Photovoltaic cells

Anyone know anything about household solar energy. Ideally I would like to make all my own energy and not have to have any fossil fuel generated electricity used chez Sloop. We have in the past 2 years fully retrofitted our house and have an A3 energy rating (we were F!).

Just looking for some general information/ advice by people in the industry or those of you who have solar panels, rather than a debate on merits etc. I’m doing this to lower my carbon footprint not (necessarily) to save money.


1 Like

Morning sjb
I had similar thoughts and inclinations a few years back.
I lived in a Skandi wooden kit house built after WWII; I renovated it, put in insulation in, double glazing, and put solar panels on its south facing roof, and installed an air-source heat pump.
I now rent it out and reliably informed that it has low energy costs.
I missed out on grants for the renewables, and its energy rating is not to passive haus standards (lack of heat recovery technology), but I consider it was well worth the investment.

I know in the UK the Vat goes up from 5 to 20% in October. Not sure if this is just UK or an EU wide increase, might be worth checking.

1 Like

I have 4k pv rig, the normal maximum for the home FiT, when it existed.
Got in at the very end of the FiT, so IIRC I get about 12p/KwHr.
The bloke also sold me a clever thing called a Solar Boost box.
This takes ‘spare’ leccy - i.e. that which is not used in my house, and uses it to heat an element in the water tank.
Anything still spare after that goes to the grid. I think I get 4p extra for selling that to the grid.
Unfortunately, the SB box just broke after about 3.5 years.
So that was a horrible loss maker, and carbon failure, esp when you consider that I called the installer out twice to look at it, and he charged me for call outs and repair of an element that it fused.
The panels as a whole are still nowhere near payback, financially or ecologically.
At a wild guess, that will take another perhaps 6 years.
But will we still be in this house then?
I don’t think the panels will add anything to most house buyers here - but that may not apply where you are. They will add something for ‘green’ buyers, but may put off others who are ‘anti-green’!
If you plan to own and live in a house for 15 years, and get good panels at a good price, then it’s a winner - if you live long enough to reach past payback with the FiT!

1 Like

When I looked into this recently I was told that you needed to get at least 8 panels, approx 1.2m x 1.8m to produce anything like an economic level of investment. This is a min generation of 3.5k. The other thing I was told was that all the electricity that was produced must go into the grid first. You then get money for selling it to the grid and then you draw down from your supplier. You couldn’t use the generated electricity first and then just sell the leftover. I would be delighted if someone could tell me that is not the case?

The pitch and direction the panels face is important and also whether you have any overshadowing. Again I was told that the potential overshadowing of our possible panels would further reduce the efficiency.

1 Like

We put a 16 panel, 4kW system in 4.5 years ago and love it. Payback period for us will be ~7 years, and from then on our electricity bill will be -£30 pcm.

We generate ~5,600kWh a year; 40% we use, 30% we export and the remaining 30% goes to heating our hot water via a “smart switch” (using energy that would otherwise be exported (with no payment)).

If we wanted to become fully self reliant we would need a MUCH larger system, as there are times of high demand and low production (obviously). I have looked at Tesla Powerwalls but they really do fall in to the “money no object” bracket.


This is certainly not my understanding; the wires from the panels to to our fuse box on the downstream side of the meter, so (presumably) our production gets used a) first, and b) directly. But with one caveat … If you have a power cut then the panels MUST trip out (so that anyone working to fix the lines doesn’t get zapped by power coming up the wire the wrong way).

1 Like

That is disappointing - our Solar iBoost box paid for itself within two years and is still going strong. I would replace it in a flash should it ever go pop.

1 Like

Haffle, thanks for that. I will investigate further with someone else! If I can get the PVs to power just my ASHP then I would be very happy.

The overshadowing thing is real though. I read a while back that even the shadow cast by a telephone wire is observable in terms of electricity generated.


Quite probably, but unless you can wash panels (difficult if on a roof - ours are in a nearby field so easy to clean) then bird $%@& will possibly have a greater impact on production …

1 Like

My installer said he’s now switched to a different brand of box that does the same thing because of quite high fail rate outside of warranty

Can look up the name of other brand if you want…

I’m now a bit over invested in solar given longer payback - although I have to admit my payback estimate is a wild guess based on cashing about £500 a year plus maybe saving around the same amount on levy bills. I’ve never taken the time to actually look up the numbers.
But it also hugely depends whether you count straight pay back of the outlay or you add whether you add what you would have got by putting it into premium bonds too.

First thing not mentioned is the Feed in Tariff stopped for new installations a couple of months ago. Second, the notion that you have to export it all and then buy back is nonsense - we have had a wind turbine for eight years now, so I have some idea of what I am talking about. Except we don’t have any solar panels - we are getting a quote but it won’t be economic to do.

I would like batteries but they are not financially viable - v hard to find out actual figures, but in terms of carbon footprint batteries are pointless as using your own renewable electricity rather than sending to the grid at the margin just means someone else using a dirty supply. The green benefit is from generation not use (although there are some transmission losses). I understand the latest battery systems do permit continued supply in a power cut though

I think there will be new arrangements in time with the grid wanting to buy electricity from you at peak times and happy to sell at cheaper prices off peak - that may work with car batteries and / or Tesla power walls and the like, but not here yet


Tesla power walls are crazy expensive; I even mulled over buying a damaged Renault Zoe and just using its battery as that could have worked out cheaper, but AIUI it wouldn’t have the appropriate wiring & controllers, so that idea wouldn’t fly. :stuck_out_tongue_winking_eye:

1 Like

I suspect battery storage may become more widespread as used EV batteries start to become available, as when they are past their best for car use, they can still have plenty of life left in them for other purposes.


This is a very interesting thread. I was aware that PV is very expensive so has a long payback time, but I hadn’t been aware of some of the other issues. Maybe like others, having seen them spring up everywhere I sort of assumed they must have become a lot affordable more economic, and was thinking maybe at next house move which will require work on a roof might be the time to invest in it. So it is really useful to hear if the practicalities and considerations - if which the buyback tariff is significant, which will assist making an informed decision.

1 Like

I can’t recall the source of the following, but: technology has come on leaps and bounds for PV panels, in theory they should be more efficient but there is a log jam in old technology (e.g. warehouses in South Wales are full of them. It’s alleged that the new technology is being stockpiled in South Wales.
This could be an urban myth, but the scientific press was full of the new thinner panels 12 months or so ago.

I have never even got a quote but I understand that the demand arising from the incentives has resulted in PV panel prices falling very significantly in the last ten years

The key thing I guess on this forum with solar cells, is RF/EM noise from the inverter (s) and the panel wiring. If care is not taken it affect audio, radio and other sensitive electronic equipment when on full power…by raising the noise floor and RF intermodulation. Even affecting broadband speeds in full sun.

Some interesting reading here (albeit US regulations)

A quality installer should be on top of this, if you get a blank look when you mention RF noise, get another designer/installer before you do anything further. Retrospectively fixing can be difficult and time consuming.

Slightly of topic but with the knowledge here, is there a way of identifying consumption of particular items on a circuit/in a house without switching everything off etc? As in, is there a gadget I can wrap around a supply lead/wire that can measure consumption? I would like to monitor the consumption of my ASHP for instance.