Solar Panels UK - is it worth it?

[Pete UK]

The cross charging wasn't there for me with the Gen1 Inverters, I believe I had the system set up completely independent to try an eliminate any chance.

It was working very well, the East would charge its battery via the associated inverter and the same via the West. The only down side was if you had better weather in the morning or afternoon, you potentially would have reduced charging to the affected battery, but in my case the panels are on flat roof areas at 10 degrees and do continue to generate all day ( although at a slightly reduced rate in comparison to the favoured side).

Once I had the Gen1's swapped out to Gen2's at the beginning of this month I noticed two issues. First is related to cross charging, whereby if one battery is at a higher capacity of charge it will begin to discharge to supplement the lower one. This can to and fro, the main problems being there will be losses and unnecessary 'wear' on the batteries being cycled.

The second issue I found, which I don't think is a problem and more of a benefit as far as I can see, either the East or West ( or both) can now charge either battery. The only problem, in my opinion is that it must be going from DC to AC and back to AC again which will also involve some losses.

To note, this was a like for like swap out so the changes in behaviour could only be in relation to the firmware ( of which I am on the latest beta for testing) and likely related to some form of AC monitoring that the Gen1's didn't have.

Both of mine are hybrid inverters, the cross charging is seen on both AC and hybrid multiple inverter set ups and apparently the AC inverter is priority for the EMS with the hybrid to follow at some point.

The software options, which I believe work very well and I'm likely to pursue myself in the short term are via Givenergy GivTCP. Facebook have a page, and have scripts ready to run to download - you just have to add some of your own details and use a raspberry Pi or something similar to operate. Link as follows:

Log into Facebook

Log into Facebook to start sharing and connecting with your friends, family, and people you know.

www.facebook.com

Thanks for that explanation. Very interesting.

So they were independent on the Gen 1’s but now somehow they can cross charge with the Gen 2’s. Presumably that’s to do with the Gen 2’s BMS firmware. Or the inverter firmware?

So for either or both inverters to now charge one battery or the other, they must both be connected to both batteries or it sounds more like one is discharging back through its inverter to the consumer unit to charge the other one (which would incur conversion losses.) Or more likely, could it just be that one inverter is charging one battery and the other inverter is not charging it’s battery and just putting the power to the consumer unit which is then charging the other battery? Either way sounds non-ideal.

Ideally they should charge non-evenly from the respective inverter and then do that when one of the batteries get full only. That would be most efficient.

Does this happen with all set ups like this or just a few?

Keep us all updated if anything changes.

 

[Rooster6655]

The only thing is with looking at the investment as a “savings” return, is that you can’t withdraw the initial capital outlay. It’s stuck on the roof!

So after 1 year at 6% ‘return’. If it was in the bank you’d have 106% of the total money. With it in a Solar system, after one year you’ve only got 6% of your entire money ‘invested’ back. So you’re basically 94% down. I guess that’s why everyone is ROI obsessed. Until you get to payback time you’re at a loss to the tune of the whole system cost minus your savings made up to that time.

Incase anyone is interested, over a 25 year period, if you have £30k in your savings to spend on a system and it brings in an annual return of 6% per year, let's say you put that into a ISA savings account paying 6% per year.

At year 12 the savings account would have £30366 and at year 25 the savings account would have £98756 in, if we deduct the cost of the system (-£30k) and sell the 25 year old system for say 10% of its initial value (+£3k), that leaves us with £71756 which over a 25 year period is an annualised return rate of 4.88% based on the initial £30k.

The system could last longer than 25 years and would be the key factor in getting a better rate of return, so its worth considering different scenarios.

 

[WannabeOwner]

At year 12 the savings account would have £30366 and at year 25 the savings account would have £98756

I'm curious about the alterative - the cumulative cost of paying the bill, inflation, and the loss of opportunity-cost of investing that money

Let's say electricity bill (the part that would be saved by PV) is £1,000 p.a., inflated by 5% p.a. and borrowing cost of 6% (to match the figure above - but maybe 5% inflation matched with 6% interest is an unrealistic scenario?)

