Hybrid solar with grid tie on Hawaii?

[BenHawaii]

Aloha,
So happy to have found this forum and that different solutions to energy generation are divided into separate sub forums. We live on Hawaii, on the rainy side, and are investigating a hybrid system. However, after reading the sticky message "Hybrid Solar, grid tied solar pv with batteries" relating to the extra cost vs financial benefit, I see we need to do more research.
We have to consider that we are on a remote island in the Pacific. There is one electric company that relies on ships to bring fuel. Shipping to Hawaii is strictly regulated by the Jones act so which makes us further vulnerable to fuel price spikes. If shipping traffic is disrupted there are minimal fuel reserves on the island. We also wanted to reduce our electric bill, possibly to just the minimum monthly customer charge of $25, since we are tied to HELCO. Having been through multiple hurricanes, with one resulting in no power for 10 days,did not have a generator at the time), self sufficiency is a consideration. We currently heat house water with propane and have propane stove. Of course, we know that propane supply could also be disrupted, so alternatives are a consideration down the road.

I have a basic understanding of small off grid systems. Wanted to get some advice on considerations for a whole house hybrid system. Home is 2,000 Sq feet 4 bed 3 bath. Currently just two of us, but have the space for our parents to visit or possibly live with us if they need to. But for now we are aware of conserving power, mostly LCD bulbs, energy star appliances. I know that going completely off grid would not be a wise financial investment. So buying some power, when batteries or panels can not supply our needs, seems more cost effective.

15 Kwh daily average
Purchased power rate .344 per Kwh

Energy inventory shows 4,000 watts total need, if everything was being used at the same time. A typical evening shows that 1700 watts might be used per hour, but I don't know how to calculate a true usage taking into consideration that this includes a refrigerator and chest freezer, that are not always running. If we had company staying here the possible evening usage could increase to 3,000 watts per hour. But company is not a regular occurance. Thinking we need to install panels that can generate 5,000 watts, under optimal sunny conditions.

Thanks
Ben

[scrambler]

15kWh/day is only 5,475 kWh per year, so not huge.

You need to determine if that may change drastically in the future, like if you add electric cars...
First goal is to determine the total energy (kWh) you should aim to produce per year.

In addition to the target kWh per year, you will need to determine where the panels will go (roof, ground...) so you can determine their orientation (south, SE, SW...) and their tilt.
One you have these numbers, you can determine the size your solar array (how many kW of panels) using the PVWatts Calculator (nrel.gov) site.
You enter an array size like 5kW, your location, Orientation and tilt, and that will give you the yearly kWh that 5kW array can produce.
You then just increase or decrease the array size to meet the yearly goal.


The next step is sizing the battery (capacity in kWh). To do that, you need to figure out a few things.
- How long are outages usually.
- During what season / periods are they usually happening
- During the seasons / periods identified above, what kind of weather can you expect, sunny days, light clouds, heavy clouds...
- What are the essential loads that would have to run during evening and night, how long would they run during that period. Keep in mind you probably wont be running any super heavy loads (like AC or charging cars) on the battery.
- What are the extra load that would need to run during the day and for how long.

The minimum battery size will be defined by the energy needed for one evening / night.
Then you can make sure the Array daily production based on season and period will be enough to both fully recharge the battery, and provide the extra load capacity during the day.

If you can provide all the above, we can help figure out what battery sizes would be best.

[Ampster]

My brother has two houses on Maui and they encountered significant stonewalling when they inquired about a grid tie system solar system. Ultimately they bypassed the Maui utility which I think is controlled by HECO. They got a building permit for solar and batteries and are running in self consumption mode only using the grid for backup. Follow the advice above from scrambler and you should be fine.
Because of the high rates on the Islands and the stonewalling by HECO it is not hard to justify a system. Only the battery size is the cost that has to be justified based on the value you place on backup. In some circumstanes it can beat the cost of propane for running a generator. I would keep the generator for rainy days.

[BenHawaii]

15kWh/day is only 5,475 kWh per year, so not huge.

