Going Solar

[NW-Bound]

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.

The MPP Solar inverter I saw will provide 3kW, if the panels can supply that. Multiple inverters can be synchronized to work in parallel, up to 6 units. That's 18kW total. Operation can be with or without batteries. If a battery is attached, it will manage the battery, meaning charging it when there is excess power, and drawing from it to supplement the solar panels when the demand is higher than the supply.

If batteries are full, and there's excess solar power, the unit will export to the grid. It can also be programmed to charge the battery at night to make use of the cheaper off-peak rate.

We will see more and more units like this.

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.

What do you do for night time, if the solar system is battery-less?

 

[samclem]

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.

And, based on your earlier post about the decrease in PV panel output as they get hot, the total power output impact of orienting them further west is even worse than the trigonometry would indicate.

For your next experiment: how about a little ground-coupled liquid cooling rig to keep the panels cooler with coolant tunes on the back of the panels? The coolant could be lifted passively by thermosyphon action during the day, back to the pool of coolant underground to shed heat to the soil.

 

[NW-Bound]

Earlier, I reported observing a 20% drop in solar panel output when the panel temperature rose by 50F. This was higher than the specs of the panels. So, I checked the setup, made some corrections, and the power loss was improved to around 15%.

About active cooling of the panels, I do not want any complications with liquid cooling. It is not simple to have a good thermal contact between the panels cells and any cooling media.

It's far simpler and costs less to mount more panels to make up for the loss. Panels are getting so cheap.

 

[travelover]

...........What do you do for night time, if the solar system is battery-less?

If you need round the clock power you'd need a battery or a generator. But it seems silly to run a generator during the day when the solar panels are doing nothing.

 

[Texas Proud]

Curiosity question....


How much would batteries cost?


How does that compare to the Tesla powerwall?


Does the powerwall do all the stuff necessary that people are talking about, and if so what other cost can you get rid of?


Not that I will be going solar... too many trees for me to do anything...

 

[tb001]

Curiosity question....


How much would batteries cost?


How does that compare to the Tesla powerwall?


Does the powerwall do all the stuff necessary that people are talking about, and if so what other cost can you get rid of?


Not that I will be going solar... too many trees for me to do anything...

Our quoted cost was 5k per battery before tax credit. I think they are LG. Cheaper than the Tesla batteries.

 

[aja8888]

Wow, seems like a lot of work and equipment is needed (panels, batteries, inverters, switches, etc) to add a really good solar system to a residence. Kind of makes one ask themselves if it is all worth it in the face of utilities changing the rules and making it more difficult to save money on power?

It would be interesting to try to accurately figure a realistic cost to operate over a long period of time and if, in fact, any meaningful energy cost saving was achieved.

Also, what is the useful life of one of these systems in terms of expensive parts replacement on a total refurbishment, which, I am sure will have to be done at some point in the life of the system?

 

[nash031]

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.

Planning to use Unique Solar. Q5 panels, SolarEdge inverter and individual panel optimizers. From what I’ve learned, this is a pretty premium setup, and his pricing was about 10c per watt less than other quotes for similar systems. Probably going with a 6.4 or 7k system.

 

[NW-Bound]

How much would batteries cost?

How does that compare to the Tesla powerwall?

Does the powerwall do all the stuff necessary that people are talking about, and if so what other cost can you get rid of?

That's like asking how much a car costs?

Nissan Versa, or an Audi Q8?

Here, you can have the old lead-acid deep-cycle type, or lithium-ion batteries. Golf-cart batteries cost about $100/kWh, while lithium-ion is about $400/kWh. However, lithium batteries last much longer and can be drained to nearly empty, while lead-acid batteries should be drained to only 50% else the life would be severely shortened. Even so, a lithium battery can undergo 2000 cycles of full-to-empty and still retain 80% capacity, while a lead-acid battery may have only 500 cycles of 50% discharge.

A Tesla Powerwall with 13.5 kWh is $6,600 plus installation of $5,000 to $8,000. It can provide 5 kW continuously, and lasts 2.5 hours at that output rate. You can have a bank of them. People use the Powerwall to do load shifting, i.e. charging it with excess solar power (instead of selling at bulk rate to the utility) to use later in the day, or for load leveling (to avoid high rate during peak hours). Powerwalls can also be used for off-grid mode along with solar panel microinverters. There are Youtube videos on this subject.

So, how many kWh do you need?

