Toward Energy Independence
G.R.Dixon, 5/1/2006
Thin Film Solar technology is one of the more promising in the solar energy field. The Department of Energy has set two ambitious goals for Thin Film: 15% Efficiency (15% of incident sunlight is converted to electric energy), and $50 per square meter manufacturing cost. Both of these goals may be realized earlier than expected (See another article). The present article explores some possibilities, assuming these two goals have been (or soon will be) reached. There are many "green" technologies being investigated at NREL (National Renewable Energy Labs) and elsewhere … hydroelectric, wind, geothermal to name but three. In the author’s opinion, the most promising of all is photovoltaics, assuming the stated goals can be met.
1. The Cost for All-Solar.
My wife and I live in a small, all-electric house. Our daily electric usage is approximately 50 kwH. Or, since
, (1_1)
our daily electric usage is 1.8E8 Joules/Day. Let us say that the national average is somewhat more, say 3E8 Joules/Day. An average household’s annual energy usage would then be
. (1_2)
The Department of Energy has set a target goal of 15% efficiency for thin film photovoltaic technology. The solar insolation during peak hours in the southwest is 1000 Watts/m2. At 15% efficiency, thin film should produce 150 Watts/m2. Assuming a conservative 5 hours of sunlight per day, and 200 sunny days per year, we can then expect
. (1_3)
The square meters of thin film needed to produce a household’s annual energy needs would thus be
. (1_4)
A square of thin film, 14.25 meters on a side, would thus do the job.
How much would be required for the entire country (households only)? Let us say that, on average, a household contains 3 people, and that our population is 3E8 people. Then there are approximately
. (1_5)
Total required thin film is therefore
. (1_6)
In other words, a square approximately 150 kilometers on a side would suffice.
USDE’s target goal for thin film manufacturing cost is $50/m2. Referring to Eq. 1_6, the total national cost, if and when this goal is met, would then be
. (1_7)
In addition to this, there would be infrastructure costs (sun trackers, etc.) Let us say the total cost would be $2E12. This is about 1/5 the present national debt.
2. Revenues.
Once thin film facilities have been installed, they will produce energy at little additional cost. When the film degrades after several years and must be replaced, the infrastructure would presumably still be robust.
A quick look at my household electric bill indicates that we are now paying approximately 7 ½ cents per kWh, or
. (2_1)
Let us suppose that future cost will be $3E-8/Joule. The nation’s total annual energy bill would then be
. (2_2)
Thus annual revenues would be approximately 16.4% of the initial cost. Including interest payments, the initial investment should be paid down in approximately 7 years. Ongoing revenues, with no further borrowing should cover subsequent refurbishment costs.
3. Off-Hour Considerations.
A 150 square kilometer array of thin film photovoltaics would certainly be a sight to see! But there are obvious reasons for dividing such a vast number of panels into smaller, geographically distributed arrays. Ultimately, however, the lower 48 states have only 4 time zones. Consequently a means of storing solar-generated energy and/or generating energy by other means (e.g. hydroelectric) for nighttime use would be required. The nation already has significant facilities for generating non-solar power. Adequately augmenting thin film energy with existing non-solar energy generation facilities should thus entail little added expense and meet household energy needs 24/7. Indeed a significant percentage of the existing infrastructure might be freed up and used to generate energy for all-electric motor vehicles.