Microgrid Power

Strategy

This all looks marvellous, but I have no time to wade through your experiences.  Give me a strategy now! Sure - go here .

The Journey

This is the story of our journey with a home level microgrid.

We have provided the information on these pages to assist friends and family who may be considering using renewable energy.  While making suggestions on what you should be considering, we also include the details of what we have done, the mistakes we have made along the way and useful things we have discovered.

As is often the case, we started out wanting a solution to a particular problem and the system has evolved from there.  We learned many lessons along the way and we wanted to share our experience to assist anyone else who might be considering ways to mitigate against the problems caused by load shedding, reducing their reliance on an unreliable power grid or trying to reduce their monthly energy expenses.

We started off with a simple system so as to not have the irritation of load shedding.  We went with a normal hybrid (either ac or DC supply, but not both simultaneously) and some batteries.  So that gave us load shedding backup for about R40K, but it meant that we had an always-on device (the inverter) that consumes about 100 watts per hour and we were recharging the batteries from the grid at grid rates.  We also had the recharge cost of the batteries (more about that later), so although it was capital inexpensive, it was expensive to run.  Our electricity consumption from the grid increased - in our case by about 20%.  I also at that point decided not to go with LiFe batteries as I worked on the assumption that I would use the Gel batteries for 2 years and then move to better batteries once that technology had matured further. [System: 2 x Growatt 5kW inverters with 9600Wh of AGM batteries] [Grid usage ~25kWh per day]

When Covid-19 hit we needed to have a more reliable system for 2 reasons.  Firstly my daughter was a university student at that stage and Internet access and having her PC and laptop operational became critical.  Secondly, my job is IT-based and we had to develop and support some new systems in a matter of days.  So I also needed reliable power to be able to work from home.  At this point we added in some solar panels to be able to run on solar whenever possible and to try and bring the running costs of the system down. [System: 2 x Growatt 5kW inverters with 9600Wh of AGM batteries with 18 x 330Wp = ~6kWp solar panels] [Grid usage ~20kWh per day]

The big change was when my employer removed my pension guarantee and our focus changed to radically reducing our running costs in the future (I am older than I look and retirement is not far off) by making a big capital outlay now.  We made the switch to a blended parity hybrid inverter.  This means that the inverter uses every little bit of solar power generated by the panels (more about solar panels and their (in)efficiency and different inverters later).  We also made the change to Lithium Ferrophosphate batteries that give exceptional performance and recharge value over their lifecycle (again, more detail later). [System: 1 x Sunsynk 8kW inverter with 3 x 3500Wh LiFePO4 batteries with the 18 x 330Wp = ~6kWp solar panels] [Grid usage ~0.2kWh per day]

We moved the previous system (1 inverter and batteries) to my Mom-in-Law's cottage to do the load shedding mitigation as we had done originally - so the system was reused and our changes and upgrades have not come at the expense of having to discard anything.

Along the way there were other reasons for improved power security.  We have a whole house filtered rainwater system (because we have an unreliable municipal water supply), as well as a greywater system for recycling our water and both of these require a reliable power system to ensure the pumps can operate when they need to.

Mindset

The mindset is around deciding if you want to make changes to the way you live and take the opportunity to be more energy efficient or if you just want to put in a system that will meet your needs as they currently are.  The way to get the best bang for buck system is to reduce your overall power needs and also to try and eliminate any major peaks - you need to try and smooth out the usage so as to minimise deviation from the average.  Otherwise you end up having to put in enough solar panels and batteries to cover the peak that then sit around unused the rest of the time.  If money is no object you can go this route, but if you are a mere mortal you probably need to scale the system to fit a budget.

One of the quickest and easiest options is to change all your lighting to LED bulbs.  

You also need to consider your geyser - it is possibly the single biggest consumer of power in any household.  We replaced our 3kW element with a 1.5kW PTC element.  This results in the geyser taking a little longer to heat from cold, but can easily be heated from the power supplied from the solar panels.  Another option is to put in a stand alone solar geyser that is not coupled to your main solar system as well.  This could also result in you being able to purchase a lower capacity inverter.  As the inverters get more expensive as they increase in power rating, getting the rating correct can yield a saving on the initial capital outlay.

Also consider moving to gas for cooking in some instances.  Of course you have to pay for gas, so it is more expensive than using the solar output to power your cooking, but you need to look at the various combinations of devices that are needed and mix and match.  We tend to use the solar to power the microwaves for cooking some parts of the meal and then using gas for other parts of the meal where we would otherwise have to use grid power.

If it fits into your lifestyle, having your main meal at lunchtime and then a lighter meal at supper time can place your main cooking time during the peak solar period (more about how solar changes during the day in Solar).

