Going Solar

[ERD50]

In 2012 I was still working and paid over $128K in income taxes. So tax credits only reduced my taxes. Even in retirement, I'm paying about $83K per year in income taxes. So I'm subsidizing a lot of government perks for many people like healthcare subsidies.

It wasn't a judgment call, just an observation on the math.

-ERD50

 

[ERD50]

Well, I am up to almost .12 now


BUT, we have a lot of pine trees and the house is not a candidate for solar... heck, I have problems keeping the grass alive in the back yard as it does not get enough sun.... had a few trees trimmed and put in grass that is supposed to live with just 25% full sun... still have dead spots...

Can you join a community solar project? These make sooooo much more sense than residential solar, your issue of tree shade being one of them. Proper sighting for angle, economy of scale, safety, and maintenance being others.

Though at 12 cents, it will probably still be marginal, electric rates at double that sure make the math work easier.

If system costs are coming down faster than annual savings (factoring opportunity costs), it seems that waiting is the best financial decision?

-ERD50

 

[NW-Bound]

My on-peak rate is $0.2215/kWh, and off-peak is $0.073/kWh. Averaged out over one year, my effective rate is $0.12/kWh.

The above is about average for the US. Why is it so much higher in CA?

 

[scrinch]

You forgot #5. "have other people pay for ~ 1/3rd of your investment".
...
It wasn't a judgment call, just an observation on the math.
-ERD50

With a $16k investment, the IRR is 25%.
With a $23k investment, the IRR is 17%.
So without the tax break it still would have been a good investment. Let's say that your contribution of criterion #5 is nice to have, but optional in his case.

 

[brett]

We live in an area with very high proportion of sunny days. I have always wondered why we don't have more solar power. We see so much of it in Europe.

Over the past few years it seems to be much more popular. We see more and more solar farms on farms in our area. Our city has placed a solar farm on the roof of a large sports complex. It will be a year long trial. Some local developers are now building homes that are heated with geothermal and also have solar panels. They are selling well-great way to differentiate the product.

Last week I read that our local technical college cannot keep up with the demand for courses and local contractors cannot get enough qualified staff.

A home not far from us recently had solar panels installed on their roof. Seems to me that the payback must be there. Tariff reductions have really helped.

 

[scrinch]

My on-peak rate is $0.2215/kWh, and off-peak is $0.073/kWh. Averaged out over one year, my effective rate is $0.12/kWh.

The above is about average for the US. Why is it so much higher in CA?

Good question. It looks like Arizona peak generation costs are a little higher than those in California, but transmission, distribution, and off-peak generation are considerably lower.

Approximate per kWh components to retail power prices (from PG&E and APS rate sheets):
Transmission AZ 0.01 CA 0.03
Distribution AZ 0.03 CA 0.08
Off-Peak Gen AZ 0.03 CA 0.08
Summer Peak Gen AZ 0.24 CA 0.19
Winter Peak Gen AZ 0.18 CA 0.10

 

[Texas Proud]

Can you join a community solar project? These make sooooo much more sense than residential solar, your issue of tree shade being one of them. Proper sighting for angle, economy of scale, safety, and maintenance being others.

Though at 12 cents, it will probably still be marginal, electric rates at double that sure make the math work easier.

If system costs are coming down faster than annual savings (factoring opportunity costs), it seems that waiting is the best financial decision?

-ERD50

Never thought of doing it as I do not see a payoff at the rate that I pay...


BUT, decided to take a look online and the only site that I saw quickly that listed them said there were none in Texas... yes, a state that has the most wind (IIRC) has zero community solar...

 

[HFWR]

No solar installation here, but for S&G:
DFW area
2017 Usage: 5058/$947.48
Rate: $0.133
Effective rate: $0.187

 

[NW-Bound]

It's still too hot for me to start installing the DIY solar and battery storage I often talked about. It takes a lot of work, including building a garden shed to house the lithium battery bank, for example.

I have been playing with some solar panels to understand more about their performance. I knew that their efficiency goes down with higher temperature, but did not appreciate it fully until I had some hand-on experience.

Example: a panel was producing 160W out in full sun. Its temperature was measured at 145F. Cooled it down with a garden hose. Temperature: 95F. Power: 202W.

Holy molly! A loss of 20% due to temperature. Note that panels are rated at 25C, or 77F. This means you only get what the specs say when it is cool in the winter, under full sun and clear sky, and the panel facing the sun squarely. It means "almost never".

 

[nash031]

In the process of pulling quotes, and leaning toward a 5.44-6.4kw system, which I calculate should pay back the up front $10-12K (after FTC) investment in about four years based on our $.25/kWh rate. Working the numbers to right size the system since credits are at the full retail rate, but any excess credits after 12 months are only sold at the wholesale rate of $0.03-0.04/kWh. Interesting learning all about how these systems are designed, and I’ve gotten great use out of some of the information and calculators shared here.

