Physical Insights

An independent scientist’s observations on society, technology, energy, science and the environment. “Modern science has been a voyage into the unknown, with a lesson in humility waiting at every stop. Many passengers would rather have stayed home.” – Carl Sagan

Archive for the ‘solar energy’ Category

The Australian Government’s domestic solar PV subsidy…

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The federal government has recently announced it will scrap the unpopular means test for the federal subsidy for domestic solar PV arrays, which restricted the rebate to households earning less than $100,000.

The size of the rebate was, formerly, $8 per watt of installed nameplate capacity, up to a maximum of $8000. The rebate will now be smaller; $5/W, up to a maximum of $7500.

Sounds good, right? But it’s horrendously expensive – the government is in effect paying $5/W for the cheapest, nastiest polycrystalline silicon PVs on the market.

There are scores of companies jumping on the bandwagon to sell these little 1-1.5 kW rooftop PV systems, advertising and promoting and installing them – because they’re making a fortune from the increase in business resulting from the subsidy.

The government rebate does not cover the full cost of such a system – therefore, in order to get as much interest as possible, the vendors are trying to keep the costs of such systems as low as absolutely possible, so that the cost that the customer pays is as small as possible. Therefore, all such systems are exclusively cheap, inefficient, basic polysilicon devices. After all, an advanced solar-concentrating collector with a high-efficiency CdTe cell or stacked heterojunction cell or sliver cell or whatever does not attract any higher subsidy than the basic polycrystalline Si device.

Advocates such as the Australian Greens say that such a scheme “supports the solar industry” – but all it does is supports the environmentally-damaging low-cost manufacturing of polycrystalline silicon in China, and doesn’t support innovation in advanced PV technology or anything like that.

What if the same amount of subsidy might be better spent elsewhere? Here’s a hypothetical idea to think about.

1. Go and find a suburb or a city or a community which has about 31,000 households. I’m certain there are 31,000 households in this country who support what I’m about to elucidate.

2. Get each household to put up AUD $1200 or so, temporarily.

3. Take that 25 million US dollars and purchase a 25 MWe Hyperion Power Module, or something similar.

4. At 25 MWe divided between 31,000 households, that’s a little over 25 GJ per year, which is a little more than Australia’s present average household electricity consumption. This doesn’t just generate a fraction of your household electricity needs – it generates 100% of it, and there will be no more electricity bills.

5. That corresponds to a nameplate capacity of 807 watts per household. Since the government hands out a subsidy of $5/W for solar photovoltaics with a 20% capacity factor, they should hand out $22.50/W for nuclear energy with a 90% capacity factor, right?

6. Collect your $18,157.50 rebate from the government. Less the $1200 investment, that’s $16,957.50 immediate profit in your pocket. This is exactly the same rate of payment per energy produced that presently exists in the form of the PV subsidy.

7. Go to the pub. Got to stimulate that economy, you know.

I wonder how many ordinary Australian households would support nuclear energy if you paid them $17,000 for doing so?

To replace one Loy Yang type coal-fired power station* with solar cells, we would need 6,082,342 homes equipped with 1.5 kW solar photovoltaic arrays.
With an $7500 rebate for each one, that would cost the government 45.6 billion dollars per each large coal-fired power station.

* (Loy Yang generated 15,995 GWh in 2006.)

Solar photovoltaics typically have a capacity factor of about 20%, and we’ll suppose the panels have a lifetime of, say, 30 years.
Therefore, this scheme costs the government 9.5 cents per kWh generated.

If the government purchases nuclear power plants, they will cost, say, 10 billion dollars (let’s be conservative) for a nuclear power plant with two 1100 MW nuclear power reactors which will operate with a 90% capacity factor and a lifetime of 50 years. The capital cost of plant dominates the overall cost of nuclear energy.

Therefore, the nuclear power plants would cost the government 1.15 cents per kWh – 12% percent of the cost of the solar rebate scheme. That’s the government’s rebate alone – without the rest of the price of these systems.

