Thread: A long overdue feature on solar power inverters

One of the things that has always bothered me about grid interactive solar inverters is their uselessness when the power goes out - which, of course, is the time you would most appreciate an alternative power supply. Up until now your choice has been between a batteryless inverter that was useless when the power went out, and a battery backed inverter which, of course, requires batteries - and the switchgear, protection and maintenance that is associated with a large battery bank.

(Battery backed inverters are indeed nice but are a lot more expensive to begin with, which is why most people go batteryless.)


SMA has just come out with a batteryless grid tie inverter which has what they call a "secure power supply." On several of their inverters you can now get up to 1500 watts at 120VAC via an auxiliary inverter. Of course this is only available during daylight hours, but 1500 watts is more than enough to run a refrigerator, recharge cellphones, laptops and flashlights and run TV/radios. (And most refrigerators will stay cold overnight as long as you run them all day.)

In fact if you wanted to get fancy you could buy a $149 computer UPS and run your lights all night with it. And when you didn't need it you wouldn't need to deal with it.

This should be a boon to a lot of people:

-People who live in outage-prone areas but don't want to deal with generators or batteries
-People with medical needs (like refrigeration for insulin) who can't afford to be without power for long periods of time
-Survivalists who want to be ready for TEOTWAWKI.

I agree it's frustrating to know there's power at hand but you can't use it and no surprise someone is trying to address it, but I think something that includes some storage is what is needed.

In Europe there is the Sol-Ion project, aimed more at developing better integration of solar with grid demand (in home storage to carry it through the evening peak demand period) to avoid the afternoon ramp-up of power from other sources. Their solution is an integrated inverter and batteries unit that would work as blackout backup, even if that's not the primary intent. Toshiba in Japan makes something similar, but the motivation is more about better use of off-peak excess supply during a time when their grid is struggling to keep up with daytime demand - ie charge overnight from the grid to run households by day. Here in Australia the motivation would be to prevent solar owners being gouged by being paid a pittance for solar fed to the grid and charged very high, via time of use/dynamic metering, for power during the evening peak demand period. I know there are others developing similar systems.

Sol-ion kit
The Sol-ion kit has been developed to accommodate PV energy production of 5 kWp (peak) with a battery rated from 5 to 15 kWh and a nominal voltage of 170 V to 350 V. Li-ion is the only technology that meets the project’s need for 20-year battery life in demanding environmental conditions. The energy conversion and system management systems are designed to handle four system functions: multidirectional energy flows; self-consumption; grid support; back-up. They are also intended to handle requirements for demand side management such as control over storage and loads using smart metering, and integration within future smart grids that will need to handle demand response and dynamic pricing.

Excessively expensive at this point, but with growing take-up of PV by homeowners expect to see these kinds of systems hitting the market, hopefully at reasonable cost.

Originally Posted by billvon

SMA has just come out with a batteryless grid tie inverter which has what they call a "secure power supply." On several of their inverters you can now get up to 1500 watts at 120VAC via an auxiliary inverter. Of course this is only available during daylight hours, but 1500 watts is more than enough to run a refrigerator, recharge cellphones, laptops and flashlights and run TV/radios. (And most refrigerators will stay cold overnight as long as you run them all day.)

I'd be concerned with the start up power for the frig...many go near 1500 for a few seconds than drop to 500 or so during the cooling cycle. And I'd imagine you'd need a solar power output with a large margin, a 3K unit for example, to meet that 1500W if there was a cloud passing overhead at the same time the frig started.

I built a small cabin with solar lighting and enough left over to run an elliptical machine and laptop but it has a deep cycle battery as back up. Sort of surprised the connected solar systems didn't allow direct connection somehow. Many owners have their homes built with back up generation connections in place--I'd think that would think hooking a solar system to that would work as well.

I don't know what inverter tech is like exactly for Solar panels, but if I had to guess then probably the reason the grid interactive inverters don't work without the grid is because maybe they don't have very precise control over the voltage. Maybe the grid serves as a means to smooth it out? Wouldn't want to damage your appliances by feeding them the wrong voltage.

