interview: Alan South from Solarcentury

At Ecobuild 2013, we had the opportunity to talk to various members of Solarcentury, the UK’s most experienced solar energy company and a beacon of innovation.  Among them Alan South who has over 20 years technical and leadership experience in innovation, at IDEO and Cambridge Consultants. He also holds engineering degrees from the University of Bath and Imperial College London, and a Masters’ degree in design from the Royal College of Art.


alan south at ecobuild

Alan South: My name is Alan South. My role at Solarcentury is Chief Innovation Officer. I’m responsible for our proprietary products and services like the PV tiles and slates you see here on the stand.  I personally have quite a significant interest in the adoption of renewables by households, so I have a point of view that I’d be very pleased to share with you.
Alvaro Feito: What are the barriers for adoption of renewable energy? What is holding back domestic renewable energy?
A. South: I think it’s one of these things that I call a multi-point problem. It’s not one thing. Because if it was one thing, someone would have found it and solved it.  There are a whole range of barriers. Fundamentally when you talk to people they say they love the idea of renewables.  They want a house that is green, they want to protect their family from future increases in energy bills.  Everybody fundamentally loves the idea. So …
What are the barriers?
1. Barrier number one: It is not yet a mature industry.  There is a whole set or services where you can pick up a phonebook and look up the classification for roofers, garages, landscaping … and you know who to contact.  But it’s still a young industry. If you ask a household if they want a heat-pump or a solar PV panel, they will say “Well, who do I call?”. That’s a barrier that in time will fade.
2. The next barrier concerns the next step.  They might say: “I’ve had this company call me back.  But I think they are only 4 people.  They are really nice people, I feel I can trust them.  But will they be in business in a few years if I need to claim my warranty?  Again, in time this barrier will fade.
3. There’s also a question of confusion.  A big amount of confusion. And I think the renewable industry often doesn’t service customers very well because it talks in very technical terms. So if you put yourself in the mind of the consumer or householder, they have been used to paying electricity bills.  The probably use the word units rather than kilowatt-hours, and they are used to the idea that they pay this bill but electricity just comes along.  And all of a sudden they are asked to take control of what they are doing. And that may feel like a step too far. So the technical nature of renewable sales may be also a barrier.
4. I think another barrier is that consumers have become used to the idea that technology comes along. But then it turns out not to be the right technology, or sometimes better technology comes along. It happens with computers, video, video recorders, etc.  So there’s a sense that it might be a good idea to wait for the next innovation.
A. Feito:  Do you think people are aware of the drop in price in the last 3 – 4 years?
A. South: I think they are. I think they are aware of the degree with which the prices have dropped.  So they might say let’s not do it this year but do it next year. So there’s all manner of barriers.  And I think the really successful companies are going to start to tackle these barriers.  So when the successful consumer facing companies start to understand these barriers, and start to find solutions the barriers will fall.
A. Feito: So you’ve spoken about the maturity of the industry and how this results in a certain lack of transparency: It’s not so easy to find a supplier or to choose the right one. Another side is the rapid evolution of the technology and the challenge of finding the right time to invest.  So what needs to happen to address these barriers? Can we make it more transparent? Easier to choose?
A. South: There are two possibilities.  One is to solve the problem directly, which is to make things much more clear and much more transparent. And maybe that can work, I’m not sure. I think it’s part of the solution. I think the other part of the solution which has worked in so many other industries is the development of consumer facing brands.  So an awful lot of quite complex decisions are being made by humans all the time.  And the branding and the trust in that brand plays a big part in it.  So to repeat:
One way is to tick off each little barrier one by one. To try and reassure the consumer.  But that starts in my mind to become a consumer education program.  And whilst I think there is some merit in that, it’s often a very difficult and expensive thing to do.   I speculate that perhaps what we will see is development of trusted brands.  By way of example a company I admire tremendously that has created a consumer facing trusted brand is Solar City in the US.  And I believe the excellent performance they are achieving as a business comes as a result of a good understanding of the purpose of a consumer facing brand.

