Any advice on Home Solar?

[Kim]

Something completely un model engine related...

I'm considering getting solar panels installed on our house.  They will save me some money, over the long run (10-15 years), but more importantly for me, they will decrease my personal carbon footprint.

I'm just starting the information gathering stage and thought I'd ask the collective wisdom of the group of you had any experience/advice that you'd be willing to share?  Good experience, bad experience, whatever.  Like I said, I'm looking to gather information.

Thanks!
Kim

[Jo]

Hi Kim,

I've had a 4KW solar array for 15 years on my house: I love it.      I do not have storage batteries, I do have a solar water heater manager. I also have Air conditioning (house and workshop) to use the free electric and no mains gas central heating (this is common in UK).


Modern solar panels are slightly larger than my old ones and produce nearly twice the power and cost about half the price. Installation (hiring the scaffolding) is the expensive thing in the UK. The money the electric suppliers are willing to pay for spare generated electricity is pathetic  In the UK they have some interesting hybrid tariffs for people who have battery storage to back feed power to them in short windows during the day which are gaining a lot of interest¹.

Storage batteries are still expensive ² . I "store" my spare power in my hot water tank using the immersion heater which is my biggest daily electrical load, the next is the Air Con. Which leads on to the question of how much electricity do you use for your home that it might be sensible to have a battery to store. I remain unconvinced that with the life expectancy of the batteries that they are cost effective and am suspicious  of how long the hybrid tariffs (where they pay good money to back feed power into the grid) will last for.


In midwinter, when you might want to use extra electric to heat the house the power generation is poor, about 300Wh for the entire day is not uncommon. Whereas this time of the year 20KWh is the norm.

Forgot to mention my Annual electric bill halved when I installed the panels.

Jo


1. The amount of power people can back feed is limited by the electrical supply cabling to their properties and the local network transformers etc. 4KW is standard in the UK

2. Second hand EVs can be used for power storage instead of stand alone batteries.
 

[uuu]

I've just moved in to a house with panels and storage batteries.  It's a rented house and the landlord gets the feed-in money  - I just pay for electric drawn from the grid.

So it's a fun game to use as much as I can during the day when the panels are generating - charge the car, do the washing, let the batteries charge up.  To minimise what I spend - and what the landlord earns!   

My electricity bills are a fraction of what they used to be - I'm very impressed.

What I don't know is how much it cost to install - so I can't work out a payback time.

Wilf

[AdeV]

I don't (yet) have a system, but once I've hopefully moved house in the near future, I will be investigating my options. And the nice thing (and also the bad thing) now is there's a plethora of options to choose from: Roof mounted? Vertical (fence) mounted? Bifacial or single face? With or without batteries? And so on...

Personally, I think a battery will make all the difference to a solar system: The peak time for electricity is early evening - just as the sun is going down; so having a battery will let you defer the power you generated during the day to evening use.

AIUI, in the USA, your biggest issue is getting the right permits. Depending on what state you're in, that might be the biggest hurdle. There's a youtube channel - Undecided with Matt Ferrell - who's covered loads of this sort of stuff, he lives in Maine IIRC. Worth picking out some of his solar related videos I'd suggest.

[AdeV]

Storage batteries are still expensive ² . I "store" my spare power in my hot water tank using the immersion heater which is my biggest daily electrical load, the next is the Air Con. Which leads on to the question of how much electricity do you use for your home that it might be sensible to have a battery to store. I remain unconvinced that with the life expectancy of the batteries that they are cost effective and am suspicious  of how long the hybrid tariffs (where they pay good money to back feed power into the grid) will last for.

...

2. Second hand EVs can be used for power storage instead of stand alone batteries.

Battery prices are, to the best of my knowledge anyway, tumbling. To the point where I'd suggest that a used EV battery is probably not an economical way to get one. I'm pretty sure that "information" about the lack of longevity of battery systems - just like the supposed lack of longevity in EVs - is misinformation. EV batteries look to be lasting far far better than even the most optimistic people estimated 10 years ago (with a few exceptions - Nissan Leafs have caused most of the whole "omg you'll need to spend £10,0000,00,0000,0 on a new battery pack after 6 months of buying a used one" rubbish. As long as any house battery you buy has decent thermal management, I don't think it'll be a problem.

