Solar panels on workshop roof ?

[garethp]

I'd go for it, when pricing up the kit bear in mind that once you've bought it you've bought it, the price of electric will keep on going up so you should factor that into working out the payback. We've had panels for 2 years now and even though they face due west we've halved our electric bill.

You'll need the panels, then I think a dc isolator unless one is built into the inverter, the inverter, you may as well get a cheap meter so you can keeps tabs on how much you're generating then another ac isolator before you connect to an mcb.

You'll need to get a sparky to test it all and you need to tell your dno about the panels even though you can't claim the fit for a DIY install. Someone mentioned power cuts and back feeding, it won't happen as the inverter will shut down if the grid connection goes off, if ours goes off it won't switch back on until the grid has been up for 5 mins

And the export limit is usually 4kw, there seems to be lots of discussions / different interpretations of the rules about having more than 4kw of panels on a 4kw inverter, in theory you'll generate more when the sun is dimmer but on a sunny day the inverter will export a max of 4kw.

 

[Shox Dr]

Just how big/old are your fridge and freezer?

45-50 units per week? If I was to leave the doors on our fridge/freezer open to force the compressor to run 24/7, it would use 2.088 units per week...

Edit for misreading my own writing - 2.088 is the 24hr figure - it's actually 14.616/week

I can only go by what data I have for the last 7-8yrs, both gas and leccy read every Monday @1800hrs.

In periods where no one has been in the house, for a week+ with only the Fridge and Freezer running they consume around 45-55units a week all yr round. Both are A++++ rated.
That leaves around 20-40units a week for TV, Kettle, w/machine etc.

 

[Shox Dr]

Yup the lot gets turned of. [our first Plasma TV used 250w on stand by, the Sky box was 20-50w).
Hot water is instant, combi. Central heating on timer only when required.

If fact the only thing left on when we walk out the house on a morning is. Fridge, Freezer, Alarm clock on side of bed. and CCTV.
Fridge [Bosch] while 12yrs old is still available and is still one of the best on the market. Freezer is 2yrs old, and always full, is twice the size of the last and uses less leccy.

Believe me I've hunted down every last unit. When I first started we used 130+units per week.

 

[MattF]

Yup the lot gets turned of. [our first Plasma TV used 250w on stand by, the Sky box was 20-50w).
Hot water is instant, combi. Central heating on timer only when required.

If fact the only thing left on when we walk out the house on a morning is. Fridge, Freezer, Alarm clock on side of bed. and CCTV.
Fridge [Bosch] while 12yrs old is still available and is still one of the best on the market. Freezer is 2yrs old, and always full, is twice the size of the last and uses less leccy.

Believe me I've hunted down every last unit. When I first started we used 130+units per week.

Now the penny is beginning to drop as to why we Yorkshiremen might be classed as being a bit tight.

 

[Shox Dr]

Now the penny is beginning to drop as to why we Yorkshiremen might be classed as being a bit tight.

Some call it tight. I call it VFM. I see no reason to burn money, all that means is I have to do more graft to pay for it. Where's the sense it that.

 

[sparkysy]

We used to fit solar pv systems you will need a dc isolator before the grid tie inverter and an ac one after it, you will also need a meter for measuring how much you produce, you have to be careful calculating the cable size back to the cut out as you are only allowed 1% volt drop iirc and you will need it signed off by an MCS and part P approved contractor to qualify for the feed in tariff if you want to grid connect.
Sy

 

[rtbcomp]

That would be correct apart from the fact that the inverter he's looking at needs a supply from the network to operate. No 220v in from the network means no 220v out from the panels.

The inverter puts power into the grid and the correct voltage, frequency and phase, and takes the same voltage from the grid so it knows the grid is up and running. How does the inverter tell the difference between its own electricity and the grid's? It could just keep going, keeping itself switched on.

 

[sparkysy]

The inverter puts power into the grid and the correct voltage, frequency and phase, and takes the same voltage from the grid so it knows the grid is up and running. How does the inverter tell the difference between its own electricity and the grid's? It could just keep going, keeping itself switched on.

A grid tie inverter needs the main supply to be present to function, it has to have 230v in to it to be able to sync parity with the grid at the same cycles per second. No grid = no output from the inverter, when the power comes back on the inverter has to start up and again pair with the grid. This is to stop western powers workers from getting fried when they are working on de-energised lv supplies!
Sy

 

[rtbcomp]

I understand that - but How does the inverter tell the difference between its own electricity and the grid's? It could just keep going, keeping itself switched on.

If it's putting 220 volts out it will see its own and the grid's 220 volts coming back, either of which will keep the inverter running. The two have to be connected together at some point.

 

[Luke]

Certified devices don't keep generating in to the grid if it goes down. They can't, by law.

If they do, the system needs to be fitted with a detection and isolation device.

Google 'G59', the situation, equipment and procedures required are well documented.

 

[sparkysy]

Certified devices don't keep generating in to the grid if it goes down. They can't, by law.
If they do, the system needs to be fitted with a detection and isolation device.

Google 'G59', the situation, equipment and procedures required are well documented.

Exactly! they know with internal monitoring that the grid is there. they have to to be able to pair with it so they are in harmony when they pair otherwise it wouldn't work.

 

[Wendelspanswick]

I understand that - but How does the inverter tell the difference between its own electricity and the grid's? It could just keep going, keeping itself switched on.

If it's putting 220 volts out it will see its own and the grid's 220 volts coming back, either of which will keep the inverter running. The two have to be connected together at some point.

It's termed 'Islanding':
https://en.m.wikipedia.org/wiki/Islanding
Do I know what it does? Yes
Do I understand how it does it? A resounding NO!

 

[rtbcomp]

Certified devices don't keep generating in to the grid if it goes down. They can't, by law.

If they do, the system needs to be fitted with a detection and isolation device.

Google 'G59', the situation, equipment and procedures required are well documented.

Exactly! they know with internal monitoring that the grid is there. they have to to be able to pair with it so they are in harmony when they pair otherwise it wouldn't work.

Yes I know all that - I was wanting to know how the inverter knows there is a fault.

It's termed 'Islanding':
https://en.m.wikipedia.org/wiki/Islanding
Do I know what it does? Yes
Do I understand how it does it? A resounding NO!

Thanks that explains it

Some methods are better than others, but I guess a belt & braces approach is called for.

 

[Luke]

I guess a belt & braces approach is called for.

The kit I've used relied on a combination of most of the techniques mentioned. Certainly, there's a voltage transient and the frequency drifts off pretty quickly. I think the PLL was biased to test the stiffness of the supply, once it's not there, the inverter drifted and tripped itself pretty quickly.

Interestingly, DNOs require that the larger micro-generation projects (> 55kW, I think) actually contribute to power quality, typically voltage control by manipulating the active and reactive power components, so Micro-generation brings other benefits to the grid other than just feeding in power.

 

[Robotstar5]

...Someone mentioned power cuts and back feeding, it won't happen as the inverter will shut down if the grid connection goes off....

That's disappointing, I was hoping having PV panels would allow me to (smugly) boil a kettle, watch TV etc. while my neighbours couldn't

 

[sparkysy]

That's disappointing, I was hoping having PV panels would allow me to (smugly) boil a kettle, watch TV etc. while my neighbours couldn't

Ah you could set It up slightly different, without a grid tie inverter and put a charge controller in and batteries and a standard inverter to get 230v out, a mate has a 2kw in his van that will boil a European kettle. Narrow boats use this method too and lots o other off grid projects!