Adding solar panels to an existing system.

[graduate_owner]

Hi all, looking for information on solar panels.

We have a 4kW solar panel system which was installed about 13 years ago and so qualifies for FIT payments. I would like to add more panels now, which will not qualify for FIT payments, plus battery storage. I don't want to jeopardise my entitlement to FITs as they are worth around £3000 a year overall now. Is it possible to have another 4kW system alongside the existing one without major issues? Could a battery be used to store energy from both sets of panels? Could both sets of panels be integraded into the existing house mains? I have contacted my DNO and they said I could expand my system without problems.

Any advice would be appreciated.

K

 

[Eshmiel]

Hello Grad,

Yes, you can do as you want - preserving your FiT arrangement whilst adding another array of solar panels, batteries etc. There are some limits and things to watch out for .....

The FiT system needs to remain distinct from any new solar and so forth so that it behaves just as it did before new stuff was added. This means that you shouldn't connect any batteries to it as this would allow you to use batteries to gather more solar from your new panels then export it via your FiT inverter. That would break and cancel your FiT agreement.

You can change your inverter that serves your FiT solar panels (they tend to have a life of only around 12 years) but you can't change or add to your solar generation equipment that is covered by the FiT agreement without breaking and losing it. In most Fit agreements, you can't even change the solar panels for different panels.

You'll probably also have excess solar from your new panels that you export to the grid if you can't use it in the house or get anymore into your batteries because they're full. You can't come to an arrangement to sell that excess solar without, again, breaking and losing your FiT agreement. You have to give it to the grid for nowt. Get an e-car to put it in instead.

Some areas have a grid infrastructure that isn't very capacious. Until recently that meant that proposals for additional solar panels that might also export to the grid (in addition to your FiT export) were sometimes refused on a "grid can't cope" basis. However, there's now a new inverter standard (G100) that allows the grid operator to prevent any excess export from that new inverter if the grid is being overloaded by exports. This means you can have more solar panels as long as they operate through such a G100 inverter.

Hope this helps.

 

[Sideways]

If you add extra panels with a hybrid inverter and a battery connected directly to it, the meter tails will still be point in common between the new system and the one with feed in tarrif. Your new installation can have a current sensor on the meter tails and that will give you a good deal of flexibility. Most of all, it will allow you to take surplus power generated by your original 4kW array and pull it into the new inverter to charge your battery. Whether this is a good thing depends on whether the FIT tarrif is more or less than the price per kWh that you are paying these days.

As to the point about the grid and exports, I was approved a G99 license by my DNO to export upto the 9kW peak of my own solar panels. In practice I can never use it. The grid wiring has highish resistance around here (1970's vintage, and much added to) and our average voltage has been set high - a legacy of the days when the power companies used to get mostly complaints about grid voltage dropping too low. There are brief times of day when I could export several kW, but for most of the day this would drive the voltage up too high and the system would repeatedly trip and reset. I found by trial and error a 3kW export limit is the best for reliability in my case. I'd recommend anyone to put a logging multimeter on their mains for a few days and see what the grid looks like - especially spring onwards when other local solar systems are doing their thing.

 

[John Brown]

If you add extra panels with a hybrid inverter and a battery connected directly to it, the meter tails will still be point in common between the new system and the one with feed in tarrif. Your new installation can have a current sensor on the meter tails and that will give you a good deal of flexibility. Most of all, it will allow you to take surplus power generated by your original 4kW array and pull it into the new inverter to charge your battery. Whether this is a good thing depends on whether the FIT tarrif is more or less than the price per kWh that you are paying these days.

As to the point about the grid and exports, I was approved a G99 license by my DNO to export upto the 9kW peak of my own solar panels. In practice I can never use it. The grid wiring has highish resistance around here (1970's vintage, and much added to) and our average voltage has been set high - a legacy of the days when the power companies used to get mostly complaints about grid voltage dropping too low. There are brief times of day when I could export several kW, but for most of the day this would drive the voltage up too high and the system would repeatedly trip and reset. I found by trial and error a 3kW export limit is the best for reliability in my case. I'd recommend anyone to put a logging multimeter on their mains for a few days and see what the grid looks like - especially spring onwards when other local solar systems are doing their thing.

If he gets £3000 a year, then I imagine the FIT is way higher than the domestic rare per kWh - we have a 3 to 4kW installation with a grandfather tariff of around 60p per generated unit, and we get slightly more than £2000 per annum.