I expect at £30K investment in PV / Battery would yield a bigger saving than £1K p.a. (I'm saving around £5K per annum on a similar investment, made a few years ago) but having a figure would allow scaling either way

I googled this so no idea if it is the right way to do the maths:

FV = future value - total amount to pay including interest (lost)
C = the initial payment amount (£250)
r = the quarterly interest rate (6% / 4 = 1.5%)
i = the quarterly increase in payment (5% / 4 = 1.25%)
n = the total number of quarterly payments (25 years * 4 = 100 quarters)

FV = £250 * [(1 + 1.5%)^100 - 1] / 1.5% + £250 * [(1 + 1.5%)^100 - (1 + 1.25%)^100] / (1.5% - 1.25%)
FV = £103,661.27

Is that comparable with your £98,756 figure, or are they Apples and Pears?

 

[bainsy]

I dont think I can go through 116 pages of posts, however I am moving house (I hope soon) and was wondering to get Solar Panels fitted when I move in.

Heard really positive things about it all, especially with the hike of these energy prices.
Of course I will look into battery storage - but I hope the general consensus is that having Solar Panels is a good thing?

 

[GRiLLA]

I dont think I can go through 116 pages of posts, however I am moving house (I hope soon) and was wondering to get Solar Panels fitted when I move in.

Heard really positive things about it all, especially with the hike of these energy prices.
Of course I will look into battery storage - but I hope the general consensus is that having Solar Panels is a good thing?

In terms of the planet, then yes, definitely a good thing.

In terms of whether they are a good thing in terms of money saving then the details discussed here make a big difference, but it's pretty hard to not show a cost advantage over 25 years. Whether the 'break even' point is in six or seven years, or fifteen years etc. is a function of the panels, battery, cost, location, how you use electricity, the contract you are on etc. That's what the 116 pages are about.

 

[bainsy]

In terms of the planet, then yes, definitely a good thing.

In terms of whether they are a good thing in terms of money saving then the details discussed here make a big difference, but it's pretty hard to not show a cost advantage over 25 years. Whether the 'break even' point is in six or seven years, or fifteen years etc. is a function of the panels, battery, cost, location, how you use electricity, the contract you are on etc. That's what the 116 pages are about.

Thank you.

I've just read the last few pages and some interesting details - especially since some are saying to invest in Stocks and Shares ISA's to compare the investment. (I also heavily invest in Stocks and Shares - both my wife and I)

I must also admit, the potential house is north facing- so I would need to consider "tilting" the panels or perhaps put them on a swivel mount of some kind.

Ill keep reading! thank you.

 

[Chimpy McChimp]

I dont think I can go through 116 pages of posts, however I am moving house (I hope soon) and was wondering to get Solar Panels fitted when I move in.

Heard really positive things about it all, especially with the hike of these energy prices.
Of course I will look into battery storage - but I hope the general consensus is that having Solar Panels is a good thing?

When I was getting quotes 2 of the companies gave me a detailed report on how much the system would cost, generate and save us over a defined period (I think 25 years maybe?). It looked like a template both companies used (identical layout, figures etc just different values based on what had been quoted) maybe see if installers will provide that for you as part of quoting process

 

[Mrklaw]

Thank you.

I've just read the last few pages and some interesting details - especially since some are saying to invest in Stocks and Shares ISA's to compare the investment. (I also heavily invest in Stocks and Shares - both my wife and I)

I must also admit, the potential house is north facing- so I would need to consider "tilting" the panels or perhaps put them on a swivel mount of some kind.

Ill keep reading! thank you.

you can experiment if you have a specific house in mind using something like PV-GIS online estimator you can zoom in on the map to the location, enter the size of panels in kw and orientation/angle and it'll spit out a monthly/yearly estimate.

