Solar / Battery Storage considerations

I don’t get a daily figure, but since installation, I have averaged 3.55kWh a day. I don’t think that is to do with which diverter model you choose, as I suspect they all do the same thing, but I suspect that I do put extra effort into squeezing more out of it. Being retired helps, but possibly the main thing is that when the water is above 65, I unplug the immersion and plug in an electric convection heater, and that way I get a lot of free heat. Now this trick I found on a forum, and I cannot recommend it to anyone, and is probably not recommended by the diverter manufacturer, however all you are doing is replacing one resistive element with another. To do this you must make sure that the convection heater is the absolute basic model, without any LCD screens, or timers, i.e. the ones that cost about £20, as they just consist of a an element/thermostat/switch/neon light and no more.

OK, scratch that warning, it looks like the model I have does allow heaters to be used

Apollo GEM can divert surplus generated PV or wind power which would have been exported to the grid to produce hot water, run heaters, power a battery charger or any other appliance. It has two outputs, allowing two heaters or other appliances to be connected to the system

I think for most households the larger battery size would be the best option.
We are having solar panels installed at present but not a battery, I have investigated batteries thoroughly but the economic case cant be made in the Australian market, the capital cost is too great to deliver a payback within 10 years, and the reliability of batteries is also a concern from the many reviews I have read.
Ideally we would like to install a battery, circa 12KW, for the 3 sometimes 4 people in the home, and primarily fill it during off peak times to use in peak hours.

Another factor is we want to operate our solar panels for a few months to see how much power they actually do generate, rather than rely on the installers forecasts, and we also want to see how good or bad we are at using it rather than exporting it to the grid.

In our case we do want a battery and won’t just base our decision on the economics of it, but will wait a year to see how our panels perform and how batteries might advance in that time.

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I think the way they calculate how much energy is produced by the panels can be quite accurate these days. In my case they underestimated the generation by 9%.

Batteries however are a different story, because it depends on so many more variables, and I think getting the panels first does make sense. Although I would still say the solar diverters to immersion heaters are a no-brainer

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I have 17 panels fitted on the roof, an i-Boost to redirect surplus power to the hot water tank and a couple of batteries. During the summer I am finding that the system does not use mains electricity from about 7 am to 9pm.

However given my age the investment in all the hardware is not sensible but it does give me a good sense of satisfaction to be able to run heavy duty devices when I want and not when the power cost is low. The FIT payment has now paid for the initial installation costs and the savings in power usage from the mains gives an invisible but ongoing saving.


I thought that too-and was expecting a high degree of correlation from the companies I approached - after all the sun is the sun, shade on the panels can be plotted and there is plenty of software around to analyse it.
I received a range from 22kwh per day averaged across the year through to 29kwh on average per day for similar sized 8.8KW systems - which I found surprising and somewhat confusing to my analysis of prices

My daily average is about 12kWh for a 4.8kW system, so that scales up similarly to your figures.
As you see from attached, this day was sunny all day with no cloud, and that reached 23kWh - Perfect Sunny Day which probably helped to power a few houses in my street.

Has anyone mentioned whether it’s safe to have a huge Lithium battery in your house?

I guess no different to having an EV or car full of Petrol in your integral garage


It depends.

There have been incidents, but there are also incidents with gas leaks etc.

The battery technology is quite mature having been used first in phones/laptops then cars. There is a risk and that’s dependent on how the batteries were constructed; before I retired one of my ‘hats’ was being responsible for ‘QA’ of a mobile phone brand that had sold many tens of millions of phones and I had audit teams in China looking over the battery production plants (I’ve visited a few myself).

We had the occasional failure and we generally understood what had gone wrong and how to avoid it. Often it was due to poor material handling causing lumps in the ‘slurry’ that coated anode and cathode punching through the separator, causing a short on charging (when the cell swells), other times it was poor handling of the rolls of aluminium/copper causing the edges to have burrs which cut through the separator with the same result.

I’d also been involved with the ‘Note4’ incidents tracking what went on and understanding the cause and how to avoid repetition.

I’m pretty comfortable with the choice I’ve made but I wouldn’t look at the bottom of the market .
I did check where the cells were made and I knew the manufacturer (who had mostly moved to automobile use). I also (planned to) situate the battery where if the worst came to the worst there’s unlikely to be anyone nearby…

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Just had a site visit and quote for adding solar panels to our house. They are suggesting 13 panels to start with. which can be extended later. They are:

“4.9kW System - 13 x 380W Sun Power P3 Solar Panels w/ Enphase iQ7A 349VA Micro Inverters”.

