Planning a first time system - battery question

[syakoban]

Hi!

I've looked into DIY solar in the past, this time it looks like we're going to do it. Now we're interested in a grid tied rooftop system with battery backup. My understanding is that in this way, with batteries, when the grid is down we can still use the electricity the panels generate.

The part that's not clear to me though, is the generated electricity only for battery recharging or can we draw from it and power appliances at the same time, as the batteries charge? If so, does something regulate where the electricity goes or is it being dumped into the batteries as we draw from them? And if that's the case, if we're drawing as much as is going in without giving them a chance to top up, are we killing the life of the batteries?

Thanks guys!

 

[12VoltInstalls]

In the ‘simplest’ a gridtie battery system the panels charge the batteries and send power to the grid. With the grid down the batteries supply power to an inverter and that is fed as 120V to your home. Conceptually.

Most whole house systems actually use one or several components that will seamlessly work together and invisibly power the house.

if that's the case, if we're drawing as much as is going in without giving them a chance to top up, are we killing the life of the batteries?

You do want/need enough solar to supply the house for several days. This should exceed the battery capacity by enough to recharge the batteries as well as run the house simultaneously.

 

[syakoban]

Thanks 12VoltInstalls!

You do want/need enough solar to supply the house for several days. This should exceed the battery capacity by enough to recharge the batteries as well as run the house simultaneously.

That leads me to two more questions:

I won't be designing the system, but keeping an eye on whoever does. Are you saying that the panel array capacity should be what we need to run our house + battery charging capacity (+ a margin)?

To get up and running the least expensive way, we may have limited battery at first and add more later. So if we have just enough battery for overnight essentials, then the next daytime have enough panel electricity to power needs and recharge, that is allowable on a grid connected battery system? Any downside to this approach?

 

[12VoltInstalls]

Are you saying that the panel array capacity should be what we need to run our house + battery charging capacity (+ a margin)?

Basically, yes.

If you only make what you use the battery bank doesn’t recharge. The ‘margin’ is to accommodate either a cloudy day or two, or to assure uptime if the grid goes down.

With lithium, extended depletion time on the batteries is less critical than with lead acid batteries (lead acid battery lifetime is reduced under extended low voltage)

My understanding is that in this way, with batteries, when the grid is down we can still use the electricity the panels generate.

If you need the overnight power you need to be able to recharge the batteries but you have to make the watt hours the batteries need PLUS your daytime usage to net out at zero- at a minimum.