It is of course very cool, such a row of solar panels on your roof. You have your own local energy factory. But how exactly does a solar system work? And how does it produce electricity? Our in-house physics teacher and Project Manager Adam explains. This time: solar panels and the grid.
HEY, WHERE ARE YOU GOING WITH THOSE ELECTRONS?
Adam: ‘Let’s start with the solar panels, I like to think from there. Solar panels convert sunlight into electricity. You can read exactly how they do that in my blog about solar cells. Electricity is actually nothing more than moving electrons. ‘ The following two concepts are important when talking about moving electrons: current and voltage. But what exactly is the difference? ‘Current is the amount of electrons per second that pass a certain point, and voltage is actually the force or the pressure with which those electrons are pushed. So they have a lot to do with each other, ‘says Adam.
Anyway, back to your own home grid: every house that is connected to the electricity grid receives electricity and that happens at a certain voltage. In the Netherlands, Belgium and Italy, that voltage is 230 volts (V).
The voltage that your solar panels generate depends on, for example, the number of panels, the type of panels, and how sunny it is. This voltage is converted by the inverter (2) to a voltage of 230 V, so that the electricity from your solar panels (1) can go to the grid. Adam: ‘You can actually see it like this. If you look at your house there are some kind of water channels. In principle, normal water comes in (5) and it has to go to all different places (4) and the intersection where the water branches off is your meter cupboard (3). And what does electricity always do? Current takes the path of least resistance.
So if power comes from your solar panels via the inverter, it really won’t feed back into the grid first. He would much rather first go to the washing machine, TV or the kitchen, just where the electricity is needed. A surplus of power at the inverter (from the solar panels) will always make up for the nearest deficit. ‘
INTO THE WIDE WORLD
Because the solar panels also supply power themselves, less power needs to be drawn from the grid. And do your solar panels supply more power than you use in your household? For example because it is a very nice sunny day, or you have very few devices on? Then the excess electricity goes into the grid. But this really only happens if they cannot be consumed in their own household first. The net is kept in permanent surplus.
Adam: ‘When this power is sent into the grid, you can see that the grid actually receives more power. But this house is no longer consuming either. So actually it becomes double: and the house is no longer consuming, and it is also back to supply. That’s annoying. If 10,000 houses do that, it will be a real problem. ‘ The mains voltage, which is normally 230 V, can normally vary by about 5 V.
Devices can handle that. But if you go to 240-250 V, many devices often don’t like that anymore. The voltage is then too high; this is bad for your devices. They will then break, so the grid operator will ensure that this does not happen.
‘If the voltage is too low, because too much electricity is being used, you can simply switch on a gas-fired power station that produces a lot of extra electricity. Then the mains voltage goes up again and every house can continue to use its electricity properly. But what if it is the other way? What are your options then? Can you switch off a gas-fired power station quickly enough if all solar panels start producing at the same time? ‘
WHAT SOLUTIONS ARE THERE?
‘It’s actually very simple, the pressure in the network is increasing, so the only thing you can do is either increase the output or reduce the input’, says Adam. ‘You can increase the output in various ways, for example, companies can turn on extra factories or network operators can encourage consumers to only use large consumers, such as the washing machine, during the day, in order to use up extra electricity from the network.
‘On the other hand, there are the options for limiting the supply of electricity to the grid:’ Firstly, you can switch off solar panels if too much is produced. There are regions, including in Belgium, where if the voltage of the grid exceeds a certain voltage, the inverters automatically switch off. An inverter also measures the grid voltage.
As a result, the inverter not only protects itself against damage, but the production of solar power is also temporarily stopped if the grid threatens to become overloaded. Secondly, you can also look at where we normally get electricity from, for example power plants or windmills. Can you turn it off for a while? ‘
A third solution is to expand or adapt the network. You can install a thicker cable, through which more current can pass at the same voltage. The power that can pass through such a cable without changing the voltage is therefore higher.
This is especially necessary in regions such as Groningen and Drenthe, where it has just been laid with the not so high population in mind. ‘We lay a cable of this thickness, so many networks, and so many transformer houses, and we’ll be fine with that. That was the idea. But when tens of thousands of households suddenly all have solar panels and start supplying them at the same time, that is not exactly built on. In addition to thicker cables, you can also expand the network, for example by connecting more users to a network, or by keeping a network more local.
STORE TEMPORARILY IN A BATTERY
And the storage options, what are they? If you can store the power that your solar panels produce in a battery, such as that in an electric car, then of course it no longer needs to be consumed on the grid. Problem solved? Adam: ‘A battery can currently store about as much energy as an average household uses in one day. Do you want enough storage to use the energy you generate in the summer in the winter, so that you can live off your solar panels all year round and never have to use the grid again? Then you now need so many batteries that half of your house will be full! So that is not yet profitable at the moment.
Batteries are suitable for compensating for the differences between day and night. The battery stores the electricity you generate during the day, which you can then use in the evening. For example, you see that batteries are very popular in Italy. The differences between summer and winter are smaller than in the Netherlands and Belgium, so you do not have to bridge that difference. A battery that absorbs the differences day to day is fine there.
But do you really want to be able to do without the net all year round in some northern countries? Then we need other types of batteries, with storage media that are more energy-dense, such as hydrogen. Various parties are currently working very hard on this.
WHO IS RESPONSIBLE?
‘The big question with all these solutions is of course, who is responsible and who takes responsibility? Consumers, companies, network operators, the government? This is currently under discussion. It is certain that something must be done if the network is about to become overstrained.
This will probably happen more often due to the energy transition. There are plenty of solutions, but the coming years will make it clear which adjustments will be made and who is participating in this. A very interesting development to keep an eye on! ‘