type of pv

[Simplysimon]

hi all,

 

starting to consider pv panels, wasn't going to bother but now starting to think about it. i had thought that monocrystalline was the best due to % efficiency but am finding that amorphous is better in low light. these are also cheaper and the returns don't seem much different when compared to the purchase costs. i'm not bothered about getting them fitted to get the FiT and would try to use as much as possible of the generation.

i did search for monocrystalline but only got two results, therefore could those with more knowledge please advise? i would like to go for 8KW if i'm allowed as looking at sunamp and future proofing with car charging point.

[SteamyTea]

Some people get really excited about the technology of PV.

But the important issue is how much sun hits your array.

Have a quick look on PVGIS, change the angles and module types and see what differences you get.

When I changed the technology types for my location, I get no difference.

 

So go for the cheapest module per kW_p.

Edited June 12, 2018 by SteamyTea

[Nickfromwales]

@Simplysimon

Can you add a little detail as to;

Orientation?

Will the array all fit on one face or split?

Any heavy shading? 

[mike2016]

Try google project sunroof which is now open to the UK and see if it recommends 8kW of panels on your roof and how much it would deliver per year. Chinese import tariffs to EU finishing in August which might offer itself up to lower prices. Check prices on a few sites. How are you going to prioritize car vs sunamp? Are you going to add a battery? If you've lots of south facing roof space going for more cheaper poly panels makes sense rather than a small number of more expensive mono ones but see what deal you can get. Saw a video recently where they recommended a battery first, then adding PV later, with E7/10 of course....One USA guy got a load of cheap panels off a repo but I think they must lease PV a lot more over there than the UK...

 

[jack]

40 minutes ago, mike2016 said:

Try google project sunroof which is now open to the UK

 

Despite saying that it's now in the UK, the website is saying it doesn't operate here yet 

[AliG]

A Tesla Powerwall costs £6000 plus installation costs(cheaper alternatives may be available). An installed 5kW EV system costs £5-6000, cheaper if you DIY. As the EV system generates free power and costs less than a Powerwall it is extremely unlikely that a battery system would be better than an EV system as a starting point.

 

It may depend on your use of electricity over the day, but in general electricity from a battery is still quite expensive. A much cheaper way to store EV electricity is to use it to heat hot water.

 

E7 electricity costs 7p per kWh vs around 13p normally. A 14kWh Powerwall could save you at most 84p a day if you filled it up every night with electricity and used it during the day.

 

However, you may not use all the electricity or you may still buy some electricity at the higher daytime price on an E7 tariff. Thus the savings might be only 50-60p a day or £200 a year versus a £7000 investment.

 

A 5kW array should generate around 3500kWh, or £455 a year of electricty plus FIT payments of around £200. You may not use all of the electricity, however. But still you would probably get a £500 return on a smaller investment. As suggested the best way to increase the return is to get cheaper panels/installation, assuming that you have the space. Generation/returns will fall considerably if you don't have a south facing roof.

 

The price of batteries needs to almsot halve before ROI becomes reasonable.

[A_L]

11 hours ago, Simplysimon said:

starting to consider pv panels, wasn't going to bother but now starting to think about it. i had thought that monocrystalline was the best due to % efficiency but am finding that amorphous is better in low light. these are also cheaper and the returns don't seem much different when compared to the purchase costs.

i would like to go for 8KW

 

Forget about minor efficiency differences between mono and poly crystalline panels. The output per kWp of panels installed will be similar and other factors much more important in annual output. Amorphous panels will output about 5% (or 50kWh) more per year per kWp but their lower efficiency will mean 30-100% more physical area required. Exact value will vary depending on which amorphous panels and with the efficiency of the silicon panels you are making the comparison. So 8kWp could easily occupy 60-80m²

[Jeremy Harris]

The best value battery system at the moment seems to be this one, at £2,800 for 4.8 kWh: http://www.thesolarpeople.co.uk/shop/sofar-solar-4-8kwh-energy-storage/

 

Still not really worth doing in terms of return on investment, though, I think.

