A few specific solar PV design questions

boots_babe

Hi,

I have a few bits of questions and thought it best to bundle into 1 post. Grateful for any help from the knowledgeable people on here, thank you.

1. Realistic system loss% ?

I've used the PVGIS calculator to input into my own spreadsheet, so I can model ROI based on our actual usage/patterns - rather than relying on the quotes from installers. The default System Loss setup on PVGIS is 14%, and despite spending ages trying to research, I cannot seem to gauge whether this is a reasonable figure to use. I've seen some figures quoted for certain panel types, but again no idea if they are actually reliable enough to use. I've used 14% for now, and this gives ~£2000 saving per annum, obviously varies a little for different panel specs. Do people think sticking with 14% loss is appropriate, or should I use a different figure? I'd rather err on the side of caution, than the other way.

2. Givenergy battery.
One of our quotes features a Givenergy battery. Reading the information on this, it looks like this enables you to actually charge the battery from the grid when it's a cheap rate, in addition to charging from solar. Is my understanding correct? And if so, are there any other batteries which offer this feature?

3. Panel brands/specs.
Have had 4 quotes so far, offering 2 different panel types. Common wisdom on these forums seems to be to go for the largest spec, and most up to date panels that you can. My first question is, what are people's thoughts on which of these may be better to go for:

405 JA Solar (JAM54S30-405/MR)

395 TRINA SOLAR VERTEX S (TSM-DE09.05) 

But also, I have seen people talking about panels higher than 405 W, but not at all commonly. Is this because they are hard to get hold of, or is there some concern making people avoid them?

4. Islanding.
I'm not overly concerned about current new reports re possible short power blackouts. However, it would seem remiss of me not to at least explore whether we can spec a system that would keep running in this scenario. If it's possible without huge additional costs, why would I not want to do that, is my thinking. But have read very conflicting reports - some people saying just not possible, as the system must go totally offline for safety during a blackout, so that any required engineer can safely work on the system. But then others seem to think it possible, but I can't seem to find any specifics as to how. Anything I could read up on here would be really helpful.

Many thanks.

QrizB

I can't answer all of your questions, but here's my contribution:

boots_babe said:

1. Realistic system loss% ?

IIRC @Martyn1981 thinks 14% is a bit on the high side. If you want a slightly pessimistic forecast, leave it as-is but you might want to reduce it slightly - maybe 12%?

2. Givenergy battery.

I can't speak for Givenergy but pretty much all the AC-coupled battery inverters can charge their batteries from grid, and some of the DC-coupled (or hybrid) ones can too.

3. Panel brands/specs.

Both the brands you mention are big Chinese ones. I would be happy with either.

Regarding panel sizes, bigger panels need fewer connections which menas (a) less work to install and (b) fewer things to go wrong over the next 25 years on your roof. However bigger panels are bigger (duh) and it can be easier to cover your roof with lots of smaller ones.

4. Islanding.

There's two aspects to this; the generation itself, and the battery storage system.

Most battery storage systems will include an Emergency Power Supply (EPS) system. With an AC-coupled battery this won't normally allow the solar panels to generate while running on EPS, so you're limited by the capacity of your battery. A DC-coupled orr hybrid battery system is more likely to keep the whole system running so (at least in principle) you'll have a unlimited runtime - although if your battery goes flat you might not be able to "cold start" the system without an AC mains supply.

ggmf

Beaten by @QrizB

1. My  South panels have usually exceeded the projected PVGIS suggestions. My East panels under perform the suggested PVGIS. It depends on many factors, orientation, mounted angle, weather, plagues of locusts or a passing heard of wildebeest etc.  I left losses at the default setting.

2. Many systems provide the option to charge from grid, solar and/or both.

3. Around 400kW (+/- 50kW) is around the normal output of panels being specified at the moment, output increases as technology develops and what's available, however, larger outputs usually mean larger size, will they fit?

