[Question]Important Considerations for Installing a Solar System

[arthur_morgan]

Hello, dear solar enthusiasts!

I'm excited to share that I'm planning to install a solar system with a capacity of 10 kW at my place. I'm considering getting an On-Grid or Grid-connected solar system. There is a concept called "Time of Day" or "ToD" tariff that is applicable to my grid-connected system. This tariff requires me to pay for electricity from the grid specifically for the period between 6 PM to 10 PM every day, regardless of the amount of solar energy my system feeds back into the grid. I generally don't use heavy or power-hungry appliances during the "ToD" period and the ones, I use will use them during the day time.

The decision to go with an On-Grid or grid-connected system is because a battery-provided (lead-acid or lithium) power source (secondary power source) during night time won't be power heavy loads like AC or other high-energy appliances for an extended period. They get discharged, and over time, their capacity to hold a charge is reduced. In an On-Grid or grid-connected system, I will consume the electricity generated from the solar system during the daytime, and any surplus electricity will go to the grid. When I use electricity from the grid during nighttime, the units used from the grid and the units sent to the grid by solar will be adjusted, resulting in a roughly zero bill. I have a medium-capacity battery-operated power backup that can run my house for two to three hours in case of a power failure.

However, before proceeding, I wanted to gather some crucial information that I should be aware of before getting the solar system installed. Please enlighten me with information that sellers/companies do not tell consumers upfront. For example, I was not aware that in the case of a grid power failure, the solar system will not provide electricity to the home regardless of the time of day (anti-islanding). Please provide me with facts so that I don't have any false or impractical expectations from my solar system.

To ensure a smooth transition, I thought it would be helpful to share my research and ask for your valuable input on the matter. If I'm wrong or mistaken for any solar concept please correct me.

Thank you in advance for your help.

 

[12VoltInstalls]

For example, I was not aware that in the case of a grid power failure, the solar system will not provide electricity to the home regardless of the time of day (anti-islanding)

There is equipment that will isolate you and be UL Listed known as UL1741 among a couple others that are related and still give you 100% uptime power when the grid is down. It sounds like you are microinverter-based.
There’s also non-microinverter systems that will give you 100% ups-quality backup

 

[SeaGal]

Welcome! What is your maximum expected load and typical kWh used in the day? - that will help sizing the system including battery storage.

Grid-tied inverters will disconnect when the grid goes down (to avoid electrocuting engineers working on the lines)... plus you wouldn't be wanting to supply your whole neighbourhood. Instead, you can get an inverter that has an ac backup or critical load port, or a non-grid-tied system that passes ac through to your house.

 

[arthur_morgan]

Welcome! What is your maximum expected load and typical kWh used in the day? - that will help sizing the system including battery storage.

Grid-tied inverters will disconnect when the grid goes down (to avoid electrocuting engineers working on the lines)... plus you wouldn't be wanting to supply your whole neighbourhood. Instead, you can get an inverter that has an ac backup or critical load port, or a non-grid-tied system that passes ac through to your house.

Hello @SeaGal, I apologize for the delay in my response. During the summer months (March to July/August), I use two or three 1.5T ACs and my electricity usage peaks at almost 1000 units (1 unit equals 1 kWh). If I were to run the same load, including the two ACs, during the ToD period (6-10 PM) daily, I am wondering what type of batteries I would need and their specifications. I am planning to invest in a 10kW solar system to ensure my future electricity needs are met. Can you please advise me on how much current and power the 10kW solar system will generate? I am also considering converting it to Off-Grid after some time (say a year or two) or maybe earlier. Can you help me decide what inverter and battery I will need for this?

Edit: Correction made. Earlier it was (1 Unit equals 1000 Kwh). Now it is corrected.

 

[arthur_morgan]

There is equipment that will isolate you and be UL Listed known as UL1741 among a couple others that are related and still give you 100% uptime power when the grid is down. It sounds like you are microinverter-based.
There’s also non-microinverter systems that will give you 100% ups-quality backup

Dear @12VoltInstalls, I apologize for the delay in getting back to you. Just to clarify, are you saying there is a device available for a grid-tied solar system that can provide power from the solar panels in the event of a grid failure, without the use of batteries or an off-grid setup? If yes, please provide me with details of such a device.

 

[SeaGal]

During the summer months (March to July/August), I use two or three 1.5T ACs and my electricity usage peaks at almost 1000 units (1 unit equals 1000 kWh).

1000 units of 1000kWh? So one unit is a Mega Watt hour, which means that your 1000 units is a Giga Watt hour? Really?

Over what time period do you consume that gigaWatt hour of energy?

 

[12VoltInstalls]

Dear @12VoltInstalls, I apologize for the delay in getting back to you. Just to clarify, are you saying there is a device available for a grid-tied solar system that can provide power from the solar panels in the event of a grid failure, without the use of batteries or an off-grid setup? If yes, please provide me with details of such a device.

There are some no-battery equipment in the marketplace. The best of these are top-tier and expensive but I think www.watts247.com has a less costly option.

But no, I was not recommending a no-battery solution. In the event of a grid failure or partial cloudiness a no-battery solution has little to no appeal to me. Well really no appeal to me.

