DIY ground mount solar PV install

[H F]

On 16/12/2018 at 20:39, ProDave said:

This thread is to document the (probably slow) DIY installation of my ground mount solar PV

 

I have just bought the panels  I will be using 16 250W panels for the main 4KW array facing south which will leave me 2 spares that I will probably set up independantly on a small inverter facing east.

 

Amazing. DIY solar. Now that's aspirational for someone like me!

[ProDave]

2 minutes ago, Home Farm said:

 

Amazing. DIY solar. Now that's aspirational for someone like me!

It's the only way for it to be viable now there is no longer any Feed In Tariff payment.

[Ed Davies]

On 18/03/2019 at 14:34, ProDave said:

So continuing with the above post, I am now thinking of fitting these 2 spare panels.

 

As I have decided on one facing E and one facing W to try and squeeze a bit more out of both ends of the day, my thought are turning to a suitable inverter and how to connect them.

 

…

 

So how to connect them?

 

I would say connect them in parallel, as only one will be generating at a time.  The question is what effect witll the non generating panel have?  Will it zap some of the power or just sit there as a high impedance load doing nothing?  Should I put s series diode in series with each panel so only the higher voltage panel does anything and the other cannot back feed and zap power?

 

Someone must have done this befoe and know how best to connect them.

 

 

Just come across this video with some nice demonstrations of the effect of shading parts of a panel when there are two connected in series or parallel. If shading is likely to be a problem (as in @ProDave's case it definitely is) then this confirms that parallel is the right answer.

 

https://www.youtube.com/watch?v=1qD3mN8VotQ

 

Their results are very much in line with what I'd expect.

[ProDave]

A couple of weeks back, I noticed there was nothing being diverted to my immersion heater.  A quick check in the shed revealed the main inverter was showing "Grid disconnected"  further investigation found the 32A mcb feeding the shed had tripped (but not the 16A inverter MCB in the shed)  So I reset that and the main inverter powered up again.

 

The cause of the trip was the little cheap Chinese inverter connected to my 2 spare panels had blown.

 

Having failed at just under 2 years old I was not particularly liking the idea of buying another, but there is nothing else available anything like as cheap.  So time to take it apart and see if a repair was possible.

 

Inside a PCB mounted fuse was blown and some basic testing found that 2 of the transistors that make up the H bridge that synthesises the output waveform were blown, short circuit.  So i ordered 5 of them from ebay from China for £5

 

They arrived yesterday and i fitted them and cautiously powered it up and it's working again, so this morning I put it back into service.

 

It will be interesting to see how long it lasts before failing again.  What I did notice is they were very short on the heat sink paste, with it only applied to one side of the insulating washer, so it's pasted up a bit better now.

[ProDave]

Another observation about my repair of the cheap little Chinese inverter.

 

When testing it, I found it's output is pulsed, in very much the same way as my solar PV dump controller is. And just like that it appears the duty cycle is varied to adjust the power output.  I wasn't expecting this.  I guess it makes it easy to design the inverter as it only has to synthesise a simple grid sychronised output and vary the power by pulsing it on and off.

 

I wonder if the big "proper" inverters work the same way or not?

[newhome]

What’s the break even position on this now @ProDave? Must be a bit more favourable? 
 

[ProDave]

My original prediction was to self use £250 per year giving a 6 year payback.  Last year that was up to £300 and this year post April is likely to be £400 per year, so is likely to bring payback to perhaps 4 years.

[joe90]

4 hours ago, ProDave said:

so is likely to bring payback to perhaps 4 years.

I am seriously thinking of doing like @ProDave as I have a south facing garage roof at 30’ that will take the panels, as many of you know i don’t do “tech” (Luddite me), but have been wondering if I timed the ASHP to only work between 10 am and 4pm then it will likely use excess lecky if it’s sunny and dump heat into my slab (if the room stat requires it) or the DHW cylinder( if the cylinder stat requires it.) Any excess after that will dump into an immersion in the DHW cylinder. I don’t fancy batteries yet but want to use or store as best I can without them. 🤷‍♂️

Edited April 7, 2022 by joe90

[ProDave]

An update and a milestone.

 

Each week I log all my meter readings, import usage, PV generation, ASHP consumption etc.

 

Today, entering the figures into my spreadsheet revealed that I have self used £1499.79 worth of electricity since installing the PV.  That has taken 4 years and 16 weeks to achieve that.  It's all free now baring equipment breakdowns,

 

That is shorter than the initial estimate of 6 years, due to the higher cost of electricity now.  If electricity had been as high as it is now right from the start, payback would have been just 2 1/2 years.

 

Starting to think of an addition to the system now.........

[Radian]

4 hours ago, ProDave said:

Starting to think of an addition to the system now.........

Kind of addictive innit!😊

Great result. I have to wonder how much in total it generated i.e. what percentage self-use you achieved. Might the most cost effective addition be one that gets you  100% utilisation for instance?

[ProDave]

In the 4 1/2 years, the total export (i.e. wasted) is standing at 334kWh (I have fitted my own export meter)

 

Export happens when generation exceeds what the immersion heater can consume and nothing else in the house is using power.  For a lot of the year I also dump to a small convection heater that is turned on when that situation arrises, but in the summer that is disconnected (though I could out of spite just move it to the garage)   More export happens on the occasions when the immersion heater thermostat has cut out when the tank reaches maximum capacity.