On the other hand, if you have a battery, then compatibility is not an issue at all. That's why you can use laptops even when you're traveling in countries that use different frequencies of AC power, without needing a converter. The battery solves the issue entirely for you.

Most of the inverters I've worked with were DC - to - AC inverters, and those are made to work with an exact voltage of DC (12 volts in my case, for my car). I have a few of them, and I'm not absolutely sure,.... but I think they're creating the AC current by physically spinning a turbine inside of them. I don't think they would work right if they were getting input from something that gives different amounts of power depending on how bright the sun is, though. Then the turbine might spin at the wrong speed. ..... Which might not even result in the right AC frequency.

Originally Posted by kojax

I don't know what inverter tech is like exactly for Solar panels, but if I had to guess then probably the reason the grid interactive inverters don't work without the grid is because maybe they don't have very precise control over the voltage.

They have as precise control over the voltage as the designer wants them to have. There's nothing very hard about the technology to do this; it's just never been implemented before. I am glad to see that it (finally) has been.

Maybe the grid serves as a means to smooth it out?

The restrictions in UL 1741 and IEEE 1547* are pretty tight; the inverter generally cannot rely on the grid to "smooth out" any defects in the current waveform it outputs.

On the other hand, if you have a battery, then compatibility is not an issue at all. That's why you can use laptops even when you're traveling in countries that use different frequencies of AC power, without needing a converter. The battery solves the issue entirely for you.

?? No, the power supply for the laptop still needs to work across a wide range of voltages (say, 90 to 264 volts) and frequencies (50-60Hz.) However it is easier to design an AC-DC power supply than a DC-AC inverter.

Most of the inverters I've worked with were DC - to - AC inverters, and those are made to work with an exact voltage of DC (12 volts in my case, for my car).

Most 12V inverters are designed to work from about 10 to 16 volts to accommodate the charging voltages seen at lead acid batteries. BTW your car's electrical system is generally at 13.8 volts. If it's at exactly 12 while the car's running something is wrong with the car.

I have a few of them, and I'm not absolutely sure,.... but I think they're creating the AC current by physically spinning a turbine inside of them.

All modern inverters use semiconductor switches to create the AC waveform.

I don't think they would work right if they were getting input from something that gives different amounts of power depending on how bright the sun is, though. Then the turbine might spin at the wrong speed. ..... Which might not even result in the right AC frequency.

1) they don't use turbines
2) a PV panel's voltage doesn't change much depending on the brightness of the sun. The primary thing that drives voltage change is load. (And dimmer sun leads to less available current, not lower voltages, at least at anything brighter than dusk or dawn.)

(* - applicable regulatory requirements for grid interactive inverters)

Living in an area where it's entirely possible for the supplier to shut the grid down when there's a fire in the region served by this part of the grid, I'd like to see the technology developed and enhanced to allow conversion from storage within an oversized solar hot water system at individual properties. There are some trials going on in the US and Germany. I want it now.

With that kind of system you could solve the re-charging your electric car and the grid going down with the an integrated inverter/ switching system. (You'd also need automatic switching off/ powering down for a/c, freezers and refrigerators to restrict the drawdown on the storage but that's better than having none at all, especially overnight when the solar system itself is out of action. )

Originally Posted by adelady

Living in an area where it's entirely possible for the supplier to shut the grid down when there's a fire in the region served by this part of the grid, I'd like to see the technology developed and enhanced to allow conversion from storage within an oversized solar hot water system at individual properties. There are some trials going on in the US and Germany. I want it now.

I think you might be mixing up two different technologies. One is domestic hot water; those systems work very well and can reduce your water heating bills by 90%. Some of them (passive convective tank heaters) can work without any electricity at all; some (like active systems) need electricity. Often this is provided by a small photovoltaic panel used just for the circulating pump. They don't produce AC power though.

With that kind of system you could solve the re-charging your electric car and the grid going down with the an integrated inverter/ switching system. (You'd also need automatic switching off/ powering down for a/c, freezers and refrigerators to restrict the drawdown on the storage but that's better than having none at all, especially overnight when the solar system itself is out of action. )

If you don't mind batteries, then such systems are available right now. They are more expensive than pure intertie systems but have decades of research and development behind them.

