Lessons on Solar Power During A Cyclone

 

In this blog, I process the effectiveness of my residential solar power system during a cyclone. This is based upon the experience of Cyclone Gabrielle in February 2023, which was 4 months after the solar system was installed. 

I review the performance while the cyclone was overhead. To be clear, I didn’t lose mains power during the cyclone, just did some test runs.  

My main lessons were

•  Solar backup still means power rationing.
• Actual generation reduced to a trickle.
• A trickle was enough to get by on.
• More realistic expectations.
• Limited benefits but still meaningful.

I had some minor disappointment and surprises due to not understanding the technology limitations. I assign this to not having done a trial run before the cyclone. Various gaps/questions arose, which I have resolved through writing this article.

I imagine the lessons are common to the type of installation – grid tied without a wired-in house-battery (I am presuming the reader knows what all that means). During an outage, the mains board stops accepting solar power. Solar power must be diverted via the inverter to charge batteries. This diversion is a feature I had built-in as part of the purchase.

Before The Cyclone

My Installation

•  Solar Array rated up to a maximum of 5.8 kWh, grid-tied
• Hybrid inverter (the capacity for future house batteries)
• No wired-in house batteries
• The ability to charge batteries directly off the inverter.
• A range of batteries from AAA up to 1200 kWh bricks, plus chargers etc. Estimate about 3 kWh total storage capacity.

My typical household daily consumption was about 10 KWh.

The built-in limitations of my installation are that during a mains outage

• When the House mains board shuts down, so does the solar input. This is required by my electricity retailer.
• Appliances wired directly into the building will not get power e.g Hotwater cylinder
• Appliances that can be run off batteries, can be powered from the inverter.

This meant that if the mains power went out during the cyclone

• Some appliances would not be available do without e.g. Hotwater cylinder, electric stove
• My useable power is limited to what was stored in the batteries.
• Replacement power would be supplied at a trickle compared to normal summer volumes.

Preparation

My initial preparation consisted of

• Setting up the batteries and chargers run off the inverter.
• Realising I didn’t know how much my system would generate during a storm - so what was my ‘power budget’ going to be?
• Realising I still needed to decide which appliances would get that power. While I had sort of known some compromise would be needed, I hadn’t connected the dots in reality.

I ended up preparing based on the following principles

1. By default, I kept relying upon my existing preps e.g. BBQ for cooking and hot water.
2. Charging up all batteries and devices from the mains beforehand
3. If the mains cut out, using the batteries to run designated ‘critical’ appliances of
• Being able to run the freezer/fridge for an hour or two per day.
• Home office laptop – continue working 8 hours per day.
• Mobile phone (radio, internet, voice).
4. Keeping this going by alternating the charging of batteries and devices.

Lessons Learnt

Solar Backup Still Means Rationing

I had an unconscious expectation that ‘’solar backup means no further rationing or decisions needed’. While I had sort of known some compromise would be needed, I hadn’t connected the dots in reality. The ‘budget’ question forced that rationing. My net situation means I had, and would have to, ration my power. Accordingly, I had to work out

• What are my priority appliances.
• How to measure power remaining in batteries.
• How much power an appliance uses.
• How to calculate the run-time remaining in a battery for a given appliance.

Total Generation Reduced To A Trickle

Cyclone Gabrielle happened to NZ over 11 to 17 February 2023. Luckily for me, it was overhead from the 12^th – 14^th. From my systems log, the key points are

• Normal summer generation is between 2.5x to 4x daily consumption.
• Generation bottomed out at about 1/3rd of daily consumption.

A Trickle Was Enough To Get By On

My priority appliances need the following charge for 24 hours:

Appliance	Watt-Hours
Fridge- Freezer combination[	2460
Home office laptop	51
Mobile phone – 1 full recharge per 24 hours	1
Total	2,512 (2.5 kWh)

Source: All figures from respective manufacturers specs for 24 hours use.

Allowing for the inevitable wastage while charging the battery and drawing from it, I can still run the priority appliances. If I ran the fridge/freezer for the minimum, that could stretch the ‘power budget’ even further.

More Realistic Expectations

There was a degree of discovering things during an emergency, which is not ideal. If you have a solar system and not used it during an outage, then I suggest doing a practice run / exercise.

I am grateful to have a more realistic understanding of

•  What I can run in a bare minimum, and
• How things could play out next time, in identical circumstances. This is how I see it now:

	Before Outage	Mains Power Outage		Once Mains Back On
		During The Cyclone	Between Cyclone ending and Mains Power Restored
Household mains status	Both mains and solar available to house.	Switched off. Solar not being passed through to house.	Switched off. Solar not being passed through to house.	Return to ‘normal’.
Electricity Source	Solar plus mains	Solar only, via inverter to charge batteries directly.	Solar only, via inverter to charge batteries directly.
Total Electricity Available	As needed   Charge batteries up.	Daily Generation: Up to 3kWh   Storage depends upon number of chargers/batteries.	Generation: Up to normal as weather improves.   Storage - as per ‘during’.
Appliances Available	All household appliances.	Priority appliances only, running off the batteries.	Priority appliances first and then plug-in appliances. Still can’t use appliances wired into the mains. Actual use limited by the rate of battery recharging.

Limited Benefits But Still Meaningful

The benefits of my solar backup are confidence that

• I can keep working from home
• I can keep the food in the fridge/freezer safe
• I can keep my lines of contact & information going (radio/phone)
• For the duration of the outage. (Some battery-management needed).

Initially, I was disappointed that this was ‘all’ I got for the money involved. However, it’s still an improvement on before. It also illustrates to me the value I get from my mains connection.

From doing this review, I have a baseline for future spending decisions and I can already see that “the more batteries the better” isn’t automatically true for me.

Next Steps

From here, I’d like to

• Define what appliances I could run during a realistic worst-case scenario e.g. washing clothes once a week
• Understand if things would be different if the outage was in the dead of winter.
• Decide where to invest further in my system.
• Identify how to make the most of the benefits e.g. if I can rely upon the fridge being there, do I reduce my stock of non-perishable emergency food?

Wrapping Up

In a cyclone situation, my solar system/batteries provides enough power to maintain a couple of key appliances/areas, likely for an extended outage with conscious management. While a small proportion of my total uses, It’s a significant improvement over my previous situation.

The biggest ‘gap’ I experienced was not having done a trial run before the Cyclone, and having to work it all out after the solar power and electrical supplies shops were closed.