Smart meter and solar panels: what you need to know

A smart meter is the digital successor to the old rotating-disc or push-button meter. It measures how much electricity you consume and, since you installed solar panels, also how much you feed back to the grid. The big difference from the old meter is that it passes on the readings automatically and remotely to your grid operator. You no longer have to read the meter yourself and phone it in or type it in.

For households with solar panels it is particularly important that the smart meter registers two flows separately. The power you draw from the grid and the power you feed back each have their own counter. That way it is known exactly how much you have drawn and how much you have supplied, and your energy supplier can base a correct bill on it.

The smart meter is by now present in the vast majority of homes. If you do not have one yet, the grid operator offers one free of charge. When installing solar panels, a suitable meter is in fact essential, because without a meter that can track feed-in your bill will not be correct.

When your panels generate more on a sunny afternoon than you are using at that moment, the surplus goes onto the grid. The smart meter adds that fed-back power to a separate counter, often referred to as feed-in or supply to the grid. When you later draw power from the grid, the other counter runs up, the one for consumption.

In practice this produces four readings: consumption and feed-in, each split further into an off-peak and a peak tariff if you have a two-rate tariff. You see those readings on your annual bill. The grid does not work as a battery that simply nets things off, but as a conduit along which two directions are counted separately.

Important to understand: a smart meter does not run backwards. The old analogue meter did, it literally ran in reverse when you fed in. That image no longer applies with a smart meter. Instead, the feed-in ticks up on its own counter, and only at the time of billing is it determined what you pay or receive at the bottom of the bill.

An old analogue meter is designed to measure power in one direction: from the grid to your home. As soon as your solar panels feed back, the power goes the other way, and that is where things go wrong. Some analogue meters simply run backwards; others wrongly add the feed-in to your consumption. In both cases the measurement is no longer correct.

A backwards-running meter may look favourable at first glance, but it does not give a clear picture of what you are drawing and feeding back. For a correct bill and for the transition to the new net-metering rules, a meter is needed that tracks both directions separately. That is why the grid operator replaces an unsuitable meter with a smart meter as soon as you put solar panels into service.

You do not arrange that replacement yourself and as a rule you do not pay for it separately either: the grid operator installs and places the meter. So always register your solar panels, so that your connection is correctly recorded. If you do not, you run the risk of your measurement and bill being wrong.

One of the nicest features of a smart meter is that you can see what is happening. On the meter itself you can read the various readings with the buttons. More convenient is the P1 port: a connection at the bottom of the meter to which you can attach a readout device or energy manager. That device sends the data to an app, so you can see your consumption and feed-in live on your phone.

With such an app you get a grip on your energy. You can see when your panels are generating the most, when your surplus is going to the grid and when you are drawing from it. These insights help you shift appliances such as the washing machine, the heat pump or car charging to the hours when the sun is shining. That way you use more of your own power.

Besides a separate readout device, many energy suppliers and inverter manufacturers also offer their own apps. The inverter app mainly shows what your panels are generating; the meter app shows what you are drawing from and feeding back to the grid on balance. Together they give a complete picture. If you want that readout capability, have a suitable setup included straight away when the installation is done.

For years you could fully offset your fed-back power against your consumption, so-called net metering. As a result it made little financial difference whether you used your generated power directly or only fetched it back from the grid much later. That scheme is now being phased out and is expected to end within the foreseeable future; always check the current state of play.

Once net metering disappears, feed-in becomes considerably less valuable than the power you buy yourself. Then what the smart meter tracks so neatly becomes important: how much you feed back and how much you use yourself. The more of your generated power you use directly in the home, the less you send onto the grid for a low rate. You can read the sums behind that calmly explained in our article on the end of net metering.