We would like to thank Alan South for taking the time to answer our questions and ask that very question to our readers:  What do you think is holding back domestic renewable energy? And what do you think companies and consumers can do to change that?
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Solar photovoltaic price free falling

This picture illustrates the dramatic fall of solar photovoltaic prices in the last 35 years.  Around the time when I was born, 34 years ago, a 3kW system for a home would have cost about £79,000.  Today the same system costs around £6,000 including inverter, cables and installation.

price of photovoltaic modules in dollar per kw

price of photovoltaic modules in USD/kW [source: Bloomberg New Energy]

The drop in price is so dramatic that it’s hard to imagine.  As a comparison consider a car today: a reasonable price would be £10,500. Now if the car industry applied the same cost reduction as the solar photovoltaic industry, a new car would cost £200 GBP 35 years later*.
This is an amazing feat.  The future of these prices is uncertain for the next years since many geo-political factors are at play.  The global crisis, the cheaper modules that China is producing, Americans and Europeans taxing imports in a potential trade war, and many companies going bankrupt are some of the obvious factors.  Most forecasts predict lower prices for 2013 but the following years are an open question.
Learn more:
1. the science of solar panels
2. Solar PV ABC’s
 

 * using the ration between $45/W (~1978) to $0.9/W (~2012)
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re.nooble selected for Startup Chile

We just received some great news last night: re.nooble has been selected for Startup Chile, a company accelerator scheme in Chile. Re.nooble and 99 other companies have been chosen out of 1577 applicants from 68 countries.
It is an honour to be part for this unique and exciting endeavour and we look forward to an amazing 6 months of hard work, tireless coding sessions and invaluable mentoring. Startup Chile is a start-up incubator created by the Chilean government to encourage a more entrepreneurial mindset in Chile and South America. The selected ventures are granted $40k of equity-free seed capital, office space in Chile, mentors and access to a worldwide network of entrepreneurs and investors.
We will start the incubator program at the end of July, so not much time to organise a move from the Isle of Wight to the East coast of the Pacific Ocean. Once the program commences, re.nooble will go through the startup Chile incubator program, receive mentorship and refine the re.nooble engine to reach a larger market after the six months program.  In addition we will promote small scale renewable energy accross the country and help more solar installers reach a wider audience.
Stay tuned for more information and exciting stories from our work in Chile.
For more information about Startup Chile, visit their blog

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New Zealand on its way to 90% renewables

When flying to New Zealand’s capital Wellington, two major aspects regarding domestic renewables in this country become immediately apparent. First of all, New Zealand possess a huge potential of wind power. This will become evident during the plane’s approach when it gets hit by major cross winds. Besides the shaky approach, you will notice that Wellington’s roofs have almost no solar panel installations. That is astonishing, since cities in the neighbouring country Australia experience less annual sunshine hours (Melbourne in the state of Victoria experiences 1955 hours of sunshine [1], whereas Wellington experiences 2110 hours [2]), but the solar industry is simply booming in Australia.

solar radiation map of New Zealand

solar map of New Zealand (Source: EECA)

But the non-existing solar panels are not a sign for New Zealand’s lack of renewables. At the moment, New Zealand is generating 75% of its electricity from clean sources (particular hydro and large scale wind power) [3], which puts them third behind Iceland and Norway when it comes to the highest renewable energy contribution. The Kiwi’s plan to extend their renewable share and they want increase it to 90% by 2025 [4].
For a long time, New Zealand policies were driven by an astonishing rational approach of free market, explains Alick Shaw, former deputy Mayor of Wellington. For renewable energies that meant that no tax incentives, feed-in-tariffs or forced power purchase agreements are present in the market. But, and that is a major difference compared to other countries,

regional price of electricity in NZ

regional price of electricity in New Zealand (Source: em6live)


the same applies to other energy sources as well. If energy utilities want to purchase clean energy to fulfill the renewable energy and carbon obligations, they purchase the clean energy on the wholesale market with prices changing by the second. If renewables would be competitive, they would be ruled-out of the market. But New Zealand proves that renewables are competitive at a market level.
But what is the situation for domestic renewable installations? Also here, the general political opinion applies and the government is not providing financial incentives to boost domestic renewables [5]. Hamish Trolove, Senior Engineer at the governmental Energy Efficiency and Conservation Agency explains, that policy makers are concerned that additional governmental support for small scale renewables e.g. in form of a feed in tariff would not replace coal or gas power plants, but older renewable energy installations. Getting closer to 90% of renewable energy share of electricity production, these measures would not increase the share of renewables. Therefore the focus for domestic energy policies by policy makers is around energy conservation, in particular home insulation [6]. At the moment, owners of homes, which have been built before 2000 can apply for insulation grants, which provide 30% of the installation costs, up to 1,500 NZ dollars [7]. Additional funding and grants are available for holders of Community Services Cards. Energy conservation for New Zealanders with low income are of strong interest to the policy makers in Wellington. Michael Begg from the Christchurch Agency for Energy points out that the energy conservation efforts go beyond purely saving energy. He explains that New Zealand, like many other nations, experience ‘Energy Poverty’, where people simply cannot afford to heat their homes. Better insulated homes will help to go further with the same amount of monthly spend. The government experiences another interesting effect through the grants. Residents of damp and poorly insulated house are heavily affected by the health issues related to cold and drafty living environment. At the end it is cheaper for the general public to provide NZD 1,500 grants than paying much larger bills in public healthcare spending. Summarising Hamish Trolove points out that the grant program seems to be a success since more than 280.000 New Zealander households have already applied for the funding support, .
The first country where wind turbines became a tourist attraction