[SteamyTea]

16 minutes ago, AliG said:

E7 electricity costs 7p per kWh

About 9p now and 25p/kWh day rate.

Getting close to not being worthwhile anymore.

 

[AliG]

 

47 minutes ago, SteamyTea said:

About 9p now and 25p/kWh day rate.

Getting close to not being worthwhile anymore.

 

 

I had just googled it, as you say checking Uswitch the cheapest E7 was 8.5p. Makes batteries look even worse value as the cheapest normal rate was still less than 13p. At these rates the maximum E7 saving would be 63p and any use at the daytime tariff would massively eat into this.

[Jeremy Harris]

I did some sums a few weeks ago, based on the Sofar system linked to above, and break-even is a saving of around £280 a year.  We have loads of excess generation, so could almost certainly get pretty good utilisation from a battery storage system, but our overall electricity consumption is just a bit too low to make it viable, in terms of economics.  In terms of the environmental considerations, plus the benefit the system above has of providing standby power to essential circuits if the grid goes, then it probably just about makes sense.

 

With the rate at which battery storage system prices are falling and electricity prices are rising I doubt it'll be more than a year or so before the economics stack up just on the electricity cost saving.

[AliG]

The economics do improve somewhat if you use batteries to store excess EV generation. The combination of that and some E7 moved from night to day could improve your returns towards an acceptable level. I was focusing on the question of EV vs batteries which I think EV easily wins currently.

 

One thing to remember is that heating hot water with excess EV is a poor use of the power if you normally use gas. Electricity is roughly 4x the price of gas, so you'd be better to try and use the electricity for something electrical and heat the water with gas if you can.

 

It somewhat depends on what people consider an acceptable ROI. I would think around 5-6% in the current interest rate environment, it seems that people tend to use higher numbers.

 

I have no doubt that battery prices will fall and make this a good investment, it's just not quite there today.

[Jeremy Harris]

The RoI question is a challenging one, as we don't yet have a lot of data on the life of battery storage systems, plus it's highly dependent on so many individual factors, like the amount of excess PV generated, and how much can be utilised if stored, plus personal considerations like being willing to accept a lower RoI in return for anything from a personal desire to reduce grid usage to things like having the option to use the battery storage for emergency power if the grid goes down. 

 

The latter is a significant consideration for us, as we're very dependent on electricity, and we often get power cuts around here, especially in winter.  The power cuts aren't usually more than a few hours, but inevitably occur at the least convenient time, so I've been thinking for some time about buying a standby generator, just to keep essentials running, like the water supply, MVHR and, perhaps, the sewage treatment plant, as well as some emergency lighting.  I've already got battery backup for our internet connectivity, primarily because of the power cut problem, but also because reduces our background grid demand slightly - the VDSL modem, router, switch, wireless access point and file server all run on battery power overnight and then the battery pack recharges during the day, when we're usually generating from the PV system.  Our case is far from typical though, as we're more reliant on electricity than most, I suspect.

[Barney12]

4 hours ago, JSHarris said:

The RoI question is a challenging one, as we don't yet have a lot of data on the life of battery storage systems, plus it's highly dependent on so many individual factors, like the amount of excess PV generated, and how much can be utilised if stored, plus personal considerations like being willing to accept a lower RoI in return for anything from a personal desire to reduce grid usage to things like having the option to use the battery storage for emergency power if the grid goes down. 

 

The latter is a significant consideration for us, as we're very dependent on electricity, and we often get power cuts around here, especially in winter.  The power cuts aren't usually more than a few hours, but inevitably occur at the least convenient time, so I've been thinking for some time about buying a standby generator, just to keep essentials running, like the water supply, MVHR and, perhaps, the sewage treatment plant, as well as some emergency lighting.  I've already got battery backup for our internet connectivity, primarily because of the power cut problem, but also because reduces our background grid demand slightly - the VDSL modem, router, switch, wireless access point and file server all run on battery power overnight and then the battery pack recharges during the day, when we're usually generating from the PV system.  Our case is far from typical though, as we're more reliant on electricity than most, I suspect.

