DIY Solar PV Battery storage for my house

[Raul]

Thanks for that advice. Can you recommend one? From what you are saying, it sounds as if my cheapest solution would be install an inverter/battery UPS which could be connected via a manual change over switch. Could that be achieved via my original suggestion of a Victron inverter and commercial LiFePO4 12v batteries?

Not the way you think it with the 12v batteries. It will have to be a isolated stand alone system that does not connect to grid. The one suggested earlier with the multiplus2, runs on 48v and it’s integrated as a energy storage system. That will run the hole house.

 

[mikebeaches]

Could you clarify the saving us money and earning a few bob bit please

How long before the savings cover the cost of installation , and are there any annual maintenance costs , cleaning solar panels etc

Thanks

To try to answer your question: how long before savings cover cost of installation? It may sound surprising, but I've absolutely no idea.

There are so many variables:

1. What is going to happen to the cost of purchasing electricity from the grid in future?

2. What will happen to the so-called 'smart export guarantee' rates for selling surplus electricity back to the grid in future?

3. Will we decide to replace our old oil-fired central heating boiler with an air-source heat pump?

4. When will we feel ready to change one diesel car and one petrol car to electric vehicles?

5. I'm aged into my 70s - how long will I last...?

I've seen mention in this thread reference to good income from 'Feed-in' tariffs. And it is true some early adopters have done very well financially. But they are no longer relevant to anybody who is not already a beneficiary: they are a legacy incentive that is no longer available to new applicants.

The reality today is that for most, a unit of electricity (1kWh) costs circa 28p to purchase from their electricity supplier, plus the daily standing charge. But when it comes to selling your own electricity back to the said supplier, they will pay between about 2p and 7.5p per unit (dependent on which supplier). The most generous is Octopus Energy, which pays 7.5p under the smart export guarantee.

As an aside, and just to clarify, all that is meant by the 'smart export guarantee' is that all major suppliers must guarantee to offer to buy back your exported surplus electricity. What it doesn't do is set any maximum or minimum prices - that is entirely up to the individual supplier. I believe there may actually be some paying less than 2p per unit?

And to try to clarify what earning a few bob means - well at this time of year we are typically exporting between 30 - 40 kWh per day @ £0.075 per unit payment. And our electricity costs consist of 25p daily standing charge and on average about half a unit of power ie 0.5 kWh* per day.

*I'll be honest, I expected our grid consumption - in the summer in particular - to be zero, as we're more than self-sufficient. However, by some quirk, a small amount of electricity does get imported from the grid, rather than 100% from our solar and batteries? And I don't believe we are alone in that - I've seen others commenting similarly. In my head I reckon it's a conspiracy on the part of the suppliers...

One final point to be made is that Octopus offer a - currently unique - so-called smart or Agile tariff for domestic customers, that buys and sells electricity at different prices at different times of day - price changes every 30 minutes. Another Funster explained to me they are making quite serious money by going on the Agile tariff, and that is something I've yet to fully get my head around and implement. But I intend to get to grips with it very shortly.

 

[Revolvor]

Not the way you think it with the 12v batteries. It will have to be a isolated stand alone system that does not connect to grid. The one suggested earlier with the multiplus2, runs on 48v and it’s integrated as a energy storage system. That will run the hole house.

I wasn't thinking of connecting to the grid. Our solar PV switches off if there is a power cut. A few years ago, before batteries were popular, I bought a 3kw inverter generator, to be used during power cuts. I still haven't used it for that purpose, but planned to get an electrician to install a socket for it, with a manual changeover switch to isolate from the grid. If I went ahead, could I connect the UPS to the socket, in place of the generator?

( After this, I will stop bothering you with stupid questions!)

 

[Raul]

Yes, absolutely doable as is isolated from grid supply. Sorry if I miss understood you. If you have a manual changeover and you are totally on your own power, you could create your own micro grid for power cuts to run essentials. A multiplus can do both, charge it up from grid when is plugged in, then run as a UPS when power is out. There are 12v LiFePo4’s out there that can be run in series if you wish to go 24v or 48v. For small power up to 2kw ish, you can stay with 12v and appropriate cabling.