The first country where wind turbines became a tourist attraction


In this very advanced renewable energy society, where does re.nooble see the future of domestic renewable installation?
We strongly think that, despite the lack of incentives, domestic generation is financially viable and can be a good investment for New Zealanders. They are not only a perfect energy source for remote off-grid properties (and New Zealand has plenty of them), but considering that New Zealand experiences a price hike in electricity prices [8], domestic renewable installations will provide a reliable and cost-stable investment for New Zealanders.
References:
[1]: http://www.bom.gov.au/climate/averages/tables/cw_086071.shtml
[2]: http://www.niwa.co.nz/education-and-training/schools/resources/climate/sunshine
[3]: http://www.eeca.govt.nz/efficient-and-renewable-energy/renewable-energy
[4]: http://www.med.govt.nz/sectors-industries/energy/pdf-docs-library/energy-strategies/nzes.pdf
[5]: http://www.seanz.org.nz/Resources/Government-Incentives
[6]: http://www.energywise.govt.nz/
[7]: http://www.energywise.govt.nz/funding-and-programmes/insulation-and-clean-heating
[8]: http://nzh.tw/10863083 or http://www.nzherald.co.nz/business/news/article.cfm?c_id=3&objectid=10863083

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which solar panels?

Here’s a nice video by the guys at which.co.uk showing an installation using roof hooks bolted to the roof. Professional roofers on a simple roof can get the job done in just a day.

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number crunch: solar thermal vs. PV

 The calculations presented here depend on a large number of factors and may not apply to your case.  If you have numbers that differ from these, please let us know so other readers can benefit from your experience.

——

Solar thermal is an older, simpler, more efficient technology than solar photovoltaics. But given the current state of the market, photovoltaics might be taking solar thermal’s job.

solar thermal vs solar photovoltaics

original image by Alfred Twu (2010), released under CC0 1.0 Universal Public Domain Dedication


After huge price drops, PV is now so affordable that running an electric water heater on solar panels might be less expensive than installing a solar hot water system. This seems backwards — how can it be less expensive to make heat out of electricity out of sunlight than to make heat out of sunlight directly?
As this article will illustrate, the key factor is the difference in FITs. In the UK, solar PV enjoys a healthy FIT schedule, while a solar thermal installation only gets a one-time £300 rebate from the government. The RHI is supposed to begin in the summer of 2014, which would see solar thermal earning 17.4 p/kWh (higher than PV!)… but the measure has already been delayed twice, and that number is not yet set in stone. So keep your fingers crossed.
The bottom line is that today, consumers would do well to consider both options for a domestic hot water system. There are many factors that might predispose your site for one technology or the other. Here’s a short list.

+Let’s say you want to get started with a renewable technology and you don’t have thousands of pounds to fork over. Solar thermal systems start at £2500 or so, while it’s difficult to find a solar PV installation for under £4000. Note that both technologies are available for financing under the Green Deal.

+If your current water cylinder is twin-coil (or has the capacity for another coil input) then you won’t need to install a new cylinder for solar thermal. Instead, you could run the solar thermal heating elements directly into your current boiler without having to mess with any plumbing. It’s too easy! And it’s likely to cut at least £800 off installation costs. But this raises another question:

+Do you need to replace your water cylinder anyway? Consider getting one compatible with the heating system you choose.

+As solar thermal is a more efficient technology per unit area, it “scales” better, requiring less additional material to do more… and making it competitive with PV for large-scale projects.

+Solar thermal is less finicky about partial shading and sun-ward orientation.

