Hello - New member looking for some advice...

[TimBe]

Hello to everybody
I'm Tim and I live in Nottingham a novice to solar but just in the process of DIY on roof solar install.
I work in the building trade and used to working at height and on roofs so no brainer to install my own panels
Had to carry out some work to my roof in preparation like swapping out any spalled/damaged/broken rosemary tiles and resetting all the ridge tiles, and now have rails fitted in preparation for the panels. I have limited amount of roof space so trying to achieve 4kw but could really use some input on solar strings.
The main roof on the house is generally South East facing but doesn't have a lot of real estate as there is a gable that comes of the main roof and also 2 skylights to provided light into a bedroom and a stairwell in the loft space. Part of this roof will also have a 30 Solar tube array fitted so I'm left with an area that I could get 3 large 550w panels fitted or maybe at a push 4 x ≈400w panels.
The gable roof that comes of the main roof is generally South West facing and is quite long but not very tall, I can mount a single row of 6 or ≈400w panels
The above would see my available roof space maxed out unless I added to North East on the gable roof or North West on the main roof but 4kw was my initial target anyway.

So the input I really need is about strings and string sizes.
I'm aware about mixing different panels on a string but what about if I had 1 string with 550w panels and 1 string with 400w panels is that acceptable?
Should strings be balanced and of equal size? Because if I did go with the 550w panels it would be 1650w on 1 string and ≈2400w on the other
Is it better have single string or multiple strings? My thoughts were 2 different strings 1 for each of the directions but open to input

And just to clarify equipment (should it make any difference) that I have purchased but waiting to be installed :
Growatt SPH3000 Hybrid Inverter
Growatt 6.5kw Battery (potentially adding another later this year when I see some results)

Thanks in advance

 

[johnb2713]

Hello to everybody
I'm Tim and I live in Nottingham a novice to solar but just in the process of DIY on roof solar install.

Welcome to this brilliant forum

I work in the building trade and used to working at height and on roofs so no brainer to install my own panels
Had to carry out some work to my roof in preparation like swapping out any spalled/damaged/broken rosemary tiles and resetting all the ridge tiles, and now have rails fitted in preparation for the panels. I have limited amount of roof space so trying to achieve 4kw but could really use some input on solar strings.

Not my area of expertise but there are others that have years of experience in this field.

The main roof on the house is generally South East facing but doesn't have a lot of real estate as there is a gable that comes of the main roof and also 2 skylights to provided light into a bedroom and a stairwell in the loft space. Part of this roof will also have a 30 Solar tube array fitted so I'm left with an area that I could get 3 large 550w panels fitted or maybe at a push 4 x ≈400w panels.

I assume a 30 tube solar array is water heating? if so ditch it and fit panels instead, much more flexibility with the energy captured. Add a MyEnergi EDDI to your system to divert excess energy to your water heating, it works really well.

The gable roof that comes of the main roof is generally South West facing and is quite long but not very tall, I can mount a single row of 6 or ≈400w panels

I have a West facing roof with 6 panels that provides a decent amount power peaking late afternoon and useful evening power.

The above would see my available roof space maxed out unless I added to North East on the gable roof or North West on the main roof but 4kw was my initial target anyway.

All sounds good

So the input I really need is about strings and string sizes.
I'm aware about mixing different panels on a string but what about if I had 1 string with 550w panels and 1 string with 400w panels is that acceptable?

Absolutely as long as the voltage rating of the inverter arent exceeded, you should be fine.

Should strings be balanced and of equal size? Because if I did go with the 550w panels it would be 1650w on 1 string and ≈2400w on the other.

Thats OK

Is it better have single string or multiple strings? My thoughts were 2 different strings 1 for each of the directions but open to input.

