Solar Power Query ??

ed110220

firefox1956 wrote: »

Might be a silly question........
If you have solar panels connected to an inverter & the inverter is connected to your household supply but NOT to the national grid what happens to the electricity you produce but do not use ??
Does it build up ( !!! ) somewhere or does the inverter cut out or what ??
Simple answers please .........

Do you mean in a home that already has mains electricity, or one that is off grid? The former wouldn't make any sense, and I cannot think of a reason for doing it. The latter is fairly standard for people who do not have mains electricity, typically because their location is remote.

In an off-grid setup you would typically have batteries and another source of power as a backup say a diesel generator.

If you already have mains power it would surely be impractical to keep it separate from the solar PV, and as it's a problem that doesn't need a solution I doubt anyone has tried. If you really wanted to perhaps you could use a complicated switching arrangement so that when you had sufficient solar electricity you were isolated from the mains and when you didn't have you were connected up.

You do realise though that with grid-tied solar PV you use what you generate first and any difference is either imported from or exported to the grid? Say your panels are producing 1 kW and you are using 500 W at home, you will export 500 W to the grid. Then you switch on the kettle and use 2 kW for a minute or two and the 1 kW difference is imported from the grid. The kettle boils and switches off, and you go back to exporting 500 W.

Ed

ed110220

firefox1956 wrote: »

Thanks to everybody of their replies.
Perhaps I should have been more specific in my OP.
What I want to do is connect 2 or 3 solar PV panels to an inverter & connect the inverter to a 1 KW immersion heater.
This would be on a property in Spain & for various reasons I do not want to connect to the grid.
So reading the replies above I would need to connect the solar PV panels to an inverter, connect the inverter to the immersion heater but then install an isolating switch to break the connection to the grid when the inverter was turned on ??
In effect when I require water heating I would turn on the inverter & turn off the connection to the grid.

Ah I see, this makes more sense now, due to the rules that Spain has brought in regarding solar PV. I would if you haven't already look into the legalities of it as it may be that feeding solar electricity into a home that has mains power would be considered grid-connected even if you use some sort of switch that means the two are physically isolated.

Ectophile

firefox1956 wrote: »

Thanks to everybody of their replies.
Perhaps I should have been more specific in my OP.
What I want to do is connect 2 or 3 solar PV panels to an inverter & connect the inverter to a 1 KW immersion heater.
This would be on a property in Spain & for various reasons I do not want to connect to the grid.
So reading the replies above I would need to connect the solar PV panels to an inverter, connect the inverter to the immersion heater but then install an isolating switch to break the connection to the grid when the inverter was turned on ??
In effect when I require water heating I would turn on the inverter & turn off the connection to the grid.

Do you need to disconnect the entire house? I know that there are some PV-unfriendly rules in Spain, after a lot of lobbying by the electricity suppliers.

Could you use an islanded-mode inverter (one that is not intended to be grid-tied) and only connect that to the immersion?

If you can get the right voltage of solar panels, you could even do without the inverter at all, and connect the panels straight to the immersion. But you would have to make sure that all switches and thermostats were rated for DC use - most aren't.

zeupater

firefox1956 wrote: »

Thanks to everybody of their replies.
Perhaps I should have been more specific in my OP.
What I want to do is connect 2 or 3 solar PV panels to an inverter & connect the inverter to a 1 KW immersion heater.
This would be on a property in Spain & for various reasons I do not want to connect to the grid.
So reading the replies above I would need to connect the solar PV panels to an inverter, connect the inverter to the immersion heater but then install an isolating switch to break the connection to the grid when the inverter was turned on ??
In effect when I require water heating I would turn on the inverter & turn off the connection to the grid.

Hi

The problem with manual disconnection is that unless you have a complex (/fool-proof) interlock and 'islanding' system which guarantees that there can be no pv operation whilst connected, you'll probably find that any connection would be seen as a grid connection ...

If you're just looking at a solution which is dedicated to water heating there are other options available other than converting DC to AC ... you could look into sourcing a small 12V PV system and fit a 12V DC immersion (300W/500W ??). If a small 12V array works out more expensive than buying whatever panels are available at the right price, you'll probably need to include a DC (xV)/DC 12V converter in the system, but these aren't very expensive .... The main thing to remember is that a DC 12V system running a 300W or 500W load will be drawing a high current, so it would be better designed & installed by someone who knows what they're doing .... getting it wrong could result in severe shock or fire ....

Considering that you're looking at a solution for heating water only and the location is Spain .... have you considered solar thermal ?, as this could not be construed as being 'grid-tied' and - depending on the property, a system with an integrated manifold DHW cylinder would be a possible low-cost option worth looking at ....

If you do want to pursue off grid electrical water heating, it's probably best if you check out the 'off grid' experiences on more specialised forums such as the GBF, Navitron etc ... they possibly have the odd member in remote areas who have done what you are looking to do ... but you'll probably find that the general consensus would be for a thermal solution ...

HTH
Z