Domestic solar PV quotes 2018

Thanks for the quick reply unkel.
If it works for you then I guess I should definitely sleep easy with my proposed install as they would all be generally facing the same (southerly) direction with maybe a 20-25 degree difference.

If you split it 4 and 4 you could wire the two strings in parallel to a single string inverter, might make it a bit cheaper.

One of around 2kW capacity would be plenty.
Keep an eye on the maximum input current it can absorb as it could be a limitation.

If you could find a supplier of some higher voltage panels (eg Panasonics) it would make things easier as 4 in series would be near 200V.

However they may not be easy to locate here.

[Deleted User]

Cost of enerergy extracted from battery + cost of night rate electricity ≠ profit compared to day rate electricity.

We can measure this & all I have said.

listermint

Northumberland wrote: »

Fair, u enjoyed reading your last 3 or 4 posts, they agree with my thinking and understanding. I have a 4.5 kW of panels here in Ireland and 2 Pylontech 2000 US batteries, installed in March this year, still waiting for SEAI grant because an SEAI inspector visited finally 3 weeks ago and required firefighter shunts to be fitted etc etc, my installer too busy fitting panels to Lidl stores in Cork to f8nish my job and help me get my gran5. Anyway, apart from that, my SERP up is working well and saving me money I am sure, I have a NIBE heat pump, so that is thirsty for power day and night. I am about to install at least 2 additional Li batteries, my observations are that would help me get close to the magical hour of 11pm (winte4 time) when Electric Ireland night rate kicks in. I have two objectives, 1) use as much solar power as I can when it is generated and store the rest. And 2) use as little grid power during peak daytime rates. Doubling my battery capacity to charge at night tariff for use during following day must make sense, even if that following day is sun-less.

I also have 4kW of panels on a house in England, fitted in time to benefit from the FIT before they stopped it. The FIT is now very low, I am not getting much back, and getting it is a major hassle, although I had a smart meter installed (before the panels), the compan6 that I sell my power to can not read the other companies smart meter, how smart is that? My perception is, although I do not have figures to hand to be sure, that my Irish system is better econ9mucally, bu5 that will of course depend on actual life of the batteries.

What's a firefighter shunt

Hi air,

air wrote: »

If you split it 4 and 4 you could wire the two strings in parallel to a single string inverter, might make it a bit cheaper.

I understood that combining the strings would cause the system to operate at the performance of the lowest producing panel? so for example in the evening the SW orientated panels would operate at the performance of the now less efficient SE panels?

air wrote: »

If you could find a supplier of some higher voltage panels (eg Panasonics) it would make things easier as 4 in series would be near 200V.

Unfortunately budget will largely dictate panel choice, hence the assumption of 300Wp (x 8) and the DIY with no battery install.

Cortina74 wrote: »

Hi air,

I understood that combining the strings would cause the system to operate at the performance of the lowest producing panel? so for example in the evening the SW orientated panels would operate at the performance of the now less efficient SE panels?

No, that would apply only if you put all 8 in series.
With two groups of 4you will get the combined output of both halves.

Cortina74 wrote: »

Unfortunately budget will largely dictate panel choice, hence the assumption of 300Wp (x 8) and the DIY with no battery install.

That's fair enough.
You should be able to find a Solis inverter around 2kW that should do the job.
Just check the input current, you'll want it to be able to handle around 15A.
Might be easier find a dual MPPT one in practice.

air wrote: »

No, that would apply only if you put all 8 in series.
With two groups of 4you will get the combined output of both halves.

Thanks air.... something tells me I should have guessed that!!
How would the two strings be connected together? Is there a special connector required?

Cortina74 wrote: »

How would the two strings be connected together? Is there a special connector required?

If you're using a single string inverter he easiest thing would be to buy 2 pre made MC4 Y harnesses and use those.

You could also put an MC4 fuse (likely 15A check the panel data sheet) and an MC4 diode in series with each string for a best practice installation that would be plug and play and fully waterproof.

The panel I'm looking at has the following rated Amp output:

ELECTRICAL CHARACTERISTICS AT NOCT
Current at Nominal Power (Imp): 7.50A

So using panels in series would result in 7.50A into the inverter whereas using two strings in parallel would result in 15A into the inverter ???
The Solis inverter range seem to be 11A.