Your thinking is 100% correct

And just to clarify equipment (should it make any difference) that I have purchased but waiting to be installed :
Growatt SPH3000 Hybrid Inverter

Inverter is too small, it will work fine but you only need to switch on a kettle and a toaster and energy will be called from the grid. I have SPH6000 and that was not enough for me, I was annoyed to see peak rate electricity being used when the washing machine was running with other loads in the house. That led me to make a bigger battery (14kWh) and fit an additional bigger inverter (5kW), now I don't use any peak rate energy, my batteries run the house for a full day with kWh to spare.

Growatt 6.5kw Battery (potentially adding another later this year when I see some results)

Thanks in advance

Battery is essential to make solar viable IMHO.

 

[Kot]

Have you tried Easy-pv its free and is useful for the novice on self educating panel locations string sizes etc etc

 

[BorisJ]

I assume a 30 tube solar array is water heating? if so ditch it and fit panels instead, much more flexibility with the energy captured. Add a MyEnergi EDDI to your system to divert excess energy to your water heating, it works really well.

Why? Direct water heating with tubes is much more efficient than using panels

 

[johnb2713]

Why? Direct water heating with tubes is much more efficient than using panels

It is more efficient but loses a massive amount of flexibility. What happens when the water tank is heated to the temp? The energy is lost. With Solar PV and energy diverter you can very efficiently heat the water with excess solar energy, charge batteries, power numerous items in the home or even export the energy rather than just inefficiently waste it.

 

[TimBe]

@johnb2713 Thank you for the thorough response I really appreciate the input.
Very impressive for you to not be using any peak rate electricity and a place that I would like to achieve at some stage.

Yes the 30 tube solar array is water heating and my reasoning for installing this is to negate the minimum 3kwh daily use of the Immersion heater (I have a dual coil Solar Cylinder installed), I can see where you are going with the flexibility and peaking out with the hot water storage so I suppose the question is
If I didn't install the 30 tube solar array I could get another 2 PV panels at say ≈550w installed instead, would those produce 3kw per day

With regards to the Inverter I had tried to research what way to go with regards sizing, and information that I had read pointed to not oversizing as it becomes inefficient, and also maybe I used the wrong information to make the decision about what i needed. So is 'the bigger, the better' adage appropriate in this case? Like I said the SPH3000 has been purchased but its not installed and still in the box so I don't mind moving that on and getting something else? I would like to stay with the Growatt for compatibility reasons and the largest on the Single Phase is the SPH6000 that you say you have? Is that suitable then for a maximum 4kw PV input?

With regards to Battery is essential to make solar viable, that's what I had sort of gleaned from doing the bits of research that I have. The idea of adding an additional 6.5kw battery later this year was to get an initial setup running and see what's happening from that but as much the initial financial outlay.

Thanks again - Tim

 

[TimBe]

@Kot I wasn't aware of that resource thanks I will have a look at that

 

[johnb2713]

@johnb2713 Thank you for the thorough response I really appreciate the input.
Very impressive for you to not be using any peak rate electricity and a place that I would like to achieve at some stage.

Its a great position to be in especially with off peak rates being low (currently 10p but companys like Utilita offer 5p per kWh)

Yes the 30 tube solar array is water heating and my reasoning for installing this is to negate the minimum 3kwh daily use of the Immersion heater (I have a dual coil Solar Cylinder installed), I can see where you are going with the flexibility and peaking out with the hot water storage so I suppose the question is
If I didn't install the 30 tube solar array I could get another 2 PV panels at say ≈550w installed instead, would those produce 3kw per day

Hard to answer this with any certainty, how sure are you that the 30 tubes will provide it?
1 Litre of water takes 0.00116kWh to raise it 1 deg C. So if you have a 200 litre tank with 20 deg C cold water and you want 50 deg C it will take (50-20) x 0.00116 x 200 = 6.96 kWh. My split south & West facing array produces an average of 90 kWh per week over the year (summer peak has been 48kWh in a day. So to break this down further 90 kWh per week = 12.85 kWh per day with 16 panels giving an average of 800w per day. So in answer to question would they produce 3kWh per day probably not during the winter, highly likely during the summer.