All this solar rebate is is another mendacious political enterprise involving renewable energy which can’t be scaled up, which hands out free money to the public, makes a bunch of money for the solar panel vendors (including many dangerous fossil fuel vendors such as British Petroleum), and mendaciously makes the government look like they’re actively getting the country running on clean energy.

ASIDE: I’m going to start cross-posting some blog content on the Daily Kos. I think it’s a nice site to engage with many, many readers – many of whom perhaps aren’t already so convinced of the virtue of nuclear energy – so, there’s plenty of engaging, active discussion, and the opportunity to maybe convince some people – even if that’s just a few people it’s still a very positive thing.

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Some thoughts on the economics of domestic solar photovoltaic installations

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Let’s say that 1 kW of solar PV nameplate capacity installed on your roof costs about $12,000. The figures that I’ve seen quoted around are typically $13,000-$12,000 for a 1 kW on-roof PV array installation.

(These are Australian-centric quoted costs, in Australian dollars, by the way).

With the rebate of $8/W for installed PV capacity (capped at $8000) offered by the government to encourage decentralised household generation, that’s $8000 offset from the cost of the 1 kW system.

With this incentive included, that’s $4000 you need to pay for such a system.

Now, based on realistic capacity factors for such a PV system, 1 kW of nameplate power capacity will generate about 5.1 kWh energy in total per day – The PV installation industry expresses this overall capacity/availability factor as “peak sun hours per day” for any given location. The 5.1 kWh is the actual figure quoted for Sydney, Australia.

Household electricity consumption in Australia is 7 MWh annually in Australia, according to EnergyAustralia. That’s 19 kWh per day.

A 1 kW solar PV installation is just not enough to completely offset your electricity bill and start making money off it.

The typical electricity cost to the domestic customer is about 14 c per kWh. It has been proposed, however, that the government could see the price paid for electricity sold into the grid from these decentralised household installations fixed at an elevated price of 44c/kWh

At a feed-in rate of 44c per kWh, that’s $820 dollars per year offset from your electricity bill – so, the solar PV installation takes just under 5 years to pay off. If you’re selling the electricity at the same rate that the domestic customer buys it at, 14c per kWh, it’s over 15 years.

However, suppose you want to consider the case of installing enough capacity to completely satisfy your household electricity needs, so that you can be making money of it all together.

(This all assumes that you’re an “average household”, presumably with several family members in the household, and “average” levels of electricity efficiency)

You’re going to need a system with 4 kW of nameplate capacity.

How much will that cost – well, we might assume that it can be done for cheaper than $48,000 – I don’t know, really, so I’ll just guesstimate $45,000. (Some economy-of-scale is to be expected, but I am not an economist, and it’s not an area which I’m familiar with in any real detail.)

Less the $8000 rebate, and that’s $37,000.

Now, you’re generating 20.4 kWh per day, and and consuming 19 kWh, with 1.4 kWh sold back into the grid at 44 c per kWh.

In this scenario, no overall electrcity purchasing is required – so overall, it’s a revenue source.

That’s $225 per year from selling the electricity, plus $971.5 saved from not having to buy the electricity that you use.

$37,000 / $1196.5 gives you a payback time of 31 years. In all likelihood, that will exceed the working lifetime of the photovoltaics.

With the government rebate of $8/kW capped at $8000, going over that amount gets a whole lot more expensive rather quickly.

Looking into Solar Thermal power systems.

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Atomic Insights has an interesting recent post asking some pertinent questions about solar thermal energy systems:

What are the steam cycle parameters? What is the overall thermal efficiency?

What is the cooling medium for your condensers?

How much water will the plant consume per unit of power?

Are the mirrors steered so that they track the sun?

What is the installation cost per unit of energy produced each year?

These are good questions – they’re worth asking. I’m very interested in learning the answers to these questions too – so I’ve done a little bit of, well, Google-ing (it seems unfair to call it “research” when it’s so fast and easy, doesn’t it?) and found some interesting information from solar thermal manufacturers. Admittedly, much of what I’ve found doesn’t really come as a surprise.

The Abengoa Solar corporation has several large-scale solar thermal systems in operation and on the drawing board, including this 280 MW (nameplate) plant which will be built near Phoenix, Arizona.

http://www.abengoasolar.com./sites/solar/en/nproyectos_eeuu_arizona.jsp

The schematic diagram on that page clearly shows that a fairly conventional water-based cooling tower is proposed as the basis of the condenser heatsink.

