Self-build Garden Room (Garden Office) with PV Solar

[Hermes]

Hello everyone,

 

Recent house purchased and plan for a garden office with PV solar installation. 

After much frustrating searching for information on solar installation found this forum where people seem to be happy to get into the technical details (unlike websites of companies offering solar installation that I’ve seen). Been a long term renter so my DIY skills low level but IT background so (like to think) have technical aptitude. 
 

Looking for advice / voice of experience on a:

 

* 3m x 5m (internal dimensions) garden room. 194 degrees longitudinal axis

* 4.2m x 6m flat room dimensions (TBC)

* approx 20m from main house at end of back garden

* mainly 2 person office

 

Considering installing:

10x 375W AE Power PV panels in E-W facing configuration with ~10 deg pitch

10x S440 optimisers 

SolarEdge SH3000 inverter

Garden Room would also have AC unit Daikin split unit (model TBC)

 

Questions:

1. Can the solar PV inverter be connected to a secondary consumer unit in the garden room or does there need to be a run for generated AC going to the main Consumer unit in the house and a feed from there to the garden room sockets and lights?

2. Maybe depends on answer above but 10mm or 16mm SWA buried spade and a half depth?

3. Looking at CAT6 and / or multimode fibre (intended home switch will have SFP so wondering whether this is a future proofing method into the same trench).

4. Options for digging trench other than by hand - digger hire from Jewson? (Have 1000mm access down side of house)

5. Views on electrical installation for garden room. Which bits need an electrician and or MCS certificate it it worth it, and which bits to do self.

 

There is potential for further PV system on potential house extension (if built) but currently main house roof aspect not ideal for solar (gable end facing south with other main surface north facing)

 

Thoughts welcome. 

[JohnMo]

8 minutes ago, Hermes said:

MCS certificate it it worth it,

No

 

9 minutes ago, Hermes said:

~10 deg pitch

Would give good summer output, next to nothing in winter, assuming 10 degree from horizontal.

 

10 minutes ago, Hermes said:

Can the solar PV inverter be connected to a secondary consumer unit

Yes

 

Consider a PV to immersion diverter also.

 

If you haven't used a digger before, they take a while to get the hang of, so allow for the learning curve in your hire time.

 

 

[SteamyTea]

1 hour ago, Hermes said:

10x S440 optimisers 

Are they really needed?

1 hour ago, Hermes said:

1. Can the solar PV inverter be connected to a secondary consumer unit in the garden room

Probably.  There are some basic rules about maximum voltage drop for PV systems, an electrician should know these.

1 hour ago, Hermes said:

2. Maybe depends on answer above but 10mm or 16mm SWA buried spade and a half depth?

Look up the regs and it will tell you.

1 hour ago, Hermes said:

3. Looking at CAT6 and / or multimode fibre (intended home switch will have SFP so wondering whether this is a future proofing method into the same trench).

Run a bit more conduit, again, stick to the regulations about separation.

1 hour ago, Hermes said:

4. Options for digging trench other than by hand - digger hire from Jewson? (Have 1000mm access down side of house)

Never know an IT person to do any physical work, ever.

1 hour ago, Hermes said:

5. Views on electrical installation for garden room. Which bits need an electrician and or MCS certificate it it worth it, and which bits to do self.

If you have to ask, all of it needs to be done by a qualified electrician.

1 hour ago, Hermes said:

Garden Room would also have AC unit Daikin split unit (model TBC)

Maximum power draw will set the cable size to the garden office.

1 hour ago, Hermes said:

MCS certificate it it worth it

t is sometimes.

General rule is that if you can use the majority of the generation on site, then it is not worth it.

Majority being exported, then is worth it.

[Nickfromwales]

1 hour ago, Hermes said:

10 deg pitch

Can you get this to 15 or 20? Would make a huge difference and also then the panels would be deemed "self-cleaning". Below 12 and you typically have to mechanically clean these periodically, then they're not 'maintenance free'.

[Hermes]

@NickfromwalesI started assuming that I was aiming for S facing and 30° tilt / pitch but the spacing required to not have 30 - 50 % of the panel in shade for half the year clearly indicated that E-W might be worth considering. Also the potential extra array on the house extension (if built) would be S facing. I have been playing with the SolarEdge designer on the website so given your thoughts I will look at trying some different tilt angles and see how that changes the numbers. There are some trees in both our garden and the neighbours so all of it is measured a certain amount against how many of those are accurately modelled or trimmed back (a couple will need to be removed for the garden room anyway).

[Hermes]

@JohnMo Wife is convinced I only want the digger to play with one so I will certainly need to factor in time to get the hang of it. Need to find a price to work out whether it is an unneccessary luxury - assuming I've not missed any other options - it seems based on searches a reasonable rental of walk behind trench diggers is a USA only sport.

[Nickfromwales]

4 minutes ago, Hermes said:

@NickfromwalesI started assuming that I was aiming for S facing and 30° tilt / pitch but the spacing required to not have 30 - 50 % of the panel in shade for half the year clearly indicated that E-W might be worth considering. Also the potential extra array on the house extension (if built) would be S facing. I have been playing with the SolarEdge designer on the website so given your thoughts I will look at trying some different tilt angles and see how that changes the numbers. There are some trees in both our garden and the neighbours so all of it is measured a certain amount against how many of those are accurately modelled or trimmed back (a couple will need to be removed for the garden room anyway).

I'm going E/W split for the majority of mine, with prob 30-40% of the array(s) getting true S sunshine ( irradiance ). Should give me a long steady solar day. I've decided on an E/W 25 degree apex for the pergola / shed at the top of my garden, with 10x400w E and 10x 400w W, plus then around 12 panels S-ish on my gazebo roof. Should see up to 4kW from E, then up to 4kW S then up to 6kW late afternoon to evening. Btteries are going in from the get-go, and just about to order them, plus a chunky hybrid inverter.

