Free solar power system. Is it a scam?

XRayDave wrote: »

So, from install in 2nd June we have generated 1780kWh. Not too shabby then

So, based on 50% usage (rough guess) and 10p/kWh (reasonable unit cost), this has saved just about £90 (which I'd rather have in my pocket than the power company's).

Season's Greetings to all,

XRD

XRD,
The total generated is absolutely in line with expectations for an ASG system - they expect a minimum of 2,800kWh pa.

However your 50% usage is just as you state a rough guess.

You might be able to use that much during daylight hours, but I suggest many(the majority?) of people will not be able to use 900kWh in just over 6 months.

I have not seen any confirmed figures where people have used that amount - the two contributors to MSE who have export meters and hence can confirm their consumption, use 500kWh and 1,000kWh per year.

XRayDave wrote: »

Trying to "educate" both my wife and my mother to use the washing machine/dishwasher when the panels are generating during the day. Rather an up-hill struggle though. My wife, for example, sets the dishwasher on either last thing at night (so that the dishes will be clean & dry for morning) or just before popping out in the morning to go to work (but I don't know why). If she'd only leave these 'till mid-morning when the panels are working well - or even better, with the sun so low in the winter sky, the panels seem to peak around 1pm.


XRD

A similar dilemma is faced by people on Economy 7.

When we had E7, my wife would put the dishwasher on overnight to take advantage of the cheap electricity. However it often wasn't full and there was room to put in the breakfast dishes for example.

So it was something of a false economy to use a machine that wasn't full.

Jon_Tiffany wrote: »

Cardew - 50% useage is perfectly reasonable to assume for the majority of people. The sample of 2 people with export meters that you keep referring to is not exactly enough to give any real figures. For example, those with smaller systems (say around 1-2kWp) will likely use more, especially if at home all day.

While obviously not a representative sample in statistical terms, I would apply a very great weighting to the accuracy of those two users with export meters compared to those who do nothing more than guess at their percentage utilisation. Afterall, all the two users with meters have to do is read the meters!

I think people in general don't appreciate just how difficult it is to use the electricity generated (which is afterall asynchronous generation - could be 1 kw one minute, and 3kw the next around midday. Away from midday, it could be 500w one minute and zero the next. The only way of ensuring a high percentage of that is by having a constant 3 or 4 kw load on for the 3 or 4 hours around midday for example. Most seem to think putting the dishwasher or washing machine on will do that (at least for an hour or so), but that is in fact totally incorrect. This is due to the fact that the load of such machines varies during the cycle - from 0kw to something like 3kw. So the real situation is the panels give you a variable supply, and the usage people propose gives a variable load - and this is why you see those with meters reporting lowish utilisation rates, even though they know the theories involved and utilise all the techniques possible to use as much solar power as possible.

I suspect this is counter-intuitive to many people without meters, and so they are very likely to overestimate the usage they'll make. If they don't ever get meters to measure their actual usage (indirectly by measuring the export), they'll probably always think they are using a high percentage - that seems to be human nature.

Of course, as you state, the lower the capacity of the system, the higher the utilisation, all other things being equal. But there comes a point for those with 'free' systems, where the benefit is almost insignificant if a low capacity system is fitted, even if the percentage utilisation is high.

grahamc2003 wrote: »

I think people in general don't appreciate just how difficult it is to use the electricity generated (which is afterall asynchronous generation - could be 1 kw one minute, and 3kw the next around midday. Away from midday, it could be 500w one minute and zero the next. The only way of ensuring a high percentage of that is by having a constant 3 or 4 kw load on for the 3 or 4 hours around midday for example.

Dont forget that not everyday consists of peak outputs at midday.

In the morning, afternoon, evening, cloudy days and during late autumn, winter and early spring the peak output will be much lower and more likely to be consumed in the house.

Also, while this thread is mainly with regard to the ASG systems, there are many people who have bought their own systems reading this and they should be aware that a smaler system will give a much higher percentage used in the house.

Jon_Tiffany wrote: »

Dont forget that not everyday consists of peak outputs at midday.

In the morning, afternoon, evening, cloudy days and during late autumn, winter and early spring the peak output will be much lower and more likely to be consumed in the house.

Also, while this thread is mainly with regard to the ASG systems, there are many people who have bought their own systems reading this and they should be aware that a smaler system will give a much higher percentage used in the house.

I agree with all that, and I hadn't forgotten that the peak isn't reached everyday.

But the fact that you will probably have 100% utilisation when the output is 100w is neither here nor there when postulating the overall utilisation. I'd estimate that around 90% of the output is produced in the four hours around midday (could anyone come up with an accurate figure?), so that period becomes is the substantive issue. That means for high utilisation, you have to have a high load (say 3.8kw) for constantly for those 4 hours (at least in the summer). That is pretty hard to do for the average household. The almost 100% utilisation of low outputs is probably typical, but that is only a small contribution to the overall utilisation.

Until there's an automatic system for sensing the generation and load, which switches in extra load when generation exceeds load, the utilisation will probably be lower than 50% if the techniques proposed are followed (i.e. switching in wasing machines at midday etc). My view is based on developing techniques of matching supply and demand in real time for the grid itself, so isn't purely uneducated guesswork. What running your washing machine at midday will do is rise the utilisation from what it would otherwise be (so it's worth doing if you have a full washload), but I expect the rate will still be below 50% typically, for a typical almost 4kw installation.

If a control system were introduced to automatically soak up the excess generation, then it's likely to be dumping the excess into heating water. While better than getting nothing for the energy, the value of that isn't then 10p/kwh, but more likely 3p/kwh for those with gas heating, because that is the cost of the energy displaced.

On the other point, my posts are mainly aimed at 'free' systems, because that is the theme of this thread. Those who own their own systems I would think wouldn't be largely concerned with anything but the fit, which is by far the bigger earner. As an aside, that situation strikes me as odd anyway - the return from installing a so called 'green' energy generator is mainly from subsidy, and very little from the 'green' generation the system was (totally illogically imv) set up to provide. As a further aside, just to be clear, I don't criticise anybody exploiting the system, just the system itself - I intend to exploit the rhi when it's introduced, although I disagree with it's aims and think that too is very expensive madness.