Alternatively, wait 2-3 years for stationary sodium batteries to mature a bit; because they should be cheap enough you could almost treat them like rechargeable AA batterys: Just buy new ones if they start to get a bit suss, because they'll cost buttons... (OK - slight exaggeration - but early figures suggest that right now they're a little more expensive than LFP batteries, but as manufacturing scales up, the price should drop 10 to 100 fold, as the materials used are so much cheaper and more abundant than even LFP.

[johnl]

I have had a 4.69 kW roof mounted system for five years.
I am setup with net metering. The power company pays 1:1 for the power I produce.
I haven’t had to pay an electric bill since the system went online and that includes charging my car.
Luckily I have an unobstructed south facing roof.
One thing to keep in mind is the condition of your roof. If its nearing replacement you may need to consider that cost as well.

[Jo]

Hi Ade,

I was quoted for a single Tesla Power Wall battery and its inverter (adding batteries later to an existing system is both less efficient as you are converting AC to DC, rather than DC to DC and adds the additional inverter cost) £8.5K.

Assuming a 20 year life expectancy on the batteries and only charging between 20% and 80% to increase the life of the battery, that provides a usable storage of 8KWh. The aged UK electrical network will only let you export at a peak of 4KW so that is 2 hours of export at 4KW = 8KWh = total usable power in the battery without you using any.

My 4KW array points directly South I have seen 3990 W from it but at the mo with a clouded sky it is only generating 380W. From the beginning of March to the end of October my spreadsheet tells me I normally generate 8KWh or more of power a day. That is 10 months when you can potentially export 8KW a day Assumption: I'm ignoring the ups and downs and rounding it to one battery worth of export a day. I have heard many numbers for the possible half hour export rates but I am going to assume 15p per exported unit (KWh): 8KWh @ 15p each = £1.20

300 days per year * £1.20 a day = £360 a year  (my FIT pays £2.5K+ annually  )

20 years at £360 = £7,200

Lets call that break even on the battery installation price. But if I put my £8.5K in a 3% compound interest paying saving account I can nearly double my money 

I've attached my last few months worth of generation tracking spreadsheet for those of you as sad as me who like analysing stuff 

Jo

[Vixen]

Hello Jo,

That's some interesting (sobering) solar power analysis. It's a long way from the ill-informed You-Tube hype

You say your 4KW panel array can produce up to 3990W on a bright sunny day, but in todays overcast, clouded sky are only generating 380W. Your spreadsheet says you could potentially export 8KW for 10 months of the year. Surly, that depends on having enough sunshine and no cloudy days? Does your spreadsheet give a more realistic estimate of the actual amount of energy that could be exported (sold back) during that period?

Doesn't make good reading for a battery storage unit, unless you can find a way into the higher export rates. Your current hot water tank excess energy storage seems to make more sense. What exactly would be required to get into those higher electricity export rates?

Mike

[Jo]

I have more figures 

In any year my 4KW array generates around 4000KWh total electrical power over the 12 months, I have seen no reduction in panel efficiency over the 15 years that I can note but the weather is the variable, the last few years have each generated over 4000KWh. Before I wired up the immersion heater manager to use my hot water tank as my spare electricity storage usage device I was paying my supplier for 4,500 KWh a year of electricity, once installed this dropped to 2,500 KWh. My storage device is my hot water tank not a battery (the replacement heater element is about £40 and it is still going strong after 28 years). We all use hot water in our homes.

Electric usage:

In the middle of summer my daily electric metered usage is 1 or 2KWh, in the middle of Winter with my night storage heaters it was going up to 35 KWh per day, the air conditioning has brought this down to peaking at 20KWh per day  I am using my Air conditioning 24 hours a day to heat my workshop during the winter and heating/cooling the house as required. Current usage sheet attached - the summer months do get better 

You need to start by understanding your peak load needs and the durations to be able to size a battery for your actual use.

