{"id":4269,"date":"2014-11-19T13:52:19","date_gmt":"2014-11-19T04:22:19","guid":{"rendered":"http:\/\/www.solarquotes.com.au\/blog\/?p=4269"},"modified":"2024-08-18T20:37:00","modified_gmt":"2024-08-18T11:07:00","slug":"coal-vs-solar-space-efficient","status":"publish","type":"post","link":"https:\/\/www.solarquotes.com.au\/blog\/coal-vs-solar-space-efficient\/","title":{"rendered":"Coal vs Solar –\u00a0Which is more space efficient?"},"content":{"rendered":"

\"solar<\/a><\/strong><\/em><\/p>\n

This is a guest post by Greg Bell – which was conceived in the comments section of another post on this blog<\/a>.<\/strong><\/em><\/p>\n

Take it away Greg:<\/strong><\/em><\/p>\n

——-<\/p>\n

Some things we can say we know for sure about photovoltaics\u00a0– the fuel is free, it’s quiet, and there are no moving parts. But other benefits are more controversial. Recently a claim was made to me that solar PV is actually more area efficient – that is, it generates more energy per hectare – than coal.<\/p>\n

Specifically, the claim was<\/p>\n

“The 1,600 megawatt brown coal Hazelwood Power Station and associated mine in Victoria covers 3,554 hectares. In a sunny location in Australia 20% efficient solar panels covering that area would produce more kilowatt-hours than Hazelwood\u2019s average output.”<\/p><\/blockquote>\n

Let’s see if that’s true.<\/p>\n

Why energy instead of power?<\/h3>\n

Why are we looking at energy instead of power? Well, coal-fired power plants are rated at their peak power generating capacity, however this pace is not kept up 24\/7, 365 days per year. Other factors come into play, like time down for maintenance, and degrading efficiency over time. So we really want a power plant’s track record over a whole year. Power times time equals energy. So we’ll look at how many GWh of energy are produced per year (which, since that’s energy divided by time, is actually power again, but averaged throughout the year). We’ll take that number and divide it by the number of hectares the power plant takes up, and that will give us a figure of GWh\/year\/hectare – our “area efficiency” unit.<\/p>\n

Why area efficiency?<\/h3>\n

Why do we care about area efficiency instead of economics or the environment? It’s not a case of “instead”, rather “and”. Area efficiency is important because whatever energy generation technology we use competes for land with other important uses – like agriculture, or (God forbid) land simply left wild. In the case of wild land, converting it to a coal or solar plant means it’s lost for good, or at least a very long time.<\/p>\n

And, if we’re converting from a less area efficient source to a more area efficient source, well then as a society, we might be freeing up some agricultural land, which if the UN is to be believed, is very important indeed. Of course, the previous energy source can’t have polluted the land or the potential for re-use is limted.<\/p>\n

The Area Efficiency of Hazelwood<\/h3>\n

Hazelwood generates 12.1 TWh\/year. That’s terawatt-hours – 1 terawatt-hour is 1,000,000,000,000 watt-hours! At 3554 hectares, it’s energy efficiency is 0.0034 TWh\/year\/hectare. Converting that to gigawatt-hours for a friendlier looking number and we get 3.40 GWh\/year\/hectare. So for every hectare of land occupied, Hazelwood produces 3.40 GWh of energy per year.<\/p>\n

The Area Efficiency of Solar Photovoltaics<\/h3>\n

So what if we levelled the whole site, and plastered it with solar panels? It\u00a0might look like this:<\/p>\n

\"Royalla<\/a>

Image from RenewEconomy (click image for original)<\/p><\/div>\n

Not just any solar panels, but let’s use SunPower’s record-setting 345 W panels. And to really give solar an advantage, let’s assume we’re able to completely cover the site – no space between tilt frames, and perfectly tilted. We’ll assume 3.6 sun-hours\/day – a weird unit that wraps up the solar energy received by a site into one convenient number. If you multiply the sun-hours\/day of a site by the power of a solar power system in kW, you get the kWh\/day that system will produce. So “Solar Hazelwood” would produce 27068315 kWh\/day. Sounds like a lot! Is solar winning? Unfortunately, no, because when we multiply that by 365 to get annual energy production, and divide by the area, we get 2.78 GWh\/year\/hectare. Solar is only 82% as area efficient as coal.<\/p>\n

The Area Efficiency of Loy Yang B<\/h3>\n

Holding up Hazelwood as an example from Team Coal is a bit unfair since Hazelwood is sort of famous for being inefficient – at least as far as how much energy produced vs CO2 output. It’s old. Let’s guess that CO2 inefficiency will mean it’s inefficient in other ways too and look at a different coal-fired power plant.<\/p>\n

The new kid on the block is Loy Yang, also in Victoria. This bad boy burns through 60,000 tonnes of brown coal a day, belching 34 kg of mercury into Australia’s air and water. But, by committing these environmental crimes, it produces 1\/3 of Victoria’s electricity – all of which I’m hoping is used frugally and responsibly by citizens ever-mindful of coal’s environmental impact.<\/p>\n

In the units we’re interested in, it’s producing 8 TWh of energy per year. That works out to 10.2 GWh\/year\/hectare, and that’s including the nearby coal mine which feeds it (but because I couldn’t find figures for it, this doesn’t include the other station, Loy Yang A, which is also fed by the mine).<\/p>\n

So where are we at? Better-than-real-world solar photovoltaics gives us 2.78 GWh\/year\/hectare, while a modern coal fired plant, including its mine, produces 10.2 GWh\/year\/hectare – coal is 3.7 times more area efficient!<\/p>\n

The Area Efficiency of Solar Thermal<\/h3>\n

But everybody knows large scale solar power is usually solar thermal – where large mirrors focus the sun to boil water, which turns a turbine, etc.<\/p>\n

There’s one in the Mojave Desert in California, serving 54,000 homes, it sounds like a monster. A fair trade for that large area?<\/p>\n

The first clue is that it only produces 250 MW of power. So it’s not even a quarter of a typical coal plant. Fine, but we’re interested in it’s annual energy output, and how efficient it is for the amount of land it takes up.<\/p>\n

Turns out, in that super-sunny location, it only generates 0.864 GWh\/year\/hectare. Loy Yang is 11 TIMES more area efficient!<\/p>\n

Conclusion<\/h3>\n

So, this is all very depressing. Solar is nowhere near as area efficient as coal. This is the conclusion we reach a lot of times when we compare the two – the energy density of fossil fuels is impressive. Clean energy sources – tidal, wind, solar – are all “diffuse”, that is, spread out over a large area. That means we have to collect it to concentrate it into useful quantities. Collecting requires land area.<\/p>\n

A more holistic analysis would include the area required to mine the coal. And even the area required to mine the materials to make the trucks which mine the coal. And on and on. PhDs are written about this sort of thing. We’d have to do that analysis for solar too, which is a high-tech product requiring all sorts of advanced civilisation behind it to make it happen.<\/p>\n

In the end, area efficiency is probably far down on the list of considerations. CO2 efficiency, sustainability, and possibly most importantly, nett energy production, which is what our civilisation actually runs on, would be more important considerations. We know fossil fuels are declining in their nett energy (EROI or EROEI if you want to Google it), so it’s only a matter of time until the crossover point happens and solar is more “energy profitable”. Then we only need to work on that fully solar-powered solar panel factory.<\/p>\n

If you want the spreadsheet I used for these calculations (corrections welcome!), it’s here:<\/p>\n