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Sunpower – is this really the worlds best panel?

Sunpower Solar Panel Review

Sunpower Panels are often touted as the best solar panel in the world – but are they honestly that good? In this review, I’ll start by briefly introducing the company and the panel. Then I’ll explain the eight potential issues with traditional panels. Next, I’ll explain how SunPower have dealt with all eight problems by building a fundamentally different panel. Following this I’ll give my opinion on the financial situation of SunPower – is Sunpower is a risky option in the current volatile panel-manufacturing climate?

The Californian based solar panel company was founded in 1985 by Dr Richard Swanson. With a world record efficiency of 21 percent, SunPower has been hailed as the world’s most durable panel, with the least degradation, the longest warranty by far, and an unprecedented 40 year expected lifespan. No wonder Sunpower have been used on some of the most interesting projects on earth.

Solar Impulse
Solar Impulse, the first solar-powered plane to fly around the world, without a drop of fuel.
Grover. NASA’s solar-operated robot used to examine the layers of Greenland’s ice sheet.
Planet Solar
Planet Solar, the first craft of any kind circumnavigated the globe powered 100% by solar energy.

Not bad on one’s resume. But before we see why these projects chose SunPower, let’s look at what makes a quality traditional solar panel.

The traditional solar panel

A standard cell
A standard solar panel today is made up of about 60 silicone squares called “cells”. Each cell is screen-printed horizontally with fine silver and joined vertically with silver ribbons.

The whole thing is then framed somewhat like a picture; the cells are protected with an EVA/polymer sheet(a bit like a laminated sheet of paper), a sheet of glass on the front, and backing material on the underside. This is all framed in an aluminium frame.Screen Shot 2016-09-26 at 8.16.54 PM

When the sun hits the silicone cell, it generates electricity that flows through the screen-print silver, up the joining ribbons and into a junction box mounted on the back of the panel. The panels are connected via MC4’s.

The silicone cell, ribbons, glass, polymer, back-sheet, frame, junction box and MC4 connectors make up the “Bill of Materials” or the BOM.

El-Cheapo solar panels

When a solar panel manufacturer agrees to sell at a ridiculously low price, the quality of the components (the BOM) is naturally compromised. Unfortunately when someone saw this part of my post they didn’t like their brand mentioned so they threatened to sue. I thought I’d be more diplomatic and take this screen shot of a panel test on my roof and let the reader infer.

MC Electrical office Panel Test
CLICK TO ENLARGE. MC Electrical Panel Comparison – 32/1/16 – 1/10/16 (dates chosen for easy comparison).

Quality Solar Panels

The manufacturing of a panel is, of course, best done with a high-grade BOM at a quality, up to date and well maintained automated manufacturing facility. SunPower, LG and Winaico would jump to the top of mind when you think of a premium built solar panel. Canadian Solar, JA Solar and Phono are examples of quality Chinese made panels at a more affordable price. However, of all the panels on earth, there is one that stands head and shoulders above the rest.

Why SunPower is the best panel

The SunPower Maxeon cell is the heart of the SunPower panel. This unique cell construction has solved at least eight problems that standard solar panels faces.

Best Solar Panel The Sunpower cell difference

  1. Fragile cells

    From time to time I’m sitting at a meeting with a client, I’ll place a traditional solar cell on my desk and talk about how it works. Intrigued, they inevitably reach over and pick it up. I sit back amused and wait a maximum of 2 seconds before they shatter the cell. The look of embarrassment is awkward, but I mercilessly act shocked and continue the gag for another few seconds. Finally, I laugh and explain that I wanted to point out the reality of standard solar panels: solar cells are fragile!

    Panels need to be shipped and handled carefully. Rookies in the industry often unknowingly create micro-cracks in the cell by laying panels flat in the trailer, throwing boxes of gear on top, and ratcheting that collection of thin wafers down real tight. They race over speed bumps (because tradies are always running late), and when they arrive at your place, the untrained apprentice bounces the panels on their head as they walk towards the ladder. Once the job is done, he’ll pose on top of the installed panels for a proud Facebook photo.

