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Squeezing more power from solar PV devices


Joyce Laird

From residential rooftops to utility-scale farms, all users of solar energy want to get the most power from their systems. Everyone is looking for technologies that enhance power harvest and get the highest wattage from a solar photovoltaic (PV) installation. Many companies are focusing on this aim while simultaneously making systems far simpler and safer. Joyce Laird looks at some of the leading companies in this area.

Many believe that National Semiconductor, which has its headquarters in California, USA, is the outright leader in the semiconductor market. In analogue power management technology for solar PV, the company's products include SolarMagic.

SolarMagic increases power harvesting across all types of solar panels by equalising the output from the full solar array at the individual panel level, ending the issue of mismatched panels. Ralf Muenster, Director of National Semiconductor's Renewable Energy Group, says they have taken the SolarMagic concept to a higher, and tinier, level in creating the SM3320 SolarMagic smart panel chipset.

“This integrates our ICs into the solar PV modules themselves,” says Muenster. “Our solution is now a mere 0.5 inches in thickness, 3 by 5 inches [in size] and weighs only about 181 g – it is very light. It integrates right into each panel's junction box.”

This new smart panel chipset incorporates 10 analogue and mixed-signal integrated circuits, providing highly reliable digital-control combined with analogue sensing and communication.

Algorithms apply localised maximum power point tracking (MPPT), extracting the maximum energy available by translating the input voltage and current to the best output voltage and current pair to maximise energy flow. The system automatically senses input voltage and current throughout the array and adjusts itself to achieve optimum string levels.

“We are increasing the energy harvest over the life of the system and we are lowering BOS cost because it allows for longer strings, makes the engineering easier and allows for full coverage on roofs. It also allows using a more simplified inverter, all of which take cost out of the full system,” says Muenster.

Integrating a smart chip also gives positive differentiation to the solar manufacturer's products with key features such as safety.

“It allows a signal to the power junction box whereby the integrated ICs can disconnect the power from the array so there will only be low voltage to deal with in case of an emergency. This makes it safe for fire-fighters to vent the roof and walk on the panels should there be a fire or other disaster requiring rescue.”

Israeli firm SolarEdge is also focused on boosting system power, adding control and safety with its own unique technology. The company is currently shipping its power harvesting solution worldwide. The system comprises panel level power optimisers, specialised inverters and a panel-level monitoring solution. Their PowerBox is a DC-DC power optimiser that is integrated into each solar module. These automatically maintain a fixed DC string voltage to the inverter.

The DC-AC multi-string inverter gives the fixed string voltage 97% constant efficiency – independent of string length and temperature. All are monitored through the SolarEdge Monitoring Portal, a web-based application that provides real-time system monitoring from every level.

The software automatically provides alerts on underperforming modules, faults and safety events, visually pinpointed on a site layout map. Module performance is communicated over existing power lines, so no extra wiring is needed.

Electrocution risk is eliminated through an automatic shutdown of all modules both during installation and in the event of a fire or natural disaster.

“We have even added theft protection,” says Lior Handelsman, SolarEdge's Founder and Vice President of Product Strategy and Business Development. “Real-time theft detection activates module immobilisation of stolen modules to prevent reuse.”

In the second half of the year, SolarEdge is introducing the first module embedded power optimisers in cooperation with some of the leading module vendors. “We are also expanding our inverter line going up to 15 kW three-phase inverters and introducing new monitoring features, including advanced automatic analysis and remote mobile phone tools,” says Handelsman.

Sustainable Energy Technologies from Canada produces advanced power inverter enabled ‘massively parallel’ systems. Their Paralex product is a unique low voltage, high-yield commercial rooftop solar power system that increases total system output while simplifying design and lowering costs. The Sunergy inverter is a key part of this system.

“We have received full certification for all solar PV global markets and currently have products for commercial installations. We are bringing out a 240 V product in 2010 that will also address the residential market in North America,” says Brent Harris, Vice President of Product Development at Sustainable Energy Technologies.

The Sunergy inverter is unique in that it offers very low voltage. Compared to most standard inverters, which run at 400-500 VDC (volts direct current), Sunergy runs at 100 VDC and generates the same power conversion rate, making it much safer.

