Good day everyone,

So I've been seriously considering getting a solar PV setup for several reasons. 

1) My wife is a developer who works from home, and I do on occasion too, and with the load shedding it's becoming more prevalent to have some form of backup solution, other than a very expensive (and super noisy) generator (which incidentally now needs a service).

2) The climbing cost of electricity.

So what's held me back is, that I've been trying to cut my usage where possible, before I shell out ridiculous amounts of money.  Now, however, with the increasingly high chances of Load Shedding again, I've decided to make the call and "Just do it".  So I've managed to cut some costs, 3x geysers converted to solar, gas hotplates, but I've also decided to change what I was originally planning, by trying to be off-grid as much as possible, and only use the grid when loads are high or when batteries drop below a certain point (provided Eskom power is available).

I was looking at the same system that another poster was looking at, with a full 10kWh Lithium battery bank and extra panels.

With this change, I have a series of questions:

1) What happens when you draw more than the rate 4.6kw of the inverter (eg tumble dryer + washing machine + dishwasher all somehow start heating at the same)?  Will the load shift to Eskom (which is what I would want), or would the inverter disconnect itself (or what ever happens with overloading)?

2) Can the house be configured that when there is Solar energy during the day, or Eskom power during the night, have everything available to run (whilst drawing from batteries first at night up to 50% DoD), but as soon as Eskom isn't available and the batteries are at 50% or less, have the load restricted to certain plugs and lighting etc.  I understand it would involve some significant rewiring of the house, but I'm curious if it's possible.

3) Aside from the cost obviously, is there such a thing as too much solar?  I'm asking as with a 10kWh battery bank, I'd need to charge min 50% of that during the day, as well as cover my load as much as possible, and I'm in the process of making changes to the way we work with regards to appliances (eg Tumble Dryer), but until that happens I'll be trying to get the solar installed.  Also I want to cater for winter, when generation will be lower (I've discovered this the hard way with solar geysers).

4) As a follow on from point 3, the inverter that is included in the Kit I'm considering, rates max MPPT input of 6500Wp.  My house is in a NE orientation, and I would have some panels facing NE, and some facing NW.  I'm not sure exactly how many I could fit on each side, as I'm not sure on the mounting requirements etc, but I estimate I could get 8 on the NW facing side, and potentially 14 on the NE facing side, which totals 22 panels and 7260Wp.  I feel the chances of getting the max power out of the panels is low, due to being in Jhb, and the panels not necessarily being at the optimum angle, and the peak power from each string being at different times of the day.

5) Next comes the issue of where the inverters and batteries will live.  So I've read that you want the DC lines to be as short as possible, but the place I want them to live is a good 20m from the nearest side of the NW facing side, and 2 storeys and about 14m from the nearest end of the NE facing side.  In the image below, the yellow box is where I'd like to put my Inverter and batteries, with the Red block (~9m x ~3.25m) being 1 string, and the Green (~3m x ~4m) and Blue (~4m x ~4m) being the other string.  The Blue block is not bigger, as I've added additional geyser solar tubes, that come to approximately where the block ends.  I'm not keen on putting the inverter and batteries close to the red block, as that is a not-so-closed "car port" area, and in heavy rains and winds, gets wet inside.  Will 20m distance from panels to inverter on each string be a big issue?

6) In reality, I'm hoping to save around 80-90% of my monthly electricity bill in summer, and 50-75% in winter (heaters etc), which will in theory mean I could "pay off" the system in about 4-5 years at current electricity prices, but I'm curious what real life is like for people who have installed solar and batteries.

7) My current usage is around 30-40kWh per day currently in summer.  Winter is still an unknown as I installed the geyser tubes in November last year, and last year winter usage was around 70-80kWh per day.  I've managed to convince my family to use the heater less, this year, but I've yet to see how well that convincing will work.  I'm hoping the geysers were the big one, as my summer usage dropped by 20-30 kWh per day, from the same time last year.  So the question is, will this size system be sufficient, keeping in mind I'm still looking to drop usage further?

8) Has anyone also dealt with Solar Advice, Mega Solar or any of the online "distributors", and has negative or positive feedback with regards to them?

