View Full Version : PV panels

31st Jul 2011, 14:13
I have been considering gettiing some PV panels onn the roof and have got some quotes . However the prices for a 3.8KW array installed range from 8K to almost 12K .
So what should I be looking for ie do I just take the cheapest or do the panels vary in quality ?

31st Jul 2011, 16:08
Not sure what PV stands for but if it's panels to generate electricity, and if you live in the S of England, it's worth popping over to France and looking at the ones in Castorama or LeRoy Merlin. They also have all the ancilliary bits to DIY.

What is the purpose of the installation ? Feed back into the mains power supply and get the subsidy or charge up some big truck batteries ? If the former, get a professional installation. Make sure the supports are strong enough, and make sure you can get at the solar panels to clean them now and then.

I did a study for my own house for the latter and found the installation would work best if you ran a 12v dc or 24v dc ring around the house and fed everything you can directly off that rather than stepping it up to 220v/230v a.c. For example 12v 1 watt LED lights are so bright these days and you could drive an awful lot with truck batteries - the LED lights remain absolutely cold, too. I have four illuminating my desk right now and they are too bright to look at directly.

Ancient Observer
31st Jul 2011, 16:30
I think there has been a recent thread on this.

31st Jul 2011, 21:29
We had PVSOLAR around to quote for a Phot Voltaic panel installation, on Thursday. We are near to Reading in Berks. For a 3.9kW system it varied between 12.5k and 14.5k pounds so 8 to 12 sounds like a bargain.

Where are you, Huntandfish, and who did your quotes?

Looks like I need to get some competitors organised.

OFSO what we were quoted for is a solar electricity and grid feed in system. The panels will generate 3.88kW in direct sunlight and somewhat less in overcast conditions. The way it is sold is that there is a subsidy payable for each kW hour of electricity produced of 43.3 pence. This is estimated to total about 1600 pounds per year. Of the electricity produced it is "assumed" that 50% will be fed back into the grid system for which 3.3 pence per kW hour will be paid (this is in addition ot the 43.3 pence) paying us another 56 pounds per year. The feedback portion is not actually measured so you still get 3.3 pence on half of your generated power whether you use it, waste it or feed it back! When the house demands exceeds the generation capacity electricity will be drawn from the grid system and this will be charged at the normal tariff rate (about 11 pence per kW hour) but overall consumption is estimated to be down by 240 pounds per year. The scheme is for 25 years. To really make it pay off you need to adjust your electricity usage so that you use heavy demand items (heating of water, electric ovens etc) when it is sunny to maximise the use of the electricity generated by your panels and to minimise usage when it is dull or dark. Don't put the washing machine on at night etc.

It might work well if you work at home and can see when the system is producing more than the house is using and can switch something else on to make the most of it. Whatever you can use by running the immersion heater is going to show as a saving on the gas used by the gas boiler which would normally heat the water.

There is no provision for storage of the generated electricity. A switch to more efficient lighting might be a good thing if the cost of those efficient lights is less than the cost of the electricity they save over their lifetime. Not sure it is just yet. A 100 Watt light costs just over 1 pence an hour to run and the bulbs are just a few pence each. They last 100s of hours. The LED lights I have seen are several pounds a piece so they need to last a very long time to show a net saving. More research needed, methinks.


31st Jul 2011, 21:54
How many square metres for 3.88 kW?

1st Aug 2011, 05:39
rans6 I think the word you need is "Deemed", and I believe the rate is 3.1p /kWh. If you are buying a system make sure the installer is MCS approved. I've got an export meter which measures actual output onto the grid. It comes in handy in working out exactly how much electricity is used from the panels. radeng my 4 kWh sys is 28.428 sqm. Oh and AO I hope we're not boring you! ;)

1st Aug 2011, 08:04
m currently investigating the possibility of having PV installed and have managed to get myself very confused over the export quota thing.

As I understand it if you get an export meter installed life is simple - it goes forward when you are taking power from the grid and backward when you are exporting power to the grid. End of the day you pay for what you used - what you exported. Easy.