The Arizona system is based on the 50 MW Solnova 1 installation, in Spain. This installation does include a mechanical single-axle drive mechanism for steering the trough collectors.

Solnova 1 has a design power rating of 50 MW. Based on the local solar resource, the plant is predicted to deliver 114.6 GWh of clean energy per year.

That’s a capacity factor of 26%.

Here’s what Adams had to say about the thermal efficiency expected from such a system:

Based on my back of the envelope computations it appears that the steam conditions will be roughly equivalent to those found in the second generation nuclear plants operating today. That implies a thermal efficiency of about 33%, and a condenser cooling water requirement that is comparable to a nuclear power plant on a per unit power basis.

Here’s what the company says:

At peak conditions, the plant converts available solar radiation into heat at an efficiency near 57%. Combined with the efficiency of the steam cycle, the overall plant efficiency is approximately 19%.

The efficiency of the steam cycle based on the manufacturer’s official claims, then, must be 19% divided by 57%, or 33%.

Well, that’s really all that needs to be said on that question!

In terms of efficiency of the energy conversion in these solar-thermal systems, there’s nothing particular special about them – the efficiency, and therefore the condenser water cooling requirement, is comparable to any other typical Rankine-cycle steam power plant.

You’ll sometimes hear this argument about water consumption put forward by the anti-nuclear-power set. It uses so much water, they say. The fact is, the condenser cooling requirements for a typical Rankine-cycle steam power system are all pretty much comparable, per unit of electrical energy output, irrespective of what the heat source is – the heat source might be solar thermal, it might be nuclear fission, it might be coal, it might be oil – it doesn’t matter!

The laws of thermodynamics certainly don’t show any prejudice against nuclear fission heat sources, or against solar thermal heat sources, or anything else.

Some power plants, particularly the common coal-fired power plants, can achieve higher temperatures – and higher efficiency – utilizing supercritical water as the working fluid. A supercritical coal-fired plant, for example, might be able to achieve improved efficiency – and therefore a reduced condenser cooling water demand per unit electrical energy output – compared to a non-supercritical nuclear generating unit. However, the same concept can be applied to nuclear generating units, too. Supercritical light-water nuclear power systems are under serious development.

(Note that that does not mean supercritical in the nuclear physics sense of that word!)

Now, how much will it cost?

http://www.azcentral.com/arizonarepublic/news/articles/0221biz-solar0221.html

Estimated build cost for the Solana project: 1 billion dollars.

Nameplate capacity of 280 MWe. Since it’s using molten-salt thermal energy storage, it’s fair to expect a capacity factor that is superior to the Solnova 1 installation discussed above. But, of course, they just have to be difficult, and not provide any mention of the actual capacity factor expected (or the actual energy output per year), and instead only providing this difficult “supply energy to n homes” stuff.

Solnova 1: 50 MW / 25,700 = 1946 W of nameplate capacity per home

Solana: 280 MW / 70,000 = 4000 W of capacity per home.

Obviously there’s something missing here – the efficient thermal-storage Solana installation should be expected to require less capacity for a given number of homes supplied, but instead it requires twice as much. I guess they assume, maybe, that Americans are going to use more electricity than the people of Spain?

Unfortunately, at this point, without some basis to make reasonable estimates of capacity factor for the thermal-storage solar thermal plant, it’s almost impossible to make any meaningful comparison of the cost.

Almost impossible. We could make the most unrealistically conservative, optimistic, renewable-energy-is-infalliable estimate conceivable. We could estimate, just for argument’s sake, that a thermal-storage solar plant like the Solana facility has a capacity factor of 100%.

Then, the installation cost comes to 3.6 billion dollars per gigawatt of “real” average power output. It’s proportionately higher if you factor in some realistic capacity factor.

And finally, here’s something else that’s interesting – but perhaps not too surprising.

