Solar battery proposal questions

[Thorfun]

1 hour ago, Beelbeebub said:

I'm just about to finish getting a similar system up. 

 

Large house - about 5,500 kwh a year demand on a single phase. 

 

24x neostar 2 (465w IIRC) on a single array with slight shading issues (big tree and house shade some of the array at various times of day/year). 

 

The large number of panels was my way of conterwcting the less then ideal site. I'm making up for lost generation from shading, pointing SW and having a low pitch by just having more panels and stopping up the inverter size from 6kw to 8kw . The step up in cost was a few hundred £, which was far cheaper than trying to get the panels in a more optimum position. 

 

The panels seem OK, honestly won't know until about 10 years from now. 

 

Dealing with the shading by splitting the array into 3 strings of 12,6 and 6 panels (inverter has 3 inputs) so the shading only knocks out the smaller blocks. 

 

8kw solax IES inverter with 3x 5kwh battery modules. 

 

I did look at the Sig system - it looks very nice (frankly a step up from the Solax) but was about 1.5k more like for like and finding a local installer was hard.

 

The Solax unit seems pretty solid, if a little more utilitarian - think Skoda vs Audi. Went in very easily took about 30 minutes. Just a case of stacking boxes. The main advantages the Sig seems to have are

A) looks

B) can have higher total battery (solax is 20kwh per inverter, though inverters can be paired up) 

C) Sig has multiple battery sizes, solax does 5kwh

D) potential V2H/car charger with Sig (though I believe solax are working on one too) 

 

The solax advantage seems to be cost and potentially availability.  They have also been established quite a while and offer various units from small all the way to industrial ie they appear to be a likely to not go bust (I hope) 

 

The solax also handles power cuts more or less out of the box. You don't need a separate gateway box like other brands (I think Sig need one) but it does require an extra 2 conductors to the unit (5 cores rather than 3) which might be a consideration if you are locating the unit well away from your consumer unit and meter. 

 

As a side note when will these modular systems put the inverter at the bottom of the stack! At the moment you would need to lift of the inverter modules (the BMS is separate module) add the battery, then restack the inverter and adjust the cables. If the inverter was the bottom unit adding modules would be very simple, just stack a new one on. 

 

 

Why don’t you just use optimisers to get over the shading issue?

[Beelbeebub]

4 hours ago, Thorfun said:

Why don’t you just use optimisers to get over the shading issue?

Good question.

 

We looked at that. 

 

The original layout was 2 strings of 12 and only the 3 corner panels of one string had a shading issue.

 

The options were to add 3 optimisers - £150-300

 

Or to use the unused 3rd string to get around the shading issue.

The panes have been wired up a 4 groups of 6 and the connectors brought down to an internal location where 2 of the groups will be connected in serial and the other 2 will get a string each.  This will allow for easy rejigging if we want to and the location of the panels makes it very easy to add the optimisers later.

 

The array is well oversized so i'm not looking for the nth degree of optimisation, but losing 1/2 the array until lunchtime because the bottom left corner panel is shaded would be a bit annoying.

[SteamyTea]

5 hours ago, Beelbeebub said:

but losing 1/2 the array until lunchtime because the bottom left corner panel is shaded would be a bit annoying.

Most domestic modules have built in bypass diodes for this very reason.

Not many installers will ever mention this.

[Beelbeebub]

2 hours ago, SteamyTea said:

Most domestic modules have built in bypass diodes for this very reason.

Not many installers will ever mention this.

My understanding is the built in bypass mechanism effectively divides the panel into 2 or 3 sub panels so is useful if a bit of a panel is shaded, as long as the shading happens to align with the sub panels but can't help if the entire (or most of) the panel is shaded.

 

But dividing the array into 3 to use the existing strings is effectively for free (just a little extra cable) and the arrangement of 4 sets of 6 panels means I could always rewire the array to be 2 strings of 12 if I wanted. 

[SteamyTea]

30 minutes ago, Beelbeebub said:

but can't help if the entire (or most of) the panel is shaded.

I thought they then just bypassed the whole panel.

I think that there is a risk of too low a voltage to be effective on marginal systems and it can play havoc with the inverters maximum power point tracking.

[Beelbeebub]

1 minute ago, SteamyTea said:

I thought they then just bypassed the whole panel.

I think that there is a risk of too low a voltage to be effective on marginal systems and it can play havoc with the inverters maximum power point tracking.

That's what an optimiser does, but I don't think the more basic bypass diodes are as effective (despite what the manufacturers claim). There's a video with someone testing the Neostar 3's which the manufacturer tours as being much more shade resistant - but shows if the shade is the wrong way, it doesn't work as well.

 

I found this with a cheap 60w panel that keeps a tractor battery topped up.  If you shaded it with a thin stick vertically you lost a bit under a 1/3 the output, but the same stick horizontally knocked it down to very little (like under 10w or something).

 

As for minimum start up, half the array is 12 panels with is pretty much the maximum that a single string can handle on my inverter. IIRC the start up is 40v, which isn't even 25% of the full output 

 

Again, because I've wired it as 4 blocks it's really easy to switch between 2x12 (if I find start up voltage is a problem) or various 12 + 2x6 configurations which deal with different aspects of my shading issue (the tree tends to cause an issue with one corner, my house will shade the entire bottom edge, creeping up as winter advances) 

 

I don't propose to switch regularly, just a few times to get a feel for which one (if any) will give me the best (as in most suited to my needs) overall production. 

[Dillsue]

Here's solaredges take on bypass diodes https://knowledge-center.solaredge.com/sites/kc/files/se_technical_bypass_diode_effect_in_shading.pdf

[Ay8452]

Thanks all for your replies.

 

I agree with many, three phase just seems to complicate the solar setup + the hosue, unnecessarily. Currently do not have any crazy electrical loads. However since it's a "forever" home, I am trying to future proof it. ASHP in the future + 3 phase EV charger etc.

 

Installer has suggested putting all 14 panels on one string all with optimisers as the 4 panels that will get heavy shading in the late afternoon won't have enough start up voltage for the inverter so essentially become useless. The 4 panels are on a single storey roof facing SE and the double storey roof is immediately above it so when the sun is in SW/W it will be very shaded on the single storey area. If this isn't a good idea, please let me know, your opinions are welcome.

[JohnMo]

6 minutes ago, Ay8452 said:

putting all 14 panels on one string all with optimisers

Possibly the easiest solution.