If you don't have an export meter however the power you generate is fed into the grid 'upstream' of your meter so the meter shows the household consumption, with no allowance for what you have generated. In this case you are deemed to have used a certain amount of the generated power, with the allowed pecentages being 0% (none used) 50% or 100%, with the normal figure being 50%. So this amount of your generated power is deemed as being used in the home so is taken off your metered usage. So if you use 5,000 kwh per year and your system generates 4,000 kwh per year you would end up charged for 3,000 kwh per year (as you would be supplying yourself 2,000 kwh).

So, at 50% personal usage, that means that I would be getting 3.1p per kwh for 2,000 kwh that was exported but then having to buy in 2,000 kwh at (about) 12p per kwh to replace it meaning. So I mentioned using the 100% personal use figure and was told, basically, "don't be so silly, you can't do that" so why is the 100% publicised as being available. (For us for the size of installation the total estimated generated is very similar to our annual usage so the 100% personal use seems most sensible).

1st Aug 2011, 08:21
Sorry error in my first post the 8K is for 3.0KW from Greener Power solns .
14 panels at 21sqm .
Schuco polycrystalline 215MPE 05 EU modules
I am near Didcot rans6andrew

Another outfit is quoting 11k for their 3 KW system which they call a premium system from Caymax .

So my question is just taking these two examples how does one decide which is the best value ?

1st Aug 2011, 10:42
So yotty is getting 140.7 watts/ sq metre. - 12.42% efficiency

HuntandFish is getting 142.9 watts/sq metre. - 12.6% efficiency

Assuming that we are talking overall efficiency, including the inverter.

Good figures, but how many kWh do you get in mid winter?

Assuming strong sunlight as per DEF STAN 133

1st Aug 2011, 11:27
The numbers I got when the guy was looking over the place here were that winter output is about 10% of summer output (being a combination of lower light levels, shorter days and more cloud).

Ancient Observer
1st Aug 2011, 11:35
Thanks for the inputs so far. I wish there were a central "pool" of articulate and thoughtful comments about this topic. How might we drive more traffic to this thread so that it becomes a really useful centre of people's experience?

1st Aug 2011, 12:22
MadsDad. It's difficult to get your head round this initially. I have got 3 meters. One measures the total generation from the panels. The second measures the kWhs which are exported onto the grid. The third meter measures supply which I take from the grid. Imagine if I'm using exactly all the power being produced from the panels in my house. The first meter will read what the panels are producing the second will be zero coz I'm not exporting and the third will be zero also coz I'm not drawing on the grid. None of my meters go backwards! :)

1st Aug 2011, 13:09
Ancient Observer
i agree getting past the salespitch is difficult . Last nighton Dragons Den there was a squabble among the Dragons to get a piece of a Company that install Photo Voltaic panels . Beborah Meaden stated that for anyone with the cash sitting in a savings account installing panels was an clear winner .
Itsthe Feed In Tarrif that gives the return rather than the electricity saving .

I have one quote that for year one estimates FIT payment at 891 Elec saving at 171 Export income ? 32 Total 1096 on an 8K investment guaranteed ? for 25 years !

1st Aug 2011, 13:24
What do the suppliers give you for the cell life? Perhaps more to the point, how long do they guarantee the invertor for? With surface mount components on PCBs using lead free solder, unless they have used large clearances, there's a good chance of growing tin 'whiskers' which short tracks to together. Sod's Law says that will result in some dead components - all electronic components contain smoke, and while it's contained, that's fine. When it gets out, it usually means the component is dead! Depending on the components, the PCB may not be repairable, so the cost could be quite high.

So a worthwhile question is 'What is your guaranteed MTBF and MTTF?'

(Mean Time Between Failures, Mean Time To Failure)

The 'tin whisker' problem is why lead free solder is not mandated for defence, aerospace and medical equipment.

I'd also ask what the inverter can stand in the way of surges and transients coming back down the mains e.g. from lightning - which doesn't have to strike the wires to induce nasty transients.

If there's anyone around you listens to HF radio of any sort (or even on some occasions, Band 2 FM) they can have problems with interference from the inverter, too. That can mean a wireless mouse won't work.

1st Aug 2011, 15:25
My experience so far.

System commissioned 20/04/2011


I have two meters, one recording units generated, currently reading 1152. The second is what I call my normal leccy meter.

