Grid-tied solar

[aczlan]

I have a large rackmount UPS which (once I put some batteries in it) should be big enough to handle overnight loads (fans in the summer or circ pumps and zone valves in the winter) if we need heat or cooling. Just thinking about possibilities with the ~15'x24' roof of the shed (which is not too sloped, is close to the ground and faces South) and what could be done in a long term outage to help stretch fuel supplies.

Aaron Z

 

[dmccarty]

You don't want to over-think setting up a grid-tied solar system to be tricked into functioning when the grid power is out. It won't do anything during the night time hours which is 50% of the time on a yearly average, and if your power is out because it is stormy, you may not have that much sun to work with anyways.

If you must have power overnight, then you will need a generator in any case. Or, install an off-grid system with enough battery capacity. That will cost more than a generator, needs a dedicated battery area that doesn't get too hot or cold, and requires some maintenance. The hybrid grid-tied/off-grid systems with some minimal battery capacity are also expensive.

There is a KISS element to it.

I don't want overnight power though it would be nice. It is ironic that if one has power production on the roof, that one cannot use it unless the grid is running. I understand the safety side of the issue but there should be a way.

Once you touch a battery for backup it seems micro inverters are out of the picture and costs go up.

Later,
Dan

 

[dmccarty]

...and what could be done in a long term outage to help stretch fuel supplies.

Aaron Z

We just want enough power to run the fridge, freezer and well for a few hours. The well only has to be run once or twice a day to fill up buckets to flush the toilets, provide a bit of drinking water, and maybe taking a shower. This could be done with solar power during the daytime. It would be nice to be able to power with batteries all of the above plus a few lights and most importantly, the network to get to TBN! :dance1::laughing::laughing::laughing:

One thought I had was to use micro inverters on the house and put panels on the well house to supply battery power but that is getting complicated. The first problem is that I would have to BUILD the well house. :laughing::laughing::laughing: Second problem is that the well house is shaded. I could pole mount the panels but that is more complication....

Later,
Dan

 

[dave1949]

I have a large rackmount UPS which (once I put some batteries in it) should be big enough to handle overnight loads (fans in the summer or circ pumps and zone valves in the winter) if we need heat or cooling. Just thinking about possibilities with the ~15'x24' roof of the shed (which is not too sloped, is close to the ground and faces South) and what could be done in a long term outage to help stretch fuel supplies.

Aaron Z

I don't want overnight power though it would be nice. It is ironic that if one has power production on the roof, that one cannot use it unless the grid is running. I understand the safety side of the issue but there should be a way.

Once you touch a battery for backup it seems micro inverters are out of the picture and costs go up.

Later,
Dan

I know several people who have totally off-grid systems; they all have generators. Off-grid systems are generally designed with enough battery capacity to get through a three day period of poor solar production. My point is that it is hard to escape the necessity of having a generator, especially in rural areas. Any complexity and expense you add to a grid-tied system is duplicating the function of the generator. It will be less costly and more useful to ensure the generator has a fuel supply than to mess with the solar system.

For the frequency and duration of power outages for most people, there is no way you could make a business case for spending a bunch of money to cover those events when you will have a generator in any case.

If I were on an off-grid system, since mid-February I would have had to use a generator to charge the batteries several times. We have had a streak of storms and cloudy weather resulting in very low solar production for over three weeks now. All the solar technology and work-arounds in the world cannot overcome a lack of sunshine.

I know it goes against the grain to see solar power go unused when the utility power is out, but in reality, how much is really going to get away when you consider night time and the possibility of low sunshine?

 

[dmccarty]

I know several people who have totally off-grid systems; they all have generators. Off-grid systems are generally designed with enough battery capacity to get through a three day period of poor solar production. My point is that it is hard to escape the necessity of having a generator, especially in rural areas. Any complexity and expense you add to a grid-tied system is duplicating the function of the generator. It will be less costly and more useful to ensure the generator has a fuel supply than to mess with the solar system.

For the frequency and duration of power outages for most people, there is no way you could make a business case for spending a bunch of money to cover those events when you will have a generator in any case.

It depends on the length of the outage. In our case, knock on wood, the longest the outage has been 10-12 hours over night. Usually it is four hours or so. While these are not long outages, it is a bit of the PITA. It would be nice to have a few batteries to run a few essentials until power is restored but the cost to do this with PV is high and almost certainly does not make money sense.

