So now I have a solar PV system how do I make the most of it???

zeupater

Helen18 wrote: »

Eric, sorry for missing the bits about micro inverters. Are optimisers the same thing? If not, what is the difference? There are such a lot of new technologies for me to get my head round. I'm doing my best in amongst getting 3 children in 3 different directions! Also I made that post before I'd seen the replies above as they didn't refresh till after so sorry about that too. I'll make time to read back through all the posts now I've got a bit more understanding to help.

Re the micro inverters... You seem to suggest the performance won't be any better than any other inverter unless there's snow or shade, the guy I spoke to today definitely said that they performed better at lower light levels. I didn't think he meant shade by this as we talked about this being an advantage with the aga as even a little generation for as long as possible is beneficial. Isn't this the case? Am I being spun a load of sales guff again or have I misunderstood what you or he meant?

Thanks
Hx

Hi

Effectively there is the possibility of having a central inverter with one or 2 MPPTs (even more on commercial-size units), an inverter which works with DC optimisers on each panel to mitigate the effect of shading (each optimiser acts as a MPPT), or micro-inverters on each panel feeding AC into the mains ..... ( http://en.wikipedia.org/wiki/Solar_micro-inverter )

If you have a single panel array and no shading, there is no possible way that either optimisers or micro-inverters will outperform a decent central inverter. If anything performs at ~97% efficiency, how can anything else outperform it by 10%, 15% or 30% ?? ..... if there is a shading issue or significant difference in the plane of the array, optimisers or micro-inverters can/will show an overall efficiency improvement .... however, if neither are an issue then any claims would just be sales-talk.

There is a possible argument to be made that the use of micro-inverters or optimisers would lead to a lower overall cost of ownership if a single unit fails (vs central inverter), but the added complexity through having more units which are open to failure in itself raised the likelihood of a failure happening. Unlike a failure of a central inverter, a small unit on the roof will likely require access via a tower or scaffolding, the cost of which probably isn't included in the failing unit's manufacturer guarantee ...

Just points to consider ...

HTH
Z

Helen18

Hmm, I need to ask some searching questions when he comes to do the survey! Will try and find out as much as possible, or as much as I can make sense of!
Hx

Martyn1981

Helen18 wrote: »

Mart,
Funny you should go back to the immersion issue again as we were just thinking about this again. The hot water is fuelled by the pellet stove over the summer. I was asking hubby how many pellets we'd used and since May about a tonne which is £220 and that's pretty much all on hot water as the heating hasn't been on much if at all in that time. So actually, the payback time would be pretty quick so this could be a good plan after all. We do have a 3kw electric immersion but have hardly ever turned it on as never needed it and petrified I'll forget to turn it off!
Hx

Hiya Helen, glad that was nagging away at me then. So it sounds like it would certainly suit you. Doesn't mean you have to rush in of course, I was just pointing out that a package deal might be a little cheaper. There's a thread mentioning other makes and experiences here:

https://forums.moneysavingexpert.com/discussion/4152489

It's a big thread, so maybe just start in summer 13 onwards, as people start to post their experiences.

Personally, I don't have a water tank, so despite loads of spare leccy in the summer months I just have to get a nice warm feeling from knowing I export lots of clean leccy instead!

PO's v's micro-inverters, I think others have explained, but basically each panel gets to work individually, without any drag from the others. Different technology, but the same effect.

Earlier I said you'd need 4MPPT's if you had two sets of panels, and sub divided onto 2 pitches, well have thought of yet another option. There is an inverter manufactured by Steca called the StecaGrid 2010+. It's 2kW with 2MPPT's but you can add 2kW slave units to it, and each slave has an additional 2MPPTs. Also very low minimum voltage of 80V which would suit 4 sets of 3 panels.

Not sure if they are any good, and efficiency wise they are a bit low, near 93% (whereas a really good inverter is 97%(ish)). Just another thought/option. Maybe ask an open minded installer, I'm sure they'll quickly tell you if the idea (or the inverter) is rubbish.

