Solar Panels Query

[Nix]

Grid tie inverters, by their very nature, have to synchronise themselves to a working grid before they add to that grid. If the grid isn't there, they simply will not work, it's part of their safety feature.

[Nix]

RS, I've had a good look round last few days and I simply can't find any quick fix replacement with what you're going to have. I was hoping to find a high voltage pv controller that you could swop with the grid tie inverter and then suggest an inverter for you to tie in as well. But, alas, the only units that take that sort of voltage are grid tie so same as what you will already have.

So, the only option is to rewire/reconnect those panels and get your own controller and inverter.

Don't think you ever mentioned exactly what you are going to want out of the system? Is it just for keeping your phone charged plus lights or more power hungry units like hair dryers (!), fridges, freezers, heaters, etc?

[Bjm]

hi, this is a discription of my system

i have a solar system installed and supplied free, they just keep the feed in tarriff and i get the electric during the day free.
i only mention this because i feel a lot of people may go this way, but the operation and output of the solar panels are monited remotely, so that if theres any problems they can arrange a call out.
the monitering can be done by one of two methods. using a built in sim card that regularly updates the control centre at predetermined times.
the second way uses a radio signal that is sent to the next solar fitted house, then the next and so on, when it gets to the last house in the loop that will contain the sim card control unit that reports to the control center, (note that is only solar fitted houses using the same company, and does not apply to privately fitted systems)
this means that if you mess about with the system in the wrong way then the company will be arranging a call out.

They have installed 18 solar panels, two banks of nine, each bank connected in series and the two banks connected in paralell. the panels cables run into the loft to an isolation switch before entering a pv controller and the grid tie inverter (which are modular in design, but under one cover and look like a single unit. the cables then run into another isolation switch then the mains.

the way the system is put together does have some flaws that would allow a feed off, or/and a system put in place ready to use when the shtf.
the trouble with having a feed off is that although it can be done covertly you would have to be willing to reverse it back to normal if they ever needed to do maintenance on the system during the lifetime of the contract.(this is i am told rare and they do arrange a day to call and dont just turn up) but a system put in place is fine and can be set up and connected when the grid goes down for good.
as said in other posts the voltages involved are deadly and not to be played with unless you have an understanding on what you are doing. and the way my system is set up may not be the same as yours.

[Nix]

Thanks Bjm, the set up you describe is exactly as I envisaged. What was news to me, in your post, was the monitoring side of things. If the installers note a drop in expected output then they would visit but it would have to be outside their parameters, I assume. Will try and ask around...

The problem still exists as to how someone with little or no knowledge can access and modify an existing system safely, cheaply and with maximum benefit.

[Bjm]

hi
may i just say that someone with little or no knowledge should not access and modify an existing system,
but it is possible if you know what you are up to.

[Steve]

What about using a battery to power a small inverter, then feeding the output of that inverter into the "mains in" on the grid tie inverter, to fool it that mains was present. Once running you could keep the small inverter battery charged from the grid tied inverter.

Obviously only of use in a grid down situation because you'd have to disconnect the "real" mains connection.

[Nix]

(10 September 2013, 00:05)Steve Wrote: What about using a battery to power a small inverter, then feeding the output of that inverter into the "mains in" on the grid tie inverter, to fool it that mains was present. Once running you could keep the small inverter battery charged from the grid tied inverter.

Obviously only of use in a grid down situation because you'd have to disconnect the "real" mains connection.

Hi Steve - wondered this myself but wasn't sure how the inverter (has to be pure sine wave of appropriate power) would handle a back feed from a grid tie inverter. It's circuits are going to be completely different and more delicate to a normal mains sub station which is acting as a step down transformer. What really made me nervous about this was that the grid tie would be trying to supply 3kW of power which can do some serious damage. Problem is I'm not sure anyone will know. I've tried querying suppliers on other issues and they are seriously lacking in knowledge sometimes. I think the only way to find out is to try it but you risk wiping out one or both of your units plus a fire!

Quote:hi
may i just say that someone with little or no knowledge should not access and modify an existing system,
but it is possible if you know what you are up to.

Thanks again for reiterating this. I keep stating this myself but my fear is that someone somewhere will ignore this with disastrous results! I could easily modify this type of grid tie system BUT finding a safe, cheap and effective way for someone else, with little or no knowledge, to do it is the problem. I still haven't got the right answer yet.

High voltage electricity is DANGEROUS!!

[Skvez]

(10 September 2013, 00:05)Steve Wrote: What about using a battery to power a small inverter, then feeding the output of that inverter into the "mains in" on the grid tie inverter, to fool it that mains was present.

The Grid-tie inverted is trying to output as much power as it can, what's not used by the house is (normally) exported to the mains.
In the scenario you describe the mains is no longer there to accept the difference between local generation and local load.

If the load is greater than the output of the array the Voltage will collapse and the array will 'notice' the loss of the mains and cut off (probably no damage but no power either)
If the load is less than the output of the array the Voltage will rise and either the array will notice conclude a loss of the mains and cut off (probably no damage but no power either) or run at too high a Voltage resulting in probable damage to your load, your original inverter that you uses to 'jump start' the system and the grid-tie-inverter too.
These systems are just not designed to work without the mains present.

[Nix]

(10 September 2013, 17:50)Skvez Wrote: The Grid-tie inverted is trying to output as much power as it can, what's not used by the house is (normally) exported to the mains.
In the scenario you describe the mains is no longer there to accept the difference between local generation and local load.

If the load is greater than the output of the array the Voltage will collapse and the array will 'notice' the loss of the mains and cut off (probably no damage but no power either)
If the load is less than the output of the array the Voltage will rise and either the array will notice conclude a loss of the mains and cut off (probably no damage but no power either) or run at too high a Voltage resulting in probable damage to your load, your original inverter that you uses to 'jump start' the system and the grid-tie-inverter too.
These systems are just not designed to work without the mains present.

Very difficult trying to get info on this stuff without talking to the designers themselves it seems!

Had a look around. Very differing opinions on even how a grid tie works, let alone if you can use an off grid with it. But apparently it all depends on what equipment you are using. I heard some off grid inverters can be bi-directional in their power flow. This means that the off grid inverter can then potentially charge your battery bank from the grid tie but only up to fully charged status and then there's a danger of overcharge without a dump load. In this scenario some off grid inverters change the output frequency to trick the grid tie to shut down thereby saving overcharge problems. So, yes, it looks like it can be done but only if you have intimate knowledge of both the off grid inverter and the tie grid inverter.

[Skean Dhude]

At the very worst we just disconnect everything and wire the panels up as we would if we bought them ourselves. So make sure you get the inverters, controllers and whatever else we need to make it your own power station.