Another Solar Noob

[binky]

As it stood I couldn’t get the battery option to add up, bearing in mind a battery is only good for so many cycles, so at a stab in the dark let’s say ten years, the last time I did the sums the capital cost of the battery system would never pay for itself so in effect would cost more to my pocket and the environment.
Of course the numbers may have changed with energy costs going up, not sure where battery costs are now.
I do use a cheap solar diverter to use up my surplus solar power.

batteries have improved and dropped in price, when the first came out they cost more than they could save you. However, charge cycles is upto around 6000 minimum, which makes a big difference. I like pylontech, relatively cheap, but seem well made. With 10kW battery packs coming in at around £5.5 / 6k fitted. So at say 30p per kWh then that's 10 * 0.3 * 6000 = £18k total savings + inflation on energy prices over that lifespan. 6000 charge cycles, 1 per day being 16 years. I'm still not a great fan of batteries, I prefer to sink spare electric into water heating if you have a water tank. Also, if you are thinking of buying and EV, that has a very big battery in it.

 

[binky]

Here’s the link:

https://maps.apple.com/?address=12A...xGtjdsu2C+r853ZfYME0ySkBBcuqrkKNG+r9QBA==&t=h

lovely big back roof, although not facing the best direction, I would be tempted to max the rear roof array and have batteries. You do have a south facing aspect that you could get a small array on, 4/5 panels, but that would add to the cost of scaffolding. The one thing I really don't like is Rosemary tiles, which you have, effing things are about as strong as a Rich Tea biscuit, so, to prevent issues down the line, ie a tile stressed during installation fails 5 years later, I would be possibly looking at the GSE in-roof system. It does add to the costs, but is a better long term bet for that roof. The other reason I would target the rear roof, and ignore the side, is that we do tend to get clearer air in the mornings. The panels will still be generating at a low level in the afternoon, but from ambient light rather than direct sunshine. Reckon your rear roof is good for about 15 of the larger higher wattage panels ie 450w, maybe the so that's an array of 6.7kW from which I would expect you to generate around 850kWh per kw of panels.

 

[Bob Smith]

**** inverter, old spec panels, in short don't bother.

Hi Binky
what make you say old spec panels? Because it is "only" 370W or is it because of the brand JA Solar?
I am keen to learn more about JA Solar as so far all the design proposal for a new PV system is based on JA Solar panels.
Thanks in anticipation

 

[binky]

Hi Binky
what make you say old spec panels? Because it is "only" 370W or is it because of the brand JA Solar?
I am keen to learn more about JA Solar as so far all the design proposal for a new PV system is based on JA Solar panels.
Thanks in anticipation

JA soalr are fine, I've used them more recently due to availablity. It's old spec becuae 370W is an older model panel, you can get a 390W panel that is the same physical size. 400+w panels are also available but physically bigger. Look for percentage efficiency (and panels that fit your roof) you want 20% efficient to be newer spec.

 

[johnb2713]

In general in the UK solar is not worth it. You will never break even on the initial cost and annual maintenance. When there was the feed in tariff it made more sence for the individual but not for the rest of us who paid for the feed in tariff through increased bills.

Thats not my experience.

I've recently had solar and battery fitted along with energy diverter and EV charger. The system works amazingly well and the payback will be rapid. We've only used a handful of peak rate units, the rest has been on 7.5p or free from the roof. Considering our tariff increase to £465, the bills average so far each month is £63. I accept it will increase in winter time but projecting forward from weather stats and previous years usage my average bill will only be £80 or thereabouts. Which gives me £385 per month saving. This gives me a payback of around 2.5 years.
I am building additional battery storage and going to add additional inverter capacity to help with heatpumps in the winter which will further cut gas from my energy bill.

 

[Bob Smith]

JA soalr are fine, I've used them more recently due to availablity. It's old spec becuae 370W is an older model panel, you can get a 390W panel that is the same physical size. 400+w panels are also available but physically bigger. Look for percentage efficiency (and panels that fit your roof) you want 20% efficient to be newer spec.

Ah OK I understand better your comment now. Thanks
yes I am looking at such panels

JAM78S30

605W

2465 x 1134 x35

JAM66S30 1000V

505W

2094 x 1134 x 35

I will also need to understand what the difference between a 1kV panel a 1.5kV and those they say 1/1.5kV. But this will be topic of another thread.

 

[binky]

Ah OK I understand better your comment now. Thanks
yes I am looking at such panels

JAM78S30

605W

2465 x 1134 x35

JAM66S30 1000V

505W

2094 x 1134 x 35

I will also need to understand what the difference between a 1kV panel a 1.5kV and those they say 1/1.5kV. But this will be topic of another thread.

max string voltage I believe. Be warned those 2m panels take some handling!

 

[Bob Smith]

max string voltage I believe. Be warned those 2m panels take some handling!

The max string voltage? Is that the sum of the Voc at 25°C of all panels on the same string or maybe the sum of the Vmp? or something else.
On the datasheets of JA Solar it reads this


so the type of connector will determine what that V is apparently.

As for the 2m, not sure what you mean. I won't be the one installing them lol.

 

[binky]

The max string voltage? Is that the sum of the Voc at 25°C of all panels on the same string or maybe the sum of the Vmp? or something else.
On the datasheets of JA Solar it reads this
View attachment 13744

so the type of connector will determine what that V is apparently.

As for the 2m, not sure what you mean. I won't be the one installing them lol.

MC4 connectors are fitted to the panels, like all electrical gear they have a maximum operating voltage, you won't get anywhere near that as most inverters have a max VOC of around 600v.

2m , they are actually bigger than that according to the spec you posted. Big buggers in layman's terms .

