Depending on the model and type of consumer unit you have, it may be possible to have a trip alarm installed on the MCB for the PV panels. Ask your electrician. If, as is more likely than not, your CU doesn't support such an alarm, you could ask your electrician to rig a DIY alarm using a relay and a buzzer (I'd just make sure that the buzzer used has its own off-switch in the event that an issue with the PV cells or circuit is causing the MCB to remain open).

Such a setup would save you having to check your CU more often than you test your RCDs... You do test them, right?

No, nobody ever told me I was supposed to test them.

I'm not surprised. That last remark was somewhat tongue-in-cheek; most people never test their RCDs. But it is recommended as they can fail. Depending on whom you ask, you should test your RCDs every three to six months.

I don't know your particular setup, but I'm going to assume you don't have RCBOs. You may have a whole-house RCD (although these are deprecated and increasingly less common and if you did I hope that whoever installed your solar panels back in 2012 would have advised you to have it changed) or, more likely, a number of RCDs each protecting a bank of MCBs. A typical arrangement in the UK is to have two RCDs: one protecting the downstairs and kitchen ring final circuits (or their radial equivalents) and the upstairs lighting circuit and another protecting the upstairs ring final circuit and the downstairs lighting circuit (the idea being that if an RCD tripped at night you would still have lighting available on both floors of your house through a combination of the main lights and plug-in lamps). Your RCDs should have a test button (typically though not always coloured red) and, depending on their design, possibly a reset button.

The test button will create a high-resistance short between line and neutral (simulating an earth fault), allowing only a slightly higher current to leak than the trip threshold for the RCD, which most commonly – and importantly for shock protection – is 30mA or less. If your RCDs protecting ordinary circuits have a higher trip threshold, have them replaced. The trip time for the RCD should be 40ms or less, so if there is a perceptible delay between you pressing the test button and the RCD opening, contact your electrician.* For an RCD with a reset button, you will need to press that first to open the test switch before you can close the RCD switch and re-energise the MCBs protected by it.

The reason most people do not test their RCDs (in addition to them not being bothered or forgetting like with testing smoke detectors) is that it isn't a test free of inconvenience. Testing an RCD involves de-energising the circuits it protects. Not only does it switch off any electrical devices that were powered immediately beforehand, but it will also require any mains-powered devices with clocks and without a battery to have their clocks reset (e.g., microwave ovens but also, by the sounds of it, your bedside alarm clock). Depending on the type and wiring of your burglar alarm, if it's protected by an RCD then opening that could trigger the alarm or require it to be reset (though, if this happens, I'd ask your electrician to take a look at the alarm's wiring). That said, if ever you have cause to open the main switch in your CU, then there's no real inconvenience to first testing the RCDs.

* Of course, even if you do not perceive a delay that does not mean the RCD is tripping within the required limits. Electricians have equipment that can verify the RCD trips within the required current and time thresholds. The onboard test feature of an RCD just indicates there's an issue if the switch doesn't open immediately upon pressing the test button.

My box is very complicated . There are six separate breaker switches for lighting and power on the two floors, plus the shower and the solar panel, and two extra red switches (which seem to be joined together) and one black one which are not labelled. I assume that these are masters of some sort. No buttons of any kind.

Your CU doesn't sound atypical (apart from the possible lack of RCDs...). The red, double-pole switch is the main switch. It's difficult to know about the unlabelled switch without seeing a photo of your CU.

The typical (at least more modern) CU arrangement in the UK, as I described in my previous post, looks like this.

You can see a photo of an actual CU here (note, this is not the most modern design). From right to left, you have the main switch (red), then an RCD (with the yellow test button, labelled with a 'T'), then a bank of MCBs, another RCD and another bank of MCBs. But they can all have slightly different appearances.

It's possible you have a whole-house RCD coming off the main switch that protects all the MCBs. Does the unlabelled breaker appear to be taking up two ordinary breaker spaces? I've not heard of an RCD without a test button, but I suppose if it's a really old installation then it may be of a design which wasn't required to have an onboard test function. I doubt that's legal now, however.

I'm not an electrician and my knowledge of BS 7671 (the wiring regulations) is limited. But the regulations have made RCDs increasingly mandatory for most circuits (e.g., in the latest 18th edition, RCDs are explicitly required for lighting circuits, as opposed to the previous implicit requirement that resulted from how most lighting circuits were run). Whilst normally previously compliant installations are given grandfather rights, the regulations normally require installations to be brought up to regs for modification work, etc. I would be very surprised if the 17th edition of the regulations in force in 2012 permitted an electrician to install new circuits and add them to a CU which provided no RCD protection for any of its circuits whatsoever. If you didn't have any form of RCD in your CU, I would think that the electrician that installed your solar panels would have quoted for the remedial work and if you rejected the remedial work he would have refused to install your solar panels.

I don't have the tech to take a photo, but the red double switch is at the extreme left. It is labelled 100 amps. The single black switch at the extreme right is labelled RCD. I thought they were all RCD's! No yellow buttons.

Which is the master mains switch? I suspect the other one is for the immersion heater.

The main switch can be on the left or the right of the CU. The red switch labelled 100A is definitely your main switch.

By the sound of it, you've got a single RCD protecting all your MCBs. That's less than ideal, but I think it still may be legal (although would be frowned upon even twenty years ago). There should be some kind of test button on it; it may not be yellow or red – I think it can be any colour and I've certainly seen white, grey and black test buttons too. If it's old, it may be an inconspicuously small button. Ideally it should be labelled in some way (even if it's just with a 'T'), but again depending on the age of your installation it may not be. I know I'm stating the obvious, but when you're taking a look at something new, it's easy to forget the obvious things: don't go testing it when it's dark unless you have a torch on your person.

Only some modern installations combine an MCB with an RCD into one breaker (known as an RCBO or residual current circuit breaker with overcurrent protection), and even then most modern CUs still use RCCBs (a residual current circuit breaker) that protect a bank of MCBs. (Strictly speaking, RCD is just a generic term for any device that detects an imbalance of current between the line and neutral that, over a certain threshold, opens the switch. There are multiple types of RCD, including the RCCB and RCBO. But given the proliferation of RCCBs in consumer units as the predominant type of RCD, the terms are often used interchangeably).

Yes, I've found it. It's a tiny black circle above the RCD with a T on it. It doesn't look like a button at all.