This currently reads 58345 and is going backwards at a rate of knots, just popped out to check - clear blue sky here (Hampshire), telly on, watching the cricket, fridge, freezers running, etc.

Reading on my leccy meter at commissioning was 59032.

Unsure about MTBF & MTTF but I expect inverter ( 5yr warranty, can extend to 20yr but not cheap > 1000) will need replacing at some point.The supplier facored this into their estimated break even calculation Panels have 5yr warranty.

Only problem so far is that my leccy supplier have still not processed application for the FIT. Have heard this is not unusual.

Cost 10K.


Will Sachin get his ton?

1st Aug 2011, 19:21
radeng the panels are guaranteed for 90% of output up to 15 years and 80% up to 25 years. The inverter is only guaranteed for 10 years. The system (apart from panels and Inverter) is guaranteed for 25 years.

1st Aug 2011, 19:29
MadsDad the second scenario is thus, panels on the roof producing 2 kWs, the cooker is on in the house taking 3kWs. The first meter is reading 2 kW, which is what the panels are producing. The second meter (the export one) is not changing. The third meter will be reading 1kW from the grid. So the house is being fed from from the panels 2kW and 1kW from the grid.:zzz:

1st Aug 2011, 19:37
@ yotty

Are these guarantees backed by the company or an insurance company ?

Guarantees are worthless if the guarantor no longer exists and I think we know how quickly small companies disappear and re-appear with different names.

2nd Aug 2011, 00:18
Guarantees are worthless if the guarantor no longer exists and I think we know how quickly small companies disappear and re-appear with different names.

So True!

In addition to guarantees regarding equipment - and availability of spare parts 10 or 15 years hence, one must wonder greatly about the subsidy rates -- when they seem generous -- continuing any longer than it takes for political winds or the fortunes of the guarantor to change a bit. Government sponsored plans are certainly not immune to sudden "Oh, nevermind" changes of meaning, intent, and availability.

Taking note that 25 years is a very long time for any contract to run, consider that inflation - if no worse than the span since 1986 (I looked it up), will see nominal electric prices increasing by "normal" inflation-- for exactly the same quantity delivered today -- with the result of a number 2.5 times the current number appearing on the billing slips of 2036. Somehow it seems to moi that the subsidy rates will not be inflation-adjusted in a similar manner, so the effective reimbursement value will drop over the stated lifespan to 40% of the present rate -- if still paid at all.

From curiosity, one has reviewed subsidy schemes of various sorts in many different countries. Few of them give away anything much, and the ones that do (Germany is/was an example) had a short contract life. The impression one receives is that neither the utilities nor the governments promoting energy redirection will reach very far to accomplish that goal, nor promise long. The trades companies, of course, will grab every penny possible in the doing and the support afterward.

One had the experience of putting in a solar water system - three panels comprising something like 10msq of surface, with pumped recirculation and valve-controlled drainage of the panels to prevent freeze damage. One spent something like US $1500 for the panels, pump and tank (about 1984) and installed it DIY, with proper permits and some improvised features added to allow computer monitoring of the performance. Subsidy for it was roughly equal to the materials cost, as a one-time lump sum off tax obligations for the year installed -- as part of a State-Federal initiative actively promoted in the US at the time. Relatively few others seemsed to buy into the program, which was a surprise. Anyhou, it worked like a charm at a site where the panels could grab (iirc) about 1300 watts/m2 for most of the summer months. Was, in fact, grossly overpowered for what was basically household consumption, so the pump ran only an hour or so a day in mid summer to keep a 125 gal tank at 120f or so (hotter was uncomfortable). In the fall it worked with less and less vigor until becoming mostly useless for the 3 or 4 coldest months - during which time electric did the heating - at a rather lower setpoiint. For a couple years it was a real charm - with electric bills maybe cut by half in the summer. Then time began to take its toll. FLexing of joints exposed to the elements caused micro-cracking on the soldered copper connections (1-inch pipes in the panels were too big, so were stepped down to 3/4, so differeng expansion characteristics may have been a cause). Result was small leaks that needed repair in Spring by re-soldering. Then the drain-down anti freeze valve acted up, finally needing replacement -- but the vendor that supplied it (a highly unique design) had gone out of business when the subsidy programs expired.... so some improvising and another start-up shut-down chore for fall-spring. Then the sequencing and temp controller went odd - no replacement available, so one hastily improvised a new one... which was always a bit strange, but not enough to justify another re-design. Net of it was that the whole thing went marginal after about six or seven annual cycles, one's time had become quite scarce, and so the whole thing was left in limbo, mostly non-solar and runnig of the electrics. There it still sits - a soldered-together half-ton on the roof, and another plumbing xmas tree on the cement floor below (on the tank, which still is in use) awaiting some inspired moment for either recycling or rehabilitation. It really worked well, and actually paid for itself --- but only due to having the lowest possible up-front cost, plus a subsidy.

