diy solar

diy solar

Running inverter with no solar panels, adding panels later

ABarbarian

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I have plans to build a new solar system with hybrid inverter to be used in a new house being built, but prior to the house being built I have no place to safely install solar panels.

I live in a location that experiences regular power cuts and am thinking of buying the batteries and inverter for the solar system now to use as an online UPS, then once the new house is complete, add the solar panels.

In the initial setup my plan is to simply hook inverter to grid and batteries, charge batteries from grid, run load off the batteries, I assume there is no problem with this, as long as the chosen inverter manages charging effectively?

A little concerned this is not the normal setup and might result in large power bills, my guess is some inverters will have settings that allow this, perhaps switching charging batteries from grid on and off depending on battery levels?
 
The settings can be set for this situation.
No problem at all. It will just act like it's always nighttime.
 
for standard AiO yes you can do this. For Growatt you can even set the options not to use the batteries UNLESS the grid goes down so as to not add needless cycles the batts.
 
Your power bill won't be any larger than if just running loads directly from grid.
Batteries (over their lifetime, if all available cycles used) will add $0.50/kWh to your cost of power. Possibly less if lower cost than premium name-brand batteries used.

Look for an inverter that can power loads from grid and charge batteries from grid at the same time. Also power loads from grid and add power from batteries, to keep current draw from grid within limits.
My Sunny Island, for instance, can be programmed for 15A max draw on AC input, if that's what's available. Or up to 56A max.
You can program it to only recharge batteries when low, but using grid while available would keep batteries floating (more important for lead-acid than for lithium.)

What you describe would serve as a UPS, maintaining power to AC loads whether grid (or generator) was available or not.

If you are going to use lithium batteries, consider a BMS and inverter which communicate, for optimum charge voltage/current so balancing of cells can take place.

With grid available, why do anything at all with batteries/inverters/PV prior to completion? Just plan your electrical panel setup for use with PV/battery, sizing to allow the breaker amperage rating you want and wired for backup of critical loads.
 
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With grid available, why do anything at all with batteries/inverters/PV prior to completion? Just plan your electrical panel setup for use with PV/battery, sizing to allow the breaker amperage rating you want and wired for backup of critical loads.
Thank you all for the replies, glad to hear it should not increase grid costs much.

To answer why: because the grid may not be available, we get regular power cuts, am powering a number of office computers and the power cuts can be costly because of unsaved work and lost worker hours for extended power failures.

I have two locations, my 9 year old system is in a rural location where in addition to the above problems computers used to fail quickly due to the bad grid power, lots of power cuts but also what seemed to be inconsistent power. I used to use individual UPS's for each computer but often they would not handle the switch, batteries would cease effectiveness after a matter of months, non-stop complications and cost replacing UPS's, those savings help off-set the solar's cost.

I setup the STECA EXTENDER XTM 4000-48 inverter and all those problems disappeared, the system was expensive at the time but we are still running on the original inverter and panels, wet lead acid batteries replaced once after 5 years, second set still running. Check out the terminals in the attached pic at the 5 year mark (I had them covered and was not aware I should watch them..)

Most of the time the grid is not connected to the inverter, not sure when I connect the grid whether it powers the inverters load directly or only charges the batteries AC>DC, which then pass back DC>AC to the load. Also not sure if it pumps out charge to the grid and grid supplied load when switched on...

Because I am so concerned about switching times in the new system I am planning on powering the load from battery all the time like my old system and only re-charge batteries from grid, rather than using grid and switching to battery when power cut, or "power loads from grid and add power from batteries". My planned configuration will spend more on batteries but ensure stable power and I guess also be offset by reduced power bills.

Side note: not keen on feeding into the grid, tricky regulations here for that..
 

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As you say, on-line UPS is the way to clean up AC power, if power quality has caused damage.
Most PV inverters don't normally do that, rather pass through grid power when present.

How many watts do you need? you could set up a battery or hybrid inverter which passes through power to normal house loads while keeping battery charged, and a second system which runs off the same batteries constantly.

This could be done with the Sunny Island I use. Either two or four 6kW battery inverters in a cluster for 120/240V split phase, with a battery shunt so it is aware of DC draw by second cluster. A second cluster of two or four inverters would draw battery power to keep your computers running, monitoring same shunt. The grid-connected cluster could accept 12kW (or 24kW) from grid, use that to charge batteries and power household loads. The second cluster could deliver up to 12kW (or 24kW) to sensitive loads, always inverting from batteries.

AC coupled PV could connect to either or both clusters. For the grid-connected cluster, either it is configured to backfeed the grid for net metering, or to disconnect from grid with PV production is excessive and connected when more power is needed (grid charge). The second cluster is always running as an off-grid system, and would slightly increase AC frequency to control PV production using frequency-watts.)

Following picture shows grid-connected cluster. Second cluster would share battery and a shunt.



"wet lead acid batteries replaced once after 5 years"

People report 15 to 20 years lifespan using forklift or Rolls Surette FLA batteries. These would be large banks, sized for about 3 days autonomy without PV production, so shallow cycled most nights. If deep cycled every day like in a typical forklift application, I think they have 5 year or so lifespan. Since you normally have grid power cycling should be infrequent and you might get by with smaller bank.
 
"petrol", you wrote in another thread.
If you aren't in the U.S. split-phase market but rather a 220V/50Hz one, a single Sunny Island can take in up to 12kW from grid for loads and for up to 6kW battery charging. That allows a smaller, more economical system.
(Inverter is 6kW, and relay can pass 56A from grid, so more watts with 220V compare to 120V line.)

Either one can also do 3-phase with three inverters. With your computer loads uniformly distributed across three phases, DC draw from battery would be steady instead of having 50/60 Hz ripple. AC coupled PV power delivered to battery could also be ripple free. But if grid is single (or split) phase, battery charging from that would carry ripple.
 
you could set up a battery or hybrid inverter which passes through power to normal house loads while keeping battery charged, and a second system which runs off the same batteries constantly.
I am thinking about 4000 watt initially, then adding another 4000 watt later. Am single phase in Thailand 230V/50Hz

I am starting to think I could split it into two systems
1. Powers loads that need uninterrupted power, eg: computers, this would be running in online UPS mode
2. Powers loads that I want battery backup for but can handle switch delay, eg monitors for the computers (which I have never had fail from unclean grid power), lights etc..

You seem to be suggesting something similar but running off the same batteries? I might not want to do that as I expect to buy one of the systems now and the other in a year or so, so batteries would not match which I understand is a no-no, or is it no longer an issue with new battery tech?
 
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