OT: solar panels

[rwsaunders]

The DOE is a good resource for financial modeling and for other links to making an assessment if solar makes sense for you. Imho, without the credits, it’s marginal and in many cases dependent on where you live.

We are working on a number of higher-ed projects where the 48C program essentially subsidizes alternative energy systems (solar, geothermal, EV stations, etc.) for non-profits, similar to a tax credit. Without the program, solar is a no-go, when you also take into account issues such as upsizing structural systems to address the additional load (3#/SF), upgrading to a reflective roofing membrane and upsizing the thickness of the membrane to match the life cycle of the panels (25 years). I.e, why install a panel system with a 25 year life cycle on a roof that needs to be replaced in 10 years?

FWIW, we are installing a 162MW system on an academic facility roof in Chicagoland and the panel system cost is $2/MW ($324,000) with an additional $100,000 to address the engineering, steel and roofing membrane upgrades, and modifications to the switchgear. ROI break even is 9 years taking into account the $127,000 rebate. System efficiency is 84% taking into account that the panels are bi-facial and the reflective factor of the white roof membrane improves the production level of the panels by 15%. Life cycle of the system is 25 years.

It’s a complex process to say the least, and the team consists of the MEP engineers, MEP contractors, CM, accountant and solar specialists.

https://www.energy.gov/eere/solar/ho...-photovoltaics

https://www.energy.gov/infrastructur...it-48c-program

[edgerat]

My recent experience with two different solar suppliers... 1800sq ft house 1500-1600kwh per month, house built in 2006 and is pretty efficient. We have limited roof south-facing, the best they could do was to offset by about 40% at an upfront cost of $38,000 for 17 panels. WA state waives sales tax and the 30% "rebate" from the gubment. The monthly loan cost would be $172, our average power bill is $185 and trending upward as our power company bills on a tier system, the more you use the more you get charged per unit. We decided to not do it. As much as I would love to lighten the load on the "poor grid", it still has to make sense at our front door to do it.

Good on you for doing what you can to make your home more efficient!

[Ralph]

I would only put them on a new roof. And even then, I don't like things installed on my roof. How do you repair a leak. What happens when the flashing rusts out around chimneys and sky lights, and vents, and most of roof is still good. Who takes off solar panels to repair or replace roof. Here in Florida, many roofs don't last as long as the solar panels. If I could put them on a stand alongside the house, and I planned to live in house a long time, I would probably do it.

[jtakeda]

What answers are you lookin for specifically?
Solar design? KwH need? If cost makes sense?

Start with an energy audit to find out how much you use and think of things you can live without or replace with more energy efficient models.


I live completely off grid and recently replaced my entire set up. Not exactly an apples to apples comparison but I know how much stuff costs and I have a pretty good idea of what kind of draw each of my appliances has.

Also what kind of property do you have? Is there a place with good sun exposure you can install ground mount?

Does your roof need replacing? Thats usually a fantastic time to add solar.\

Just for reference I have a fairly well insulated house, with pretty poor solar exposure in the winter due to large towering redwoods.
My battery bank is 18kw and if I use energy at a normal rate that will last me about 5 days. Propane stove, propane fridge (for now), wood heat.

The fridge is your first place you should be looking if you want to reduce your energy consumption. Freezer on top model with standard doors (not french doors) has the best efficiency generally speaking

[old fat man]

We've been leasing solar panels since 2014. Wow, almost 10 yrs. $70 a month with zero up front. In 2023, we generated about 5000 kWh via solar and from what I can see on my electric bill, we've never exceeded 700 kWh used in a month. Usually we're under 400 I believe.

2800 sq ft house from 1938 in Connecticut. Central air added in 2022 and all appliances are 9 yrs old or younger. Primarily Oil heat with one ductless split used year round. Electric range and dryer. Four people all with electronics running frequently and I work from home full time.

What the heck are people doing that pulls 1200+ kWh a month???

I did the math and for 2023, we spent an average of $95 total on electricity which includes the fixed lease price. I think these panels paid for themselves right away because my bills before solar were always at least $100 and I didn't shell out anything for the panels up front.

Original lease was with Sungevity. They went bankrupt and sunrun bought/inherited my lease. Sunrun has been great for the most part. We had to move some of the wiring when we remodeled and they sent sunrun certified techs to do the work. They even forgot to bill me the $2k they had quoted.

Like another poster, I wish my system was larger since we added central AC and will probably add an ev or two within the next 5 yrs. I have ample, good southwest facing roof top available but I'd have to invest in a completely separate second system and that's not worthwhile for a 20-30% overall increase.

