Regular readers will have noticed that this blog has been very quiet over the last few months. One of the main reasons for this? I’ve been dealing with problematic audio noise which started after we had a solar PV system installed at the house.
What was the problem? And what was the solution? That’s what I’m covering in today’s Studio Diary entry. Grab a drink … this is going to be a long post.
tl;dr
We had a solar PV + battery system installed at our house in mid-January. Since then, I’ve been dealing with constant, persistent audio noise whenever our home solar inverter was connected to the house. The audio noise could clearly be heard while playing and attempting to record electric guitar.
Eventually, we discovered that our house’s Ze measurement (the resistance of our path-to-earth) was over 190 ohms. We’ve had that fixed, and it completely sorted the noise problems.
It took almost five months to discover the fault – and us both withholding final payment and threatening to reject the system for a full refund. It caused a lot of stress and disruption, and (amongst other things) left me barely playing guitar at all.
Table of Contents
- tl;dr
- How Did All This Start?
- What Did You Get?
- When Did The Problems Start?
- What Was The Problem?
- What Did You Try, To Resolve The Problem?
- How Did You Find The Cause Of The Problem?
- What Was The Problem?
- How Did You Solve The Problem?
- Why Did It Take So Long To Resolve?
- Could This Have Been Prevented?
- It Was A Very Stressful And Disruptive Time
- Final Thoughts
How Did All This Start?
In the summer of 2022, energy prices in the UK sky-rocketed, with average household energy bills more than doubling.
At the time, it wasn’t clear:
- if further price rises would happen (it looked likely), and
- how price reductions could occur (the UK is an energy importer, and therefore at the mercy of international energy markets that it has little influence over in reality)
This coincided with a UK Government that was partially paralysed by the end of the Boris Johnson🤡 era.
Competition in the UK domestic energy market ceased to exist. Some suppliers went bust. All the remaining ones set their price to the maximum allowed by OFGEM, the UK’s energy regulator.
Our house is already about as well-insulated as possible. The only way we could bring our energy bills down was to look at micro-generation with our own solar system.
What Did You Get?
This blog post isn’t about solar PV systems in general, so I’m only going to cover enough of the backstory to help explain the situation we ended up in.
We bought a solar system consisting of:
- 10 solar photovoltaic panels
- a Solis hybrid solar inverter
- a PureDrive battery
How it works is this (as best I understand it):
The Solis inverter is the brains. All the various power sources (solar panels, battery, and the mains supply) goes through the inverter. It decides how much to draw from each source, and when, in order to meet demand.
There’s an isolation switch between the house’s normal fusebox and the inverter. It’s a physical switch: we can use it to switch the house back to the mains-only feed, taking the solar inverter completely out of the circuit.
When Did The Problems Start?
Immediately.
The install started on Tue 17th January 2023. Missing parts meant that the install was paused on the following day, Wed 18th January. The solar system was able to generate, but it wasn’t complete.
As far as I know, the missing parts weren’t the source of the problem. But no-one knew that at the time, and it’s likely that it caused a lot of distraction over the coming months.
What Was The Problem?
We immediately noticed audible noise through our guitar amplifiers. It sounded like the kind of noise you get when there’s a grounding issue.
It wasn’t something that I could hide in a recording: it could be clearly heard even while playing. It was so loud, it defeated the noise gates and downward expanders that I’ve got setup on my Axe-FX 3.
And, of course, we don’t have those kinds of options on our value amps.
What Did You Try, To Resolve The Problem?
My main rig already sits in a 12U studio rack, powered by a Furman power conditioner. Other than providing surge protection, I’m not sure what practical help the Furman actually provides, to be honest.
Regular readers may remember that, last year, I rewired my studio rack? Well, I went through all of that again to make sure there were no faulty cables. I also eliminated the two longer cable runs out to the pedalboard and back, in case they were picking up EMI from the solar panels on the roof. Those longer cable runs were picking up noise from the power extension that my amps are plugged in. Sorting that out has eliminated the main cause of the noise you may have heard in audio demos in last year’s blog posts.
