Further reading on Solar for those in Cape Town

Some info on what City of Cape Town has been doing regarding feeding back into the grid, for single phase users (hint, not much). As for three phase – nothing..

Info on why net generators get charged a base fee (NERSA!), why council has been dragging their feet on renewables, feeding back, and other issues (by the very helpful Brian Jones) –
Brian Jones_Challenges to get RE going in municipalities_CoCT

Latest SSEG application form Grid tied form SSEG


The system has been running nicely for the last 3 months without issue, and we’ve generated a little over 2MW so far!

We still don’t have all the panels on the roof – only the 16 ones we put up last year!

Quite impressed with the yield, and the inverter.

I did have one issue the other day though – the inverter fan came on late afternoon (which is unusual), and I could hear it working overtime.
As thats strange, I plugged in a computer, and took a look at the stats.
Our Eskom side was actually under supplying, and our inverter was working overtime to keep it running smoothly. I noted the issue, and went on with my day.

Guess what was in the news that evening – Eskom declares power emergency!

Was rather cool to troubleshoot an issue back to the Electrical provider, and find out I was right πŸ™‚

Post Install notes

Mine has been running for a week now, albeit with only half the panels mounted and installed, as I didn’t have time to mount the rest yet this visit – I’m back in Shanghai, China again now..

It finally went live on the 14th. Its working out well though, although I am getting slightly less output than I expected – panels are in theory 4800W total for 16 panels x 300w, but looks like they’re really 250w panels, as we get about 3.9x KW peak off the 16 we have mounted at the moment after inverter losses etc.

Everything survived the massive storm that hit Cape Town last weekend too, so that was a relief!

Still need to do paperwork for council approval, and arrange a new digital 4 quadrant Landis & Gyr meter so I can eventually “feed into the grid” as a SSEG (similar to Arthur), but we’re generating electricity on a separate circuit in the interim, and our power is down to pretty much zero usage daytime.

The Landis & Gyr people are a pleasure to deal with too. They answer questions, and are quite helpful. Thanks again to Arthur for their details!

Although the whole install so far was fairly painless given that it was all DIY, I did have one issue.

My DC switch for the panel side decided to fry itself almost immediately, and lose its magic smoke (black and stinky that it was). It was only there as an extra safety precaution, so it wasn’t a huge problem, I just wired MC4 connectors to the cable from the roof (after safely disconnecting from the roof), then plugged directly into the inverter.

I think the DC switch was just bad from the factory, and the inverter does have an off/on switch for DC, so it wasn’t a calamity.

Other than that oh faaark moment, its all been great.

I need to do an update on the blog to show current working status, then its the fun part of documenting all of it, getting council signoff’s, paying more money to get a bidirectional smart 3 phase meter (+-R4k with gprs and ethernet) , and becoming a small scale provider! (or not, depending on what the base charges will turn out to be).

Total costs:

Panels – approx R1600 / panel x 30
Inverter – approx R20,000
DC, AC Cabling, Mounting – approx R5600
Distribution panel side + 3 phase, 1 phase, dc switches etc – approx R500
Total – about 75k

I did get dinged for storage charges for 20k due to incompetence at freight forwarder, and clearance was expensive too, as the freight forwarder *****ed me on that too, that came to about 40-50k for that portion of the shipment, but I did have other stuff in the container, so its hard to calculate it out.

Assuming I use 40k for shipping, clearance, and taxes (no duties on panels or inverters), then looking at about R115,000

Installation took us 2 days (3-4 hours of work a day for 2 people), and there will be some ancillary costs for electrical signoff, and other paperwork bits n bobs, and of course a new meter, so for my 3 phase setup, total will probably be about R120,000 all in*

*At todays RMB-> Rand rate. I did buy most of it when the RMB was at R8.5 or so, but we are at 10.2 ish again, so used 1-> 1.6 for rmb->rand values.

Its grid-tied, and although I can go off-grid completely would probably cost me another R100,000 to do so at current prices in China for equipment + batteries.