Many have built their own solar storage systems using salvaged batteries off totaled EVs. The price on eBay is around $200/kWh for batteries off the Chevy Volt, or the Nissan LEAF, or Tesla cars. Battery condition is of course unknown.


Here are the venerable Trojan T-105 golf-cart batteries.

Here are the lithium-iron-phosphate batteries.

Chevy Volt battery. Watch out for the wrench shorting across battery terminals!

Nissan Leaf battery.

Typical DIY storage installation

Tesla Powerwall

 

[nash031]

Wow, seems like a lot of work and equipment is needed (panels, batteries, inverters, switches, etc) to add a really good solar system to a residence. Kind of makes one ask themselves if it is all worth it in the face of utilities changing the rules and making it more difficult to save money on power?

It would be interesting to try to accurately figure a realistic cost to operate over a long period of time and if, in fact, any meaningful energy cost saving was achieved.

Also, what is the useful life of one of these systems in terms of expensive parts replacement on a total refurbishment, which, I am sure will have to be done at some point in the life of the system?

I’ve run the numbers and expect about 6- 8% CAGR on my investment based on tax credit, power rates and expected inflation. Could end up less than that, but odds are it’ll add value to the house as well as saving me money after four years. High power rates, good roof...

 

[Another Reader]

I’ve run the numbers and expect about 6- 8% CAGR on my investment based on tax credit, power rates and expected inflation. Could end up less than that, but odds are it’ll add value to the house as well as saving me money after four years. High power rates, good roof...

I may have missed it, but what is the price per watt before the tax credit for your system? I'm thinking of a similar size system. I'm in the southern Bay Area and have PG&E. Tired of their high rates. However, the roof exposure is mostly west so I'm not sure how much energy I would actually harvest. Bids collected through Energy Sage recently were $2.50 to $3.30 per watt. Had a bid two years ago at $3.75, so it does look like prices are coming down.

 

[Cat-tirement]

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.

+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.

We had a system installed last year with this kind of inverter (info here). Our intent was not to be able to run the whole house or even a major portion of it, but just a few select items. I have an outlet box on a long cord that can be brought into the house from the special outlet at the inverter in the garage. While we haven't had to use it yet beyond doing a brief test, our plan is to use it mainly to run our freezer for a few hours during the day (it can hold food frozen for at least 2 days without power), charge small electronics and LED light batteries, and run the electric fan on a gas fireplace.

If battery systems become substantially cheaper in the future, we might consider adding one later.

 

[nash031]

I may have missed it, but what is the price per watt before the tax credit for your system? I'm thinking of a similar size system. I'm in the southern Bay Area and have PG&E. Tired of their high rates. However, the roof exposure is mostly west so I'm not sure how much energy I would actually harvest. Bids collected through Energy Sage recently were $2.50 to $3.30 per watt. Had a bid two years ago at $3.75, so it does look like prices are coming down.

Quotes from Energy sage were $2.72-2.81. Guy I will likely go with is 2.57.

 

[Another Reader]

Quotes from Energy sage were $2.72-2.81. Guy I will likely go with is 2.57.

Is he local only?

 

[nash031]

Is he local only?

Think so. Out of North county San Diego.

 

[scrinch]

Quotes from Energy sage were $2.72-2.81. Guy I will likely go with is 2.57.

For historical comparison, my 3kW system cost a little more than $7.00/watt installed 12 years ago. After rebates and tax credits my net cost was about $4.00/watt. Operating and maintenance costs so far have been zero (knock on wood). We've only had to pay about $200 for electricity over these past 12 years. Most years our true-up comes out with PG&E owing us $50-100. A couple of times we ended up owing them about the same amount. The system paid for itself after 8 years, and the ROI has been growing since then.

 

[NW-Bound]

Solar panels have been getting so cheap, I cannot believe it. Here locally, an outfit has been selling SunPower panels, the very best commercial panels and American made, for $0.50/Watt or lower. Some are used, some are new. The efficiency is 21%, compared to the usual 15-16%. It is worth it to pay a bit more to use smaller panels for the same wattage, particularly if you mount them on the roof.

I wish I had more land. I could just build a very simple ground mount frame, and have my own solar farm for free AC in the summer.

 

[ERD50]

Originally Posted by nash031
Quotes from Energy sage were $2.72-2.81. Guy I will likely go with is 2.57.