 

Jeremy’s point about grid outages is a big one for me. Tesla still haven’t enabled the ability for the battery to kick in if the grid goes down. If it finally gets approved by the national grid the Tesla will move up my want list considerably as short term power outages are common up here on the moor. 

[Jeremy Harris]

4 minutes ago, Barney12 said:

 

Jeremy’s point about grid outages is a big one for me. Tesla still haven’t enabled the ability for the battery to kick in if the grid goes down. If it finally gets approved by the national grid the Tesla will move up my want list considerably as short term power outages are common up here on the moor. 

 

The Sofar system I linked to earlier has a UPS function, where the battery bank can run the inverter to supply power to a non-grid tied output, which is one reason why I've been looking at it closely.  It's also a lot cheaper than the Tesla Powerwall, with the 4.8 kWh system costing £2,800 (inc VAT and delivery) and the 9.6 kWh version costing £4,600.  The UPS capability is the same as the grid tied output, and allows a maximum load of 3 kVA, which would be OK for us for emergency use.

[Simplysimon]

@Nickfromwales SSW and WSW no shading, btw this is your fault for suggesting SA+PV instead of ASHP ?

@mike2016 don't have an EV car but may do so in the future so will put in the necessary wiring.

i'm just trying to find out more info and options and hadn't thought of battery storage, more complications......

[Nickfromwales]

On 12/06/2018 at 20:58, Simplysimon said:

@Nickfromwales SSW and WSW no shading, btw this is your fault for suggesting SA+PV instead of ASHP ?

@mike2016 don't have an EV car but may do so in the future so will put in the necessary wiring.

i'm just trying to find out more info and options and hadn't thought of battery storage, more complications......

You could always just fit a WBS  

[SteamyTea]

I have been pondering this battery storage issue.

Couple of things crossed my mind:

 

Power Density

Power Delivery

 

We usually talk, and record, how much energy we need or generate, but at the relatively small scale of a single house, power is what matters.  No matter how much you generate and store, you still need to get it to a machine i.e. your kettle.

So one of the problems of self consumption is the size of an inverter needed.  Up to 5 kW is pretty cheap, starts getting expensive after that.

5kW is pretty large, but can soon be used to capacity i.e. immersion heater and a kettle, put an induction hob on and you have exceeded that capacity.

 

Taking a lithium ion battery with a power density of 300W/kg, to deliver 5 kW you need 17 kg of batteries.

That will give you a storage capacity of 3.3 kWh.

Except that is the mathematical maximums and you have to apply Peukert's Law, which basically states the higher the discharge, the less time it work C = I^k.t

Nothing clever there really, but something to remember.

Typically batteries are discharged to 80% (well for lead acid ones) of maximum capacity to prolong life.  Some more modern chemistries claim a safe 90%.

The trouble with that is that they warm up, and it is the warming that causes the degradation to a certain extend (along with oxidation and other chemical reactions).

This basically means that if you discharge a battery too much, and too quickly, then you have to let it cool before you can start charging.  Charging/discharging rate is affected by temperature, why Tesla warm the batteries up when you press 'Ludicrous' mode.

There was a rule of thumb of lead acid batteries of 5:1 i.e for every 1kW you wanted delivered, you needed 5kWh of storage.  I am sure there is a similar metric for lithium ions, but not looked it up.

 

So basically what I am saying is that you need to know your power delivery, which means doing so proper modelling or monitoring and then decide if the costs of that large battery pack and secondary inverter is worthwhile.

 

As for electric cars, still a bit early to put in the infrastructure, we are probably going to have a Betamax/VHS war and we know where that ended, with a totally different method of storing movies (.mp4 .mpeg .avi .mov .flv .wedm .mkv .vob .ogg. vog .drc .gif .gifv .mng .qt .wmv .yuv .rm .rmvb .asf .amv .m4p .m4v .I have lost the will to live).