Still, I think its a fair investment, as electricity is only going to go up in price in future, and if / when I do move, I can take it all with me! (Or sell it to the next buyer!)

I’ve learned from the experience though, and will probably be up for doing it again, as it was quite painless aside from the freight company royally *****ing me. There is a fair amount of interest in smaller (single phase) systems from everyone thats seen it, and I can put together a 4k + single phase inverter setup for reasonable prices for family+friends in future, and hopefully make a bit of cash doing it!

Mounting systems and Panels

If you recall from my last update, I unpacked the Solar Panel crate, and moved the panels to the back garden. It does no good having a pile of panels in the garden, they need to be mounted!

Panels sitting around, lazing in the afternoon sun

Mounting is probably one of the lesser discussed area’s of installing Solar. Its almost an afterthought for most people, although it’s just as important as the rest of the system.

There are a few area’s of concern for mounting – first one is can your roof sustain the extra weight.

30 panels and mounting brackets will add another 850kg of weight onto the roof, albeit spread out over a large area. We had a look inside the roof, took some photos, and spoke to a structural engineer friend first – his take was that ours is an older victorian house, and as is quite common for older houses, its built reasonably well from substantial materials.
Essentially, its been quite substantially over-specced, and has more than enough beams for weight distribution, so there won’t be an issue.

Another major concern is wind. In Cape Town, its not uncommon to get extreme wind conditions – we’re not called the Cape of Storms for nothing! Any system used, needs to be sufficiently strong to withstand gale force winds on a semi regular basis, annually.

Our local conditions dictate that mounting needs to be extremely strong, as a flying panel can and *will* cause substantial damage. Surprisingly, given this, there are no real laid out Solar installation requirements, unlike other parts of the install, its quite unregulated.

There are no substantive national standards for mounting compliance, or local ones, other than the requirement that things mounted on the roof can stick out no more than 600mm. I asked City of Cape Town what their rules are and received this:

All PV roof top installations: No building plans are required to be submitted provided the panel(s) in its installed position does not project more
than 1,5 metres, measured perpendicularly, above the roof and/or not more than 600mm above the highest point of the roof.

This is quite permissive, and looks like its aimed more at Solar Heating, rather than Solar PV.
Our panels will be flat mounted on the roof at a total height of about 100mm (including panel), so we’re well within compliance.

I did a bit of research on some options, and went with something thats German designed, but produced in China, from a company called NiceSolar.

Nice Solar has a number of different mounting choices for various roof types – The first choice of what you’ll use is dictated by what type of roof you have; in our case, its a galvanised steel/zinc sheeting, as opposed to roof tile.

The mounting system I chose mounts directly into the roof beams via screws, and is composed of aluminium mounting brackets. Its reasonably well thought out, and simple to install. We had most of the bracket mounting done in 2-3 hours, with just 2 people, and that included carrying everything upstairs onto the roof, and the usual going up and down to get the extra tools that you need. Finding the roof beams was quite easy from the roof – we just had to follow the existing screws holding the sheets in place, and mount accordingly.

Initially when I opened the box of component parts shipped for the mounting system, I was worried, it all looked horribly complicated – lots of different pieces.


Turned out to be quite simple though.

My system uses L shaped brackets to mount into the roof, then an aluminium mounting channel is screwed onto 3 brackets. Panels then sit on top of the mount and are held in place with a T piece or a C piece for ends. Mounting channels are joined together with a sliding clamp system.

Below is a shot of a T piece, and the L shaped bracket in a mounting channel
example mount

This is what the L shaped bracket looks like close up
L Bracket

My system needs 3 x L brackets per mounting channel, so the first thing we did was to setup a dummy channel with L brackets screwed in for sizing, and mark out our holes for drilling. You can see both in the shot below:

Drilling for oil

Unsuprisingly, this was the longest part of the job, as we had to think about and plan where the panels would go due to Chimneys, Skylights, Solar Hot water Heating and other obstructions getting in the way of a clean easy install.