About $15k all up and running.

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Mike unless you have deliberately chosen to limit the system to 4.9KW, I wonder why they would suggest extending it later- would surely be more economical to install it all at once.
Markets will be different in NZ from Aus - but seems a high price for 4.9KW

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It’s good to see that panels have now gone up to 380W. My 3 year old ones are 300, and I think they had only recently gone up from 250W. If you think you may need more in the future, it’s worth asking what the cost is now, especially if you are going EV. Also you need to check what your Inverter will support, as if its only 4.9, then you would be changing a lot more to expand.

I think in the UK there is a limit on what you can have before you need special permission from the local electricity company - 5 or 6 rings a bell?

More like 3.6kW


Also some manufacturers now producing 415W and 440W panels - I think the overall panel dimensions are consistent with lower output panels - certainly helps get more power in the same area.

Still surprised that LG pulled out of the solar market though

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He basically said they recommend starting with the best configuration of panels for the sire for a base level of power generation. As they are micro inverters, you can just add extra panels on later at a similar cost per panel. The price seems, but that is the NZ market rate. Building materials here range from expensive to very expensive to unaffordable unfortunately. The panels are from the US and have very long warranties, including for coastal areas, where we live.

It might be a bit of them trying not to go over board budget wise, as we are looking at a couple of heat pumps too.

Here is the roof / panel plan, north is directly up the page. The next area that could be done is the rear roof, which is flat and would have slightly tilted panels. I’d be interested in your thoughts. We can afford to add more, as the retirement investments are going nowhere and it seems better to divert some of that into this project whilst I’m still working part time?

These are micro inverters, each panel has its own inverter, so you can just add as many as you want. The price includes all the power meter and electric company requirements. Fortunately we have an old single phase supply that apparently makes things easier.

That’s interesting, not something I’d heard of. So presumably each inverter spits out AC current, then they are joined somehow before going back into your Consumer Unit. How do you monitor the output? Do they all go into some sort of intelligent WiFi enabled junction box, in which case you would need spare inputs for further panels?

(Sorry, I realise I am not helping, just interested)

Do you get a lot of birds around you? I’d imagine you would want a good gradient to keep them cleaned by rain and not collect dirt.

Did you ask about Solar Excess Power Diverters? Especially useful if you don’t go for batteries? Plus payback in a year to two.

Mike you have great roof space for solar and could fit a much larger sized system on their if you needed, using north, east and west facing roof space.
I would suggest the starting point is your daily consumption of electricity, then how much of that you use or could use during daylight hours and then have a system sized to suit that.
We did that to determine we needed around a 9-10 Kw system and also as you are doing to install a heat pump for hot water.
Our aim was to send as little as possible of any generation back to the grid - as only receive around 8c for it. Three phase supply has a greater capacity than single phase supply so would send more back to the grid per hour.
From looking at your roof surrounds you dont seem to have any major issues with shading of the panels from large trees or nearby properties- these are the circumstances when micro inverters are said by some to give improved output. I would be surprised if micro inverters were the best cost option for you, as if there is shading over parts of the area where the panels are proposed then I would simply put some panels on the east facing roof.
In terms of cost single inverter, optimisers, micro inverters in increasing order, dependent on how much power you want to generate I would think a 6-7kw system with a single inverter would be more cost effective.
Any installer should be able to provide an estimate with their quote of output from the system per day ( to compare against your electricity usage) and a shade plan.
If you want to limit the number of panels on the roof but still need a larger system- then look at 415w or 440w panels.
Im not an expert but the above is based on the research and discussions with installers that I have done over the past couple of months.
If anyone is proposing optimisers or micro inverters - I would question that quite firmly given shade doesn’t seem to be an issue for you

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yes micro inverters convert the DC to AC on each panel- the theory being that if some panels are in shade then the remainder of the panels will still generate power as they are not connected in a string- that is each panel operates independently and connects into your supply. You can then monitor the output of each panel via an app.
Evidence varies to say that micro inverters produce 15-20% more output than a string inverter - but they are more expensive - and offer little benefit for unshaded roofs. I would venture to say if you have a large roof space - then more panels or higher rated panels is more cost effective than micro inverters.
Some are also nervous of having AC running around the roof - due to increased fire risk