solar panels perth australia image

 

Solar Micro Inverters or DC optimisers V String inverters

Let's start with price.

A 20 panel Enphase Micro inverter system costs $5,100 for single phase and $5,600 for three phase. That's just for the gear (20 x IQ7+ 72 micros, Envoy, Relays and the rest), installation and panels etc are extra.

 

By comparison a single phase Huawei hybrid inverter is $1,600, three phase, $1,900, again just for the inverter, installation and panels are extra.

 

So why would anyone pay so much more for twenty individual little inverters, as pictured above, compared to a single, central battery ready 'string' inverter installed in your garage?

 

Shade

Many people, in fact probably most, who purchase micro inverters, do so in order to combat the negative effects of shade on some of their solar panels. A neighbours (or their own) roof, trees, Air Con units etc. Shade is bad news for solar panels.

 

Micro inverters handle shade as well as the other available technology, DC optimisers, by limiting shade power losses to just the shaded panel(s), leaving the unshaded panels to perform as normal.

 

If you had shade and bought the above mentioned Huawei inverter you could put Huawei's DC optimisers on any of the panels that are going to get shaded. Let's say you decided to put an optimiser on ALL twenty panels. At $90 each, that adds $1,800 to the Huawei price.

 

Now you wanted to prove that your optimisers were doing their job on each and every panel, by seeing the individual output of every solar panel in your reporting software, so you need to buy Huawei's 'Smart Energy Box', adding another $400.

 

So now, we have a level playing field, Huawei price is now up to $3,800 for single phase and $4,100 for three phase. We used Huawei in this comparison but SolarEdge would be almost identically priced. The only difference is Huawei is a ready to go hybrid (battery) inverter whereas Enphase and SolarEdge are not.

 

So, Huawei is still a LOT cheaper than Enphase, so why else would someone buy micro inverters?

 

High Voltage in the roof

String inverters like the Huawei, even if they have optimisers on every panel, have the panels connected in 'series', which means that you start with one panel, let's say pushing out 30 Volts DC, then join it to the next, which adds another 30 Vdc, and so on, to perhaps 12 panels with a combined voltage of 360 Vdc. This, by law, means that the cables have to be run inside heavy duty conduit inside your home from the roof to the inverter location (usually in your garage) where the DC is converted to 240V AC

 

However, micro inverters are connected in 'parallel' with the conversion from the solar panel DC voltage to 240V AC done there on the roof. So as the panels fitted with micro inverters are connected together, the voltage is a constant 240V, but the current (Amps) increases by 1 AMP per panel. If you had two runs, 10 panels on each, now you have 240V pushing 10A through your roof. Pretty normal stuff that we all have in our roof already.

 

Your choices

If your major concern is voltage in your roof, then its Enphase for you.

 

If your issue is shade then the choices available are much wider.

Enphase micro inverters
Any string inverter with Tigo optimisers

SolarEdge and Huawei string inverters with their own brand of optimisers.

 

Enphase and SolarEdge require an optimiser or inverter on every single panel, Huawei and Tigo optimisers can be 'selectively deployed' only on the panels that will be shaded. That's a much cheaper way to go, because if ALL your panels are being shaded, then you probably shouldn't be getting solar on that roof area in the first place.

 

Did you know a South facing roof can be used for solar?

We see so many homes where people are trying to solve shade problems on their North, West or East facing roofs, whilst they have a huge entirely unshaded South roof.

 

"You can't put solar on a South facing roof in Australia !!" everyone yells, but you can and here are the numbers to prove it.

 

6.6kW of panels installed on a North facing or a South facing roof with the table below showing average daily production for each month in kWh.

e.g. January, North facing roof makes average 42kWh per day, South facing 41.3kWh

 

  North South
January 42 41.3
February 39.5 33.3
March 36 23.2
April 31.4 13.7
May 24.1 8.3
June 22.4 6.2
July 23.7 7.1
August 26.3 11.6
September 31.4 19
October 36.3 28.4
November 36.7 34.6
December 39.5 40.5
     
Annual 32.2 22.2

 

Bet you didn't think that a South facing roof in December could make MORE power than a North facing one?

 

Anyway, the point is that if you have a shaded North facing roof that's going to lose 30% of its annual output because of shading, then that's no better than putting the panels on an unshaded South roof. As you can very clearly see from the table above, South facing is terrible compared to North from April to September, but the rest of the year, very similar.