Tuesday, April 19, 2011

Renewable energy is all very well , but .......

My good friend Anthony Keen has been trying to become as energy efficient as possible. His home boasts 3.8kW of photovoltaic cells on the roof, as well as the ultimate solar water heater. With the best will in the world, he has been driven to conclude that the awful, fossil-fueled grid is a blessing in disguise. Read on ....

Some promoters of renewable energy imply we can survive on renewables alone. I wonder how many of them have actually tried to live on wind or photovoltaic (PV) energy alone? Living on solar energy (by choice) has taught me some lessons.

We all know most renewables are intermittent, but do we really understand what that means? Your power just goes off, Poof ! when the sun goes away or the wind drops. Then you need at least one of three things:

(1) access to a nice stable grid running on coal/nuclear base power

(2) some means of energy storage or

(3) a stand-by fossil-fueled generator.

You don't like (1) and (3), so what about storage? Storage really is the key to all intermittent renewables. The only viable storage on a commercial scale today is the pumped storage system. Eskom has 1400MW pumped storage capacity and 1300MW being built. Cape Town has 160MW. These can only run for a few hours before the dams empty but that generation is vital at busy times.

Nice places to build more such expensive schemes are scarce, hence Eskom’s interest in seawater pumped storage on our coasts. A pilot seawater system has been running commercially in a nature reserve in Okinawa, Japan, for 12 years after successfully overcoming technical and environmental challenges. It can be done. Ireland, Hawai and Portugal are interested.

Commerce and industry cannot run on intermittent renewables without massive investment in (pumped) energy storage. A nice stable basepower grid can absorb up to about 25% renewables but after that the grid becomes difficult to manage and storage becomes necessary.

On a small scale and in specialised applications batteries are useful, but inefficient and expensive. Only when we have efficient and cheap large scale batteries will renewables come into their own. At a residential level, batteries are just acceptable, but if you wish freedom from worry you will need to spend as much on batteries as you spend on PV panels . Plus you still need the grid or genset (or candles !) as backup. All this effectively doubles the initial cost of solar or wind power and this true cost of reliable renewable energy is commonly overlooked. And batteries have to be replaced every few years.

A sad sight was some smart solar PV panels on the roof of a remote Cederberg cottage, some discarded (lead !) batteries lying in the dust and candles in use. Replacement batteries were unaffordable, the weakest link in the now useless chain. Many other promising energy storage technologies are being pursued but none are economic as yet.

Renewables do have their important place in an energy mix for a country, but without adequate storage (or friendly neighbours), I doubt they could entirely replace baseload generating stations. For baseload we need to be weaned off coal , and I see nuclear fission as a temporary but necessary lesser evil until we can copy the sun with fusion power.

Anthony Keen, Rondebosch

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