On top of those factors, you’ll have to decide between the technologies within solar thermal and PV as well, and of course, some are more expensive than others. So even with site-specific details, an exact pound-for-pound comparison is nearly impossible. You’re best off finding all the variables, doing as much figuring as you can, and then getting quotes from installers.
Nevertheless, I’ve promised a number crunch, so I’ll take a stab at 2 likely scenarios here. The goal is to walk through the process of how to calculate savings for each technology. Insolation data is based on Manchester, England; electricity price is 14 p/kWh. Also, I’m keeping the export_tariff out of this comparison, so I’m assuming the the consumer uses every kWh generated. Okay, here goes.

Round 1: light usage

You’re a household of 2 people with moderate electricity consumption and gas heating. You’re considering a PV installation to cover electricity use only. You decide on a 3.6 kWp array, which is about 15 panels. It costs you £7500, which includes the panels, the inverter, installation, hardware, everything. Your installation is predicted to generate 2890 kWh/year. Considering this is 2890 kWh that you’re not buying from the grid, this installation saves you about £400/year. Additionally, the generation tariff brings in £445/year. So excluding the export tariff, you’re netting £845/year with this array.
But for £3390 more, you could add 5 panels, upping your system to 5.3 kWp and a projected 4350 kWh/year in total. With this wattage, you can cover hot water usage in addition to household electricity. To do so, you’d have to install an electric water heater or combi_boiler (at £800, say) to preheat your water before it enters the gas tank, shifting almost all your hot water use to your solar array, leaving the gas on just in case. If you concentrate your hot water usage around dusk time, then these additional panels could cover 60 of your 70 liters per day, the other 10 coming from your gas cylinder*. That’s an additional savings of about £160/year, plus an additional generation tariff of £225/year.
Or! For the same price of the extra PV panels, you could install a small solar hot water system. Putting numbers to solar thermal is more difficult, but it is feasible that for the same £3390 it takes to expand your PV system (+ the RHI’s current £300 rebate), you could install a “properly-sized” solar thermal system… which means it covers 55 – 85% of your hot water use, depending on how much you synchronize your usage.* (You might have to install a new storage tank as well, but for our purposes, you would have to do the same with a full PV setup — the £800 combi boiler — so this cancels out). For a similar price up front, then, you’re saving slightly less, say £140/year.
You can see then that from the standpoint of shear savings, a PV-only system is a slightly more economical option for the light usage consumer: £160/year in savings vs £140/year earned from covering your hot water usage . This is assuming your gas comes from the grid into your “reasonably efficient” gas heating system. But what really puts financial distance between the two technologies is the generation tariff: £225/year for the extra PV panels, 0 (currently) for solar thermal. So in this case, here’s the final score:
thermal + PV:     savings of £985/year                pays for itself in 11th year
PV-only:             “savings” of £1230/year            pays for itself in 8th year
Remember that the site and usage are the main determining factors. As was discussed in the skinny on solar hot water, solar thermal is better-suited for heavy use applications. The next matchup explores this scenario.

Round 2: mid-heavy usage

Let’s assume that your family of 4 (or your small restaurant) uses 200 liters of hot water per day. Your annual power bill is £2k+ for electricity and heating together. A solar PV installation to cover most of your electricity and hot water use would be near 10 kWp, which, if we’re talking about standard polycrystalline silicon modules, is on the order of 60 square meters. Is your roof that big? Probably not. A PV installation that size could cost up to £20k, but if the use stays steady, it will pay for itself in well under 7 years.
So instead of going for one enormous PV array, you divide it up, devoting 4250 kWh of your annual usage (household appliances, say) to your PV system. This would justify a 5.3 kWp system (a modest 28 square meters, £10,500). For your 200 liters/day of hot water, you opt for a solar thermal installation, which is likely to cost £5-6k. So in this case, the solar thermal system costs 60% of its comparable PV system. Here, solar thermal seems to make more sense.
Until you get to the FITs! With a full PV system, you’re earning over £550/year more than a PV + thermal system (plus any export tariff), which again makes PV — if you have the space for it — the better buy in the long run.
thermal + PV:    savings of £2695/year            pays for itself in 5th year
PV only:           “savings” of £3120/year            pays for itself in 6th year
Notice that the PV + thermal system actually pays for itself first. However, it looks like the PV-only system will “out-earn” the other in the long run. Note also that under the proposed RHI, the outcome would be much different.
So it’s become clear: under the current state of FITs, PV usually wins.
The last word? It’s still a case of apples and oranges.

—–

* The spare kWh’s come from the nature of a yearly average. Accounting for ample hot water in the summer and much less in the winter, I average daily hot water generated to something like 87% of total usage for solar PV and the range of 55 – 85% for solar thermal.