 

[Revolvor]

Yes, absolutely doable as is isolated from grid supply. Sorry if I miss understood you. If you have a manual changeover and you are totally on your own power, you could create your own micro grid for power cuts to run essentials. A multiplus can do both, charge it up from grid when is plugged in, then run as a UPS when power is out. There are 12v LiFePo4’s out there that can be run in series if you wish to go 24v or 48v. For small power up to 2kw ish, you can stay with 12v and appropriate cabling.

Thank you very much. You have been very helpful.
John

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[autorouter]

Our solar PV switches off if there is a power cut.

Many installations use a simple grid-tied inverter that needs a reference from the grid to stay synchronised. If the grid is lost, the inverter loses synchronisation and packs up, so no power during a power cut, even on a sunny day.

You could replace it with a hybrid inverter, plus a lithium battery, that would generate its own synchronisation signal in the absence of grid power. That would at least give you solar power and some battery power during power cuts. Only a small battery is necessary for this, maybe 1kWh (about 100Ah), but obviously the more battery you have, the more power you can store during the day for use at night/morning when the sun isn't shining.

The hybrid inverter will (if you tell it to) fill up the batteries from solar before sending any power to the grid. It will use solar energy to power your loads if any is available. It will use battery power to power your loads if there is no solar. It will only use grid power if the batteries are empty.

 

[autorouter]

How would the 13.5 kWh from a (for example) Tesla Powerwall translate into the number of 200 Ah lithium batteries?

To translate kWh to Ah, you need to know the battery voltage. 13.5kWh is equivalent to 13500 / 12 = 1125Ah of 12V batteries. That's about five and a half 200Ah batteries.

For 13.5kWh from a 48V battery, that would be 13500 / 48 = 281Ah of 48V batteries

 

[autorouter]

I was thinking along the lines of a large Victron Multplus charger/ inverter (or equivalent) and a large number of Lithium batteries.

Would this be feasible? I'm aware of the requirement to isolate the system from the mains if there is a power outage. I'm not sure quite how my existing panels/ Inverter would interact with another inverter and batteries.

Victron have an 'app' that runs on a Victron Multiplus inverter/charger called ESS (Energy Storage System). There is a lot of documentation on their website for this. There are various configurations, some of which play nicely with an existing grid-tied inverter.

The Multiplus can work with any type of inverter and battery, but some particular brands have partnered with Victron to allow exchange of data and control using wiring or Bluetooth data comms. This allows much better monitoring and control, for example when to divert solar to batteries or send to the grid.

 

[Raul]

If the op wants power in a outage, then victron ESS assistant will not help him. If you load the assistant also needs country code to run on ESS. That means no stand alone.

 

[Howard B]

Our installer connected a few circuits to a separate consumer unit fed direct from the invertor/ batteries. Provides power to the boiler, fridge / freezer &a few sockets in the kitchen diner living area in the event ofa grid cut.
We have 16.4kw of battery storage coupled to 4kw of solar (due to add another 1.5kw shortly.

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[mikebeaches]

Our installer connected a few circuits to a separate consumer unit fed direct from the invertor/ batteries. Provides power to the boiler, fridge / freezer &a few sockets in the kitchen diner living area in the event ofa grid cut.
We have 16.4kw of battery storage coupled to 4kw of solar (due to add another 1.5kw shortly.

We had our installer arrange a double socket which will provide 230-volt solar / battery power in the event of an outage on the grid. Thus enabling us to run central heating pump, freezer, internet/wi-fi etc.

 

[Raul]

We had our installer arrange a double socket which will provide 230-volt solar / battery power in the event of an outage on the grid. Thus enabling us to run central heating pump, freezer, internet/wi-fi etc.

Only certain inverters has that feature, a secure power outlet at reduced power when grid down. Not all inverters come with this feature, you pay for it, and is limited by the sun in that moment, no buffer.

 

[mikebeaches]

Only certain inverters has that feature, a secure power outlet at reduced power when grid down. Not all inverters come with this feature, you pay for it, and is limited by the sun in that moment, no buffer.

Yes, I believe our Growatt smart hybrid inverter has the facility - we paid an extra £450 to have a supply available in the event of a grid outage.

You mention, 'limited by the sun in that moment', but our set-up is designed to bring the battery into play for emergency power.

 

[rod_vw]

Raul may I intrude and ask a question (or two).

