Deleted

ABrass

Deleted_User said:

In my location published historical data tells me that I can expect 0.36 peak sun hours a day. According to my configuration that would generate total power of 360 watts (360wh energy) per 1kw array.  However, you need to take account of system inefficiency too. Even in summer under optimal conditions the best you can hope for is 80% efficiency. So that brings you down to 288watts of power (288kwh of energy) per day. If I installed 8kw of panels that's at most 8 x 288 = 2,300w of power generated (2300wh of energy). So despite that massive outlay of 6kw of extra solar panels and the extra battery backup and inverter power to make full use of it in the summer - I'd still have a shortfall of 2700w power (2700kwh of energy) per day in winter.  

In winter it's much harder to make efficient use of solar. This is due to the system running costs. When you're powering through 5000watts of power a day the running costs of the system (inverter, power on, fans) is a small percentage of power used. When you're only getting 2700watts of power a day the system overhead is a much bigger percentage of energy consumed. Therefore, system efficiency (unless you jump through hoops to manage things differently) goes down. 

You are other than reiterating what I've said from the outset - diminishing returns on investment. Yes you can do it if you throw enough kit but with diminishing returns on investment.

I am saying that in order to get off grid you need to find alternative solutions to solar in order to get through winter comfortably. Solar will give you a little bit of help,  but not enough.

Don't try to work out the kWh yourself, PVGIS will do it for you and not get it wrong. You'd do much better to leave the units off because you keep getting it wrong.

PVGIS also factors in efficiency, it defaults to 14%.

If you keep feeding junk data into your calculations then you'll continue to get junk out. 

ABrass

ABrass said:

Assuming you're in the Midlands a SSE orientation and 10 degree slope and no shading you'll generate 1750kWh total over the year according to PVGIS using standard assumptions.

https://re.jrc.ec.europa.eu/pvg_tools/en/

How much do you think you're going to generate a year?

Deleted_User said:

ABrass said:

Deleted_User said:

In my location published historical data tells me that I can expect 0.36 peak sun hours a day. According to my configuration that would generate total power of 360 watts (360wh energy) per 1kw array.  However, you need to take account of system inefficiency too. Even in summer under optimal conditions the best you can hope for is 80% efficiency. So that brings you down to 288watts of power (288kwh of energy) per day. If I installed 8kw of panels that's at most 8 x 288 = 2,300w of power generated (2300wh of energy). So despite that massive outlay of 6kw of extra solar panels and the extra battery backup and inverter power to make full use of it in the summer - I'd still have a shortfall of 2700w power (2700kwh of energy) per day in winter.  

In winter it's much harder to make efficient use of solar. This is due to the system running costs. When you're powering through 5000watts of power a day the running costs of the system (inverter, power on, fans) is a small percentage of power used. When you're only getting 2700watts of power a day the system overhead is a much bigger percentage of energy consumed. Therefore, system efficiency (unless you jump through hoops to manage things differently) goes down. 

You are other than reiterating what I've said from the outset - diminishing returns on investment. Yes you can do it if you throw enough kit but with diminishing returns on investment.

I am saying that in order to get off grid you need to find alternative solutions to solar in order to get through winter comfortably. Solar will give you a little bit of help,  but not enough.

Don't try to work out the kWh yourself, PVGIS will do it for you and not get it wrong. You'd do much better to leave the units off because you keep getting it wrong.

PVGIS also factors in efficiency, it defaults to 14%.

If you keep feeding junk data into your calculations then you'll continue to get junk out. 

So how about you illustrate your point by taking one of MY calculations and showing me how it should be done.

Then we can compare results and see if we came up with the same answer. 

I did that already, I used the source data and calculated the output with PVGIS. But I don't know where you live, or the complete details of your system.

I can't work out how your method works. Presumably you've got values for the average irradiance and have factored in angle and other factors, essentially hand crafting PVGIS, but clearly it hasn't worked.

zeupater

Deleted_User said:

zeupater said:

Hi scarter

Reviewing posts for clarity ....