 

[tb001]

In the process of pulling quotes, and leaning toward a 5.44-6.4kw system, which I calculate should pay back the up front $10-12K (after FTC) investment in about four years based on our $.25/kWh rate. Working the numbers to right size the system since credits are at the full retail rate, but any excess credits after 12 months are only sold at the wholesale rate of $0.03-0.04/kWh. Interesting learning all about how these systems are designed, and I’ve gotten great use out of some of the information and calculators shared here.

Who do you think you’ll use? We ended up going with Sullivan solar. Taking a longer than we expected on their end to get permits and install scheduled. At this point just hoping we’ll be installed by end of year to get tax credit.

 

[TwoByFour]

In the process of pulling quotes, and leaning toward a 5.44-6.4kw system, which I calculate should pay back the up front $10-12K (after FTC) investment in about four years based on our $.25/kWh rate. Working the numbers to right size the system since credits are at the full retail rate, but any excess credits after 12 months are only sold at the wholesale rate of $0.03-0.04/kWh. Interesting learning all about how these systems are designed, and I’ve gotten great use out of some of the information and calculators shared here.

I agree, it is interesting how they are designed. I see lots of opportunity for improvements. I got frustrated by the lack of support for what I thought were some very obvious capabilities. One of those things is dealing with the grid-outage requirement for grid-attached systems. Most (all?) utilities require that the PV system shuts down if the grid goes down. This makes sense, as linemen need to work on downed power lines and want them to be reliably de-powered. But for most of us that means we cannot rely on our PV-system to be our local power source if the grid goes down, unless we have a way to detach from the grid. The only way to do that so far is with batteries and a controller/inverter. But I don't want batteries, just the controller. But nobody makes a controller/inverter that does not also require batteries.

I have been talking with Enphase and they are coming out with exactly what I need - a batteryless controller that will allow a PV system to detach from the grid and just power the house when the grid goes down. So that will be cool. It might only work with their own micro-inverters, not sure.

 

[NW-Bound]

... we cannot rely on our PV-system to be our local power source if the grid goes down, unless we have a way to detach from the grid. The only way to do that so far is with batteries and a controller/inverter. But I don't want batteries, just the controller. But nobody makes a controller/inverter that does not also require batteries.

I have been talking with Enphase and they are coming out with exactly what I need - a batteryless controller that will allow a PV system to detach from the grid and just power the house when the grid goes down. So that will be cool. It might only work with their own micro-inverters, not sure.

There is an important technical reason for having batteries. They serve as a buffer or temporary storage to allow operation of appliances with motors.

An AC may draw 3 or 4 kW when running, but the startup requirement is 3 to 4 times that. Let's say you have a grid-tied system that can supply a constant 5 kW, but when your AC starts up, you actually rely on the grid to supply that temporary surge demand to get the AC motor moving. And that 5 kW is really under the best condition, i.e. with the best sunlight condition of the day.

Without a battery, an off-grid system would have to be underutilized, else nothing works. A fridge may take only 300W when running, but to start the motor turning may take 1 kW for a few seconds. If an off-grid solar inverter cannot supply that momentary surge along with all other appliances and lightings that happen to be on at that time, the voltage will drop, and the fridge motor will stall. Many fridges have a protection circuit to cut-out the motor and turn on a warning light. The ones without such protection will stall, and burn out their motors.

Maybe a system can be designed to cut out some loads when the power demand exceeds supply from the solar panels. Some large motorhomes with two ACs have this type of protection to stagger the AC startup, in order for the generator to handle the load.

And even while everything is running, a passing cloud will reduce the solar power significantly. You will always need a smart load controller to start shedding appliances and lights according to a preprogrammed priority. Without a smart system, the inverter will simply have to shut down altogether, and you lose all lights and appliances for any slight overload, or solar panel power reduction.

 

[TwoByFour]

I understand the high current draw for starting any induction device like a motor, but that draw is for a very short period of time, like a second or less. Using a giant battery to source current for short periods like that is a bit of overkill - the power draw might go up from 1 kW to 3 kW, but because of the short time, the total energy used is still low. I have no idea what Enphase is cooking up. Maybe a giant capacitor bank? There probably will be limits on what it can do.

 

[NW-Bound]

The mention of Enphase is interesting to me, because the company is known for its microinverters. And I did a bit of search on the Web about their off-grid work to see what is being done.

Traditional grid-tied inverters are not meant to be run independently. As the name implies, they are designed to work with the grid, meaning they will synchronize with the grid frequency. When there's no grid power for them to synchronize with, they will shut down because they no longer have a master to synchronize to in order to play the role of a follower.