 

 

Edited June 26, 2018 by SteamyTea

[Simplysimon]

12 hours ago, Nickfromwales said:

You could always just fit a WBS  

@Nickfromwales don't go there, OH wants one, in a near/passive house ? currently have one, 4.8kw 40min on and you can't sit in the room without the windows open.

[SteamyTea]

11 hours ago, Simplysimon said:

40min on and you can't sit in the room without the windows open.

People that like WBS would point to that as proof about how great they are.

[richi]

On 12/06/2018 at 16:51, JSHarris said:

the 4.8 kWh system costing £2,800 (inc VAT and delivery) and the 9.6 kWh version costing £4,600.

 

Wow, that's still a lot of cash, unless I'm missing something. A "leisure" 12V lead-acid specced at 110 Ah is £85 from the local leisure shed. So be generous and call it £100 per kWh. No idea how much the inverter and BMS would be, but surely not thousands? Even if the L-A batteries have half the useful life of the Li-ion cells, the Sofar and Tesla systems seem pricey.

 

I bet I'm missing something important.

[Jeremy Harris]

The main difference is life and efficiency.  Peurkert factor for lead acid struggles to get better than about 0.85, that for lithium ion is close to unity, to round trip losses from lithium ion are around virtually non existent, versus 20 to 30% for lead acid.  Lead acid cycle life may be as high as 2000 cycles if babied, lithium ion will easily make 20,000 cycles.

 

The conservative life of a Lithium ion system would be around tens years, that for a similar cycled lead acid pack might around 5 years for equivalent capacity reduction.

 

Looking at the pay back from self-consumption, ignoring the standing charge and assuming 0.15p/kWh, then if you could realistically average 80% of the rated storage capacity all the time for self-consumption, you might be able to save around 3.5 to 4 kWH per day for self use, so about 50 to 60p per day energy saving.  At £2,800 the basic (and fairly optimistic) payback period might be as short as 5,600 days, or over 15 years, for the very best case.

 

BTW, a 110 Ah 12V leisure batter might do 400 to 500 cycles at the very most, and only store a total of 1.32 kWh, and a usable kWH of only about 70% of that.  Used in a household system they would barely last a year, and would only deliver around 1 kWh per day  at the very most.

[Dreadnaught]

@JSHarris Nickle Iron?

[Jeremy Harris]

10 hours ago, Dreadnaught said:

@JSHarris Nickle Iron?

 

 

NiFe cells get around the limited cell life problem pretty much completely; they last practically forever in my experience of using them for a decade or more (although don't ever mention that fact on a certain other forum - you'll get kicked off for heresy...).  I've personally used 50 + year old NiFe cells that were still at full rated capacity after all those years, and pulled very high current from them to run high speed 35mm cine cameras with no problems (a 10,000 fps 35mm cine camera needs a couple of hundred amps or more to spin up).

 

They are far from perfect though.  The have a Peukert number that's lower than that for lead acid, plus a higher self-discharge current and a relatively wide voltage range between discharged and fully charged.  They do self balance, like lead acid, though, and only require a simple constant current charger with a voltage/temperature triggered cut off, so battery management is a great deal easier than any lithium ion chemistry.  They are massive for their capacity, too, and require watering regularly, but again that's easy to arrange with an automatic cell watering system.  All told, as a long life house supply NiFe cells are a very good option, if you can generate enough excess energy to make up for the fairly high round-trip loss because of their Peukert number.  If we could still get hold of the really big NiFe cells that were very readily available on the surplus market a few decades ago then I'd use them for sure.  However, right now the choice is to make your own (not that hard to do if you can find some old telephone exchange glass cases) or import them from somewhere like China (the Chinese are manufacturing them in large sizes, for standby power, submarines etc).

 

[Dreadnaught]

A UK supplier of Nickel Iron batteries? https://www.bimblesolar.com/batteries/nifebatteries