1. You are not off grid for electricity and have solar+battery as a mains failure backup solution which is also used to reduce mains usage ?
2. Your plan is to maximise solar consumption in the summer ?  
3. You have ~2kWp of panels mostly facing SSW, mounted on wood-stores in the garden ?
4. The panels you have are 175Wp because 200Wp panels would be too big to mount on the log store roof ?
5. You have 12 of these panels (2000/175=11.4) giving a true nominal capacity of 2.1kWp ?
   
6. You have a total of 7kWh of battery storage capacity ?
7. You have 2xBluetti AC200Max portable storage units, each having Energy storage capacity of 2kWh & delivering 2kW of Power ?
8. You have additional Bluetti expansion battery capacity of ~3kWh ?
9. This would be a single B300 expansion unit connected to one of the AC200Max units ?
10. The Bluetti AC200Max has a maximum solar connected charge rate of 900W ?
11. The Batteries are charged directly via DC connection to the panels?
12. Your ~2kWp of panels are not connected as one array but operate as 2x 1kW DC arrays each connected to one of the Bluetti devices ?
13. You expect to return batteries to a fully charged state using the attached solar panels each day?
    
14. You still have mains gas connectivity for cooking & heating, although you are attempting to minimise it's use through use of solar ?
15. Your total outlay for 2kWp of DIY solar + portable batteries was ~£7k ?
16. You installed (/expanded) the system in September this year?
17. You are currently (as of Nov 2020) saving ~1.5kWh/day, so around ~45p/day ?
    
18. You expect to heat water, use a dehumidifier/refrigeration etc in summer with the current setup with an ultimate goal of eventually going off grid ?
19. Going off grid means both gas & electricity, so all appliances,, cooking & heating will be via a combination of solar & biomass ?
    

Any chance of addressing the above as it may help ... Z

No to pretty much every one of those points (a couple are correct). 

I'm using my situation to illustrate the basic concepts to help those that aren't grasping the concept of diminishing return on investment. But you can insert any scenario you like.

Essentially the point of the thread is about the diminishing returns on investment from simply adding more solar and obviously from that flows the question of what you CAN do to get you through winter more comfortably (or with less reliance on the grid). One such example is that you get more bang for your buck by using your system in a more optimal way.

Solar alone will not get you offgrid (off grid means not reliant on the national grid) during the winter unless you throw crazy amounts of cash at it. Most people wouldn't have the space to install enough panels!!

The thread isn't about my system. The thread is about the basic concepts, most/some of which apply to all systems. 

Hi

Can you explain which of the 19 20 points are the 2 correct ones then ? ....

I'm pretty confident that the points are all based on what you yourself have posted, so where is MY error in understanding ? ... I'd guess that there'd be a number of contributors to this and other related threads that would develop their understanding of what you're attempting to achieve if you help us!

By the way, offgrid means offgrid, that's no connectivity to the grid, not keeping connectivity to the grid but choosing to minimise it's use .... for example, we have connectivity to gas, but haven't used any at all since March 2022 when we used <80kWh, yet we're still connected to the gas mains ...

As an aside, the thread revolves around a basic concept that you yourself see a diminishing return on investment as installed PV capacity increases .... however, consider taking this outside the bubble of what you have, see & assume and look at an extremes logic case .... at one end of the thought process you have a small system with little access to economies of scale showing little return due to low consumption and at the other end you have a community based solar farm scale investment serving a relatively high demand ... both could be on grid, off grid or even have micro-grid connectivity, but the return isn't related to the amount of storage or the installed capacity, it's directly based on the optimised relationship between the both of these relative to satisfying demand .... what's more, the same concept applies to scaling this to the entire grid, not only in the UK, but elsewhere too ... further than that, when you consider that what we're considering effectively boils down to demand, production & stock, we can see that it's not unique & applies to absolutely any form of supply chain ...

