Thin Film PV

Alta Devices is a US-based specialist in thin and flexible mobile power technology. PV Insider speaks to Rich Kapusta, VP of Marketing soon after the company has had its technology tested at NREL in real-life conditions, which is getting certain industries excited at the prospects.

Last week The U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) and Alta Devices reported that they have jointly demonstrated that Alta’s solar material retains its high efficiency in real-world conditions, particularly on hot days. The primary reason is that Alta’s modules stay cooler and lose very little efficiency as the temperature rises. Combined with Alta Devices’ energy density advantage, this has the potential for significant benefits, specifically in roof-integrated applications such as automobiles and buildings.

PV Insider speaks to one of the product innovators in the thin-film space to learn which industries have the most to gain from flexible thin-film technologies and how soon these industries will be able to integrate Alta Devices’ technology into their end products. 

Q: How close to market are you at your recent thin film efficiency record of 30.8 per cent?

A: We have three different efficiency records that we’ve set.  Two of them are for single junction: a solar cell efficiency record at 28.8 per cent; a module efficiency record at 24.1 per cent. And we’ve recently set a dual junction cell efficiency record at 30.8 per cent.

The dual junction cell, the higher efficiency one, at 30.8 per cent, we haven’t productised yet. We plan to commercialise it sometime next year. 

Our single junction cell is available today. That’s the one that’s 28.8 per cent efficient. We currently manufacture our single junction cells and we can sell them to customers as individual cells, or as sheets of interconnected cells called ‘matrices’. 

Q: So you market a single cell directly for end use in an electronic device?

A: Right.  We have a very different go-to-market strategy.  We sell our material directly to other manufacturers of devices where they integrate one or more cells directly into their product.  One of our cells is roughly 10 square centimetres. 

Anything that moves, can be carried, or worn, which has great applications for our technology. Our very high efficiency means that our material can generate quite a bit of power in a small surface area.  And what we’re finding is that there are many applications where surface area and/or weight is a constraint, such as small wireless sensor devices, unmanned aerial vehicles, consumer electronics, and automobiles.  Some of these applications need just a single cell. 

Q: Thin film can have a lack in efficiency; how is yours breaking such records?

A: Nobody else makes thin film gallium arsenide (GaAs) like Alta does. We chose GaAs, because it’s known to be the best solar material and our proprietary manufacturing process delivers the high efficiency of this material in a thin film form factor.

Gallium arsenide has been used in the space program for decades. Any satellite with solar panels on it most likely has gallium arsenide cells, but they are rigid and produced using traditional wafer based techniques. That makes them brittle, expensive and heavy.

These space applications are willing to pay multiple hundreds of dollars per Watt – several orders of magnitude more than terrestrial solar cells. The reason they (NASA) are willing to pay that much is their extreme need for efficiency.  Our mission is to provide this same level of efficiency, but at a much lower cost point.

Q: How is performance in hot and humid conditions?

A: Gallium arsenide has much better high temperature performance than silicon, and that’s completely because of its temperature coefficient. 

Our temperature coefficient is practically zero, which means as temperature rises, our material continues to operate at the same level, whereas silicon loses roughly four per cent for every 10 degrees Celsius.  

When it's 40C out, a silicon solar panel typically runs another 40C hotter (thus 80C total).  Our material would run only 30C hotter (10C cooler) and with our temperature coefficient, our output would still be at the full rating. So when you are operating in hot climates - our material produces significantly more energy than any other technology.

When you factor in humidity, you can actually see a benefit. A recent study by the National Renewable Energy Laboratory saw that sunlight passing through water vapour actually changes the sun's spectral performance of that light a little bit, giving us a bit of a boost. It’s very minor, but certainly humidity doesn’t hurt us.

Q: Why did the US Department of Defence choose to work with you? 

A: When you think about the forward operating environment for the military, they need electricity. They have a lot of electronic gear, so generally what powers them are small diesel generators. A real benefit is being able to charge batteries without diesel generators.

A typical dismounted soldier carrying 100 pounds of pack weight includes 15 pounds of batteries.  A solar based recharging solution allows them to reduce that burden and still be completely operational.

Furthermore, the cost to get diesel to the forward operating environment for the US army costs hundreds of dollars per gallon. 

Every time you man a fuel convoy or you have to secure a landing zone to do a fuel drop, you put soldiers at risk, and statistically, there’s one human life lost for about every 14 fuel convoys that make it out to the forward operating environment. So if you could eliminate those fuel convoys you could save human lives, which is certainly not measured in dollars per watt.

Q: Konarka also contracted with the military for flexible thin film on military tents and now they are among the dead on the thin film battlefield. Why have you succeeded where they failed?

A: They utilised an organic photovoltaic material. Organics are known to be very low efficiency. Their promise was to be very low cost but with efficiencies of 7 or 8 per cent, it had no competitive advantage over other low efficiency thin films. 

The ability to generate more power in a smaller area is critical for these markets. 

Konarka had the right form factor, the right idea, and the right ambitions with regard to cost, but they were dealing with a material that from a physics standpoint was never going to be efficient. So they were coming at this problem from a cost direction. But you can’t just solve one of the problems. You have to solve both the efficiency and the cost problem.