“Europe is looking at this safety aspect most closely,” says Harris. “They have what is known as an extra low voltage limit of 120 VDC. It is believed that 120 VDC or less will avoid the chance that anyone could accidentally be killed by electric shock.

“When you hear about systems that are set up with individual inverters on the modules with individual disconnects, all they are really doing is cutting the system up into little pieces so each module is under 120 VDC. Our system maintains the whole solar array at under 120 VDC operation all the time so you don't need any of those individual disconnects.”

Although Sunergy inverters are part of Sustainable Energy's Paralex solar interconnecting system, Harris says they are now being widely used in all types of solar systems.

“They work with anybody's system. In fact, most of the Sunergy inverters we've sold recently were sold to installers who built their own system around them,” he says.

Monitoring and control

With everyone getting more from their solar PV system, what good is all that power if it is not being used efficiently? What if what you think you are getting is not actually true?

This is where sophisticated monitoring and control systems come in, to ensure the system installed today is still generating what it should tomorrow. Some companies are focusing on easy-to-understand residential monitoring while others are tackling the giant needs of utility-based systems.

On the utility side of solar it is possible to buy the best installation in the world with the highest harvest efficiency, but there is still a necessity to track and monitor it effectively. One solution has been developed by Germany company Solon SE, which has a full monitoring SCADA (supervisory control and data acquisition) system.

The Solon SCADA is a web-based monitoring, control and reporting system specifically designed for use in the energy provider and large-scale power plant sectors. It delivers real-time, 24 hour information on a power plant's vital data, from the current output to the components and detailed analyses. Rapid detection of potential malfunctions in the power plant's operations can minimise downtime and maximise yield.

“Historically with a solar system, even large utility-scale projects still use a basic data acquisition system (DAS). This acquires data on the weather, production, temperature and so forth, but it isn't doing anything with that data in real time,” says Bill Richardson, Director of Research and Development at Solon.

“The Solon system mimics the same type of system large utility plants have been using for supervisory control for years on their fossil fuel systems, but it is tailored for the specific needs of solar power systems. This is important because as the scale of these solar plants grows, storage rates will become a very large part of all solar utility systems. Without a way to control and monitor that storage rate it is simply generating power without control. Power is nothing without control,” says Richardson.

“The SCADA system allows utilities to look at the full solar plant and at all the arrays in the same way they would look at a natural gas or coal-powered energy plant. They can ramp it up, ramp it down and call on it when they want the power. They are able to control reactive power in a positive way to always stabilise the grid. This may not be what is happening tomorrow but, as solar grows, this is what will be and must be happening.”

The system's innovative interface makes it possible not only to monitor remotely but to control and provide maintenance for solar power plants; no additional software is required. Users with a computer connected to the internet can access data on the weather, production and even the servicing status of the system.

According to Richardson, it is possible to retrofit the Solon SCADA system to existing systems. “It is fully backwards compatible. An existing system can either be removed and replaced with this SCADA system, or our SCADA can be added to their existing system.”

Energy at home

SunReports, which has its headquarters in San Francisco, CA, is looking out for residential customers.

“Our Apollo1 monitoring system is designed to provide both monitoring and system performance verification for both solar PV electrical generation systems and solar thermal hot water systems,” says CEO Tom Dinkel. “We provide web-based data collection and analysis with graphical user interface software to provide current, historical and predicted system performance information for both the system owner and for the installer.”

The Apollo1 is a device that plugs into the inverter's communications card, takes all data and uploads it to the internet using the customer's own internet connection.

“We process the data at our servers – which are a 100% renewable server farm – and we can present that on demand, in a way people can understand, on any web-enabled device whether a computer, iPhone, iPad, or BlackBerry,” says Dinkel.

“To get the cost under US$1000, we created our own PCB [printed circuit board] design with an SOC [system on a chip], which would do exactly what was needed and only what was needed. We take whatever the installer's forecast has been to the customer on payback time, average power generation and general system performance and show the customer that data in real time 24/7. It gives both the installer and the customer a way to see whether the system is or is not meeting the forecast. If it isn't, then the installer can take corrective action.”

