A Hybrid system that can switch between using power from Solar panels and the Grid

[Maitland Gill]

Experimental Solar System (Update)

A Grid Assisted Uninterruptible Power Supply (UPS) that can use the power from a wall socket as it's alternative power supply.

Being able to produce our own electricity, allows us to reduce our power bill. The amount we save from this, can be used to expand our system. So the sooner we can start doing this, the faster we can become self-sufficient. Rather than wait until we can afford to install an Inverter to our Fusebox, what if we used a Grid-Assisted Uninterruptible Power Supply (UPS), that could automatically switch to using power from a wall socket (The Grid). This is for when the Solar panels don't provide enough current and require an alternative power supply.

In other words, a system that uses batteries, charged by Solar panels, to power you're device through an Inverter. When the batteries are drained to a certain level, the power supply switches to the wall socket (Grid), while the batteries are recharged again. This way, even if the Solar panels don't produce enough power to run a device, they can still help reduce you're power bill.

When you're ready to make changes to the Fusebox, the equipment that makes up a UPS could then be used in supplying power to the entire house. In Australia, the cost of replacing a switchboard is about $700. New circuits and having to rewire cables could bring this up to $5,000 [01].

This is how I think it could work:

1. A Solar panel is connected to a Charge Controller (Or Solar Controller), which supplies the correct amount of current to a Battery.

2. A Shunt is placed in between the Charge controller and the Negative terminal of the Battery.
This allows a Pentametric to measure the amount of charge coming from the Battery on the Negative side.


What is a Shunt?

[02] [03] - This is also described in Section 2: Page 13 of this manual.


The Battery, Shunt, and Charge Controller are all connected together by using 3 Lugs. This is because the Shunt, which is located on the Negative side of the circuit, requires two Lugs which are half the length of the Positive one.


What is a Lug?

A Cable Lug is an electrical fitting used to connect a cable to mechanisms. The Lug is fastened to a matching terminal or connection point using a bolt, screw or spring clip. A Cable Lug is easy to install or remove (For repairs or maintenance) and can be used when a transfer of power is required from one location to another, across multiple devices [04].


3. The Batteries Positive Terminal is connected to the Inverter, by using a single Lug. However, the Lug from the Battery's Negative Terminal, is attached to a Relay Switch first and then to the Inverter. The Pentametric can use this Relay Switch to allow or interrupt the current that flows between the Battery and Inverter. The Pentametric does this when it senses that there isn't enough charge left in the battery. For this, another 3 Lugs are needed.


What is a Relay?

A relay is an electrical switch operated by a relatively smaller electric current, which can turn on or off a much larger electric current [05]. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching [06]. They can be used in the same way as a Circuit breaker, which interrupts the current in a circuit [07].

Devices switching more than 15 amperes or in circuits rated more than a few kilowatts are usually called Contactors.
Contactors can make loud sounds when they operate, so they may be unfit for use where noise is a chief concern [08].


4. The Inverter, which converts DC to AC, is connected to an Uninterruptible Power Supply (UPS). These provide emergency power to a load when the first input fails. For this project, the battery is made into the primary source of power and the Wall Socket as it's alternative.

5. The Shunt is connected to the Pantametric, so that it can measure the State of Charge (SOC) within a battery.
The (SOC) is an indication of how much charge the Battery has left, which can be measured by observing the current [09] [10].

The Pantametric can be made to turn on the Relay, when the Battery has the same Voltage as the one predetermined by the user.

On page 24 (P30 - P31) of the "PentaMetric Main Instruction Manual" by Bogart Engineering, it is explained that the Programs P30 and P31 will allow you to enter the two set Voltages, that will turn the Relay Off and On. The Voltage that turns the Relay on, needs to be equivalent to the battery being at no more than 75% of it's total charge, least it be damaged. The Voltage that turns it off, is the same Voltage that the Battery has when fully charged. However, this will decrease over time, so it may need to be lowered.

When the Relay is switched Off, the UPS will resume using the Battery as it's primary source of power. Even if the Solar output isn't enough to support you're load, it can still help to reduce you're power bill and you won't need to worry about the batteries going flat.

