Solar for grid tied AND backup - where to begin?

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LTLFTcomposite

Well-known member
Joined
Apr 23, 2010
Messages
4,780
Location
Central FL
With recent power outages here after Irma whole house generator flights of fancy have returned. I'm thinking instead of sinking a bunch of money into something with zero ROI for the next decade waiting for another outage that may not even happen it's time to start thinking seriously about solar.

So much of it still looks like it's targeted at the enthusiast and is pretty bewildering. I guess for a grid tie system the basic components are the panels, a racking system and the inverter. Adding backup capability adds complexity, more components, more cost, but this caught my eye:

https://www.pika-energy.com/

Is the Pika energy island a unique product or are there other things like it? I'm fine with isolating a few circuits to be powered by backup.

The last thing I want is to get mixed up with a sales guy pushing something when I don't know what I'm getting into. Frankly I'd rather have people on this forum tell me what to buy; even if their recommendations are less than ideal at least they don't have an ulterior motive.

I think we use about 1000 kwh per month average, obviously more in the summer than winter.
 
Start with your average daily use, and peak draw of what you want to operate from solar. This will help to size the battery bank, and the output of the inverter. The maximum amount of daily sun, for the winter months, should be used to help calculate the number of solar panels needed to keep the batteries charged to accommodate your needs. Look at any 240v loads to determine if you need a 240v system, or if transformers can be used to operate those loads. If your electric utility has favorable grid-tie policies, you can sell back excess production during the summer months, depending on the system capacity and number of panels installed. If they don't, just use them as a supplemental supplier when the solar system needs an assist.

There are sites like Wholesale Solar and Northern Arizona Wind and Sun that have calculators and other tools and information that can be quite useful.
 
I recommend that you look at SolarEdge and Tesla PowerWall (or an equivalent Li-ion battery). While this may not be the cheapest option out there, this equipment is reliable and is certainly the most efficient grid-tied PV solution that also provides some backup. Since your largest load is your air conditioner, you don't need a huge amount of storage to meet your daytime loads.

I also strongly recommend that you move to a heat-pump water heater. Those only draw 600W, use 1/3 the energy of a resistive water heater and provide cooling and dehumidifying to boot.
 
Heat pump water heater is interesting, although I've wondered if AC heat recovery would be a better option. I don't really need the water heater to be on backup power, plus I learned a handy trick in the hurricanes, you can put a 120v pigtail on the water heater and run it at a more generator-friendly 1100 watts instead of 4400. The water heater really only needs to run about every third day in a backup situation.

Unlike some folks I'm not trying to reproduce my usual lifestyle in its entirety in an outage. If I can have 1000-1500 watts of continuously available backup power that's plenty to run the fridge, a small window AC, some lamps and a TV. The four ton central AC can sit on the sidelines.

I'm new to this and don't have any feel for how to size this. Depending on the time of year presumably there isn't much sun hitting the panels from about 6pm until 9am, so 15 hours of 1.5kw is 22.5 kwh. That sounds like a lot; maybe this isn't really practical.

As for net metering, I'm not really sure what the differential is on power pulled vs pushed with FPL. AC loads are highest in the afternoon and evening and things like the water heater and pool pump can be optimized to run when then panels are producing. If the FPL bill could be reduced that would help justify the cost of the system vs a generator that only incurs cost if there's no outage.
 
Solar is always a good idea in my book but I would rather look at V2G options instead. Would be better if Nissan brought that over here (among SEVERAL other things like a 40 kwh mini cargo van or something similar) At least its something you can use every day.

Now if the money is not a problem, then sure a dedicated backup is the most foolproof and your contention that it will be another 10 years before you will need it is something I have to think is probably about 9 years off.

I remember back in 94-95 we had a "100 year flood" it really sucked especially when we had another one in 96... (shortest 100 years EVER!) but that is how we gauge weather. Well as one might guess, doing this "100 year" thing every couple months was ridiculous so we fast forward to Sept 2017 and the "500,000 year event" of Texas (missed the million year event but a few inches) all in an area that had recently had 2 "1000 year events"

So yeah, overbuilding for possible future events is not really all that bad of an idea.
 
OP mentioned grid tied and talked about backup capability adding complexity. Without backup capability, a grid tied solar system will not provide any power during an outage, which is what the OP wanted in the first place. Grid tied solar with backup is a great alternative to a backup generator which has no ROI except when it is in use for emergencies.
 
I see people spending $40k for 70kw generators to run three zones of AC and burying 2000 gallon propane tanks in their yards. It's crazy.