 

If I was able to get paid for the export at the silly low 5p per kWh that would only have earned £16.70  If I had a smart meter and signed up to one of the more lucrative export payment deals, that might have earned perhaps £50 in export.  But any export payment would require it to have been an MCS install.  Clearly the extra of an MCS install vs DIY would NEVER repay itself in export payments.

 

If I add more PV that will be with battery storage, that is another topic for the future, I have to build the car port first where it will likely be mounted.

[JohnMo]

Just shows the benefits of self install, save money in the first place on initial install, then a few years later you are in profit. Even in the north of Scotland.

 

Out of interest had a quick look at my export, since my new meter was installed last year I have exported 131kWh, the previous meter was at about 36kWh. So 170kWh in a couple of years. Generation stands at just about 3000kWh

 

The excessive export is mostly due to the immersion diverter failing.

 

Mine also is a self install so get no export payments. Certainly don't regret the none MCS install.

[Dillsue]

On 20/05/2023 at 08:37, ProDave said:

(I have fitted my own export meter)

Interesting. Would that be a standard dumb digital meter wired in reverse??

[ProDave]

1 hour ago, Dillsue said:

Interesting. Would that be a standard dumb digital meter wired in reverse??

Yes exactly the same as my generation meter.

 

 

Note the writing on it to avoid misunderstanding with any meter reader. 

 

Note also my import meter is displaying rED  that means Reverse energy Detected (the small amount of export)  It alternates between that and the import reading.  Nobody has raised this as an issue yet.

[Dillsue]

4 hours ago, ProDave said:

Note also my import meter is displaying rED  that means Reverse energy Detected (the small amount of export)  It alternates between that and the import reading.  Nobody has raised this as an issue yet.

Ours displays RED too on account of the not so small ammount of export. I read somewhere a bit ago that your style of meter(ours to) actually records energy flow in both directions but can only display one figure. I have it in my head that there is a way to display the second figure but can't remember how to change it or where I read it!!

[ProDave]

It can be read via the IR port, that red flashing light is one of 2 IR sensors / receivers and the right gadget can read all the data.

 

The rED thing was initially there to detect people trying to reverse the meter in the hope it would run backwards.

[Radian]

On 20/05/2023 at 08:37, ProDave said:

 More export happens on the occasions when the immersion heater thermostat has cut out when the tank reaches maximum capacity.

 

It's an interesting game. Play it right and you might save a whole tenner! Seriously though, batteries are the only practical solution but it's a toss-up for anyone over the age of 65 to ever see a payback. For this reason I'm on the lookout for ways to eek every last drop of self-use out of our investment.

 

Until I actually had a few kW of generation available, It wasn't so obvious to me that appliances with resistive heaters could do with being less 'Watty' i.e. I wish we'd bought an 1800W kettle when we replaced our old one recently. The thing is, with a G98 three-and-a-bit kW array, even on the best days if you stick on your standard 3kW kettle, you'll nearly always be paying for some amount of imported energy. Sure you could have more PV with G99 but without a decent export tariff or batteries it's just more wasted investment. So with a more modest G98 three and a bit kW, most of the time a dishwasher or washing machine goes on, you're going to be importing. Typically plug-in appliances tend to have 2.5kW resistive heaters to get the maximum out of the available power to accomplish the task in the minimum amount of time but this doesn't leave much headroom. And it also requires a little care in staggering their use.

 

This would therefore be so much simpler if they had more modest power requirements - I really couldn't care less if the wash cycle took twice as long if it meant I didn't see little import spikes on a sunny day. I did try this when testing my PV diverter using the kettle - a lot of pulsing but it got there after a couple of minutes. Fine! The same principle of incorporating PV diversion into other 'Watty' appliances would be the ideal solution, and while I doubt this could ever be commercialized, I could easily retrofit a few of my own appliances - were it not for the fact that many manufacturers controllers flag an error if a water heater doesn't respond in the time expected. "Solar friendly" gadgets might make a market appearance but I doubt it (solar immersions are an exception).

[Dillsue]

13 minutes ago, Radian said:

The thing is, with a G98 three-and-a-bit kW array, even on the best days if you stick on your standard 3kW kettle, you'll nearly always be paying for some amount of imported energy. 

I think/hope you already know this but G98 restricts your inverters export capacity, not the size of the array. Within the inverters limits,  put a bigger array up and your G98 inverter can sit at 16amp(3.68kw) output for much of the day. Don't switch big loads on at the same time and there's not much in a typical house that will need more than 16amp.

[Radian]

11 hours ago, Dillsue said:

I think/hope you already know this but G98 restricts your inverters export capacity, not the size of the array. Within the inverters limits,  put a bigger array up and your G98 inverter can sit at 16amp(3.68kw) output for much of the day. Don't switch big loads on at the same time and there's not much in a typical house that will need more than 16amp.

I guess I used a poor way to describe the size of the generating system. of course you're right to point out that the limit is with the inverter but the motivation here is to maximise the use of a minimal resource. I don't actually have any prime roof space left for an array so even if I did add more modules, they would be partially shaded.