question

spanishflyer avatar image
spanishflyer asked

Need a battery backup for the night alone; thought of a single PYLONTECH 48V 2.4KWh

Hello friends

I currently have 37 panels feeding two 5.0 kW inverters with 4 MPPT total. Different position and size panels force me to have all strings covered. During the day I have between 60 to 80% of my power needs covered (on grid installation).

My problem comes once the sun goes, where I have nevertheless some consumption that I want to sort it out. The usage ranges from 250 to 500W on a constant basis, so I thought of getting a simple inverter/charger and one Pylontech 48V 2.4kWh, with no panel attachment; the battery would be charged during the day and if the Pylontech runs out of juice I would then allow the grid to take over.

What do you suggest I use as an inverter and how well do you think a single Pylontech will cope with that small consumption?

Best Regards,

SpanishFlyer

battery capacity
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2 Answers
tozz avatar image
tozz answered ·

I'll give you an idea of my installation. First of all you can see my VRM here:

https://vrm.victronenergy.com/installation/101152/dashboard

This setup consists of:

- 4x5 kWh MG batteries (thus, 20 kWh)

- MultiPlus-II 5kVA

- Cerbo GX

- MG BMS (compatible with Lynx BMS from Victron)

- 69 solar panels (375 Wp)

- Heatpump

- EV

- EM24 Ethernet meter

- Electric cooking


When doing nothing in particular my power consumption is around 350W when sleeping and about 500W during the day and about 800W during evening television watching.

Between April and October my EV can only charge from PV power, thus it won't draw any power from the grid. Additionally, in this period (April - October) my heatpump is turned off when PV power drops below 500W and goes back on when PV exceeds 500W.

Nevertheless, 10 kWh usually isn't enough to make it an entire night without grid usage. There are a couple of reasons for this:

- Dishwasher

- Some washing/drying

- Cooking when there are clouds around ~17:00.


When we have a perfect sunny day, my batteries are about 70% full in the morning. But on a cloudy day this drops to around 20%. On two consecutive cloudy my ESS is shutdown due to low battery. This is primarily because when my heat-pump turns on in the morning, it will consume about 15 to 20 kWh a day. When my PV only yields around 30 to 40 kWh that's not enough to fully charge the batteries because I consume about 10 kWh daily for generic power usage (lights, internet, standby appliances, coffeemaker, etc, etc).

So, with your ~300W idle consumption and the generic household appliances (dishwasher, tv, lights, etc).. I don't think 2,5 kWh will get you through the night. I could barely do it with 10 kWh and 69 solar panels.



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gherlt avatar image
gherlt answered ·

Your consumption is only 250/500W ?
No higher consumptions ?
If I understand correctly, you would have it grid connected during the day, charging battery, and once no PV is available, you use battery for whatever, but only 250/500W until it is empty.
I mean: 250W * 8h minimum are 2kwh. In Winter time the "night" will be more hours, and starting much earlier in the day.
Are you trying to overcome a few expensive tariff hours ?

I have a Quattro 48/5000, about 4.5 kwp solar on AC out, 8 units 2,4kwh Pylontech US2000 at home, all working as an island/off grid.
The base consumption goes from 400W to 250W in the night, when all are asleep, but we cook diner with a vitroceramic hob, that makes about 25000-3000W peak consumption, for 5 - 10 minutes.
In winter, in the morning the batteries are down to 62/65%, in summer to 70%-75%.

I tried to start with 2 units US2000 and failed. The batteries delivered the requested power (not the oven), but the voltage dropped so fast that "low voltage alarm" was very very common.
Then I bought 2 more units, after that in summer each each morning SOC came very close to 50%. Also, low voltage alarm still common once in a while. After installing 8 units, now all systems work and I can sleep well ;-)




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