In NZ, Victron have only 115W 12V panels available and the sizing calculator tells me that to have 1700W during Spring and Autumn I will need six of them, in two strings of three in series with an MPPT 100/20.
My power audit showed I use between 65 and 70 A per day (70 x 24V → 1680W) and the chart on the sizing calculator is shown in the screenshot.
Choice of panels comes down to what your personal preference is aesthetically / availability / price, as long as you get combination of panels to make voltage / amperage you require.
My opinion is to over panel , as mppt’s / settings will ensure max voltage/ charge amps are within required parameters.
Is the idea to have sufficient panels to run everything during the day so the batteries are not needed and any excess power is “shed” by the MPPT? In other words, if there were to be no usage after sunset, I would not need batteries at all?
Think you misunderstood.
Chances are You’ll never have enough panels to run anything you want during the day without grid and or batteries.
On a gloomy day you may only produce a few hundred watts as a peak, which isn’t enough to say power a kettle on it’s own, thats when a battery comes in to play.
Without knowing what your maximum peak power requirement is and knowing what your lowest PV productivity would be it is impossible to answer your question.
To give as an example of PV production day by day variable - atttached is my systems production for the last 30 days- single day peak is 23.5kwh and lowest is just over 2kwh.
Oh, there is much misunderstanding going on in my head… so thanks for this.
My power audit showed that I need about 70Ah per day, on a 24V system that is about 1700W. This power audit leaves out heavy electricity users like kettles, toasters, etc because I have gas for these.
I don’t have any panels / MPPT yet and I am trying to work out what to buy in terms of capacity. Then I can go looking to see what is actually available in NZ. Thanks for your help with this.
If I put “600” into the search box on the MPPT calculator and pick any 600W panel, the calculator only allows me 2 in series and 3 strings to suggest a 150/100 MPPT.
The screenshot shows the expected daily yield for a 24V system in NZ. If I only need 1700W what am I going to do with the 10-14 kWh this configuration will produce?
Well, this is a average over a month. For safety i’d go to 2-3 times of what you need, its not as if its getting overly expensive. And calculate the batteries on one week without sun.
My battery bank is 24V / 240Ah (4 x 12V 120Ah AGM batteries) and should give me about four days at 1700W per day (after one day I was at 25.3V, about 90%). I run it all through a 24V 3000 Multiplus II charger / inverter.
I do have a generator for emergencies and my fresh water capacity allows about a week away from a hose so once a week I need to find a fresh water source and being able to plug in at the same time could be useful.
All that to say that aiming for about 3kW yield per day makes sense. Thanks for your help.
You say 1700w, what do you mean by this?
W is a measurement of power / what something produces or uses.
Wh is measurement of if you like what something produces or uses over a given time.
Or putting it another way a kettle may have a w rating of 1500w and if this is on for 1hr it would use 1.5kwh.
You need to work out what kwh you need in a given day to work out what battery size is required, plus allow a healthy % over.
Then you can work out amount of pv panels, best look on https://pvwatts.nrel.gov/ or similar to see what panels may achieve throughout the year.
Ps it’s a balancing act of maximising how much you want to produce in the winter months, but this will be over producing in the summer months.
I have an electric air DC heater / Ac immersion water heater / air con unit to utilise as much excess power thoughout the year, but still could produce way more in summer if i could use it.
It all depends on your goals how much you do.
As long as the sun is cost-free overproduction doesn’t matter.
My installation gets my batteries filled every day of the year, i really don’t care if in the sommer my SoC of 100 is reached at 10am, main thing is that in the winter its done at 4 pm.
Ofc with some spare to fill the batteries after a couple of rainy days, but ofc i have a generator, the alternator of my rv also delivers 100a flat out.
My power audit came to 70Ah per day so I guess I meant 1700 Wh per day on 24V.
I have AGM batteries that give just under 6000W (24V / 240 Ah) so I know that I can run what I need for a couple of days without taking them below a safe SoC. If necessary, I simply don’t use certain things.
For the foreseeable future, the Winter months are not an issue because I leave the country for warmer climes… so the solar only has to keep the batteries topped-up. There will be no load on them for 5-6 months of the year.
so thanks for this.