9) And lastly, are there any solar installers in the Ekurhuleni (or greater Gauteng) area that people would recommend? 

Many thanks in advance.

25 minutes ago, BluStorm said:

but I've also decided to change what I was originally planning, by trying to be off-grid as much as possible, and only use the grid when loads are high or when batteries drop below a certain point (provided Eskom power is available).

Battery power costs more than ESKOM.

Sizing an off-grid inverter for your peak demands in an unnecessary expense.

This decision has no up-side that I can see.

29 minutes ago, BluStorm said:

Aside from the cost obviously, is there such a thing as too much solar?

With a grid-tied system you would be restricted to a certain size inverter by regulations.

30 minutes ago, BluStorm said:

(eg Tumble Dryer),

Use sunshine to dry clothes, or is that what you meant?

 

33 minutes ago, BluStorm said:

I feel the chances of getting the max power out of the panels is low, due to being in Jhb, and the panels not necessarily being at the optimum angle, and the peak power from each string being at different times of the day.

Don't worry about this, optimum efficiency is trumped by having a longer day's production.  You have what you have to work with.

36 minutes ago, BluStorm said:

So I've read that you want the DC lines to be as short as possible

This is true, but the reason behind it is that generally the PV string voltage are low, meaning the current is high. and if the current is high so are the cable losses.

This means that your cabling has to be thick (expensive).

However, going with a higher voltage MPPT (250V) or including an AC-coupled PV inverter will overcome this.

There are cable loss calculators on the web.

On the other-hand a longer string's production can be ruined by partial shading of even on panel in the string. So your panel configurations do matter quite a bit, see below for more.

49 minutes ago, BluStorm said:

In the image below, the yellow box is where I'd like to put my Inverter and batteries, with the Red block (~9m x ~3.25m) being 1 string, and the Green (~3m x ~4m) and Blue (~4m x ~4m) being the other string.

Do you mean "array" not "string". A "string" denotes a number of PV panels in series, the maximum size of the string will be dictated by other components in the system.

 However an array can be made of multiple strings.

With this in mind, it depends on other components in your system, as to your string sizes.

My thinking would be to parallel equal strings of each aspect into an MPPT input, that way you'll make it work longer during the day.

Consider shading with these string combinations, it looks like you have quite a bit.

Thank you for the reply @phil.g00

Quote

Battery power costs more than ESKOM.

Sizing an off-grid inverter for your peak demands in an unnecessary expense.

This decision has no up-side that I can see.

So I see the BYD are guaranteed to provide 60% of the charge after 10 years or after 21.4 MWh (for the 10 kWh pack).  Perhaps the cost is more than Eskom over the time, but I do need the battery backup for load shedding etc.  I was sure I saw it was rated for 6000 cycles, but I cannot find that officially anywhere.

Agreed, sizing for off-grid with my current usage is not affordable.  

2 hours ago, phil.g00 said:

Use sunshine to dry clothes, or is that what you meant?

Yes.  I do have a clothes line, but with 1 teenager and 3 adults, there's quite a bit of clothing and bedding that needs to get washed.  I'm arranging more hanging space, but the tumble dryer will always be needed, hopefully only "overnight emergencies" in future.  Also the sun really only reaches the line in the afternoon, and in summer, that's the domain of the Highveld thunderstorm.

3 hours ago, phil.g00 said:

Don't worry about this, optimum efficiency is trumped by having a longer day's production.  You have what you have to work with.

I was more concerned that I didn't exceed the maximum rating of the inverter.

3 hours ago, phil.g00 said:

However, going with a higher voltage MPPT (250V) or including an AC-coupled PV inverter will overcome this.

I see the Goodwe is rated at max DC input of 560v (presumably combined across both MPPT inputs), which in theory means I can have 2x string inputs of 250v .  However, due to the layout of my house, that may not be ideal.  

I had originally considered micro-inverters (not sure if that's what you mean) due to the "scalability" and potential shading aspect, but I've seen very little info on them locally, and everything I've read implies they're expensive, and not ideally suited to battery backup / off-grid systems.

Realistically, I can find another location for the inverter and battery bank. That was just the "best" location - out of the way, secure and safe from people and pets.