I think you might be mixing up two different technologies. One is domestic hot water; those systems work very well and can reduce your water heating bills by 90%. Some of them (passive convective tank heaters) can work without any electricity at all; some (like active systems) need electricity. Often this is provided by a small photovoltaic panel used just for the circulating pump. They don't produce AC power though.

Nuh.

Just did a search and couldn't find it. There are systems being trialled to use oversized hot water systems, preferably solar, as reserve power sources. There's one project somewhere on the US East Coast and another in Germany. (That's my memory there, might be as unreliable as my bookmarking.)

Here we go.

Water Heater Energy Storage: “Inefficient” Electric Heaters May Have Role in Smart Grid | Climate Denial Crock of the Week

I don't want it just for grid storage, I'd want it to back up or modulate on-site solar use.

Originally Posted by adelady

Here we go.

Water Heater Energy Storage: “Inefficient” Electric Heaters May Have Role in Smart Grid | Climate Denial Crock of the Week

I don't want it just for grid storage, I'd want it to back up or modulate on-site solar use.

Still, that's not generating electricity from your water heater. It just reduces the water heating load when less generation is available.

Originally Posted by adelady

Water Heater Energy Storage: “Inefficient” Electric Heaters May Have Role in Smart Grid

That sounds like a smart load (good for load shedding and dealing with large scale renewable use) rather than part of a local solar power system. However I am not in favor of making inefficient loads smarter; I would much rather make them more efficient. For example, in the case of a water heater, you are better off with a heat pump to heat your water and are MUCH better off with a solar hot water heater. (Compare efficiencies; 15% for solar electric to solar water heater vs. 80% for direct solar heat.) And of course the system of solar panel -> charge controller -> battery -> inverter -> AC heater is an order of magnitude more expensive than a solar hot water system.

To put it another way, for every watt of heat you get from a solar power system to heat your water you could easily afford 100 watts of direct solar heating.

From your original request:

With that kind of system you could solve the re-charging your electric car and the grid going down with the an integrated inverter/ switching system. (You'd also need automatic switching off/ powering down for a/c, freezers and refrigerators to restrict the drawdown on the storage but that's better than having none at all, especially overnight when the solar system itself is out of action. )

These are available off-the-shelf. For example the Radian system:

OutBack Power Radian Inverter Systems

This system sends solar power to the grid when the grid is up. When the grid goes down the big loads drop (A/C, pool pumps etc) and an "essentials" panel remains powered. This gives you 8000 watts for refrigeration, lighting, communications, water pumping etc. This requires batteries of course, but is a great way to provide reliable power in areas that lose power often.

In areas with more reliable power a simpler backup system (such as the SMA Sunnyboy inverters provide) is more appropriate.

Crap those interters are expensive! Wonder how much of the prices are purely inflated by current tax subsidizes, credit and requirement for professional (aka often monopoly) installations.
--

As for solar water, they should already be in most American homes--it's been reliable and effective for many decades.

Originally Posted by Lynx_Fox

Crap those interters are expensive!

That one is, yes. Keep in mind that that one is unusually expensive since it is:

1) prewired with all the 'bits' included
2) a battery backed system
3) an unusually large amount of backup power (8kW continuous, 17kW surge)
4) the latest/greatest/shiniest

As for solar water, they should already be in most American homes--it's been reliable and effective for many decades.

Agreed. We currently have solar-PV but no solar hot water; that's next on our list.

I am totally solar in Hawai'i almost three years now...however...if the power goes out....I LOSE ALL my power BUT I actualy get a little light from back up in the system for an hour or two except of course on my computer

Originally Posted by babe

I am totally solar in Hawai'i almost three years now...however...if the power goes out....I LOSE ALL my power BUT I actualy get a little light from back up in the system for an hour or two except of course on my computer

You gotta get you one of these SMA inverters!

billvon

How would this topic include small wind generators? The link below includes a list of 256 Small Wind Turbines from 129 manufacturers indexed:

All Small Wind Turbines | Portal to the world of small wind turbines

Many of these small wind generators work at very low wind speeds and are relatively inexpensive and some of them run very quietly.