Big panels are ok but they won't suite every roof due to their sheer physical size

 

[Bob Smith]

MC4 connectors are fitted to the panels, like all electrical gear they have a maximum operating voltage, you won't get anywhere near that as most inverters have a max VOC of around 600v.

2m , they are actually bigger than that according to the spec you posted. Big buggers in layman's terms .

Big panels are ok but they won't suite every roof due to their sheer physical size

Thanks for the clarification regarding the voltage. It does make sense.

Regarding the size of the panels, I know they are longer than 2m I am trying to cover the surface available as much as possible. It will be a mix of panels to achieve this. As you surely know, sometimes it is better to have a smaller panel where you can fit more of them eg if you can fit a 4 * 400W it is better than 3 * 500W
In my case, I am playing with 3 different sizes in order to cover the most available area.
To give you an idea, the original design had 9 panels, all the same for a total power of 3.6kW. After playing with different panels I now reach 4.75kW still with 9 panels. (I am just filling the gaps with the different sizes)

There will only be 2 of that monster beast at 2.5m. One fitted on a wall and the other on a lower roof.

 

[johnb2713]

In my case, I am playing with 3 different sizes in order to cover the most available area.
To give you an idea, the original design had 9 panels, all the same for a total power of 3.6kW. After playing with different panels I now reach 4.75kW still with 9 panels. (I am just filling the gaps with the different sizes)

There will only be 2 of that monster beast at 2.5m. One fitted on a wall and the other on a lower roof.

You need to be careful mixing different panel ratings, the chain (string) is only as strong as the weakest link. If you put a low powered panel in series with higher powered ones it will restrict the higher powered ones unless you have some form of wizardry that bypasses the lower powered panel.

I think I'm right in this, I'm sure one of the experts will confirm / shoot me down.

J

 

[Bob Smith]

You need to be careful mixing different panel ratings, the chain (string) is only as strong as the weakest link. If you put a low powered panel in series with higher powered ones it will restrict the higher powered ones unless you have some form of wizardry that bypasses the lower powered panel.

I think I'm right in this, I'm sure one of the experts will confirm / shoot me down.

J

Thanks John,

There are effectively some constraints. It is nonetheless possible. It is similar to when you have a string of identical panels but one is faulty or has a lot of shade.
There are devices that help called Optimizer. Maybe you know them.
I have started to look at them. Actually, one type for now. Tigo optimizer. (I need to look at SolarEdge too but I have not had a chance yet, and maybe others).

Tigo Optimizer recommends the following

You can mix and match modules in the same string if the current ratio (Cr, lowest current divided by highest current) is larger than 0.75. Use this result to calculate the current mismatch (Cm): Cm = (1-Cr); it must be less than or equal to 25%.

Source
https://support.tigoenergy.com/hc/e...xt=You can mix and match,than or equal to 25%

 

[binky]

Thanks John,

There are effectively some constraints. It is nonetheless possible. It is similar to when you have a string of identical panels but one is faulty or has a lot of shade.
There are devices that help called Optimizer. Maybe you know them.
I have started to look at them. Actually, one type for now. Tigo optimizer. (I need to look at SolarEdge too but I have not had a chance yet, and maybe others).

Tigo Optimizer recommends the following

You can mix and match modules in the same string if the current ratio (Cr, lowest current divided by highest current) is larger than 0.75. Use this result to calculate the current mismatch (Cm): Cm = (1-Cr); it must be less than or equal to 25%.

Source
https://support.tigoenergy.com/hc/e...xt=You can mix and match,than or equal to 25%

I'm not a fan of such gadgets, you are effectively adding potential failure points to the roof, and if roof access involves £600 of scaffolding... You may also find whoever you are buying panels from will charge for multiple pallets for the delivery, a pallet being around £125 per go. So, yes you can mix and match panel sizes, but it may not be the best idea. Of those 2 systems I would go with Solaredge, they also do an inverter that will charge EVs I believe, with surplus energy.

 

[Bob Smith]

Thanks Binky,
Fortunately, a scaffolding is not required. It is not the main roof of the house. A simple ladder will do (This said, they may bring a scaffolding for the installation but that is a one off and won t be required for maintenance)

I am not considering to charge EV from the PV, That is one less concern as part of the design

Can you please, if you have time of course, elaborate why this may not be the best idea?
I have the 9 panels will be facing different orientation (3 facing South (on a garage roof), 2 facing South-West (flat roof) and 4 West (on a wall).
They will be subject to shading through out the day. For instance the 3 facing South will not get the sun at the same time as the house main wall create shades on that garage roof. From about 10am, the garage roof start to get some sun and about 11h30 the 3 are exposed to the sun). In addition, there is a tree that creates shade from about 5pm (this is June time, obviously in winter this is a bit different)

In addition, in order to cover most of the surface available, I need to combine different panel size. If I were to take the same size for all panels I get about 3.8kW, if I were to mix, I reach 4.7kW. This is 23% improvement.

In order to mix panels, I need to ensure compatibility. One of the criteria is the current mismatch. There is also a voltage mismatch calculation if I were to use more than one string. However, I intend to have the 9 panels on one string (the min and max string voltage needs to be calculated of course).

Regarding the delivery, I see what you are saying, what's the point to get one particular panel if it only comes in bulk. This is a one of struggles while the panel will be in situ for 20 years. This said, this is a point I will consider once I have narrowed down a couple of possible considerations. I will start with the best one and if I cannot source the panel in an appropriate way, I will move to the second best and so.

Here are some background info. I am very keen to be challenged and proven wrong. Therefore, I would really like to understand why you are saying it may not be the best idea to mix and match panel sizes. What would be the best idea from your point of view and for what reasons?

Thank you