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Going for grid parity

Going for grid parity
The global solar power business promises a period of significant growth through a combination of government incentives and the development of new manufacturing technology. Malcolm Brown sheds a little light on BP Solar’s plans to stay ahead of the game
Something extraordinary happened at BP Solar last year: the company made its first-ever profit, which although modest was very welcome. This was no aberration, no flash in the pan. The move into the black followed a major reorganisation, which included pulling out of manufacturing thin film photovoltaics, and improving both the quality of the company’s solar cell product range and the productivity of its four factories.

‘All this has put BP Solar on a very firm footing to go on making profits for a long time to come,’ says Steve Westwell, BP group vice president, Renewables. ‘BP Solar is at an incredibly exciting place in its history. We’ve moved the business into a position where it can now grow profitably and significantly.’

At present BP Solar has around 12% of a $5 billion annual global market, with manufacturing facilities in the USA, Spain, Australia and a joint venture in India. Industry watchers believe the market will grow to something like $30 billion a year by 2030, and BP Solar expects to retain or increase its market share.

The key to success in the highly competitive solar business – and BP Solar’s key to continuing profitability – is a mixture of technology and economics. The technological challenge is to make the modules that collect sunlight and change it into electricity as efficient as possible. The economic goal is to cut costs to the minimum, consistent with good quality.

Solar panels providing power at BP’s remote Wolf Point natural gas fields in Colorado, USA
Solar panels providing power at BP’s remote Wolf Point natural gas fields in Colorado, USA
In the global solar business, the ‘Holy Grail’ that all players seek is achieving grid parity – reducing the cost of solar energy to be competitive with conventional grid-supplied electricity. Most people in the industry believe that once grid parity is reached, demand for photovoltaic products will increase significantly. Consumers will realise that they can get their electricity at the same price, or lower, than they can get it from the grid, but with the added attraction that energy derived from the sun’s light is much more environmentally friendly than traditional power generation.

Grid parity will be achieved first in those areas of the world that have a combination of abundant sunshine and comparatively high grid electricity prices, places like California and Japan. Westwell says Japan is already on the brink of grid parity, having one of the highest retail electricity prices in the world and good sunlight. It also has a government that has been prepared to encourage the use of solar power with incentives.

‘Japan has had government incentives in place for over five years that have enabled the build up of a very large installed base of solar power,’ says Westwell. ‘By next year solar will be close to competitive with retail electricity. There will likely be many Japanese citizens who will be ready to pay the small premium for solar given its superior environmental credentials.’

This is a pattern the solar industry would like to see repeated elsewhere and several countries – including Germany, Spain, South Korea and Greece – are putting into place new incentive programmes.

solar montage
Clockwise from left: BP PowerGlaz panels; Solar canopy on gas station; Roof shingle-sized panels

Changing the game

Japan may be the first country in which grid parity becomes a reality, but when will the rest of the world catch up? Westwell believes that there are two technological routes to widespread grid parity. One is incremental, in which existing silicon-based photovoltaic technologies are steadily improved by, for instance, the use of cheaper forms of silicon and improved and more cost-effective methods of production. The other is the revolutionary route which will involve completely new technologies, the ‘game changers’ that would bring about a paradigm shift in solar power’s technology and economics.

Currently, the most widely used semiconductor material at the heart of solar cells is silicon, produced in the form of monocrystalline or multicrystalline wafers. By doping the silicon with gas at high temperature, its electrical charge is slightly altered so that when a photon of sunlight passes into the semiconductor the silicon is ‘excited’ and liberates electrons. The flow of electrons can be captured in a circuit to produce electricity.

The present efficiencies of commercial silicon-based solar cells – efficiency is the percentage of sunlight striking the solar device that is converted into electrical current – are between 14% and 17%, with a theoretical limit in the region of 30%. BP Solar’s industry-leading monocrystalline silicon solar cell – the proprietary Saturn range – is rated around 16% efficient with proven capability of up to 18%. But BP Solar also has its eye on two potential game changers: organic photovoltaics and nanocomposite solar cells.

‘Organic photovoltaics and nanocomposite solar cells still have very modest efficiencies,’ says Eric Daniels, BP Solar’s vice president, technology and product development. ‘Scientists working on organic photovoltaics talk in terms of 3-4% at the moment, but their theoretical limit is in the region of 50-60%. That, plus the fact that the manufacturing processes could be much cheaper than those for silicon-based cells, could fundamentally change the economics of solar.’

Organic solar cells are based on polymers. They are like light emitting diodes (LEDs) in reverse. In an LED, charges from electrodes are injected into the display material, the charges combine with one another and excite the material, which then emits light. In organic photovoltaics, light shining on the material generates the excited state and creates electrical charges that are collected by an external circuit to produce electricity.

Quite apart from their efficiency, organic cells, which are being worked on at several universities with the help of BP funding, should be much cheaper to manufacture than silicon-based ones, since they could be made by chemical processes at low temperatures. They could also be printed onto substrates using a relatively cheap technology similar to that used in inkjet printers. Being polymer-based, the organic cells would be very flexible, so that they could even be rolled up into sheets, something that is impossible with comparatively rigid silicon cells.

Another solar game changer is based upon nanocomposites. Nanotechnology involves engineering materials at the atomic level to deliver a required set of material properties – in this case the ability to produce and conduct electricity. One idea, being developed at New York’s Rochester Institute of Technology with BP Solar’s support, is to create a thin polymer film containing carbon nanotubes that respond to specific wavelengths of light to maximise energy conversion.

