What is solar power?

The Carbon Pollution Reduction Scheme is on the table, with concessions flying thick and fast to some of Australia’s biggest polluters. But to many, the debate should be looking towards the future — and renewable energy. Solar power is often the most talked-about possibility. After all, we do have all this sun. But could Australia actually be 100% powered by it? Evan Beaver takes a look.

So first things first, what is solar power?

Broadly speaking, it is any energy derived directly from the sun.  This includes direct-heat uses such as the hot-water systems people are familiar with, but also includes drying applications such as salt production and sludge drying in sewage treatment plants. This little robot has what I consider the worst job in the world, and will be the first to go if the robots ever form a union.

In the developing world, solar power, particularly the UV radiation associated with it, is widely used for sterilising water. Just fill a PET bottle with water and leave it in the sun for eight hours. Voila! Sterile water.

But the big-ticket item is electricity production.

What are the technologies competing to produce electricity from solar power?

There are two distinct categories, with a few different technologies within each.

Photovoltaic (PV); literally electricity from light. This is becoming more common on roofs and street lights around Australia, and has been popular for small-scale RAPS (remote area power supplies) for many years.

Solar thermal; concentrating the heat of the sun to make steam, then using this steam to drive a turbine as in coal-fired power generation.

Which is the best?

That’s a tough question. They each have advantages and disadvantages and the “best” will depend on regional variations, resource availability and relative costs.

PV has the advantage of very simple operation. Put it in the sun and electricity comes out. That’s it. No need for moving parts, maintenance crews or sophisticated tracking mechanisms. There’s more efficiency to be gained by adding tracking, but it’s not really necessary.

On the other hand, they don’t generate much electricity per unit area compared to the other technologies, and at grid scale, tracking becomes mandatory. I’ve somewhat unkindly heard them described as “23% efficient; 77% dicking around”.

But, efficiencies are improving in labs across the world. One company is claiming that it is  on track for cost parity with coal-fired power by 2010. The Institute of Electrical and Electronics Engineers think they’re being optimistic.

Also, because they are a direct-light electricity conversion, once the sun stops hitting it, say if a cloud or very large bird passes over, the electricity production stops instantly as well.

Further, within the PV category, there are some more sophisticated technologies. Such as  concentrating solar PV, so called ‘thin film’ (like Origin Energy’s Sliver technology) and flexible or organic PV.

The concentrating PV uses a magnifying glass or curved mirror to focus the sunlight onto a very sophisticated and small PV cell. The goal here is twofold; minimise the amount of silicon (which is expensive) and concentrate the sun, which brings efficiency benefits. This last point is true of all technologies.

Thin-film technology pushes the boundaries of the “minimise the silicon” aspect, by making  slivers of photovoltaic material to minimise cost.

Organic solar is cutting edge; again, they try to minimise production costs, but instead of silicon they use organic chemistry. The drawback is embarrassingly poor comparative efficiency numbers (~5% vs. ~25% for silicon PV). However, research continues because the costs per unit electricity are getting close to silicon PV. Organic PV is also useful because they can make fancy flexible films that allow some interesting military applications.

Solar thermal

Thermal in general makes use of higher temperatures and better energy reclamation over a unit area. It is also much easier to incorporate storage into a thermal plant. There are a bunch of different methods of doing this, broken down broadly into linear (troughs, Fresnel), arrays (tower systems, including Lloyd Energy’s excellent carbon block storage) and parabolic dishes (such as this Stirling engine, one of which has the highest efficiency measured at ~40%, or Wizard Power)

Most of the bigger installations worldwide are solar thermal, usually using trough-based reflectors.

Sounds expensive.

It is, but only compared to coal power, which is really cheap. Solar thermal exploits subtle energy gradients by concentrating solar energy. Coal power comes from digging a hole and burning what you find in the hole.

As with all of these sorts of financial analyses, they vary greatly, depending on the starting assumptions. Here and here, you can see what I’m talking about.