Solar electric is, of course, quite different. Am gradually building up a small, distributed pv-panel solar system that is completely decoupled from mains power, except that a supply from the mains can now also drive that set of circuits, as desired. One function the PV system serves is as a general power backup, since we tend to have quite extreme and intense winter weather at that site, and power can go off in Winter for days or weeks. With FP's available for heat, one mostly doesen't need mains electrical for outages of a few days to a week in Winter, so the PV system is scaled to run a half-dozen energy-optimized computers and a bunch of high-brightness LED lamps, plus misc things like antenna amps for TV and misc critical electric circuits. A petrol generator sits waiting, but it has'nt really been started for so long that one does not expect it to run. Car batteries charged off the PV (and available to be topped by the mains, or by one of the autos cranking out 12V -- or by a bicycle thingy one cooked up that is definitely the hardest way of all.)

2nd Aug 2011, 05:16
You are probably better off with deep cycle lead acid batteries rather than car batteries.

So the guarantee is for an 87,000 hour MTTF. Impressive. I'd love to see their MTTF/MTBF calculations. Pacemakers expect at least twice that, but they aren't handling high power and thus getting junctions hot. Additionally, all the parts carry a premium price...AlpineSkier has it right - and in any case, even a manufacturer's guarantee is worthless if they don't exist any more. Anything using a custom ASIC (Application Specific Integrated Circuit) may well have no spares available in ten years (well, say 9 years 9 months!), and even standard ICs can disappear in that time.

Maybe 47 years in the electronics industry has made me rather more cynical, but a lot is based on hard experience.

2nd Aug 2011, 08:05
@ AlpineSkier PV Panels are covered by a REIGA guarantee and also an insurance policy. I also checked with house insurers and the panels are covered for most conceivable damage, riot, act of god, storm damage, vandalism etc. Arcniz re the Government Grant, the feed in tariff has been allowed for in Parliament (UK) in Primary Legislation, which is about as good as you can get! The rate goes up each year in line with RPI.

2nd Aug 2011, 09:01
I expect the insurance has the usual exclusion about nuclear explosion damage, though!

Whats is the REIGA guarantee? Does the insurance offer 'new for old' if the inverter cannot be repaired?

2nd Aug 2011, 09:51
You are probably better off with deep cycle lead acid batteries rather than car batteries.

Point taken - actually I misspoke (miswrit) somewhat -- our storage batteries of choice now are labeled as Golf-Cart batteries - which are a sort of deep cycle battery (I think), quite massive relative to auto-designs, and come in 6V config so that 18v,24v, etc. are possible upgrade paths for scaling up in some time future. Their main virtue otherwise is relatively good availability though cost-efficient channels, and about one quarter to one third the price of the Marine variety that seem to be the locally available high-end deep-cycle cells.

During some work in me early years developing downhole logging instrumentation and signalling bits for oil-production, it was impressed on me that (in their world) batteries of all sorts are handled as the exact equivalent to high-explosives. Thus imprinted, I still feel uncomfortable with more than 5 or 10 kwh of battery -- as one pile -- in a residential-agricultural environment, unless with purpose-built separate buildings and safety systems in place. That's why the cobbled concept-testing PV solar package is targeted toward short-term degraded operation during outages, with a relatively inexpensive , easily replaced petrol motor-generator as the real backbone for extended-need situations. Having a near-inexhaustible wood supply - when sufficient labour is applied, logic might suggest a steam engine with that, but for the hassle of stoking. Kibbles and floating-bed combustion could probably handle that bit, too.