In your situation I would utilize a grid-tie “no sell” system or AIO with batteries and use as much solar energy as possible (SUB - solar first, utility second, batteries third priority) which will at least provide a daily ‘savings’ which may achieve a return on investment at some point.

 

[arthur_morgan]

1000 units of 1000kWh? So one unit is a Mega Watt hour, which means that your 1000 units is a Giga Watt hour? Really?

Over what time period do you consume that gigaWatt hour of energy?

In my country 1 Unit = 1 Kwh. I apologise for any confusion.

 

[arthur_morgan]

1000 units of 1000kWh? So one unit is a Mega Watt hour, which means that your 1000 units is a Giga Watt hour? Really?

Over what time period do you consume that gigaWatt hour of energy?

It should have been 1 Unit = 1 Kwh. Thank you for pointing out the mistake.

 

[arthur_morgan]

There are some no-battery equipment in the marketplace. The best of these are top-tier and expensive but I think www.watts247.com has a less costly option.

But no, I was not recommending a no-battery solution. In the event of a grid failure or partial cloudiness a no-battery solution has little to no appeal to me. Well really no appeal to me.

In your situation I would utilize a grid-tie “no sell” system or AIO with batteries and use as much solar energy as possible (SUB - solar first, utility second, batteries third priority) which will at least provide a daily ‘savings’ which may achieve a return on investment at some point.

Thank you for the suggestion. This helped me clear my mind regarding the battery aspect of the system. After reading and understanding your reply I now understand that the connection from the grid is highly important in some conditions like the one you mentioned (cloudy days). During the monsoon, the solar system wont be able to generate much electricity to suffice my needs.

 

[DIYrich]

I am guessing that 1,000 kWh is monthly, or about 30kWh per day. What is your peak kW usage for any short period of time? What is the startup amps for the largest AC?

How many continuous cloudy days are typical during monsoon?
Electric generator ok?
What is your budget?
What is your power (voltage, phases)?
Can you feed power to the grid and get paid for it?

 

[arthur_morgan]

I am guessing that 1,000 kWh is monthly, or about 30kWh per day.

Yes, the consumption of 1000 kWh is monthly (during summers).

What is your peak kW usage for any short period of time?

To be honest I have not looked into this.

What is the startup amps for the largest AC?

It is a 1.5T AC, so it must be around 10 Amps (excluding inrush current). Does it matter? I'm curious as I do not have much knowledge about it.

How many continuous cloudy days are typical during monsoon?

During the monsoon season, which typically lasts 100-120 days, there is only about 20-30 days of sunlight. As a result, I will mostly rely on the grid for electricity during this time.

Electric generator ok?

I do have a diesel generator set. What is an Electric generator?

What is your budget?

The budget outlined by the contractor is close to $7300 (excluding the subsidy being provided by the government). For my system (10 kW) government will provide approximately $1300 in subsidy (the government will credit the subsidy amount directly into my account after the first 30 days of installation of the solar system).

What is your power (voltage, phases)?

The voltage is between 230-250V (mostly 240V). As per government instructions any solar system above 7kW will have to use a 3-phase connection compulsorily from the grid. I am confused as to why the government wants this. As of now, I have a single-phase connection.

 

[12VoltInstalls]

per government instructions any solar system above 7kW will have to use a 3-phase connection compulsorily from the grid. I am confused as to why the government wants this. As of now, I have a single-phase connection

That is because of the government caring, and wanting to make sure all your needs are cared for. Because they care enough to assure that needs you didn’t even know you had are met, I’m sure.

 

[DIYrich]

With 20 days of sun out of 100 during monsoon, batteries would be crazy large. So, next thought is longest time grid is down? Hours, days?

 

[DIYrich]

>What is your peak kW usage for any short period of time?
To be honest I have not looked into this.

It is a 1.5T AC, so it must be around 10 Amps (excluding inrush current). Does it matter? I'm curious as I do not have much knowledge about it.

30 kWh average per day is helpful for sizing the solar panels. In addition, you need to know how much power you want to deliver to your load at any moment in time. 30kWh is 1.24kW per hour, on average. But, you may need 0.5kW at night, 1.5kW most of the time during the day, but 7kW peak needs. It is the Peak Needs that determines what size inverter you need. A 1.5 ton AC at 240v is about 5 amp RUNNING. It could need 15 amps to start. The inverter has to be able to supply that plus whatever other loads are on (2 other AC units drawing 5 amps each, electric oven, electric stove top, electric dryer, etc.). Then you might want to consider two of them trying to start at the same time (get home and turn on both AC units). Refrigerator is another high amp start-up device.

During the monsoon season, which typically lasts 100-120 days, there is only about 20-30 days of sunlight. As a result, I will mostly rely on the grid for electricity during this time.

Ok. How many days of power do you want your batteries to provide? One 6-10pm TOU period? 24 hours in case the grid is down? 3 days of 6-10pm TOU periods during cloudy days?

I do have a diesel generator set. What is an Electric generator?

Same thing. I suppose "electric" is redundant since what else does a generator do?

