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Solar Micro Inverters or DC optimisers V String inverters

In this FAQ we are going to be talking about Enphase Micro inverters, Huawei, Tigo and SolarEdge DC optimisers and comparing both to a top quality string inverter made by Austrian company Fronius (but what is written applies to SMA, Goodwe or any other string inverter too).


Enphase micros (there are other brands, but Enphase are the market leader)

A micro inverter connects to each and every solar panel. Each micro has it's only MPPT so it operates independently of every other micro. It also converters the DC panel power to 240V AC, right there on the roof.
The combined current produced by all these micros is then sent down to your electricity meter and switchboard. There is also a small WIFI enabled (or it can use your regular AC cabling) monitoring device called the 'Envoy' that provides statistics on the system as a whole, or at an individual panel level (if enabled) via their software product Enlighten. The Enphase system can have their own AC coupled battery system connected (or any other AC coupled such as Tesla Powerwall 2 system)

The principal advantages of these micros are that they

1. Allow panels to be placed in roof areas where shading occurs at some time in the day as the power loss caused by the shaded panel will only reduce the current produced by that panel, and not bring down all the others.

2. They allow the panels to be located on multiple roof orientations (e.g. North, West and East), and at different roof tilts, because each micro (and it's connected panel) is a law unto itself

3. They allow different panel sizes to be connected. e.g. Large 72 cell, 320W panels can be used where they fit, and in tighter areas, smaller 270W panels could be used.

4. All the power running through the cables in your roof is regular old 240V AC instead of potentially up to 600V DC with a string inverter

5. You can monitor the output of each panel individually.

Huawei, SolarEdge and Tigo DC optimisers

Pretty much ALL of the above that is written about Enphase micros applies to Huawei and SolarEdge, except that they do not convert DC to AC on the roof. They have DC optimisers that have an MPPT tracker but the DC to AC conversion happens at their centralised inverter. Tigo optimisers can be connected to any panel on any string inverter to combat shade. These $100 boxes are a cheap way to solve shade issues when you are buying a regular string inverter like Fronius, SMA, Goodwe etc.


Which is best?

Our experience with existing customers shows a typical 6% annual power gain from micros and optimisers compared to a string inverter where there is NO shading of any of the panels from anything other than clouds. In situations where there is shading we don't place panels in those locations if using a string inverter, or we recommend SolarEdge or Enphase, so providing an accurate power comparison isn't possible.

If we had to choose between DC optimisers (Huawei and SolarEdge) and Micros, we could come down in favour of Optimisers. There is so much less to go wrong on the roof with their system compared to all the cables and couplers and more complicated electronics than micros. The Huawei is particularly good beause it lets you install optimisers only on the panels that would get shade. At $80 an optimiser, that can add up to a very significant saving.

Is it worth spending the extra money?

If we take the unshaded situation first, then 6% more power on 6.48kW of panels is probably about 600kWh per annum more power, worth anywhere between $42 and $150 depending on home day time consumption. On that basis, it's harder to justify spending an extra $100 for every panel, but if only a few panels are getting a little shade, then Huawei and Tigo on just those panels may well be fully justified.

If there is unavoidable shading, or you want panels in three or more orientations or tilts, or want to mix up panel sizes, or you want to get as much on your roof as possible and don't care if a few panels are shaded some of the time, then it's likely you will see a return on the extra investment in Enphase Huawei or SolarEdge in reasonably short order.

Connecting batteries.
With the Enphase solution you can only connect an AC coupled battery system. Huawei and SolarEdge provide you with a choice of DC or AC coupled batteries.




Cutting your power bill in half

If you install a 5kW system on a North roof it will make 30 units per day in Summer, 15 units per day in the middle of Winter, and average 24 units per day across the whole year.

If you use 80% of that power and sell 20% back as surplus then the solar is worth $2,000 a year at current Synergy prices and cutting the typical Perth power bill in half.


News & updates

Barnett backflip 12-08-2013
The WA State Government took on WA solar customers and lost. In a very hasty backflip the hugely unpopular decision to remove the feed-in tariff from customers was reversed by Premier Colin Barnett today.