting myself again!
The cost between the two inverters is negligible and I don’t mind waiting for a G99 application. With that in mind, is there any benefit to going for the 3.68kW over the 5kW inverter with the arrays as described above (other than it being quicker to start the install)? I will also be installing a Powerwall 2 if that makes any difference.
The only other consideration is that I do have the option to install another 3 panels (totalling 1.26kW) on a lower pitched roof above the porch on the west side. The wife is not keen on the aesthetics of this so it won’t happen immediately but could be an option in the future if I can talk her round once she starts to see the savings. I’m guessing that future proofing with a 5kW inverter now would make sense in case these panels get added later.
Also a big thanks to everyone for the advice. I’m a bit ocd when it comes to making decisions like this and all the help offered here is really useful.
Pete UK
Member
With a very shallow 23 degrees pitched roof like yours and 6.72 kW array size I imagine you’ll be getting almost full power on both arrays in summer for at least an hour or two at midday, maybe longer.
And if you add 3 more panels you’ll have an 8kW array, so you’d be mad going for a 3.68kW inverter. Get the 5kW or 6kW inverter for sure.
Start up voltages aren’t really a problem any more. I mean, mine start up producing 1w initially. I’ve never really thought “ah, you know what, I’m missing out on 0.5 of a watt for an xtra 5 mins in the day.” But losing 2kW or more due to clipping for a few hours a day would be crazy.
I’d also try and talk the Mrs into the 3 extra panels from the start. It’ll cost hardly any extra to do it all on one go, compared to adding later, plus the same panels might not be available and I imagine no one would want to come back to just add 3 panels. Or they might but they’d add a huge premium.
Random spanner on the works: The powerwall 3, I believe you can plug the solar panels directly into a DC input on it, so that might be worth considering a PW3 to save 6% on the extra AC/DC/AC losses of a Pure AC system like the PW2 - But others may be able to advise more on that.
And if you add 3 more panels you’ll have an 8kW array, so you’d be mad going for a 3.68kW inverter. Get the 5kW or 6kW inverter for sure.
Start up voltages aren’t really a problem any more. I mean, mine start up producing 1w initially. I’ve never really thought “ah, you know what, I’m missing out on 0.5 of a watt for an xtra 5 mins in the day.” But losing 2kW or more due to clipping for a few hours a day would be crazy.
I’d also try and talk the Mrs into the 3 extra panels from the start. It’ll cost hardly any extra to do it all on one go, compared to adding later, plus the same panels might not be available and I imagine no one would want to come back to just add 3 panels. Or they might but they’d add a huge premium.
Random spanner on the works: The powerwall 3, I believe you can plug the solar panels directly into a DC input on it, so that might be worth considering a PW3 to save 6% on the extra AC/DC/AC losses of a Pure AC system like the PW2 - But others may be able to advise more on that.
I have the same size of panels, 8E 8W, and a 5.5kW Inverter and a 40 degree roof. I briefly exceeded 3.6kW peak generation on Tuesday this week, but if I go back to August I would have been over from 11:45 to 3pm daily. So sure, for say 8 months of the year it's going to make no difference, but for those other 4 it's worth the extra few hundred pounds.
Also this is assuming that your chosen inverter doesn't get fried by the voltage with that many panels, many smaller inverters won't like to be over panelled.
I also don't see the point of being AC coupled, just seems like double the losses to me, even Tesla see this which is why PW3 has built in MPTT. An oversized inverter means you can also charge and discharge at a higher rate. My inverter can charge/discharge/MPTT all at 5.5kW
