The Great 'Get Paid To Generate Energy' Hunt

zantos

Hi Dave
SunnyBoy inverter was rated 2.5Kw but behaved very strangely anyway, if it was switched off it would never synch again until the following morning. Temporarily they have reconfigured the array and dropped off two panels increasing the voltage according to the installers. The result is the inverter gets a little warmer and seems to operate correctly. The new inverter is rated higher it's the 3100s and hopefully will allow the connection of the other two panels again.

Hi John
The slope of the roof is about 40 degrees as near as I can tell.

Dave_Fowler

Hi Zantos,

The decision to move to the new inverter will probably sort out your problems.

Looking at the specifications of your panels, the nominal output voltage is 42V per panel, with a current rating of 5.13A.

The SunnyBoy inverter has an input voltage range of 224V - 480V and maximum current of 12A.

The Diehl AKO inverter input voltage range is 314V - 630V, maximum current 9A.

Twelve of your panels in one series string would give an output of 12 x 42V = 504V on a sunny day. This is outside the spec of the SunnyBoy but inside the spec of the Diehl AKO. When you reduced the number of panels to 10, the maximum voltage produced was 420V - so the SunnyBoy would work correctly.

The SunnyBoy does give you the option of running up to three parallel strings. By splitting your twelve panels into two strings of 6, the maximum voltage would be 252V. Whilst this is within the range for the SunnyBoy, it is very close to the minimum voltage, so on a cloudy day the inverter would cut off early and there would be no output. Also, if you have more than one string, the overall efficiency of the panels will be reduced if the strings are not perfectly matched.

Your experience has shown the importance of matching the panels to the inverter. It is not just a matter of working out the maximum kWp and getting an inverter to handle the power, the current and voltage specifications have to be considered too. If your installers had chosen panels with a lower output voltage but a higher current rating this would have given you the same power per panel and would have worked with the SunnyBoy.

Dave

zantos

Hi Dave
Couldn't agree more. I had the option of lower spec panels when I ordered but was advised to go for the "best", other option was Yingli YL 235 P-29b / 1650x990 SERIES. Looking at the circuit diagram they supplied for the original layout it appears to have been done as two parallel strings of six panels - the failure in bright sunshine was attributed to the voltage dropping under bright light and then the failure of the SunnyBoy to kick in, which would seem to agree with your close to the minimum figures. I don't know if this voltage was that close that the inverter would only "start" first thing in the morning when the sun would be at it's lowest and then the voltage would have been within spec. as anytime later in the day it just wouldn't start up. I think mine was probably the first installation that they had installed with 12 panels as when I first had problems they swopped my inverter for one of their own (to test it) and of course mine worked for them (after it started the next morning!) but their's didn't for me. I would think that ALL of their installations have been suffering with this marginal voltage level as they seem to accept the fact that the inverter never starts until the following morning after a switch off. Since they have "re-configured" my array it starts instantaneously and even drops in and out during periods of low light - that being said I usually am producing from 6.30/7.00am until 7.00pm every day.

Doc_N

In case it's of any use to anyone, there's a pretty good calculator (you can set your own parameters) here which will help you decide on the economics of solar panels:

http://www.reuk.co.uk/REUK-Feed-In-Tariff-Calculator.htm

Cardew

Doc_N wrote: »

In case it's of any use to anyone, there's a pretty good calculator (you can set your own parameters) here which will help you decide on the economics of solar panels:

http://www.reuk.co.uk/REUK-Feed-In-Tariff-Calculator.htm

Thanks; that makes things a lot easier to work out using whatever optimistic or pessimistic assumptions you want.

The biggest omission(and I can understand why) is they haven’t included any provision for repairs/inspections. A new inverter costing £x hundred after a few years will skew the figures.

They have also made no provision for degradation of panel’s output over the years or the requirement for cleaning panels in some situations.

One error in the calculator(I believe) is that if you include the 3p/kWh you get for exporting electricity in the savings figure, it is inflated at whatever rate you enter for fuel inflation – and that is incorrect. However it won’t make a huge difference.

The calculator also assume that you have the capital in savings, should you need to borrow the money payback times will be longer.

The biggest factor in determining ‘pay back’ time is the installation costs. This is a quote from the Energy Saving Trust

The reported prices for installed PV systems we see (which are Low Carbon building Programme MCS certificated) tend to be around £6/Wp. However recently we have seen installed prices around £4.50/Wp. Sadly, aware of the 'feed in frenzy', some installers are quoting way above this and our advice is to shop around and not be too time pressured.

So they believe £4,500 to above £6,000 per kWp is the going rate.

Unfortunately there is no ‘one size fits all’ answer to the ‘break even’ point. Apart from the difficulty of predicting future inflation rate, fuel inflation rate and interest rates, the output from panels can vary tremendously depending on where you live in UK

Using what I consider to be reasonable assumptions it calculates the ‘break even’ point at between 12 and 15 years.

I wonder how many people would invest in other schemes where it was going to take that period of time to get your money back and start making a profit(provided all the assumptions made come to fruition) and that 'investment' was fixed to your roof and couldn't be take with you if you moved! - Just a thought.