This set-up only works if the cost is less than what it would be if you were to install a Grid-Tied system to you're Fusebox.

The intention of this, is to obtain Solar energy as quickly as possible. Is there any advice you could give me on what parts I may need?


Notes:

The charging source needs to provide a Voltage that's greater than the batteries, so the current can effectively flow through it [11].

This type of set-up is best used for smaller applications (Bar Fridges, Air-conditioners) so that it can take the strain off you're power bill while allowing you to gradually expand. The cost and reliability of such a system could help make Solar more accessible than before.

There are also systems called 'Plug and Play Solar Panels', which can send power back to the grid from a wall socket.
A Grid-tied Inverter shuts itself off during a blackout, so as not to harm the workers fixing the power line.
I do not know how safe these systems are during this scenario, so I cannot recommend them yet.

A Solar Regulator is a Charge Controller designed for Solar systems. The Regulator can also provide a direct connection to appliances, while continuing to recharge the battery [12].

[donald]

The Tesla systems should easily provide these gross savings in larger homes in Hawaii. It's a big world, with all sorts of different needs and costs. Early adopters will of course be more specialized users, as well as hobbyists. But that's hardly the point. Net metering is only beneficial to encourage the initial development of solar. It has to go away.

Where I live, long power outages are always weather related. I can see a battery system that normally automatically conducts arbitrage and earns a couple dollars a day, but converts to power saving mode based on a bad short range weather forecast. My $150 home automation controller already acts on current weather, and displays the forecast.

The Tesla battery system today is designed to last about tens years with daily cycling. If they can build that on commodity batteries, so can many other companies.

[Mike90250]

Sir, if you have a load shift scheme that generates actual $ in your pocket, and can pay for the batteries it consumes, I bow to you.

Generally, the TOU schemes don't allow for any reasonable cash back at all, just a credit on the bill that resets once a year.

[donald]

Totally a waste if you are in an area with reliable power. ...................

Now what if that storage earns $4 a day? $6 dollars? There's a tipping point of battery cost where the ability to load shift some solar in the home makes sense. That change will correspond with the $40,000 200 mile range electric car.

A $5000 systems that last 5 years and returns $4 a day pays for itself. We're near the point in growth where solar supplied to the grid from the home will need to be priced rationally.

[Mike90250]

.... Anyone considering a good backup generator should consider batteries instead. Anyone looking at a new system today should consider they may want to add batteries in the future.

Totally a waste if you are in an area with reliable power. For 20 years, I could count the number of grid failures longer than 5 minutes, on less than 1 hand. Investing in two $5000 battery banks, that would sit mostly idle, slowly dieing till it needs replacement in 10 years (2 batteries, 10 year ea, $10,000 for 20 years) would be a horrific waste of money, when a single, $1,000 genset and transfer switch and 20 gal propane tank would have done the same job. As long as you have reliable grid. Once the grid is sick, and down for a day each month, then the expensive batteries may become a consideration.

[tasman]

I see only half of the information to help me agree with you that your way is cheaper then purchasing from the Utility.

How about telling us roughly were you live and how much a kWh costs you. $400 to 500 a quarter doesn't mean anything to me because I do not know how many kWh you are using in that time period.

What is the make and model of the LiFePO4 batteries and how are they wired? We can calculate the kWh it can generate a year and estimate a range of life in years.

What is that 7kw array consist of. Panel make and model as well as the charge controller and inverter.

One top of that, where did you purchase those panels and batteries for that $11,000? Did you add in the shipping cost and possible tariffs? How about what it cost you to install that system. It all adds up to a big $$$ and when you do the math you can estimate what it costs to generate a kWh from your system.

You may think you are saving money by using batteries at night instead of the "grid" but I still think you are truly unaware of what the cost is to generate your own electricity.

Can't tell you any more about the 7KW system, as it's not mine, but got most of my stuff from the same suppliers. Ours is 700ah lifepo4 and 2kw solar. Built it all myself, the current 24v panels are 250w and cost $235 each delivered.

