Old Solar Panels - is it worth getting a battery now?

BoBoDobie

I had my solar fitted in 2014, I have 3.6kW.  I've since heard that you can have batteries to store up energy, is this something that a company could fit to my existing solar panels?  I don't know where to start or even if its worth the cost (or how much the cost would be).  Are there any solar experts on here or can anyone point me to where I can find out more information please.

Ectophile

If you want the batteries linked to the solar, then you need an inverter that is compatible with batteries.  Older ones wouldn't have been, and not all newer ones would be - it adds complication to the inverter so most people wouldn't specify it unless they intended to get batteries.

When my old inverter failed, I got a new one that does support batteries, and got a small (3.3kWh nominal, 3kWh usable) battery.  The new one is also internet-enabled, so I can see whet it's doing whenever I like.

BoBoDobie

Thank you Ectophile, are mine old enough to not be compatible then by the sounds of it?  And there is no way round that bar getting new panels?

EricMears

BoBoDobie said:

Thank you Ectophile, are mine old enough to not be compatible then by the sounds of it?  And there is no way round that bar getting new panels?

If you're producing 'mains' electricity from solar panels or even just buying it on a time of day tariff,  you can install some sort of battery system to save it for later.

The process might not be quite as efficient as a system that stores SP output without converting it to AC and back to DC but it's the only way you'd continue to benefit from the FIT scheme.

QrizB

BoBoDobie said:

Thank you Ectophile, are mine old enough to not be compatible then by the sounds of it?  And there is no way round that bar getting new panels?

As EricMears says, there are lots of people on this forum with retrofitted batteries. The simplest system is an AC-coupled system where you add a separate inverter for your batteries. This avoids making any changes to your solar PV system and doesn't affect any feed-in tariff payments you might be receiving.

One popular system is that offered by Lux; there's a long thread here discussing Lux AC-coupled inverters and batteries. Other systems are available from other suppliers, including (if you have deep pockets) the Tesla Powerwall.

Edit: zeupdater has given a longer and more detailed reply below. Thankfully we appear to agree!

zeupater

Hi

You don't actually need to change the inverter as the batteries can be AC or DC connected ...

With DC connectivity your new (replacement hybrid) inverter acts just as your current inverter regarding PV and grid export, with the added benefit of charging a battery bank (PV and off peak mains) and provision of that stored power to load in dull/dark conditions. (this is what Ectophile describes)

AC connect is slightly different in that the solution is usually independent, therefore having no impact on your existing setup. Normally you would have a separate inverter/battery charge unit connected to the mains in parallel to your current system which monitors (clamp sensor or separate new meter) for import/export mains conditions and mitigates by battery charging or load provision ....

Some AC connect systems (eg Victron) have the ability to connect your current PV setup in series where the new battery setup sits between your current system and the mains, which (depending on what you want to have the system support & the spec of the inverter/battery bank) allows for powering of either critical circuits or the whole house in case of power interruptions ...

Both approaches have their benefits and/or disadvantages, for example, with a new hybrid PV/Battery inverter charger (DC option), your FiT TGM would under-report generation by the round trip efficiency of battery storage (DC-DC), whilst an AC connected battery system would add the inefficiencies of the DC-AC-DC-AC conversion cycle, thus being less efficient in overall energy terms, but more efficient in maintaining your FiT income ... swings & roundabouts come to mind!

HTH -Z 

Edit - AC/DC options cross posted with QrizB/EricMears      

jimjames

BoBoDobie said:

Thank you Ectophile, are mine old enough to not be compatible then by the sounds of it?  And there is no way round that bar getting new panels?

Just to clarify, even if the inverter did need to be replaced (and as above it doesn't) then you still wouldn't need to replace the panels themselves.

mickyduck55

My inverter did not need to be replaced I had an additional one just for the batteries...

Heedtheadvice

...and just to add to the above great posts...

To try and give some indication as to the thread title question...worth it?

Depends (like most things!) on your aim and use of power.

They are expensive and payback time is many a year, possibly as much as the battery life. Consider professionally installed ones that might cost £5k or £6k (just ballpark figures and depend upon several factors such as amount of storage). They probably have only half the life or less of a solar panel..

Batteries can help smooth out the peaks and troughs imbalance between demand (for power in your property) and supply (solar generation).   Good idea if you need to do that if you generate in daytime but most of your use is outside that period. They can also store cheaper night time tariff electricity if you have or can move to one of those tariffs. With high power prices that is becoming very attractive.

Payback time varies on what excess you generate(and then potentially store and use later), how much you can time shift that 'free' generation or cheap purchased import from grid via the storage.

It has generally been considered that batteries are not a good move financially, especially if you factor in potential investment of the capital cost and inflation (much like solar panels were part way though the FIT scheme) but power finances and inflation etc has changed much recently. They might just be an excellent buy but who can predict the future? There are probably few people who are not very glad they installed solar years ago when Which? the consumers association urged caution for financial reasons.

They are good to help your better use of green generation.....but contain non green metals etc. which might be better employed in electric vehicles which could in the near future be used for storage as well as transport.

So my post shows there are many factors to consider, mostly beyond my ability to quantify. There are some other threads and I hope more knowledgeable contributors will post. Maybe a thread dedicated to battery pros and cons?

For me I am going ahead with adding them to my solar system but that decision and conclusion does not and should not apply to everyone!

Reed_Richards

How do you make sure that your panels and your separate AC-coupled battery don't end up exporting more than the 3.68 kW most of us are limited to?

EricMears

Heedtheadvice said: There are probably few people who are not very glad they installed solar years ago when Which? the consumers association urged caution for financial reasons.

No idea why the CA were advising caution !  It was obvious at the time that the guaranteed returns would recoup the installation cost in 10-12 years and a fair bet that index linked payments and the likelihood that electricity prices might rise suggested even quicker break-even. With a 25 year life,  the scheme would continue to be profitable (even without reduced imports) for at least a further 10+ years.

I even suggested at the time that for anyone without 'spare' capital getting a further advance on a mortgage seemed worthwhile.

In the event,  my breakeven point was a little over 7 years (probably less if I'd bothered to calculate import savings) and I've already had 4 'sheer profit' years with another 14 to come