A grid-tied inverter that turns itself into an independent inverter when the grid power is lost is called a hybrid inverter. Of course a transfer switch must be installed to cut it out from the grid, lest it tries to power up the whole neighborhood.

The old grid-tied inverters simply do not have the circuit to do this. New grid-tied inverters can have this new function designed in. It looks like several companies are working on this, which is good.

The design is more complex for microinverters, because of their distributed fashion. A communication path for control will be needed for all of them to synchronize together. I think that's what Enphase is working on.

Hybrid inverters are simpler when in the form of a string inverter, meaning a centralized inverter that combines the power of all solar panels in a string. Some are available now.

A Taiwanese company called MPP Solar already has a hybrid inverter that can work with or without batteries. Without any battery, the surge output power will of course be limited by whatever the solar panels can produce at that moment.

 

[NW-Bound]

Some people experimented with using the existing grid-tied inverters along with a stand-alone pure sine-wave inverter running off a battery, with the intention of using the latter in the role of a grid. This is an obvious thing to think of, and so they did it.

The above works, when there is a sufficient load on the system. When the load is reduced, the excess power from the solar panels has no place to go. You see, traditional grid-tied inverters are designed to dump all available power from the solar panels onto the grid. It is permissible, because the grid is an immensely "stiff" source/sink relative to the individual solar system.

When the source/sink which serves the role of the master is as small as the stand-alone car-battery-operated inverter plus the household load, if the load is not enough to absorb all the power produced, the voltage will rise. An experimenter on Youtube reported having his stand-alone inverter blown out. That is to be expected, as the existing microinverters have no throttling function.

PS. By the way, when there are millions of household solar systems tied to the grid, the grid is no longer that "stiff". Where does that excess power go? California had to pay Arizona money to take its surplus power in early spring last year, when the power produced exceeded the demand inside the state. Yes, the power to Arizona was more than free that time. AZ utilities got paid to use it.

 

[ERD50]

I understand the high current draw for starting any induction device like a motor, but that draw is for a very short period of time, like a second or less. Using a giant battery to source current for short periods like that is a bit of overkill - the power draw might go up from 1 kW to 3 kW, but because of the short time, the total energy used is still low. ....

In addition to the excellent info NW-Bound provided, I'll point out that it is more complex than just handling start-up currents, which could be done with a relatively small battery, and an inverter sized to handle those peaks (the micro-inverters only need to handle the max output of the panel). You also need to deal with a cloud going over for several minutes. Or what about a cloudy day, and of course, over-night? You need enough battery capacity for whatever scenario you are looking at, plus some buffer, and a 'plan B' when the batteries get drained (shut off circuits X,Y,Z?) . Maybe you decide to keep only a few circuits alive, you can size it for that.

And then consider that those batteries have a limited life, and will need replacement in X years (depending on type). Unless black-outs are really common, alternatives might be more practical.

...I have no idea what Enphase is cooking up. Maybe a giant capacitor bank? There probably will be limits on what it can do.

Capacitor banks are getting cheaper, but they are still far more expensive than batteries. They fill a niche where you need very high short term currents, and need them often. The 'super caps' can be cycled almost forever w/o degradation. That's where they shine over batteries, and can be economical, even at their high price.

BTW, A 'super-cap' can only be used up to ~ 3.3 Volts! So to store practical voltages so you are not dealing with super-high currents (requires huge wires to limit losses), they need to be stacked in series (stacking 2 of them reduces the total capacitance to half - and you probably need stacks of 10 or more to be practical). Stacking also requires a balancing circuit, to keep the voltage even across all those caps. It ain't easy or cheap.

-ERD50

 

[NW-Bound]

I don't think companies like Enphase promise users the full functionality of the grid when power is out. The users also know that without batteries, there will be no power at night.

During a black out, I think that people want to have some use of solar power so that they can keep their fridge cold during the day, with the understanding that they will need to fire up their Honda generator at night. If so, then yes, the new breed of grid-tied inverters will provide this limited function.

If you want more functionality, then several companies such as Panasonic and LG have offered lithium battery banks for solar power storage, similar to Tesla's Powerwalls. They are all slick and very cool. The only problem is cost.

 

[tb001]

Batteries are expensive but I think in certain markets they’re starting to make more sense. We have some of the highest rates in the nation and the utilities have fought back against solar by changing time of use rates, extending them later and later. Having battery backup means you get a little extra juice from your system during those evening hours when your system isn’t producing and rates are still higher. The math doesn’t 100% work yet, but we went with battery back up so we can take advantage of this and have the benefits of a backup power source. In the top tiers our rates can reach over 50 cents though. Insane.

