Home energy monitors in the UK: measure your base load before plug-in solar
Before you worry about panel wattage, batteries or whether a plug-in solar kit is worth the money, it helps to understand one simple thing: what your home is already using.
A good home energy monitor can show your real-time demand, your overnight base load and how your usage changes through the day. That makes it far easier to judge whether plug-in solar, a battery or a wider solar setup is likely to help in a meaningful way.
Short answer: yes, an energy monitor can be genuinely useful.
Why? Because it shows what your home is doing in real time. That makes decisions about plug-in solar, battery storage and energy-saving upgrades far more evidence-based and far less guesswork.
On this page
If you have already read my guides on whether plug-in solar is worth it in the UK, plug-in battery storage and backfeed and export, this page sits underneath all of them.
The reason is simple. Before you can make sense of generation, self-consumption or storage, you need a clear picture of the load side of the equation.
What is base load?
In plain English, your base load is the electricity your home keeps using even when nothing obvious seems to be happening.
It is the background demand that never fully disappears. That might include your fridge, freezer, broadband equipment, alarm systems, controls, standby supplies, AV equipment, chargers left plugged in and all the little electronic loads most houses accumulate over time.
On top of that base load, you then get temporary peaks when a kettle, oven, shower, washing machine, dishwasher, immersion heater or other larger appliance starts pulling serious power.
Why it matters: if your background demand sits around a few hundred watts for much of the day, a modest solar setup may be used quite efficiently. If your base load is very low, you may find that even a small plug-in solar system produces surplus energy more often than you expected.
What is a home energy monitor?
A home energy monitor is a device that tracks electricity usage in real time and presents it in a way that is easier to understand than a monthly bill.
Depending on the product, it may show live power in watts, accumulated energy in kWh, historical trends, peak periods, import patterns and sometimes separate channels for different parts of the installation.
In practical terms, the most useful monitors let you answer questions like these:
- What is my house using right now?
- What is my overnight base load?
- When do my biggest demand spikes happen?
- Would a small solar setup mostly cover existing load or produce excess energy?
- Is there an appliance or circuit using more power than I expected?
For readers looking at products such as the Shelly EM or EcoFlow Smart Meter, that is the real value. They are not magic money-saving boxes on their own. They are measurement tools that help you make better decisions.
How CT clamp energy monitors work
Most domestic energy monitors used for whole-home tracking rely on a CT clamp. CT stands for current transformer.
The clamp fits around a conductor and measures current without needing the conductor to be cut. The monitor then uses that measurement, along with voltage information or an assumed supply voltage depending on the device, to calculate or estimate power and energy use.
Diagram 1: basic idea
Diagram 2: what you learn
In domestic use, the clamp is often fitted around one of the main tails so the monitor can see the overall house demand. Some systems can also watch additional circuits or generation channels if the hardware supports it.
That is why devices such as the Shelly EM are popular. They offer a relatively simple way to see what is going on electrically, without needing a full commercial metering setup.
What an energy monitor can show you in real life
The most useful thing about proper monitoring is not just the live number on a screen. It is the pattern over time.
Once a monitor has been in place for a few days or weeks, you can normally start to see:
- your overnight background demand, which is often the clearest indicator of base load,
- your regular morning and evening peaks,
- whether an immersion heater, EV charger or electric heating is dominating usage,
- whether standby and always-on loads are higher than you thought,
- how much headroom there may be for small-scale solar self-consumption.
Practical takeaway:
Most people are better at estimating their annual bill than they are at understanding their real-time load profile. For solar decisions, the load profile is often the more useful piece of information.
Why this matters before plug-in solar or battery storage
This is the part that links directly back to the rest of the site.
A small solar system helps most when its output lines up with demand already present in the property. If your house is sitting at 250W to 400W for a good part of the day, a modest solar setup may be able to cover a decent proportion of that demand. If your daytime load is much lower, the economics may look different.
That matters for all of these questions:
- Is plug-in solar actually worth it?
- Can you really plug solar into a normal socket?
- Would a battery help, or just add cost?
- How much energy might end up flowing back towards the grid?
