Is Renewable Energy Adequate For Our Needs?

Posted on Sun 05/30/2010 by


By Don Petersen and Bill Stratton

This excellent article is somewhat technical by nature, but it is really informative, and shows that this rush to construct renewable power plants is ill advised, because of the very small amounts of power they provide…..TonyfromOz

Commitment to renewables deserves close examination and appreciation of the dimensions of an effective international emissions reduction program – unilateral U.S. action is meaningless.

Almost everything published about renewable energy relates in some way to the desirability of harnessing the vast amount of clean energy delivered free every day by the sun. All carbon based life forms including man, depend entirely on the sun’s energy and proponents argue that it makes sense to collect part of that sunshine to satisfy energy needs without emissions from burning fossil fuels, and predicted anthropogenic global warming. In most cases the argument cites an enormous number compared to current utilization and suggests that solar energy is the ultimate solution to the energy shortfall now looming because of pressure to eliminate fossil fuels, and ever increasing energy demand.

Each 24-hour day, one full revolution, calculation indicates that the sun delivers, on average, 164 watts to every square meter on the surface of the earth. That amount multiplied by the number of square meters on the earth’s surface is 84 petawatts arriving daily – the enormous number. Now, on a daily basis, the earth’s 6 billion people use about 12 terrawatts from all sources, but mostly from fossil and nuclear with only a small amount from renewables, so there is about 7,000 times more solar energy delivered than all the energy we currently use. For perspective, 12 terrawatts (12 million megawatts) is the numerical size of the U.S. gross domestic product, or the national debt of over 12 trillion dollars. Petawatts (a billion megawatts) are a thousand times more.

To harness solar energy in all its forms – solar, wind, biomass and hydro – several facts must be kept in mind. It is intermittent because the sun sets, the wind does not blow constantly and the collectors are stationary. Since inherently diffuse solar energy does not fall uniformly – more falls near the equator than the poles – solar collectors should be placed where insolation is highest, and wind turbines should occupy windy corridors. At small fractions of a watt per square meter–far less efficient than either solar or wind – hydro requires rain as well as specific optimum locations, and useful biomass/biofuel needs enormous area, energy intensive planting, fertilizer, cultivation and seasonal harvest.

The square meters between the Tropic of Cancer and the Tropic of Capricorn are the only ones that receive perpendicular irradiation some time during the year. Farther north and south, solar collectors must be tilted to catch perpendicular sunlight, with more and more tilt to collect fewer and fewer watts at higher latitudes. Lamentably, less than half of the earth’s land mass falls in the prime equatorial collection zone – the rest is deep water – and the only parts we own are a few Pacific islands. Widely distributed biomass collects the most solar energy at about one percent efficiency, but all renewables share the same daily solar allocation. Because so little of the currently used energy comes from renewables, the total collection and transmission system, involving significant distances, must be built from scratch.

Although the collectors for renewable energy in their present form are not considered optimum, they are all within about a factor of three of their theoretical maximum efficiency – the room for improvement is limited. Regardless of design, vagaries of wind and sunlight delivery further restrict collection over time. Data on the average yield in kilowatt hours per year from existing installations, critical for sizing future systems, are proprietary and unbelievably difficult to obtain. Annual performance data are desirable because they express real world energy yield experience after any losses. Some information, e.g. kWh per swept square meter per year has been found that provides annual performance numbers and energy densities can be deduced. We have used 10 blade diameter spacing recommended by National Renewable Energy Laboratory to define the footprint of wind farms. Optimally sited Midwestern U.S. wind farms annually provide a little over a watt per square meter of real estate despite large nameplate capacities, attractive short term measurements, and optimistic projections. California Energy Commission reports coupled with total collector area estimates reveal that solar thermal and photovoltaic collectors yield a measured annual average something over 6 watts per square meter from the large, multiple collector installations of known area. These energy density values are lower than projections based on capacity factors using average wind velocity and insolation, and must result from input variations since collector efficiency should not change. It is the reason why measured output over protracted periods is essential for sizing installations to satisfy known demand. As collector efficiencies improve, values will increase but not by more than the approximate factor of three afforded by design improvements, the amount of energy arriving from the sun is fixed and necessarily diffuse. Dividing the watts needed by those average power density values for solar and wind gives the minimum land area in square meters required to satisfy the demand. Areas for maintenance accessibility and infrastructure add to the total and the numbers are astronomical.