North facing house isn't as important as the roof - if you have a N/S roof how big are the areas for panels? North isn't worthless - in summer it can be similar to south but drops off more steeply in the early/late months (so the curve is sharper). I'm getting north facing panels to augment a small south array. 'fill your roof' seems a good approach

 

[ringi]

Be careful as the price of electricity on peak PV generation days will likely at some point drop to a low level, hence I can't see how its possible to calculate long term saved energy costs.

 

[The_Cable_Guy]

you mean because eventually they will have an excess they cant use?

 

[ringi]

you mean because eventually they will have an excess they cant use?

Yes and that excess will be at the times that our PV is also creating the most output.

 

[Rooster6655]

I'm curious about the alterative - the cumulative cost of paying the bill, inflation, and the loss of opportunity-cost of investing that money

Let's say electricity bill (the part that would be saved by PV) is £1,000 p.a., inflated by 5% p.a. and borrowing cost of 6% (to match the figure above - but maybe 5% inflation matched with 6% interest is an unrealistic scenario?)

I expect at £30K investment in PV / Battery would yield a bigger saving than £1K p.a. (I'm saving around £5K per annum on a similar investment, made a few years ago) but having a figure would allow scaling either way

I googled this so no idea if it is the right way to do the maths:

FV = future value - total amount to pay including interest (lost)
C = the initial payment amount (£250)
r = the quarterly interest rate (6% / 4 = 1.5%)
i = the quarterly increase in payment (5% / 4 = 1.25%)
n = the total number of quarterly payments (25 years * 4 = 100 quarters)

FV = £250 * [(1 + 1.5%)^100 - 1] / 1.5% + £250 * [(1 + 1.5%)^100 - (1 + 1.25%)^100] / (1.5% - 1.25%)
FV = £103,661.27

Is that comparable with your £98,756 figure, or are they Apples and Pears?

Complex calculation but I can see what you mean, the £103k would apply if the bill amount was never repaid and interest kept accumulating over the 25 year period, it is similar to £98,756 ROI from investing the returns on the £30k solar install.

If you brought a £30k Pv/Battery and then you invested the bill amount £1k (income from solar) with a 5% inflation and a 6% return rate at year 25 you would get £90551 back, minus the cost of the system so year 25 you end up with £60551 assuming 0 value for the solar system, giving an annualised ROI of 4.52%

Now if we add finance for the system at 6% APR for £30k, the total repayable over a 25 period would be £57115 or over 10 years £39,680.65

I can run other numbers if anyone wants, I'm just using a spreadsheet and some online calculators.

 

[Rooster6655]

Thank you.

I've just read the last few pages and some interesting details - especially since some are saying to invest in Stocks and Shares ISA's to compare the investment. (I also heavily invest in Stocks and Shares - both my wife and I)

I must also admit, the potential house is north facing- so I would need to consider "tilting" the panels or perhaps put them on a swivel mount of some kind.

Ill keep reading! thank you.

Once you have worked out your estimated saving on your electric you can then work out an estimated annual return rate of your install cost of the solar system, people will get a different rate of return depending on their usage and if its being financed then this can reduce the ROI dramatically.

The thread is about whether solar panels are worth it, so having the good and bad calculations along with ROI is important as its no longer a no brainer with increasing interest rates and with many installers charging through the roof, I think solar/battery can be a good alternative investment if the numbers work but its important to not go in blind.

About the ISA/Shares, Solar for most a 25 year+ investment which makes it comparable to other long term investments, many index funds have long term annual returns of 6%+, so it's worth working the numbers out and comparing before going ahead.

 

[yessuz]

guys, just a questions:
how does the system with 2 inverters act?
in my quote I have one inverter for east, one for west.

Which one would feed to house (hey, inverter 1 - you feed kettle, I will feed oven), grid, or there is some management system?