SunReports recently announced a partnership with Schüco Solar USA, a major manufacturer of solar PV and solar thermal systems. Schüco will be offering the Apollo1 with their solar thermal installations.

Xtreme Power, based in Texas, makes efficient dynamic solar power resource systems for the renewable energy utility market. Darrell Hayslip, Chief Development Officer is quick to point out that these are fully configurable systems, not simply battery backup resources.

“We use a bi-directional inverter that can take power on and off the grid and partner this with a very intelligent control system that can be configured for specific and changing applications to protect the batteries. We have the ability to take our PowerCells and build a storage component as large or as small as needed,” he says.

This solution can be used for all forms of renewable energy generation systems. It can be custom designed to suit any necessary power rating and storage to meet a specific project or market, but the company is currently focusing only on utility-scale applications.

“Much of the system is created through monitoring the grid at the point of connection. We monitor the actual transfer of power, exact voltage and grid frequency at that interconnection. If the frequency decays or rises above a certain bandwidth, our system can respond very quickly. All that is needed is to programme the desired parameters into the control logic,” Hayslip says.

“I've been working with a potential customer in Italy and they are talking about some changes in market rules where they will actually have to schedule the output from a solar PV project a day ahead. Then they would be held to within a 10% variance over a period of time, say 8 am to 8 pm. If they overproduced or under produced during that schedule, they would pay a penalty.

“Our system manages the real dynamic change in output to create a continual, stable output that is always compatible with the grid.”

Taking solar PV power to the maximum

The idea of ‘going green’ is becoming more mainstream and companies are starting to offer products for serious sustainability. US company Hallowell International, based in Maine, has a product that is a bit different from most solar PV systems discussed so far.

Their flagship product is the Acadia, a combined heating and cooling system based on geothermal heat pump technology. The tie-in is that it draws its energy from any renewable source, the foremost being solar power.

Although standard heat pump systems for eco-friendly HVAC (heating, ventilating and air conditioning) are likely to be familiar to readers, the problem with them has always been that they only perform well in mild conditions.

This renders them useless in many parts of the world. In order to solve this problem, Hallowell has developed a pump that provides solar-driven heating and cooling under all conditions, including extreme heat or cold.

“It basically uses electric energy efficiently,” says company President Duane Hallowell. “The Acadia handles the job without the need for supplemental sources such as fossil fuel or standard electric heat.”

For Hallowell, the real goal of all renewable energy is to use it efficiently, which means looking at the full picture. To get a true return on investment, lighting is simply not enough.

“When someone pays US$1000 to US$2000 a year on home heating and cooling, using solar panels in this area will make the payback come in pretty fast,” says Hallowell.

“Keep all appliances electric ‘efficient’, not just electric. For instance, heat pump water heaters use 40% less energy than a state-of-the-art energy-efficient electric hot water heater. The Acadia takes over the full work of a boiler or furnace and an air conditioner and does not suffer from external temperature swings. This is a very efficient argument to go solar electric with geothermal heat pumps.”

Solar module manufacturers are concentrating on continually bringing down costs and enhancing module energy efficiency at the module level. Meanwhile, other companies are working to take the best that the solar manufacturers can produce and improve it. Each firm is an expert in its own technology and together they support the final goal of more efficient, safer and cost-effective solar energy systems.


About the author:

Based in California, Joyce Laird has been writing for a wide range of industrial magazines for over a decade. Her extensive background in the semiconductor industry created a perfect transition to covering developments in photovoltaics.

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Energy efficiency  •  Energy infrastructure  •  Photovoltaics (PV)  •  Solar electricity

 

Comments

solarMD said

01 May 2011
Ms. Laird did a great job with this survey article, although strictly speaking, simply reporting on output does not help with squeezing more output from a system. One needs to know if a system is performing as it should. That's where analytics comes in. Wattminder.com is focused on offering analytics for photovoltaic array for now, see www.pvmonitor.net. SHW is our next target application.

tebruya said

23 December 2010
MS Laird I read about a metal roof that has energy collecting chips in them and connect at one site per roof for electric energy in Kiplinger but cannot find the company name ? Dupont. could you help? tebruya@aol.com. Thanks Tim Bruya

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