Seems like a very good companion to solar.

I wish I could like small wind turbines more than I do, as they act as a nice compliment to small scale solar systems. The problem is there's little independent testing for output or reliability, both of which are severely lacking in the few independent studies done on these systems. If have a great location and are a handyman they can be a good investment-even than you'd probably get two--because at least one of them is going to be down for maintenance several times a year.

Originally Posted by Lynx_Fox

I wish I could like small wind turbines more than I do, as they act as a nice compliment to small scale solar systems. The problem is there's little independent testing for output or reliability, both of which are severely lacking in the few independent studies done on these systems. If have a great location and are a handyman they can be a good investment-even than you'd probably get two--because at least one of them is going to be down for maintenance several times a year.

I've seen this and a similar model on a one hour TV program and they looked very good. The magnetic barring is absolutely quiet and it never wears out, and it's small enough to be mounted on your roof.

Magnetic levitation residential wind turbines

Originally Posted by billvon

Originally Posted by babe

I am totally solar in Hawai'i almost three years now...however...if the power goes out....I LOSE ALL my power BUT I actualy get a little light from back up in the system for an hour or two except of course on my computer

You gotta get you one of these SMA inverters!

No clue what they are!

We chose not to sell our extra power back cause they charge you! *L*

Originally Posted by Bad Robot

How would this topic include small wind generators?

Sort of independent, since the inverter is separate from the power source. But overall, wind is a good complement to solar IF the homeowner is willing to spend the money on a good tower and is in a good location. Generally you are talking a MINIMUM of a 75 foot tower, and generally people "cheap out" on the tower and end up unhappy with the result.

and it's small enough to be mounted on your roof.

Never ever do this.

1) It won't be high enough to collect much energy.
2) It won't be big enough to collect much energy.
3) The noise will drive you nuts. Houses are great resonators for wind turbine conducted noise.
4) Roofs are not designed to withstand the sort of stresses wind turbines create and you may see part of your roof departing in a storm some day.

Originally Posted by babe

No clue what they are!

See here: SUNNY BOY 3000TL-US / 4000TL-US / 5000TL-US.*SMA America, LLC

We chose not to sell our extra power back cause they charge you! *L*

You're net metered, right? In effect you are selling your power back; you use their power at night and sell it back during the day, and you only pay for the net power used. That's a pretty good deal for homeowners even if they don't pay you for extra power generated, since you can zero your bill out. (Well, almost zero - around here there's a minimum $5 a month charge.)

Originally Posted by billvon

Originally Posted by babe

No clue what they are!

See here: SUNNY BOY 3000TL-US / 4000TL-US / 5000TL-US.*SMA America, LLC

We chose not to sell our extra power back cause they charge you! *L*

You're net metered, right? In effect you are selling your power back; you use their power at night and sell it back during the day, and you only pay for the net power used. That's a pretty good deal for homeowners even if they don't pay you for extra power generated, since you can zero your bill out. (Well, almost zero - around here there's a minimum $5 a month charge.)

A charge of about 250.00 a year....

Sounds like Kojax was talking about the old type of inverter which has a DC motor running an AC alternator. These were common before modern electronics allowed the design of solid state switched mode inverters - (so-called "static" inverters, because they have no moving parts)*


*except cooling fans perhaps, but these are not directly involved in the conversion process.


OB

Here's a summary of the disappointing results from one test of a dozen home windmills; all produced far less than expected and 25% broke the first year:
Low-tech Magazine: Small windmills put to the test

Originally Posted by Lynx_Fox

Here's a summary of the disappointing results from one test of a dozen home windmills; all produced far less than expected and 25% broke the first year:
Low-tech Magazine: Small windmills put to the test

For the great majority of small windmills that article is probably right on the mark. But they only tested a small number of small windmills and no mention of small vertical windmills using magnetic bearings. Also, I was only thinking that they might be used in conjunction with solar systems. Neither of which usually supplies 100% of a homes power needs. But I do know a few places where a 3 bedroom house easily uses between $300 & $400 dollars per month and any help they can get in reducing that bill is a big help and a good selling point if one wants to market the house.

