Stupid n00b solar questions.

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Poindexter

Minister of Fire
Jun 28, 2014
2,815
Fairbanks, Alaska
Just asking. The wife and I are looking to retire to someplace warmer (but not too warm) in the next few years. Like just far enough south we can grow tomato, but not so far south we have to deal with humidity or poisonous snakes.

In the lower 48, electricity rates are uniformly lower than the 25 cents per kwh I am paying right now.

1. What kind of resale value do EVs have? Is this going to get better? Right now I am driving a 2015 Tacoma, SR5 trim, 90k miles, I paid $33-34k for it and I could probably get $30k for it tomorrow. I can't get a new Tacoma to replace it at all, the local dealer is selling whatever the factory has committed to produce 2-3 months before the vehicle arrives on the lot. A similar replacement truck would probably set my back $42-45k if the factory committed to making one without the expensive decals on it and I happened to stop by the dealership on the correct day to sign on the dotted for a truck that hasn't been built yet. I can easily get another ten years out of the one I have, I can see selling it on 2035 with 300k miles on it for probably $10k in 2022 dollars.

2. When does it make financial sense to put up a solar array and a battery pack on the wall to charge up during the day, and then transfer from the wall battery into the vehicle battery at night? I don't know of anyone doing this, so it probably doesn't make financial sense for most people, but I see lots and lots of folks selling their solar output to the utility for cheap and then paying dear for the kwh they take from the grid.

3. What is really the expected service life on current and future expected batteries? It seems to me if I was starting with bare studs wiring whole house lighting to run on 12 volts dc with LED bulbs would be easy with solar/ battery that would almost never have to hit the grid for lighting, especially down in climate zone 5 or 6.

4. What about 220 vac? My wood working hobby is at the point where I really 'need' a 3-5 horsepower dust collector to go with my electric shop donkeys. I could make do with a 3 horse, only using one of the lathe or planer or jointer at a time, but that is still 18 amps at 220vac just for the dust collector while the (110 volt) lathe or planer or jointer is running. Those machines will run for less than one hour per day average, but really once every week or so the machines will be running all day making racket, and then I can go back to wood working with hand tools in peace and quiet for six days.

Let us imagine gasoline is going to stay at $5-7 per gallon for several years, and electric rates are going to be what they are in July 2022, once the fuel surcharges catch up, for several years as well. We'll plan on one high quality vehicle like maybe a Rav4 or Camry or similar for the wife, and a half ton truck for me to haul my boat around and bring lumber home. One ICE, one EV. FWIW I am very unlikely to ever have a boat/trailer combination over 1000#, but I can't think of a boat launch I use up here that isn't either mud or sand. Just driving around with an empty bed and no trailer I am averaging about 20 mpg in the Tacoma.

What makes sense as far as size of solar array, house battery capacity, and vehicle choices? What are the variables that have the biggest influence on the teeter-totter? It seems to me the big three variables are the price of oil/gasoline, the price of electricity, and the service life expectancy of large battery arrays.

I saw somewhere on this site one of y'all paid $70 for 18 MBTU of natural gas. That is a cord of green spruce to me, dropped in the driveway as 16" splits that still needs to seasoned, and then carried upstairs to the woodstove one canvas tote at a time, $350 dumped in my driveway. Also, how many square feet is that solar array you are advocating? I am over drilling unnecessary holes in my roof, the solar array is going on posts in the lawn.

Thanks in advance.
 
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peakbagger

Minister of Fire
Jul 11, 2008
7,685
Northern NH
Boy you are asking a lot of crystal ball questions. What is your time window? Climate change is definitely stirring up things 20 to 50 years down the road but unless you are building for your grandkids it may not be an issue unless you want to buy oceanfront (hurricanes and sea level rise are aready an issue along the eastern seaboard.

There are poisonous snakes up to southern VT (TImber Rattlers which are extremely rare. Eastern Copperheads are up to the Mass border and predictions are that they will be moving north.

Battery tech is changing exponentially, every year you wait, EV choices will increase, and gas engine choices will decrease. Ford has admitted that the Lightning is a transitional truck that admittedly proves demand but my guess there are going to be clean sheet designs coming out in 3 to 5 years that will be less costly and longer range. If solid state battery tech goes commercial, battery range may double.

