I am thinking about investing in Solar PV.  Partly to save the environment, and partly to save me ££.  I live in an all electrically heated house.  No access to mains gas.  Well OK I have a wood burner.

I have a south facing roof which I could get a 4 or 4.5 kWh system, which i predict would generate 3000+ units a year.  Now given most of this is over the summer and most of my usage is over the winter is it worth it?

Battery storage doesn’t seem to make economic sense yet.  Has anybody invested in Solar PV recently?  I am looking for real world experiences since the tariff has dropped.

Whatever you do factor in anti pigeon netting. The buggers love solar panels as a nesting place. Just had ours done and it cost about 2 years FIT.

Do you use much heating in the summer when solar generates electricity or in the winter when they put out about 10%?

Invest in insulation and maybe some add-on MHRV units to keep the place ventilated and dry (humid air needs more energy to heat and leads to mould).

Now that FITs have gone to almost nothing it doesnt seem to make sense. At least with decent FITs you could sell most of your electricity in the summer to offset the cost of buying it in winter but you don’t have that option anymore and a battery won be much use as it is short term storage.

I still think its worth while long term, without the FIT. A 4kw setup will heat your hot water tank nearly year round, with an immersun, or similar setup. Plus if you have someone working from home, or home most of the time its a no brainer, because you can do all your washing etc through the day when sun is out.

For water a direct water heating panel might be a more efficient option but it will probably require more work and maybe a new tank. PV may well be a cheaper route and just power the immersion element.

I would get my electricity bills out and take a look at what the summer/winter split is like and do some back of the envelope calcs on how much you think you can spend being realistic with the generation figures.

We are still planning a PV system for our new farm but that will be in the region of 10-12kW and will be the lambing/tractor/hay shed roof (no metal roof underneath) and be a full new build so we can integrate as much into technology to make use of it as possible into the whole build.

A friend recently installed some himself (about 4kw) , he does a have them with  big bank of lead acid batteries and via an inverter runs most of his house lights and sockets off them. Longer term he plans to use them to change an electric car (solar into the batteries during the day and then into the car at night).

If you have an old spinning disk meter a lot of them still spin in reverse once you hook them up to a grid tied inverter. Not legal, but the onus is on them to upgrade the meter with your permission so as long as he uses slightly more than he generates he reckons he’s OK, that’s his version of the truth anyway. Didn’t do that in the end though as the batteries and his usage balance.

He did get most of the kit secondhand as payment for a job we worked on though so the economics are very favourable in his case.

Not legal, but the onus is on them to upgrade the meter with your permission so as long as he uses slightly more than he generates he reckons he’s OK, that’s his version of the truth anyway.

The in-laws have solar PV and an old meter; it currently reads what it said back in March and is going backwards every day. They tell their supplier and FIT provider (same company) each time, but they don’t care!

It amazes me that the incentives for PV weren’t made dependent on having a smart meter…

… Smart meters didn’t exist when PV/FIT started.

Your in-laws need to be prepared – once the supplier does get its act together they are fully within their rights to charge for power used from the date of the PV installation.  They will estimate usage and you can guarantee that the figure won’t be in your in-laws favour!

Currently I’m experimenting with a single panel and micro inverter. We think it’s cut the bills in half during the day we export a small amount but import nothing. It’s not there to make money just to see what could be done with what.  Worth it even without the fit. Most commercially installed systems are excessive. But you’d do well if you heated your water on solar alone.

But you’d do well if you heated your water on solar alone.

Depends how you convert the energy, if you used GSHP then you could well manage it but that obviously comes at  a cost.

I’ve been working at home over the last month and was thinking Solar PV + aircon might be a good idea…….

As in dedicated fully fitted air con? Air source heat pump with reversible mode is essentially an air con unit that heats your house using the same principle. Not as efficient as ground source but still worthwhile. well, knocking the snot out your house to fit ducting aside…

As in dedicated fully fitted air con?

Just to cool though in summer when it can be run for free by the PV. If we start getting more summers like this one, I might invest….

/thread hijack

A question – if I am to re-roof a south facing extension, can you get solar panels that *Are* roofing material, so saving a duplicate cost? And would the saving be much (I suspect not).

A question – if I am to re-roof a south facing extension, can you get solar panels that *Are* roofing material, so saving a duplicate cost? And would the saving be much (I suspect not).

The only ones I know of are Tesla’s new roof tiles which are not widely available yet.

Supposedly the cost is cheaper than normal tiles + 20 years worth of electricity, but they cost more than a normal tile…

as of a couple of years ago (when my involvement in PV ended) the tile type PV panels were a lot less efficient, and a lot more expensive than standard panel, and certainly a lot more expensive than roof tiles and on-roof panels.

you can get ‘in roof’ panels that mean you don’t have to tile the roof then put panels on – there is a slight premium to pay for this system but its not as expensive as the tile-type panels.

the financial argument for PV is one that will come down to individual circumstances.  are you in the house during the day during the summer? if not, then to get the best use of the power, you’d be advised to look at some of the battery storage solutions so you can offset your electricity use when you are in the house.

you mention a 4.5kW system – you’ll have to make a grid connection application for a system of this size, unless you already have a 3phase or twin single phase connection.  this will take time and may cost if you ask a  company to do it on your behalf.  if you only have a single phase connection, the most you can fit without a grid application is 3.68kW although most installers will fit 4kW of panels with a 3.6kW inverter.