Originally Posted by Lynx_Fox

Here's a summary of the disappointing results from one test of a dozen home windmills; all produced far less than expected and 25% broke the first year:
Low-tech Magazine: Small windmills put to the test

Looks like all those made the classic mistake of mounting on small towers. The rule of thumb is that the tower has to be a MINIMUM of 30 feet above the nearest obstacle that is within .6 miles the height of the tower. So if you are planning for a 100 foot tower, it has to be 30 feet above the highest obstacle within about 1/2 mile. (And that's to the bottom of the rotor, so your tower has to be even higher than that to get the bottom edge above the obstacle.) Looking at that picture I see trees on one side and a fence to the other that look like they come to within 30 feet of the bottom of the rotors - thus you're not going to see rated output even in good winds. About the only time you can skimp on tower height is if you are guaranteed a flat surface where the wind is blowing from - a seaside turbine where the winds are always off the sea, for example. In that case you could get away with a 40-50 foot tower, although it is always true that going higher gives you more power due to wind shear.

However they have a very good point that swept area is very important. Bigger is always better.

Originally Posted by Bad Robot

Originally Posted by Lynx_Fox

Here's a summary of the disappointing results from one test of a dozen home windmills; all produced far less than expected and 25% broke the first year:
Low-tech Magazine: Small windmills put to the test

For the great majority of small windmills that article is probably right on the mark. But they only tested a small number of small windmills and no mention of small vertical windmills using magnetic bearings. Also, I was only thinking that they might be used in conjunction with solar systems. Neither of which usually supplies 100% of a homes power needs. But I do know a few places where a 3 bedroom house easily uses between $300 & $400 dollars per month and any help they can get in reducing that bill is a big help and a good selling point if one wants to market the house.

The cold reality is the payback for small windmills is often 20 years or more and often never returns even the energy it took to manufacture them. Saving a few bucks based on an initially expensive, noisy, long-payoff and not entirely reliable windmills is false savings of time, effort and money.

It's a much better fit for larger community based systems with an ideal location, and I think that's where our efforts should focus.

there is no way my CC&R's would let me build a 30 food tower...

I am happy with my solar panels....my bill went from $800.00 a month (NOT KIDDING) for one to two person with NO AIR CONDITIONING to between 20.40 to my worse was 228.00

Originally Posted by babe

there is no way my CC&R's would let me build a 30 food tower...

I am happy with my solar panels....my bill went from $800.00 a month (NOT KIDDING) for one to two person with NO AIR CONDITIONING to between 20.40 to my worse was 228.00

What kind of power company charges that much with no air conditioning? That's insane.

Originally Posted by Bad Robot

Originally Posted by babe

there is no way my CC&R's would let me build a 30 food tower...

I am happy with my solar panels....my bill went from $800.00 a month (NOT KIDDING) for one to two person with NO AIR CONDITIONING to between 20.40 to my worse was 228.00

What kind of power company charges that much with no air conditioning? That's insane.

My water bill is 350 a month......go figure...for one person..I do two loads of laundry every 9 days and dishwasher once every five......irrigation yes, but 1/3 acre....isn't much to irrigate.....once a day at night...

I think I need to bend over and grab my ankles.

Rmember, my husband lives on the MAINLAND and I live in Hawai'i! SO he isn't there more than 3 months MAX a year!

Originally Posted by babe

Originally Posted by Bad Robot

Originally Posted by babe

there is no way my CC&R's would let me build a 30 food tower...

I am happy with my solar panels....my bill went from $800.00 a month (NOT KIDDING) for one to two person with NO AIR CONDITIONING to between 20.40 to my worse was 228.00

What kind of power company charges that much with no air conditioning? That's insane.

My water bill is 350 a month......go figure...for one person..I do two loads of laundry every 9 days and dishwasher once every five......irrigation yes, but 1/3 acre....isn't much to irrigate.....once a day at night...

I think I need to bend over and grab my ankles.

Rmember, my husband lives on the MAINLAND and I live in Hawai'i! SO he isn't there more than 3 months MAX a year!

Damn!!! Dig a well and double your solar power or pick a better place to live.