But devising high-efficiency organic or nanocomposite solar materials is only part of the challenge, says Daniels.

‘You have to incorporate them into workable devices and be sure that they can stand up to the rigours of the real world over a long time period. Ultimately, even if they have 50-60% efficiency, we need to consider how we collect the electricity and how they’ll survive in the environment when they are exposed to the sun for 20 to 25 years.’

The scientific challenge is huge, but BP Solar believes that if viable organic or nanocomposite solar devices could be made on an industrial scale they would totally change the solar business.

‘If someone tomorrow found the technology, the game changer,’ says Westwell, ‘and it was really possible to bring it to market within three years, at scale, then I surmise we would change our whole business, our whole investment process, to support that game changer. The present generation of technology would be left behind in a fairly short period of time. As a result we have to be continuously aware of new technologies while at the same time ensuring short payback times on new investments.’

Silicon supply

That said, Westwell’s judgement is that any such paradigm shift is at least 20 years away. If that is so, the solar industry cannot just sit around waiting. It has to try and move towards grid parity by incremental improvements to the existing silicon technology. Westwell says that incremental improvements are already cutting costs by around 10% a year while at the same time improving cell efficiency.

‘Five to ten years ago, probably the best the industry could do in a commercial sense was 120 watts per solar module, using cells with around 12% efficiency. Now, cell efficiencies are achieving upwards of 15-18% depending upon the technology. That’s a significant improvement in power output, especially when considering that production costs are lower.’

Incremental improvements are also being achieved in many manufacturing aspects: in cheaper materials, more cost effective fabrication processes, in cell efficiency through increasing the active area of the silicon wafer, and electrical circuit optimisation. And these are being accompanied by significant reductions in system and installation costs.

Above all, one big change Westwell and Daniels would like to see is a move to the continuous processing of silicon. ‘I started my career in the steel industry,’ says Westwell. ‘My challenge for the solar business is to get silicon processing looking more like the techniques used in steel making, with continuous casting of silicon rather than the present batch processing.’

The batch processing approach is inherently wasteful. Traditionally, silicon has been cast into ingots and then the ingots have been sawn with very fine wires to produce wafers. But sawing produces a great deal of waste. As wafers become progressively thinner, more silicon is lost as silicon ‘sawdust’ than is used in the wafer itself.

Click link below to view a panel on silicon wafer production methods
Click link below to view a panel on silicon wafer production methods
One way to tackle this could be to move to ribbon or sheet manufacturing. Instead of starting with a cast ingot, the silicon would be produced as a flowing stream, rather like steel, and processed as it travels down the production line (see diagram, link on right). It would emerge at the end of the line as a silicon ribbon or sheet of precisely the dimensions needed for solar cells or possibly even solar panels
But the technical challenges standing in the way of that are still formidable, notes Daniels. For example, as the silicon cools, mechanical stresses and impurities within it produce so called dislocation sites, points which ‘block’ the processes that would normally release the electrons that are collected from solar devices.

Another possible area of incremental improvement over the next few years is to move from very pure forms of silicon – those just one notch below the silicon needed for semiconductor devices such as microchips – to slightly less pure grades. Until recently, the oversupply of silicon meant that it was competitively priced. But now, as the solar industry begins to consume more silicon than the semiconductor industry, there is a looming shortage and silicon prices have shot up.

As a result, companies like BP Solar are investigating ways of purifying so-called metallurgical grade silicon so that it can be used for solar devices.

All silicon processes begin with the thermal reduction of pure quartz to produce metallurgical grade silicon. In the Siemens process, the most widespread process for making semiconductor grade silicon, the metallurgical silicon goes through additional chemical processes to produce the compound silane which, when heated, deposits high purity semiconductor grade silicon.

An alternative process being evaluated by BP Solar is simpler, employing chemical leaching, heat and directional solidification to drive sufficient impurities out of the metallurgical grade silicon for it to be suitable as a feedstock for solar silicon ingots. Because this skips the silane step, the resulting purified metallurgical grade silicon should be much cheaper than semiconductor grade silicon.

‘We’re striving for a significantly cheaper silicon manufacturing process that provides us with a quality of silicon that doesn’t compromise efficiency,’ Daniels points out. ‘We are currently working with several partners to trial metallurgical silicon at scale. If it’s successful – and all the indications are that it will be – it will result in a significant reduction in costs.’

The drive towards metallurgical grade silicon illustrates one of the dilemmas facing the solar industry. Metallurgical grade silicon furnaces will be capable of producing 5000, 10,000, even 20,000 tonnes of silicon a year, but the solar industry only consumes about 11,000 tonnes a year at present. So, it would only take two new 5000 tonne furnaces to meet almost all of present demand. This is fine if demand holds up. But a significant part of present demand has been stimulated and sustained by government incentive schemes, which have built up demand and given the solar companies breathing space to move forward towards grid parity.

‘The solar business needs to feel confident that incentives will remain until the industry, using incremental improvements and cost cutting, gets closer to grid parity,’ observes Westwell. ‘BP Solar is ready and willing to invest in new technology and manufacturing capacity to help us grow our business at 30% a year – the incentives and the scale of the industry are now making this both possible and attractive.’

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