Adding a single panel and micro inverter on the QT?

[Jeremy Harris]

I'm part way through building a stone box a few metres up from our treatment plant, alongside the drive at the top of a steeply sloping section.  The box has two halves, sealed from each other, a top entry compartment that will hold the air pump and alarm unit and an open-fronted compartment (with a roof overhang and the floor sloped slightly outwards) to hold two or three bags of rock salt, as the drive becomes impassible with even a thin layer of snow, I've found.

I was semi-thinking of fitting a battery and DC air pump, with a 250V solar panel as the roof.  The roof is mono pitched and faces almost due South, and doesn't get that much shade.  However, there are no affordable and reliable brushless DC air pumps around, it seems, so I've had another thought.

What if I fitted a standard 250W panel as the roof and fitted a microinverter and just connected it up to the existing connection box?  The cable running to this unit already has a DP RCBO, so it'd be safe.  The export wouldn't register on the export meter, but would offset a little bit of electricity usage, so there would be no effect on our FIT or export readings for payment.  The only slight issue is that I have a G59 system, so technically I'd need to get permission.  However, an extra 250Wp is barely going to make a difference to the local grid, and much of the time the power generated by the panel would be used locally by the air pump, with not a massive amount of export.

Panels are so cheap now that a panel and microinverter is only slightly more expensive than me making a roof and covering it with slate to match the house, and fitted a panel to a timber roof frame would be dead easy and look neat (I'm thinking of a black panel).

My inclination is to just do it, and not worry about any consequences, as I doubt whether they would ever come to light, or attract attention if they did.  What are the thoughts of others?

[ProDave]

I would do it personally but of course that is not official advice. 

[SteamyTea]

It is sending out the wrong message though.  The consequences if something goes wrong, either administratively, or safety, would be tiring at best, prison at worse.

Have a word with the DNO and see what they say.

Edited May 28, 2016 by SteamyTea

[Nickfromwales]

What sort of power does the DC motor have to turn out ?

I've got some whoppers in our 1/8th scale RC rally cross / monster trucks. They do around 30-35mph with current gearing but could easily do 40-50mph if I geared them accordingly. The two monster trucks will do a wheely from a standing start, and if I turn the launch control off they'll simply flip 360+ degrees and land back on their wheels again ! Crazy power. 

Point being those DC motors take a beating, are brushless and have bags of poke. Can you connect one of them to a pump?

[Guest Alphonsox]

1 hour ago, JSHarris said:

The only slight issue is that I have a G83 system, so technically I'd need to get permission. 

I thought you had a mega G59 approved array ? Anyway You will have got permission for a peak export amount - say 6kw - This was true on the day it was installed a couple of years ago since then the panel output has been constantly degrading. All you are doing by adding an extra panel is putting your peak export back to where it was when initially installed.

[Jeremy Harris]

1 hour ago, ProDave said:

I would do it personally but of course that is not oficcial advice. 

I think you and I are on the same wavelength here!

 

1 hour ago, SteamyTea said:

It is sending out the wrong message though.  The consequences if something goes wrong, either administratively, or safety, would be tiring at best, prison at worse.

Have a word with the DNO and see what they say.

Just to be clear, no laws are being broken here and the system would be safe and it is legal to DIY a connection to an existing circuit, provided it is within the appropriate ratings.  The inverter would be an approved one (I'm not sure you can easily buy non-approved ones anyway), the connection is a 2.5mm² length of SWA, terminated in a connection box that has spare ways, and at the other end has a 20 A DP RCBO that was installed and tested in accordance with Part P (and has a chit).

The only thing I'm not doing is informing the DNO, for two reasons.  Firstly, I don't want FIT for it.  Secondly, I can't get it to run through a second export meter without a lot of faffing about, connecting to the existing system is easy.  Thirdly, as Alphonsox says, the additional generation is both well inside the tolerance on the existing G59 system (and thanks for pointing out the typo - I'll fix it!) and probably within the degradation that's already occurred in output, so in practice there will be no change.  In fact my current system has a 6 kW nominal inverter on a 6.25 kWp registered system, so I'd technically still be inside my G59 approval anyway.

 

38 minutes ago, Nickfromwales said:

What sort of power does the DC motor have to turn out ?

ive got some whoppers in our 1/8th scale RC rally cross / monster trucks. They do around 30-35mph with current gearing but could easily do 40-50mph if I geared them accordingly. The two monster trucks will do a wheely from a standing start, and if I turn the launch control off they'll simply flip 360+ degrees and land back on their wheels again ! Crazy power. 