You need to determine if that may change drastically in the future, like if you add electric cars...
First goal is to determine the total energy (kWh) you should aim to produce per year.

In addition to the target kWh per year, you will need to determine where the panels will go (roof, ground...) so you can determine their orientation (south, SE, SW...) and their tilt.
One you have these numbers, you can determine the size your solar array (how many kW of panels) using the PVWatts Calculator (nrel.gov) site.
You enter an array size like 5kW, your location, Orientation and tilt, and that will give you the yearly kWh that 5kW array can produce.
You then just increase or decrease the array size to meet the yearly goal


The next step is sizing the battery (capacity in kWh). To do that, you need to figure out a few things.
- How long are outages usually.
- During what season / periods are they usually happening
- During the seasons / periods identified above, what kind of weather can you expect, sunny days, light clouds, heavy clouds...
- What are the essential loads that would have to run during evening and night, how long would they run during that period. Keep in mind you probably wont be running any super heavy loads (like AC or charging cars) on the battery.
- What are the extra load that would need to run during the day and for how long.

The minimum battery size will be defined by the energy needed for one evening / night.
Then you can make sure the Array daily production based on season and period will be enough to both fully recharge the battery, and provide the extra load capacity during the day.

If you can provide all the above, we can help figure out what battery sizes would be best.

Thank you for the feedback. Visited pvwatts.nrel.gov and based on location, second story 45 Deg NE facing roof mount and a 5kW array the tool reported 6,030 kWh per year.

My goal is to have battery capacity to power current evening power usage needs and reduce power bill. Evening usage is 8.5 Kw (which includes fridge and chest freezer that don't run constantly), with inverter that will auto switch over to grid if batteries can not supply power needs.

[BenHawaii]

My brother has two houses on Maui and they encountered significant stonewalling when they inquired about a grid tie system solar system. Ultimately they bypassed the Maui utility which I think is controlled by HECO. They got a building permit for solar and batteries and are running in self consumption mode only using the grid for backup. Follow the advice above from scrambler and you should be fine.
Because of the high rates on the Islands and the stonewalling by HECO it is not hard to justify a system. Only the battery size is the cost that has to be justified based on the value you place on backup. In some circumstanes it can beat the cost of propane for running a generator. I would keep the generator for rainy days.

Helco and HECO are monopolies except for those of us that have grid service and a solar system that depends on them just for extra power needs. Yes, I think that is the question we need to ask, "how much do we value having backup?"

[scrambler]

Evening usage is 8.5 Kw (which includes fridge and chest freezer that don't run constantly), with inverter that will auto switch over to grid if batteries can not supply power needs.

I assume you mean 8.5kWh (not kW) of energy during a single evening night period?
If so, that is a lot, wonder what you are running at night beside fridge, lamp and TV...

Are you thinking of an OFF grid system or a Grid Tied system?

[BenHawaii]

I assume you mean 8.5kWh (not kW) of energy during a single evening night period?
If so, that is a lot, wonder what you are running at night beside fridge, lamp and TV...

Are you thinking of an OFF grid system or a Grid Tied system?

Apologies, will be more careful with terminology. My inventory shows that in the evening I might have 1,700 watts of lights, appliances, TV, phone chargers, fans on for 5-6 hours. Hope this is a correct way to communicate this. Wanting to install a grid tied hybrid system, with inverter switching over to grid if power needs require it.

Thanks
Ben

[Ampster]

My brother reports that HECO woke up to the fact that they were facing significant grid departure and may have eased up on the stonewalling that they were doing historically. That may bode well for your application for grid tie.

Reportedly the biggest problem is that there is so much solar on different parts of the islands that some substations are seeing reverse flow during the middle part of the day.

[scrambler]

Apologies, will be more careful with terminology. My inventory shows that in the evening I might have 1,700 watts of lights, appliances, TV, phone chargers, fans on for 5-6 hours. Hope this is a correct way to communicate this.
Ben

If you need 8.5kWh for the evening and night, given you may also need some for early morning, you probably need at least 10kWh of battery or more like one Powerwall for 13kWh I believe.
Then you need to answer the other questions about outage duration, season, period, weather.... so you can get an idea of what is the worst case scenario for solar production on days of outage.

