Wish to run my Room Air-Conditioner on solar during day time

[Johann]

I think it is possible to power your AC without an battery if you do not mind getting service disconnects with clouds. I will find out next summer.


All you really would need is to hook up a voltage regulator to the panels so the output has the same voltage at all times. Then you incorporate a voltage sensor that you can set the 'on' and 'off' voltages to turn the inverter on and off. Hook your inverter up to your voltage regulator output.

Now when a clouds comes the inverter will turn off and when the cloud passes the inverter will resume to power up again without having to reset the inverter.

As long as your panel wattage and sun output is high enough to overcome the starting wattage of your AC you should be ok.
With AC you may have to install a 5 minute time delay after power is disconnected before power is applied again to avoid that the compressor is trying to start under pressure/load.

Mod note - Johann is also following the route I mentioned in the previous post - As I lack in brilliance I have to go the BS route!

[SunEagle]

I think it is possible to power your AC without an battery if you do not mind getting service disconnects with clouds. I will find out next summer.


All you really would need is to hook up a voltage regulator to the panels so the output has the same voltage at all times. Then you incorporate a voltage sensor that you can set the 'on' and 'off' voltages to turn the inverter on and off. Hook your inverter up to your voltage regulator output.

Now when a clouds comes the inverter will turn off and when the cloud passes the inverter will resume to power up again without having to reset the inverter.

As long as your panel wattage and sun output is high enough to overcome the starting wattage of your AC you should be ok.
With AC you may have to install a 5 minute time delay after power is disconnected before power is applied again to avoid that the compressor is trying to start under pressure/load.

Mod note - Johann is also following the route I mentioned in the previous post - As I lack in brilliance I have to go the BS route!

Even with all those low voltage and time delay "safeties" you still run the risk of cycling your AC system too many times in one day and probably cause the compressor to fail. You need a constant power source for an AC system. Batteries can do it (although will be expensive). A generator will be a better solution if you lose grid power.

[Mike90250]

Possible, but not likely. Maybe if you are in a cloudless area (desert) and can be assured of 99% sun during the core hours.

Maybe somewhat more likely with a "mini-split" system that can modulate it's compressor speed a bit, and has better restart capability.

The main problem is solar PV cannot supply any "surge" power. A generator has pounds of rotating mass that can "flywheel" though a compressor start. A battery & inverter can "surge" for a second. PV has no such feature, so you have to have 5x the running power, available in PV to start a compressor. 400W running, you need 2,000w on line. (about 2,500w of PV nameplate installed).

[nomadh]

This would be a fairly different track but if the others don't work and you do not want batteies The sunnyboy inverters have a new feature that can continue output during a grid outage without batteries. But it is a manual switchover. Not too convenient if your grid is going up and down constantly.

[SunEagle]

This would be a fairly different track but if the others don't work and you do not want batteies The sunnyboy inverters have a new feature that can continue output during a grid outage without batteries. But it is a manual switchover. Not too convenient if your grid is going up and down constantly.

That feature on the SMA inverter is pretty nice but still is limited to only working continuously if the sun doesn't play "peek a boo" with clouds. Without continuous sunshine even that sunnyboy feature won't help you.

I don't mind a light fixture going on an off but I would have a big issue if my refrigerator or AC unit kept cycling.

[paulcheung]

Which way is cheaper? to increase the panels size by 5 X the need wattage or just buy 4 automobile 12 volt battery which cost about $80 each have 500 amps crank power?

[Johann]

That feature on the SMA inverter is pretty nice but still is limited to only working continuously if the sun doesn't play "peek a boo" with clouds. Without continuous sunshine even that sunnyboy feature won't help you.

I don't mind a light fixture going on an off but I would have a big issue if my refrigerator or AC unit kept cycling.

Hum...
Last time I checked a AC and and a fridge is cycling regardless.

Looks like everyone is following the route that got mentioned in the previous post - As I lack in brilliance I have to go the BS route.

[SunEagle]

Hum...
Last time I checked a AC and and a fridge is cycling regardless.

Looks like everyone is following the route that got mentioned in the previous post - As I lack in brilliance I have to go the BS route.

There are two types of cycling. The normal way when a set point like the AC or fridge thermostat is satisfied and the compressor comes to a stop. This is ok and the equipment is designed for that type of operations.

Now when the power goes out in "mid cycle" for an AC or fridge the compressor has not gone through it typical operation of shutting down by relieving the pressure. So when the power comes back the AC or fridge compressor now starts under a much higher load which puts a strain on the equipment. Especially if the cycle of power being on - off - on is very short. Better for the equipment if the power has been off for a while allowing the compressor to release some of the pressure it built up while it was running before it starts up again.

Does that clear up what I have tried to say?

[Johann]

There are two types of cycling. The normal way when a set point like the AC or fridge thermostat is satisfied and the compressor comes to a stop. This is ok and the equipment is designed for that type of operations.

