So now I have a solar PV system how do I make the most of it???

sly_dog_jonah

Hi edwink,

When hubby goes up to the roof, ask him to count the number of cables connected to the inverter. At least two cables, or even better four (for a dual string system), should come from the roof (the DC inputs) and there will probably be a single cable for the AC output (probably thicker) which will run down the wall towards your fuse box / consumer unit.

A photo of the panels on the roofs may help to explain why you are seeing the outputs you are seeing (you have to upload photos to some other website then use the 'Insert Image' button to specify the URL of that image).

If today is sunny, go out at several times during the day and look to see when any shadows are cast on any of the panels. The start/end time of any shadowing from trees/chimney/soil pipe vent will probably mark the start/end time of an appreciable difference in generation. Any shading, however small, can have a dramatic effect on the output of any set of panels that all connected in series (on the same 'string'). Hopefully the installer has taken this into account and tried to minimise how long shadows will fall on the panels by steering well clear of any shadow-casting objects. Shading is unavoidable in some cases though, but can be mitigated by connecting the panels on different strings so that the panels which are least likely to be shaded are on a separate string to those that run the risk of shading.

For example, our system is shown the photo below. This photo was taken early afternoon when our garage was casting a shadow on the back of the house. We get similar shading early morning by next door's house as the sun rises in the morning, which means the bottom row is in the shade for longer than the top row as the sun rises above the roofline. To mitigate this and maximise morning output, the top row of panels are on a separate string to the bottom row. As we are SE facing, the right hand chimney should never cause any problems wherease the left hand one will cast a small shadow late afternoon on the top row, depending on the height of the sun. In these circumstances the bottom row's output should likewise be unaffected by the top row's shading. Note we didn't have any panels put between the windows as the dormer roofs cast a shadow as can be seen below.

r.cordrey

Zenoka wrote: »

Does anyone know if there is a device that can sense when you are exporting and send that electricity to a hot water heater? We would really like to use the surplus to help towards heating our water, DH is good at diy and is already talking about fitting a 500w imersion, but we want a system that will automatically control it for us.

Does such a thing exist? I've searched but not been able to find anything.

I replied to this query, but the forum did not treat it as a response and the search facilities on this forum do not find it!

Yes, there is a solution. A current-sensitive relay is introduced to divert power to a 1kW immersion heater whenever PV output exceeds this level. The thermostat on the immersion heater determines whether it takes power or passes it on. Effectively, this solution stores PV energy in hot water.

Our solar suppliers are pushing the system but at quite high cost (£999 including all fitting). Any competent PV-certified electrician should be able to do this work. :T

sly_dog_jonah

r.cordrey wrote: »

Yes there is. My solar panel supplier has been promoting this option to effectively store PV energy in your hot water tank. When your output exceeds 1kW, a current-sensitive relay diverts power to a 1kW immersion heater (which obviously takes as much as it needs according to the inbuilt thermostat).

The cost, including fitting, was quite high at £999, and we are away for much of the summer so the cost/benefit was not appropriate to us, but might well be for others.

It is not rocket science for a competent electrician certified for PV.

:T

Such a device doesn't divert power, it simply switches the immersion on when the PV is outputting over a threshold current. Immersion heaters generally consume a pretty constant amount of electricity (eg 1kW) until the thermostat on the heater turns it off. Which local supplier was quoting £999 for this?

I've seen two similar solutions, one using a current-sensing switch and the other a light sensor, both considerably cheaper than £1k:

http://www.reuk.co.uk/Water-Heating-with-Surplus-Solar-PV.htm
http://www.chrisrudge.co.uk/immersion.htm

The limation of these devices is that they can't tell what other appliances are using power at the same time, so may result in you importing electricity from the grid even when you are generating well over the threshold power to turn on the immersion. Also it makes it quite difficult to override the controls in the event your boiler packs up and you want to use the immersion to heat water temporarily (irrespective of sunlight). I'm seriously considering the current-switch method, on the basis that if we set the threshold high (eg 2kW) then it will only trigger when our 3.7kW is making in excess of that, leaving 1kW for other appliances we stagger through the day (dishwasher, washing machine). The lack of manual override is a pretty big limitation though.