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Mosaic photovoltaics

a mosaic about solar, kinda
The american company Solar Mosaic has opened a new round of investment on their site Their innovative business model marries multi-million project finance, crowdfunding and investment.  In simple terms:  Instead of seeking financing from bankers, pension funds or investment banks it connects individual investors with solar energy projects.  People can invest anything between a few tens of dollars and a couple thousands.  The payments that result from selling the electricity give each investor slow, constant and profitable returns. But above all it means their money is not invested by a bank or fund in something they disapprove of (say cluster bombs, drugs or sub-prime mortgages).  Instead it’s a carefully and ethical investment.  In their own words:

The fundamentals of solar makes it an attractive component of a diversified investment portfolio: reliable technology, predictable energy output, and stable cash flows. Every Mosaic project is carefully vetted and structured to minimize risk while maximizing benefits to investors and to the planet.

With treasury notes and savings accounts barely keeping up with inflation (1% – 2% yield) it’s no wonder people are investing in renewable energy which promises returns between 4% – 6%.  In the UK we have similar initiatives like Abundance Generation or Energy Share but we will cover them in another article.  In the future, we are hoping to incorporate these investment opportunities to our renewable energy search engine.  Stay tuned!

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the skinny on solar hot water

In 2004, the average UK household energy bill was £522. Last year, it was £1334.That’s a jump of over 150% in under a decade (1, 2).
If you’ve started your attack on these numbers, then you know that insulation and smart usage are the first steps. With these measures out of the way, next you can look into generating your own electricity, maybe with a wind turbine, maybe with a solar photovoltaic array.
But you may have skipped a step!
For the UK and similar latitudes, a properly-sized solar hot water system can supply around 75% of a family’s hot water over the course of a year. That’s hot water you don’t have to pay to generate, knocking a solid 15-20% off your annual energy usage (3).
Solar hot water (a.k.a. solar thermal) uses sunlight to heat your water. Some systems use no electricity at all. Because the technology is daylight-dependent, an installation is best used in conjunction with a pre-existing water heater. The idea is to lighten the heating load rather than to make a full-on conversion. Going entirely solar thermal can be done, but it would probably require a change in lifestyle.
As is the case with any renewable technology, you need to make careful cost-benefit analyses before you begin shopping. There currently aren’t many subsidy or FIT options out there for solar thermal, although there still is a £300 rebate on your installation. If your hot water usage is light — say, under £150/year — then you could be looking at a payback time of over 25 years, which isn’t desirable. In fact, it seems wrong, but a solar photovoltaic array might currently be more cost effective than a solar thermal installation, even though PV is a less-efficient technology and requires a higher upfront investment. I’ll explore this issue in a future article. Keep in mind that the renewables industry is rapidly growing and morphing, and this claim wouldn’t have been true three years ago.
There is a plan in the works to give solar thermal a generation tariff, though. In summer 2014, the RHI is slated to take effect, which will bring in 17.3 p/kWh — a higher rate than solar PV, and one that promises to make solar thermal much more competitive (15). Keep your fingers crossed, though, because it’s already been pushed back two times now.
That said, usage-heavy applications stand lots to gain even without the aid of FITs. If you’re looking into solar thermal on behalf of a college dormitory, restaurant, laundromat, etc., then your payback time could be under 3 years. If you’re looking to cover the four hot showers your family takes every evening, then your payback time could be desirable as well.
How expensive your system is depends not only on its size (i.e., the surface area of the panels), but also on the kind of system you choose. This, in turn, is largely predetermined by your site and your usage. For a technology so simple, there are quite a few variations to solar thermal, but by the end of the article, you should have an understanding of which one is right for you.
Continue reading

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making electricity out of sand: a short history of solar PV technology

To wrap up the series on solar PV, here’s a rundown of the science, brought to you by Alvaro. See this article if you’re looking for a practical introduction to solar PV.
 

Henri Becquerel. Image taken from saints.sqpn.com, via the New Catholic Dictionary. Date and photographer unknown.

Henri Becquerel. Image taken from saints.sqpn.com, via the New Catholic Dictionary. Date and photographer unknown.