Energy storage lags far behind collection methods and terrawatt storage is not feasible by expansion of any known technique. A breakthrough is desperately needed and until a massive, novel storage method with dispatch capability is invented, renewable energy will temporarily displace but will never replace some fraction of baseload. Spinning reserve, most likely hot natural gas generators, will be essential to maintain uninterrupted energy availability – fossil generation cannot be abandoned.

Ignoring intermittency and assuming that land acquisition for collectors and transmission lines is possible, that adequate exotic materials are available for manufacturing collectors, and cost is no object, with today’s technology how large an aggregate system would be required to convert from fossil/nuclear to 12 terrawatts of renewables for 6 billion people now? How large for 18 terrawatts in 2050, with 9.4 billion? Using existing data, the best possible case for solar thermal or photovoltaic is now approximately 6 watts per square meter and it will not get much better until major collection areas move closer to the equator. Thus, solar arrays totaling 2 trillion square meters – the area of Texas,New Mexico,Arizona, California and Nevada – are needed now, and 3 trillion square meters – add Utah, Colorado, Nebraska, Kansas, and Oklahoma – in 2050. Wind farms, using NREL’s 10 blade diameter unit spacing recommendation to define the perimeter of the farm, would require 10 trillion square meters now, and 15 trillion in 2050 – five times the area requirement for solar collectors although land between the turbines can be shared. This example, using the western United States, only gives a notion of the size of collector areas scattered over the earth. Acquiring or confiscating that much real estate is not very likely, but only 45 percent of the earth’s land mass lies between the Tropics – optimum solar collectors must be built on one sixth of the total global area. Simple arithmetic indicates that exclusive use of renewables cannot support energy demand much beyond the 18 terrawatts needed in 2050, even with aggressive exploitation of equatorial locations for solar and wind beyond coastal limits.

This analysis clearly suggests that from the practical standpoint of energy collection, renewables are limited. Neither the footprints, nor that many collectors seem practical or economically feasible, facts rarely considered in the rush to declare advanced nuclear energy, with a comparatively miniscule footprint, too expensive. Electrical output is a thousand times greater but physically, gigawatt advanced nuclear plants are not much larger than megawatt light water reactors – a million square meters per unit. The continuous availability of power, significantly increased fuel supply – all uranium isotopes and thorium – without plutonium accumulation and attendant concern about nuclear weapon proliferation, the thousand fold megawatt to gigawatt economy of scale, the ability to site generators close to demand, and the cost per kilowatt all argue for a prominent place for modern nuclear power in the future energy mix. It is the only current power production scheme that could be ramped up to accommodate the burgeoning population expected during the rest of this century. Twelve thousand advanced design gigawatt power stations, operating at over ninety percent of capacity, occupying 12 billion square meters – an area slightly larger than Maryland – provide twelve terrawatts continuously without emissions and almost trivial waste, with land left over for a picnic. Contributing Editor Don Petersen, Ph.D., writes for the Los Alamos Education Group and is a retired former Leader of the Los Alamos National Laboratory’s Life Sciences Division. Since Operation Desert Shield, he has served on the Deputy Undersecretary of the Army for Operational Research advisory panel for development of chemical and biological weapons detection and protection equipment. Bill Stratton, Ph.D., writes for the Los Alamos Education Group. Now retired, he spent his career at the Los Alamos National Laboratory working on reactor safety. While a member of the working staff of the President’s Commission on the Accident at Three Mile Island, was instrumental in explaining why almost no Iodine-131 escaped from the reactor core. He has consulted for nuclear utilities, reactor vendors, the Department of Energy, the Nuclear Regulatory Commission and was a member of the Atomic Energy Commission’s Advisory Committee on Reactor Safeguards.

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