My 16kWp Domestic System

graememk · 31-08-2021 5:20pm

https://www.boards.ie/discussion/comment/117828743#Comment_117828743

Yeah there's a big difference in a bright overcast day and a dark day.

bullit_dodger · 31-08-2021 6:11pm

I know a little off topic of the thread, but went digging a little and found

core.ac.uk/download/pdf/97494428.pdf

Doesn't really answer what I was looking for (and I can appreciate that it's a tricky question with many variables as to the type of clouds, the depth etc) but I was just wondering on a general level what are people seeing with their panels. Sort of

Broken clouds = 40-50%

Overcast = ~20%

Raining cats-n-dogs = 5-10%

*My purely speculative figures above just thrown in to give an example. I've no idea as I'm still waiting to get my own installation put in :-)

SD_DRACULA · 31-08-2021 7:00pm

https://www.boards.ie/discussion/comment/117829366#Comment_117829366

Basically impossible to tell, to my eyes both yesterday and today were fully overcast, yesterday generated 7kwh and today 10kwh, max August was 38kwh, go figure.

How about you Mr. 16kwp what was the lowest fully overcast day this month?

the_amazing_raisin · 31-08-2021 7:25pm

Actually, it should be reasonably straightforward to figure out the how the output is affected by cloudy days

You can use previous weather reports and irradiance data to figure out how much solar energy is reduced by given a certain level of cloud cover

After that, you can pick a sunny day when your system was performing at close to peak power. Compare the output power to the irradiance data for that day and that'll tell you how much sunlight you're converting into electricity

Then you can compare this to the data you worked out earlier for more overcast days and that'll give you an idea of what to expect on those days

the_amazing_raisin · 31-08-2021 7:33pm

Someone pointed me at this site a while back for solar forecasting data

https://solcast.com/rooftop-solar/

I haven't used it so can't make any statements as to its accuracy, but if anyone wants to have a go at building some API calls then you could make your own little forecasting toolkit

mp3guy · 31-08-2021 7:58pm

https://www.boards.ie/discussion/comment/117829685#Comment_117829685

Worst Day: 20th (13.27kWh)

Caspero · 07-09-2021 10:27am

Hi mp3guy,

Very interesting thread. I just finished installing 11Kwp and am considering what to do with my surplus, plus some automation.

You mentioned you had written custom Python, yaml and Jinja. Would that be something you could share or put on github by any chance? I know basic Python and am reasonably ok with T-SQL so I might be able to handle this particularly if I have a guide written by someone else to follow.

I'm also curious about your bitcoin mining setup if you could provide more details? edit: nevermind I see you already covered that in an earlier reply to unkel

07-09-2021 10:39am

@mp3guy, what was the total cost of installation ?

My thinking about this is that it's not viable unless there is a decent FIT so I can export and buy back during the darker periods until then I don't see it as viable having to dump energy I otherwise don't need.

Most of my heavy loads are during the night and battery adds a lot to the cost and at that it would want to be pretty big to charge the car, I'm not home during the day to charge and in Winter this won't do anything for me anyway or very little battery or not unless I have an equally large array.

Currently 9-10 Mwh needed per year and most of the heavy loads are during the night.

I was reading recently that when the FIT is offered it will be to the first person on a shared transformer and for only a paltry 3500 Kwh a year, no mention of cost yet.

bullit_dodger · 07-09-2021 11:23am

I guess unless your fully depleting car battery every day, you won't need a correspondingly large (30-50Kwhr) battery? You may know this already, but ... (depending on the car of course) 1kwhr~5-6km in range. Maybe you can fill it completely at the weekend when at home, and while you won't be able to fill it during the week from batteries maybe the "top up" you give it every night of 15-20% is enough to get you through the week until the next weekend? Course in Winter.....all bets are off :-)

If you haven't already checked out the battery thread - there's some good solutions there on DIY batteries which would enable you to get into that large ballpark. DrPhilG made a nice array there recently from cells sourced from China.

https://www.boards.ie/discussion/2058165926/solar-pv-battery-options#latest

A little off topic, but if anyone out there is doing some crypto mining, I'm also an old pro - PM me and we can talk :-)

(mined about 1.5 million Dogecoin back in 2014 - if only I'd held them!!! Fu....!!

the_amazing_raisin · 07-09-2021 3:24pm

https://www.boards.ie/discussion/comment/117857303#Comment_117857303

Well depending on the loads you could shift them to the day (e.g. dishwasher & washing machine). So that's one way to reduce your battery needs

The EV is tricky one I agree, it doesn't make sense to charge it from a battery unless it's urgent and if it isn't at home during the day then it doesn't benefit from Solar PV much

What I'm doing is discounting the EV from my energy usage and trying to work out what I need to cover the house's needs. Then if I have excess during the day and there's at least 1 EV at home then I can use it as a diverter