If I were on an off-grid system, since mid-February I would have had to use a generator to charge the batteries several times. We have had a streak of storms and cloudy weather resulting in very low solar production for over three weeks now. All the solar technology and work-arounds in the world cannot overcome a lack of sunshine.

I know it goes against the grain to see solar power go unused when the utility power is out, but in reality, how much is really going to get away when you consider night time and the possibility of low sunshine?

When we lived in the city we were lucky in that our power came right off a main distribution line so even in a power outage the longest we were without power was 8-12 hours. Subdivisions next door were out for almost a week because their power was from a different direction. Where we are now, people were without power for about a week after Fran. Our outages are wind storms, ice storms and hurricanes. All three blow through very quickly and we have sunshine back quickly. While a generator would still be needed in a long outage having PV doing most of the work, especially if it is on the roof, would be more than helpful. The fact that one cannot use the PV in an outage without expensive batteries is a big negative.

I think you are too hung up on night time. We do not plan to run the generator 24 hours nor would we want too. No way we could afford to run that long. Even running an hour or so every 3-4 hours gets expensive after a few days. We would just want to power the fridge, freezer, and well a few times during the day. The well not as much since we can store water. Even if the PV only provided power for the five hours a day, it would be the critical hours when we would be accessing the fridge for food, and the PV could keep it cool. Generator usage/expense would be much reduced.

Because PV CANNOT do this at low cost, one of the guys in class is most unhappy, since this is exactly what he wants to do.

Later,
Dan

 

[Redneck in training]

The off grid system are always compromise. Well, unless you are rich and can overkill it. You have to watch your consumption, take short shower, sleep in hotter house etc. Off grid systems make sense when the house is remote making the power line too expensive and when the house is built as energy efficient.
We are spoiled and don't want to sacrifice our comfort though. Therefore the grid tie makes sense to us. Nevertheless I am thinking about a storage of energy because we don't have net metering. We are selling power for 3.5 cent during the day and buying it back at night for 11.5. It sucks.
One way is to put pressure free tank in the garage and heat or cool it during the day when there is an excess generation and then use it at night to heat and cool the house. We have floor heating so for heating we need only about 100F and for cooling about 34F. That is the easy part. The hard part is to match the power consumption with power available because we don't want use more than what is available and also no less.
Another option would be to place a large tank (in example a swimming pool) on the high point of our place and pump there water from the pond that is located around 50 ft or so lower. Then release the water during t high demand through a turbine running a DC generator with inverter.
Third option is to win a lottery and forget all this nonsense. And that is my real plan. They just don't want to sell me the wining ticket.

 

[dave1949]

It depends on the length of the outage. In our case, knock on wood, the longest the outage has been 10-12 hours over night. Usually it is four hours or so. While these are not long outages, it is a bit of the PITA. It would be nice to have a few batteries to run a few essentials until power is restored but the cost to do this with PV is high and almost certainly does not make money sense.



When we lived in the city we were lucky in that our power came right off a main distribution line so even in a power outage the longest we were without power was 8-12 hours. Subdivisions next door were out for almost a week because their power was from a different direction. Where we are now, people were without power for about a week after Fran. Our outages are wind storms, ice storms and hurricanes. All three blow through very quickly and we have sunshine back quickly. While a generator would still be needed in a long outage having PV doing most of the work, especially if it is on the roof, would be more than helpful. The fact that one cannot use the PV in an outage without expensive batteries is a big negative.

I think you are too hung up on night time. We do not plan to run the generator 24 hours nor would we want too. No way we could afford to run that long. Even running an hour or so every 3-4 hours gets expensive after a few days. We would just want to power the fridge, freezer, and well a few times during the day. The well not as much since we can store water. Even if the PV only provided power for the five hours a day, it would be the critical hours when we would be accessing the fridge for food, and the PV could keep it cool. Generator usage/expense would be much reduced.

Because PV CANNOT do this at low cost, one of the guys in class is most unhappy, since this is exactly what he wants to do.

Later,
Dan

It's always possible to find negatives if we look for them. But tasking a grid-tied system with something it is not designed to do is sort of silly in the big picture. 99% of the time, grid-tied systems do an excellent job of doing what they are designed to do: make power when the sun shines and reduce our dependency on non-renewable energy sources. If they become commonplace, they will also allow re-thinking some of the grid management and load growth challenges.

Extending the design capabilities of grid-tied systems to function off grid would not be rocket science. It would require some parallel hardware that is engaged when grid power is off like an oscillator chip driven circuit to provide the 60 cycle clocking, and some device to satisfy the on-demand aspect of home power use.

