I agree 100% … but that calc does not factor in the weather where one is based, shade, smog … Cpt winter and most importantly, each individuals needs/usage usage.
Your advice on pallet of panels, as later their may be no stock, is sound, have seen my arse a few times on that! The 350w Canadians I now want 2 more of, they have changed the specs on the new 350w panels. Cannot add them to my older 350w panels.
It is a fine balance.
Not forgetting … more panels, need more batteries, need a bigger inverter … now I need more panels … ROI is gone.
5kva inverter, get 5kw array and sit back an watch it. If you need more panels, their are many ways to skin that cat.
Watch this calc… (No losses taken into consideration)
I have a 1kwh load constant load for 24 hours with a 3.5kwh peak for 5 minutes a few time a day when i need coffee, so i need to produce a minimum of 24kwh per day to run this of solar completely. This will require a solar array of 5.45kwh. I also need to store enough power to carry me through 14 hours of bad to no production = 14 x 1= 14 / 0.8 = 17.5kwh battery bank. For this scenario I would need a 5kva inverter
Now i increase the load to 3.5 kwh constant, I would need to generate 72kwh and that requires 16.36 kwp on the roof and you would need to store at least 52.5kwh in the batteries, but still I only need the 5kva although I now have triple the panels and batteries.
More panels and more batteries normally dont need a bigger inverter.
Max peak determine inverter size, how long you want to run a certain backup or how many units you need for the night time usage, determine the battery bank, and the total daily usage determine the panels you need.
I am also not on the same page here, Adding panels ,the “cheap” part of an installation, shortens the ROI period. Adding to many makes no sense, but adding within your needs, normally shorten the payback time.
It’s a simple enough calculation to do. But I think I buy your argument. If you size it until it barely clips (and you aren’t an idiot who make your strings too short), it is unlikely you’ll breach the current limits.
It is tongue in the cheek … NEED’s WANT’s HOBBIE’s.
We start off with a kit, sums made perfect sense, and happily, we use the system UNTIL …
We add more batteries, we WANT them = we now NEED more panels to recharge them and still power the daytime loads.
O but wait, I have more evening kWh! So we reason to use more of them, ROI and all that, by taking more of the bigger evening loads off Eskom … NEED a 6kw inverter now … this rabbit hole goes deep, if we don’t take care.
I absolutely 100% agree with you and Phil. Those sums are absolutely crucial.
But I’m not talking about sums … after this Cpt winter, and ANOTHER storm and whatnot on us this week … I “laugh” at solar calcs.
Ok ok ok … come summer, I will smile again, but till then, I’ve seen me arse solidly as we’ve gone now month after month after month with 600 units on the dot each and every single f…ing bl…dy month!!!
And IF there were “spare” units left over from the previous month … next month it would be gobbled up like THAT! "
(Ok, deep breaths … deep breaths … summer is coming.)
Ok, I’m relaxed again … my core titbit is, do the maths, you HAVE to but for Pete’s sake, keep a very big eye on what you do and why, when, and how BEFORE one goes down the rabbit hole and expand and expand … take a year and learn/watch the system over 12 months … I was caught flatfooted after the last panels went up … I thought I needed like 2 x 350w more …
I’m still adding 3 x 350w panels for spring/autumn… summer … not a damn for winter.
Buy that pallet of panels … IF it makes sense … but don’t buy it unless you know you can use it … and not go down a rabbit hole.
If “we” means the normal DIY installer or hobiest, then your argument is true and from the approach you took this makes sense, but please remember that a small persentage off peole take that approach.
Normally we just establish the requirements, make the calc and do the install once off. Maximum savings, less hassles, quickest ROI and less money wasted on equipment that might need changing in the future.
Out of more than 200 current clients, maybe 10 took your approach. Although the approatch "we’ took is not wrong, it does not represent all aspects and available options.