Cortina74 wrote: »

The panel I'm looking at has the following rated Amp output:

ELECTRICAL CHARACTERISTICS AT NOCT
Current at Nominal Power (Imp): 7.50A

So using panels in series would result in 7.50A into the inverter whereas using two strings in parallel would result in 15A into the inverter ???
The Solis inverter range seem to be 11A.

Yes, 15A max in theory. Given the fact that you will be orienting both strings only slightly differently their peaks will overlap somewhat.
Your peak output power would be clipped at 1760W ( assuming panels are 40V maximum power voltage)
Now the impact on your total annual energy harvest would be fairly minimal in practice and it means that you can use a fairly small / cheap inverter.
You wouldn't see any clipping at all worth talking about for 8 months of the year.

Sir Liamalot wrote: »

Cost of enerergy extracted from battery + cost of night rate electricity ≠ profit compared to day rate electricity.

Yes I agree on this. Best case you save 1-2c. Worst case you lose 4-5c or more. Not worth it financially in my opinion. And the environmental cost for the marginal best case gain doesn’t justify it either. Best case you are saving about €20 a year. Is a 2000 Euro investment in batteries worth it?

Sir Liamalot wrote: »

Cost of enerergy extracted from battery + cost of night rate electricity ≠ profit compared to day rate electricity.

We can measure this & all I have said.

That's too much of a generalisation.

If you pay the going rate for a lithium battery, you will lose money doing this. If you got your lithium battery as part of the €3,800 subsidy, it is borderline as garo has demonstrated a few times. But if you got a lead acid battery very cheaply or for free you sure will make a profit loading it up with night rate in winter.

murphaph

listermint wrote: »

What's a firefighter shunt

I assume it's the same as the fireman's switch we have (optionally) here in Germany. The problem with PV (typical setups with no module level optimisers) is that in the event of fire the fire brigade can't pull the main breaker and be sure than the house is safe (electrically) to fight the fire in. You can still have hundreds of volts of DC coming down from the roof even if the main breaker (I assumed the fire brigade in Ireland can open the mini-pillar, if fitted, outside and interrupt supply, they can here anyway) is open. In some places here such fireman's switches with appropriate relays/bypass diodes are required and some fire brigades will not fight the fire inside the building if there is PV on the roof which can't be isolated to bring the voltage down to safe levels.

I have recently seen lithium modules (complete with BMS) at close to €200/kWh ex VAT so storage may become much more viable in the medium term.

This is pricing direct from the manufacturer but bodes well.

air wrote: »

I have recently seen lithium modules (complete with BMS) at close to €200/kWh ex VAT

That's pretty good. Any link?

unkel wrote: »

That's pretty good. Any link?

No link sorry, B2B pricing only.

Only mentioned it as an indicator of where things are at currently at that level.
It should trickle down to us mere mortals eventually.

garo wrote: »

@ Northumberland How much are you getting the Pylontechs for? Be prepared for not getting your money back for 8-10 years. Also charging at night is marginal at best. You save maybe 1-2c at most. Given winter is approaching if I were you I would wait till March. Batteries could likely be another 10% cheaper by then. Lithium wholesale prices have come down a lot in the last couple of years.

Garo, I have a place in Dublin with an online presence, but they say I can pick up a Pylon 2.4kW US 2000 for Euros 936 plus E 215 VAT - this is probably not the cheapest, but if you do not get a unit in Ireland or the UK freight is large because of the Li battery restrictions. Please pm me on dalnwick@gmail.com if you know of better dealls.

I do not really understand your statement 'charging at night is marginal at best', I pay 50% or slightly less per unit of electricty used between midnight and 9am (summer), so if I can store that in my batteries (at what 98% efficiency? less?) and then use it in the day instead of paying full price, surely I am saving? since I only have 5kW of battery storage, I will of course only save 50% of the daytime cost of 5KW, but that is more than '1- 2 c', or did I mis understand you there?

Northumberland wrote: »

Garo, I have a place in Dublin with an online presence, but they say I can pick up a Pylon 2.4kW US 2000 for Euros 936 plus E 215 VAT - this is probably not the cheapest, but if you do not get a unit in Ireland or the UK freight is large because of the Li battery restrictions. Please pm me on dalnwick@gmail.com if you know of better dealls.