Now when the power goes out in "mid cycle" for an AC or fridge the compressor has not gone through it typical operation of shutting down by relieving the pressure. So when the power comes back the AC or fridge compressor now starts under a much higher load which puts a strain on the equipment. Especially if the cycle of power being on - off - on is very short. Better for the equipment if the power has been off for a while allowing the compressor to release some of the pressure it built up while it was running before it starts up again.

Does that clear up what I have tried to say?

I know exactly what you are saying.
As soon as power is disconnected or lost to the AC or fridge, such unit will start to equalize pressure without power and this will take 1-2 minutes after that 2 minutes or so there would be no head pressure present at the compressor.
Now if you talk about a 80 ton (960,000BTU) trane unit, that is a different story and power is required to go through a shut down procedure on it.
Most 5,000 BTU AC's do not have a time delay build in. On the other hand a 18,000 BTU and fridges may have a time delay build in so the compressor may be able to start but with an 5 minute delay ( a $5 delay timer will do this). That is why I mentioned in my previous post ''that a time delay may be needed to power an AC unit'' and this was to protect the AC compressor. AC compressors are designed for an 15 minutes on cycle and 15 minutes off cycle to repeat it over and over again, so some cycling will not hurt the compressor and motor as long as there is no head pressure.

[nomadh]

I was thinking if an extended outage I'd move some food and drinks to the mini fridge then just be careful. If the power drops then unplug it for a few min. Same with a small ac system. If there are clouds then hopefully it isn't so hot and then the ac wont matter. I would also consider a small pc type battery backup ups. I think that could let a compressor get through intermittent clouds. Would it help somehow getting a compressor started with the battery boost. I think the cheaper PC type ups are mostly offline switching ups so it would not help a compressor during startup. Is that correct?

[inetdog]

Would it help somehow getting a compressor started with the battery boost. I think the cheaper PC type ups are mostly offline switching ups so it would not help a compressor during startup. Is that correct?

Unlike a hybrid off-grid system with generator support, a UPS will pretty much either switch off the grid source (which is actually the SPS) and use only the batteries (normal consumer UPS) or will constantly provide DC from the AC input to drive the output AC inverter for a seamless transition when the "grid" goes down (many commercial units).
In the case of the latter, you would have to look at the surge capability of the inverter portion of the UPS, which might be enough to carry through motor starting. But the UPS output power would always be coming only from its output inverter and not from a combination of UPS inverter output power and SPS power.
Look carefully at the specs and maybe contact the manufacturer for a more complete curve of surge power versus time.
You could hope that the UPS would also brown out gracefully under overload instead of shutting down completely as the SPS would.

[paulcheung]

An UPS that can start the Air condition unit will cost thousands Dollars, What is wrong with a set of cheap batteries? The UPS use batteries too, they are to be change every two to three years and will be quicker in this situation.

[SunEagle]

I know exactly what you are saying.
As soon as power is disconnected or lost to the AC or fridge, such unit will start to equalize pressure without power and this will take 1-2 minutes after that 2 minutes or so there would be no head pressure present at the compressor.
Now if you talk about a 80 ton (960,000BTU) trane unit, that is a different story and power is required to go through a shut down procedure on it.
Most 5,000 BTU AC's do not have a time delay build in. On the other hand a 18,000 BTU and fridges may have a time delay build in so the compressor may be able to start but with an 5 minute delay ( a $5 delay timer will do this). That is why I mentioned in my previous post ''that a time delay may be needed to power an AC unit'' and this was to protect the AC compressor. AC compressors are designed for an 15 minutes on cycle and 15 minutes off cycle to repeat it over and over again, so some cycling will not hurt the compressor and motor as long as there is no head pressure.

Exactly. The problem is knowing when the head pressure has been reduced enough for a safe start. An intermittent power source is not "time reliable" so an "on delay" timer would have to be installed to keep the compressor from starting too soon after the power comes back on. Still depending on how many times the power goes out may add up to a lot of more starts for that compressor over a period of time and shorten it's life.

[ZoNiE]

You really are better off buying an inverter Air conditioning unit and selling your non-inverter unit to recoup "some" cost or keeping it to run when on Genny. I'd bet in your neck of the woods, you can get them pretty cheaply as minisplits are the norm where in the US they are the exception. I have seen them as low as $300 US in Malaysia.

You should also put in a properly sized battery bank as discussed previously to handle the load, and provide enough panel wattage or genset to ensure you fully recharge the batteries or keep them charged while under the load of the Air conditioner unit or they will have a short life.

If you have a dry desert heat, consider an evaporative cooler. Look them up on wikipedia if not familiar with them. All they are is a large fan and a small water re circulator pump. Use much less power than an AC unit. They do NOT work when the humidity is high, they just make it worse (Swamp cooler). They are also pretty easy to make.

[inetdog]

Just keep in mind that not all mini-splits are inverter units (which can very efficiently drive the compressor at lower speeds with correspondingly reduced power consumption.)
On the other hand, with very few exceptions (such as unit ACs designed for 48V DC power) all of the inverter units are found in mini-splits.