IMHO contrary to what any politician says the long term price for fossil fuels will increase more rapidly than electrical power. The current major supply imbalance typically works its self out in 2 to 3 years, but my guess is they will come down but no where near the artificial low caused by Covid The current fuel price shocks are driven by decisions made in the last ten years to cut refinery capacity, even if oil drops, prices will lag quite awhile as the US is short of refinery capacity especially on the east coast. A new US refinery would cost billions and is inherently a superfund site the day it starts up, most large oil companies have decided that they will not build new ones as its a potential stranded investment. Far easier to build off shore, tweak a bit more life and more capacity in existing units and let someone else worry about it.

Solar with battery is technologically viable, there used to be a pretty big split between on grid and off grid solar. Off grid was 48 volt DC based, that meant the strings were wired for 48 volts to match the batteries, most off gird units ignore or are not covered by Rapid Shutdown rules so they go with string inverters. Grid tied are high voltage strings as high as 500 volts, many have to be Rapid Shutdown compliant and microinverters are a logical choice. That has recently changed with AC coupled hybrid systems (note SMA has had the Sunny Island for several years). The logical approach now is put in a grid tied system, and then throw in an AC coupled battery that can either be used on grid to shift loads around or islanded in a microgrid. The battery inverter electronics provide a stable microgrid so the grid tied string inverters or microinverters in the system just keep pumping out power. I have that set up at home currently and it works pretty well. I have lead acid forklift batteries but my guess is when they die, I will just change the charge controller settings to charge a set of whatever battery chemistry is available. Odds are its a reconfigured battery pack from a EV that no longer has the charge capability for cars but plenty for a house. Maye it will be BEV.

BTW when I charge my plug in hybrid (16 KWhr) really does not matter to me as I have one power rate 24/7. Its going to be different with a full EV if I drive a lot. The Lightning has a 98 KWh or optional 131 KWh pack. The stated "economy" is 0.48KWh/mile, my Rav 4 hybrid is 0.33KWh per mile and a Chevy Bolt is reportedly 0.212. To store a complete battery charge during the daytime to charge overnight is a big stretch but most folks drive 30 miles a day on average. So do the math, the Ford will require 14.4 KWhrs overnight which is just over the capacity of a single Powerwall battery (13.5 KWh). Switch over to a Bolt and its 6.4 KWh. I have 52 KWh of batteries in my system so the 16.2 KWh my Rav 4 to go around 45 miles takes about a days worth of generation on the 2.4 KW of panels on my solar trailer. I am in rural area and on occasion need long drives so for the short term I will stick to a plug in hybrid. BTW my RAV4 has receiver hitch rated for 2000 pounds (possibly 2500)

I dont see a lot of use for low voltage DC house wiring, the lower the voltage the bigger the amps and wire. Insulation on wires for higher voltage is far cheaper than copper. Much of the world long ago put in 240 VAC for primary voltage in homes and with modern switching power supplies most electronics and many appliances are built for either 120 or 240 input, the only difference is the supplied plug (many electronics now come with a couple of different plug and voltage formats. Many LED fixtures have switching power supplies and they also can take 120 or 240. I could see the temptation to wire a home for 240 volts although unsure what the NEC would say about it. Off grid folks used to go with low voltage DC wiring but they usually were severely battery and inverter limited so DC made sense.

My heat in northern NH is 3 to 4 cords a year supplemented with a minisplit heat pump in shoulder seasons. Its a small house, around 1500 square feet heated. It was built to current efficiency standards 30 years ago but I would build a new home much more efficient to the point where I can leave in the winter and I can heat it with surplus solar. If I do not build a new home I am considering doing some energy retrofits on my house to reduce its heating load even further.

With respect to solar panels, I have four arrays. One is a pole mount with adjustable angle, I upgraded the panels at one point and the lower edge of the array is below the local snow pack so I do need to snowblow in front of it. If I built another one it would be higher. It puts out more power per watt of installed panel per year as I adjust the angle seasonally. My solar trailer is effectively a fixed angle ground mount. It puts out the power in the summer but needs to be shoveled in the winter. I have a small wall mounted array that has adjustable angle. It acts as an awing over a large window so nice in hot weather but it does impact my view. The last array is a roof mount. It has shallow angle so optimized for summer but roof temp cuts the output. Its a second story roof and a major PITA to keep the snow from building up and staying there for weeks. Next house will be pole mounted adjustable angle arrays but its hard to find sites that have good enough sun exposure.