I do not really understand your statement 'charging at night is marginal at best', I pay 50% or slightly less per unit of electricty used between midnight and 9am (summer), so if I can store that in my batteries (at what 98% efficiency? less?) and then use it in the day instead of paying full price, surely I am saving? since I only have 5kW of battery storage, I will of course only save 50% of the daytime cost of 5KW, but that is more than '1- 2 c', or did I mis understand you there?

When you subtract the cost of cycling the battery (total cost/(number of lifetime cycles * kWh capacity)) you're not better off than just using daytime electricity is what he's saying.
When you allow for the cost of capital you're probably losing money in reality.

air wrote: »

When you subtract the cost of cycling the battery (total cost/(number of lifetime cycles * kWh capacity)) you're not better off than just using daytime electricity is what he's saying.
When you allow for the cost of capital you're probably losing money in reality.

Ok, I understand that. But that is really only true if the only justification for batteries is storing cheap night electricity. It is less true (but I accept still partially true) if the batteries are there primarily to store absolutely free electricity from the sun (free of course less depreciation of panels), which is the case with my set up. So, having installed the batteries (one of which will hopefully be almost free thanks to SEAI grant if it ever comes) to store panel generated electricity, it obviously makes sense to use them to store night rate power as well. But I think what he is underlining is the general premise that it is economically the very best to use as much of the energy generated from the panels at the same time that it is generated, hence the argument about panel orientation to try to maximise the time that the panels generate a useful current.

Northumberland wrote: »

it obviously makes sense to use them to store night rate power as well.

Nothing obvious about that! Your battery will have a much shorter life span if you load it up with night rate power. The additional benefit (10c saving per kWh) does not weigh up against the extra cost of the shorter life span, or at best there is very little profit in it - garo has done the sums in this thread. Look it up.

unkel wrote: »

Nothing obvious about that! Your battery will have a much shorter life span if you load it up with night rate power. The additional benefit (10c saving per kWh) does not weigh up against the extra cost of the shorter life span, or at best there is very little profit in it - garo has done the sums in this thread. Look it up.

Hmm, ok, food for thought and perhaps action!

Garo, Unkel, I have re-read Garo's nice post ( of 16th Sept 2019 if others want to find it easily) on the maths and economics of battery storage, particularly charging batteries overnight on cheaper night rate tarrif. Garos maths clearly warrants a cautious approach. But my question to you two is this - Garo's assumption appears to be that the batteries would be completely discharged before midnight (or 11pm in winter), then completely re-charged by 9 am or 8am from overnight charge, then discharged again in the low sun morning hours, charged up around 3pm from mid-day sun and discharged again in the evening, so there would be 2 nominal charges and discharges each 24 hours, eating in to the 10 k cycle life of the batteries. Depending on how the hybrid inverter/charger is set, this may well be close to reality. But with a large enough bank of batteries (expensive I know) there would seem to be the possibility of managing the charge/discharge times so that perhaps there was only one complete charge/discharge cycle per 24 hours. In most battery systems, particuarly electic cars (I have a Leaf) it is rare to go from completely discharged (or 10%) to completely charged - It is more usual to go from 30% up to 80% then down to 40% back to 85% etc, do all of those half or one third cycles count as full cycles in the batteries life, and eat in to the 10k cycles, or do they indeed count as just half cycles in the life expectation? In essence, my question is, is there a careful way of managing or manipulating the charge discharge cycles so as to change the economic maths away from Garo's calculations in favour of doing some re-charging at night, but perhaps not complete re-charging of the battery bank?

The short answer is nobody knows. You would need detailed performance data on your proposed battery as well as an estimated usage pattern in order to model various usage scenarios.

One thing in favour of night rate cycling is that batteries have a calendar lifetime as well as a cycle life so it may make a little more sense from that point of view to cycle them more while you have them.

It also gives you a bit more protection against power cuts if you have an essential load setup as the battery will be fully charged more of the time.

All told though I'm not convinced it's worth the hassle, charging from excess PV that would be otherwise exported for free is a much better business proposition.