For historical comparison, my 3kW system cost a little more than $7.00/watt installed 12 years ago. After rebates and tax credits my net cost was about $4.00/watt. Operating and maintenance costs so far have been zero (knock on wood). We've only had to pay about $200 for electricity over these past 12 years. Most years our true-up comes out with PG&E owing us $50-100. A couple of times we ended up owing them about the same amount. The system paid for itself after 8 years, and the ROI has been growing since then.

Is solar still on the same %/year cost reduction path? It seems like the cost of the system goes down annually roughly by the same amount of annual savings. Does it make sense to wait? The amount invested is less, so less at risk, lower 'opportunity cost'.

BTW, I often find that people don't include the opportunity cost in the payback. 3kW @ $4/watt is $12,000. At a 4% WR, that represents $480 a year in lost income. That's 4~5 months electricity usage for many people.

-ERD50

 

[Totoro]

According to Lazard, it seems residential seems to be slowing down significantly while utility level still has a way to go. Probably has to do with non-panel costs.

https://www.lazard.com/media/450337/lazard-levelized-cost-of-energy-version-110.pdf

 

[scrinch]

BTW, I often find that people don't include the opportunity cost in the payback. 3kW @ $4/watt is $12,000. At a 4% WR, that represents $480 a year in lost income. That's 4~5 months electricity usage for many people.

-ERD50

I agree, payback really isn't the best way to look at the economics of an investment like this. It's really better to calculate the ROI for the investment and then compare that to alternative investment returns, taking their different risk profiles into account.

My forecast ROI looked to be about 8-10% when I made the solar investment, which seemed plenty high to me, given its low risk. So far the returns have been right about as expected.

 

[Totoro]

The interesting part is that as long as the annual cost reduction % is higher than the % ROI, you're better off waiting for installation.


So with an ROI of 10% and if solar install costs drop 15% (for example), you actually are best off with not buying.


Purely financially speaking, other factors come in obviously.

 

[ERD50]

Yeah, payback really isn't the best way to look at the economics of an investment like this. It's really better to calculate the ROI for the investment and then compare that to alternative investment returns, taking their different risk profiles into account.

My forecast ROI looked to be about 8-10% when I made the solar investment, which seemed plenty high to me, given its low risk. So far the returns have been right about as expected.

Can you provide an example of an ROI calculation for solar? I'm not sure what is all factored into that.

-ERD50

 

[nash031]

Is solar still on the same %/year cost reduction path? It seems like the cost of the system goes down annually roughly by the same amount of annual savings. Does it make sense to wait? The amount invested is less, so less at risk, lower 'opportunity cost'.

BTW, I often find that people don't include the opportunity cost in the payback. 3kW @ $4/watt is $12,000. At a 4% WR, that represents $480 a year in lost income. That's 4~5 months electricity usage for many people.

-ERD50

$450 can be one month here with heavy AC use. I didn’t include opportunity cost in my calcs, though I did consider it, and at 8+%, it’s at least break even, and that 8+% is based on conservative power inflation in CA, a general .25/kWh which is actually low in many months, and that ROI isn’t subject to market volatility. “Guaranteed” 8ish% over ten years is pretty damn good. Also before you take into account any home resale value added.

Waiting until 2020 also costs more than 10% of the Federal tax credit... and I’m getting nearly 7kW at $2.59/kW... since we expect to be in this house for about ten years, no. Waiting does not make sense for us.

 

[nash031]

Can you provide an example of an ROI calculation for solar? I'm not sure what is all factored into that.

-ERD50

Pvcalc.org

 

[skipro33]

There are a couple points folks may be forgetting about with solar and especially with delaying an install;
1. The grid is getting close to being built out. Meaning; at some point the percentage of generation from residential solar mandated by the government will be met and the utility company will cut off any future solar installations onto their grid.
2. The agreement of rates for buying back or banking electricity off your solar plant is tiered. What the original solar rate payers were signed up for regarding rates, time-of-use, etc is not the same for future solar rate payers. I get a better deal with my utility company than someone who is just now installing solar on their home. This is because investing into a roof top solar plant was a riskier investment years earlier than it is today.

3. The faster electric rates increase, the sooner my system will pay for itself. My investment is paid back from the moneys I'd be paying to the utility company. If their rates go up, my investment is paid off quicker. So the sooner a system is on the roof, the sooner it starts paying for itself. This is a lot like taking SS early at 62 vs at FRA.