So trying to figure out the best approach is going to be specific to your specific circumstance, and your time window
 

EbS-P

Minister of Fire
Jan 19, 2019
3,530
SE North Carolina
1) Who knows what EV resale will really be in 4-8 years. battery cost will come down that will hurt resale. At some point ICE resale will be up as supply of them shrinks. I was looking at 4WD E-350 passenger vans Before Covid and was astounded.
If you told me today I needed to buy an EV it would be a 7 seat model Y AWD.

I think they may be the EV equivalent of and RX350 in terms of resale and popularity. Probably a tier or two below the RXs reliability. They new batteries are rated at 180 wh/mile for decent sized car. Fords mach E is 30% less efficient…..

There will be some new EVs that won’t go over well. So I think in the next 4-8 years resale value could be highly model dependent.

2) now??? Probably. I trust this YouTuber as far as I can throw him and he looks scrawny but I think his math checks out.



He went from homeless to owning a models s Plaid and a model 3. People are consuming whatever he’s selling.

3)10 years+

4). It’s a hobby. Any solar system for car charging should be 240v. I’m not sure I’d want to drain my batteries as quickly those loads would. I have a 120v dust collector on wheels. I don’t have any stationary equipment. I wheel most of it outside when it’s have big jobs.

Looking at my usage living where we have almost equal heating degree days and cooling (2300) and a rate structure that pays wholesale cost for your excess generation. But 13 cents/kWh power I’m having a hard time tying money up in a big solar array. Putting that money in the stock market might make more sense. And then there are the fun ways to spend money.

Looking at my real-time usage for a big family in a 1968 southern home. Only energy improvements are windows but not great ones, HPHWH, and a 13 year old 16 seer 3 ton heatpump hooked up to original ducting. If one was committed to wood heat EVs will be the biggest usage by far. Battery’s and solar is really the only viable path I see. 600 miles a month we are using 200-300 kWh to drive. My super fast math says that’s a 5kw system (give or take a lot for my haste). If you are able to charge at off peak for some discount, which I think will be a thing covering 100% of your usage will take a quite large install.

That said retirement changes your daily habits. And technology will really change quite a bit in the next 5 years.

I have dreams of designing my own house. Probably won’t ever happen but if it did it would have enough space for a prime ground mount 5-10kw solar install.
 
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woodgeek

Minister of Fire
Jan 27, 2008
4,776
SE PA
I'll take a stab:

1. There are two cases. First case: if the BEV comes with a $10k tax rebate at sale new, then it depreciates by $10k the second you drive it off the lot. Second case: if there are no rebates (GM, Nissan and Tesla) resale is same or better than ICE vehicles. Sales of BEVs are up in the current $$ gas era, while ICE vehicles are down. My 7 year old Volt plug-in hybrid is only down 25% according to KBB since I bought it almost 4 years ago.

2. If you have an on-grid option, likely NEVER. With solar and an EV and TOU pricing, you can always charge your EV during low demand periods. Buying a second battery to charge your solar and store it so you can charge a second battery.... the cost of the second battery outweigh the benefits. At $100/kWh (optimistic near future price) and 2000 cycles (you could probably do better), the cost of storing a kWh is $100/2000 = $0.05. That is a lot of capital tied up, and you need to save > > $0.05/kWh with your scheme.

3. With moderate temps, both BEVs and off-grid lithium batteries are warrantied for 8-10 years in normal use. Most will likely keep working (with slightly reduced capacity) somewhat longer than that. Off-grid people are switching en masse to lithium (from flooded lead acid) as their old cells age. The new Li cells are smaller (Ah) for the same useful capacity, are smaller, weigh 1/4 as much, and last 2x longer. Each battery in the bank has its own internal battery management system so you can assemble them like 12 lead acid, and they will equalize their internal cells themselves.... plug and play. Lots of YouTube videos showing the basics.