We have a 3.75kW PV array running into a Fronius grid-tie inverter which has been in service for just over nine years. Thus we are receiving about 25p per kWhr FIT. We are almost perfectly south facing and up until these recent price hikes the FIT has been covering ALL our energy bills. The FIT is paid by British Gas who are quite quick with payment unlike some!

My questions are.

1. Is there any advantage in installing a battery pack which I assume will involve a new inverter? Currently we have no intention to go electric for a car.
   
   
2. If we were to add a battery pack is it installable in the loft adjacent to the inverter?
   
   
3. How would installing a battery pack affect the FIT agreement? i.e. do we still get paid for all we generate even if we use the battery stored capacity when there is no output from the PV panels. I ask this as BG always ask if there have been any modifications to the system when I send in a FIT meter reading.

Sorry for all the questions.

 

[Raul]

Yes, I believe our Growatt smart hybrid inverter has the facility - we paid an extra £450 to have a supply available in the event of a grid outage.

You mention, 'limited by the sun in that moment', but our set-up is designed to bring the battery into play for emergency power.

Sorry I missed the battery, the reason I did missed it, is some inverter do have secure power outlet without battery, like sunny boy. Assumed you had one of these, then you edited and I seen it,

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[Raul]

Raul may I intrude and ask a question (or two).

We have a 3.75kW PV array running into a Fronius grid-tie inverter which has been in service for just over nine years. Thus we are receiving about 25p per kWhr FIT. We are almost perfectly south facing and up until these recent price hikes the FIT has been covering ALL our energy bills. The FIT is paid by British Gas who are quite quick with payment unlike some!

My questions are.

1. Is there any advantage in installing a battery pack which I assume will involve a new inverter? Currently we have no intention to go electric for a car.
   
   
2. If we were to add a battery pack is it installable in the loft adjacent to the inverter?
   
   
3. How would installing a battery pack affect the FIT agreement? i.e. do we still get paid for all we generate even if we use the battery stored capacity when there is no output from the PV panels. I ask this as BG always ask if there have been any modifications to the system when I send in a FIT meter reading.

Sorry for all the questions.

Hi Rod,
The battery over fit tarif in your case, will gain you 5p per kWh. Since you get 25p it’s not to be sniffed at.
Battery in the loft it’s doable with one caveat: heat ventilation and frost protection. It’s not the ideal place even for inverters but manageable.
Fit and battery is not a issue, as long as you don’t feed from battery when grid is down, that means accredited hybrid inverter alongside to manage that.

 

[rod_vw]

Hi Rod,
The battery over fit tarif in your case, will gain you 5p per kWh. Since you get 25p it’s not to be sniffed at.
Battery in the loft it’s doable with one caveat: heat ventilation and frost protection. It’s not the ideal place even for inverters but manageable.
Fit and battery is not a issue, as long as you don’t feed from battery when grid is down, that means accredited hybrid inverter alongside to manage that.

Hi Raul,

What's the deal with the 5p, Is it government backed and guaranteed for a period like the original FIT and is it similarly index linked?

Thanks, Rod

 

[Raul]

Hi Raul,

What's the deal with the 5p, Is it government backed and guaranteed for a period like the original FIT and is it similarly index linked?

Thanks, Rod

Oh no, you buy with 30p you sell with 25p, if it was to store it you would not get the 25p. Any you buy at 30p off sets from your stored. Hope that makes sense.

 

[DandG5515]

Oh no, you buy with 30p you sell with 25p, if it was to store it you would not get the 25p. Any you buy at 30p off sets from your stored. Hope that makes sense.

Just a bit confused by this, my system is about 1 year newer and gives about 17p / unit for what is produced, but still referred to FIT irrespective of using it or export. Currently I have no way of measuring how much I export or would be able to save by storing it. I would of though you would want to have all the 25p/ unit for produced plus the value of 30p for what you would export.

 

[Raul]

This is getting confusing now, each you have diferent deal to fit tarif, and different price to buy back.
You should look at your inverter gives data daily production and yearly. Also some have a app where you can put the value of kwh in to calculate the cost save.
Also, you should have a generation meter, that gives total production reading, but you can take a note each day to calculate.

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[jongood]

Just a bit confused by this, my system is about 1 year newer and gives about 17p / unit for what is produced, but still referred to FIT irrespective of using it or export. Currently I have no way of measuring how much I export or would be able to save by storing it. I would of though you would want to have all the 25p/ unit for produced plus the value of 30p for what you would export.