The final mindset consideration is the use of a generator.  I am not a great fan of generators - I consider them to be noisy antisocial polluters, especially in a residential neighbourhood.  However, one has to be pragmatic.  You need to decide on the maximum length of time you can go without grid, including if you want to go off-grid completely.  We are very close to off-grid (most days it is just the 10W trickle feed into the inverter coming off the grid supply).    If I wanted to be completely off-grid without a generator, I would need to ensure I had sufficient batteries.  Let's say I wanted to be able to go a full 24 hours with no solar and battery providing all the power - I would probably need 5 batteries @ R20K per battery - so a nice round R100K for the day.  And for every day I wanted to be able to go without grid or solar, I would need more batteries @ R100K per day.  So if you want to be absolutely sure that you will always have power without a grid connection and able to withstand all the days without sunshine to power anything or replenish the batteries, you need to look at the absolute maximum number of days you need to cover.  If you chose 5, that might not be enough and you are now in it for R 500K of batteries.  And then you probably need more solar panels for when you do get sun again to charge them up.  And an inverter capable of handling what would be a considerable amount of energy flowing through it.  On the other hand, a 7kW to 10kW generator will cost about R10K to R20K depending on features (of course you will have to pay for fuel).  So I have gone with having enough battery for about 12 hours and an inverter that can take a generator input.  If I ever feel that we are getting into a situation where we are getting day-long power outages without the chance of solar to recharge, then I will rather buy a generator and use that to recharge.  It just does not make sense to me to sit on many hundreds of thousands of rands worth of batteries that are then just in case you need them in an extreme case.

Inverters

The inverter is a crucial part of the system - it is what links all the other systems together and ensures that they each perform in the most optimal way.  It is the heart of the microgrid.

We will go into some depth about inverters in a separate section, but I recommend getting a fully featured Parity Hybrid that can blend all the different energy sources.  The Sunsynk Parity Hybrid inverter that we use is able to maximise every watt of available solar and then blend in either battery or grid if demand exceeds the solar supply.

Storage

The simplest storage method for a home microgrid is battery based.

Choosing the correct battery type and then sizing it correctly is critical for using the system effectively and efficiently.

You will need to determine how much energy (measured in kWh)  you need to store in the battery as well as the maximum power that the battery can deliver (in kW).  This is done by firstly calculating what devices in your home are possibly all going to be requiring power at the same time during an outage and the sum of those requirements will give the maximum power that will be needed.  You also need to calculate the average power needed over an hour.  As an example, in a simple case you might want to keep on some lights that draw a total of 50W, your Internet router that draws 10W of power and then you might want to boil a kettle that requires 1800W of power.  Therefore your peak power requirement would be 50+10+1800=1860.  The kettle may only be on for 10 minutes while the lights and Internet router need to be on the whole time, so the power requirement for one hour would be 50+10+(1800/6)=360W.   This gives a maximum or peak power requirement of 1.86kW and an energy requirement of 0.36kWh.

More on Energy Storage 

Generators

A necessary evil if you want to go fully off-grid is probably the best way I can describe my feelings about generators.  They are typically noisy polluters of the environment that are costly to run.  At the moment having a grid connection satisfies the requirement for another power in addition to solar.  If there are any changes to the costs of being grid-tied in the future, we may need to look at adding in a generator.

If you do need to add one to your microgrid mix, you should probably look to a system that is as quiet and as fuel efficient as possible.

I will deal with generators in a different section later as this resource builds up, however, my current leaning is to a fairly small generator that will not carry the full load, but will be used to replenish the battery storage as that gets low.

At the moment I am leaning towards this little beauty: ecoflow smart generator 

The End Goal

Finally, what will my system ultimately be?

This is what we think the final system that will run both the house and the cottage will be.  It will be a microgrid with a single connection to the municipal grid and a single generator for long-term emergency power.  The house and the cottage will each have an inverter, but they will be connected to the same microgrid to allow them to both share outside resources as well as share their own resources with each other.  But watch this space - we may make some changes as we live and learn with what we currently have.

1 x 20A municipal grid connection on a bi-directional prepaid meter [microgrid]

1 x 1.8kW petrol generator (if remaining grid-tied becomes not cost effective) [microgrid]

1 x Sunsynk 8kW blended parity hybrid inverter [house]

4 x Pylontech US3000C 3.5kWh batteries (13.3kWh at 95% DoD) [house]

24 x 330Wp solar panels (~8kWp) [house]

1 x Sunsynk 5kW blended parity hybrid inverter [cottage]

2 x Pylontech US3000C 3.5kWh batteries (6.6kWh at 95% DoD) [cottage]

8 x 500Wp solar panels (~4kWp) [cottage]

Acknowledgements

We certainly could not have achieved what we have without all the advice we have received along the way.  Many thanks to everyone who has assisted, offered an opinion or shared their experiences.

Particular thanks to Edward Everton of East Cape Electrical.  If you need someone to advise you and then supply and install the system, Ed is certainly worth talking to.  If you are in Grahamstown or the wider Makana area and want to have a system installed, I highly recommend contacting Ed.

Disclaimer

I am an independent DIY enthusiast.  All items discussed and reviewed have been purchased by our family.  Any information should be used as an input into your own design.  There are no warranties or guarantees applicable to any of this information.  Experiences and opinions expressed are done solely with the intent of sharing knowledge for others to use or discard as they see fit.