    Micro-cracks in panels are a serious issue with cheap panels. As manufacturing technology gets better, and prices are squeezed, silicone wafers get thinner and thinner. To cut costs further, the protective glass and the aluminium frame get thinner and thinner. Combine that with rookies on your roof and the micro-crack phenomenon gets bigger and bigger. Unfortunately, if not handled correctly, premium panels are not immune to the micro-crack phenomena either.

    All but one.

    After I have completed the cell shattering demo with my unsuspecting client, I pass them a SunPower cell. They notice the cell takes far more pressure to bend it. It eventually breaks, but the copper back keeps the cell in one piece. When we combine the cell strength with the high-quality SunPower panel glass and frame, SunPower cells are virtually immune to micro-cracks in real world conditions.

    panel1breakmini panel3breakmini


  2. Shade intolerance

    If you don’t need to know why -skip to the next point and just believe me that: SunPower panels perform better in partial shade. But if you are remotely interested, let me do my best to briefly explain why:

    A standard silicone cell has the positive on one side of the cell and the negative on the other. Because of the large electrical separation between the positive and negative, when the cell is shaded, it needs to produce a comparatively higher reverse bias voltage to overcome the resistance. A typical conventional cell has a ‘reverse bias voltage’ of 15V to 20V. This high voltage on a standard panel causes detrimental hot spots and reduces the panel’s efficiency. When the reverse bias voltage gets high enough, it will activate the protective bypass diode. While bypass diodes are installed in each third of a panel to protect it from hotspots, as each bypass diode activates, the panel reduces its production by one-third.  To make things worse, bypass diodes have a limited lifetime. The more often they are activated, the sooner they will fail.

    Sunpower has designed the Maxeon cell to have positive and negative on the back of the cell – just a fraction of a millimetre apart. When shade occurs, instead of a huge 15 to 20 volts, the “reverse bias voltage” is 2.5 volts (X series) or 5.5 volts (E series). In summary, the advantage of the Maxeon back-contact in shaded conditions are:

  3. The reverse voltage is lower, therefore
  4. the heat created is less, therefore
  5. the more current and power flows, and
  6. bypass diodes operate less frequently giving more power and increasing their lifetime.Contrary to a popular myth, SunPower panels do have bypass diodes. One SunPower YouTube clip claims bypass diodes are in individual cells. They are not. Bypass diodes are installed at the string level, at each third of the panel. So if we get SunPower panels, there is no need for optimisers on a shaded roof right?
    Wrong. In heavily shaded situations, there will still be a current mismatch in a string of SunPower panels – albeit with significant less severity than a traditional panel. So optimisation (preferably in the form of a Tigo TS4 or SolarEdge) can still be advantageous. Optimisation can also have advantages of individual panel monitoring and a higher degree of safety in case of fire etc. Read my explanation of the purpose of optimisers at the beginning of this post.
  1. Light-induced degradation

    To get silicone cells to produce power, they are “doped”, man. Most panels are doped with phosphorous and boron, producing a P-type silicon. The problem with P-type silicon is that it is prone to “light induced degradation”. LID is a well-studied phenomenon that degrades the average panel by 1 to 4 percent within hours of the panel being exposed to light.

    All SunPower panels (along with some LG panels) use an N-type silicon. N-type is way better crack and does not have the side effect of LID – not to be confused with LSD.

  1. Temperature fluctuation intolerance

    Standard panel manufacturing requires a highly finicky process of joining the cells together with delicate ribbons. If done correctly, slack will be left for expansion and contraction as daily temperature cycling in the panel occurs. However, even when this process is done correctly, this method of connecting one cell to another is known to be the weak spot of the panel.

    SunPower panels use robust but flexible copper connections that are designed to expand and contract.

    Side by side comparison
    Standard vs. Sunpower cell conections
Standard Cell.
Standard cell connections
Sunpower cell connects
Sunpower cell connections
  1. Heat intolerance

    Contrary to what people often think, panels don’t like hot days. A windy, cool sunny day is the optimum weather condition for solar. As solar cells heat up, they lose their efficiency. This intolerance is measured in the form of a “temperature coefficient” on any panel’s spec sheet. Because the SunPower Maxeon cell has a copper base drawing heat away from the cell, SunPower panels handle higher temperatures better, so have a lower temperature coefficient which means they lose less efficiency on those hot summer days.