Once we decided where things would go we went pretty fast.
You can see some of the L brackets already mounted below:
L brackets mounted

Once the L brackets were on, the next step was to mount the channels.
This is where my choice of system came in handy – mounting was a breeze!

Below is a channel waiting to be screwed into the mounts

Its obvious that some thought went into the design, as there are some design concepts that integrate together cleanly, and ensure both a strong connection, and ease of mounting.

The L mounts, and the mounting channels are corrugated so that you get a tight fit, and the L brackets mounting screws angle into the channel from any location and lock into place.

Below is a shot of one half of the install team in his farmer hat, busy fixing a channel onto the L mounts. Don’t forget the importance of protection from the sun when you’re on a roof!
Joel wearing a stylish Farmer Hat

Here’s the other half –

Once mounted, each channel was joined together with a slide in joiner bracket. This was a little fiddly, as some channels got slightly damaged in shipping and needed coaxing with a screw driver and pliers before we could slide them on. Luckily only 2 or 3 channels were affected. It was extremely minor damage though, and didn’t take us longer than a minute a channel to resolve.

Eventually, we had our mounting done, and had lines of mounting ready to roll

As you can see, we managed to drag one panel up onto the roof to test mounting.

I recommend involving additional friends and family if possible!
We brought our tools and equipment down, adjourned till the next day when we could rope in some rather reticent workforce, and continue.

The next day involved most of the hard labour – we had to carry 15 panels up onto our lower roof area, then from there up onto the roof.

Once we had a panel on the roof, we mounted it immediately using the T pieces, and things went rather rapidly.

T Piece, waiting for 2 panels –
T piece

Took another 3 hours to get to this point

You can see the roof line with the panels mounted below. We made the executive decision to mount the end flush with the mounting, as we had concerns about leaving a lip for the wind to get under. The way its mounted should negate that issue for the highest area’s. Cape Town has substantial wind conditions, and this needed to be addressed.

We’ll be inspecting the mounting in a day or so, then in a few weeks to ensure that the mounting is still secure, and there are no issues. Today has been fairly windy, but I’ll be on the roof tomorrow for final inspection, and hookup.

We’re still not live, as I haven’t hooked up the panels yet.


For safety reasons.

The panels haven’t been connected together, as they shouldn’t be connected while live.
As they’re live when there’s sun, I’ll need to go up at dusk or early evening to connect up.

I also still need to run DC cables to the roof from the Solar Board.

The astute among you will have noted that there are only 16 panels on the roof currently.
Well spotted!

The other side of the roof is at an extreme angle, and we’ll need to hire safety harnesses, and possibly a scaffold. Due to that, I’ll be hooking those up at a later date, so will only have half the system up and running this week.

I’ll be running the panels in 2 x 15 sets (strings).
Each string will be running at 562.5v @ 8A for a total of 4500W per string.
(Panels are 37.5v @ 8A / 300W each nominal voltage)

My inverter has MPPT inputs for 2 separate strings, so this works out nicely.
A voltage of 562v is also under its maximum of 1000v per string.

If everything goes well today, and I get time to install the cabling, and hookup the panels early evening, I’ll be able to test the system on Tuesday morning, when the sun rises.

The inverter won’t power up until it see’s at least 300v DC from its inputs, so I’ll need to wait till about 6am when there is sufficient sun to see my creation come to life!

Lastly –
Many thanks to my cousin Joel for his assistance in mounting all of this on the roof, to Wesley for taking a look at the cabling to double check I haven’t done anything silly, and to Angie & my brother Jerome for their assistance in getting the panels on the roof.

Three Phase

As my system is 3 Phase, I thought I’d talk about some of the different 3 Phase standards for wiring.

3 Phase, as you may or may not know, is better for transmission of power.

Power stations generate electricity at 22 000 volts (3 phase 50Hz). To transmit this power over long distances, Eskom steps up the power to to the following voltages for transmission: 220kV; 275kV; 400kV or 765kV. This electricity now goes into our national grid.