Note this is different to the EMMA product which can monitor generation and consumption and only dump the excess generated energy into an immersion heater (by regulating the power delivered to the immersion) to minimise export and import of electricity. These cost in excess of £1k though, so I doubt that is what your local supplier is refering to.

Martyn1981

edwink wrote: »

Hello Mart

Thanks for your reply and your help. I will endevour to get the information you suggest reagrding the inverter. It is up in the loft so will need hubbie to retrieve that info. The other questions I will hopefully have answers for you later today.

I'll get back to you later when hubbie is home and hopefully offer more info. Thanks so much for taking the time to help!

Ed

No probs Ed. Sly Dogs' post is excellent at explaining shading and panel strings. That's what you and hubbie need to try to ascertain.

Also, just to remind you, check both roofs are IDENTICAL slope. Do you mean full height extension to side / directly next to main roof, or extension out, ie a single story roof lower down? If the roofs are a different angle, (mine are 20deg and 30deg) then they will operate differently as the relative angle of the sun to the panel will always be different. If I'm being really pedantic, there will be a brief sweet spot when the sun angle is equally wrong to both roofs, but now I'm just trying to confuse you, sorry.

Mart.

EricMears

Zenoka wrote: »

(but from a year ago !)Does anyone know if there is a device that can sense when you are exporting and send that electricity to a hot water heater? We would really like to use the surplus to help towards heating our water, DH is good at diy and is already talking about fitting a 500w imersion, but we want a system that will automatically control it for us.

Does such a thing exist? I've searched but not been able to find anything.

Asking similar questions elsewhere, I've received following links :-

openenergymonitor(dot)org/emon N.B. doesn't start www

&

www(dot) electriciansforums (dot)co(dot)uk/central-heating-systems/23969-immersion-heater-pv-electricity-4.html

I've not tried either of suggestions for myself.

Martyn1981

grahamc2003 wrote: »

1st sunny day here (Surrey) since I got my system, and I now realise I've got major problems. What a killer shading is! Panels (1.75kW) face SW. Generation built up nicely to 1.1kW at about 11am when is started getting shading from trees. It just plopped down to 100-200W most of the rest of the day - there are about 4 trees (two evergreens, the rest not even any leaves yet!) which go from S to SW. They're massive - owned by council/road people. Maybe in a few weeks the sun may be above a couple, but the other two are closer and I doubt it'll ever clear them. The shadows aren't hard or distinct. The near one, the worst, a now enormous beech) is one I planted after the 87 storm - thought so many trees gone I should replant one. We're in a country lane with houses just one side - the other side is just about 40 feet of trees (publicly owned) then a road then a private golf course.

So - how do I get rid of a massive tree or two? I'm ok with a chainsaw, but I know my limits, and these are beyond them. Any council workers here? If I asked the council/road authorities or whoever owns them, are they likely to prune it (heavily) if I ask them? Or slap a protection order on them? I only want to save the planet afterall.

Graham, don't get too depressed, as John said, it can be quite deceptive how much the sun angle changes.

We've got a Silver Birch that causes about 30mins of shading to the lower system. It's about 45ft high and about 50ft from the lower system which starts at about 10 feet above tree base. In December the sun was about 10 ft up the tree, now about 30+ft up, and will clear it in another month.

Also from the timings you gave, it sounds like the trees run from SE to SW of you (but a photo might help), so again you'll benefit from the fact that this is when the sun is highest, so fingers crossed! Sadly, as you recognised, 2 months from Winter Equinox 'on the other side' there will probably still be leaves on all the trees, though what I've found is that even a spindly tree like the Birch still has a big effect due to dispersal of light, not just full blown shade, so it might not be even worse.

If it's not a motorway, nor private road, then it should be the responsibility of the LA. However, careful wording may be required, "Dear Sir/Madam, can you cut down 4 trees to help me save the planet?" may not be a winning approach!

Best of luck.

