Battery-less off-grid? Panel -> controller -> inverter -> load

[cdevidal]

Is it possible to connect panel to controller to inverter to load? I see from this schematic that a battery is in parallel with the inverter, would one be able to remove the battery from this circuit and it still function?

Of course, that means you'd only get action ~5 hours a day, right in the middle of the day. I just want to know if it's possible, or if it'd burn out the controller or cause other issues.

This assumes that the load is always "on."

[cdevidal]

I found this thread after I changed the search terms. I didn't find the info I was looking for at first or I wouldn't have asked. (Sorry)

http://www.solarpaneltalk.com/showthread.php?18456-Battery-less-off-grid-set-up

[cdevidal]

Correction, that thread didn't answer my question. I have in mind a water pump, so that's a good find, but I also want to know about other kinds of loads.

Any thoughts?

[jony101]

I would say no, the controller needs the battery power to function. When I unplug the battery from my controller while connected to the panel, my controller resets. When I reconnect the battery I need to tell it what size battery it is 12 volt or 24 volt, then it will restart again. Even my simple pwm controller stop working if i unplug the battery.
It didnt burn out my controllers but it just didnt work without a battery connected.

But saying that, I have seen videos in youtube of people running large fans off a solar panel with no controller or battery.

[Sunking]

No next question. Panels are current sources. Inverters need voltage sources of sufficient capacity.

[Wy_White_Wolf]

Correction, that thread didn't answer my question. I have in mind a water pump, so that's a good find, but I also want to know about other kinds of loads.

Any thoughts?

Well pumps can be ran off grid without batteries if the system is properly designed. But it's not the way you describe.

I have such a setup on my well at the cabin for our household water an the orchard. It uses a 24V solar panle hooked to a LCB (linear current booster) then to a 24VDC pump that fills a cistern for storage. It'll run fo 5 to 7 hours on a sunny summer day. We don't leave it hooked up in the winter so it won't freeze. The cabin is not pressurized and we have to haul the water up to the cabin to use.

Build it solar has several example this type of system here

Mine is explained in this thread in a different forum

You can run some loads like this as long as you can design the load around the limits of solar and match your componets together.

WWW

[SunEagle]

Correction, that thread didn't answer my question. I have in mind a water pump, so that's a good find, but I also want to know about other kinds of loads.

Any thoughts?

I would say the most inverters require a constant voltage source to work.

Now if your load was DC like a pump or fan then you can connect that load directly to the solar panel.

I have a couple of DC roof vent fans that each have a 10watt panel. They run just fine without a battery except their speed changes when the sunlight intensity changes.

So if you don't mind a fan or pump that changes speed and only runs during "good" sunlight you won't need a battery. If you want to inverter that panel output DC into AC a battery is a must have.

[cdevidal]

As for other loads, one of them might be a well-insulated AC-powered freezer, which is a kind of energy storage.

So if we know that a controller requires a battery, what if only the barest minimum spec of battery is used? When I see the schematic above, the inverter is directly in line, so I'd suppose that what happens is that when the sun is shining, the battery charges and excess power is sent directly to the inverter. I wouldn't suppose that when the sun is shining, the freezer only runs as long as the battery has capacity.

So for example, a thought experiment: 700W of panels, a 10AH battery (charged to 100%), a 3000W/1500W inverter, and a 110V freezer that when running consumes 600W. (Ignoring startup current for the moment.) That's 5.5A per hour, which means the battery cannot last any longer than two hours, yet the freezer runs for five hours, as long as the sun is shining, because it's not running off battery power, it's running off excess current from the charge controller. Correct?

In my limited understanding of PV systems, I'd say the answer is "Yes." (And this is only a thought experiment. I realize that you don't want your batteries to go below 50%. In such a situation I'd switch off the appliance at dusk. And yes, there'd be risk of melt if I switched it off.)

By the way, the purpose of this thread is crisis planning for either an extended grid-down event or regular blackouts. The goal is to both save money on electricity today and have the absolute minimum we'd need on hand for a long-term power outage/rolling blackout, and later expand batteries if we can. If there is a power outage we can hobble along on a minimum amount of battery, only getting 5 or so hours of power per day. I'm OK with that. So if I can get away today with buying only a very small battery I'm OK with that.

[Sunking]

So for example: 700W of panels, a 10AH battery (charged to 100%), a 3000W/1500W inverter, and a 110V freezer that when running consumes 600W. (Ignoring startup current for the moment.) That's 5.5A per hour, which means the battery cannot last any longer than two hours, yet the freezer runs for five hours, as long as the sun is shining, because it's not running off battery power, it's running off excess current from the charge controller. Correct?

Where are you getting these numbers from?