When doing any costing, you always include freight etc. never buy brand names, always buy what is recommended by people in the know and gives the best price. When we want to buy more, we do it as a group with others and get the best prices available. The capacities range from 40-60ah, never use large capacity cells. That way if a cell goes wrong, you can take it and a couple of others out and still have an almost full system, but with 100+ah cells, if one goes down, that's probably it for the entire system. I have spare cells, which are used as my test pack and always carry a 120/60 x 12/24v pack when we travel, yet to use it for anything but testing BMS and other parts of the system.

Our lifepo4 are sourced from manufacturers of industrial and military cells, which have overrun orders and badly branded cells, which means we seem to get them pretty cheaply. Our last set of 45ah x 3.2v cells, cost 59 cents an amp and totalled 83 cents an amp delivered, yet they are branded as 1400ma, 20v.

[tasman]

How many 20% - 85% cycles for lifepo4 ? about 2,000 ?
365 x 5 years 1,825 days/cycles.
365 x 20y = 7,300 days/cycles - which I find very hard to believe. What battery mfg is giving that number ?

$5000 for lifepo4 cells At what watt-hour size ? 2000ah at 12V or at 48V ?

I do understand the LFP cells are over 95% efficient, but I don't see the watt-hours or expected lifetime of the system spelled out. Panels I can see 20+ years, but the inverter, I think the better guess is 10 years, same with charge controller.
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Their system is 2000ah at 24v, believe cycling in lifepo4 is very different to LA. With lead acid, you have approximately 30% of usable energy in a 2000ah battery bank. With lifepo4 you have 100% if you want to use it, which would definitely create cycling. By only using 80% and with proper computer control of your entire energy system, cycling becomes rare as most properly set up systems rarely reach their upper and lower voltage parameters to create a full cycle. With lifepo4, you never have to fully charge them, they are more than happy at 80%. Very different to LA which requires to be fully charged to get the best performance and longevity, so they cycle every time you use 15-30% of the supposed capacity.

It took me a long time to understand and see this in action and like most, doubted it possible, yet my 700ah lifepo4 house system in almost 2 years, has yet to reach it upper or lower limits and that is 80% of charge and 80% discharge. So have no idea whether or how many cycles it has been through, but could say none because it has never had to stop charging or stop supplying load. No LA system can say that ever.

From what I've learnt, seen in action and told by those who have been using lithium technology for at least 5 years, cycling only occurs when you reach upper or lower battery parameters. This comes from a company that designs, builds and installs lifepo4 off grid and grid connect systems and has a number of test packs of different lithium technologies. One lifepo4 has been running their office for more than 5 years they say and has yet to reach cut off voltages. Got my idea of fully computerising my home system with open source from them and can say it is a wonderful way to utilise and control energy.

I still have a couple of 80w panels operating from the 1980's which are now on my workshop and two inverters. One is a modified sine wave 12v x 300-600w I built which was used to construct our house, still use it for power tools running off a tractor or a vehicle. The other is a 12v x 1500-2500w pure sine wave I built in the late 1980's and still works in my workshop, since I bought a cheapo Chinese 3000w-6000w 12v inverter on an ebay auction a couple of years ago for the house.

The life span of any system relies upon it's management and with lifepo4 and computer control, you enter a totally different energy world. If you have a computerised system then you have even more control, so our house runs on 12v and 240v, with LED lighting and no need for heating or cooling, as our home sits 1.5m in the ground.

I'm working on a very old Compaq 256k ram laptop at the moment, to get it to the stage where it can run our MH (RV) lifepo4 system instead of doing it manually with BMS at the moment. Probably preferable to use a raspberry Pi, but got this dinosaur brick for $5 at a garage sale.

[donald]

I've had generators for years, both running on gasoline and mains natural gas. I would gladly pay more for batteries and forget the generator. In fact I did this in my camper. But my idea of backup power at home doesn't include air conditioning.

[SunEagle]

The only place it may pay are businesses using battery at peak rate times. The ROI can be 10-20%.
But the potential for a positive return on investment will improve as battery prices drop. The first solar system I installed was off grid. It's very odd for me now that people are discovering that batteries can be added to solar. Anyone considering a good backup generator should consider batteries instead. Anyone looking at a new system today should consider they may want to add batteries in the future.

