Ideology, Solar power, Technology, Wind power

“Dear Aunty, are you SURE we need fracked gas? Can we really not succeed with renewables alone?”

Oh dear, sweeties, it seems that some amongst you really haven’t got to grips with the limitations of renewable sources of energy yet.

I’m afraid we can’t meet all our needs with renewables alone, and that we need other sources of energy to compliment them.

I’ve covered this topic here before, but to recap:

1. Renewable energy sources are intermittent

2. They suffer from low power density

3. Conversion of Capacity into Output is typically low

The reality, cherubs, is that whilst these challenges may one day be overcome with advancements in technology and with energy storage techniques, we need to do something different right now if we’re to reduce global CO2 and other damaging atmospheric emissions – and that means continuing to install renewable capacity whilst at the same time phasing out our use of coal and replacing it with cleaner burning natural gas and nuclear energy.

Sadly, pumpkins, a number of individuals and groups continue to signal that a world powered by renewable energy alone is available imminently, when it’s not.

They do so by illustrating plans and investment with big, headline grabbing numbers, like this from Greg Barker MP – 20GW of solar PV sounds fantastic, especially compared to the average 35GW of electricity demand we have here in the UK.

But, alas, it’s not actual output he’s talking about, bless him, but installed capacity.

Which is a very different thing when you consider that the amount of electricity produced by solar panels averages between 10 and 20% of installed capacity, and so these ambitious plans would at best generate only 4GW of actual power, equal to 11% of demand. But only during the day, because solar’s biggest limitation is that it doesn’t produce anything at night, which is often when we need it most my dears.

According to the fantastic free e-book “Without Hot Air” produced by David MacKay (before he became DECC Chief Scientist) the limitations of solar PV are quite clear:

“The power of raw sunshine at midday on a cloudless day is 1000W per
square metre. That’s 1000 W per m2 of area oriented towards the sun, not per m2 of land area. To get the power per m2 of land area in Britain, we must make several corrections. We need to. compensate for the tilt between the sun and the land, which reduces the intensity of midday sun to about 60% of its value at the equator (figure 6.1). We also lose out because it is not midday all the time. On a cloud-free day in March or September, the ratio of the average intensity to the midday intensity is about 32%. Finally, we lose power because of cloud cover. In a typical UK location the sun shines during just 34% of daylight hours. The combined effect of these three factors and the additional complication of the wobble of the seasons is that the average raw power of sunshine per square metre of south-facing roof in Britain is roughly 110 W/m2, and the average raw power of sunshine per square metre of flat ground is roughly 100 W/m2.”

It’s likely that we’d run out of optimally south-facing roof space long before we got anywhere near adding meaningful generation…an average 10m2 solar installation would be 22 watts per m2. I’ll let you crunch the numbers to figure out the total roof area we’d need to obtain anything like even 1GW of actual electricity cherubs.

What about wind energy?

Here’s what David MacKay has to say about that:

“The windmills that would be required to provide the UK with 20 kWh/d per person amount to 50 times the entire wind hardware of Denmark; 7 times all the wind farms of Germany; and double the entire fleet of all wind turbines in the world.”

I promise, darlings, that I’m not trying to talk down the advantages of greater renewable energy production. It’s obvious to anyone that fossil fuels in their current form will eventually run out, and that burning them to create the power we’re all hungry for releases carbon dioxide and other pollutants into the atmosphere.

But we need to be realistic about what we can achieve, in a sensible time frame and at a sensible cost – both financially and to the environment (because renewable technologies also come with an environmental cost – rare earth metals are used in solar panels for instance).

Utilising domestically sourced natural gas to generate electricity is much better than continuing to extract and burn coal, and better than burning imported Liquefied Natural Gas (LNG) which will only increase as North Sea reserves run out. Fracked gas could be part of the equation and shouldn’t be ruled out.

Simply repeating “renewables, renewables, renewables” as some sort of mantra isn’t going to make the slightest bit of difference dears.

Until next time xxx


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