solar PV system

No you won't save anywhere near 70% on your electricity bill. Unless you go for a battery storage system. But these are mostly very expensive.

It's not all about money though. You can get a basic PV install that will give you much better returns than money in a savings account. And you will be doing the world a favour. It's not all about money. We need to tackle climate change, if we aren't already too late.

No. You can install an immersion diverter that will send all the electricity that you aren't using to heat the water. This will be a big help in summer, on many days heat your water if you have a large PV setup. But it won't do much in winter unless you have a very sunny day.

astrofluff wrote: »

I myself have a bit of a dilemma and need some guidance of what other people think without being pushed by the sales agents for a PV panel company.

I have 4 thermal panels taking up the best area on a West facing roof (slightly more South than North). I only have enough space left for 4PV panels giving me 1.2kW on that side. The other side which is east-facing I have much more space and could get in 6-8 panels giving me upward of 2.4kW, or even more if I went with bigger 400W panels.

So the question is, should I take out the thermal panels and Max out my better West-facing plane, or stick to an East-West split? If I get an array with over 2kW I might as well get a hybrid battery setup to maximise the use, a separate question whether I'd get the use out of it.

I have not seen any 400W panels on sale in Ireland but that might have changed in last couple months. You need to take into account that 400W panels will be big in size ~1x2m, so depending on your roof area you may not have space to fit many of them on your roof. I think one advantage of PV is that you can get electricity and hot water(with diverter) out of them. But then you probably looking at 4kW system with battery or drop the battery. You need to do some calculations on your average usage and usage patterns and size based on that.

pjwhite99 wrote: »

Got a price any one know what battery is best here?

5.6kwh GivEnergy

Or

3.5kwh BYD

One system is 7600 after grant that’s 5.6 battery and 3.25 on the roof

Other is 3.5 battery and 4kw on roof 7050

What’s better?

The way I look at it, it is much easier to add battery to the system later,
compared to adding new panels on the roof(unless you're roofer). Also ideally you'd want panels to be same as previous ones. I would get as much kW on the roof as possible.

3.5kWh is a very decent start. Have you the spec sheet of the battery?

How useful it is depends on more than the capacity. The maximum charge and discharge rate is important too. The market leader is probably Pylontech and their 3.5kWh battery can charge / discharge at 37A

I'm with reklamos here. Get as much PV on your roof as you can first and don't spend too much on the battery.

That's a good price for the big system. And no, it's not too big. Your electricity consumption will probably grow over time and we are likely to see a feed in tariff where you will be paid say 5c/kWh for any electricity you send to the grid. Your large system got €3,800 subsidy

The pay back period for the large system with the battery will be shorter than that of the smaller system with no battery, and it only got €1,400 subsidy

astrofluff wrote: »

East/west split with no battery, say 1.6kw on West with 2kw on east. Would love to know what a good average generation is for an e/w split over the year of that size.

I'd guess around 2.7-2.9MWh per year in a good location (i.e. Dublin area)

astrofluff wrote: »

If deciding to go for a battery and hybrid inverter, yes maybe that would make sense of there's no FiT coming, but seeing as there is, when is the crossover point for having a battery v using FiT?!

If you can't get the grant, don't even think about going for a battery. It will never pay for itself unless you get it more or less for free.

garo wrote: »

.... I am currently guesstimating a cost of 10c per kWh to get power into the battery and out which is lower than the day rate.

Good to know this for running an approx calculation for RoI. FiT would definitely help in an over sized system. I've a few decisions to make and hopefully get this done soon.

Obviously the number varies based on battery size and make and you need to include hybrid inverter costs over a normal inverter. And while batteries state they are good for 6,000 cycles the number could be higher or lower. But I think 6c on the lower end and 10c on the higher end is a good bound. It does mean that using a battery to charge at night rate does not make sense.

My calculation was based on 1600€ for a 3.5kWh Pylontech installed. 80% DoD and 8k cycles and an additional 650€ for a hybrid inverter.

It will be interesting to see what FIT will actually be in here.
In some EU countries people accumulate enough electricity credit during summer, that allows them to survive during winter without buying from grid.
As a comparison in Alabama you have to pay $55 a month for the privilege to export to grid.

Yes IMHO it doesn’t make sense. Take the cost of the battery and divide by number of expected cycles times the usable capacity. That should give the cost per KWh. My calculations say it ranges from 6-10c. Then take into account the inverter inefficiencies ~90-95% in and out. It gets pretty marginal.

Alkers wrote: »

But if he already owns the battery?

The life of a battery is simply put a number of cycles. So if you use your lithium battery just for your solar (no charging up on the night rate), the battery might get 400 cycles per year, and with a 6,000 cycle expected battery life, it will last 15 years. If you charge it up an additional 200 cycles per year on the night rate, the battery will only last 10 years. And if you do the sums on this, the savings are barely worth your while. That is garo's point. And it's a good one.

Personally I reckon that the cycle life figures of lithium batteries are on the low side, they typically represent a degradation of about 30%. After which the battery still is very useful (and not to be written off or replaced). Also when your battery has degraded after 10 years, it is quite likely you can add another battery to it (or replace it) for far less than batteries cost now. If you follow this slightly more optimistic line of thought, then yes, you will save money by (partially) charging up your battery from night rate in winter. I plan to do this on my lead acid battery (or at least experiment with it), but that battery didn't cost me anything.

What battery and inverter do you have? Let us know how you get on.

I haven’t switched to night rate yet so even though I believe my Pylontech + Growatt combo allows for this, there is no point playing with it yet.