Making hay while the sun isn't shining

"Make hay while the sun shines", as the saying goes. But what happens when the sun shineth not? That is the £64m question.

Making hay while the sun isn't shining

What do we do when the sun is not shining, be that at night, when it is pouring with rain, foggy or just plain old fashioned British miserable?

Thanks to the fantastic weather the past few days, solar PV has been providing a reasonable amount to the supply. For the past week, there has been a peak supply of around 6GW every day, a peak at midday in a classic bell distribution curve of course. However, at the same time, wind has been struggling due to the low wind speeds (associated with large High pressure systems) and this morning when I snapped the attached graphs Wind was only providing 0.29GW (0.78% of demand).

Now, it is this variability in supply that is the Achilles Heel of so called 'renewables' (personally I hate the term along with 'carbon-free', preferring 'sustainable' - but that's a discussion for another day). In order to maintain a balanced supply for demand, we have to have backup generation for every KW of solar and wind. At present, this comes from gas and coal plus pumped hydro or even diesel generators.

The big change in the sustainable energy industry has got to be development of energy storage systems.

Imagine a worst-case scenario. Massive high pressure situated over the UK, average wind speed around the country less than 10mph and banks of thick fog rolling over the southern half of the country (where many of our PV stations are located). No problem right now as we can fire up extra gas turbines and get the coal boilers going to cover. Imagine, though, we had turned off and demolished all the coal stations and were in the process of decommisioning all the old gas stations (say, halving gas capacity) - what now?

Boom. The lights go out, industry grinds to a half and we all lose the Internet as our Wifi routers switch off. Panic.

OK, maybe not quite that dramatic, but we could be faced with a shortfall in supply to meet demand. Rolling blackouts could be required, or heavier industrial users might be requested to power down to preseve supply particularly overnight as we lose whatever watts solar PV might be providing through the fog or from more northern sites.

Pumped hydro might be able to provide a short-term supply but, once the upper reservoirs are empty, would there be enough power available to pump the water back uphill? We might be able to squeeze a few more GW from our nuclear stations but do we want to run the reactors at 100% (imagine red-lining your car engine for a prolonged time).

Right now, there is not enough energy storage capacity in the country to last more than a few hours. While batteries do provide a storage option, they are not suitable for long-term supply. If you have a 200amp-hr battery (50% depth of discharge to avoid damaging it gives 100amp-hrs usable supply) and a 10amp-hr solar supply, it takes 10 hours to recharge the battery (from 50% depth of discharge). As the bell curve of solar PV shows, you only get peak supply (10amps in this case) for about two hours either side of midday (see my blog with my real-world figures to see how a basic 12v set up with a 135amp-hr lead acid battery and two 35w solar panels performed). In order to recharge your hypothetical 200amp-hr battery (from 50% depth of discharge) you would need a full 16-hour day of bright sunshine with zero demand on your battery. If it was foggy or raining, you would be looking at days to recharge. That's physics and "you cannae change the laws of physics, Captain!"

To avoid this nightmare scenario, we have got to start developing large-scale energy storage. Be that converting traditional hydro into pumped hydro, building new pumped hydro, building cryogenic and compressed air storage, developing new and fancy battery technologies, installing domestic battery systems (think big, uninteruptable power supply units) or other technologies, so that the UK has enough energy stored to meet full demand for several weeks not just a few days.


Topics: Renewables
Tags: | coal | energy storage | Fire | gas | nuclear | renewables | solar | water | weather
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