Modular 'home' smart renewable and grid connected controller.

Thread Starter

madtom1999

Joined Jun 9, 2019
2
My apologies if this is a repeat - I've tried searching but got no results.
My first job out of uni (1981-90) was a chip designer and one of my colleagues worked on a power device on a technology that would have allowed you to make a 72v 20A inverter amplifier suitable for an inverter for around $5. Given this was 30 odd years ago I'd like to think it would be cheaper and better now. I have been looking around to see if I could make a collection of circuits that would allow a modular 'home' power controller allowing you to:
Drive an expandable inverter from PV,Wind,Water etc - modules of various power can be added simply by connecting to a set of power and controller bus bars(?) as new generating devices are added, rather than having to replace the whole inverter.
A controller that drives the above, generating 50/60Hz with option for grid syncing and other smart options.
If the controller is based around something like a RaspberryPi Zero then it could have the capability to OCR 'smart' meters that are available in the UK to read the price allowing the controller to heat water/space/storage heaters when the price point falls to a certain point. intelligent charging control would not be beyond this either.
If could also measure flow to/from the grid to control water/space/storage heaters to use any excess power generated locally at reduced voltage to allow some heating of (say) water when the domestic generation excess is below the 3kw needed to power the immersion heater at full AC voltage, the voltage to that device (or devices) could be reduced to ensure only excess power is used. In the UK currently new PV installations have no feed in tariff and as a result the electricity companies get free power and some people I have spoken to would actually love to use or dump excess power than give it away for free!
I'd like to build a set of interconnectable open source circuits, software PC layouts etc with the aim in the long run of possibly crowd-sourcing the production of monolithic solutions for modules where applicable.
Its time to bring domestic renewables into the late 20th century!
 

mvas

Joined Jun 19, 2017
538
Does the price fluctuate randomly during the day or are there specific time periods of higher prices (Peak) vs lower prices (Off-Peak) ?

The are many Grid-Tie Inverters that have "Zero Grid Export" mode.
You would need to install C/T's at the Main Panel.

Also, some GTI's support a Battery Bank.
A Battery Bank allows appliances to shift their Time-Of-Use (TOU) from Peak Pricing periods, to Off-Peak periods.

In the USA, anything that connects to the Power Grid must be UL approved.
The testing to obtain UL & CE Certification is very expensive.
 

Thread Starter

madtom1999

Joined Jun 9, 2019
2
Price changes will, it seems, be random.
The main problem I have seen is inverters are not expandable. If I was to put up (say) 1Kw of PV and then add to it later I'd need install a complete new inverter, where all that is really required is the amplifier/transformer to cope with the extra power. We have a situation now where you tend to be locked in to your starter setup. I've got a 4KW PV setup and I cant add wind at all even if I wanted to even if I could restrict the power sent to the grid to 4KW - which is technically easy but seemingly a nightmare for the power company.
The rules in the UK are similar and even the document covering what is require for certification is expensive. I have reason to believe that much of what I'm hoping to achieve is well past drawing board stage but industry has no need to invest in the hardware at the moment - its a slow moving market and they would like to keep it like that. An open source/hardware approach can provide some lower cost technology in the meantime, and even edge towards getting laws changed - from what I saw over 30 years ago it should have been possible to make the silicon for transformerless inverter technology capable of safe* direct connection to the grid for less than $10 KW + controller costs.
*safe self destruction/disconnection if the case is well designed!
 

mvas

Joined Jun 19, 2017
538
The typical Solar String Inverter is not scalable.
As the Solar Power Watts increases, the size of the wire, the conduit, the circuit breakers and the disconnects switches all need to grow too - How?
When we back-feed Solar Power Watts into the Main Panel, we are severely limited on the amps.
To offset 100% of the power used by my entire home, I would need a "Line Tap" connection.

Enphase makes Micro-Inverters which is somewhat scalable, and they have an AC Battery Pack.
SMA has a Modular Line of products
SolarEdge has a transformer-less semi-scalable system, allowing up to 3 different sized Solar Strings to be added to one Inverter.
 
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