With regards to the Inverter I had tried to research what way to go with regards sizing, and information that I had read pointed to not oversizing as it becomes inefficient, and also maybe I used the wrong information to make the decision about what i needed.

I think modern inverters dont have the efficiency disadvantages that are often quoted, especially ones like the Growatt which are fanless and transformerless designs.

So is 'the bigger, the better' adage appropriate in this case?

Thats my thinking, it may be wrong but is my belief. Think about wasteage when switching the kettle and toaster on, 3 kWh will come from the inverter and batteries but a further 2 kWh will be sucked from the grid at 40p kWh as opposed to the free or 10p kWh off peak energy via the inverter. 30p kWh can make up for some efficiency loss.

Like I said the SPH3000 has been purchased but its not installed and still in the box so I don't mind moving that on and getting something else? I would like to stay with the Growatt for compatibility reasons and the largest on the Single Phase is the SPH6000 that you say you have?

Yes I do BUT be aware that when running on battery only the SPH6000 will only supply 3kW max, why I dont know, it is in the spec and was a complete pain for me. I should have read the specs more closely

Is that suitable then for a maximum 4kw PV input?

From the spec sheet, 8000W is the max recommended input

With regards to Battery is essential to make solar viable, that's what I had sort of gleaned from doing the bits of research that I have. The idea of adding an additional 6.5kw battery later this year was to get an initial setup running and see what's happening from that but as much the initial financial outlay.

If youre up for a bit of DIY it's not difficult to build your own battery (see my other posts). I built a 14 kWh battery with a 5 kW inverter so I now have 11 kW of inverter capacity for £4200. It's payback is rapid on tariffs like Octopus Inteligent. There are other sources of batteries much cheaper than the Growatt one and allegedly compatible.

 

[TimBe]

With regards to the 3kw max on the SPH I can now see that is the case on all the single phase models from SPH3000 to SPH6000, are all Hybrid inverters limited to around this or is it just particularly with Growatt? I suppose what I'm asking is are there better off the shelf options out there for 'plug and play'? While mine are still boxed I could potentially move them on and go for something else. Or what about keeping what I have at the moment and when I go for another battery I get another Inverter? Would that increase me to 6kw from battery storage? Not against some DIY either though so I'll have a look at your other posts.

By the way thanks for showing the breakdown of calculating Increase of Temperature, will help to understand whether I keep the tubes or go for more PV..

 

[johnb2713]

With regards to the 3kw max on the SPH I can now see that is the case on all the single phase models from SPH3000 to SPH6000, are all Hybrid inverters limited to around this or is it just particularly with Growatt? I suppose what I'm asking is are there better off the shelf options out there for 'plug and play'? While mine are still boxed I could potentially move them on and go for something else.

From my limited experience, Victron has proved to be a superb manufacturer of all things solar / battery / inverter etc. Their system literally plug and play together very well. That said, they are a premium price product.

Or what about keeping what I have at the moment and when I go for another battery I get another Inverter?

Thats exactly what I did, if the SPH3000 will cope with your solar without restricting it then that would be a good route to take.

Would that increase me to 6kw from battery storage?

If youre talking about another SPH3000 I would guess yes it would, I dont know how well Growatt inverters work together.

Not against some DIY either though so I'll have a look at your other posts.

No problem, if you fancy an afternoon out and trip a little further North, youre welcome to come and have a look at it in action, compare notes and have a coffee if you wish.

By the way thanks for showing the breakdown of calculating Increase of Temperature, will help to understand whether I keep the tubes or go for more PV..

No problem at all, I run my tank at 80 deg C to effectively store more, you cant do that with the wet system. I do have a temperature mixing valve on the outlet to make the hot taps safe.

 

[TimBe]

No problem, if you fancy an afternoon out and trip a little further North, youre welcome to come and have a look at it in action, compare notes and have a coffee if you wish.

