The grid must balance every second
- A power station makes a little moreThe wires carry it across the countryYour kettle draws it
All in the same instant. Electricity is not stored in the wires. When you switch on a kettle, a power station somewhere has to make a little more that same instant. The wires that join every power station to every socket in a country are called the grid. Every second, what is made must equal what is used.
- 0 units97 units194 units4amMidnight
A country like Britain on a winter day, with the night's low set to 100. Use changes all day. It is lowest at about four in the morning, jumps at breakfast, and peaks around six in the evening when dinners cook and lights come on. Someone has to have stations ready to switch on for that peak, and off again by midnight.
- Used at 4 in the morning100 unitsUsed at 6 in the evening173 units
At six in the evening people cook and turn the lights on. What must the grid do at that moment?
Make more electricity at that moment, by switching more stations on.
Right. Nothing was saved from the quiet night; what was made at four was used at four. The extra 73 has to be made now, by something that can be told to start.Use electricity saved up from the quiet night.
Not yet. A grid stores almost nothing. The wires hold what is flowing through them and no more. Whatever was made at four in the morning was used at four in the morning.Nothing. The wires hold plenty.
Not yet. The wires hold nothing at all beyond what is passing through them this instant. If more is drawn than is made, the whole grid's rhythm slips and stations start switching off to protect themselves. - 6 in the morning0%9 in the morning40%Noon100%3 in the afternoon60%6 in the evening5%9 at night0%
How much the panels make through a clear summer day, as a share of their best. Now add the sun. A solar farm makes most at noon and nothing at night. It does not care that dinner is at six. Wind is stronger in some hours and seasons than others, and it can drop for days. Both are cheap to run, because the fuel is free. But you cannot switch them on.
Set the hour of the day and how much solar the country has built. The numbers are made up but the shape is real.
People want125 unitsThe sun gives0 unitsOther stations must fill125 units6 in the morning · A little6 in the morning: people want 125, the sun gives 0. Other stations must supply 125.
People want125 unitsThe sun gives0 unitsOther stations must fill125 units6 in the morning · A lot6 in the morning: people want 125, the sun gives 0. Other stations must supply 125.
People want125 unitsThe sun gives0 unitsOther stations must fill125 units6 in the morning · Huge6 in the morning: people want 125, the sun gives 0. Other stations must supply 125.
People want155 unitsThe sun gives40 unitsOther stations must fill115 unitsNoon · A littleNoon: people want 155, the sun gives 40. Other stations must supply 115.
People want155 unitsThe sun gives120 unitsOther stations must fill35 unitsNoon · A lotNoon: people want 155, the sun gives 120. Other stations must supply 35.
People want155 unitsThe sun gives250 unitsOther stations must fill−95 unitsNoon · HugeNoon: people want 155, the sun gives 250. There is 95 more than anyone wants; it must be stored, sent away or wasted.
People want173 unitsThe sun gives2 unitsOther stations must fill171 units6 in the evening · A little6 in the evening: people want 173, the sun gives 2. Other stations must supply 171.
People want173 unitsThe sun gives6 unitsOther stations must fill167 units6 in the evening · A lot6 in the evening: people want 173, the sun gives 6. Other stations must supply 167.
People want173 unitsThe sun gives12 unitsOther stations must fill161 units6 in the evening · Huge6 in the evening: people want 173, the sun gives 12. Other stations must supply 161.
People want118 unitsThe sun gives0 unitsOther stations must fill118 unitsMidnight · A littleMidnight: people want 118, the sun gives 0. Other stations must supply 118.
People want118 unitsThe sun gives0 unitsOther stations must fill118 unitsMidnight · A lotMidnight: people want 118, the sun gives 0. Other stations must supply 118.
People want118 unitsThe sun gives0 unitsOther stations must fill118 unitsMidnight · HugeMidnight: people want 118, the sun gives 0. Other stations must supply 118.
With a huge amount of solar, what happens at noon and at six in the evening?
Solar covers the evening peak and floods the night.
Not yet. The evening peak is the hardest hour for solar, not the easiest: the sun is nearly down. At night the panels make nothing at all, so there is no flood to have.Solar covers both, if enough is built.
Not yet. Building more helps at noon, where there is already too much. At six the panels make 5 in 100 of their best, so even the huge setting leaves a gap of 160 out of 173.At noon there is more than anyone wants. At six the gap is nearly as big as with no solar at all.
Right. The sun gives about 5 in 100 of what the panels could at six, however many panels there are. Twenty times more panels still gives little at dinner time, and a flood at noon that has nowhere to go.Move both controls.
- A typical grid battery4 hoursA pumped water store10 hours
How long each can keep giving power at full rate. A dull, windless week is 168. There are three ways round it. Store the noon surplus, in batteries or by pumping water uphill, and use it at six. Run long wires, so a windy coast feeds a calm city. Keep gas or river stations ready to switch on. Each costs money, and that cost is not in the price of a panel.
- Wanted at the peak40 unitsFrom the sun at that hour2 unitsFrom the wind that evening8 units
A country's evening peak is 40 units. Solar gives 2 units at that hour. Wind that evening gives 8. How many units must other stations supply?
unitsRight. Thirty of forty from stations that can be switched on. On another evening the wind might give 25, or 1. The backup has to be sized for the worst evening, not the average one. Solar panels made about what share of the world's electricity in 2023?
Pick one. Nothing is scored.
0%3.1%6.2%20132023Solar's share of the world's electricity. About 6 in 100.Guesses run high because solar is in the news and on the roofs you can see. About 6 in 100 in 2023. But it was about 1 in 100 ten years earlier and has been doubling roughly every three years. The share is small and the slope is steep. The next lesson is about the slope.- Panels built to make twice the year's useNine in the evening, every evening
A sunny desert country builds enough solar to make twice the electricity it uses in a year. Can it close its gas stations?
Yes. Twice what it uses is more than enough.
Not yet. The grid balances every second, not every year. Twice the year's total, all made in daylight, is a noon flood and a midnight gap. The gap is what the gas stations were filling.Not on its own. Nights and cloudy weeks still need power the panels are not making at that moment.
Right. A year's total is not an instant. At nine in the evening the panels make nothing, whatever the year's total says. Without a store, a long wire or a station on standby, the lights go out at nine.Yes, if it sells the extra at noon.
Not yet. Selling the surplus brings in money. It does not put power in the wire at night. Money is stored easily; electricity is not.
Lesson complete
Electricity is made the instant it is used. A source you cannot switch on needs another that you can.