If you've chosen to not have your system connected to the grid, yet still be connected to the grid then that describes the limiting factor in what you are seeing ... for others the limiting factors may be their own demand, space availability, money, storage, access to grid resources and many others, yet there are still ways & options available to enhance the ROI if that's what they're looking for .... for example, it's likely that within a very short timescale, many will either be selling their excess solar generation at peak demand times for a decent profit against their investment, or simply using arbitrage type offerings to import & store grid electricity at cheap overnight rates & selling it back (through demand based scheme) at peak demand daytime rates ... all of these can have a positive effect on ROI that you're not considering because they don't apply to your own circumstances ....

Swings & roundabouts ... now what about addressing the points that are based on interpretations of what you've posted, they must be relevant to this thread, because they form the basis of the assessments that you're attempting to 'sell' to us ...

HTH - Z

Edit: Change 19 points to 20 to reflect amended list

QrizB

ABrass said:

I did that already, I used the source data and calculated the output with PVGIS. But I don't know where you live, or the complete details of your system.

scarter has previously said they are in West Scotland. That's quite a large area but pick a likely-looking town and you won't be far off the mark.

For details of their system, use zeupdater's post above since, while it's "no to pretty much every one of those points" it's also close enough until such time as we're given anything better by the OP.

Deleted_User said:

In winter it's much harder to make efficient use of solar. This is due to the system running costs. When you're powering through 5000watts of power a day the running costs of the system (inverter, power on, fans) is a small percentage of power used. When you're only getting 2700watts of power a day the system overhead is a much bigger percentage of energy consumed. Therefore, system efficiency (unless you jump through hoops to manage things differently) goes down.

and

Deleted_User said:

One such example is that you get more bang for your buck by using your system in a more optimal way.

You would get more bang for your buck by doing it differently, I agree. If I was in your position, and starting from scratch, I'd look for:

• Cheaper, longer-warranty 60-cell panels intended for fixed installations (either saving money or allowing a larger array for the same price);
  
• Put my panels in a location where they can see the sun for pretty much the whole day, at an angle that gives me the longest effective generation season; and
  
• A single central battery storage system intended for permanent installation (giving higher efficiency and a single shared battery bank, rather than having it permanently shared between three separate systems).
  

Here's a plot from PVGIS of 2kWp of panel, facing SSW inclined at an angle of 22 degrees, located in Oban:

The total output for the year is 1543kWh, weighted heavily towards the summer months.

Here's a plot for the same location, but this time oriented S and inclined at 65 degrees:

The total annual output is about 60kWh less, and the summertime peak is lower, but you're now getting at least 3kWh/day (on average) from February through to October, and Nov/Dec/Jan are higher too.

One last thing:

Solar alone will not get you offgrid (off grid means not reliant on the national grid) during the winter unless you throw crazy amounts of cash at it. Most people wouldn't have the space to install enough panels!!

Even in Oban an 8kWp array, installed facing south at 65 degrees, would generate around 160kWh in an average December. That's over 5kWh per day, on average, and if backed with a suitalbe battery would see many of us through the winter. There are some members of this forum with arrays that size or larger, and at least one with a 20kWh battery.

Martyn1981

It's been a decade, but I recall having discussions with some folk in the early 2010's, as they explained why PV doesn't and won't work in the UK.

They (several different people, at different times) all made the same claim that you get about 10x as much generation in the summer as the winter. I challenged that suggesting even the best v's worse month (so more extreme than a 3v's3 month comparison) for a typical roof mounted south facing array is about 4 to 1 (as can be seen in the PVGIS numbers I've posted on here).

All of the responses I got, telling me that I was still wrong, referred not to actual UK PV generation, but to sunshine hours, typically showing a 9x (they rounded up) difference of Dec v's June.

Their error is largely down to two issues, temperature, which impacts generation as colder panels are more efficient than hot panels, and secondly the angle of the sun to the panels. In the winter, a south facing panel will have a good angle to the sun all day (not ideal, of course) as it rises in the SE and sets in the SW. But in the summer, a lot of the time the angle is poor as the sun rises behind the PV in the NE and sets behind it in the NW.

