Solar Cells Info

by Tetsuo Nozawa, Nikkei Electronics / May 8, 2008
Source: TechOn Column
http://techon.nikkeibp.co.jp/english/NEWS_EN/20080508/151451/?P=1

I went to the US on business last week. Gasoline prices seem to have risen again and created a stir in Japan, but circumstances were no different in the US. In Los Angels, for example, TV news reported street pricing for gasoline exceeded US$4 per gallon (about 3.8L) in line with the rising oil price.  Compared with Japan, the price is still quite low as it corresponds to about ¥110 per liter at ¥105 per US dollar. Yet the price has risen surprisingly fast compared with less than US$2.5 per gallon two years ago or before that.

I am concerned that the energy issue will become more serious and force us to drastically change our current lifestyles in the near future. I remember the time I experienced the so-called oil shock in Japan at the end of 1973. Although I was yet to enter the elementary school, I could see that the adults were making a huge fuss about something.

Articles that featured the theme, “What if we run out of oil?” were printed again and again – even in magazines for school children – for years after that and I had a feeling of uncertainty, worrying about what might happen in the future. I have recently started to feel the same kind of uncertainty again. Am I exaggerating if I describe today as being “the eve of another oil shock?”

The skyrocketing oil price has already caused more people to use bio fuels, which is one of the factors behind the food crises in developing countries. If this situation worsens, impacts could extend to cows and pigs that eat a large volume of grain, resulting in higher prices of meat.

Reasons why electrical bills have not risen as much…

However, something strange is happening at the same time. Although the price of crude oil surpassed US$20 per barrel in 2002, US$50 in 2005 and US$120 this year, growing about six times larger in six years, electrical bills for general households have not varied much from ¥21 to 23 per kWh over the last few years in Japan.

One of the factors behind stable electrical bills is the fact that power companies have endeavored to prevent rates from rising by shifting the fuel of thermal power generation from pricey oil to less expensive coal.

In Japan, power derived from oil accounts for about amazingly low 9% of the entire amount of power generated today (in fiscal 2006, data provided by Japan’s Ministry of Economy, Trade and Industry).

According to the data provided by sources including Tokyo Electric Power Company Inc, thermal power generation constitutes roughly 60% of all power generation in Japan, but power derived from oil only seems to make up less than 20% of thermal power generation as that derived from coal and natural gas provide more than 40% and slightly less than 40% of it, respectively.

Oil still generates about 50% of Japan’s overall primary energy, but the nation’s dependency on oil is sharply decreasing in terms of electric power (based on data provided by Japan’s Agency for Natural Resources and Energy and other sources). Meanwhile, coal-based power generation is rapidly increasing, in contrast with oil-based power generation (based on the same data).

Nevertheless, it is not a given that electrical bills will continue to be stable in the future. This is because the price of coal has also risen over the last three to four years, although not as fast as crude oil prices.

In addition, criticism will be focused on power generation using coal, which emits more CO2 per power unit compared with other fuels. In fact, several firms including Toshiba Corp essentially gave up on the commercialization of coal power generation in Yamaguchi in February 2006.

Toshiba cited factors such as “slowing demand for electricity, lower rates for power, the rising price of fuel coal and increasing concerns about the global environment” as increasing uncertainty in the outlook for profitability of thermal power generation.

Unlike the oil shock in 1973 that ended up shortly, there are no clues of a solution to stop the ongoing rise of fossil fuel prices. Some people even say the so-called “peak oil,” in other words “the time when oil production hits the ceiling,” arrived early in 2007. We apparently have no choice but to increase the amount of alternative energies such as nuclear, solar and wind powers to solve the problem.

Solar cells equivalent to 3 nuclear power generators to be produced every year in 4 years

Of the alternative energies, solar power generation has potential to play a more significant role than generally thought in terms of the amount, cost and efficiency of power generation. As for the amount of power generation, maximum output of solar cell modules totaled roughly 3.7GW in 2007.

This amount is expected to grow to 15GW per year in four years in 2012 (data provided by Sharp Corp). Compared with nuclear power generators that generate maximum 1GW per unit on average, the 15GW represents a large volume.