When it gets to the end user it is stepped down. This could be 11kV for a large factory or 400V(380V) for shops/homes. If you take a phase to neutral (single phase voltage) i.e. 400V/sqrt(3) you will get 230V single phase @ 50Hz.

When it gets to the house, it generally gets split up into single phase, and different circuits get each phase. So, the lights might be on one phase, the plugs on another, and heavy equipment may use all three (eg an old 1950’s Oven dating back to the Union of South Africa!).
Plug sockets at home are single phase 230VAC 50Hz.

There are two main connection standards for 3 phase; Delta wiring – which uses 3 wires, and Y wiring (also known as wYe), which uses 4.

Delta has one wire for each phase so 3 wires total.
Y wiring has one wire for each phase, plus a neutral, for 4 wires.

In my house, we have 4 wires, so its the Y standard.

You can check this by looking at how many wires go from the house to the street.
In our case, this is 4 separate wires, as you can see below:

So, what exactly is 3 phase?

AC current runs in a sine wave. This sine wave runs at 50hz for South Africa (50 ups and downs a second). In 3 phase, each phase is run at an offset of 120 degrees, so each phase peaks at an offset of the other. The 3 phases add up to a total of 380v – although these days is more likely to be closer to 400v, as the rest of the world has migrated to that. Either makes no difference, as they’re both values within the margin of error for provision of electricity.

Its extremely important to know what you have with regards to wiring, as it involves large amp circuits, and you don’t want to wire things incorrectly and cause Eskom to come smack you for tripping the street transformer!

Three phase is relatively easy to turn back into 1 phase – I’ll be doing that on one leg to provide an additional “solar” circuit for our laundry room.

Those of you who like the technical aspects should take a look here –

Some basic calculations for 3 phase below. These can be used to work out your maximum load or other important wiring details, like how thick your electrical wire should be if you’re carrying whatever max current your supply provides…

Basic electrical calculation:

Volts = Watt Γ· Amps
Volts = Ampere x Ohms
Amps = Volts Γ· Ohms
Amps = Watt Γ· Volts
Ohms = Volts Γ· Amps
Volt-Ampere (VA or Watt) = Volts x Ampere

For 3 phase, we need to use the square root of 3 for our calculations as an additional factor.
The square root of 3 is 1.73 (rounded off to 2 digits).

So, to calculate VA its: Volts x Ampere x 1.73

Example calc:

KVA = (Volts x Ampere x 1.73) Γ· 1000
= (400 volts x 60 amps x 1.73) Γ· 1000
= 41520 Γ· 1000
= 41.52 KVA

We can also work out the Amps as below:

KVA = (Volts x Ampere x 1.73) Γ· 1000
41.52 KVA = (400 volts x A x 1.73) Γ· 1000
41.52 x 1000 = 400 x A x 1.73
41520 Γ· (400 x 1.73) = Amps
41520 Γ· 692 = 60 Amps

If we wanted to convert KVA to KW, we need to use a power factor (this represents losses in transmission). The figure used for this is typically 0.85, so

KW Γ· 0.85 = KVA
KVA x 0.85 = KW


A more detailed explanation of power factor losses is here – http://www.energyaction.com.au/australian-energy-market/power-factor.html

Status Update

As its been a while (understatement!), I thought I’d update on the progress.

Well, I finally shipped my container of goodies all the way from China to SA, encountering a few issues on the way. Β Β A groot fok jou goes to DN Freight / Temoore Freight for being complete doos’s – Shawn Patience, Elize Werner you know exactly what I’m talking about; Β managing to screw up, get a charge of an extra R20k+ in Storage fee’s, *then* having the audacity to try bill another R10k on top for fee’s *already paid* in Shanghai. Β The sea freight pretty much turned into air freight pricing… Grrr.

They tried to cover it up too, then backtracked and changed story. Β Couldn’t even be bothered to show up for a meeting they booked, then literally blackmailed me into paying the charges – if you don’t pay, fee’s go up daily. Β I’m still considering getting lawyers involved in that..