4. You will be limited buy the inverter and battery output (my battery is limited to 3kWh), really depends what you want or need to keep running on a power cut. My EPS output is only enabled in the event of no mains power, so having secondary circuits and changeovers installed is not worth it for us. I have a 4 way extension block connected to mine, so I can run  some lights, router and low power devices, but no change or running the oven. Also is clearly dependant on the battery charge when the power cut occurs, if notified of a power cut then you can take steps to charge the battery, however that is not always the case,  how to time that?

I'm sure you will get plenty of other responses.

Screwdriva

boots_babe said:

2. Givenergy battery.
One of our quotes features a Givenergy battery. Reading the information on this, it looks like this enables you to actually charge the battery from the grid when it's a cheap rate, in addition to charging from solar. Is my understanding correct? And if so, are there any other batteries which offer this feature?

Hello again! I'm sure you will receive a variety of opinions on all these topics, so I've reserved mine for the areas where I believe an added dimension may prove useful. 

GiveEnergy are a good battery manufacturer. Would I pick them over LG, SolarEdge (if I had their inverter) or Tesla? Probably not. But definitely would pick them over most other brands on the market. 

3. Panel brands/specs.
Have had 4 quotes so far, offering 2 different panel types. Common wisdom on these forums seems to be to go for the largest spec, and most up to date panels that you can. My first question is, what are people's thoughts on which of these may be better to go for:

405 JA Solar (JAM54S30-405/MR)

395 TRINA SOLAR VERTEX S (TSM-DE09.05) 

But also, I have seen people talking about panels higher than 405 W, but not at all commonly. Is this because they are hard to get hold of, or is there some concern making people avoid them?

My thoughts tend to diverge from existing owners of Chinese components. I would never spec budget brands for a system I plan to own for decades - especially given the similarity in price and performance. There are plenty of quality brands from reputed corporations on the market at a range of price points. My picks are Aleo, Solarwatt, REC, Panasonic, Hyundai or Sharp. 

4. Islanding.
I'm not overly concerned about current new reports re possible short power blackouts. However, it would seem remiss of me not to at least explore whether we can spec a system that would keep running in this scenario. If it's possible without huge additional costs, why would I not want to do that, is my thinking. But have read very conflicting reports - some people saying just not possible, as the system must go totally offline for safety during a blackout, so that any required engineer can safely work on the system. But then others seem to think it possible, but I can't seem to find any specifics as to how. 

This is a no brainer in my humble view. The system can be designed to function in the event of a blackout - this is why I remain a huge fan of the Tesla Powerwall (the storm watch feature + massive 5kW throughput/ discharge rate are theoretically excellent to have). 

If there was a single line of advice I have to share, it would be do not settle, no matter what any installer claims is inconvenient, especially given the quantum you are about to spend. 

rew81

https://midsummerwholesale.co.uk/buy/trina/trina-vertex-s-plus-415

If you go for Trina at least choose their latest technology. 

boots_babe

Thanks for the helpful replies. I didn't know that most batteries can be set to charge from the grid, so that's really good to know. We are already on Economy 7 with Octopus's standard tariff, so definitely worth looking at charging the battery overnight.

Appreciate the feedback re realistic loss % on the panels, that helps to reassure me that I'm not being overly optimistic. I want to ensure I have built a robust model for determining the ROI.

Screwdriva - I take on board your comments re brands. For lots of things I am quite happy with a non-branded item (I am an MSE-er after all!) but you're right, PV is a huge investment and I guess as it's still early days the long term reliability of the various panel brands is not that well tested. I think I will ask how much the quote would differ if we went for a more premium brand, as I think may be worth it. Although I haven't yet asked the question re availability/lead time, so do wonder if the premium brands haven't been quoted for due to that reason? I will find out.

I've since joined a couple of PV Facebook groups, and it seems as though for <£500 the islanding can be easily achieved. At such a relatively small % uplift against the overall cost, definitely seems worth exploring.

Thanks all.