That is enough to supply 25,700 homes and to reduce CO2 emissions by more than 31,200 tons per year. To supplement power generation under conditions of low solar radiation, Solnova 1 is equipped to burn natural gas. This can be used to deliver 12-15% of the plant output.

Emphasis is mine. Obviously this clean, green, greenhouse gas emissions free energy is clearly so much more preferable to any kind of nuclear energy. I’m sure Amory Lovins would be proud of them.

Carbon-Free and Nuclear-Free: A Roadmap for US Energy Policy

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The Institute for Energy and Environmental Research and the Nuclear Policy Research Institute have just released the Executive Summary of Carbon-Free and Nuclear-Free: A Roadmap for U.S. Energy Policy. It is a report that will be published in October 2007 detailing recommendations on how the U.S. can meet future energy demand while eliminating carbon-intensive fossil fuels, as well as eliminating nuclear energy.

Figure 2 on page 9 of the summary details how the US electric grid will be configured by 2050 without fossil or nuclear power.
Solar PV and solar thermal are assumed to generate 40-45% of the electricity supply.

How much solar capacity would be needed to provide 40-45% of the electricity supply?

If solar is to provide 1,824,000 GWh to meet this demand – 45% of current generation capacity – the US would need 1095 GW (1,824,000 GWh / (8760 hours in a year * 19% capacity factor) = 1095 GW).

So the US would need to build more solar capacity than the total current capacity of all the generating capacity in the country just to provide less than half the electricity just at current level of demand.
Ignoring the growth in electricity demand, to build 1095 GW of solar by 2050 the U.S. would need to build roughly 26 GW of solar capacity each year… 500 MW per week.

If this is all from photovoltaic cells, and assuming you can get, say, 170 W per square meter of photovoltaics, you have to build… about 3 square kilometres of photovoltaic panels per week .

IEER claims, for comparison, that 2500 GW of nuclear capacity would need to be built worldwide by 2050 to make a difference to CO2 emissions, and they’re quick to point out that that corresponds to about one nuclear reactor per week. Of course, a nation such as the US does in fact have the capacity to build more than one reactor at a time.

If it takes, say, 150 weeks to build a nuclear power reactor, then 150 need to be built at once in order to meet this rate of construction. Sounds like quite a challenge, but no less so than building PV modules a square kilometer at a time.

Yes, we have better photovoltaic technologies in the pipepine today, that are far cheaper to build, a bit more efficient, and so forth. Sliver cells, which reduce the cost of cell materials greatly, Titanium Dioxide photoelectrochemical devices, and so forth. Whilst in some cases they offer significant increases in efficiency, they still have a low capacity factor, and they still don’t work in the dark.

Don’t get me wrong, I think solar energy is great, and I support its use, and I support research and development – and government money for same – into improving it.

But it’s important to understand what the limitations are. The most fundamental limitations to solar energy are not that that clever physics and engineering of the cells can ever get us around.

Proponents of solar cells say that the key is to do away with large, centralized generation – install solar energy on site, on every building and home.

But in reality, what’s the difference? The electricity demand is the same, except for the relatively small losses over long transmission lines. With the same cell technology, the same amount of cells are needed to meet the same electricity demand.

We often hear the ideas for large-scale pumped hydroelectric storage and so forth, but are there practical alternatives for smaller-scale energy storage systems for the homes and buildings? Electricity storage systems are the key to making large-scale solar energy workable – We’re gonna need something better than a basement full of Lead-acid cells. Hydroelectric pumped storage is all well and good, it’s proven on a large scale, but it only works with large, centralized capacity, and it only works if your country has enough spare water to support expanded Hydroelectricity. Here in Australia, for example, expanded hydroelectricity is really not an option.

Vanadium redox flow cells? Perhaps. Molten-salt thermal storage? Perhaps. Hydrogen? Perhaps.

In future, technologies will develop, and some of these technologies will continue to prove themselves on a large scale.

But today, the set of well-proven workable technologies is limited. Nuclear is one of those. Can we afford to gamble the future on the large-scale adoption of unproven technologies today? No, we can’t , but at the same time, we can’t gamble on ignoring research and development into these potentially promising energy technologies, either.

Written by Luke Weston

August 7, 2007 at 7:25 am