The good news is that despite the unexpected extra charges, all the stuff arrived in one piece, and the panels even made it without a breakage.




The forklift did have issues though in our front yard – it got completely stuck, and had to be towed out!

Next up, was wiring.
As I was already redecorating the house, wasn’t too bad – I had the builder’s electrician pull the 3 phase to the front for me, and a separate 1 phase to the laundry room, so I could terminate (puts on best Arnie voice and asks – “are you Sarah Connor?”) at my leisure.

I also had my builders mount the Inverter, and my electrical boxen, as I’m rather lazy. The inverter is also bloody heavy at 40kg, so made sense to get stronger people than me to mount that πŸ™‚

Laying out how much cable is needed:


Running it into the conduit that I had builder put in for this very purpose:

The astute will note that I have 4 cables there. I have 3 phase in the house, so thats Phase 1, Phase 2, Phase 3, and Neutral. The smarter folks than me will ask what about ground?
Yup, I forgot! Doh. Running ground from a separate wall plug in the room though, so wasn’t a major disaster, although the electrical gods may frown upon me..

This is what it looked like pre-termination.

<img src="http://farm3.staticflickr.com/2826/10573372014_665f3e57e5 viagra se vende sin receta medica.jpg” />

…and this is what it looks like after a few hours of my time (wiring the MC4 connectors is fiddly business!)

Once I had that done, then it was a matter of waiting till a less rainy day, so that I could open my magic box of panels πŸ™‚

An hour of hard labour later, and all 800kg of panels were in the back garden!

…and thats where we’re up till currently.

Next steps will be to mount everything (hopefully this weekend), then do a test of the system to see that the panels can power up the inverter.

If thats all good, then I’ll pay for the electrician to come back and sign off on the setup, so I can go all Frankenstein and turn it on for a few minutes to configure, and check everything before I shut it down again, and start on the paperwork side with the City of Cape Town.

Luckily I snarfed a pre-made SSEG (Small Scale Electricity Generator) document from Arthur @ MyBroadBand, so I have a lot less prep work to do. Yay!

I have the power! (Ripple Control, and load shedding in power systems)

As I have an invested interest in consistent electricity back home (see my other recent post on Solar for details) and have been in discussion with the council about net metering and grid tie, I’ve been doing quite a bit of random reading regarding electricity distribution and its various facets.

Not many of us know that the power company / municipality also uses in-line signalling (aka ripple control) to implement power control and load shedding, so I thought I’d do a little writeup on that.

Many of us have noticed that streetlights don’t always come on, or go off when its light or dark – they appear to be on a timer system.

What most people don’t know is that the timer system controls are actually implemented centrally at substations, and these add signals to the power lines to tell the equipment to turn off / on when instructed.

This is done using ripple control codes.

With ripple control, a small signal is added to the incoming A/C at a distribution location – eg a substation. This signal is read by a special relay in place on the larger circuits (typically the Geyser), and turns power off or on when the electricity company requires – usually when power is scarce, and they need to shed some load.

As this signalling can work on multiple channels, each listening relay can be set to listen to a specific channel, and used to power specific things on / off remotely (e.g. Streetlights).

In South Africa, we use DECABIT signalling to tell things to turn off and on, as well as the older K22 signalling standard.

When load shedding needs to occur, the electricity distribution system needs to act fast to avoid system failures. Most things are automated, and happen in order of timing.

Implementations of the protection mechanisms in place have a specific time to occur – eg a latency. Responses to conditions also have a latency – eg getting additional idle power plants online to provide more power when needed, so its important to the grid to have multiple control and response mechanisms to respond to loads. Each response mechanism also has a different cost impact, so its also important to the electricity provider to best manage these.

A diagram of this is below (Excerpted from http://www.anime-za.net/tech/literature/Enermet_Farad.pdf ):


For light variances in load, frequency changes as generators speed up or slow down to supply enough electricity to the supply. If there isn’t enough supply to meet load, then frequency drops, and large scale equipment will disconnect until load decreases. This happens almost instantaneously – responses to these issues resolve with a latency of within a few milliseconds to a second. This is called Under-Frequency Load Shedding (UFLS).