Yes Unkel has it right. One Pylontech 2000 is costing you €1150. It has a stated life of approximately 6,000 cycles after which it only holds 60% charge. Let’s be generous and assume your battery will take 8,000 full charge cycles equivalent. Each cycle of the US2000 is with 2.2kWh as it has a 90% DoD. So 1150/(8000*2.2) gives you 6.5c cost of extracting a unit from the battery. You pay 8c for it at the night rate, lose at least 5-10% in charge and discharge and AC/DC transform. So let’s say 1 unit out the battery actually cost you 8.8c. So in reality your cost of one unit from the battery is 15.3c You are not saving much after that. 1-2c if my assumptions are correct. Over its lifetime the battery will save you maybe €250 if used just to charge at night rate. Not a great return after 15+ years on an investment of 1150. If the battery only lasts the stated 6000 cycles your total cost per unit goes up to 17.5c. Pretty sure you can get a day rate cheaper than that.
A battery has a finite life. So every time you put energy into it or take energy out of it you are using up its life so you have to account for the cost.

Northumberland, Yes if you charge and discharge in the middle of the capacity range LiIon batteries last longer. Google batteryuniversity for some nice graphs. In my calculations above I assume a 90% cycle so going from 100% to 10%. Pylontech is Lithium Iron Phosphate which tolerates 100% charge better than other Lithium chemistries.
If you go from 40% to 85% and back you do get more cycles but you get less usable energy. Each half cycle only gets you 1.08 KWh so if you get 16,000 cycles your cost per unit is still the same. 1150/(1.98*16000) is 6.6c

AidenL

garo wrote: »

Yes Unkel has it right. One Pylontech 2000 is costing you €1150. It has a stated life of approximately 6,000 cycles after which it only holds 60% charge. Let’s be generous and assume your battery will take 8,000 full charge cycles equivalent. Each cycle of the US2000 is with 2.2kWh as it has a 90% DoD. So 1150/(8000*2.2) gives you 6.5c cost of extracting a unit from the battery. You pay 8c for it at the night rate, lose at least 5-10% in charge and discharge and AC/DC transform. So let’s say 1 unit out the battery actually cost you 8.8c. So in reality your cost of one unit from the battery is 15.3c You are not saving much after that. 1-2c if my assumptions are correct. Over its lifetime the battery will save you maybe €250 if used just to charge at night rate. Not a great return after 15+ years on an investment of 1150. If the battery only lasts the stated 6000 cycles your total cost per unit goes up to 17.5c. Pretty sure you can get a day rate cheaper than that.
A battery has a finite life. So every time you put energy into it or take energy out of it you are using up its life so you have to account for the cost.

Is it fair to say it’s sensible to get a battery to avail,of the extra grant, but it should only be used to store free panel generated electricity then. And even then, it costs 6.5c, but offset by the additional grant?

Yes even then it costs 6.5c per unit. At that rate you have a much quicker payback because that is substantially less than the day rate which you’d be paying for your evening usage which a battery would typically cover.

Note that if you get a battery set up you also have to fork out for a hybrid inverter which costs 5-800€ more than a normal inverter. On the other hand you get to claim up to €2400 extra in SEAI grants. So if you are getting 4kW of panels then it is a no-brainer to get a battery. I went for a small battery as it is a flat battery grant so you don’t get more for a larger battery. I’m hoping for some form of FiT or net metering or a substantial drop in battery prices in the coming years. If battery prices halved, I would add more in a heartbeat.

AidenL

garo wrote: »

Yes even then it costs 6.5c per unit. At that rate you have a much quicker payback because that is substantially less than the day rate which you’d be paying for your evening usage which a battery would typically cover.

Note that if you get a battery set up you also have to fork out for a hybrid inverter which costs 5-800€ more than a normal inverter. On the other hand you get to claim up to €2400 extra in SEAI grants. So if you are getting 4kW of panels then it is a no-brained to get a battery. I went for a small battery as it is a flat battery grant so you don’t get more for a larger battery. I’m hoping for some form of FiT or net metering or a substantial drop in battery prices in the coming years. If battery prices halved I would add more in a heartbeat.

I’m on that trail of a deal based on those specs.

I guess 6 kw of panels as opposed to 4 would be sensible if a fit appears? The panels are relatively cheap, and would cost more to bring installers back? Still use the small battery with the 6kw of panels?