Lastly, extending the system at a later date. I've added a section onto the FAQ, see section 10 all about extensions. So, if you get hooked, you could think about adding some ESE panels at a later date, all other factors permitting.

For now, I'm guessing what you really need to know, is what is the maximum kWp you can squeeze onto the south roof, and whether or not it can be done with just two strings, connected to a 'normal' dual MPPT inverter. Depending on the answer, you'll then need to decide the next step.

All the best.

Mart.

Helen18

Btw we have two sections of south ish facing roof, each big enough for 6 panels, separated by two east/west gables with plenty of space. The south bits have a change of pitch, upper section at 40 degrees and lower at 22degrees. Also, next door almost touches our house and has a higher roof so creates some shading on outer two panels (more on the 22deg pitch). Or we could scrap putting last two panels there and add them to any east panels.
Hx

Helen18

Earlier I said you'd need 4MPPT's if you had two sets of panels, and sub divided onto 2 pitches, well have thought of yet another option. There is an inverter manufactured by Steca called the StecaGrid 2010+. It's 2kW with 2MPPT's but you can add 2kW slave units to it, and each slave has an additional 2MPPTs. Also very low minimum voltage of 80V which would suit 4 sets of 3 panels.

Not sure if they are any good, and efficiency wise they are a bit low, near 93% (whereas a really good inverter is 97%(ish)). Just another thought/option. Maybe ask an open minded installer, I'm sure they'll quickly tell you if the idea (or the inverter) is rubbish.


All the best.

Mart.[/QUOTE]

Hi Mart (all),
Trying to gather a list of questions for when this guy visits to survey tomorrow. You mention about this Steca inverter above. I'm wondering if it's generally deemed better to have one inverter inside, rather than micro inverters on each panel (if you ignore all the shading etc issues) and if so why? Is it just the practicality and cost of getting up on roof if there are problems? Or are there other benefits?

I think we'll need to do something more complex but just trying to figure out where the extra costs lie and where any increases in performance can come from. The micro inverters suggested apparently have a 25yr warranty and diagnostic software but need to check if labour/scaffolding etc is included. Plus that's useless if the company goes out of business!

So far I'm thinking, having panels on south and east roofs totalling 4kw is prob going to be a sensible cost/generation route.

Optimising in some way seems important because of all the diff pitches and orientations. This will prob increase generation because of each panel working independently and prob not for any other reason (although the wiki link suggestes they improve performance - will read that again!)

On top of that presumably we can improve performance by choosing better panels? Haven't begun to explore this really. Any one able to comment? It would seem things like the Sunpower ones end up too expensive unless space is a huge problem, but I'm guessing there are other less expensive ones. Do we look for highest wattage? Is there a general consensus of a particular brand or panel that performs better than others? I'd like to feel that we make an active choice about which panel rather than just getting whatever we're given.

Then we can think about which switching devise (solar immersion thing).

Anyone think of any other ways to get maximum output from the system at this stage. Have I got anything wrong above?

Thanks
Hx

Ps, bit at top should be a quote, tried to delete some so it wasn't so long but that hasn't worked. :-?

jackieblack

Helen18 wrote: »

Ps, bit at top should be a quote, tried to delete some so it wasn't so long but that hasn't worked. :-?

That's because you deleted the bit at the start of martyn's quote which would have said

Martyn1981 wrote: »

Martyn1981

Helen18 wrote: »

Hi Mart (all),
Trying to gather a list of questions for when this guy visits to survey tomorrow. You mention about this Steca inverter above. I'm wondering if it's generally deemed better to have one inverter inside, rather than micro inverters on each panel (if you ignore all the shading etc issues) and if so why? Is it just the practicality and cost of getting up on roof if there are problems? Or are there other benefits?

I think we'll need to do something more complex but just trying to figure out where the extra costs lie and where any increases in performance can come from.

Thanks
Hx

Hiya Helen, IMO and despite having PO's on one system, I'd say it's better to have an inverter within reach, rather than PO's or MI's (micro-inverters) where access may be an issue. Unless ..... shading is a serious concern, as it is with my WNW. So you will have to balance all these factors.