My lease ends in 2034. I will have the option to extend it, buy the panels outright, or tell sunrun to take the system off at their cost. There's no price set for extending the lease nor for a purchase price. I'm counting on the fact that a 20 yr old system is of no value to sunrun so they've got every incentive to leave it in place via sale or lease extension at a reasonable price. We'll see what happens in 10 more years.

[jtakeda]

Originally Posted by old fat man

We've been leasing solar panels since 2014. Wow, almost 10 yrs. $70 a month with zero up front. In 2023, we generated about 5000 kWh via solar and from what I can see on my electric bill, we've never exceeded 700 kWh used in a month. Usually we're under 400 I believe.

2800 sq ft house from 1938 in Connecticut. Central air added in 2022 and all appliances are 9 yrs old or younger. Primarily Oil heat with one ductless split used year round. Electric range and dryer. Four people all with electronics running frequently and I work from home full time.

What the heck are people doing that pulls 1200+ kWh a month???

I did the math and for 2023, we spent an average of $95 total on electricity which includes the fixed lease price. I think these panels paid for themselves right away because my bills before solar were always at least $100 and I didn't shell out anything for the panels up front.

Original lease was with Sungevity. They went bankrupt and sunrun bought/inherited my lease. Sunrun has been great for the most part. We had to move some of the wiring when we remodeled and they sent sunrun certified techs to do the work. They even forgot to bill me the $2k they had quoted.

Like another poster, I wish my system was larger since we added central AC and will probably add an ev or two within the next 5 yrs. I have ample, good southwest facing roof top available but I'd have to invest in a completely separate second system and that's not worthwhile for a 20-30% overall increase.

My lease ends in 2034. I will have the option to extend it, buy the panels outright, or tell sunrun to take the system off at their cost. There's no price set for extending the lease nor for a purchase price. I'm counting on the fact that a 20 yr old system is of no value to sunrun so they've got every incentive to leave it in place via sale or lease extension at a reasonable price. We'll see what happens in 10 more years.

I’d prob have sun run pull em off honestly.


You could replace the panels with newer panels and get 3-4x to energy with the same footprint.

I replaced some 15 year old panels with panels that are 4x more efficient in the same footprint as the old panels

[old fat man]

Originally Posted by jtakeda

I’d prob have sun run pull em off honestly.


You could replace the panels with newer panels and get 3-4x to energy with the same footprint.

I replaced some 15 year old panels with panels that are 4x more efficient in the same footprint as the old panels

Cost to replace versus cost to keep will determine what I do. May also coincide with timing to sell our house.

[rice rocket]

Should be re-iterated that net metering can go away at any point, as it has out west and south, which might leave you upside down on the whole deal.

[jtakeda]

Originally Posted by old fat man

Cost to replace versus cost to keep will determine what I do. May also coincide with timing to sell our house.

True. I suppose it also depends on what panels you have now.

I replaced 120w panels with 380w panels.

Panels have become so cheap in comparison to before. 380w panel was $330

[paredown]

I have not looked into solar panels recently, because we are too shaded to see much benefit. But a number of years ago, my build partner and I were asked to look at them for a commercial business--IIRC,the break-even was about seven years. (This was a classic flat roof, fairly large commercial building from the 1960s, and the estimate was that it would cover 100% of the building's demand.) They decided not to go ahead with the project.

While we were involved in that my partner got the same company (Sunrun?) to install panels on her roof--she lives up the street on a sunnier lot. (Already had a new roof, so that was good--and the installers were super professional.)

We're in the Hudson Valley, so lots of grey days, snow etc, but they have generated enough to cover their needs, typically building up a credit during the summer days and have covered the lease payments as well, even though our local power company is not known for their generous terms... They are well past payback and everything still works great.

We also looked at ground source geothermal for our house--we had one of the young guys from Dandelion come and (try to) estimate. Tl; dr--it seems as if geothermal would not be cost effective for retrofits and would work much better in a new build situation (which is what our friends (whose system I admired) had done. (I also had the more traditional guy who did our friend's installation and the back of the envelope was over $30,000 ten years ago.

[NHAero]

Originally Posted by jtakeda

I’d prob have sun run pull em off honestly.


You could replace the panels with newer panels and get 3-4x to energy with the same footprint.

I replaced some 15 year old panels with panels that are 4x more efficient in the same footprint as the old panels

That's not consistent with my own experience both personally and in the industry. If you got panels making 3X as much power they'd need to be a lot larger.

