Current Limitations of High Concentration PV

Current HCPV systems typically consist of an array of HCPV panels mounted on 2-axis mechanical trackers. Sufficient space must be left between the trackers to prevent the panels from shadowing, or colliding with, one another. The efficiency of a lone HCPV solar panel in open space is excellent (25% or more), and substantially in excess of that of SiPV (15%-20%). However, when multiple solar panels are placed in a tracking array, the efficiency of the entire power plant, as measured in terms how much power is generated from the total land area used, can drop appreciably if some of the land is not covered in PV material. In fact, if the fill factor of an HCPV array is 50%, and it is often much less than this, then one would actually derive more energy by completely filling the collecting area with fixed flat SiPV solar panels!

The first limitation is the enormous land usage required for renewables. Few people yet grasp the planetary-scale nature of engineering that is needed to replace fossil fuels sources with renewables. The reason HCPV currently makes any sense is that current prices for desert land, and current generating capacities of HCPV power plants, are both sufficiently low that the land cost can be neglected. However, if we truly seek to use solar energy to meet a significant fraction of our total power needs by 2050 (> 30TW), the amount of land that needs to be devoted to renewable power generation is staggering. So much land is needed, in fact, that the area-efficiency of the renewable energy technology becomes the dominant consideration as renewable energy is scaled up, not simply due to cost, but also in response to increasing community and political opposition to wasteful land area-utilization. XE is addressing this issue by eliminating the need for the conventional 2-axis mechanical trackers of a conventional HCPV power plant. Instead XE-CPV incorporates SunStalker eTrackers into each HCPV solar panel to significantly increasae the area efficiency.

A second limitation of current HCPV is that although HCPV uses a 40% efficient solar cell, the optical losses in the concentrator, and the electrical losses in the circuitry, drive the typical HCPV panel efficiency down to around 25%. Clearly, if we could eliminate some of these loss factors, we ought to be able to boost the panel efficiency quite considerably. XE is addressing this issue by using an entirely new proprietary, patented, especially low loss SunRise concentrator design.

A third limitation of current HCPV is that although a 40% efficient solar cells seems good, this is still short of the theoretical limit of about 64% for triple junction cells. Moreover, current HCPV solar cells use certain chemical elements that are somewhat rare. Luckily they only use very small amounts of these elements. Nevertheless, if we could use solar cells that are at 64% efficiency or more, and which avoid the use of rare chemical elements entirely, we would have a far more cost-effective and scalable HCPV system. XE is addressing this issue by conducting a research project on our nanostructured SUPERcell design, which has a theoretical conversion efficiency in excess of 64%.

A fourth limitation of current HCPV systems is that, because they lack energy storage, they can only provide power when the Sun is shining and the weather is good. Moreover, without storage, if the power is not consumed when generated it is lost. This makes people think of solar photovoltaic power plants as peaking plants rather than baseload plants. However, there is no fundamental reason this has to be the case. Consequently, XE plans a longer term development program to integrate energy storage technology directly our XE-CPV panels to allow them to store unwanted energy at one time for distribution at a later time.