Mart.

r.cordrey

sly_dog_jonah wrote: »

Such a device doesn't divert power, it simply switches the immersion on when the PV is outputting over a threshold current. Immersion heaters generally consume a pretty constant amount of electricity (eg 1kW) until the thermostat on the heater turns it off. Which local supplier was quoting £999 for this?

I've seen two similar solutions, one using a current-sensing switch and the other a light sensor, both considerably cheaper than £1k:

http://www.reuk.co.uk/Water-Heating-with-Surplus-Solar-PV.htm
http://www.chrisrudge.co.uk/immersion.htm

The limation of these devices is that they can't tell what other appliances are using power at the same time, so may result in you importing electricity from the grid even when you are generating well over the threshold power to turn on the immersion. Also it makes it quite difficult to override the controls in the event your boiler packs up and you want to use the immersion to heat water temporarily (irrespective of sunlight). I'm seriously considering the current-switch method, on the basis that if we set the threshold high (eg 2kW) then it will only trigger when our 3.7kW is making in excess of that, leaving 1kW for other appliances we stagger through the day (dishwasher, washing machine). The lack of manual override is a pretty big limitation though.

Note this is different to the EMMA product which can monitor generation and consumption and only dump the excess generated energy into an immersion heater (by regulating the power delivered to the immersion) to minimise export and import of electricity. These cost in excess of £1k though, so I doubt that is what your local supplier is refering to.

You are right, it does not divert electricity, it makes power available to a separate immersion heater (supply and fitting is included in the £999) which can be switched off if you want to use the power elsewhere.

It is a simplistic solution, which (for me) is a benefit!

Plot_Vendor

Hi all,

Quite a helpful site, this.

My 3KWp system commissioned on 8 Dec and I've been rather underwhelmed by things so far. So I was pleased yesterday, when I saw 7.2814KW on the dial, my highest so far. Then I saw jackieblack and don0301's figures (nothing like a bit of the ol' green-eyed monster, eh? ) and started to wonder if there's something wrong with my system. I've got Mage panels, west facing, with an Aurora Power One inverter. I'm in SE London and not got any overshading.

Any thoughts, etc.
thanks. Plotty

Cardew

r.cordrey wrote: »

You are right, it does not divert electricity, it makes power available to a separate immersion heater (supply and fitting is included in the £999) which can be switched off if you want to use the power elsewhere.

It is a simplistic solution, which (for me) is a benefit!

The economics of this surely cannot make sense and of course it rules out those who have a combi boiler.

£999 invested in a long term savings account will produce presently £46 (£37 after tax)

If you have gas, the 1kW immersion heater has to run for approx 1,000 hours a year just to break even with the lost interest.

Then if you manage to get the immersion to run for another 1,000 hours a year(2,000hrs in total) and save a further £37 the system will have paid for itself in 27 years!

Of course systems like this never need repair!!!

Discuss!!

r.cordrey

Cardew wrote: »

The economics of this surely cannot make sense and of course it rules out those who have a combi boiler.

£999 invested in a long term savings account will produce presently £46 (£37 after tax)

If you have gas, the 1kW immersion heater has to run for approx 1,000 hours a year just to break even with the lost interest.

Then if you manage to get the immersion to run for another 1,000 hours a year(2,000hrs in total) and save a further £37 the system will have paid for itself in 27 years!

Of course systems like this never need repair!!!

Discuss!!

Your logic and mathematics are sublime - if we are comparing like for like.

I would not pay £999 for the installation: the current-sensitive power relay costs about £150 and the wiring is not onerous (supply companies want to make a profit).

Unless you have a very large solar array the utility companies will not fit an export meter, preferring to assume that 50% of the output will be exported (they know that the average household will in fact be exporting 70%+). You will be paid the output in kWh/2*3.1p regardless of how much you actually use.

If you can utilise as near as possible all the power the panels are generating, the power drawn is free. Employing an immersion to heat water is a simplistic way of storing the PV output during the day when the sun is most productive, which is also the time that many are at work.

Now do the sums for heating water by gas in the evening, if you have failed to utilise the free solar energy.