My BP Solar panels in 1999 were 14% efficient and were state of the art then. New Maxeon panels 25 years later today are 22.8% efficient. The 2011 panels on my current roof were then state of the art Sunpower at 19.2% efficiency, so at 13 years old efficiency of the best panels has jumped just under 19%.

What's also interesting is that the rate of efficiency gains has slowed. Over 25 years the rate has averaged 2.0% annually, but between my first panels and the 2011 panels the rate of efficiency gain was 2.7%/year and in the past 13 years it's been 1.3%/year.

If PV is a decent deal I don't think it makes sense to wait for efficiency gains. I have off-grid friends in northern VT and in Duluth, and though they have augmented their systems for sure, they have 40 year old panels making power. These last a long time, especially if you don't get cheap Chinese panels. If you're buying PV, look at the warranty, and at the company's financial strength. A new Maxeon panel is warrantied to make 88% of rated power in 40 years. The parent company, Sunpower, has been around over 35 years.

[roydyates]

Originally Posted by rice rocket

Should be re-iterated that net metering can go away at any point, as it has out west and south, which might leave you upside down on the whole deal.

This matters more than might be obvious, at least to me. I own a solar system and I learned something quite surprising from the SolarEdge app. If on a given day my system generates, say, 35 kW-hr and my house consumes 35 kW-hr, the percentage of my consumed energy that comes FROM THE GRID on that day typically ranges from 50% to 80%. On a 60% day, what that means is that I am pumping 60% of the energy I generate into the grid and 60% of the energy I consume comes from the grid.

The key thing is that solar power operates instantaneously. At every instant, the generated energy has to go somewhere - either my house consumes it or it goes into the grid. Because the energy generated and the energy consumed both fluctuate, any instant where the solar system is generating more than the house is consuming is an instant where energy goes into the grid. As it happens, my system is in Maine and YMMV for other places, houses etc. I’m kinda curious to hear what kind of percentages others see.

Also one fun fact, on a sunny summer day in Maine, my system will generate around 80kW-hr, which pretty much matches what my son’s Ford Mach-e consumes in a fill-up. I’ve been meaning to check (when he visits this summer) if on a Mach-e fill-up day whether the energy percentage that stays at home goes up.

[saab2000]

Do any of you with solar have battery storage? There are many but the Tesla Powerwall is well known.

Eventually the day may come that an EV has 2-way power with the vehicle being that storage solution, controllable of course to not drain the car beyond a point.

Some of you may be aware of a well known YouTuber, Marques Brownlee. He purchased the Tesla roof and battery and has a video on his experience, which is mostly positive but not all. It’s a very expensive system but he reports that it works well generally, obviously especially in summer and not so much in the winter. Interesting video if anyone looks for it. His house is in New Jersey for reference regarding latitude and sun exposure.

[roydyates]

Originally Posted by saab2000

Do any of you with solar have battery storage? There are many but the Tesla Powerwall is well known.

Eventually the day may come that an EV has 2-way power with the vehicle being that storage solution, controllable of course to not drain the car beyond a point.

Some of you may be aware of a well known YouTuber, Marques Brownlee. He purchased the Tesla roof and battery and has a video on his experience, which is mostly positive but not all. It’s a very expensive system but he reports that it works well generally, obviously especially in summer and not so much in the winter. Interesting video if anyone looks for it. His house is in New Jersey for reference regarding latitude and sun exposure.

I don’t have a battery and I’ve wondered if a battery would reduce the flows in and out of the grid.

[NHAero]

Originally Posted by roydyates

I don’t have a battery and I’ve wondered if a battery would reduce the flows in and out of the grid.

In my first house on Martha's Vineyard I persuaded the electric utility to give me a commercial meter so I could track import and export of power to my net metered house. The system made more than we used at the time (before getting an EV). We used 27% of the energy contemporaneously and the rest was exported.

Batteries, if they are set up to discharge to the house and grid daily, can significantly increase the amount of energy generated and used on site. But that approach (vs. keeping them floating as backup in an outage) will reduce the service life. My best friend ran a solar business on St Croix for years, with $0.55/kWh electricity and a cap of 5 kW on a grid-tied system. His bread and butter was 20-50 kW systems for hotels and restaurants and commercial owners, and they all had batteries and were off grid.

With air-to-water heat pumps or ground source-to-water heat pumps, the potential exists to design a low temp heating system that stores excess solar PV energy in a tank of water, using that energy when the sun goes down. A thermal battery instead if an electric one. I've modeled that for a small airplane hangar client and it looks pretty do-able.