Export rates:

In the UK Octapus Energy does an agile tariff where sometimes for one 1/2 hour time slot they will pay you to use electricity or pay to export. The max I have seen is 65p for a 1/2 hour slot exporting.  The price per slot comes up a few hours before and you have to be ready to make use of it or store it - a basic computer program and your wifi would control this for you. The offered rates peak up and go down all over the place  You could possibly charge up the battery directly from the mains, get paid to do that and then give it back when they are going to pay you even more. Sounds good but does it sound too good to be true

Jo

[AdeV]

Thanks Jo - I confess, I haven't yet done the full on analysis of my own usage; hopefully a house move will give me the latitude to install panels (I could install them here, but I'd never get my money back as I plan to move this year...); I will have to investigate whether a battery is the right option for me or not. I already have the EV, which gets little use - I don't know if it supports V2G though (It does support V2L, so maybe if I can trick it into thinking it's got a load attached...)

[Jo]

I would recommend getting the solar, with an immersion solar manager,  with air conditioning for house and workshop.

I looked into the trendy Heat pump stuff and the cost of all the gubbins to enable it to produce mildly hot water and luke warm radiators is not cost effective (whatever the government tries to tell us  )

However.... it is still cheaper to use mains gas and a boiler if you get the chance

Jo

[Vixen]

Thank you Jo,

More numbers I like numbers.

It also appears that those offering the higher export buy-back rates need you to have had your solar panel and battery/ power management system installed (at highest cost??) by that particular supply company. If you have an existing installation, only the lower rates (typically 15p per exported unit) will be available.

How to make best use of a solar panel installation would seem to depend entirely on where you start from, i.e. what is your current electricity/gas installation and usage.

For a mostly electrically powered home, like yours Jo, using any excess solar power to heat the hot water tank is a very good way to harvest the sun's energy and half your electricity supply bills during the summer months. Heating the house during the winter months will always require buying some mains electricity.

I have a mixed gas (heating, cooking and hot water) and electrical (lights, kettle, TV and washing machines) installation. That made good sense when gas energy cost less than the equivalent electrical energy. But times change. Even a small solar panel installation would exceed my daily requirements (at least in the summer months). I do not have a hot water storage tank, so a storage battery and a sell-back scheme may be worth exploring. Converting my present heating, cooking and hot water arrangements to use more use of the 'spare' electricity rather than gas could lead to yet more installation expense and longer pay-back period. At the moment, I do not even have a hot water storage tank.

It is an interesting trade-off study, understanding your future needs and current installation limitations are important. Knowledge of future energy prices trends would be nice. But beware, counting every coulomb can become a full time passion.

Mike

[Art K]

I'll reply when I'm home from work!
Art

[Kim]

Wow! Lots of good info here.  Thank you!

So, no problems with leaks in your roof, or failure of the solar panels or inverters that need to be repaired? Or things like that?

On the battery, another plus with that is that you can continue to run your refrigerator and freezer when there's a power outage.  I don't know about you guys, but we seem to have a power outage every year.  They usually only last a few hours, but there have been multi-day outages in the past.  So that's one benefit of a battery, even though it may not pay for itself.

Oh, and Ade, I follow Matt Ferrell.  He's always got interesting things on his channel!

Kim

[Jo]

My panels are Sanyo and have a lifetime guarantee. I was told when they were fitted: Sanyo have made millions and only had a handful fail so will come and replace any failures and take away the faulty unit as being Japanese they believe in quality control.

My inverter is German and has a 20 year guarantee. The electrician who fitted it said the only failure he had ever known was an electrolytic cap popping and showed me where it was just in case.

My first £200 solar immersion heater manager failed after 5 years. Keeping my fingers crossed for this one   


Modern Chinese stuff may not be to the same standard 

Jo