Eventually I'll put another 10 on the E roof and another 10 on the W roof, and aim to provide a lot of space heating from A2A during the winter. 🤞

8 minutes ago, Hermes said:

@JohnMo Wife is convinced I only want the digger to play with one so I will certainly need to factor in time to get the hang of it. Need to find a price to work out whether it is an unneccessary luxury - assuming I've not missed any other options - it seems based on searches a reasonable rental of walk behind trench diggers is a USA only sport.

A machine plus driver will get the job done very quickly without damage. It also needs some thought as to spoil and residual useable manoeuvring spaces which is gained by experience only. Liability resides with them then also. You may have to get separate insurance for the machine also. Check it all out properly first

[Hermes]

@SteamyTea S440 requirement - was assuming that if going E-W alignment (and some tree shading) that if not micro-inverters / optimisers then either side will be limited by the panels in other orientation in morning / evening? does add about £600 to the install equipment costs

 

Voltage drop from my reading up seems to be 5% but if consumer unit in garden room then the cable run to the consumer until would be ~2m so really a question about voltage drop on the run to the garden room from house (which I'm assuming would be the same problem if no PV installation there?)

 

Quote

If you have to ask, all of it needs to be done by a qualified electrician.

Well I get your point, to a point. But there are some things you can learn to do that are still legal without having to become a qualified electrician. There seems to be a whole YouTube DIY electrical nudge-nudge-wink-wink thing going on where the only people who would want to watch the videos of anything electrical are people that would already know how to do them "confident and competent". If confident means "doesn't ask" then I guess there are a lot more things you can do, but how do you know you are competent therefore?

 

So far I've got to the point of replacing a couple of back boxes with deeper ones and a switch with a dimmer in the house so I'm more in the space of photographing a cable in a trench I've dug myself and asking an electrician to sign it off than attempting Consumer Unit install myself

[Nickfromwales]

1 hour ago, Hermes said:

S440 requirement - was assuming that if going E-W alignment (and some tree shading) that if not micro-inverters / optimisers then either side will be limited by the panels in other orientation in morning / evening? does add about £600 to the install equipment costs

You can go for a dual string inverter and put E in one input and W in the other, without optimising, as long as there’s zero shading. 

[Iceverge]

3 hours ago, Hermes said:

Wife is convinced I only want the digger to play with. 

 

That's perfectly fine! 

 

Since when can't grown-ups have fun. 

[Hermes]

20° panels drop down the calculations for generation by about 80 kWh pa (self-consumption) but this might more than be made up for in less dirt on the panels.

Edited March 5, 2023 by Hermes
self consumption

[Hermes]

10° panels E-W

[Radian]

10 hours ago, JohnMo said:

10 hours ago, Hermes said:

MCS certificate it it worth it,

No

 

I know it's not worth it with the current energy market but what if things change down the line? What if Octopus follows the trend in Europe and offers more lucrative feed-in tariffs in the future? Export needn't reach full parity with the import tarrif to make battery storage economically unviable. Then, unfortunately, an MCS cert will become a requirement to join in with the fun.

[markharro]

Whats the trend in Europe? I am trying to reach a decision on a battery as well as its a crazy amount of cost for the storage capacity compared to the cost of a car battery.

[SteamyTea]

8 hours ago, markharro said:

crazy amount of cost for the storage capacity compared to the cost of a car battery.

Does a different job.  A car battery has to deliver a huge amount of power for a second or two, then has a long time to be recharged.  It also has to work in extreme temperatures i.e. -20°C to + 80°C.

If I take my mean usage profile, and exclude the space and DHW heating period, my mean power usage is 80W over 21 remaining hours, with a maximum power draw of 10.1 kW.

I am not sure what size battery system would be needed for this, 5 kWh?, and an inverter that can reliably deliver say 12 kW_p.

It would also have to be able to cope with the 16.3 hours a day when the house is drawing zero power (well less than a watt).  Some inverters need a minimum power draw to work reliably (have read that this is 200 W).

 

 

I don't think that battery storage is financially, technically or environmentally worth while at the moment.

I also suspect that the generation companies, who are already investing £millions in storage, are going to have a lower £/kWh than any domestic installation.

 

 

[JohnMo]

9 hours ago, Radian said:

What if Octopus follows the trend in Europe and offers more lucrative feed-in tariffs in the future

A G98 size PV array with an immersion diverter, there is next to nothing to export, so no feed in tariff adds up to value for money for the extra costs involved with MCS registration.

 

If you have a big array and battery and you can selectively export at peak times and consume electric at off peak, that may be a different story.  But not check to install.

 

We have a smart meter, but are 4 miles from town and the smart meter can't find anything to communicate with, so is dumb.  We couldn't play if we were MCS registered, as all the schemes require a working smart meter.

[Radian]

2 hours ago, JohnMo said:

A G98 size PV array with an immersion diverter, there is next to nothing to export, so no feed in tariff adds up to value for money for the extra costs involved with MCS registration.

But even at as low as 15p per unit, the divert to immersion is already close to parity with using gas to heat the water at 11p per unit (plus a bit for calorific conversion inneficiency) But Octopus's new Flux tarrifs are paying up to 36.5 p/kWh for export at peak demand time (9.4 p/kWh, 22 p/kWh, 36.5 p/kWh for the cheap medium and high rates respectively).

 

I know it's horrible but the market is constantly evolving, while self installing locks you out of potential game changers in the future without an MCS cert.