Point being those DC motors take a beating, are brushless and have bags of poke. Can you connect one of them to a pump?

These air pumps are low pressure reciprocating diaphragm pumps, so use coils running at 25 Hz (half wave mains, they use diodes to halve the frequency to the coils) that had no bearings, because they run 24/7, 365 days a year.  The moving armature is supported on spings, with a magnetic alignment thing, and just moves sideways 25 times a second, pushing/pulling a diaphragm at either end, to give near-continuous air flow.  The pressure is low (typically 0.2 bar maximum) and relatively high volume (typically 60 to 100 litres/minute).

Bigger commercial systems use centrifugal blowers, and I did seriously look at making one.  It would need a very high speed brushless motor (50,000 rpm or more) to get the pressure and flow rate, and my thoughts were to use the compressor side of a small turbocharger connected to a model type brushless motor.  The main problem is that I would have had to build in a lubrication system, as neither the turbo shaft bearing or the motor bearings would survive for long without regular lubrication.  I did look at a US made brushless blower, but the price was silly.

[Nickfromwales]

If the purpose is just to move air ( assumption ) then why not devise an alternative?

i don't quite understand the criteria you're working to, sorry. 

[SteamyTea]

When your PV system was installed, a design drawing of the system should have been sent to the DNO.  It would show location of modules, inverter, isolators, meter... as well as the type approval.

I have no idea what they do with this info but I do know, that if it is not correct, the system needs to be shut down and rectified.

So adding 'something else in' still needs notification.

I see it as akin to driving with a bald tyre.  Most of the time it is fine, but you can get pulled up for it (administrative) or have an accident (safety).

[Jeremy Harris]

17 minutes ago, Nickfromwales said:

If the purpose is just to move air ( assumption ) then why not devise an alternative?

i don't quite understand the criteria your working to, sorry. 

 

I have looked pretty closely at this.  The requirement is to pump air at up to 0.2 bar at a rate of around 60 to 100 litres per minute, for 24 hours a day, non-stop, for years on end.  The sort of pumps normally used last two to three years or so between servicing (usually the diaphragm fails, the "motor" parts last practically for ever as there are no bearings).  A piston type pump won't deliver the volume, and would wear out too quickly, as you cannot have any oil on the air delivery side (because that would contaminate the tank).  You're basically looking at the same requirement as a large fish pond aeration system, and the pumps used in these treatment plants are ones originally designed for aerating big Koi carp ponds (hence the reason many are Japanese).

There are a couple of US firms that have come up with smaller scale centrifugal fan blowers, but they suffer from bearing problems, and only one firm makes a DC pump, and that has a bad reputation for early failure. 

As I mentioned above, a small turbo compressor, driven by a high speed brushless motor, could do the job, but would need some form of lubrication system, that used a food-safe lubricant.  That's not just for the bearings, but also for the shaft seal.

It's perfectly possible to build the brushless motor into the impeller of the pump, so the coils were fixed and the magnets were set into the rotor, and then devise some form of air bearing support.  It would be a lot of close tolerance machining, but I'm pretty sure it could be made to work.  It would not be cheap though, and would always be a one-off, so not good for maintenance).

 

13 minutes ago, SteamyTea said:

When your PV system was installed, a design drawing of the system should have been sent to the DNO.  It would show location of modules, inverter, isolators, meter... as well as the type approval.

I have no idea what they do with this info but I do know, that if it is not correct, the system needs to be shut down and rectified.

So adding 'something else in' still needs notification.

I see it as akin to driving with a bald tyre.  Most of the time it is fine, but you can get pulled up for it (administrative) or have an accident (safety).

There was no drawing or diagram sent to the DNO, I know because I submitted all the documents myself, not the installer (long story, but it centred around there being no registered address for the installation).  All the DNO have is what's on the MCS cert.

As above, there is no safety issue.  The microinverter will be an Enphase or similar, so will have the same certification and safety cut off as any other, and it is perfectly legal to DIY install these on a non-FIT install.

99% of people are just going to assume that we have a PV powered treatment plant.  This was offered for a time by BioPure, but they stopped marketing it as the DC pumps failed regularly and the batteries and panels were very prone to being nicked.............