Doc_N

Cardew wrote: »

Using what I consider to be reasonable assumptions it calculates the ‘break even’ point at between 12 and 15 years.

I wonder how many people would invest in other schemes where it was going to take that period of time to get your money back and start making a profit(provided all the assumptions made come to fruition) and that 'investment' was fixed to your roof and couldn't be take with you if you moved! - Just a thought.

I reach the same conclusion on the break-even point. Using fairly pessimistic options gives me an estimate of 10-11 years.

For me, that's fine, because I can envisage no circumstances in which I shall need to move from here, but not so good, I agree, if you may need to move.

On the plus side, after the break-even point there's a pretty substantial tax-free income rather in excess of £2000 pa, which is pretty good, I think, for a £14K outlay - and will more than take care of a replacement inverter and any other costs.

Cardew

Doc_N wrote: »

I reach the same conclusion on the break-even point. Using fairly pessimistic options gives me an estimate of 10-11 years.


On the plus side, after the break-even point there's a pretty substantial tax-free income rather in excess of £2000 pa, which is pretty good, I think, for a £14K outlay - and will more than take care of a replacement inverter and any other costs.

Pessimistic in what sense?

My 'take' would be that it is optimistic to consider you will break-even in 10 -11and pessimistic to think it would take 20 years to break-even.

How, and in what timescale, do you get an income of £2K from a system costing £14k? You were quoting a system cost of £17.5k earlier in the thread.

Doc_N

Cardew wrote: »

Pessimistic in what sense?

My 'take' would be that it is optimistic to consider you will break-even in 10 -11and pessimistic to think it would take 20 years to break-even.

How, and in what timescale, do you get an income of £2K from a system costing £14k? You were quoting a system cost of £17.5k earlier in the thread.

Pessimistic in the sense that the % figures used below do, I think, err on the side of caution in calculating the break-even point. One can agree or disagree with that comment, but it's essentially a matter of personal opinion for each person to decide on.

As for the £2K+, this would be, as I said, after the break-even point, and at about year 10. The calculations are below. I did indeed quote £17,500 earlier, but I now have a rather better quote for an almost identical system.

Quite happy to accept that these projections could be flawed, with an obvious inverter replacement and other maintenance issues, of course, but an inflation-proofed £2K+ pa will amply cover these costs, I reckon. Am I missing an obvious flaw in the projections perhaps?

Cardew

Doc_N wrote: »

Pessimistic in the sense that the % figures used below do, I think, err on the side of caution in calculating the break-even point. One can agree or disagree with that comment, but it's essentially a matter of personal opinion for each person to decide on.

As for the £2K+, this would be, as I said, after the break-even point, and at about year 10. The calculations are below. I did indeed quote £17,500 earlier, but I now have a rather better quote for an almost identical system.

Quite happy to accept that these projections could be flawed, with an obvious inverter replacement and other maintenance issues, of course, but an inflation-proofed £2K+ pa will amply cover these costs, I reckon. Am I missing an obvious flaw in the projections perhaps?

You haven't given your figures but it would appear that you have now managed to get a quote for a 4kWp system for £14,000 instead of the £17,500 you quoted earlier.

That is way lower than the EST estimate for the cheapest installed system; and much lower than anything I have been able to find.

You are assuming an output of 3,200 kWh pa which would indicate you are fairly far North?

You are using a figure of 50% of generated output saved costed @ 9p/kWh and 50% exported @ 3p/kWh?

Your projected 10 year break-even point illustrates what I stated earlier, namely that the crucial issue is the cost of installation and you getting a quote some £4,000 less than the cheapest EST quote, reduces the 'break-even' point by about 3 years.

I would also suggest that you must consider any repair/inspection costs before the break even period as that will lengthen the time to the break-even point.

The major source of income is obviously the inflation linked FITs but personally I think the assumptions err in favour of PV.

I use a figure of 7p/kWh for used electricity which is easily obtainable.

40% used in the house is more realistic for many people.

3% inflation year on year is above any Government targets and forecasts. That of course has a big impact on income.

Cost of repairs will have a greater effect than envisaged.

So I would 'gamble' on people lucky enough to have the capital sitting in a bank account breaking even in 13 to 15 years. For those who have to borrow, even on a mortgage, much longer.

Obviously once past the Break-even point(whenever that is!!!) you are on a gravy train!

noncom_2

I've had several quotes for a (almost) 4KW system, although actually due to the output of panels we're buying, the real o/p will be 3.7 or 3.76kW. They've all come in just over the £15k mark (£15.2k for the installer I'm going with, including a 5-yr insurance backed warranty). So 14k sounds cheap, but not extraordinarily so.

Cardew, yes, in pure money saving terms it is possible (in some areas of the country?) to achieve 7p per kWh Tier 2 price, but again I would state that some people don't buy their electricity on price alone. For some of us, the actual fuel mix is important (Green tariffs of various descriptions) and we are prepared to pay a premium for that standpoint. Therefore, although you may argue that I am throwing money away, my Tier 2 price will be higher than you quote whether or not I install panels, and so the calculation of how much I save from getting free electricity is higher.