The budget outlined by the contractor is close to $7300 (excluding the subsidy being provided by the government). For my system (10 kW) government will provide approximately $1300 in subsidy (the government will credit the subsidy amount directly into my account after the first 30 days of installation of the solar system).

Don't know what prices are in India. $9,000 would get you solar only in the USA (maybe not even that). On a DIY basis, batteries would be about $3,000 for 15kWh.

The voltage is between 230-250V (mostly 240V). As per government instructions any solar system above 7kW will have to use a 3-phase connection compulsorily from the grid. I am confused as to why the government wants this. As of now, I have a single-phase connection.

May need to rewire your main panel to split your loads across the 3-phases.. When you are off-grid (grid is down), the inverter will want the 3-phases relatively close to each other (5kw, 3kw, 2kw?). It will definitely have trouble with providing all the power on one phase, and nothing on the other two (10kW, 0kw, 0kw). Put each A/C on different phases. things like that.

I'm guessing the reason for 3-phase connection is to keep the power grid balanced across the 3 phases. Any one small load is averaged over all the other small loads being on various phases. If a lot of people put a lot of power onto one phase, that could be a problem. Could be a small local problem (your local distribution sub-grid). The power company wants to keep that balanced too.

 

[arthur_morgan]

That is because of the government caring, and wanting to make sure all your needs are cared for. Because they care enough to assure that needs you didn’t even know you had are met, I’m sure.

I'm really confused about this 3 phase matter my friend. I don't know if what you said was sarcasm but I'm interested to know about the 3 phase reason.

 

[arthur_morgan]

30 kWh average per day is helpful for sizing the solar panels. In addition, you need to know how much power you want to deliver to your load at any moment in time. 30kWh is 1.24kW per hour, on average. But, you may need 0.5kW at night, 1.5kW most of the time during the day, but 7kW peak needs. It is the Peak Needs that determines what size inverter you need. A 1.5 ton AC at 240v is about 5 amp RUNNING. It could need 15 amps to start. The inverter has to be able to supply that plus whatever other loads are on (2 other AC units drawing 5 amps each, electric oven, electric stove top, electric dryer, etc.). Then you might want to consider two of them trying to start at the same time (get home and turn on both AC units). Refrigerator is another high amp start-up device.

In case there is not enough sunlight, how long does the switchover to the grid take? Is it instant like it is when we use battery-operated inverter as a secondary source of power?

Ok. How many days of power do you want your batteries to provide? One 6-10pm TOU period? 24 hours in case the grid is down? 3 days of 6-10pm TOU periods during cloudy days?

I have done the math for using batteries and it will not be a good idea to use batteries solely for ToD or ToU period. It will take more than 10 years to get the return on investment if I use batteries for Tod or ToU. So I have dropped the idea. The possibility of having 24-hour grid failure is rare but, when I moved to my new home I considered that possibility that's why I purchased a diesel generator set.

Same thing. I suppose "electric" is redundant since what else does a generator do?

I apologise, I failed to understand. My bad. Thank you for pointing it out. It thought new sophisticated gadgets have hit the market so that electric generator might be one of them. In our place, we rarely call it an electric generator (which it definitely is). We call it a DG set.

Don't know what prices are in India. $9,000 would get you solar only in the USA (maybe not even that). On a DIY basis, batteries would be about $3,000 for 15kWh.

Yes, I have seen a few videos on YouTube regarding solar and batteries. I agree with you that the prices are too high in the US for the same.

May need to rewire your main panel to split your loads across the 3-phases.. When you are off-grid (grid is down), the inverter will want the 3-phases relatively close to each other (5kw, 3kw, 2kw?). It will definitely have trouble with providing all the power on one phase, and nothing on the other two (10kW, 0kw, 0kw). Put each A/C on different phases. things like that.

I'm guessing the reason for 3-phase connection is to keep the power grid balanced across the 3 phases. Any one small load is averaged over all the other small loads being on various phases. If a lot of people put a lot of power onto one phase, that could be a problem. Could be a small local problem (your local distribution sub-grid). The power company wants to keep that balanced too.

As of now, I have a three-phase wire connecting my house and the grid out of which two phases are functional (connected to the grid). They (grid workers) will need to attach the third wire to the third phase. The load is split across two phases. I will try to further split the load so that the load is uniform across all three phases.

I agree with what you think could be the reason to have 3-phase connections for a solar system above 7kW capacity. Maybe a single phase on the grid can handle only a limited load or the subs station.

I have one more query. The amount of current that could be supplied to electrical appliances, is it dependent on the inverter or the capacity of the solar panels? What about the inrush current when starting the water pump or AC? I won't start multiple power/current-hungry appliances at once.

 

[DIYrich]

When grid is connected, it is instant (for all practical purposes) the change between import/export power to grid. What takes time is disconnecting from grid when it goes down.

The amount of current supplied is limited by the Inverter. Inrush too. On grid, some inverters can take excess from grid. For example, the sol-ark 15k can provide 50 amps from the inverter and pass 200 amps total when on grid.

 

[DIYrich]

Regarding batteries: you posted that you already have a battery backup. Can you attach those batteries to the solar inverter? Or sell it to buy batteries for the inverter?