Of course, these are nothing but maximum amount of power generation and we must take working rates into consideration to compare average amounts of power generation. If all the solar cells are used in Japan, the working rate of solar cells is approximately 0.12, according to the New Energy and Industrial Technology Development Organization (NEDO). In other words, solar cells can achieve sufficient performance for (24 hours x 0.12 =) 2.88 hours per day.

On the other hand, the working rate of nuclear power generators is 0.6 to 0.7 in Japan, where mechanical accidents and earthquakes often take place. Based on these working rates, the annual output of solar cells will correspond to the amount of power generated by 2.5 to 3 nuclear power generators in four years.

Considering that solar cell production will continue to increase from 2012, am I the only one that feels that the amount of power generated by solar cells will be larger than expected?

The substantial amount of power generated by solar cells could even surpass this in real terms. That is because their working rates can be greatly increased if they are located in places such as deserts. Moreover, considering that demand for power is strongest during the daytime in the summer, the value of maximum power generation may matter more.

Cost to equal a household electrical bill in 3 years

The cost issue that solar cells have always been facing could also find a solution in the near future. Solar cells have continued to experience the rule that states “the cost of power generation is lowered by 80% as the amount of cumulative production doubles” for nearly 30 years.

If this experimental rule is applied to the global cumulative solar cell production of about 5.7GW and power generation costs of about ¥46 per kWh as of 2006 (data provided by the Japan Photovoltaic Energy Association), assuming the production of solar cells will continue to increase at the current rate, the cost for power generation will equal the current level of a household electrical bill in 2011.

This estimate almost meets the ¥23 per kWh in fiscal 2010, a cost goal for solar cells indicated in the NEDO’s “PV Roadmap Toward 2030 (PV 2030).”

As I explained above, power companies may only increase rates from now on and the likelihood that they will lower them is slim. Therefore, the solar power generation business may autonomously start operating in several years even without “feed-in tariffs,” a system in which administrative organizations purchase solar power at high rates.

The last factor is the efficiency. Instead of conversion efficiencies, I will discuss “energy payback time (EPT),” a benchmark that indicates how long it takes for solar power to pay back energy spent to manufacture, maintain and manage them.

EPT means much for solar power generation. If EPT is longer than the solar cell system’s lifecycle, it means the more the solar cell is produced, the more energy is wasted. This makes no sense when it comes to a measure to solve the energy issue.

However, opinions about EPT greatly vary even among people concerning solar cells. Some say, “Even crystal Si solar cells have already achieved an EPT of less than 2 years,” while others insist, “EPT extends to 8 years for a module alone and 20 years if peripheral devices are included,” “EPT does not factor in the energy required for transportation of materials,” and “It exceeds 20 years if taking into consideration the energy spent for plant construction.”

Such variations in the recognition of EPT values seem to be primarily attributed to a fact that the reference data was collected at different times. In other words, the data, from which EPT of 8 and 20 years are derived, are old.

According to data announced by the NEDO, current EPT of polycrystalline Si solar cells is 1.5 years at an annual output of 100MW per year. That of amorphous Si solar cells is less than 1.1 years at the same output. These figures themselves still cannot be described as new as the NEDO announced them in 2000 or around.

Some manufacturers have recently claimed that their flexible CIGS solar cells achieved an EPT as short as 1 to 2 months. The EPT also appears to be quite short with the dye-sensitized solar cells that manufacturers have just recently begun to mass-produce (see “Volume Production of Organic Solar Cells Begin, Great Advancement in Efficiency, Durability” in the May 5 issue of Nikkei Electronics).

The development of solar cells has a long history of more than 40 years, but the technology advanced so fast over the last few years in particular that knowledge acquired ten years ago is too old to be of any use.

For example, silicon wafers that require 70 to 80% of all energy used to manufacture crystal silicon solar cells used to be 300μm thick on average in 2004, but were 150 to 200μm thick in 2007, becoming more than 2/3 slimmer in about three years. Even 50μm silicon wafers could emerge in the near future.

As silicon wafers have gotten slimmer, the solar cell EPT has also been greatly shortened. Some recent remarkable data has shown annual volume production has also increased from the 5MW per line as of 2000 to nearly 100MW. If the size of volume production grows, initial costs for plants and others will get smaller and smaller on a module unit basis.

Solar power generation is often discussed in an environmental context, in other words a matter that concerns the reduction of CO2 emissions, but in my opinion, it could be a quite effective measure to solve the energy issue that is more imminent.