As seen in the diagram above Eskom implements automated under frequency load shedding in an increasing percentage margin based off frequency rates.

(Additional details are in the PDF below)


The next set of load shedding is the one we’re interested in – ripple signalling. If the system still has too much load after 1 second, then it sends out a signal over DECABIT to turn off more equipment. DECABIT signalling has a latency of about 7 seconds – a minimum DECABIT signal frame is 6.6 seconds, so this is a second stage response to issues.

As each substation can be connected to up to 20,000 homes/customers (depending on substation load capacity), this allows localized load shedding where its needed, when its needed.

Eskom calls this Demand Market Participation, and has roughly 800MW of systems added into this mechanism. Municipalities are particularly keen on putting loads onto these mechanisms via DECABIT compliant relays, as this saves them peak power fee’s when loads are high – if they can temporarily cut off power to consumers for 10 seconds – 10 minutes for non-essential high loads, then they can substantially reduce what power costs them from Eskom, and make additional profits.

A good writeup on Demand Market Participation is below:


Eskom benefits as they can temporarily avoid adding more infrastructure to cope with growth.

This has been the case for a few years now, but it only delays the inevitable – you do need to invest in infrastructure, not incentivize clients to use less.

Eskom also has a secondary mechanism (using the same theory – lets encourage you to turn off power) called VPS. They have an additional 50,000MW of connections using this on a contractual basis – typically industrial users., and are looking to increase this number.

Its only been through introduction of these mechanisms that we’ve been able to stave off grid collapse. Its gotten so bad, that industrial users have been looking closely at what they can do to provide their own power when Eskom can’t.

Other countries – notably Germany, and the UK, have allowed consumers to become producers, by encouraging localized small scale production of electricity, thus helping the grid without requiring additional investment from the incumbents. This is called net metering – where both inputs and outputs are metered.

Eg – if you have a solar system that provides excess power during the day, it can feed into the grid – (when it needs it most), and they’ll credit you for your participation.

So far, South Africa has been rather reticent to implement this, as the short sighted vision is that its “stealing” from the incumbents profits.

A choice excerpt from that PDF is this –

Residential load can also be incorporated within the VPS, particularly when integrated with Smart Metering systems. Numerous pilot and small scale projects are being undertaken within both Municipalities and Eskom in response to the DOE’s Regulation 773 of 18 July 2008.

The Department of Energies regulation can be found here –


These state that all systems over a certain size require that smart metering be installed by 2012. As you may have guessed, quite a few municipalities have not met this deadline, and Eskom has been dragging its feet on that too.

Ironically, introduction of smart metering would actually help the grid here in South Africa, as IPP’s (independant power producers) would make the grid more stable by providing additional energy when needed, and at a lower cost than the incumbents can create it for.

This however does have its issues – most municipalities generate revenues from Electricity, and so are loath to change the status quo, even when it would benefit the country from a whole.

So, its unlikely to be implemented in the short-medium term, unless the government drags them kicking and screaming through the process.

In summation, this –







DECABIT Ripple Signal Guide

Thesis on the financial implications of relaxing frequency control as a mechanism.

http://www.energy.gov.za/files/policies/Electricity%20Regulations%20on%20Compulsory%20Norms%20and%20standards%20for%20reticulation%20services%2018Jul2008.pdf – DoE Regulations

http://www.enerweb.co.za/brochures/AMEU%20Conference%20-%20Enerweb%20VPS%20Paper%20-%20201109%20-%20%20V1.0.pdf – Demand Market Participation

http://www.systemoperator.co.nz/f3210,36010947/Appendix_A_-_A_Collation_of_International_Policies_for_Under_Frequency_Load_Shedding.pdf – Load Shedding in International operators

Going Solar

I’ve been interested in going completely solar for a while now back home in South Africa, as pricing for electricity has rapidly increased past the pricing for solar; return on investment is in the 3 year range currently.

