Solar panel design

[Isetech]

This is why I design our systems to operation in the middle of voltage range, 370-425 max, 3 years in and we seem have got it right.

This is why we go in a little smaller with room for expansion, it helps to tweak and optimize the system to suit the customers requirements.

Everything seems fine on paper, but what I have learnt, there is not one system we have installed that has the same setup.

Every single customer is different, be it the power time of use, the system parameter setup, the amount of panels or even batteries.

If you have unlimited cash them you just go big, but in most cases, there is a budget, that budget will determine the way the system is designed to suit the customer.

Some customers work during the day, others have home executives who do washing, ironing and cleaning during the day, which could result in the geyser switching on/off all day.

To help optimize the setup, we introduce smart switches and smart socket outlets, add panels or batteries as required.

The standard startup basic setup at the moment is an 8 kw with 2 or 3 batteries and 12-14 panels depending on the budget. Over time we monitor the data and upgrade to optimize, in some cases we add panels, others we add batteries.

The systems never charge batteries off the grid and run off the batteries from 9/10 m until the morning when the panels start producing power again. This is also why we prefer to install east/west facing panels, the battery starts charging from early in the morning and the customer is still using solar power late afternoon.

We do have a few north facing panels, but between the trees and time the sun is powering the panels, we only get decent power from around 9 am till 3 pm



As much as people are saying EV's are not going to happen, like the solar industry took off in mid 2022, the EV market is going to kick off sooner than later, the question is are you ready?

Best you make sure your solar system is going to have the capacity to handle the additional load. This is where I think the 5 kw 6 panel 1 battery installs could require an upgrade.

When load shedding started a 5 kw was a good entry level backup system to keep the lights on.

You need to keep Voc of the strings below the PV Input Vmax of the MPPT.
This is because the way the inverter reduces the power being supplied by the panels is by increasing the voltage the MPPT operates at. Effectively the MPPT reduces power production by increasing the operating voltage in order to choke the current.
If the panels can push a voltage above the Vmax of the MPPT, things can (and one day probably will) go pop!

Next thing you need to take into account on this front is the edge-of-cloud effect. This can boost the Voc of the panels by 10%.
So unless you are trying to squeeze every last watt, set up your strings so that their Voc do not exceed 90% of the Vmax of the MPPT you are connecting the string to.
The rest of the equation relates to derating factors - angle, temperature, solar radiance per square meter. But if you leave some margin on the Voc and make sure Isc is less than Imax of the MPPT, relying on the standard label values of the panel should keep you out of trouble. If you are getting close to the limits, best you take a closer look at V-I curves and derating factors in the panel datasheets.

[Derlyn]

So just when one thinks you know it all, along comes Dave and teaches us about edge of cloud effect. That's very interesting and thanks for that.

I suppose the golden rule is not to exceed 90% voc as well as 90% of mppt's max current input.

I've learn't loads from this thread.

Thanks all.

[Dave A]

Fortunately Isc is pretty much a hard limit as to what a solar panel can generate.
(And I stress generate as opposed to pass through...)

[GCE]

If you look at the numbers put up earlier in the thread by Isetech - Allow at least 20%
They tend to allow 20% of ideal then another 20% from max to really max

That edge of cloud on a cool day with high radiation and cloud the inverters sound like a DC drive ramping up a motor

Most inverters taht have damage to MPPT are due to overvoltage -

Then we look at the PV input voltage range 550 Vdc ( 160 Vdc - 800 Vdc)

The MPPT input voltage range 200 Vdc - 650 Vdc

[Isetech]

I designed the setup for the 12 kw 3 phase inverter using the information provided on the spec sheet I downloaded from the Sunsynk website.

Used 550 Vdc as a guideline, which would have ample tolerance either way.

What I couldnt understand is why the PV range and MPPT range is not the same, considering the PV range starts at 160 V will not switch on because the MPPT range is 200 Vdc.

YOu would have a problem trying to do a warranty claim if you tell them the PV voltage was 700 Vdc

I contacted Susnsynk, however the response I got was that you must use the MPPT range not the PV range. Can anyone tell me why the PV and MPPT range are not the same?

If you look at the numbers put up earlier in the thread by Isetech - Allow at least 20%
They tend to allow 20% of ideal then another 20% from max to really max

That edge of cloud on a cool day with high radiation and cloud the inverters sound like a DC drive ramping up a motor

Most inverters taht have damage to MPPT are due to overvoltage -

[Isetech]

I had my second fault on one of our installations, since we started installing solar.

F23 - AC leakage current is trans over current Leakage current fault
1.Check the PV module and inverter cables.
2.You may have a faulty PV panel (earth short)
3.Restart inverter

12.00 midday, click it went into a fault condition the red light started flashing and you could see on the app that the solar had shut down (went to zero) after about 4 minutes it the red light switched off and the solar started producing power again.

I reduced the solar to 1 kw and let it run until the following day.

I went to site the next day and carried out a number test, including L-N, L-E, N-E with all the switches off just the panel input, nothing seemd out of the ordinary, I also tested the voltage on the the SPD which I thought might be faulty.