Interestingly, the utility companies are now also limiting the number of batteries you can have per system.

 

[samclem]

The math doesn’t 100% work yet, but we went with battery back up so we can take advantage of this and have the benefits of a backup power source. In the top tiers our rates can reach over 50 cents though. Insane.

Is the rate differential enough to justify batteries just to allow you to buy power at the cheap times and use it whenever you need it (i.e. disregarding the issue of PV generation)? At some point I guess it might, and the power companies/regulators should have little to say about it, since you are doing what they are trying to encourage. Of course, it would drive up total energy use (due to charging and battery losses). And it would seem that utilities could do this energy storage much less expensively at the "bulk" level, but maybe they don't have much incentive to do it (if they can just pass along the higher peak generation costs to consumers).

Interestingly, the utility companies are now also limiting the number of batteries you can have per system.

How do they know?

 

[ncbill]

The mention of Enphase is interesting to me, because the company is known for its microinverters. And I did a bit of search on the Web about their off-grid work to see what is being done.

Traditional grid-tied inverters are not meant to be run independently. As the name implies, they are designed to work with the grid, meaning they will synchronize with the grid frequency. When there's no grid power for them to synchronize with, they will shut down because they no longer have a master to synchronize to in order to play the role of a follower.

A grid-tied inverter that turns itself into an independent inverter when the grid power is lost is called a hybrid inverter. Of course a transfer switch must be installed to cut it out from the grid, lest it tries to power up the whole neighborhood....

A Taiwanese company called MPP Solar already has a hybrid inverter that can work with or without batteries. Without any battery, the surge output power will of course be limited by whatever the solar panels can produce at that moment.

The grid-tie inverters I've seen that can "island" when the grid goes down so far have a single outlet capable of delivering a whopping 1500W...not much.

 

[travelover]

The grid-tie inverters I've seen that can "island" when the grid goes down so far have a single outlet capable of delivering a whopping 1500W...not much.

That would be very useful to me. Mostly I want to keep the refrigerator running and a few LED lights in windowless rooms, like bathrooms. Obviously you'd want to have it hard wired like generator circuits are done.

 

[samclem]

That would be very useful to me. Mostly I want to keep the refrigerator running and a few LED lights in windowless rooms, like bathrooms. Obviously you'd want to have it hard wired like generator circuits are done.

+1. If it was enough to run a fridge, some LED lights, and either a furnace fan (winter) or some room fans (summer) it would be good. "Deluxe" would be the ability to start/run a small window AC unit or a furnace fan.

 

[tb001]

Is the rate differential enough to justify batteries just to allow you to buy power at the cheap times and use it whenever you need it (i.e. disregarding the issue of PV generation)? At some point I guess it might, and the power companies/regulators should have little to say about it, since you are doing what they are trying to encourage. Of course, it would drive up total energy use (due to charging and battery losses). And it would seem that utilities could do this energy storage much less expensively at the "bulk" level, but maybe they don't have much incentive to do it (if they can just pass along the higher peak generation costs to consumers).


How do they know?

Hmmm, not sure on your first question. I think the way they’re set up it’s just our solar generation that feeds into them? Which is the same in a way, in that the times of highest use are when our system is likely getting full sun.

And they know because they have to inspect and give approval to turn on the system. It’s really annoying. The solar rep said we can install another battery after the fact if we want, so we upgraded the inverter to be able to handle the extra and may add another as costs come down on the batteries.

 

[NW-Bound]

Batteries are expensive but I think in certain markets they’re starting to make more sense. We have some of the highest rates in the nation and the utilities have fought back against solar by changing time of use rates, extending them later and later...

I am in Arizona, and my utility is SRP (Salt River Project), a state government agency and not a for-profit commercial enterprise. SRP recently changed the rate structure, and home solar owners cry foul. But if one sits down and listens to SRP, what they say make sense.

I don't know about California, but here in the Arizona low desert, in the mid-summer the air temperature stays above 100F until near midnight. AC usage stays high way past sunset, long after solar generation is gone. In fact, in the late summer month of August/September, the sun starts to set early already and solar generation is down significantly after 5PM due to the sun angle, yet the AC power consumption may peak at that point due to the heat soak and thermal delay.

When all these home solar systems power down and draw from the grid en masse, where does all the power come from? SRP has hydro power from reservoirs but that is limited, so they fire up natural gas peakers. That power is not cheap.

So, SRP changes the rate schedule to reflect that. They advise solar owners to orient their panels for peak power late in the afternoon. Up until now, the goal is to get max total energy during the production day, which means the max power production occurs at noon. But noon time is not the hottest time of day.

Well, the truth is that home installations have no choice of the roof orientation, let alone angling the panels to maximize late afternoon output. Hah!