Thank you I would like to take you up on that, I'm north of Nottingham (between Nottingham and Mansfield) and wouldn't be too far to travel and well worth the trip for the input I could gain from it. I don't know anybody with solar using battery storage so opportunity to gain some knowledge. Thx

 

[TimBe]

Why? Direct water heating with tubes is much more efficient than using panels

Sorry I missed this response earlier and just seen it as I was scrolling through.
Do you have any tubes set up? And maybe any input on best way to utilise?
I have done some basic testing of a solar tube in my back garden a few weeks ago and got some interesting figures which has encouraged me to install the Solar Tube setup that I had purchased about 10 years ago and had stored in my loft rather than on the roof

 

[johnb2713]

Thank you I would like to take you up on that, I'm north of Nottingham (between Nottingham and Mansfield) and wouldn't be too far to travel and well worth the trip for the input I could gain from it. I don't know anybody with solar using battery storage so opportunity to gain some knowledge. Thx

Message sent

 

[bladerunnerpv]

Hi TimBe,
Easy-pv will give you resulting daily profiles of import, export and battery, and behaviour over a year for your specific setup, assuming you enter roof size, orientation and pitch that is.

You can easily experiment with the string configurations for you chosen inverter. In addition to the available selection of kit you can enter the panel, inverter and battery specs into easy-pv as custom components if needed. It's possible to enter obstructions on the roof too so the panel fitting jigsaw can be assessed.

There are several inverter powers ratings to be aware of, one relates to the max PV input, another to the max battery charging and discharging capability, etc.

It's helpful to visualise how a low rated inverter can throttle the input to the battery resulting in export to grid instead. Best savings usually come from maximum self-use of PV power.

Battery storage can help get the most out of the PV generation. Easy-pv will not help with assessing the effects of overnight tariffs for charging of batteries, e.g. with Economy7, though, you'll have to get the calculator out for that!

Another free option is PVGIS, have a search on the forum, there are some useful posts around regarding both.

enjoy!

 

[Scott Charles]

Hello to everybody
I'm Tim and I live in Nottingham a novice to solar but just in the process of DIY on roof solar install.
I work in the building trade and used to working at height and on roofs so no brainer to install my own panels
Had to carry out some work to my roof in preparation like swapping out any spalled/damaged/broken rosemary tiles and resetting all the ridge tiles, and now have rails fitted in preparation for the panels. I have limited amount of roof space so trying to achieve 4kw but could really use some input on solar strings.
The main roof on the house is generally South East facing but doesn't have a lot of real estate as there is a gable that comes of the main roof and also 2 skylights to provided light into a bedroom and a stairwell in the loft space. Part of this roof will also have a 30 Solar tube array fitted so I'm left with an area that I could get 3 large 550w panels fitted or maybe at a push 4 x ≈400w panels.
The gable roof that comes of the main roof is generally South West facing and is quite long but not very tall, I can mount a single row of 6 or ≈400w panels
The above would see my available roof space maxed out unless I added to North East on the gable roof or North West on the main roof but 4kw was my initial target anyway.

So the input I really need is about strings and string sizes.
I'm aware about mixing different panels on a string but what about if I had 1 string with 550w panels and 1 string with 400w panels is that acceptable?
Should strings be balanced and of equal size? Because if I did go with the 550w panels it would be 1650w on 1 string and ≈2400w on the other
Is it better have single string or multiple strings? My thoughts were 2 different strings 1 for each of the directions but open to input

And just to clarify equipment (should it make any difference) that I have purchased but waiting to be installed :
Growatt SPH3000 Hybrid Inverter
Growatt 6.5kw Battery (potentially adding another later this year when I see some results)

Thanks in advance

Hi Tim
you will be fine using different panles on different strings, like you said dont mix different panels in the SAME string otherwise your output will drop to the lesser panels spec. Regarding the string size, most inverters will look for an slightly unequal length between strings but it all depends on your inverter, check the manual/tech support. Also check on the MPPT start up voltage and the base/MPPT max voltage as well.