A local friend of mine loaned me one of those portable house-wiring test tools. Standards have definitely advanced since these old houses were last rewired, and he suggested using this tool just to make sure there were no obvious problems. The tool is quite limited in what it can do, but it found nothing that needed fixing.
I turned to a professional musician that I know, and he recommended the Tacima CS947. It’s a power extension with some electrical isolating features. We tried it, but it made no difference for this problem. I have kept it, though, because it has to be better for my gear than the standard household extension lead I was using before.
Someone pointed out that hybrid Solar PV inverters do leak a certain amount of DC onto the outgoing power cables. And someone else recommended the Audiolab DC Block for handling that. We tried that too, but it made no difference for this problem. I didn’t keep that, because it only works with gear that uses IEC connectors. I have gear – like my Fender Tweed Deluxe amp – that does not 🙁
Ultimately, the only thing that worked was to isolate the solar plant, and have the house running entirely off the regular mains supply.
How Did You Find The Cause Of The Problem?
Sheer dumb luck. Well, that and refusing to budge.
Seriously, we got lucky: the solar installation company was expanding, and one of their new hires was also a guitarist. When he came out to troubleshoot the problem, he immediately understood the problem.
He did everything he could to improve the grounding of the solar inverter, and when that didn’t solve it, he went back to basics, and checked the path-to-earth that everything (the house, and the solar inverter) were bonded to.
That’s when he discovered what was wrong.
What Was The Problem?
Our house’s path-to-earth’s resistance rating was far too high.
Our house isn’t a modern build, and like many in the area, it uses a “TT earthing rod” system. There’s literally a metal pole rammed into the ground, providing a path-to-earth to ground everything in the house.
A path-to-earth has a resistance rating, often referred to as ‘Ze’. Here in the UK, the maximum allowed Ze value is 200 ohms. (Modern regulations recommend a max Ze value of 100 ohms.) Ideally, it should be far lower than that.
When James the electrician did a Ze reading, he discovered that our TT earthing rod system’s resistance was over 190 ohms 😱 So it was legal, but way too high for modern equipment like a solar inverter.
How Did You Solve The Problem?
Here in the UK, earthing problems are the responsibility of the various Distributor Network Operators (DNO for short). They all offer a service where they’ll come out, inspect an earthing problem, and advise on what solutions are available.
You need to hire an electrician yourself to come and do an earthing check. They will give you a written report, which you can then use to contact your local DNO. In our case, we already had the information from James from the solar installer.
We contacted our local DNO (in our case National Grid, formerly known as Western Power Distribution), and told them about our Ze reading. 30 minutes later, there was an engineer knocking on our front door! (I’m assuming we got lucky, and it was a quiet day, and not that our house was overly dangerous … but the engineer did work over lunch …)
The electrical engineer was able to install a PME terminal in the house on the same visit. PME is short for Protective Multiple Earthing, and (as I understand it) it basically provides a path-to-earth via the local power grid. In the UK, PME is the gold standard for earthing. This work wasn’t free. I’m still waiting for the bill to arrive. It will be somewhere between £100-200 pounds.
(PME isn’t available to every house. It all depends on the cables that connect the house to the grid. And not every DNO can install a PME terminal so quickly either. We got very lucky there.)
After that, we “just” had to find a local qualified electrician who could switch the grounding over from the TT earthing rod to the PME terminal. (This “last mile” type activity is something that UK DNOs do not do.) That proved more difficult that it should have been, but we got there in the end.
Our Ze reading went down from over 190 ohms to below 1 ohm.
And the audible noise from the inverter was gone. Our amps now have the exact same amount of noise whether we’re connected to the solar inverter, or only connected to the regular power grid 🥳
Why Did It Take So Long To Resolve?
I’m including this information to help anyone else who is going through a similar problem.
All in all, including the time it took to switch over to PME for our earthing, it took 5 months 5 days to resolve the problem:
- Problem first reported Jan 19th
- Path-to-earth problem discovered May 11th
- House switched over to PME on May 23rd
This bit is going to be subjective, and from my point of view – so please keep that in mind.