In 1839, at age 19, a French physicist named A.E. Becquerel was experimenting with silver and platinum plates bathed in an acid. This amounts to something like your car battery. The surprise came when shining light on this battery seemed to produce a tiny bit more electricity that before. Neat, but how could he explain this?
For the next 80 years, hundreds of scientists experimented with this phenomenon. They called it the photoconduction (“light-increases-electricity”) effect. They tried and tried to reproduce it, using all manner of cocktails: selenium squashed between gold and brass, copper and lead coils with glass on top, and platinum sprinkled throughout it all. These experiments delivered very expensive and inefficient (less than 0.5%) solar cells by the 1930s.
The breakthrough came gradually over the 40 years that followed. A breed of materials came to light which weren’t quite metals, and weren’t quite insulators either. Plug in some electricity and nothing happens. Heat them a little, still nothing. In fact, most light didn’t do anything either. But each one was found to have a “sweet spot,” so if you gave them just the right electric current, they’d emit light. Heat them just right (or even hit them, just so!) and you get electricity.  They are all different types of semiconductors.
The major discovery — the prototype of today’s solar module — was that by finding two semi-conductors with close “sweet spots,” you could make them work together efficiently without losing heat or electrons, maximizing the amount of current they generate. So when light from the sun bounces some electrons off material A, material B has just the right sweet spot to catch the electrons and channel them to the next cell, then the next one, and finally to a wire, through the_load, and back again to the solar panel. Even more exciting, one of these crystals was plain and cheap ground up sand, better known as silicon.
bell labs early solar cell 1954

Bell Labs’ solar cell 1954


In the 70’s, semiconductors were engineered to have uber-precise sweet spots. These are more technically called band gaps. Some expensive crystals like Galium Arsenide have wider band gaps, and so can catch light of many different colors. They’re used in satellites and other ventures in which efficiency trumps cost. But the most common solar panels use cheap crystalline silicon. In photovoltaic panels, you’ll have two layers of c-Si. The top one has been sprinkled with phosphorous to widen the band gap in one “direction,” and the bottom one with boron. This process is called doping, and the important thing is that it primes one layer to throw an electron and the other layer to catch it. When electrons jump across the gap between these layers, shazam — you have current.
So that’s the basic science behind solar PV. Most thin film technologies work something like that as well.
With the next post, we’ll venture into a new technology, solar thermal. It’s much simpler, but no less fascinating. Stay tuned!

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Partial shading is worse than it sounds.

This post addresses a problem specific to solar PV modules that use string_inverters, which are the most common kinds of inverters. For an introduction to solar PV technology, see my previous post.
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Every manufacturer will tell you to avoid obstructions to your array—trees,antennae, bird droppings, what have you. But they really mean it, and the reason might not be so obvious.
The long and short of it is that partial shading of one module can compromise the output of the entire array. Here’s how:
Remember that it’s the inverter’s responsibility to convert the DC power generated by the solar panels into AC power for use in the house. Well, one reason we use AC is because it’s especially easy to get along with. AC power is expressed as a ratio of voltage to current (volts to amps), and it can be converted between different ratios rather easily. This way it can conform to the requirements of everything from your washing machine to your cell phone charger. Each appliance’s voltage/current preference is determined by how it uses electricity to perform its tasks.
When a string inverter changes the DC power from a solar array into AC power for the house, it has to choose a voltage/current ratio, too. The optimal ratio is whatever ratio provides the most power, so it’s referred to as the maximum power point. Under varying conditions of temperature and sunlight, the maximum power point is constantly changing. Many solar inverters available today come with maximum power point tracking, a.k.a. MPPT, which means they’re constantly probing the system to find the right ratio and making adjustments in real time.
Now, at any given time, most string inverters can only accept one MPP—one voltage/current ratio—for all the modules under their charge. Partial shading means there’s at least one module that can’t generate at the power of the other ones. In this case, most systems have two options. The first option is to compromise: the inverter’s MPPT will choose a lower power point at which all the panels can generate together.* In this sense, the entire array is only as strong as its weakest link. The inverter’s other option is to refuse the power from the shaded module. This isn’t an ideal situation; it means the shaded module has to dump what current it is generating through a bypass diode so that it’s discharged peacefully. But think of the poor bypass diode… it would be like entering and exiting a building through the fire escape every day – your apartment’s not designed for that! Clearly though, either situation — the bypass or the lower power point — is undesirable.
There’s a technology called the microinverter that seeks, among other things, to avoid this problem altogether by giving each panel has its own small inverter. So if one module has partial shading, then it generates at whatever power point it can, and the others carry on in peace. Some microinverters are even built-in on the level of the solar cells. The technology has been around for a while, but only recently has it become economical.
String inverters are tried and true, but to keep things running smoothly, keep your panels sunny!
 
* For this reason as well, you’ll want to get more than one inverter if your array features modules with different orientations.

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