This looks like another interesting option:

https://www.wholesalesolar.com/2430013/schneider/inverters/schneider-conext-xw-6848-inverter

Since I need an inverter no matter what for solar isn't it better to go with a unit that combines battery charging and backup DC-AC inverter operation? I suppose this is a pretty expensive unit compared to what I might need just for a grid tied system, and that's before adding any batteries. Presumably the battery helps too though if the utility isn't buying power back at retail price.
 
BillHolz said:
OP mentioned grid tied and talked about backup capability adding complexity. Without backup capability, a grid tied solar system will not provide any power during an outage, which is what the OP wanted in the first place. Grid tied solar with backup is a great alternative to a backup generator which has no ROI except when it is in use for emergencies.
Solar and backup generator are each tough to justify on their own, but solar that provides backup generation capability starts to look interesting.
Correct me if I'm wrong, but netting this out it looks like the difference between a plain grid tied system and one that provides backup capability is the latter requires a costlier inverter unit (like that schneider or pika) and some amount of battery storage. In addition to providing backup power you also pick up some benefit if the utility is paying less for what you push than they charge for what you pull.
 
i have thought about it a little bit too. I do have solar and collect about 49kWh peak during a clear day in the summer, only 10kWh on a dull dark September day this week, but i use most power at the end of the day to charge my car or right before I leave each morning, so to be off grid I'd have to get some serious batteries. I'd also have to figure out some sort of solar water heating system which is not impossible but I have no experience of those systems but that could remove the heating pressure on gas and electric by large margin. When "the big one arrives" the earthquake we are all waiting for in Utah, we'll probably be offline for some serious days on end, if not weeks. Not sure what I'd do. I don't even know how to use the solar I have coming in from my array off grid. I know I'd had to switch off from the grid and have some islanding going on so the solar inverters will produce and then how do I handle the unused power? I could just unplug a few inverters I don;t know. I like to think about it though.

If I were serious, I'd look at ways to lower the energy usage of my needs.. and hopefully make them manageable enough that I could get by with less. I'd look at better insulation, tree shading the home, Metal aluminum roof to reflect the heat and not store heat loads in the roof. better windows to let in light and not air, yeah I hate my sash windows.. so leaky. Seal up air leaks around the home, install air exchange systems to let in new air and out the stale old but balance the heat or cooling losses through that. I'd setup my heating system to hydronic so I can heat water with electric, gas or solar storage tanks and run that through the floors and radiator panels to heat the home and potable water.

Aim at the big ones and see what you can arrange or get more for less and work down the line.

My big users are
Cars
A/C
Heating boiler (fans, pumps and other tech)
Oven/stove
washer and dryer (the best dryer is one that has a great washer next to it, gets more water out in a spin cycle.)
Microwave
Kitchen things
Fridge and freezer (yes I have them separate)
computer things
other appliances
window and room fans
lastly lights and charging phones.

thanks for sharing the links.. I'm going to check those out.
 
I installed a Tesla Powerwall 2 with a SolarEdge system. The system works well. During the day excess solar power is first used to charge the battery and when it is fully charged the power is sent to the grid using a net metering power purchase agreement. When the sun goes down the power is first drawn from the battery via an integrated 5 kw inverter and when it is depleted, power is drawn from the grid.

If the grid fails the Powerwall isolates itself from the grid and uses its integrated inverter to supply a 240 VAC signal to the SolarEdge net tied inverter to allow it to function in backup mode. There are two subpanels in my system, one for backed up circuits the other for unbacked circuits. The criteria used to decide if a circuit is backed or not is the power capacity of the integrated inverter. It will handle 7 is peak and 5 is continuous, you have to decide which circuits you want backed based on their power consumption and the capacity of the battery. The subpanels are next to each other so it is relatively easy to move a circuit from one subpanel to the other. In my system I backed all the 120 VAC circuits and put all the heavy load 240 VAC circuits in the unbacked side. I should add when the system is operating normally the battery supplies power for both subpanels when solar power is not available.

The battery capacity is around 13.6 kwh. You can set the amount of usable capacity in the Tesla app. The battery is liquid cooled. The Tesla app has been very useful showing power flows between the solar, battery, home and grid in instantaneous and accumulated power over different periods.

The main advantage of the battery for me is rate arbitration. With solar I'm forced on to a time-of-use rate schedule where the main daylight hours are classed at off peak and late afternoon and evening hours are the peak period. Off peak is around $.25/KWH, peak is double that at $.50/KWH. So instead of sending excess solar power to the grid, it makes much more sense to store this power in a battery that becomes active during peak hours. This could save up to $7/day on a 14 KWH battery. The new net metering rates being forced on new solar users without this battery, is in my opinion totally useless.

Here in California a Self Storage rebate is being offered which significantly offsets the cost of the battery.
 