Another trick I'm thinking for a diverter is to install an oversized buffer tank for the heat pump. I'll be upgrading the current Dimplex POS if I do an extension, which will also involve putting on Solar PV. The typical buffer tank is around 50 litres, but if I can afford the space I'd like to put something like 200 litres. In a well insulated tank I could in theory store heat in it and use that to heat the house during the night when it's colder. The same could be done with a DHW tank (probably an easier starting point)

07-09-2021 3:45pm

I'd love to retrofit a HP and I know they can heat to 60-70 deg C for older homes with radiators, I've tonnes of radiators but question the efficiency still of such a system in a not so well insulated 80s bungalow, we need to do renovations and extension at some point, question is if I want to go from being rent/mortgage free to paying a decent loan and paying interest and possibly having to move out and pay for storage and deal with builders lol.

Currently I don't think it's viable to spend the money on Solar PV, compared to the cost of Night rate electricity, the only proper way to benefit is with a f.i.t and a lot more than 3500 Kwh export but Ireland INC always makes sure the companies benefit more but fail to realise the potential of every roof top in Ireland to have solar PV.

bullit_dodger · 07-09-2021 6:35pm

Currently I don't think it's viable to spend the money on Solar PV, compared to the cost of Night rate electricity, the only proper way to benefit is with a f.i.t and a lot more than 3500 Kwh export but Ireland INC always makes sure the companies benefit more but fail to realise the potential of every roof top in Ireland to have solar PV.

Not sure I follow with you there Mad_Lad. Did you mean "solar is not viable for charging EV's" or solar in general? Solar esp on days like today is a viable investment, but the EV issue is a tricky one alright. Esp where you don't have the car at your house during the day.

It would very much depend on your base loads/production, but I guess that a 20Kwhr battery storage, you could probably fill for 200+ days a year with a 10Kwp system. OK, you won't be able to completely charge your car every night from 0%->100%, unless your EV is pretty small, but if your system storage could give the EV (say) 30-40%....I'd say the battery would pay for itself in 5-6 years. How often would you realistically have a 0% EV battery that you need to charge to 100%?

You'd have to do the math on the battery costs, but my gut feeling is that it's a viable solution. Winter though....yeah, not much love from the sun at 53-54 degree north. <sniff>

the_amazing_raisin · 07-09-2021 9:06pm

https://www.boards.ie/discussion/comment/117859701#Comment_117859701

I feel like bord failte should advertise Ireland as the only country in the world where you can stare at the sun without any eye proctection 😂

graememk · 08-09-2021 12:22am

Just to add re the FIT

Nothing's been announced yet, all we have is the consultation.

That proposed 2 tariffs,

A subsided one - export limits, ber requirements etc

And a standard one - at the wholesale rate of electricity - set by the regulator.

Thats all we know right now.

Solar PV is definitely worth it, as MadLad has said they have a lot of the loads on night rate already. - good keep that going.

How many day units would you use in a month? That's the units solar will replace.

A lot of people are going down the line with solar as a service, I think that company is offering 8 panels(about 2-2.5kwp) for 20 euro a month for 10 years* (*I could be a bit off with the number of panels but it's in the 2.5kwp -ish)

It's a small system but nearly all solar generated would be used, no battery needed.

SouthWesterly · 08-09-2021 7:10am

https://www.boards.ie/discussion/comment/117861463#Comment_117861463

They have the option to buy extra panels from them and pay upfront for them for about 400 each.

slave1 · 08-09-2021 9:06am

Charging batteries during the day to charge EV at night is littered with losses in and out, not recommended.

My night rate is 5.83c via Energia EV package, why attack batteries when you have that cheap a night rate.

Also, not being at home questions oversized arrays and what to do with excess. When FIT announced I'm pretty sure it will be paltry and any money in will be eliminated by 5pm to 7pm price hike.

Your car will be at home at some stage e.g. good summer mornings/evenings, weekend, odd day off.

However forget about PV for EV for 6 months of the year and even then you need a good day to make it worthwhile

Bobeagleburger · 08-09-2021 10:14am

Don't be relying on FIT. You'll need a smart meter for that, and the tariffs aren't attractive. Plus nobody knows what the FIT will be, or when it will even be introduced. Was supposed to be introduced in July remember.

Get as big a system as you can afford, but price around. You'll payback a good priced system fairly quick, especially with the way prices are going.

bullit_dodger · 08-09-2021 10:20am

https://www.boards.ie/discussion/comment/117861942#Comment_117861942

Sure you'll have losses. Maybe 15-20%, but that's what a battery is for. No reason not to cycle a battery, they're good for 3,000-5,000 cycles mostly unless you go for cheap/nasty brand, or run it at adverse temps. Not using it is similar to buying a car and then not driving it as you'll wear the thread down on the tyres. You'd be missing the point of why you bought it. No?