I point this out as its so important to look at reality, and in this case I think PVGIS can be that reality, as it has proved for me (and I think most MSE PV'ers) over a decade to be extremely reliable. Been a very long time since I've noticed someone using estimated sun hrs for their calculations, rather than estimated PV generation.

zeupater

Deleted_User said:

Good points that I 100% accept and will take into consideration when crunching the numbers!!

I mean at the end of the day, you need to do the best you can with estimates and projections then see how it tallies up with what happens in the real world.

I'll dig deeper into figuring out differences in efficiency due to temperature. I know you're right re tempt as I've read that before. But I don't know how much of a factor it is.

Cheers.

Hi

Then why not have a look at PVGIS as a number of contributors have recommended ... (link : https://re.jrc.ec.europa.eu/pvg_tools/en/ ) ... as your panels are low down (compared to roof mounted) you could also model the shading for their specific location in your garden ... if you're worried about the default 14% inefficiencies as raised, then change it to what you believe is more appropriate for your system, I did based on the factory measured performance of the panels received, our inverter specifications & the losses expected on our upgraded DC cables, as many others have probably done too ... 

As well as the efficiency losses you mentioned a few posts back, you'll also need to consider that there's a likely degradation of panel efficiency with age ... our panels are currently covered with little presents left by a couple of pigeons which need some attention, but a steady build up of dust etc will definitely have a negative effect over time ... then there's the inevitable battery performance loss over it's cycle life to consider .... the more you cycle the battery, the shorter the time to reach the manufacturer's battery 3500 cycles to 80% capacity threshold ...

All of these 'things' are likely understood by many that have replied and you'd get the answers you're looking for if you were to simply ask and not assume. Looking at who's responded on this thread alone, there's probably well over 100years of combined PV generation experience totalling many hundreds of MWh ... our PV and thermal systems alone when combined would likely be >3x larger than the setup you've described, and that's on top of experience with various thermal & off-grid PV setups going back to the 1970s .... In my experience, the information normally offered on this forum is about as sound as you can find such information anywhere, mainly because it's openly offered by a community of experienced users as opposed to those marketing goods & services or quoting theoretical conditions from published specifications etc.

HTH - Z

70sbudgie

This post has been highly addictive. 😂

It has also prompted me to have a look at my blank south facing wall to see whether the winter shading (from next door) is too much to make it worthwhile installing vertical panels for increased winter generation. I will also be visiting PVGIS to see how my location impacts.

Solarchaser

You know something clicked in the last couple of pages of reading, and maybe it's clicked wrong, but it clicked all the same.

All of us who love PV, accept with a grimace that PV generates loads when you don't really need it, and not enough when you do (summer/winter).
Our default is to optimise (or plan to) for the best possible generation for winter as that's when every kwh is a prisoner, and I think Mart, QrizB and Abrass have demonstrated that very well.

I may be wrong here, but what clicked was that's not actually what you are interested in, because in the winter you are more likely to just switch it off, because its so inefficient to run your generators all day, and make a pittance of energy, or even run negative if the PV is poor, and you don't really care about the maximum amount of PV generation in a day, but only running your system to its maximum efficiency. 

In this way the summer is most efficient as it has the most solar, hence why everything has been about return on investment when pretty much running a summer system.

If im wrong, fair enough, but it just seems that we have all tried to push the majority held belief that you stack up solar panels as many as you can to get the best production in winter, but you have railed against this on grounds of overproduction in summer.... most of us accept this is what happens. 

Weirdly it's the fact you said you sent something to your husband which changed my view. This is, I assume, (because there is no real identifier), a majority male "domain" and so my default is to assume I'm dealing with a male, unless it's made obvious I'm not. I believe 70sbudgie and silverwhistle are female also from previous posts.
As a male of a certain age, I'm aware that males talking to males can be more *direct* than if talking to the fairer sex, and so I had a flash of "oh, I hope I wasn't too direct" and weirdly that led me to think, maybe you are coming from a different direction all together. 