 

[Pete UK]

Just watch out for the cross charging of the gen2 inverters, a new piece of kit called EMS will control it, but when it is out is anyone's guess!
There are third party solutions if you fancy tinkering.

Thinking about this a bit more. Could you just set the battery that fills up the most first (East side most likely) to NOT discharge during the period when you’re noticing the cross charging? Or at least for some periods within that time?

That would surely illuminate the problem?
Then the one with the higher charge wouldn’t cross charge to the lower one but both could continue to charge and if extra house load was needed, it would come from the lower state battery? Then once the higher state one is filled, both inverters would fill up the lower state battery.

Just an idea. Might be less hassle than trying to faff about with a Pi and home assistant. IDK. Maybe the faffing about might be easier than it sounds?

Do you know what logic they are using in the home assistant to prevent the cross charging?

Cheers !

 

[WannabeOwner]

I dont think I can go through 116 pages of posts

There's plenty in there that won't be of any relevance!

Here's my summary - things I think important, but also things I have learnt during this thread

Heard really positive things about it all, especially with the hike of these energy prices.

For those who installed Solar Panels before the price increase it has turned out to be a good decision ...

... but since then price of everything has gone up, and lead times (e.g. for PowerWall battery) can be 12 months ... and installers are spoilt for choice, so probably adding cream on top ...

... and maybe prices will come down (but inflation will still effect Electricity Bills over the next 25 years life of PV)

Of course I will look into battery storage - but I hope the general consensus is that having Solar Panels is a good thing?

All sorts of reasons ... maybe you just want to save the planet?

My view is:

if you are able to use savings (rather than borrow money to pay for it), and even more especially if you are in your forever home, its a no brainer.

You are faced with paying your electricity bill for the next 25 years. Price might come down (North Sea wind expansion) but there will still be inflation.

So you can pay £X for solar panels / battery, and reduce your electricity bill by, say, 80%. So you will only pay 20% of your electricity bill, whatever the price of electricity becomes. If you are approaching retirement that might be particularly attractive.

If you have an EV (or will have soon ...) AND if it is parked at home during weekdays, then that is a great way to soak up any excess PV.

A house Battery will also soak up excess PV and, in Winter, will enable you to buy-cheap during Off Peak and use when rates are high during the day.

Beware that Winter PV is pants. So don't even think about any possibility of using PV to run Heatpump winter central heating (at UK latitudes). Mid winter insolation (sun power) is 90% less than mid Summer. But by March the PV contribution is significant (some wall-to-wall sun days, but plenty overcast / wet too), so its really only Nov-Feb that is "bad", with May-Aug "awesome" and the rest is in the middle.

My personal view is that Time-of-Use tariff will become the norm. And that will likely mean that evening-peak use will be the most expensive. A battery will mean that you can "use your own" during expensive periods. There will also be some very-cheap-periods - probably daytime on days when sun-shining and wind-blowing. Fill your battery at those cheap-times. Depending on the battery you choose you can also have "no powercuts" - if that is a problem where you live, or you work from home and "Sorry, someone dug through the cable" would be a major inconvenience. The time may also come where you can sell your Battery Power, to the gird, at a generous price - instead of the grid having to fire up a gas turbine peaker-plant when the Coronation Street adverts come on they will buy from your battery instead. The Grid will be able to avoid the cost of building peaker-plants and rely on everyone's batteries instead ...

I think it is also likely that EVs will "soon" - 2 or 3 years - have V2H (and/or V2G). That will be a help because EV battery is huge, compared to house battery, so much easier to "save" the excess PV from a really really sunny day, and to tide-over on overcast days.

In terms of Solar Panels have a look at PVWatts calculator. Put in your location, you can then "draw" your roof - zoom in on a satellite map and draw a rectangle (repeat for each sloping face of your roof, so you get separate predictions for each roof-face - N, S, E, W)

When you install PV I recommend that you "fill the roof". You only want to pay once for scaffolding, and inverters, and installer-admin of coming-to-site and raising-an-invoice and all that ... additional panels won't add much to the bill.

