Payback on Solar and 5kwh battery

k123456

I am guessing this questions is impossible to answer but for those who have taken the leap, from your calculations , how long before the system pays for itself

Every situation is different

mine is

I consume approx 3000 kwh a year

thinking of ten to 12 panels, aspect is SE and S . I have been told I will gain 4300kwh a year, I will be selling back excess to grid at 24 c a kwh

smart metre Yes

Elec car 28kwh battery Yes, however only do 100 k a week, charge it between 00:00 and 08:00

2 people in house , but not 9 to 5 Mon to Friday

Water is heated currently by gas, but there is an existing timer switch in situ , 300 litre well insulated tank

I currently do not have an EV elec rate (approx 8 cent per kwh), but considering one, when my current elec contract expires

to 1 charge car, and 2 top up battery at 8c

Not planning to get a smart car charger, because , I can time to my car to charge , when 8c per KWH is avail, which is approx a three hour window after midnight, have a dumb wall charger , several years old, I am open to correction there, so looking for advice

Also planning to use the 8 c rate to top up 5kwh battery if the solar panels cannot

Not planning to get a EDDI to heat water, because there is an existing timer switch wired to the immersion, I am open to correction there, so looking for advice

The various sales people in Solar companies , have said my payback is 6 years , which Im sceptical about

loyatemu

i"m in the middle of getting quotes - I reckon 6-8 year payback on panels alone. Adding a battery probably makes the payback longer but you're adding some insurance against FIT rates going down (which they probably will); dynamic pricing being introduced and just the general environmental benefit of using more of your own power. You can also charge up the battery at EV rate as you say which is useful in the winter.

k123456

https://www.boards.ie/discussion/comment/121861361#Comment_121861361

Whats dynamic pricing, please

micks_address

https://www.boards.ie/discussion/comment/121861461#Comment_121861461

its where the price you pay and the price paid to you for electricity you export can change every 30 minutes.. the rates are typically published 24 hours in advance.... its up and running in the uk a while and they have tarrifs around it

k123456

Thanks Mick, and in the UK is it seen as good or bad, in other words , with dynamic , you pay more per unit and receive less ? or do some consumers do well out of it

micks_address

https://www.boards.ie/discussion/comment/121861600#Comment_121861600

depends... its set up to give you most money for export when grid would benefit from you exporting.. peak times.. 5 to 7 pm.. i guess its a good thing in general but you probably need more battery and good automation to make the most of it.. few offerings in the uk now from companies where they will manage your battery import/export to maximise revenue for you

DC999

https://www.boards.ie/discussion/2058339345/payback-on-solar-and-5kwh-battery

Here’s how to do the maths without a battery for now so you can see that figure. 

Solar: Assume you sell 80% of what you generate as FIT at 20c a unit (I’ve plucked that from the sky based on you not being home during the day, so seems reasonable guess as will be higher during the week but you'll use more of it at weekends when home). That’s a credit on your bill.

Then solar generates the other 20% that isn’t sold for FIT (or 860kWh), meaning you buy 2140kWh from the grid (3000-860kWh).

Of that, assume you move 30% of your house usage to cheap night rate (EV which is low usage you said, dishwasher, washing machine so 30% is very easily achievable).

So then the other 70% you buy is split between a night rate and day rate (ignore peak rate for now for simplicity). You can decide that split based on your usage

Then you can see what your bill will be for kWh you buy. You can’t reduce the standing charges of course. Close enough is good enough I’d suggest.

