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.

 

[Lard]

Having read that some of you are getting £2k-£3k p,a I immediately thought 'Christ! they must be living on the equator! We're in south wales and get, on average just under £300 p.a

Then I realised that you obviously had your system fitted when the fit payments were much, much higher than our very late installation (near the end) of the fit scheme.

Having said that I bet your break-even period is still around 9-10yrs, as is ours?

 

[Agent_zed]

This is exactly what I've been thinking of doing and have the same scenario of 4kw of FIT, so didn't want to effect that by adding another set.

Something to think about is the term 'batteries'. A lot of people want to store electric in batteries but in reality how much electric do you use at night? The answer is very little, unless you are running your appliances at night. The trick is to run your appliances in the day when the sun shines and use that 'free' electric. Paying £5k+ for a battery, that lasts 10 years or less, so you can run your dishwasher at night makes no sense to me, when all it takes is to set the timer for it to come on when you are likely generating the most electric in the day.

So instead of thinking of a battery as a lithium battery pack, I think of a water tank as my battery. A solar diverter is very cheap and from what I can see is not against the fit rules. Any excess solar goes into heating water. You are storing energy just like a battery, just in a different form. Heating water is the most energy intensive part of your homes usage, so to me makes the most sense to put the energy into that first.

The solar diverter takes care of making sure you aren't heating water when you want to use the electric for running your appliances so no problem there, along with a few timers and you are good to go.

As an aside the other thing is rather than spending all that money on a battery is to put it into improving your house efficiency. A heat recovery system on your shower can save around 40% of the waste heat just going down the drain. That heat was very expensive to put into that water. Stopping the heat leaving your house with improved insulation is obviously the usual way of saving energy. Both of these things are thousands cheaper than a battery.

 

[Dabop]

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

You will really have to look at what your current FIT contract terms are- many won't allow any export modifications at all!!!! (if modified, then you may lose your 'grandfather' status on the original setup... and its current payment levels...)



As you are looking at a battery and new hybrid inverter anyway, a way around that is to leave the existing system as is, and simply have a parallel NON-export hybrid (most can be set up like this in the menus) and have your house loads on the hybrids output, with a feed from the meterbox tails to the hybrids mains inputs...

Set up correctly, you will get zero export from the hybrid (so not affecting your FIT original system in any way) and the house loads will run off the hybrid and its battery pack, unless the battery goes flat, in which case it will 'fall back' to the mains input connection ie the house loads connect back to the grid as they currently do...

With the battery bank set to charge from solar only, this will minimise or even zero the grid usage (with correct battery bank capacity and panel wattage calculated to handle your 'normal' household loads)- you may use a smaller hybrid/battery bank and only have 'some' of the house circuits on its output, with other larger loads still staying on the mains grid instead- doing it this way allows almost unlimited rearrangement to suit anyone's budget/requirements...

You won't be able to use the existing FIT system during blackouts obviously, but you will have the hybrid system running the house when all your neighbours are lighting candles lol plus as your mains grid usage can be reduced/zero'd, the FIT system becomes purely a money making exercise...

(this is a hybrid inverter- actually my 12kw one here (being used offgrid) and it shows the mains in (from the meterbox tails via a suitably rated breaker, mains out (which feeds some/all of your household circuits ie feeds your consumer unit) the PV 1 and 2 (mine can handle 3kw of panels on each PV input) and the battery terminals (48v in mine)- they come in a wide variety of inverter wattages, battery voltages and solar wattage limits (plus you can always add more battery capacity or more solar panels simply by adding external MPPT charge controllers with their own arrays attached directly to the battery bank...)

Obviously LFP lithiums are the best choice (L/A can be used, but they really are a bad choice these days) and can be either individual cells like mine or a 'component box' (BYD for example make their 48v range of 'powerwalls' as do several other brands) and hybrid inverters contain their own inbuilt ATS (automatic transfer switch) as well...
My 20kwh battery bank (15x 400Ah single cells- wired in series for 48v nominal)

BYD 48v 'battery in a box' thats it sitting on the floor (not mine lol)- most brands are 'modular' and you can increase the capacity simply by 'stacking another drawer'... good for those that want a simple 'plug and play' system where everything is in the one box...

Best part is that you can literally have the entire system isolated from the grid for those places that dont allow export solar at all- just use a standard external ATS wired up as a 'backup genny switch', but running in reverse ie the primary source is the hybrid rather than the grid connection, and the mains grid is connected to the 'backup generator' connections when wiring it in- the hybrid will run the house loads until it hits its programmed lower battery limit and then shuts down, and only then do the house loads 'fall back' on the 'emergency generator' aka the mains grid... Set up like this, the hybrids solar ONLY does its own battery bank, it has ZERO export at all (for those that aren't allowed solar exports) and the whole system is classified as an 'external generator' to all intents and purposes (meaning that non 'gridtie inverters' can be legally used- as they are NEVER connected to the grid...)