Hard to argue with 5.83c though. Assuming you had 10Kwhr storage, and could fill it every single day of the year (you won't), that would be €0.58/day saved, or ~€200/year. That's a long "payback" for a 10Kwhr battery, even if you go DIY. That's assuming you were using the battery solely for EV use. You'd do better in reality as you could use it for other loads, but you'd also have to take out the days such as weekends where the car could charge directly, so the payback would even be longer.

Course if you weren't paying 5.83c.... (future price hikes etc) or could source some cheap batteries, there some "crossover point" there where it's viable, but yeah, you've convinced me slave1 :-)

slave1 · 08-09-2021 11:43am

More savings than that, say 6c to fill at night and avoiding 20c during the day, that's 14c saving time say 10kW so €1.40/day over Winter when electric more in demand...

Sorry OP, gotta stop going OT now

RingSting · 08-09-2021 12:09pm

If you have a battery can you program when it discharges ?

I guess yes is the answer and is it done via your hybrid inverter?

slave1 · 08-09-2021 12:34pm

Yes/Yes for Solis 4G and Pylontech anyhow

bullit_dodger · 08-09-2021 1:38pm

https://www.boards.ie/discussion/comment/117862634#Comment_117862634

True - although I wasn't thinking here about the viability of a battery "in general" which I firmly believe that it is a good deal for 80% of people, even just doing exactly what you suggest using it to get cheap leccie during the day......but rather the viability adding additional storage (brining you from say a baseline of 5Kwhr up to 20Kwhr) hooked up to charge specifically an EV from power captured from large production during the day.

I think what you've mentioned that with night rates so low and the fact that you can charge and EV sometimes in the morning before work, or evenings, or at the weekend....it becomes a harder equation to balance and see a "value add" , unless you somehow had access to really cheap storage. Like really cheap.

Interesting little problem/thought experiment that :-)

poker--addict · 08-09-2021 8:11pm

latest quote (before grant) below, and can i ask any rule of thumb about how big a system one might wish to install if they have the space.

20 PANELS 340WATT 6.8 KW. JA SOLAR.

6KW SOLIS HYBRID INVERTER

5 KW PURE DRIVE BATTERY.

WIFI DONGLE.

PRICE 11500 EUROS INC.VAT.

the_amazing_raisin · 08-09-2021 8:27pm

https://www.boards.ie/discussion/comment/117865178#Comment_117865178

Personally I would say it depends mostly on your energy usage, if your house is heated by oil/gas and you drive a petrol/diesel car then you're probably close to the average Irish household of 3,500kWh per year. Then is becomes a balancing act of installing enough to cover your needs without dumping too much excess to the grid for free

Now that goes out the window slightly if a semi decent FIT rate comes in. Then it becomes a case of install as many panels as possible to maximise your export. But I expect there'll be limits and conditions to stop this from happening

On the other hand if your household is heated by a heat pump, has electric cooking and 2 EVs, you'll be using close to 12,000kWh per year (taken from personal experience). In that case, you'll want to cover every available surface with panels

Bobeagleburger · 08-09-2021 8:35pm

Don't worry about dumping excess for free tbh. Provide of course you get a good install price.

Good for the environment for one.

Whats your yearly usage?

poker--addict · 08-09-2021 8:40pm

excuse the quote, wrong thread!

Heat pump + electric cooking here, no EV (yet).

the_amazing_raisin · 08-09-2021 8:43pm

https://www.boards.ie/discussion/comment/117863167#Comment_117863167

The problem with charging an EV off solar batteries is that you'd need a LOT of batteries to make it work. For example, Mad_lad is currently waiting on an EV with 77kWh of usable battery, and I know he's going to be using a big chunk of that every day

So you could build a battery big enough to store every bit of excess solar you generate from a big rooftop system and still fall far short of your needs

Plus as slave1 mentioned, when charging an EV on the night rate is so cheap, it'll almost be impossible to pay back the costs of those batteries

Incidentally, solar PV and batteries are starting to be used for public EV chargers, but the batteries in particular tend to be used for peak shaving of power usage. When you have a bit charging hub with something like a 1MW grid connection, then you get charged for the amount of power you're using at a given time. The more you use the higher the rate goes. So it makes sense to use something like a battery to store up energy from solar, or when the grid is cheap and then use it to flatten those peaks

Anyway, back on topic, I think the best way to handle an EV is to treat is like an extra battery that's only available when you're home. Base your home battery around your house's needs only and install an EV charger like a Zappi which can divert extra solar PV into the car instead of the grid. At weekends you'll drive for free and then during the week it's still cheap at the night rate.

Install as many panels as you can fit and hope there's going to be a decent FIT rate to give you some money for all the excess you'll be dumping to the grid on sunny weekdays