The way ours works is that we are deemed to have exported a certain percentage (50 I think) and paid the export element on that. We could have chosen to fit an export meter but as we are 100% electric would probably be worse off.

 

[stevewagner]

The generation meter is fitted in line between the inverter and the consumer unit. Therefore you will always receive the total generated income regardless of what installed downstream

 

[DandG5515]

Am I wong in thinking I could have a storage system fitted between the generated meter and the supply meter?

 

[autorouter]

Am I wong in thinking I could have a storage system fitted between the generated meter and the supply meter?

That's what a lot of people do, it's a good idea. Especially if you're out at work all day when the sun is shining, and need electric power in the mornings and evenings when there's less/no sun.

 

[Revolvor]

Some advice please.

I already have 3kW of Solar on my house and am considering having battery storage installed.

We currently generate about 3300kW per annum, which almost exactly matches our consumption from the grid.

There seems to be shortage of installers (and batteries) so I was wondering if it would be possible to install my own system, and just get the final connections and certification done by an electrician.

I was thinking along the lines of a large Victron Multplus charger/ inverter (or equivalent) and a large number of Lithium batteries.

Following on from my Original Post, I have done quite a bit of research and believe there is a cheaper solution than a Growatt or Tesla type storage.

The attached schematic shows what I think would work. It includes (with suitable programming) :

1. Battery Storage, charged by Solar or Mains, or Generator
2. Solar production can still take place during a power cut. (For self consumption)
3. UPS for Protected loads, with additional circuits powered by Generator
4. Use Battery Power at night - Limited to Lights, Sockets and Central Heating

The schematic is just a Draft, and does not include Fuses etc which would be required.

I have also attached The Multiplus II Manual, plus a document on self consumption.

I have some questions though, that Raul or others may be able to help me with.

My intention was to go with the Multiplus II 3000 or 5000. I want to be able to supply 500W for 12 hours2kW for brief periods, from the batteries. I had originally thought of using FLA batteries, but now think that LiFePO4 would make more sense. How many batteries would I need? I had thought that 3x 200Ah would be sufficient, but would need 4x to achieve 48 volts. Is there much advantage in running it at 48 volts?

After I've got it clear that it is achievable, I will contact a local company for advice and a quote.

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[autorouter]

Solar production can still take place during a power cut. (For self consumption)

Your solar inverter is 'grid-tied', and takes its reference voltage and synchronisation from the incoming grid, even when it is exporting power to the grid. Most grid-tied inverters stop producing when the incoming mains fails, because they have no reference voltage to synchronise with. Difficult to believe, but it's true. If this is a high priority, you have further work to do.

The Victron website discusses this, they have an 'app' for a controller, called ESS (Energy Storage System). The controller is similar to the remote panel, but with a lot more capabilities. There are 3 different controllers available: Venus GX, Colour Control GX and Cerbo GX. They all run the same software. For true geeks they provide a version of the software that can run on a Raspberry Pi.

Search for ESS on the Victron website, there's various documents about it.

The Multiplus can generate its own voltage waveform, and can synchronise with the incoming mains as well. So it has the potential to keep going when the grid fails, in the right setup.

 

[cbrookson]

Not sure if it helps but here is a write up of my system using Victron and Pylontech. The SMA Sunny Boy is capable of working with the Victron when islanded (disconnected from the main grid).

Looking like this today:

Cheers

 

[Revolvor]

Not sure if it helps but here is a write up of my system using Victron and Pylontech. The SMA Sunny Boy is capable of working with the Victron when islanded (disconnected from the main grid).

Looking like this today:

View attachment 657522

Cheers

Thank you - an interesting article. I just wish I had got something installed before prices and lead-times went crazy.

 

[Puddleduck]

We had a storage battery installed last October. We have a 4kw of panels on the roof.

I was skeptical about the battery and pay back as when it was installed I thought 8 or 9 year pay back but it was a good move given the massive price hikes. I usually pay more in standing charge than what we use.

We get the original FIT tariff and are now £8K in profit.

 

[Revolvor]

I've just re-read this whole thread, and realise that both Raul and autorouter have already answered most of the questions I've posed in my latest post. I'm sorry - I must pay more attention!

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