Originally Posted by billvon

Originally Posted by babe

I am totally solar in Hawai'i almost three years now...however...if the power goes out....I LOSE ALL my power BUT I actualy get a little light from back up in the system for an hour or two except of course on my computer

You gotta get you one of these SMA inverters!

You come over and show me how and I might *L*....I am clueless

We just wanted to be independent and use the energy that is so plentiful. He's promised me the pool. It's only 77 degrees and I am w/o much body fat so I freeze in the pool!! The ocean is warmer, but for swimming laps....the pool (which is saline) is a better option.

Anyhow...water heaters were our first Solar endeavor there. We just need to figure out regulators still....funny how once they put the system in some (not the ones who did the main house) are like hell to get hold of!

Originally Posted by Bad Robot

Originally Posted by babe

Originally Posted by Bad Robot

Originally Posted by babe

there is no way my CC&R's would let me build a 30 food tower...

I am happy with my solar panels....my bill went from $800.00 a month (NOT KIDDING) for one to two person with NO AIR CONDITIONING to between 20.40 to my worse was 228.00

What kind of power company charges that much with no air conditioning? That's insane.

My water bill is 350 a month......go figure...for one person..I do two loads of laundry every 9 days and dishwasher once every five......irrigation yes, but 1/3 acre....isn't much to irrigate.....once a day at night...

I think I need to bend over and grab my ankles.

Rmember, my husband lives on the MAINLAND and I live in Hawai'i! SO he isn't there more than 3 months MAX a year!

Damn!!! Dig a well and double your solar power or pick a better place to live.

a better place than THIS? Sheesh...kiss a monkey!

Originally Posted by babe

My water bill is 350 a month......go figure...for one person..I do two loads of laundry every 9 days and dishwasher once every five......irrigation yes, but 1/3 acre....isn't much to irrigate.....once a day at night...

Some suggestions:
1) Irrigate with graywater
2) Cover the pool
3) Go to low flow toilets and showers
4) Get a more efficient washing machine (expensive but if you save $50 a month it's worth it)
5) Composting toilet

Originally Posted by babe

a better place than THIS? Sheesh...kiss a monkey!

If you have an automatic pool leveler to keep your pool water level without you having to manually do it. I've heard of pools that get small leaks in them that cause your automatic leveler to run all the time. (Very bad for the water bill). Next I personally had a water softener that went berserk and ran my water bill up over $600 once. The water company wasn't very sympathetic with my problem.

Originally Posted by billvon

Originally Posted by babe

My water bill is 350 a month......go figure...for one person..I do two loads of laundry every 9 days and dishwasher once every five......irrigation yes, but 1/3 acre....isn't much to irrigate.....once a day at night...

Some suggestions:
1) Irrigate with graywater
2) Cover the pool
3) Go to low flow toilets and showers
4) Get a more efficient washing machine (expensive but if you save $50 a month it's worth it)
5) Composting toilet

Thanks for the suggestions, but they aren't feasible. The pool one is well ...it's an eternity pool! You can't cover it....we don't HEAT it, and if we do, it will be solar....

Please realize that we did the ENTIRE house in solar 2 1/2 years ago, and my washer dryer are one's for a condo size not full size now.

I always appreciate suggestions though and if implementable, I shall check into them!

Originally Posted by Bad Robot

Originally Posted by babe

a better place than THIS? Sheesh...kiss a monkey!

If you have an automatic pool leveler to keep your pool water level without you having to manually do it. I've heard of pools that get small leaks in them that cause your automatic leveler to run all the time. (Very bad for the water bill). Next I personally had a water softener that went berserk and ran my water bill up over $600 once. The water company wasn't very sympathetic with my problem.

Thanks and yes we have a pool water level. It is checked every week, and I also keep an eye on it.

Your water bill, seems to be determined by where you live. Nine mile up Kawai'hae road, they pay 40.00 a month...and they have a pool etc, also. Sometimes I just feel the need to bend over!!! If ya know what I mean! Trust me......I have had discussions with the County Water Department about this in LENGTH!. I may be small, but I wasn't nicknamed from a friend "mighty mouse" for nothing!!