You also to evaluate minimum daytime needs, for outages lasting longer than an evening like a day or more if they occur.
IF the outage lasts over a day, and that happens top be days with heavy clouds, solar production may not be enough to recharge the battery and satisfy daytime needs.

Wanting to install a grid tied hybrid system, with inverter switching over to grid if power needs require it.
Ben

Are you saying you would want to be off grid all the time except when you need more power that solar/battery can provide?
Because I don't know that there are any inverters that can manage that automatically.

The usual scenario is that you are tied to the grid all the time. then, assuming your inverter has a self supply mode, in that mode, it will use Solar and battery before using the grid. But this has a drawback, is that you could be hit by an outage after having depleted the battery.
To alleviate that, you can define a minimum reserve to keep in the battery while in self supply mode, and that means you strike a compromise on using the grid more often (using less battery), in order to keep more reserve in the battery in case of an outage.

[Mike90250]

Don't forget that a hurricane may blow all your carefully planned panels away, or you may have clouds for a day or two afterwards.

[BenHawaii]

If you need 8.5kWh for the evening and night, given you may also need some for early morning, you probably need at least 10kWh of battery or more like one Powerwall for 13kWh I believe.
Then you need to answer the other questions about outage duration, season, period, weather.... so you can get an idea of what is the worst case scenario for solar production on days of outage.

You also to evaluate minimum daytime needs, for outages lasting longer than an evening like a day or more if they occur.
IF the outage lasts over a day, and that happens top be days with heavy clouds, solar production may not be enough to recharge the battery and satisfy daytime needs.



Are you saying you would want to be off grid all the time except when you need more power that solar/battery can provide?
Because I don't know that there are any inverters that can manage that automatically.

The usual scenario is that you are tied to the grid all the time. then, assuming your inverter has a self supply mode, in that mode, it will use Solar and battery before using the grid. But this has a drawback, is that you could be hit by an outage after having depleted the battery.
To alleviate that, you can define a minimum reserve to keep in the battery while in self supply mode, and that means you strike a compromise on using the grid more often (using less battery), in order to keep more reserve in the battery in case of an outage.

Yes, the "usual scenario" of remaining on grid and inverter with self supply mode (solar and battery used before switching over to grid). For this investment to have value the goal would be to reduce grid bill as much as possible, while maintaining battery longevity. If there was an outage we also have a generator and would adjust power usage to shift as much as possible to daylight (fingers crossed for sunny days), and minimal evening usage.

One way I am looking at this is that if we save $2,000 a year in grid bills, use AGM batteries with most lasting 7 years, we would look at the system "paying for itself in about 7-9 years or so. Although, there is added value in having backup and self sufficiency and protection from rate increases.

Thank you
Ben

[khanh dam]

david poz growatt - YouTube
watch above videos. if you are paying $.34/w you can diy your own battery and soalr set up and it will pay for itself in several years. dont use agm batteries lifepo4 is chepaer in long run.

[khanh dam]

I thought hawaii was a no brainer for solar hot water panels? maybe being on the rainyside means less sunshine? but I'd switch to solar insteads of propane for water heating

[BenHawaii]

I thought hawaii was a no brainer for solar hot water panels? maybe being on the rainyside means less sunshine? but I'd switch to solar insteads of propane for water heating

Yes, it's in the plan for future. A few people I know had solar hot water heaters installed on their roofs. But at a cost of $ 8,000. I know this isn't the only solution. We are only spending $40 a month for propane for hot water, stove, and dryer.

[BenHawaii]

david poz growatt - YouTube
watch above videos. if you are paying $.34/w you can diy your own battery and soalr set up and it will pay for itself in several years. dont use agm batteries lifepo4 is chepaer in long run.

This is worth a look --good videos!. One problem could be the dreaded Amazon message "This item cannot be shipped to your selected delivery location. Please choose a different delivery location." which we receive for any lithium batteries now, but not products with a lithium battery, like lawn trimmers etc.