New UK user

Hi All

I currently have a 4kw solar system on the UK's old Feed-in-tariff plan. So the panels run through an inverter then to a production meter before going into my consumer unit. The UK government pays for me for electricity generated based on that generation meter. After that the electricity is free for me to use or export to the grid. Ihave had the system for 8 years and i've only recently started thinking of making more use of it. In the summer i'm generating and exporting lots of power then having to buy it back in the evening.

My first step in making more of the power was to build my own power diverter for my immersion heater. The off the shelf solutions seemed fairly pricey and i wanted a solution that gave me good date on what my solar system was doing. This led to me installing a Shelly EM to monitor import/export and solar production. I've hooked up a PWM voltage controller to my immersion heater and i control it with a Shelly uni based on the EM reading.

This got me thinking, could i not use the same system to divert excess power to batteries? It seems the answer is not so straightforward and i've seen a thread on here i would like to add to so will go from there, but thought i'd say hello here first. There is so much info about the batteries available so i'm thinking that's the easy bit. Getting a setup that will charge based on my requirements seems to be the challenge.

Ideally i'd like to go in 3 phases to build confidence:
Phase 1 would be about 5kwh just so that excess i generate in the summer days can be used in summer evenings.
Phase 2 would be about 10kwh so i can purchase off peak electricity during the night and supply my electicity needs during the winter days
Phase 3 (maybe over-reaching) is about 25kwh so that i would store enough off peak energy to run an air source heat pump instead of using a gas boiler

So that's me and why i'm here. Like i say i'll be posting in another thread or 2 but very happy to hear if anyone has similar requirements and how they achieved it.

Thanks

Welcome to the forum!

I don't have a specific solution for you as I'm 100% off-grid and not familiar with in/outs of hybrid... howerver... I'd like to be encouraging that I don't see why you can't succeed. And I'll be interested to follow what you do.

>....could i not use the same system to divert excess power to batteries?
Why not. Think of a battery as a "Charger -> Cells". A charger is just another 'appliance' that takes in power - but instead of running a light or a coffee maker or a stove it transfers that power to Cells. Once the cells are full.. the charger (basically) turns off.

Once the Cells are full - i can think of ways to use that power... I do this thru Automatic Transfer Switches (ATS) in my off-grid situation and you could too. You need a 'device' that can flip a relay based on the battery voltage and/or timing device (for night use if Cells are full) type of logic.

There may be some equipment that someone will point out that does all this. I recently deployed an MPP Solar / PIP that might be adapted here to achieve some of you're goals... but I'm sure this could be DIY'ed.

Let's see if you get some comments.

Welcome I have seen several posts over the years on doing what you want to do. and many people use tine of use energy shifting buy and store in when cheap, use it at peak times or even sell stored power back to the grid. OffGridInTheCity is a great resource. as are many others here.

later floyd

OffGridInTheCity said:

A charger is just another 'appliance' that takes in power - but instead of running a light or a coffee maker or a stove it transfers that power to Cells. Once the cells are full.. the charger (basically) turns off

Click to expand...

So turning things on and off depending on load is easy enough but modulating is what I don't understand. Pwm ac to a heater is perfect. Can I send pwm ac into a charger? Can I send pwm dc into a solar charge controller?

OffGridInTheCity said:

Once the Cells are full - i can think of ways to use that power

Click to expand...

How else would you use excess power? Once battery is charged and water is heated what else is there?

floydR said:

I have seen several posts over the years on doing what you want to do.

Click to expand...

Any chance you can point me to one please? I haven't been able to find exactly what I'm after.

Thanks both for the replies.

OffGridInTheCity's build thread as some ideas/solutions
daromer I believe has several videos detailing how he does things.
ajw22, Wolf, Redpacket any of the highly rated members are good sources to read.

Laer floyd

Hamalot said:

Can I send pwm ac into a charger?

Click to expand...

As I understand things... a PWM charge controller is just a less efficient form of an MPPT charge controller. So you have PV (solar panel) power going into a PWM Charge Controller? and the output of the PWM Charge Controller is AC? or DC? or both?

- If its DC (PWM Charge Controllers typically have settings / produce DC power to charge batteries) then you may be able to find the specs and build/buy a battery to match. This would be a bit more efficient than converting DC to AC and powering an AC charger....

- If its AC, such as 220v in UK? then you need a 220v battery charger to match the battery you build or buy. For example, here's a 14s (48v nominal) lithium ion battery charger @ 3amps - https://*******.co.uk/products/52v-lithium-ion-battery-charger-3-amps-uk-plug

Hamalot said:

How else would you use excess power? Once battery is charged and water is heated what else is there?

Click to expand...

I power most of my house (lights, appliances, heat pump/AC, etc...) thru several ATSs (automatic transfer switches). These have a grid input and a generator input. By default - the grid power flows thru, but when a generator fires up and it senses power on the generator input it will automatically switch to generator power. When the generator is turned off - it automatically switches back to grid power.

Now - substitute a battery -> inverter for generator and you can automatically consume stored energy in your battery. I do this by turning on my inverter at a certain voltage and then off at a low battery cut-off voltage. You can also do this by voltage + time-of-day.... so you could charge your battery during 1 part of the day and then consume that power at a different part of the day thru ATSs.

Here's an example of a simple 30a 'single phase' (single circuit) 120v AC (US) ATS as an example - https://www.amazon.com/Go-Power-TS-...+power+ats&qid=1618271002&s=automotive&sr=1-2
I'm not up on UK power but I'm sure you can find something similar for UK - either individual phases or perhaps a larger 3-phase unit.

@daromer (DIY Tech & Repairs and a staff member of this forum) and has some youtubes on ATSs... to help explain how they work. Here's an example:
In my case - I have a 240v@50a ATS -> 10 circuit Manual Transfer Switch wired into my main home panel so I can use the Manual Transfer Switch to select individual circuits to be powered by the ATS. The main panel provides 240v@50a to the grid input of the ATS and a 12,000w AIMS inverter provides 240v@50 to the generator side of the inverter. Here's a picture from my build thread (https://secondlifestorage.com/index.php?threads/offgridinthecity-build.8514/) :

Hamalot said:

Any chance you can point me to

Click to expand...

My system is US and off-grid and individual component DIY. These days they make UK / all-in-one 'boxes' that might even have all the features you need.

I offer the comments above to help you start asking the right questions - rather than as a 'ready to go' solution for your case.

There are several members of this forum from UK and/or all-in-one systems that might do more of what you want. If you don't get a response after a while - perhaps I can help you pin down the actual specs with some more back and forth.

Thanks both for spending time trying to help me here. I've read through the suggested threads but can't see anything that relates to my situation exactly. I'll do some more reading and come back