If you know your base load, those conversations become much more grounded. Instead of saying “I think we use quite a bit during the day”, you can start saying “our house idles around 300W overnight and climbs sharply at breakfast and in the evening”. That is a much better starting point for system planning.
Shelly EM, EcoFlow and similar monitors
There are a few different types of products in this space.
Some are general-purpose CT clamp energy monitors aimed at tracking circuits or whole-home demand. Others are more ecosystem-based products that are designed to feed data into a wider battery or home energy management platform.
The Shelly EM is a good example of a compact, widely used monitoring device that can give you useful visibility of household demand. EcoFlow's Smart Meter sits a little differently, because it is designed to work more closely with EcoFlow's wider energy ecosystem.
My view: for most readers of this site, the important thing is not brand loyalty. It is whether the monitor gives you a clear picture of your demand, whether it suits the installation, and whether the data it provides actually helps with your decision-making.
How these monitors are usually installed
In the simplest arrangement, the CT clamp clips around an accessible main tail feeding the consumer unit. That is often the neatest way to get a whole-house view of demand.
In some properties, that may be straightforward because the tails are accessible in a suitable enclosure or meter arrangement. In others, there is no sensible external access and the only realistic place to fit the clamp is inside or immediately around the consumer unit area.
Important safety point:
If the CT clamp cannot be fitted safely on accessible tails and the work needs to be done inside the consumer unit, that is not a casual DIY job. At that point it should be treated as electrical work for a competent electrician.
That is the right line to take with domestic readers. The clamp itself may be non-intrusive in principle, but that does not mean every installation location is safe for a homeowner to access.
So the practical rule is simple:
- if the tails are safely accessible and the product instructions are clear, installation may be straightforward,
- if access is restricted, cramped, exposed or only realistically possible within the consumer unit, get an electrician to do it,
- if you are not fully confident about identification, safe isolation, enclosure access or the environment around the main supply, do not guess.
Diagram 3: preferred simple arrangement
Diagram 4: when to stop and call an electrician
What an energy monitor does not tell you on its own
A monitor is useful, but it is not a substitute for wider electrical understanding.
It does not confirm that a proposed plug-in solar setup is legally acceptable. It does not replace DNO requirements. It does not answer protection-device questions. And it does not remove the need to think properly about backfeed, earthing, connection method and product suitability.
That is why it is worth reading this page alongside:
Is a home energy monitor worth it?
In my view, yes — especially if you are about to spend money on solar, batteries or other energy hardware and you still do not have a clear picture of your own usage.
It is not the first thing every household must buy, and it will not transform the economics of a system by itself. But as a planning tool, it can be one of the more useful pieces of kit you fit.
The better your understanding of your own demand, the easier it is to spot where solar helps, where storage may help, and where you are simply adding hardware without solving the right problem.
The bottom line:
If you are considering plug-in solar or a battery, a proper energy monitor can help you understand your base load, your daily usage pattern and your likely self-consumption. That makes it one of the most sensible places to start before making bigger decisions.
Common questions
Can an energy monitor help size plug-in solar?
It can help you make a more informed judgement, yes. It will not design the system for you, but it does show whether your house has a steady background demand that small-scale generation is likely to offset.
Can I use a smart plug instead?
Smart plugs are useful for checking individual appliances, but they do not replace whole-home monitoring. A CT clamp monitor gives you a much better picture of the total load seen by the installation.
Is the Shelly EM enough for most domestic readers?
For many homes, a simple monitor of overall demand is already enough to learn something useful. The right product depends on what you want to measure and whether you need integration with a wider ecosystem.
Can I fit a CT clamp without opening the consumer unit?
Sometimes yes, sometimes no. It depends entirely on whether there is safe access to the tails or conductors that need monitoring. If the work has to go inside the consumer unit, that is where an electrician should take over.
Related guides on PluginSolarHub
This page is intended as practical guidance, not a substitute for manufacturer instructions, current standards or competent installation work. Product features, layout and installation method vary. Where monitoring equipment needs to be fitted inside or around the consumer unit, use a competent electrician.