    On a 40 degree day, the SunPower x series will run about 4.8 percent better (per watt) than a standard panel tier 1 panel, and the SunPower E series will run 1.2 percent better.

  1. Humidity intolerance

    High humidity can have a detrimental corrosive effect on panels. Over time, water can pass through a standard panel’s back sheet, corrode the panel’s fine silver grid lines, and in turn degrade the output of the panel. With well-built panels, this corrosive effect will take longer. However, over the next 10 to 20 years, signs of corrosion will occur. The graph below shows how damp heat testing detrimentally affects a standard panel after as little as 2000 hours of extreme cycling.

Damp heat test

  1. The front contact

    The traditional cell relies upon fine screen printed silver and the thin ribbons to transport the energy from the silicone to the junction box. The obvious disadvantage of having this on the front of the panel is that it is shading the front of the cell. No need to be a rocket scientist to work out that shading the front of a solar cell is not optimal. This ties in with the next point – rooftop limitations

Sunpower cell
Sunpower back contact cell
Standard front contact cell
  1. Rooftop limitations

    The goal of solar panel efficiency has always been to put more solar power in a smaller footprint. Efficiency is essential where your roof space is the limiting factor. At 21 percent, SunPower has bragging rights to the most efficient panel on earth – which just means you can get a bigger solar system in a smaller area.

    With the eight points above, you can see why Solar Impulse, Grover, and Planet Solar were all fitted with Sunpower panels. Given that SunPower is designed to last in extreme conditions, it would only be natural that they would back their panel with the best warranty on the market.

Panel warranties

The industry standard warranty

I’ve quizzed several CEO’s of panel manufacturing companies on what their panel warranty means. They always smile and fess up. Almost every panel manufacturer play tricks by giving you a 25-year performance warranty but a 10-year product warranty. This is really saying, if the panel works after 10-years, it will perform well. If it doesn’t perform well after 10-years, that’s unfortunate because your 10-year product warranty is out. Yep, this is the dodgy stuff that goes on in the industry I work in.

SunPower’s warranty

SunPower put their money where their mouth is with a full 25-year replacement warranty. They will even pay for the cost of getting a sparkie on your roof to replace the panel. I guess that’s not a huge expense when they boast only one warranty issue per 20 000 installed.

But that’s all well and good, as long as SunPower are around in 25 years right? How likely is that looking?

Is SunPower going bust?

The elephant in the room. Unsurprisingly, SunPower assures me categorically no – all is fine and dandy at SunPower. However, concern was raised when SunPower recently dropped their panel price so dramatically to compete with LG and announced a future closure of their Philippines manufacturing plant. Their share price on the NASDAQ dropped from around $30 to $10 in a matter of 6 months

I’m not an expert on the NASDAQ – but this looks bad. Google to the rescue!

One source I use is Macroaxis. According to their site, using a normalised Z-Score, SunPower has a probability of Bankruptcy of 51 per cent. Macroaxis are quick to point out that this does not mean what it sounds like. They explain:

Probability of Bankruptcy SHOULD NOT be confused with actual chance of a company to file for chapter 7, 11, 12 or 13 bankruptcy protection. Macroaxis simply defines Financial Distress as an operational condition where a company is having difficulty to meet its current financial obligations towards its creditors or to deliver on the expectations of its investors.

So lets look at the other solar companies position according to Macroaxis (as of 25 September 2016).

Solar manufacturers likelihood of bankruptcy – Macroaxis

  • Sunpower:51%
  • Trina Solar: 49%
  • Risen Energy: 77%
  • LG Electronics: 28%
  • JA Solar: 51 %
  • Jinko Solar: 1 %
  • Canadian Solar: 52 %
  • Renesola: 51 %
  • Hanwha q cells: 48%
  • Sharp Corporation: 51%
  • CSun: 57 percent%

The solar panel manufacturing industry as a whole is not having a great time at the moment.
But for the record: Coca-Cola, 40%, BMW 43%, Telstra 62%, Qantas 47%.