Having said all of that now, I realise you may indeed be a man married to a man, which nulls everything above. Its strange how my mind meanders sometimes 

Martyn1981

70sbudgie said:

This post has been highly addictive. 😂

It has also prompted me to have a look at my blank south facing wall to see whether the winter shading (from next door) is too much to make it worthwhile installing vertical panels for increased winter generation. I will also be visiting PVGIS to see how my location impacts.

My idea will suffer a lot of shading, but still viable I believe. Crucially I'm chasing winter generation, so the poor performance in the summer doesn't concern me, so that may be the trade off you need to consider.

At the bottom (ESE) end of our garden is a large and ancient Magnolia, so it will shade ground mounted PV to its SE, and at the upper end of the graden is the house (of course), shading the SW, so I need to pick a sweet spot along the northern fence. Originally I was planning a 3 panel south facing ground mount, probably 70d, specifically to target winter sun in the SE to SW which should be unshaded.

3 panels to avoid planning permission which is required if you exceed 9m2, but also no more than 3m on any one side. I even have some tower scaffolding for the face, and a SB1700 inverter, all donated by a lovely bod from another forum. However, I've now been seduced by the thought of doubling my winter gen, requiring ~2kWp of PV, so 4 or 5 panels of the oversized (2m(ish)) variety. So now plan a wooden frame, which I'll panel off to the lower front and sides, making it a ladder store, on which PV can be mounted without PP.

I mention all of this to point out that it's far from ideal on an annual basis, which is of course a valid concern when first considering PV, but this would be aimed solely as a top up measure for poor generation periods. And not just the winter, but also a boost during low gen in the shoulder months, such as cloudy weather, when I need about 1kW of PV generation, to allow the use of the a 3.5kW heat pump (roughly 700W draw) for 'free'.

And lastly, to give all the lucky 'southers' a giggle, in the worst 2 or 3 months, my gen actually dips during mid day - the ESE sees a bit of sun in the morning, and the WNW a bit later on, but mid day when the sun is really low in the south, it can't hit the E/W panels, so actually drops from poor to carp generation. It's a hard life! 



Ohhh, lastly (again) all of this is due to the fact that PV panels themselves are now so cheap, so that part of the ponderings is of less/little concern. My troubles are instead one of a DNO nature as I'm at max, and hinge on getting a zero export home battery approved by the DNO. Whilst this would be an AC side battery, I'm looking at ones with hybrid inverters and an additional DC PV feed. So the PV would piggyback off the battery certification, with no direct mains connection with the battery managing everything, and when the battery is full, the inverter/charge controller would simply shut down the DC side PV.

Returning to the thread purpose, is this cost effective, I think so, but only based on getting a battery anyway. Will the additional PV be best placed - not if maximising generation, but yes if maximising my needs, as summer gen is already more than enough, even with BEV's.

Martyn1981

Makes a lot of sense to me now. I was thinking that the DC losses should be low, and on scrolling back up you've given that info. So I can see a definite benefit now to what you are saying, where you shutdown the AC, but not the DC side. The battery charges with little loss from the PV, then when you have a decent amount stored, you use it via the AC side.

Is that close(r) to what you've been saying? My reading was that the losses meant it wasn't worth the PV / battery / DC side, and I was thinking anything is better than nothing (when exceeding any losses), and couldn't square the bigger picture.

Not exactly the same, but similar I suspect to using a battery to smooth out / buffer variable generation in cloudy weather, to prevent expensive import. For instance I've had days with generation bouncing between 1kW and 3kW, averaging around 2kW, but I have to charge the BEV at 1kW, to avoid expensive import (I have the fall back of cheaper night rate leccy). Just a small amount of storage would do the buffering and help. The same applies to cloudy weather and variable generation when I want to run the small A2A heatpump.