I disagree with your logic. Mu logic is based on the existing cost of batteries that installing them NOW is less cost effective than using a generator. Hopefully sometime in the future "energy storage technology" will not only improve but be much lower in cost. Then you should look into (if the cost is justified) to add that storage system.

The generator is both the right choice for emergency backup as well as required if you have batteries. So that comes up front no matter what the cost of batteries.

[donald]

Pure and blatant BS - nothing more. You made a nice mess and now you are trying to convince yourself it was a good deal.

What was a good deal? What mess ? The only lithium batteries I have are in the usual small electronics. The only solar I own is typical residential technology.

[russ]

The only place it may pay are businesses using battery at peak rate times. The ROI can be 10-20%.
But the potential for a positive return on investment will improve as battery prices drop. The first solar system I installed was off grid. It's very odd for me now that people are discovering that batteries can be added to solar. Anyone considering a good backup generator should consider batteries instead. Anyone looking at a new system today should consider they may want to add batteries in the future.

Pure and blatant BS - nothing more. You made a nice mess and now you are trying to convince yourself it was a good deal.

[donald]

You may think you are saving money by using batteries at night instead of the "grid" but I still think you are truly unaware of what the cost is to generate your own electricity.

The only place it may pay are businesses using battery at peak rate times. The ROI can be 10-20%.
But the potential for a positive return on investment will improve as battery prices drop. The first solar system I installed was off grid. It's very odd for me now that people are discovering that batteries can be added to solar. Anyone considering a good backup generator should consider batteries instead. Anyone looking at a new system today should consider they may want to add batteries in the future.

[SunEagle]

The hard part of teaching a safety class is convincing the students that actions they have taken many times can be dangerous or deadly. "Getting away with it" is no big deal in the short term - what happens over time is.

I agree with you it is sometimes hard to convince someone of what is safe and what is dangerous. The learning point hopefully comes with just a little "damage" and a lot of OH S**T!!!!

At least with his way of thinking the bad part ends up being just the loss of money. With safety the end result usually ends up with much worse like dismemberment or death.

[SunEagle]

No you're not following it right. They charge their batteries during the day from the panels, as well as feed into the gird. At night they use the lifepo4 batteries for power. The generator is for when there is lots of cloudy days and no wind, or for their 3 phase workshop. When the generator is running, they are charging the batteries, 2000ah of lifepo4 and 7kw of solar is adequate for what they need, to pay back and make a profit from their system.

Don't know what you lot are using, but if haven't exoerienced good lifepo4 storage systems and the massive adivatages oif them, then you don't have a clue and using very primitive 19th century technology.

Let's say, down here, the avergage quarterly energy bill is about $400-500, that's $2000 a year, which is very conservative. A lifepo4 system of 2000ah and 7kw of solar, costs $6000 for panels and $5000 for lifepo4 cells, $1000 for a 6kw generator and required assecories. The life of the system is more than 20 years, yet you can recoupe your invest in less than 6 years. Make a loyt of sense to me , rather than denial of the reality.

I see only half of the information to help me agree with you that your way is cheaper then purchasing from the Utility.

How about telling us roughly were you live and how much a kWh costs you. $400 to 500 a quarter doesn't mean anything to me because I do not know how many kWh you are using in that time period.

What is the make and model of the LiFePO4 batteries and how are they wired? We can calculate the kWh it can generate a year and estimate a range of life in years.

What is that 7kw array consist of. Panel make and model as well as the charge controller and inverter.

One top of that, where did you purchase those panels and batteries for that $11,000? Did you add in the shipping cost and possible tariffs? How about what it cost you to install that system. It all adds up to a big $$$ and when you do the math you can estimate what it costs to generate a kWh from your system.

You may think you are saving money by using batteries at night instead of the "grid" but I still think you are truly unaware of what the cost is to generate your own electricity.

[russ]

The hard part of teaching a safety class is convincing the students that actions they have taken many times can be dangerous or deadly. "Getting away with it" is no big deal in the short term - what happens over time is.