To me, the value premium in user-site domestic solar comes from displacing day-time peak-rate electricity consumption as much as possible -- preferably through greater efficiency on the demand side (for insulation, lighting efficiency, reduction of useless loads, etc.) rather than by adding acres of collectors. Using solar to directly heat water certainly is more savvy than using inefficient PV to electric to heat as the path.

the feed in tariff has been allowed for in Parliament (UK) in Primary Legislation, which is about as good as you can get!

In most places i know < rules change every election _ (keyboard has gone funny) so look out for that>>> but good luck with it>>> aiming for a ten or eight year breakeven might be a realistic limit to put on costs>>> see if ya can make that work>>

2nd Aug 2011, 10:15
arcniz.. I'd sort of penciled in 10 years, but anyone's guess is as good as mine! :eek:

12th Aug 2011, 11:44
have any of you got solar panels AND a Landis & Gyr 5325a domestic electricity meter?

What I want to understand is how the meter copes with you putting electrickery back into the grid. Does it count down? Does it not count at all? Does it count up?

The meter (digital with a blinking LED), according to it's data sheet, is a true Wattmeter. This means that it should take account of the direction (by phase with the voltage) of the current flow and perform a dynamic multiplication of the voltage and current to give WattHours counting up when the house is taking power from the grid and counting down when power is being returned to the grid. The data sheet does not even hint at whether it can cope with power being put back to the grid.

I have asked the question of the folk at L&G but the response has been underwhelming. Nothing for nearly a week. I guess they don't know.......


12th Aug 2011, 12:31
Or maybe the only guy who has a clue what you are asking about is on holiday!

12th Aug 2011, 13:00
Haven't the time to pursue this to the level of real facts - at the moment - but many years of developing data acquisition systems and circuits and gadgets and such suggest that a standard electronic meter - not specifically intended to permit local supply feed back to the grid - will calculate the watt-milliseconds flowing through and average them into the cumulative demand total, so that local power offsetting demand will bring the incremental adds to lower and lower values as local generation reaches demand...... but local power generation in excess of demand during any sampling period (of maybe a millisecond per sample) will result in a zero consumption value rather than a negative number or value that can be subtracted from either past or future demand excesses.

Technically it's not difficult to include the extra functionality (to run the total backward in some fashion), but that is not likely to be a feature of the specific meter unless it is part of the spec function set, and enabled, etcetera.

The first-level answer surely is all in the model number of the meter, and in the options "enabled" when the unit was fabricated or when it was installed. Try to get the detailed functional spec sheet for the product & give it a careful reading -- if you can't get straight answers from mere humans.

12th Aug 2011, 13:45
thanks arcniz, I understand what you are saying, but I really need the answer, proper.

The reason is for me to be able to work out the best strategy for running our new solar system, when it is installed. If the meter runs backwards, at the correct rate whenever power is fed back into the grid it may be best just to let it get on with it. Meter unwinding will reduce my electricity bill by around 23 pence per unit at some times and about 11 pence per unit at others. (our tariff is for the first n units per quarter at 23 pence per unit and the remainder at 11 pence, both rates and n change from statement to statement!)

But, if I let the power flow back while on the 23 pence part of the tarrif and then once it goes onto the 11 pence part attempt to use the power within the house to do something useful (heat water to save the gas boiler firing up, indicate a good time to use the cooker/breadmaker/kettle etc) I can maximise my savings. If the meter never unwinds then it will pay me to fully use the excess power generated by our solar system. If the meter counts up, even when power is flowing to the grid then again, it would actually save money if I just waste all of the excess generation capacity.

Just trying to figure out how many current transformers I need to get a full enough picture of the situation so that I can get them installed while the electricity is off for the solar installation.


12th Aug 2011, 15:59
Just trying to figure out how many current transformers I need to get a full ...

You seem to have a plan in place that really does require information about the specification behavior of the utility meter installed.

More than likely, the company meter uses an inline shunt circuit on each phase to directly measure the voltage variations across a calibrated and standardized resistance. Also likely is that these measurements are integrated from digitized samples at an effective sample rate of 1khz or more. The current transformers you are talking about installing may have a response very different from the utility meter for low-level and high-frequency variations in current on the lines, such that you may have significant differences in power readings that cannot be averaged or otherwise calibrated out due to the inherent difference in the natures of the two measurement paths being compared. For instantaneous readings the incompatibility of methods likely won't matter much, but the integrals of the differences - what the billing process uses - may possibly diverge much more dramatically, and also may vary in the variance at different loads and temps and with different types of demand - (such as switching power supplies vs incandescent lamps).