LKK said:
I installed a Tesla Powerwall 2 with a SolarEdge system. The system works well. During the day excess solar power is first used to charge the battery and when it is fully charged the power is sent to the grid using a net metering power purchase agreement. When the sun goes down the power is first drawn from the battery via an integrated 5 kw inverter and when it is depleted, power is drawn from the grid.

If the grid fails the Powerwall isolates itself from the grid and uses its integrated inverter to supply a 240 VAC signal to the SolarEdge net tied inverter to allow it to function in backup mode. There are two subpanels in my system, one for backed up circuits the other for unbacked circuits. The criteria used to decide if a circuit is backed or not is the power capacity of the integrated inverter. It will handle 7 is peak and 5 is continuous, you have to decide which circuits you want backed based on their power consumption and the capacity of the battery. The subpanels are next to each other so it is relatively easy to move a circuit from one subpanel to the other. In my system I backed all the 120 VAC circuits and put all the heavy load 240 VAC circuits in the unbacked side. I should add when the system is operating normally the battery supplies power for both subpanels when solar power is not available.

The battery capacity is around 13.6 kwh. You can set the amount of usable capacity in the Tesla app. The battery is liquid cooled. The Tesla app has been very useful showing power flows between the solar, battery, home and grid in instantaneous and accumulated power over different periods.

The main advantage of the battery for me is rate arbitration. With solar I'm forced on to a time-of-use rate schedule where the main daylight hours are classed at off peak and late afternoon and evening hours are the peak period. Off peak is around $.25/KWH, peak is double that at $.50/KWH. So instead of sending excess solar power to the grid, it makes much more sense to store this power in a battery that becomes active during peak hours. This could save up to $7/day on a 14 KWH battery. The new net metering rates being forced on new solar users without this battery, is in my opinion totally useless.

Here in California a Self Storage rebate is being offered which significantly offsets the cost of the battery.

I was lucky, i installed my solar array when they did like for like net metering.. so anything I put in I get back at the same rate. They could change that I think, at anytime to suit them. so this setup is the best, the one you have. I'd do it. But since our power company has a flat rate all day each day.. not much of an incentive to do such a system yet. I'll have to watch closely to see what happens. right now the grid is my battery but they've been harping on about it some recent mailings to the city, which pretty much calls residents with solar 'thieves', though they don't go as far but it's implied.
 
LTLFTcomposite said:
LKK said:
I installed a Tesla Powerwall 2 with a SolarEdge system.
What model SolarEdge is that? So that's it? Panels on the roof, Tesla Powerwall 2 and the SolarEdge box?

(12) LG 335N1C-A5 panels with AS P400 Solaraedge optimizers.
Solaredge SE3800HD Inverter
Tesla Powerwall AC battery

The Powerwall comes with a Tesla Gateway which acts as the brains of the system directing the powerflow between all the components. I don't have line item pricing but I believe the Powerwall and Gateway was around $7500 all of which is applicable towards the Federal Tax credit.
 
LKK said:
(12) LG 335N1C-A5 panels with AS P400 Solaraedge optimizers.
Solaredge SE3800HD Inverter
Tesla Powerwall AC battery

The Powerwall comes with a Tesla Gateway which acts as the brains of the system directing the powerflow between all the components. I don't have line item pricing but I believe the Powerwall and Gateway was around $7500 all of which is applicable towards the Federal Tax credit.

Thanks. Looks like those panels are about $325/ea, the inverter is about $1100 and the Powerwall is $7500 so $13k - 30% - $9k, not counting anything for installation or other components. At .50/kwh I can see these quickly become no-brainers, at .11/kwh it's a lot tougher to get them to pencil out.
 
LTLFTcomposite said:
At .50/kwh I can see these quickly become no-brainers, at .11/kwh it's a lot tougher to get them to pencil out.
Comparing the cost of a system which will likely last over 25 years (except for the battery) to TODAY's price for electricity often leads to incorrect conclusions.

I recently purchased new grid-tied microinverters to REPLACE existing functioning inverters which have used seven of their 15-year warranty. I suspect these inverters will not outlive their warranty by much, so I decided to extend the warranty by 17 years with this purchase. Using the following calculations, I convinced myself that this purchase was better than any Roth 401k investment we could make today.

Data:
- Electricity currently costs $0.12/kWh here
- The solar array being upgraded produces about 4000 kWh of electricity each year
- The warranty on the current inverters continues through the end of 2025.
- The warranty on the new inverters is good through the end of 2042.
- The new inverters cost $1100 installed.

