Expensive pv panels or double the quantity

[gravelrash]

Looking for maximum bang for buck with pv panels and looking at around 12000kwp minimum. Now should I go for expensive mono panels at £200+/330kwp or poly £85/270Kwp and double the number of panels...both have same warranties and both around 17.5% efficiency.

[SteamyTea]

More panels if your DNO will support it.

And it is kW, not kw.

[ProDave]

Things to consider:

 

How much roof space?

 

Do they have to be a particular colour for planning reasons or just because for example you prefer black?

 

How much can you afford Vs payback time?

 

And a very important one, how much will your DNO allow you to fit?

[joth]

15 minutes ago, SteamyTea said:

And it is kW, not kw.

Actually I think in this case the OP means W not kW, otherwise:

 

21 minutes ago, gravelrash said:

looking at around 12000kwp minimum

 

..this would be a 12MW generation plant, which would need maybe 50 acres of land and a 110kV supply

 

?

 

(enough with the smart-arse  replies already)

 

 

 

 

[ToughButterCup]

Both you @joth and @SteamyTea make a good point (if a little unkindly here).

 

The concepts concerned are not easy to get your head round if all we do most days is shove money around our world.

Very few of us shove electricity around the place. Or have a clear idea that  a commonly available one bar electric fire switched on for one hour consumes a kW and so calling it a kW hour is another way of describing the same thing. So when it comes to kWp, or kW/m squared per annum ...

4 years on, and I'm still cautious about units where electricity is concerned (pun accidental)

[MikeGrahamT21]

Since presumably you are installing Solar PV for environmental reasons, then go with less panels which are better, as they will have less embodied carbon, and all of the other chemicals and rubbish which get created during their production.

 

And if nothing else, its less bits to go wrong!

[Jeremy Harris]

kW is a unit of power, so the measure of the maximum output at any instant that the system can deliver.  With generation systems it's common to add a "p" as a suffix to indicate that this is the peak power, not the average power, or the power on a dull day.  The kWp figure is the absolute maximum that the panels are likely to be able to deliver under their rated conditions.

 

kWh is a unit of energy, so power delivered over 1 hour.

 

Power is generally a less useful way of describing a system, in much the same way as it can be for cars.  Using the car analogy, the maximum amount of power available determines how fast the car will go, yet most of the time cars are driven at speeds that are much lower, so many might be more interested in how much energy they use, i.e. how many miles per gallon can the car achieve.

 

DNOs are mainly interested in the maximum power that a system can deliver to their network, though, as all they are bothered about is whether their cables, transformers etc are able to accept the maximum generated power whilst staying within limits for the local grid voltage.

 

The maximum "bang for the buck" isn't determined by the peak power, but by the amount of energy generated over the course of a year.  Matching the positioning of the panels to the times when the house uses most energy may give a better outcome, in terms of value for money, than having a system that generates more peak power, but over a narrower window during the day.

[SteamyTea]

28 minutes ago, AnonymousBosch said:

I'm still cautious about units

Goes back to the Unit of Energy, the joule [J].

A joule can be expressed as more simple, understandable units of the kilogram [kg], the metre [m] and time in seconds

 

J = (kg.m²) / s²

 

Once you have a joule, which can be considered as a box of energy, power, is the rate you take the energy out of that box.  Power is the watt [W].

 

There is a direct conversion between J and Wh.

 

I wish we always dealt in joules, rather than watt.hour.  It is just messy.

Edited November 1, 2019 by SteamyTea

[SteamyTea]

I had this annoying strike though problem before, is someone playing with the forum software at the moment.

[ProDave]

The DNO limit is an annoyance.  It was made pretty clear to me that if I went over 3.68KW (16 amps) there would be a network upgrade charge. I never got as far as formally applying to find out how much.  The silly part of that is I self use almost all of what I generate and in the first year have only exported 128KWh and most of that will be at mid day when my immersion heater is running at 100% soaking up as much as it can and the export will only be a few hundred watts.  They are not open to reason on that, they work on the basis you might export all that you generate and so their network has to cope with it.

 

Anyone installing PV now, with no more Feed In Tariff, must be working on maximising self usage and exporting as little as possible, so you would think the DNO should be open to a reasonable scheme in place to limit export?

 

 

[joth]

23 minutes ago, JSHarris said:

The maximum "bang for the buck" isn't determined by the peak power, but by the amount of energy generated over the course of a year

 

This is a great point and I'll highlight it (in case it is lost under the helpful SI unit preface)

 

To the original question, if there's no space or DNO constraint, and all panels are equally well positioned, I think the larger array of 270W panels will give more bang (annual yield) for buck then having half as many 330W.

It's fairly easy to do some modeling with the PVGIS ( https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html )  tool to verify this. AFAICT that doesn't differentiate mono vs poly panels, so if they both have the same efficiency it will just be a matter of the larger array giving more output

 

37 minutes ago, MikeGrahamT21 said:

Since presumably you are installing Solar PV for environmental reasons, then go with less panels which are better, as they will have less embodied carbon

Thing here is both have the same efficiency, so the more expensive one isn't automatically better.  I think we'd need to know the relative dimensions of them to estimate which requires more resources to manufacture and from that estimate which option has larger embedded carbon. But still, for a fixed cost, my gut instinct is go with the solution with highest annual yield and over its lifetime it will payback any higher carbon as well as economic capital cost.

 

1 hour ago, AnonymousBosch said:

Both you @joth and @SteamyTea make a good point (if a little unkindly here).

 

Sorry if came across as unkind, my comment was meant as gentle jesting with a small dose of self-deprecation.

 

(in the context that nit picking usage of numerical units seems a well established tradition in this place  )