dumb charging/solar panels question

06 Aug.,2024

 

dumb charging/solar panels question

I agree, this is a good way of approaching the question. One minor nit, though - the first bullet is unnecessary. The second bullet includes the charging losses (it is measured "wall-to-wheels"). So your final calculation has double-counted those losses. This should make sense if you think about it. The car is rated at 110 miles on 28.9kWh usable, yet it requires 31kWh to drive 100 miles (or 34.1kWh to drive 110 miles). The difference is the charging losses (28.9/34.1 = 84.6%). Note, however, that the 4.2 mi/kWh you get does NOT include those loses since the car does not count them. It is only battery-to-wheels that the car measures.

Bottom line, assuming the rest of your numbers are correct (I didn't double-check), it's actually 3.23 mi/kWh * kWh = 5,168 miles.

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Question about Solar + battery + grid

I feel your confusion - I had much of this 'lack of understanding in my gut' when I started my off-grid system. I'm off-grid and you want a hybrid system... but I can offer some 'laymen' level comments.

Electricity can flow simultaneously even when controlled by separate entities. For example,
- A charger checks the battery voltage and based on that - follows its internal wiring/settings... and will push max power till it nears top voltage and then less and less till the battery is charged.
- An inverter pulls electricity to create AC to power things. The inverter has its own operating range of min/max voltage and max power and will pull from the battery to meet the load demand.

These 2 things happen independently and simultaneously over a shared wires physically connected a battery! Electricity will go 'on the wire' from the charger and 'come off the wire' to the inverter with the battery operating as a buffer. In/out changes happed as fast as electrons can swizzle around - e.g. the speed of light basically. Electrons are really cool/easy in this regard - they simply flow to the demand as they are allowed.

In the same way, hybrid units can take in grid power + PV power... monitoring each one - and run a charger (power to charge the battery) and an inverter (power to loads) all simultaneously. It is sophisticated electronics - but nothing 'mysterious' - and the demand is high enough today that there are a good range of affordable products.

The difficulty is in picking the exact combination of features and matching operating parameters to meet your needs. For example, every unit that has PV input has a voltage range and a max power. This means the panels need to be hooked up to operate within the specs of the unit you purchase. Units typically settle on nominal battery voltages - such as 24v or 48v. On the AC side, the US is 240v/120v split-phase and elsewhere is 3 phase. When you hook to the grid - the key question is will you push power BACK to the grid... in which case you'll need permissions from power company and they may limit your equipment choices.

You could help get good responses on this forum by working up details. For example - you made a start with detail but folks will need a bit more to provide any specific equipment suggestions....

>I am in the stage of building a 48 Volt lithium battery using cells.
How many cells are you planning to use - 14s? - etc. This will lead to a specific battery 'Killowatt Hours' capability.

>We are looking at solar panels with micro inverters (meaning 230V from the roof)
OK we have 230v (good). How many panels (e.g. total 'Killowatt' capability) are you thinking?

>And I am connected to the grid.
Grid into your home only - or are you planning to also push/sell power back into the grid?

What kind/size of things do you plan to power? - e.g. lighting?, refrigerator?. power-tools?, cooktop?, AC?, electric car charging? .. The idea here is to arrive at a planned max "Killowatt' capability.

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