Assumptions:
- Basic (no TOU) net metering will be in force through 2042. (We live in the country and growth here is quite limited by law.)
- All warranties are honored by the manufacturer through 2042.
- The old inverters will fail shortly after the end of the warranty period. (This is the shakiest assumption here, since they could fail just BEFORE the end of the warranty period, in which case all would become new again.)
- The price of electricity in January 2026 will be 50% higher than it is now, or $0.18/kWh. (This MAY be aggressive, but I think it will be close.)
- The price of electricity in December 2042 will be 100% higher than it is now, or $0.24/kWh. (This is likely a conservative number.)
- The photovoltaic panels last until December 2042. (These panels where installed in 1999, so that implies a 42-year life. Time will tell.)

Calculations:
- Average cost of electricity between January 2026 and December 2042 is $0.21/kWh.
- Total value of the electricity produced between January 2026 and December 2042 is $14,280.00.

In other words, I expect my $1100 investment today to yield over $14,000 dollars between the years 2026 and 2042. I don't know of any financial investments which I can confidently expect to yield such a return.
 
Maybe I'm jumping to conclusions here too quickly but it looks like the backup power/storage capability is more than doubling the cost of the system vs simple grid tied. Considering that such outages really are quite rare I'm probably better off just spinning up the Honda generator to keep the fridge going in such situations. Who knows, a storm could easily damage the panels and that's what I'd be doing anyway.

Still, if it was just a matter of getting a fancier inverter to enable upgrading the system later to have backup capability it might be worth considering. Years ago we had an RV with a 2kw inverter and it was pretty amazing what you could run off four golf cart batteries. Do we really need a fancy $7500 powerwall? I suppose the difference there is while that might give me some backup capability it wouldn't do much for not pulling power after the sun goes down.
 
I started small, with 2 marine batteries and an inexpensive inverter. then added a few panels. We now have 3kw of solar, 8 L-16 batteries and a xantrex XW6048 inverter with most of the house on that electrical subpanel. The problem is you have to piece most of this together yourself or pay someone a good chunk of change to do it. Basically our system is what you are looking for but not something most people could setup or maintain.

Most of the time it is less expensive and a lot more straightforward to just go with a small genset. We have a Honda EU2000i and after trying over a dozen gensets or 20 years I would strongly recommend just skipping the rest and pay for a good one, the quietness of it alone is worth it, not to mention fuel economy and reliability.

Or take a look at this thread

http://www.mynissanleaf.com/viewtopic.php?t=13097

You already have the 24kWh pack ;) But again get a good quality inverter to start with.
 
BrockWI said:
Most of the time it is less expensive and a lot more straightforward to just go with a small genset. We have a Honda EU2000i and after trying over a dozen gensets or 20 years I would strongly recommend just skipping the rest and pay for a good one, the quietness of it alone is worth it, not to mention fuel economy and reliability.
Sounds like good advice and I should just stick with the generator. After fighting with a big box store POS generator after storms back in 2004 I upgraded to a Honda EB5000. That performed well after storms in 2005 but mostly sat around ever since. It was a tank, like 275 lbs; I just recently sold it and got an EU2000. Less is definitely more in this situation. At least I managed to get it right on the third try :)
 
Great question! I had the same needs/wants and actually just had my grid-tied PIKA system commissioned a week ago. I have 7.45kw (21 panels) from Seraphim with the Pika inverter, grid-tied. Their battery setup is done with Panasonic and is super easy to integrate later, its literally 2 wires plus a sub-panel with your backed up loads. I hope to add it in a year or so to allow grid-down usage.
The other nice part was their flexibility with operating modes when the battery is connected. I can set it up to give priority to sending excess to grid, never send to grid, priority to keep battery always charged, or self supply where it will use entirety of battery before tapping back into grid.
I was also looking at the Solaredge Storedge system with a powerwall but ultimately was swayed by a few things:
- Powerwalls are all but impossible to get in the US, they're only NOW starting to be somewhat available, mostly in mandated states.
- The Pika setup is a simpler system. There is no additional auto-transformer for battery backup needed, the one box does it all
- Both the Pika and Seraphim panels are made in the USA. I personally talked with the guys at Pika and they were very helpful.

Check out my production here!
http://profiles.pika-energy.com/jeff
 
Beardedjeff said:
Great question! I had the same needs/wants and actually just had my grid-tied PIKA system commissioned a week ago. ...
Thanks for the reply, great info there. So do I understand correctly, you got the Pika inverter with backup capability, but you didn't buy the batteries yet? How much additional did the backup add-on capability cost?
Did you consider the Schneider Conext box?

Lots of articles in the press here about how you can't use solar during an outage. Many are written to convey a narrative it's the evil power company keeping control over the masses. No doubt a bunch of people read the headlines and take away confirmation they're better off not having gotten solar.
 
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