(that shows a three phase supply, but single phase ones are readily available as well)

 

[Chris Puttick]

This is exactly what I've been thinking of doing and have the same scenario of 4kw of FIT, so didn't want to effect that by adding another set.

Something to think about is the term 'batteries'. A lot of people want to store electric in batteries but in reality how much electric do you use at night? The answer is very little, unless you are running your appliances at night. The trick is to run your appliances in the day when the sun shines and use that 'free' electric. Paying £5k+ for a battery, that lasts 10 years or less, so you can run your dishwasher at night makes no sense to me, when all it takes is to set the timer for it to come on when you are likely generating the most electric in the day.

Or you can treat your battery as a place to put cheaper electricity to use when the rates go up. Whether that's PV power on the sunny days or cheap power at night for use during the day depends on the weather and the time of year. But the cheap power at night will pay for the battery pretty fast.

 

[Eshmiel]

This is exactly what I've been thinking of doing and have the same scenario of 4kw of FIT, so didn't want to effect that by adding another set.

Something to think about is the term 'batteries'. A lot of people want to store electric in batteries but in reality how much electric do you use at night? The answer is very little, unless you are running your appliances at night. The trick is to run your appliances in the day when the sun shines and use that 'free' electric. Paying £5k+ for a battery, that lasts 10 years or less, so you can run your dishwasher at night makes no sense to me, when all it takes is to set the timer for it to come on when you are likely generating the most electric in the day.

So instead of thinking of a battery as a lithium battery pack, I think of a water tank as my battery. A solar diverter is very cheap and from what I can see is not against the fit rules. Any excess solar goes into heating water. You are storing energy just like a battery, just in a different form. Heating water is the most energy intensive part of your homes usage, so to me makes the most sense to put the energy into that first.

The solar diverter takes care of making sure you aren't heating water when you want to use the electric for running your appliances so no problem there, along with a few timers and you are good to go.

As an aside the other thing is rather than spending all that money on a battery is to put it into improving your house efficiency. A heat recovery system on your shower can save around 40% of the waste heat just going down the drain. That heat was very expensive to put into that water. Stopping the heat leaving your house with improved insulation is obviously the usual way of saving energy. Both of these things are thousands cheaper than a battery.

That all makes a lot of sense. It is possible to make a hierarchy pf costs/benefits, spending least to get the most effects. But the use-cases will vary a lot with the property being updated. For some houses, insulation is not so much very expensive as impossible, for example. Others may already be highly insulated. In short, it helps to quantify all of the costs and the potential savings, to get to best-strategy for getting more energy for less money.

There are also other considerations besides cost/benefit in purely cash terms. I'll once more mention the health-dangers of wood and coal burning fires. There's also the matter of risk - if the grid disappears for a day it can be bad enough but what about if it goes for a week, as has happened to an increasing number of folk because of the increasing storm-occurrence that's blowing and submerging bits of grid infrastructure to destruction.

A battery (plus may be a car battery) + solar + UPS can save a household from that, so ..... how reliant on electricity is one's particular household? Ours (and the car) run entirely on the e, including not just heat pumps, lights, cooker, my tablesaw and such but also the pump that pumps water up from a private supply and another that pumps sewage from the collection tank up to the main sewage pipe 5 metres above. No e in winter would be ..... awkward. How much do hotels cost, especially when the storm-damaged are all looking for a room!?

 

[Dabop]

Or you can treat your battery as a place to put cheaper electricity to use when the rates go up. Whether that's PV power on the sunny days or cheap power at night for use during the day depends on the weather and the time of year. But the cheap power at night will pay for the battery pretty fast.

Some do that ie 'timeshifting'- but the savings are minimal really in most cases (which pushes the payback time (ROI or return on investment) out longer...)

Say you have a 'cheap' offpeak rate of 20c per kwh, and a peak rate of 30c/kwh- every kwh of 'saved' usage is only 10c per kwh...

My panels cost me $27Au for each 250w panel secondhand (new they cost about 4 times that), and each panel generates 0.78kwh a day here...

(currently have 6 'temporary' panels in use feeding my caravan and shed, the rest of the 72 panels are sitting in the shed waiting for me to finish the house...18kw of panels for under $2000Au lol)

So each panel makes up that 10c every day and a half approximately...
In just over a year (just under 400 days), it has paid itself off- and is now 'making electricity for free' where the 'timeshifter' is still paying every day to buy that cheap electricity...

The new panels obviously take a bit longer- about 4 years, and then they are again 'making electricity for free'

(I've ignored the battery cost as you obviously need the battery in both cases, so both have to spend the same on that)

 

[Agent_zed]

Something to consider is whether you are doing this to save money or to be more environmentally friendly. I come at this from the environmentally friendly side.

It requires far less resources to store energy in a water tank. They last a very long time and can be recycled very easily. They pose very little environmental risk. A lot of houses already have one, so minimal new equipment required.