Note that whilst South is best even North Face of a roof is worth having. BUT ... if you do have a North facing roof it is worth actually measuring the slope (that's easy if you can get into the loft - especially if your phone has a Tilt-Angle APP). For S, E, W the angle doesn't make much difference (unless the roof is either flat or vertical, in which case you can guess the angle ). North panels, provided the North slope is not too steep, will generate 70-80% of South in Summer (and also a useful contribution to Morning / Evening than South)

People tend to think that South is best. Well ... in terms of peak power production that is true. But that is at mid day in summer when you may be out at work

An East / West roof will generate 10-15% less than South (per unit area), but East + West has twice the area of a South roof. Also, East starts up to an hour earlier than South (and West finishes up to an hour later), which means you have useable electricity for more of the day (and fewer "night" hours when your battery has to cover)

 

[Avendit]

So nice to see green tech sticking together well. Solar+ thermal panels from Germany hitting 80% efficiency (all be it with some dodgy math I would say).

German manufacturer achieves 80% overall efficiency with new PVT solar module

Sunmaxx says Fraunhofer ISE has confirmed the 80% efficiency of its new photovoltaic-thermal (PVT) module. It consists of 108 PERC half-cells in M10 format, with 400 W of electrical output and 1,200 W of thermal output.

www.pv-magazine.com

I've always loved the idea that panels get less efficient as they heat up, so by whacking a thermal collector on the back you can cool them and steal the heat for your own use. Wasn't really a popular option when I started looking tho. Also not sure how effective it would be up in Scotland, but solar thermal does work, so presumably so would this.

 

[yessuz]

So nice to see green tech sticking together well. Solar+ thermal panels from Germany hitting 80% efficiency (all be it with some dodgy math I would say).

German manufacturer achieves 80% overall efficiency with new PVT solar module

Sunmaxx says Fraunhofer ISE has confirmed the 80% efficiency of its new photovoltaic-thermal (PVT) module. It consists of 108 PERC half-cells in M10 format, with 400 W of electrical output and 1,200 W of thermal output.

www.pv-magazine.com

I've always loved the idea that panels get less efficient as they heat up, so by whacking a thermal collector on the back you can cool them and steal the heat for your own use. Wasn't really a popular option when I started looking tho. Also not sure how effective it would be up in Scotland, but solar thermal does work, so presumably so would this.

There was some process of solar panels to utilize running water (read rain) resistance to generate. Very little of course, but 24x7

 

[yessuz]

guys, quick question from your perspective:

2 Inverters:
1 x Growatt, SPH 4000 - 4 kwp west panels (10 x 415 W, Trina, TSM-415 DE09R.05)
1 x Growatt, SPH 3000 - 4 kwp east panels (10 x 415 W, Trina, TSM-415 DE09R.05)

If I understand correctly, such setup would be connected on paralel and total output from inverter would be up to 7 kw?

This would be paired with:

Pylontech US3000C x 3 (10.12 kWh)
OR
Pylontech US2000C x 4 (9.12 kWh)

Price is absolutely the same. Only difference is that with 3 batteries I get 1 kwh more AND looks like better discharge rate (marked with arrows).. Do I read tech spec correctly?! Does it make any difference to have 4 vs 3 batteries if system is with 2 inverters?!

 

[scdoubleu]

guys, just a questions:
how does the system with 2 inverters act?
in my quote I have one inverter for east, one for west.

Which one would feed to house (hey, inverter 1 - you feed kettle, I will feed oven), grid, or there is some management system?

Works just fine - both inverters will add to the pool of available solar power. In the case of our Powerwall system, the Gateway sums the output of our two inverters (one in the house loft, the other in the detached garage) via CTs on the feeds from each one. The sum is what is shown in the Tesla App. The fact there are two solar arrays/inverters is unimportant.