Sounds like you're serious about tuning the end-price results. Please post some progress reports and analysis as you get it all running.

12th Aug 2011, 21:10
If we are going to spend 11 grand on a power system we really want to get the shortest payback time we can, by playing the system to the full.

What has inspired me to do this was finding that our gas and electric standing orders cost me more than my aircraft hangarage every year. Don't tell our airfield operator!


12th Aug 2011, 21:25
The FIT is funded by a huge levy on all the UK electric bills and guaranteed by UK Govt legislation so it wont be cut as part of any Govt cuts.

For a useful solar forum try navitron solar - both PV & hot water.

13th Aug 2011, 22:38
If you find PV confusing wait till you try to get your head round the RHI !:E

14th Aug 2011, 00:00
I have barn roofs capable of taking the current maximum tariff load of up to 50Kw (see later) so am engaged in finding out as much as I can - but I've only been at this a couple of weeks or so - accordingly I have a lot to learn.

Basically - the return is comprised of

1 The FIT tariff payable to the generator for every Kw provided by the panels - whether used on site or exported

2 The saving on payments for Electricity when using "own" power

3 The sale price of power exported

Item 1 is index linked and guaranteed (by HMG - so far as I can divine) to rise in line with RPI for twenty five years - tax free - but the amount of generation cannot be guaranteed as it depends on the power extracted by the panels - and that can only be averaged at the outset

Item 2 will be a growing benefit

Item 3 is apparently a moveable feast - this needs serious study

The systems will need to be robust, mounted on roofs capable of supporting them for the period in question for the full service life if the maximum return is to be obtained.

The panels, rectifiers, etc will need to be guaranteed, both as to quality, and as to generating capacity, and maintaining production levels - again across the life of the scheme.

There are many other variables such as the sweet spots

4Kw is the usual capacity of a dwelling house roof

10Kw is the maximum that can be installed without a prior survey by the regional distributor and potential costs being incurred

Between 10Kw and 50Kw the local network and substation may need upgrading - at your cost

Above 50Kw the government has taken fright at the amount of independent generation proposed over the last eighteen months and has reduced future guarantees and applied time limits for the completion of new schemes - basically April 2012 for up to 50Kw -

The industry has responded robustly and the review is now being itself reviewed

My advice - if you can find a real independent consultant to guide you through this - do so - and if you do find one - please let me know their name

16th Aug 2011, 14:01
I finally got an answer from L&G regarding how my meter might respond to the backwards flow of electricity which ought to happen when our solar panels are installed.

it might

a) accumulate forwards and reverse flows in independent registers internally, which may be displayed in sequence on the digital display.+

b) accumulate forwards and reverse flows, displaying the forwards total when the power is flowing forwards and "RED" (Reverse Energy Detect) when electricity is flowing in reverse.

c) accumulate forwards and reverse flows in independent registers and then add them together and display the sum.

The mode of operation is programmed in at manufacture. There is nothing to show which mode the meter is set to when it is in a "normal" installation.

So I called the electricity supplier to find out what mode our meter was programmed to do. They "think" (didn't seem too confident though) that we have been programmed to show RED when the electricity flows in reverse, the digital counter should give proper total of the forwards electricity usage. This is my preferred option. Option C has you paying to put the electricity into the grid rather than making money on it.


18th Aug 2011, 09:11
Rans6.. your tariff seems a bit steep. Mine starts off at 15p / kWh and reduces to 11p / kWh after a certain consumption. I found that "jockying" with consuming electricity at certain times is a bit cumbersome. Having said that we operate dishwasher/washing machine/ ironing sequentially. I looked at another installation in Burgess Hill where the meter ran backwards when electricity was being "exported", If I had a meter like that I'd stick with it! After an excellent April and May the rest of the summer has been a bit disappointing generation-wise. I'm just about on course to get over 3000kWhs this year though (hopefully).