A 600 watt load at 12 volts consumes 50 Amp Hours every hour. I have no clue where you came up with 5.5 AH. If the fridge ran 5 hours would consume 250 AH. Secondly a 700 watt panel on a 10AH battery, would make the battery explode. Third no way in hell would a 12 volt 10 AH battery even start a 600 watt load on a 1500 watt inverter. A 700 watt panel requires a minimum 12 volt 450 AH battery which is not enough to supply you with 5 hours run time. Lastly a inverter with a battery connected runs until the battery dies from under voltage.

[SunEagle]

As for other loads, one of them might be a well-insulated AC-powered freezer, which is a kind of energy storage.

So if we know that a controller requires a battery, what if only the barest minimum spec of battery is used? When I see the schematic above, the inverter is directly in line, so I'd suppose that what happens is that when the sun is shining, the battery charges and excess power is sent directly to the inverter. I wouldn't suppose that when the sun is shining, the freezer only runs as long as the battery has capacity.

So for example, a thought experiment: 700W of panels, a 10AH battery (charged to 100%), a 3000W/1500W inverter, and a 110V freezer that when running consumes 600W. (Ignoring startup current for the moment.) That's 5.5A per hour, which means the battery cannot last any longer than two hours, yet the freezer runs for five hours, as long as the sun is shining, because it's not running off battery power, it's running off excess current from the charge controller. Correct?

In my limited understanding of PV systems, I'd say the answer is "Yes." (And this is only a thought experiment. I realize that you don't want your batteries to go below 50%. In such a situation I'd switch off the appliance at dusk. And yes, there'd be risk of melt if I switched it off.)

By the way, the purpose of this thread is crisis planning for either an extended grid-down event or regular blackouts. The goal is to both save money on electricity today and have the absolute minimum we'd need on hand for a long-term power outage/rolling blackout, and later expand batteries if we can. If there is a power outage we can hobble along on a minimum amount of battery, only getting 5 or so hours of power per day. I'm OK with that. So if I can get away today with buying only a very small battery I'm OK with that.

Technically you are correct with your assumption. The problem I see is unless you baby sit it throughout the day there is always a good chance of either draining or overcharging your battery system. If the sun goes away for even 30 minutes you could easily drain that small battery. And with a large PV array you can easily exceed the charging parameters of that battery. You can't charge or discharge a battery outside of it's spec or you will damage it. That is why it is safer (although more costly) to have a balanced system (panel wattage = battery Ah = inverter wattage) or it will be easy to tip the cart due to one of those components being too big or too small to work properly.

[Sunking]

A 1500 watt inverter with a 600 watt load would trip instantaneously with a single cloud passing by from under voltage on a 12 volt 10 AH battery. The second the cloud passed, the battery would be slammed with 60 amps of current (6C) and spew acid everywhere.

[SunEagle]

A 1500 watt inverter with a 600 watt load would trip instantaneously with a single cloud passing by from under voltage on a 12 volt 10 AH battery. The second the cloud passed, the battery would be slammed with 60 amps of current (6C) and spew acid everywhere.

Could be fun to baby sit that and watch the show.

I agree there is a limitation to how big a panel array wattage is compared to how small a battery Ah size, compared to inverter wattage, compared to load type.

Although there is a chance of being able to run a small AC load from an inverter directly off of the panel input with a stabilizing battery in the circuit. The load can't have a high inrush start current and the battery needs enough meat to handle power swings with relation to sunlight swings. You still have to watch to make sure the battery doesn't drain or charge too fast. It can be done but why take the chance?

[cdevidal]

Where are you getting these numbers from?

The air. It's a thought experiment. If those numbers don't work, please have a look at the stated goal and mentally compensate.

[cdevidal]

Technically you are correct with your assumption. The problem I see is unless you baby sit it throughout the day there is always a good chance of either draining or overcharging your battery system. If the sun goes away for even 30 minutes you could easily drain that small battery. And with a large PV array you can easily exceed the charging parameters of that battery. You can't charge or discharge a battery outside of it's spec or you will damage it. That is why it is safer (although more costly) to have a balanced system (panel wattage = battery Ah = inverter wattage) or it will be easy to tip the cart due to one of those components being too big or too small to work properly.

Thank you, I think you're understanding what I'm asking, whereas the others seem to be tripping over imaginary numbers.

Now, why is overcharging a problem? Don't today's smart chargers trickle batteries when they're at capacity? Where does the excess current go if not through the inverter to the load?

[cdevidal]

A 700 watt panel requires a minimum 12 volt 450 AH battery

Where are you getting these numbers from? Is there a chart that you have which says a 700W panel array needs a 450AH battery, and a 1000W array needs a XXXAH battery, etc.?