Solar system with AC backup?

[trader800]

Hi this maybe a dumb question. I know people usually use solar power as a backup to the main power. I'm wondering if there is a system doing the opposite? Meaning using solar power as main, with AC from house as backup. I'm planning to build a DIY solar power system (with battery) to run pumps/lights etc outdoor stuff in my backyard/pond, but would like to use maybe a AC from a house outlet as backup in case battery in the solar system drains. Is there such thing exist? Thanks for any pointers.

Jay

[Sunking]

That would be foolish.. But yes there are manufactures that sell such products. Off-Grid Solar battery system electricity cost anywhere from 10 to 20 times more for the electricity than buying it from the Power Company for the rest of your life. So why would anyone run solar battery power if they have commercial power available?

[Shmel]

Hi this maybe a dumb question. I know people usually use solar power as a backup to the main power. I'm wondering if there is a system doing the opposite? Meaning using solar power as main, with AC from house as backup. I'm planning to build a DIY solar power system (with battery) to run pumps/lights etc outdoor stuff in my backyard/pond, but would like to use maybe a AC from a house outlet as backup in case battery in the solar system drains. Is there such thing exist? Thanks for any pointers.

Jay

Samlex offers inverter/charger which use the grid as a backup for solar system. From their manual:

The TN-1500 series inverter chargers have an in-built solar battery charger and UPS functionality. Preference is given to the solar panels and batteries as sources of power and in the eventuality that these are inadequate; the load is transferred to the utility power supply, resulting in energy-saving.

Note, that these energy saving will never end up in money savings

[russ]

It is just a hybrid system but there are far better ways to be green (if that is what you want) than to go with a hybrid arrangement - Sunking pointed out the cost.

[PNjunction]

... I'm planning to build a DIY solar power system (with battery) to run pumps/lights etc outdoor stuff in my backyard/pond, but would like to use maybe a AC from a house outlet as backup in case battery in the solar system drains. Is there such thing exist?

You could always have a fully-charged battery as a hot-swap arrangement on standby. Perhaps use a quality charger running from household AC that eventually floats your standby battery. Or perhaps use a solar charge controller that will handle two separate batteries like the Morningstar SunSaver Duo. I haven't looked into how you'd switch them online, other than manually swapping them. Up front, I have NO experience with the duo, so keep that in mind...

[daveb]

Lol.. Welcome....

I have a small DIY solar system that I use for outdoor lighting. I like knowing that as they glow I'm not paying the electric company for the power. I didn't pay much for the components because I am frugal and recycle and reuse lots of materials.

So basicly it sounds like you need to set up a 12 volt system with everything runing on 12 volts DC? If you don't get eneough Sun you just want to charge the batteries? A 12 volt battery charger would charge the batteries for you and you could just use a 110v to 12v DC transformer to run the stuff.

[billvon]

I have a small DIY solar system that I use for outdoor lighting. I like knowing that as they glow I'm not paying the electric company for the power. I didn't pay much for the components because I am frugal and recycle and reuse lots of materials. So basicly it sounds like you need to set up a 12 volt system with everything runing on 12 volts DC? If you don't get eneough Sun you just want to charge the batteries? A 12 volt battery charger would charge the batteries for you and you could just use a 110v to 12v DC transformer to run the stuff.

A 12v system with a 12v "transformer" (inverter) is going to be a hideously expensive and dangerous way to do this. At 12 volts you'd need on the order of 600 amps to handle even normal starting surges for things like pumps and air conditioners. That's doable but is VERY costly - and at 600 amps, if you get a terminal even dirty before you cable it up there are going to be fireworks. A 48v system is far more reasonable for a whole-house system. It will be costly as well but will perform better.

[billvon]

Hi this maybe a dumb question. I know people usually use solar power as a backup to the main power. I'm wondering if there is a system doing the opposite?

Yes, there is. Often this mode is called something like LBX (low battery transfer) which transfers to the grid when the batteries get low.

But it's a very bad idea. Consider:

At some point you will have an inverter, a charge controller, batteries, cabling etc connected up and ready to go. You'll have spent at LEAST $10K or so on all that stuff. At that point you will have two choices:

1) Go with LBX. Result - you will have to replace all your batteries after a year or so. And if there's a blackout generally you'll be out of luck, because your batteries will already be low.
2) Go into standard grid-interactive mode. This feeds back power when you have excess and switches to battery during blackouts. Result - your batteries will last 5-10 years since they will be floating 99% of the time.

Which will you choose at that point?

[daveb]

A 12v system with a 12v "transformer" (inverter) is going to be a hideously expensive and dangerous way to do this.

That's how most landscaping electrical components are run. His original post states he want to run outdoor stuff.... not a house.

[billvon]

That's how most landscaping electrical components are run. His original post states he want to run outdoor stuff.... not a house.

Ah, then he should be able to go direct with no "transformer" needed. His lights will vary somewhat in brightness depending on charge state but that shouldn't be a big deal.

[daveb]

Ah, then he should be able to go direct with no "transformer" needed.

Yes but his original post stated he wanted an AC backup. A transformer would work as the backup but you would need to switch manualy between the two systems.

[Sunking]

Well if all he wants is backup and he has AC out there already, no solar is needed at all. Save yourself a bunch of money for a system that will work a lot better for a whole lot less money. Just a battery charger and battery powered by AC. When AC is on the battery charger supplies all the power. When AC fails the battery takes over until AC returns.

Al though I see no mission critical application for landscape lighting. Maybe security or life support.

[billvon]

Yes but his original post stated he wanted an AC backup. A transformer would work as the backup but you would need to switch manualy between the two systems.

Well, you'd need a transformer and a charger. Best to dump the transformer and just use a charger then.