I'm having second thoughts about that Steca inverter, it only has a 5 yr warranty, and I've no idea if they are popular, or rare as hens teeth. So worth asking an installer (or two), but don't hold your breath.

At the risk of confusing you further, I've thought of yet another idea. Partly because you seem more open to an install on both the ESE and SSW and something you mentioned.

You suggested dropping 2 panels on the SSW roof that would be effected by shade. If so, does that mean that all of the panels on the 40d roof can be linked on a single string, without 'harming' each other? If so, and if the same for the 22d roof then you're back in business with a 'normal' dual MPPT inverter.

Stick 10 panels (2.5kWp to 2.7kWp) on the SSW, then the remainder on the ESE with their own inverter. Yes you'll have two inverters, and this will probably work out the same cost as a single SolarEdge inverter plus PO's, but if no shading issues, then less concerns for the future. In fact in 10 years time if one inverter fails, you may get lucky and there may be a triple MPPT model inverter .... but I digress.

Small problem .... here we go .... using two inverters means that you won't be able to cap output at 3.68kW if the panels total more, so you may need DNO permission. But again ask the installer for thoughts and ideas. They could, of course, dial down the inverters, so that their max outputs total 3.68kW and just put that on the paperwork (they may even forget to actually dial them down ).

Happy to explain in more detail (or anything else I've posted earlier), just worried that I've completely confused you by now. Basically, every problem has a solution.

Mart.

PS. If dropping panels from one side of the roof, don't forget to consider aesthetics as it may look 'unbalanced' to the eye. M.

Martyn1981

Helen18 wrote: »

On top of that presumably we can improve performance by choosing better panels? Haven't begun to explore this really. Any one able to comment? It would seem things like the Sunpower ones end up too expensive unless space is a huge problem, but I'm guessing there are other less expensive ones. Do we look for highest wattage? Is there a general consensus of a particular brand or panel that performs better than others? I'd like to feel that we make an active choice about which panel rather than just getting whatever we're given.

Thanks
Hx

Me again. Remember, don't be misled by 'higher efficiency' panels, this generally means that they can do the same job but with a smaller footprint. At the end of the day a 250Wp panel is the same as any other 250Wp in terms of actual output.

The bonus is usually claimed that they perform better at low light levels. Whilst this shouldn't be sniffed at, and I've no reason to doubt their claims, you do need to put it into perspective. If the panels perform 20% better, that sounds really good, but low light might mean only 10% of panel rating, so a 20% improvement takes it up to 12%, which doesn't sound quite so impressive. Every bit counts, but cost has to be considered too.

As regards what panels are best, no offence, but I always stay well clear of such discussions. I've no idea, and it probably won't be for another 10 years or so, before we can make any real comparisons. Doesn't help you I know, but just being honest.

Mart.

tunnel

Martyn1981 wrote: »

Small problem .... here we go .... using two inverters means that you won't be able to cap output at 3.68kW if the panels total more, so you may need DNO permission. But again ask the installer for thoughts and ideas. They could, of course, dial down the inverters, so that their max outputs total 3.68kW and just put that on the paperwork (they may even forget to actually dial them down ).
QUOTE]

Do they really need to be informed? It would be a very rare occurance to exceed 3.68kWh from the crossover between the 2 systems and i am talking from experience.

Martyn1981

tunnel wrote: »

Do they really need to be informed? It would be a very rare occurance to exceed 3.68kWh from the crossover between the 2 systems and i am talking from experience.

Hiya T. Doubt the systems (if they totaled 4kWp) would ever generate more than 3.68kW for any sustained period. But if the panels and inverters total more than 3.68kW, then it will be an issue. You might be able to multiple the panels by the inverter efficiencies and that might do it.

Actually, you've just made me think of a much simpler solution, you just install two inverters that add up to 3.68kW or less, eg 2.4kW + 1.2kW. Doh!

Personally, I'd say blow the top FiT rate, and slap 2.5kWp SSW + 2kWp ESE (or more if there's room) but only AFTER asking for permission from the DNO first.

Mart.