Ignore the immersion diverter. Not needed now FIT is so good. Assume FIT will drop in time but no one knows what crystal ball that will be

curioustony

Or stick your figures into this app. If you have a smart meter, use the beta as it will save some data input. You can copy the 'usage', and try/compare different scenarios over a year (battery, big battery, no battery, more panels, panels on different roof, ...). You can also modify costs for optimistic or pessimistic outlooks. It simulates a single year, and uses PVGIS for solar data. But of a learning curve, but you have a lot of the numbers needed and the default values will get you a long way

https://play.google.com/store/apps/details?id=com.tfcode.comparetout

k123456

Amazing app,

worth mentioning on payback , is lack of interest received on your funds

Say you spend 10k

you would get 3.25 percent pa from AIB , assuming rates do not go down, you would get 3250 in interest, you 10k would be worth 13,250 in ten years

conor_mc

I used https://www.calculator.net/roi-calculator.html to calculate the RoI over the 25 year lifetime of an €8k system that returned €25k savings or thereabouts (many factors to estimate/ballpark though). From memory, it returned 5.2% or so. That’s a better return over the system lifetime than cash on deposit or mortgage prepayment. I assumed today’s electricity rates (they’ll probably be higher on balance over 25 years), today’s deposit rates and mortgage rates, both of which I personally consider neutral, i.e. neither high nor low. Therefore I believe that return to be conservative. YMMV.

oaklands

https://www.boards.ie/discussion/comment/121862285#Comment_121862285

Less DIRT, deducted at source?

graememk

https://www.boards.ie/discussion/comment/121862285#Comment_121862285

Well interest is more, €3,768.94 as it's compounding

But then dirt at 33% gives a net figure of 2512.94.

thejuggler

My Father in law purchased a solar system with Eddy, home charger plus an electric car in his mid 70s. He doesn’t drive any great distances and it’s unlikely he will ever recoup his outlay but it gives him a great deal of satisfaction monitoring the generation output with the app etc. No one knows what the future holds regarding technological improvements which may make the current equipment less desireable or efficient but he seems happy for now.

graememk

https://www.boards.ie/discussion/comment/121862723#Comment_121862723

And I would do the same. Cant take it with you. My dad moved to an automatic (and now EV) before he got too stubborn to move from a manual!

curioustony

@k123456 Thanks for the feedback

Cash in the bank also suffers from inflation.

ZMOONY

https://www.boards.ie/discussion/comment/121862723#Comment_121862723

theirs no improvement in the PV tech coming any time soon.

wind turbines yes.

k123456

https://www.boards.ie/discussion/comment/121862530#Comment_121862530

Good point forgot about compound , and less dirt

Seventy Plus

I do not think it is worthwhile buying a Battery at their current prices.

But to cover yourself get a hybrid Inverter.

conor_mc

I asked for a quote to be re-priced without a 5kwh battery, only reduced by €1250. That’s less than a 4-year payback on importing at 7-8c overnight to offset 4x 30-something cent units during the day, every day. In round numbers, call it a 25c saving per kwh, multiply by 4 units per day (80% depth of discharge), by 365 days equals a €365 saving per year. 1250/365 = 3.42 year payback in this particular case. My only problem was they said it would cost €2200 to add a second battery, so that’s a 6 year payback! Allegedly due to wholesaler bundling prices, etc but will probably challenge it once I’ve ironed out a couple of other kinks in the quote.

yankinlk

https://www.boards.ie/discussion/comment/121863957#Comment_121863957

Good approach. I think a lot of installers are motivated to bundle batteries. Unless u can get a cheaper quote for same size system without battery (diff supplier?) it might be worth it.

ColemanY2K

https://www.boards.ie/discussion/comment/121863034#Comment_121863034

I read an article yesterday in PV magazine which was saying battery cell prices have fallen by 50% in the past year and are forecasted to fall another 10% over the coming months. These drops are slowly feeding through to the customer.

I reckon I'll bite the bullet before next winter sets in when battery cell prices should have plateaued.

slave1

https://www.boards.ie/discussion/comment/121863957#Comment_121863957

Sounds funny, check that requote again, did they leave in a hybrid inverter by chance? elimination of a hybrid inverter and 5kWh battery should be much more than €1,250 or else your original quote also was questionable

conor_mc

https://www.boards.ie/discussion/comment/121866114#Comment_121866114

Yeah, it was supposedly due to passing on a wholesaler bundle discount, but I’ll be revisiting it in due course for sure. Just finalising the spec first.