Everything seemed normal, so I reset the sytem and cranked up the solar power to 8500 watts (slightly less than it was set prior to the fault). It has been running fine for the past 3 weeks. Returned to site a couple days ago, opened the DC control and checked the voltages again, it seemed fine.

I am wonder if it wasnt because the power was set to the inverter limit.
One thing I did find a bit strange, when I switch on the isolator on the side of the inverter, the voltage between N-E was constant at 247 Vdc however the L-E was fluctuating and then settled, it kept doing this every time put the test lead son the terminals.

I have read that it could have something to do with the MPPT adjusting itself.

Anyone else experienced this?

[Justloadit]

Can anyone tell me why the PV and MPPT range are not the same?

Solar panels are what we call a Current Source, as opposed to ESKOM being a Voltage source.
Voltage Source - Voltage remains constant and current can vary depending on load. Power is V x A
Current Source - Current remains constant and varies depending on the sun radiance, and voltage varies depending on load. Power is also V x A, however while the current remains constant and you load too much, then the voltage drops and the V x A also drops. There is a critical point where the current remains constant, but if you load it just right, you can get the maximum power out of the panel - Hence MPPT or Maximum Power Point Tracking. As the panel heats up or cools down, due to the nature of silicon which the panels are made from, this voltage point can go up (Cooler) or down (Warmer), so as the panel works so the temperature may change and the MPPT will track this change and readjust. If the panels are installed in an area where the panel is exposed to negative temperatures, then add an extra 5% to the open circuit voltage to accommodate the open circuit voltage during this period.

Another interesting fact about open circuit voltage and MPPT voltage, is that firstly they are referred to at 25°C, so the value will change with temperature. There is a percentage value that changes per °C, higher voltage when cold to lower voltage when hot. One also tends to forget that the power rating of the panel, also means that the panel is working at the power rating, so at midday it is say 500W, the panel is generating 500W, and hence the heating of the cells that in some cases the glass of the PV may be around 80°C and poses a dangerous temperature for human hands.

[Isetech]

Load shedding is taking a break, which is great news, back in 2008 the same thing happened, the generator industry went crazy, people started importing tons of generators and if you were in the petrol station market, man you were as busy as heck.

It looks like 2008 has repeated itself, there was a shortage of solar, prices went through, people made millions. IF you were in the petrol station industry you made a ton of cash again, now they all have a generators and a roof full of solar panels I am sure they are ready for the next wave, water tanks and booster pumps, if you are not already on this bus, you missing out. If not, you must be in the rock and stone industry, coining it, so much money to be made and I hear people complaining that work is quiet, really, which rock are you sleeping under, you need to wake up and make the dash for the money, it feels like we living a mad max movies, look for the opportunities and give it horns. Unless you have figured out which bus to get on in the domestic market or doing commercial solar, your bus is going to run out of fuel, quickly as they normally do.

[Isetech]

With the break in load shedding everyone is looking at the app on their phone/PC and reading their electricity accounts, that 65 % reduction in electricity bill people are still advertising on the radio doesn't seem to be happening, while there was load shedding the R100/200/300/400 000.00 plus investment seemed like money well spent.

The reality for many is that the municipalities are going to catchup sooner than later, systems will need to be registered (all SSEG's).

At this point in time, there seems to be a shortage of meters, if you register today, you will have to zero export your system until they can start rolling out the new meters and you will be instructed not to charge your batteries from the grid at more than 15Amps (25%) for a 60 amp supply.

So where to from here do you just disconnect your system and scrap it, or switch it off until load shedding starts again?

If your system was designed specifically for load shedding chances are you just going to be throwing more money at the system. These are the single inverter with 2 batteries and 6 panel type installs.

If you decide to continue with the solar, you are going to have to look at the ROI people keep telling you about.

During load shedding, 2 hours was all you had to consider, once you apply to register, you are going to have to take a whole lot of things into consideration, the cost of the system, the ROI, the municipal connection and monthly fee, the solar production capabilities, system maintenance, registration costs, COC's (if you didnt get one with the installation), the costs to upgrade your non compliant installation, if it was done DIY or by a green card or cardboard electrician.

We better hope the insurance companies dont catch on to what is going on, one of 2 things is going to happen, either they going to request a valid COC and check that they are filled out correctly or they going to increase premiums to cover for the risk. I am yet to see a valid COC that is filled out correctly.

[Isetech]

The question you sitting asking yourself right now, was it all worth it, if not how can we improve it.

The way I see it, you are going to have to take a good look at what you have and how you are going to improve it, starting with the panels on the roof.

If you only have an inverter and batteries, you might want to look at fitting panels on the roof. If you leave it plugged in, you are just going to be wasting electricity and if you disconnect the system and leave it unplugged, you will need to discharge the lithium batteries to around 50 % and recharge at least every 3-6 months. FLA batteries will need to kept fully charged.

If you have a load shedding solution, 5-6 panel on the roof, an inverter and 1 or 2 batteries, then you will need to look at the data and figure out how to improve it to a many saving system, this could mean more panels or more batteries.

If you have taken a loan or used money from and investment, you are going to have to take a look at how you can improve the system from a load shedding solution to ROI system.

IF you paid cash and just want to cover the additional costs that the municipality will add to your bill, then you might also want to pay attention.