Renewable Energy

From the few examples mentioned in this column, new methods of generating electricity will also require new materials solutions to deal with the environments they will work in.

In November, last year, the International Energy Agency (IEA) published their annual World Energy Outlook (WEO). It is an excellent resource that always provides a great insight into global energy trends during the previous year and describes potential scenarios for the future.

When discussing "energy" it's important to define what we're talking about. The IEA had a useful diagram (figure 1) in their WEO a few years ago which explained the situation quite well. On the one hand, there are the traditional "power" applications such as electricity generation and heating. Then there are the applications that the WEO describes as "transformation", which includes transport and industry. The industry category also includes steel making - a huge user of coking coal - and petrochemicals, which are derived from feedstocks coming from oil and gas. Renewable energy is conveniently located entirely within the "power" segment.

Figure 1: Sankey diagram showing the 2 main uses of "Energy" products from WEO 2015.

The Renewable Energy Options in Today's Electricity Mix.

Until quite recently almost 100% of the renewable energy that was used for power applications came from either hydropower or biomass. You may be surprised by the biomass, but most of this has been what the WEO calls “traditional” biomass. There are large areas of the world where people still collect wood for cooking and warming their homes and this is what is referred to as “traditional” biomass.

However, in the “power” segment things are changing fast and the two main trends responsible for this change are:

  1. A major increase in the electrification of many applications including heating and personal transport
  2. The rapid increase in renewable electricity generation

The second point is driven by the rapid reduction in the cost of renewable technologies, particularly solar photovoltaics (PV*) and wind turbines. In terms of percentages, the share of the electricity mix generated by renewables stands at around 25% today and a very large proportion of that is still hydropower. What is remarkable is that now, more than 50% of all new electricity capacity being built is based on renewable energy and this is a trend that is set to continue and increase. By 2040, which marks the end of the period that this year’s WEO models, PV and Wind energy could each be equal in size or even larger than hydropower.

*Kanthal supplies cassettes used during the manufacture of silicon wafers used in PV cells.

Fig. 2. Wind Turbines and PV are contributing big changes to the overall electricity generation mix.There are some important differences in the type of electricity generated by hydro and PV or Wind though. When it is either sunny or windy, the fuel for the latter plant types is free, unlike using coal or natural gas. But the weather is never that cooperative. If there is water in the rivers and dams that are used for generating electricity, hydropower can make base load electricity twenty-four hours a day if necessary. Another form of hydropower called “pumped hydro” acts as a wonderful means of storage for electricity generated when it is not needed, by using the excess electricity to pump water uphill into reservoirs holding potential energy that can be released when demand peaks. Unfortunately, the availability of such reservoirs is limited by the suitability of sites to build them in. Because of this limitation, alternative solutions for energy storage remain a hot topic today.

One thing that surprised me was the lack of overlap in engineering these structures with the offshore oil and gas business, which has been building platforms to be installed offshore since the 1970s. Turbines require hydraulic tubing to control the heave and yaw of the structure to ensure that it is facing in the best direction to most effectively capture the energy in the wind as it shifts direction. But those offshore experts have apparently not been consulted. We know from many years of supplying hydraulic and instrumentation tubing to the oil and gas segment that seawater presents a very corrosive environment that can lead to pitting corrosion of ASTM 316L tubing in the seawater splash zone. 2RK65™, Sanicro™ 28, 254 SMO and SAF 2507™ have all been employed as hydraulic tubes to combat corrosion in the splash zone on offshore platforms. Had the builders of offshore turbines known this we would probably have already seen enquiries for this application but it looks as if corrosion must occur before material upgrades are decided upon.

Other Kinds of Renewable Energy

So, renewable electricity, now including PV and Wind is certainly beginning to make its presence felt but the newer forms have their shortcomings due to their intermittence. However, there are other forms of renewable energy that can provide baseload electricity or incorporate storage and future projections show them making an impact on the energy mix. STE stands for Solar Thermal Energy which includes Concentrated Solar Power. This is where the heat of the sun heats a transfer medium such as fused salt or molten metal which can be stored until a demand peak requires energy. The stored heat can then be transferred to steam via a boiler which is then used to drive a turbine like those in a conventional coal fired power station.

One form of renewable energy which is particularly interesting is geothermal energy. This comes in a variety of forms but basically generates heat or electricity from volcanic heat and access to that heat is limited to certain geographical regions. In its most usual form a well is drilled into an aquifer from which steam is used to power a Rankine turbine. These aquifers tend to be very saline (at saturation the chloride content can reach 25%) creating a very corrosive environment. Newer designs for Geothermal plants don’t use the aquifer water/steam to drive the turbine, but transfer the heat to a cleaner working fluid via a heat exchanger which is exposed to the corrosive fluids in the process.

Fig. 3. IEA scenario describing the potential development of the electricity generation mix.

Figure 3 also describes a growing biofuel segment in the future. In this case, it wouldn’t be “traditional” biomass but other types which come in very different forms such as wooden pellets that can be burnt in modified coal fired power stations or ethanol fermented from energy crops such as sugar beet or maize. Ethanol can also be fermented from lignocellulose (which basically means “woody”) but where the feed material needs to be hydrolyzed first in acid.

Future Materials Needs for Electricity Production

Given that boiler tubing for coal fired power stations has been the largest single application segment in the seamless stainless steel tube market, the use of stainless steel in the future electricity market is going to look quite different from the way it has been in the past. The Paris Agreement on climate change is, at its core, designed to decarbonize electricity generation. The backbone of which has been coal. Coal fired plants are also the largest emitters of CO2 so we can expect fewer of these being built in the future. However; from just the few examples I’ve written about in this column, new methods of generating electricity will also require new materials solutions to deal with the environments they will need to work in.

Mark Newman

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