Some of “we” wants more PV and a larger inverter but cannot be arsed to pony up another small fortune to do it. I want to get a Fronius or an SMA and throw some panels on the back garage, but I just finished installing a bathroom and right now my priority is to plug money holes rather than create more…
So right now, this part of the usual “we” is on the other side. The system works. Leave it alone
While I now get your point, there are some who do advocate for that, and it does make sense to some extent. What they do is oversize the PV to the extent that they get clipping for several hours of the day, but they gladly take the compromise because that gets them more energy earlier on (and on overcast days). Visually speaking, they take the traditional bell curve, stretch it upwards to get a more square profile lower down, then chop off the top
If you do that, then you absolutely must watch that PV input current part
Even though my 4.8 kWh Pylontech’s are enough to last me through the night, my WANT is another battery so that i can top up the geyser early morning instead using the grid, plus another excuse for wanting another battery is to be able to run an aircon at night, again so as not to use the grid
Sorry Tariq, to run and aircon through the night takes a lot more power than one Us2000. Normally 4 x US3000s will get a normal household including a 12000btu inverter aircon through the night in hotter areas of Sa.
@JacoDeJongh , I should have clarified the running of the aircon, am only talking about running it for a few hours after pv drops off, till we go to sleep ( usually don’t use the aircon while sleeping ), thinking of the Pylontech 3000, if i can snag a 3000B at great price, since i have the Pylontech 2000’s with the 80% DOD
As Plonkster mentioned, he just renovated a bathroom, and so did I , so moola for a HOBBY/WANT is also a little tight and the reason for the B ( used ) is also IF i get it at a GREAT price
I don’t know any of those 200 … ok, maybe 1 or two if I think hard.
What I do know, “we” are 10’s of thousands who are constantly throwing around new ideas to improve/adjust/alter/expand … it has an allure all by itself, via all the forums, the Youtube videos, Victron Community that “we” spend a lot of time on … two different worlds here, the professionally installed vs “we”.
At least my figures I can back up from a real data base, it’s not thumbsuck. Some day you might realise the road you are on is not the only road.
That fact that 10s of thousands of people joins forums to ask questions, does not mean they think exactly like you, or that they looking for the same things you are looking for or that they have joined the forums for the same reasons you did.
I think that the theoretical output of panels is misguiding though. I think those 1000W/m2 conditions are only achieved by spotlessly clean, temperature-controlled, perfectly angled conditions.
In a domestic setting, you are working with the roof pitch and directions you have.
Your panels are only ever going to be spotless on the first day they are installed.
Typically, in the domestic setting, the rear panel clearance is relatively small compared to a commercial setting and the highest sunlight hours will correspond to the highest panel temperatures (and greatest losses).
So what I say is to add extra panels to compensate for this difference between the ideal and reality. In other words, make sure the MPPT is getting the current at the voltage that the ideal panels would have provided. There can no danger in doing this with any MPPT, it is just getting exactly what it is rated for.
In reality, you are not over-panelling, you are just providing sufficient PV to compensate for the local less than ideal conditions.
However, that said:
I have seen a study where arrays deliberately oversized by 25% to clip, had annual total losses of 0.1%.
These losses climbed to 1% when the residential array was oversized by 44%.
Keep in mind that these losses are at noon in summer. They are also relative to the extra production that is gained in the morning and later afternoon and in Winter, (times when you need more power).
The way I read that study is that this oversizing was over and above my recommendation.
Even if it wasn’t, I do think that there is an economic argument for designing in an intelligent degree of clipping. The input current limitation will come into play when designing a system like this.
This discussion has prompted me to do a bit of research as to light intensity vs current/voltage. I used to think of a PV module as a “constant current” device, but that is only true at a constant light level. The current appears to be (as far as I can see) proportional to the amount of insolation. So you are absolutely right: Increasing the amount of “paneling” until it clips… is simply compensating for environmental conditions.
In Germany they have a 70% rule. You are allowed to oversize, but your grid feed-in must be limited to 70% of the array size (I am surely leaving out some parts of it). That’s because for most of the year, environmental conditions are not ideal. In July, it is… and then you need to clip off the top