The EST (http://www.energysavingtrust.org.uk/) have a good generation estimation tool that is pretty accurate – site is under maintenance just now.  would be worth checking any estimate of performance on there to double check the salesman’s figures if you do get quotes.

if you do look at a system that diverts unused electricity to your hot water tank, bear in mind that a 210 lite cylinder requires about 16kWh to heat from cold.  at ~15p/kWh you’ll save no more than £2.40 per day when you can generate at least 16kWh and dump it into the tank.  you’ll also need to ensure that you amend your lifestyle and heating system timer to ensure you have a cold tank after about 9am for this to be an effective energy dump.

Hope this helps

you’ll have to make a grid connection application for a system of this size,

Given FIT has vanished, why would you bother paying so you can export when you don’t get anything for it? Just use / store what you can and switch the panels to o/c when your batteries are full…

because it is illegal to connect any generator to the grid without notification, and its only the smaller systems discussed above that can be notified post-install.

because it is illegal to connect any generator to the grid without notification, and its only the smaller systems discussed above that can be notified post-install.

I was suggesting not connecting to the grid….

I had a system costed last year where the PV installation was in excess of the allowable size.

You need permission for this and need a controller to limit grid input.

Cba to look it all out but I think it was 6kw of PV running Tesla batteries (ten year no quibble guarantee) a mini gas boost boiler and Air to Water heat pump. Was also thinking of changing to an electric vehicle as well. As I remember the battery supply never runs at 100% just something like 30% plus mains. Already had a newish wet central heating system so that did not need to be upgraded. In the end we did the garden and chucked more insulation in the roof but as my gas bill keeps rising might revisit the quotes. Gas will soon be as expensive as water and that just falls out of the sky.

If I was building new would definitely include something like this but the key is really insulation insulation and insulation.

@footflaps – unless you have a manual switch over, its illegal to link it to your domestic main on your side of the meter.  you COULD have a manual switch between battery/generator and mains – lots of folk in rural areas do in case of a power cut, but that would be a real PITA for day to day use IMO.

all interesting stuff.

basically what were seeing is that unless you can get a significant subsidiary then theres no point in going down the green routes (financially?)

unless you have a manual switch over, its illegal to link it to your domestic main on your side of the meter.

Which part of “not connecting” to the grid don’t you understand?

My point was very simple (well I thought so). If the LEB would charge you to connect to the grid so you can give them free electricity, just don’t connect to the grid. If it’s a large system (needing 3 phase etc), either go off grid with battery storage or have separate system for industrial use etc..

It’s really not that complicated as a concept….

There is a church somewhere in the UK that has solar PV roof tiles as they were not allowed to put normal panels on the roof.

Maybe we should replace all those falling down gravestones with etched solar panels..hmm

Which part of “not connecting” to the grid don’t you understand?

hmm, bit condescending but hey ho.

Op is clearly not an expert in the field and i was explaining the standard options.  off grid electrical systems are absolutely uneconomical right now, especially when there IS a grid connection.

as a ‘concept’ its very simple.  in practice (speaking as someone who designed and installed a 12kW PV and 3kW wind off grid islanded system) its actually quite complicated and expensive – hence me discounting it when offering options to the OP, given that he already has a grid connection.

also to be clear, you are unlikely to need to pay for a 4.5kW domestic system to be connected to the grid, you may have to pay for the application if you cant do it yourself.

When I last looked at the costings for us it didn’t make much sense even though we are at home and use some electricity during the day. Payback period is about the life of the panels, meaning we might just about get our money back before they pack up.

Sunnier areas are available of course.

Globally, solar is the answer, and even in the uk at scale. But domestic installation is not great value IMO.

Payback period is about the life of the panels, meaning we might just about get our money back before they pack up.

also this.

If you have an old spinning disk meter a lot of them still spin in reverse once you hook them up to a grid tied inverter.

We had that to start with but the electric company cottoned on quite soon and we changed it.

We might have to re-tile the house for various reasons , so were looking at the inset panels that replace tiles.

The salesmans figures were very funny – it was amazing how many things cut 30% off the bill

Voltage Optimiser – to reduce the voltage supplied to the house to 220v

Tado central heating controller – to reduce heating costs ?!

Hot water switch (save gas by using electric) ££

Solar income ££

electricity savings from solar ££

but crucially all of these were on a 9% inflator each year so by year 25 the  £68/year voltage optimizer savings are £430/year

Full system installation cost £15k !!!