It will get close to 1 1/2 year return on investment when Eskom new pricing increases happen, so its a no brainer to install.

I’ve already replaced our geyser (hot water system) with a solar based system, plus all the lighting in the house is already LED based (yay China!), so our base load of electricity is low for the size of the house. I can still improve though by installing solar, to make the electrical costs approach zero, and at some indeterminate point in the future when Eskom allows for legalized grid tie, a profit center!

As I’ll nominally be a 10KW producer (I can add 2 panels to get there), I should be able to at some point pump back into the grid sooner rather than later – as the trial projects for Cape Town all sit at the 10KW range and up…

From what I read –

Eskom will pay out R 1.20 per kilowatt hour

generated by your solar system for the first three years, 70% immediately after installation

and the balance at 10% for the next three years.

More here – http://www.capetown.gov.za/en/EnergyForum/Documents/Eskom%20IDM%20small-scale%20renew%20energy%20-%20Lodine%20Redelinghuys_31Aug2012.pdf

(Yes, currently this is only available for commercial use, but I do expect that to change at some point. My system should be in use for at least 25 years, so I should get some benefit at some point in the future.)


Before I get to pricing though, I need to explain how it all works.

For any system, you’ll need some kind of input.

As I’m looking at Solar, thats my input. I can also look at thermal or wind based. Wind based is a distinct possibility in Cape Town, but I have been advised that its probably too windy to use! (turbines can’t run during extremely windy weather or you break the turbines).

So, I’m going with Solar.

There are 2 types of solar panel out there. Monocrystalline and Polycrystalline.

Monocrystalline is more expensive per watt, as its a more difficult process to make panels from.

Mono panels are also slightly smaller per watt of output. On average mono panels are about 14% smaller. They also work better in hot climates.

Aside from those differences, they’re fairly similar.

Panels are typically rated in watt terms.

A 300w panel will give you 300W of power at peak output (eg mid-day).

This 300w of power is at DC voltage though, and for house use, we need A/C

The 300w panels I’ve been looking at give 36V @ 8.3A.

I’ll probably go with polycrystalline, as the pricing isn’t really worth the extra 30% for mono crystalline for my needs.

Panel info below – (click me for pdf)


Basic calculation for power output is P = V * A

This works out to 300W a panel (303W = 37.6V * 8.06A)

I’ll be getting 30 panels, as thats about the max I can fit on my roof in theory.


(My brother hasn’t gotten me the exact sizing yet).

To use this, we need an inverter though, as something has to convert the DC power into AC.

In my house, I have 3 phase power, and an antique metering system.


3 Phase is good, as i have sufficient power for my needs, but its bad as I need a more advanced inverter to give me 3 phase.

I could use 3 x single phase inverters, but for simplicity, I’ll be going with a single 3 phase inverter.

If you see the cabling here – you’ll see we have 3 phases + 1 neutral = 4 cables.


To work out what sort of inverter I can use, I need to do some basic math.

I’ll have 30 Panels total.

Each panel gives out 36V @ 8A., and that will give me approximately 9KW output. As the smallest *decent* 3 phase inverters I could find are 10KW ones, thats a good size.

I have a choice of running the panels in series or in parallel.

If I run them in series, then the Voltage increases.

Eg 1 panel = 37v, 2 panels = 74v @ 8A…

If I run them in parallel, then the Ampage increases.

Eg 1 panel = 8A, 2 panels = 16A @ 37v

If you’ve ever seen welding cables or car battery cables, you’ll see what sort of cabling is required for high Amps. So, everyone wires using DC voltage.

My inverter of choice is probably going to be this: Growatt10000UE


That 3 phase inverter has the following characteristics.

It will power up from 300V (min voltage to run), and accepts voltage up to 1000V.

It also has 4 inputs for panels.

Generally each input is called a “string”.

As I’ll have 30 panels, I’ll probably be balancing them out in 2 x 15 piece strings -> the inverter.