Regardless, Sunpower is in some degree of financial distress, and it has not currently met the expectations of its investors. Just ask LG who recently finds joy in letting the industry know about it. However, one recent and less-biased financial analysis about SunPower is written by Travis Hoium: “Is SunPower the next horrific solar bankruptcy or just misunderstood.”

Here is an exert of Travis’ analysis:

The savior waiting in the wings

SunPower has a lot of risks ahead with uncertain solar demand in 2017, but it has an ace up its sleeve as well. Total owns two-thirds of the company and probably doesn’t want to see that investment go up in smoke if there’s a gap in demand for a year or two (2018 and 2019 projects are already flowing in). Total could provide a line of credit or back a debt offering, as it has done in the past, keeping SunPower afloat until better days arrive.

That’s worth considering if you’re betting on a SunPower bankruptcy. Total would have to allow it to happen, and I don’t see that being likely, given Total’s financial interest in the company.

Is disaster on the horizon?

When you look at the full picture at SunPower, there’s a lot of uncertainty and risk, but I don’t (yet) see the tell tale signs of a solar company that’s in serious financial trouble. It doesn’t continually need cash to finance projects, debt costs aren’t rising rapidly, and there are no debt maturities on the horizon.

Travis Hoim, The Money Fool, 17 September 2016

As I am not the financial Guru myself, I would approach the risk of installing SunPower panels with a more pragmatic approach:

  • The solar industry is volatile. Recently the world’s largest solar company SunEdison went bust. There are no guarantees with any panel you purchase.
  • Total owns 66% of Sunpower. Total is a French multinational integrated oil and gas company and one of the seven “Supermajor” oil companies in the world. It turns out that Total is doing alright. Yes, I get the irony, however, despite Total’s oil agenda, I reckon Sunpower is safe.
  • Sunpower is not acting like a company in distress. Chris Brown from Sunpower Melbourne is travelling to NSW, QLD and ACT in the next 3o days. Andy Gilhooly is presenting at Australia’s biggest solar conference All Energy in Melbourne next week on Sunpower’s new 435w Panel  launch. Put that in your pipe and smoke it LG! It’s business as usual at Sunpower Australia.
  • SunPower panels used to be ridiculously expensive. Now the E27 are about on par with LG 320w Neon panel – not out of reach if you are thinking of staying in your home long-term.
  • Quality is in SunPower’s DNA. I don’t believe they will try to get out of a tight financial year by devaluing their product and cutting corners.
  • Only one in 20 000 panels have been replaced under warranty. Even if SunPower does go bust as a company, there are good odds your panels will at least outlast the 10 or 12-year warranty that the next closest panel manufacturer has on offer.
  • If your panel fails after ten years, I (MC Electrical) have every intention of still being in business. Under Australian Consumer Law, your failed SunPower panel will become my problem. Given the published 1 in 20 000 failure rate, I don’t feel I am exposing my business to too much risk. I’ll keep installing Sunpower.


SunPower makes the best solar panel on earth. The cell is less susceptible to micro-fractures during transit, installation and extreme weather events. It will work better in shade, is more tolerant to temperature fluctuations, and it will produce more power on hot days. It won’t degrade anywhere near as quickly as any other panel in humid conditions. Thanks to its high efficiency, you’ll be able to put more solar on a roof where space is the limiting factor. While SunPower is going through some financial stresses currently, we know that just about every panel manufacturer is in the same boat. Even if you guess wrong, and SunPower do end up going bankrupt, you probably won’t need to claim the warranty, and you’ll be the proud owner of the best panels on earth.

I’m keen to hear your thoughts on SunPower, or why you think LG or any other panel is superior. Leave your comments below!

Mark Cavanagh

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Mark Cavanagh

Mark is the Owner and Manager of MC Solar & Electrical. He’s an Electrician, accredited solar installer/designer and an electrical contractor.

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