Solar systems like ours are installed by electricians. They have relatively limited tools and processes available for troubleshooting. In software engineering terms, it’s very similar to black-box testing. In particular, no-one has equipment to look at the electrical signal itself and see what it looks like.
The noise from our guitar amps was literally the only diagnostic tool demonstrating that something was wrong. If we hadn’t been musicians, no-one would have been the wiser.
So that was the first cause. It was an unusual problem, and it fell outside the scope of your average UK electrician to troubleshoot and resolve. If the solar installer hadn’t hired an electrician who was also a fellow musician, it might never have been found.
And (I suspect) this fed into the second problem: (from my perspective) the solar installer showed reluctance to keep trying to solve it, and in mid-April tried to claim it wasn’t their problem to solve. Eventually, we took legal advice, and threatened to require a full refund under the Consumer Rights Act 2015 if the problem wasn’t resolved.
(A full refund was a lose-lose situation for both parties. Yes, we’d have gotten our money back, but we’d have been left without the solar install that we wanted. And while the solar installer could have reused the solar panels etc for another customer, they still would have lost a fair bit of money on the job.)
Fair play to them, though: at no point was there a demand for us to pay the final payment. (We’d paid something like 60% in advance. The remaining balance was due on completion of the installation. We refused to pay until the problem was resolved.) While the experience was very frustrating and stressful, it never turned outright nasty. It could have been a lot worse.
It’s also important to note that this problem was so fundamental, virtually no-one thought of it as the cause. I asked for advice online, in specialist solar groups, and from a friend at a university. My friend at the university told me about DNOs and earthing checks, but until James the electrician got involved, it didn’t make much sense to me tbh.
As far as I can tell, because our house had a modern fusebox (installed in 2021), everyone assumed that someone else had previously measured the Ze value, and that it was fine. That’s how the system is meant to work: trust that the previous electrician did everything to code.
Could This Have Been Prevented?
Absolutely.
This problem could have been caught by a simple electrical survey / health check. This could have been done before the installation, or it could have been done as part of the installation process.
Should the installer have done this? With hindsight, of course I’m going to say ‘yes’.
But, at the time of writing, it isn’t clear if there’s any regulations that require the installer to do such a survey at any time. It’s not my field, and I haven’t been able to find a clear answer to this question online.
I’m going to follow up with the relevant regulators to see if they can provide a clear answer. I don’t want anyone else to go through this kind of avoidable stress if it can be prevented.
It Was A Very Stressful And Disruptive Time
A solar PV + battery install is a serious expense. It’s a lot of money to fork out only to then have months of problems. So that alone caused a lot of stress.
On top of that, my wife and I are both musicians. It’s our major hobby. Having to choose between cutting energy costs or music was a pretty rotten feeling, and at times it did lead to arguments between us over the whole thing.
For myself, I largely gave up playing guitar or writing about it. That’s why the blog has been so quiet, and why I stopped creating audio examples for blog posts.
Earlier, I mentioned that I felt the solar installer was reluctant to keep trying to solve the problem? I was regularly chasing them to come out and solve the problem. I had to cancel travel plans, partly because I never knew if they were going to come out (they promised to call back, but never did), and (towards the end) partly because I didn’t know if we were going to have the whole thing ripped out and refunded.
Stress makes me ill. I live with an incurable autoimmune disease, and it limits how much stress I can physically tolerate. So I’ve had months of feeling increasingly worse while the whole thing was resolved.
At least it’s all over now.
Final Thoughts
I’m writing this up the evening before publication. Earlier this afternoon, I disabled all the noise gates on the Axe-FX 3 for something that I was doing. It took me an hour to notice that I hadn’t switched them back on. Things aren’t entirely noise-free, but what noise there is … it ain’t a problem for me.
At the end of all this, my little home studio is better than it was when I started. In the process of trying to solve the cause of the noise from the solar inverter, I’ve also found and sorted causes of noise that were already there.
[Update: it’s not just the Axe-FX 3 & pedals that are quiet now. Since original publication, I’ve tested my valve amps too, and I’m happy to say that they’re just as quiet as the Axe-FX 3 is.]
It’s going to take a while to get used to being able to enjoy guitar again, though.
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