Using the salesmans numbers the total savings / income of the system was £25k

Energy saving trust = £6k

But aside from all the fluff and waffle the solid point made was that domestic energy prices will go up as we have to pay for all the domestic feed-in tarrifs for others and the cost of building Hinkley power station.

I cant see that we will be going ahead

Full system installation cost £15k !!!

How large was the installation?

I installed a 12 kw system, with the hot water switch for using excess to heat hot water, for about £12 k.

WTF is “voltage optimizer” for? What other voltage apart from 220v would you want in your house?

It was only a domestic system – 18 Viridian 300 panels – but with high(er) performance ?

I am sure it was claiming 5.6kw or something like that. (above what I thought was possible as “normal”)

The idea of a voltage optimiser is that the UK supplies 230/240volts but “everyone else” uses 220v so a switching transformer corrects the voltage to 220v

https://en.wikipedia.org/wiki/Voltage_optimisation

I can see that there may be a valid logic to this if you had old skool transformers and somehow any excess voltage was just burnt off as heat, but a kettle will simply boil faster and anything with 110/220 transformer (laptop power supplies etc.) I am sure would be as efficient at 320v as 220v.

I am sure it was claiming 5.6kw or something like that. (above what I thought was possible as “normal”)

In the UK, with a standard domestic single phase supply you need permission to install more than a 3.7kw system. Not sure how they were going to get 5.6kw?

The rule of thumb at the moment is 1kw = £1000.

From the quote I got it breaks down as 1/3 parts 2/3 labour or profit. The calculated payback time is mostly paying for the install. I can’t see the industury continuing in the same form.

As a DNO man (the wires bit of the old electricity board – we transport power but don’t buy sell or own it), Smudger is giving good advice.

The only thing I’d add is the reason grid (small g) connections make sense is diversity.

Most of the time you draw about 200-300W from the grid into an average house (yes no one on here is average…), and across 24 hours you average say 400W.

But you will peak at around 12-18kW.

So you have to size everything (inverters, battery output etc) for 18kW, which you hardly ever use.

If you grid connect however then the diversity (there it is) between you and your neighbours drops the effective peak drastically. On 100 houses the peak is typically less than 2kW per house. On 1000 houses, 1kW.

So in terms of kit installed you (and your mates, neighbours etc) just need less in an interconnected world.

At the moment of course that economic truth can be hidden by tariff structures, tax farming and subsidies (less so subsidies these days but there are some hidden ones).

Long term a system that outputs around 10kWh per day per house and per (domestic) electric vehicle will probably be the sweet spot and use the grid for balancing, trading with neighbours, reliability and resilience, and your maintenance periods.

It isn’t necessarily so today, for the reasons above.

PS – 3.68kW is correct, but most (all?) DNOs interpret that as 3.68kW export. They will normally accept higher rated installations with export limiting devices.

Alternatively you may find when you apply that say a 6kW installation fits on the existing network (first come, first served boys and girls). Known as “connect on existing” in our company – minimal cost, possibly some design fees and commissioning witnessing.

Doh1nut – higher voltages do lead to more power consumption (even though with things like LEDs, switch mode etc you wouldn’t think so).

We’re dropping the volts by a couple of percent where we can (and it’s not everywhere sadly) which will save customers around £20 per annum at no cost to them and effectively no cost to us.

That’s significant when you have 3.8m customers.

Doh1nut – higher voltages do lead to more power consumption

How does that work at single phase level?

Bear with me here, I’m mechanical biased so obviously thick 😉

My understanding is that with a drop in voltage your VA drops, fair enough as it’s a vector quantity and three phase obviously runs with an inductive or capacitive bias. But single phase doesn’t have lag or lead so power is power regardless, any adjustment to voltage will see a proportional adjustment to current. Unless of course your adjustments at the transmission level carry through?

SquirrelK – at the simplest level, with a resistive load, reduce the voltage and the current reduces too so the product of V & I reduces.  Think about old style incandescent light bulbs

The surprise is that this also happens with the generality of load, not just the specific resistive subset.

(PS you can have leading and lagging power factors on single phase – but normally the pf is very close to unity anyway)

I’m puzzled by the assumption that reducing power is good. If I’m doing something that needs a fixed amount of energy (Joules), like boiling a kettle, then if the power (Watts) is reduced the only effect is that it takes longer. If I had an incandescent bulb, and the voltage is down 2%, and that drops the current 2%, then the power is down 4% and my 100W bulb is only 96W. You might say that 4% isn’t significant, but there’s always a point where the user has to decide whether to use a brighter bulb, so if 100W was just OK, 96W would push me to 150W (=142W). If that effect carries across non-resistive loads, all my devices are running at less their design performance.

But if what’s being done is just keeping the voltage closer to the target, that’s one of the things I’d assume the DNO was there to do.

(Hmmm – the UPS for my PC reports the mains voltage at 242V – perhaps I should monitor that!)