What is the max ideal length for the DC cables?

3 hours ago, phil.g00 said:

Do you mean "array" not "string". A "string" denotes a number of PV panels in series, the maximum size of the string will be dictated by other components in the system.

However an array can be made of multiple strings.

With this in mind, it depends on other components in your system, as to your string sizes.

Apologies for my poor use of the term.  I'm seeing a string as an input to the Inverter.  I assumed I would need to separate the NW and NE facing panels, and bundled them each as a "string".  This goes back to the max MPPT input of 6500Wp, where 1 input would be higher in the morning and the other higher in the afternoon. 

3 hours ago, phil.g00 said:

My thinking would be to parallel equal strings of each aspect into an MPPT input, that way you'll make it work longer during the day.

Are you saying I should have both aspects be part of each input?  How would you recommend that be done, with an 8 and 14 split?

4 hours ago, phil.g00 said:

Consider shading with these string combinations, it looks like you have quite a bit.

The picture does show a nice section of shade over the blue block, but the 2x Cyprus trees that caused that have been removed as they were planted next to my boundry wall, and were starting to lift it.  Since my roof is 2 storeys up, I'm not entirely sure about shading during the day, will have to have a look over the weekend.

 

7 hours ago, BluStorm said:

I see the Goodwe is rated at max DC input of 560v (presumably combined across both MPPT inputs), which in theory means I can have 2x string inputs of 250v .

No that'll mean 560V across each MPPT. DC cable length wont be a problem at this voltage. The Goodwe does limit you to 1 string/ MPPT though, with a maximum of 11A /input.

 

7 hours ago, BluStorm said:

I'm seeing a string as an input to the Inverter.  I assumed I would need to separate the NW and NE facing panels, and bundled them each as a "string".  This goes back to the max MPPT input of 6500Wp, where 1 input would be higher in the morning and the other higher in the afternoon. 

With only one string per inverter ( because of the Goodwe) this is sound logic. So in other words the the midday peak is a combo of NW and NE panels still below 6500W.

It'll be a bit of a guessing game,  but I'd think about 4kW of panels per aspect would be about right. Your 560V input constraint would limit you to less than 4kWp if you are using 350W/280W panels though, so you will be good with 10 or 13 panels/string resp.

 A 280W (60cell) panel is shorter, so may not suit the available spaces, or alternatively it may provide better utilization. Your call.

You want every panel within the same string, to be the same, and to have the same tilt and aspect.

Extra space that  you want to use for even more panels can be done with a 3rd party MPPT and appropriate settings that works independently of the BMS.

A stand alone MPPT will be able to accommodate  multiple parallel shorter strings, but here you may run it cable length issues so a use the closest panels.

So long as the panels within a string are equal in tilt and aspect, the strings themselves can have different tilts and aspects (using the same type of panels).

7 hours ago, BluStorm said:

Are you saying I should have both aspects be part of each input?  How would you recommend that be done, with an 8 and 14 split?

Not for the Goodwe,( with its 11A input limit), but for another type of MPPT that could take multiple strings /input yes.

Your limitation will be about 3 strings in parallel/ cable run. If you stick to MC4 connections/combiners. MC4's are rated for 30A. 

7 hours ago, BluStorm said:

I'm not entirely sure about shading during the day,

This is important especially with longer strings. If you choose to use an additional DC coupled MPPT use any shade suspect panels in shorter parallel strings with it.

Edited May 14, 20197 yr by phil.g00

9 hours ago, BluStorm said:

Yes.  I do have a clothes line, but with 1 teenager and 3 adults, there's quite a bit of clothing and bedding that needs to get washed.  I'm arranging more hanging space, but the tumble dryer will always be needed, hopefully only "overnight emergencies" in future.  Also the sun really only reaches the line in the afternoon, and in summer, that's the domain of the Highveld thunderstorm.

Tumble dryers are energy hogs, consider a spin dryer, And by spin dryer I don't mean the 1200 rpm cycle on your washing machine, I mean a 3000 rpm stand alone unit that will dry your clothes 95% in 10 min without heat. There is a big difference, and they are cheap at least where I am.

Stuff comes out about iron-able dry.