As a coarse summary, solar is somewhere in the range of 50-100% more expensive than coal (without capture and storage) and pretty close to nuclear projections. Translating to a carbon cost, solar would need at least $20 per tonne to be competitive.

OK, there’s lots of technology. But does it actually work in any installations outside quirky labs, research organisations and hippy communes?

Currently, the US, Spain, Portugal and Germany are leading the solar charge.

In the US, the SEGS 1 plant has been operating, and generating useful electricity since 1984. This was the first stage of the massive solar energy generating system in the Mojave Desert. This collection of plants (there are nine) now produce about 350MW; typical coal plants are 500-1000MW.

In recent years, favourable government policies in Spain have led to an explosion in solar power projects. In 2008 alone, more than 3000MW were installed, with another 1300MW announced. Government support, through ‘feed-in-tariffs’, has changed the economics considerably for solar, so much so the government has created a maximum project size (50MW) to prevent a budget blow-out.

What about baseload? Won’t we need electricity at night and on cloudy days as well?

Leaving aside objections to the term ‘baseload’, there are a couple of ways of skinning this particular cat.

What’s needed is energy storage; either as heat or as electricity. Then, during the times when electricity demand is less than electricity supply, we can store some for use later. This technology already exists and is part of a normal electricity grid. But, the energy storage needs are likely to increase dramatically with the introduction of more renewables.

Energy can be stored as electricity in a number of ways. For grid scale storage they’re mostly different types of advanced batteries. These can be deployed anywhere in the grid. There is also ‘pumped-hydro’, good for large amounts of energy, but geographically difficult to build.

Storing energy directly as heat is a little easier and well suited to solar thermal projects. Even a “standard” solar thermal plant has about an hour of storage, due to the mass of hot material (steam)in the system. This is enough to ride through cloud cover, which can be a big problem for PV. There are plants in Spain with 7.5 hours of storage, (essentially just steam in a boiler) which is just about enough to get them all the way through the night. This amount of storage increases project costs by about a third, putting them in the upper ranges of solar costs. But this has benefits for the generating company because more reliable electricity production is more valuable to electricity retailing companies.

Heat energy storage has been an area with a lot of research directed at it recently and the results are starting to improve. Lloyd Energy has an innovative storage system that stores heat directly in 10-tonne blocks of graphite; this provides “on-demand” solar. Wizard Power stores heat by dissociating ammonia in a reverse of the industrial classic Haber Bosch process. I’m a big fan of this project for two reasons; it’s being built in Canberra and the dish they use as a test bed could easily be modified into a death ray (I’ve seen it burn a hole in a ceramic heat shrouds like it was butter).

Can we power the whole country with the sun?

The answer is probably yes, but there are some risks and some serious costs associated.

Professor Keith Lovegrove, a solar researcher from ANU, is fond of saying that an area about 150 x 150km (from this presentation), covered in a solar thermal power plant could power the whole country, even including storage to get through the night and average conversion efficiencies. This is approximately the same size as greater Sydney.

But, if it’s raining there for a few days, we’re stuffed.

Most reports discuss the advantages of geographically spaced plants, to spread the weather chances, and a mix of generation technologies. These would include natural gas turbines that can peak as demand ebbs and flows; wind turbines and a smart grid. A mix of wind and solar offers synergies when Mother Nature is playing games with us; also high pressure over Australia means no wind, but lots of sun. Low pressure systems bring wind and rain, but no sun. Perfect!

Enough with the tech nonsense and caveats. Is it the final solution or not?

Using more evasive language, hardly anyone would advocate one generation technology and one only. Smart energy investors will realise there are little regional variations that push the favourability of a project back and forth depending on the resources available.

With that in mind, Australia has a lot going for it with solar thermal. Plenty of sun, bugger-all rain and sunny places where the grid already exists and people are living.

If it’s not viable here, it’s probably not viable anywhere.

Apologies for the Wikipedia links, but for this sort of general information it’s perfect, albeit a little out of date on some specifics.

Evan Beaver is an engineer, recent chook owner and convicted public servant.