Having millions upon millions of lithium batteries manufactured so that someone can buy electric a bit cheaper and have electric if there is a powercut (touch wood I don't think we've had a powercut in 2+ years and that was only an hour or so), does not seem, to me, to be the best use of resources in most cases.

There is also the chance that in the next 5-10 years that 'cheap' night time electric won't be as cheap as more and more electric cars will charge overnight. Once the demand reaches a certain point, there will be little incentive for energy companies to offer lower rates.

It could be argued that the current global unrest is partly due to this new rush to gain resources before anyone else does. The US wants Greenland and Canada for it's mineral resources. There will be fights over who has access to these resources as demand increases, just like oil, and it will only get worse as demand increases.

 

[Eshmiel]

Something to consider is whether you are doing this to save money or to be more environmentally friendly. I come at this from the environmentally friendly side.

It requires far less resources to store energy in a water tank. They last a very long time and can be recycled very easily. They pose very little environmental risk. A lot of houses already have one, so minimal new equipment required.

Having millions upon millions of lithium batteries manufactured so that someone can buy electric a bit cheaper and have electric if there is a powercut (touch wood I don't think we've had a powercut in 2+ years and that was only an hour or so), does not seem, to me, to be the best use of resources in most cases.

There is also the chance that in the next 5-10 years that 'cheap' night time electric won't be as cheap as more and more electric cars will charge overnight. Once the demand reaches a certain point, there will be little incentive for energy companies to offer lower rates.

It could be argued that the current global unrest is partly due to this new rush to gain resources before anyone else does. The US wants Greenland and Canada for it's mineral resources. There will be fights over who has access to these resources as demand increases, just like oil, and it will only get worse as demand increases.

There's certainly a very good case for pursuing energy supply and use that's far less environmentally damaging. We humans have become a plague on the planet, which has already done immense damage to other species, the environment in general and, inevitably ourselves. However .....

We're creatures of habit but also creatures locked into large socio-economic arrangements that have a vast momentum. Change is difficult, even if many of us yearn for it.

So, for example, consider the average citizen ("subject" is probably a better description) who is a wage slave locked into the producer-consumer economy including an unavoidable energy-demanding commute each day. Public transport is decimated and sparse, unreliable (if there's any at all) and costly. So .... a car. One alternative solution is to cycle there and back (I did a 50 mile round trip for some years) but this is very difficult for most to do unless they already have cycling fitness. Next option is a car. If it's "a necessity" then its still better, environmentally, to have an e-car than an ICE car. It's still damaging but less damaging.

This is the syndrome that'll do for us all. We really need to change our lifestyles far more drastically than that half-ersed compromise. But how, without being rejected from the neoliberal hegemony to a life of poverty, ill-health and early death?

 

[Dabop]

Something to consider is whether you are doing this to save money or to be more environmentally friendly. I come at this from the environmentally friendly side.

It requires far less resources to store energy in a water tank. They last a very long time and can be recycled very easily. They pose very little environmental risk. A lot of houses already have one, so minimal new equipment required.

Having millions upon millions of lithium batteries manufactured so that someone can buy electric a bit cheaper and have electric if there is a powercut (touch wood I don't think we've had a powercut in 2+ years and that was only an hour or so), does not seem, to me, to be the best use of resources in most cases.

There is also the chance that in the next 5-10 years that 'cheap' night time electric won't be as cheap as more and more electric cars will charge overnight. Once the demand reaches a certain point, there will be little incentive for energy companies to offer lower rates.

It could be argued that the current global unrest is partly due to this new rush to gain resources before anyone else does. The US wants Greenland and Canada for it's mineral resources. There will be fights over who has access to these resources as demand increases, just like oil, and it will only get worse as demand increases.

Actually, there is a real case for homeowners having batteries and rooftop solar- it decreases the usage of grid power- which is in many cases generated from non renewables like oil, gas and coal (even uranium is a non renewable- at current usage levels, we have less than a century left before all known easily accessible reserves are used)

In my case- I went offgrid as getting a mains grid connection onto my property was exorbitant in price- my entire offgrid system (20kwh of lithium LYP cells, 12kw inverter, solar charge controllers, racking and wiring etc) was under $18k Au, where getting the mains grid connection (with a 8kw limit on it mind you) was $42k Au- and thats with yearly elec bills of nearly a grand a year for the same usage I get for free from the sun...
(not to mention the almost daily blackouts when storms hit in the wet season...)

It saves on tax payers money being spent on expensive grid upgrades (my old town started having issues with the local substation and cross-country lines back in the 1980's- they were saying that new ones double the capacity would be needed by the mid to late 1990's...
Then solar came in in the mid 1990's- and they are STILL today using that same substation and grid quarter of a century on... despite the towns population increasing fivefold in that time...
Sure more economical appliances helped, but industry demand had risen sharply since then- and almost all of that extra demand for industrial electricity is coming from rooftop solar- in the same town...