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LTLFTcomposite
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Solar for grid tied AND backup - where to begin?

Sun Sep 24, 2017 5:25 pm

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.
LTL
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baustin
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 3:16 am

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.
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RegGuheert
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 6:49 am

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.
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LTLFTcomposite
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 7:05 am

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.
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DaveinOlyWA
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 7:43 am

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.
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BillHolz
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 8:11 am

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.
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LTLFTcomposite
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 8:15 am

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/ ... 8-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.
LTL
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LTLFTcomposite
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 8:24 am

BillHolz wrote: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.
LTL
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DuncanCunningham
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 8:50 am

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.
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LKK
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Re: Solar for grid tied AND backup - where to begin?

Mon Sep 25, 2017 9:07 am

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.

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