Each string will work like this

37V * 15 = 564V DC * 8A (4.54KW of power)

37V * 15 = 564V DC * 8A (4.54KW of power)

This will give me a rough total of 9W peak power.

As conversions are never perfect, and panels can output more during peak than they are rated for, I’m getting a 10KW inverter. This will allow for some small headroom in future if I need to expand slightly.

It also is fine for something I haven’t talked about yet – open circuit. The panels I’m looking at run at 36v open circuit (i.e. before they kick in), the inverter also needs to be able to work without issue at open circuit voltages. As the inverter supports 1000v, open circuit of 564v isn’t an issue.

So far, costs are:

30 Panels = 720RMB / poly panel = 21,600 (mono panels are about 900-1000 per piece). Poly panels are physically 1.9M x 1M @ 300w / 28KG , Mono 1.9M x 1M @ 300W / 25kg

10KW 3 Phase inverter = 9,000RMB

Weight = 1000KG with packing.

Shipping + clearance – roughly 15,000 + duties @ 20%

Total landed in Cape Town = 45,000RMB / R60,000

That gives me a rough pricing of R6.6 a watt *installed*.

It also gives me a system that I can hook into the grid (illegally currently!), but won’t provide for power in case of failure.

I actually don’t need something that size, but sadly, due to the cost of clearance being a complete rip off, it doesn’t make sense to ship less

Currently our power bill sits at about 700-1000 rand a month, over a year this is around R12,000 using worst case scenario maths

My intended system will cost me about R60,000 + install labour. At current electricity pricing, I should see a complete payback for the system in about 5 years. Given that electricity prices are going to be *doubling* over the next 5 years in Cape Town, this will actually be achieved in about 3 years or so.

Not too shabby!

Our current monthly electricity usage looks like this for those who may be interested.


You’ll note that electricity use spikes on certain days (mainly weekends) – this generally ties into when the maid is there, as then the washing machine, dish washer etc get run, or on the rare occasion that my brother actually cooks

Initially I’ll be feeding excess power back into the grid, and using that as a “battery”.

How will that work?

Well, as I have an older meter, it can run backwards. So, daytime when I have _substantial_ excess, i’ll be running backwards, and nighttime, when the solar panels are not generating, I’ll be running forwards.

Essentially, using the grid as my battery..

Eskom will be benefiting from all this, as I’ll be a net producer far over what I consume – so they’ll get all the free electricity I’ll be generating.

Its also safe – as the inverter will not feed back into the grid if its offline – eg when we have one of our rather too regular power outages (3 in the last month from my logs).

Longer term I’ll be installing a battery system to allow for complete off grid, but funds don’t currently stretch to that yet..

Do note that the above is for my needs – your needs might not be my needs!

I need a 3 phase system. Most people _don’t_. I’m also going grid tied for the moment due to funding available. Others might find it better to have a hybrid grid tie/ battery system. If I could afford it, I’d go that route!

I’m also *heavily* overspeccing the output – clearance costs are substantial for South Africa (highest in the world almost), so it doesn’t make sense for me to ship a small system, as there is only a marginal cost for what I’m speccing.

A suitably sized system for us would be 8 panels, and a 3kw inverter. I’d be crazy to ship that though, as the clearance is more than the cost of the system. So, I’m heavily overspeccing on requirements so that it makes sense. Long term its also a no-brainer for me, as I’ll have substantial excess I can sell back to the grid.

In case anyone is interested how I’ll retrofit this sort of system with a battery backup – here is a diagram of a single phase implementation – I’d be doing something similar:


That said, I do have another easier solution – I’ll probably go cheap – stick the things that may not lose power(tm) circuit on a 2KV UPS, and have an isolator switch in circuit for when the grid goes down so its isolated from Eskom. This will accomplish the same thing pretty much, and should tide us over for the average 3-4hour outages we seem to experience every few weeks. It will also sit nicely in the computer rack that will contain the media side of the house and data storage needs