A grid-tied system relies on the grid to supply on-demand usage peaks. It also gets its 60 cycle clocking from the grid, whether you use distributed micro inverters or centralized inverter(s). The system must be in phase with the grid to push power back to the grid.

An off-grid system relies on its batteries to supply those peak demands. As long the demand does not exceed the battery/inverter capacity, the power stored in the batteries fills in for what the panels are momentarily not producing. The off-grid inverter also supplies the 60 cycle clocking, and of course it need not be in phase with anything.

Filling the on-demand peak usage is the challenge to using a grid-tied system with no grid. Power has to be more or less instantaneously supplied because that is what most electric devices expect and take for granted in their own designs.

If you have to have it, there are a couple of manufactures of hybrid grid-tied/off-grid systems with limited battery capacity. They are expensive, and I think you would still want to have generator. It is just a question of cost versus utility.

 

[rmorey]

It's always possible to find negatives if we look for them. But tasking a grid-tied system with something it is not designed to do is sort of silly in the big picture. 99% of the time, grid-tied systems do an excellent job of doing what they are designed to do: make power when the sun shines and reduce our dependency on non-renewable energy sources. If they become commonplace, they will also allow re-thinking some of the grid management and load growth challenges.

Extending the design capabilities of grid-tied systems to function off grid would not be rocket science. It would require some parallel hardware that is engaged when grid power is off like an oscillator chip driven circuit to provide the 60 cycle clocking, and some device to satisfy the on-demand aspect of home power use.

A grid-tied system relies on the grid to supply on-demand usage peaks. It also gets its 60 cycle clocking from the grid, whether you use distributed micro inverters or centralized inverter(s). The system must be in phase with the grid to push power back to the grid.

An off-grid system relies on its batteries to supply those peak demands. As long the demand does not exceed the battery/inverter capacity, the power stored in the batteries fills in for what the panels are momentarily not producing. The off-grid inverter also supplies the 60 cycle clocking, and of course it need not be in phase with anything.

Filling the on-demand peak usage is the challenge to using a grid-tied system with no grid. Power has to be more or less instantaneously supplied because that is what most electric devices expect and take for granted in their own designs.

If you have to have it, there are a couple of manufactures of hybrid grid-tied/off-grid systems with limited battery capacity. They are expensive, and I think you would still want to have generator. It is just a question of cost versus utility.

Could you define expensive. We have an "off grid" system as hydro is "$150,000 due south of our location". We installed a PV system with a dual centralized inverter system and batteries that handle our complete home for up to 5 days, with generator backup. Total cost is about $27,000. My battery bank is large and expensive at $8,000. For an existing system, needing battery backup for a 1 day coverage, would probably be in the $1,500 - $2,000 range. The other option as has been said by others, is a backup generator. The problem is, generators wear out. Depending on usage, 2 - 5 years and your done. So, $1,500 gone.

Some would argue, batteries wear out too. Most batteries will handle 1,500 charge cycles. If you dont use 'em its not a charge cycle. So they should last you for years with proper care and maintenance...just sayin'.

 

[Tororider]

For the record my knowledge of solar is extremely limited. But if you wanted a grid tied system with a separated battery bank couldn't you use the electricity made through your solar array to charge a battery bank with a float type charger from an outlet in the basement. Then treat the battery bank like a generator, when the grid goes down throw a switch on your electric panel in the basement and transfer to battery power? I understand this is a grossly simplified description and by going from dc to ac back to dc there would be efficiencies lost but wouldn't this allow a battery back up to a grid tied system?

 

[aczlan]

For the record my knowledge of solar is extremely limited. But if you wanted a grid tied system with a separated battery bank couldn't you use the electricity made through your solar array to charge a battery bank with a float type charger from an outlet in the basement. Then treat the battery bank like a generator, when the grid goes down throw a switch on your electric panel in the basement and transfer to battery power? I understand this is a grossly simplified description and by going from dc to ac back to dc there would be efficiencies lost but wouldn't this allow a battery back up to a grid tied system?

Are you talking about a charger feeding a battery bank, then a inverter running off of that? Something like the diagram below?

I could see that working with a couple of caveats:

1. You would have to have a mechanical interlock so that the battery bank inverter couldn't be turned on when the utility power is on
2. You would have to have some way to shut the battery bank charger off when the panels or a generator are not running (perhaps a trigger on the battery bank inverter to turn on/off when it is putting out more than x amps)
3. You might need an additional loadbank depending on how the solar panel inverters handle less than a full load

Aaron Z