4. They make two-phase 240 V sine-wave inverters to run your house. BC most off-grid folks these days want to have 'normal' AC appliances, not 12V appliances, etc. For your blower, 5 hp is about 4 kW. If you are building a small off-grid bank, say 50 kWh capacity, which is 40 kWh to 20% SOC (minimum), it could put out 4 kW for 9 hours (assuming 10% ohmic and inverter losses). Power is not an issue for the bank, most lithium can easily do 1C (which is 50kW out of 50kWh pack). You would be doing less than a tenth that.

Example: the 66 kWh pack in my new Bolt happily puts out 150 kW (200 hp) surge when I floor it, the motor inverter under the hood is the size of a breadbox. Cruising at 75 mph up hill, it will put out 50 kW as long as I want (until I need to recharge it).

So, short answer, is all this tech exists and is prime-time. EVs work for many use cases, are warrantied, and are cheap on a TCO basis. You can off-grid now and have a 'normal' house. The bad news is off-grid still costs MORE than a simple on grid situation. And it will continue to cost MORE IMO forever. BC as solar tech gets cheaper, the utilities can use the same tech at larger scale to make grid power cheaper than you can.
 
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begreen

Mooderator
Staff member
Nov 18, 2005
96,312
South Puget Sound, WA
A quick 2¢
1) I got our 2018 Volt 2 yrs ago from a single owner in CA that babied it, always garaged. It had 14k miles and every option except Navig. I paid $25k. Now, 2.5 yrs later this car with low miles is selling for $29-30k. The demand is very high for used EVs, hybrid or BEVs. Most west coast cars see no road salt. With low miles, they command a premium price on the market. Keep the Tacoma, they have always held their value and will last a long time with normal servicing.

2) The wall battery makes the most sense in areas where the grid supply is not always dependable. Parts of the country where it is sunny, but there are rolling blackouts due to high grid power load due to AC cooling, are good candidates. In our area a generator makes more sense for the typical winter outage. This of course presupposes grid power is an option. If not, then storage is needed.

3) Most off-grid systems I have seen run the house off an inverter for normal 120vac power. It's less complicated, the wiring is less expensive, there are more options, it's easier to grid-tie in the future, and it's more likely to be bank loan/insurance friendly.

4) Big motors require some serious energy. That will require a large grid array and battery backup system. An alternative might be siting near a year-round creek for water turbine power or a standby generator. If one is really trying to be self-sufficient, then run a propane generator on cleaned-up methane from an anaerobic digester system, or wood gas?
 

Poindexter

Minister of Fire
Jun 28, 2014
2,815
Fairbanks, Alaska
Appreciate the input. Alaska is a great place to raise children, and a great place to be a young person. It is OK for middle aged folks. As we are approaching the end of middle age, closer access to sophisticated health care is moving up our list of priorities quickly. I don't see trying to be "off grid" in the lower 48 and elderly as a goal, but being independent of the grid, at least in a limited fashion, seems prudent.

I guess I will wait until to closer to time for running 220vac shop equipment on solar versus generator versus on grid to make a choice; clearly a rapidly changing field.

Thanks again.
 
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woodgeek

Minister of Fire
Jan 27, 2008
4,776
SE PA
I would love to visit Alaska sometime.

A full off-grid arrangement is indeed overkill is you are in an area with a grid connection. It sounds like what you want is an on-grid house with a solar array (and a grid tie) with the ability to 'island' off the grid using a wall battery in an outage situation. Obv solar with grid-tie is standard nowadays, and in many areas of the lower 48 will have simple paybacks of less than 10 years, and service lives of 20+ years. And thus are as good investments as a low rate of return bond and the same risk (zero with warranty).

A LOT of folks want the solar backup/island capability, like a Tesla powerwall provides, but get cold feet on the price tag. There are competing non-Tesla products (IIRC) that are slightly cheaper. Prices for these systems will likely fall. I think for most users these things are a sunk cost, but some utilities will use the battery for load regulation on the grid (under utility control) and pay the owner a fee for the service. Thus, this system might also pencil out (pay for itself after a long time) in some markets. But this seems rare in 2022. The powerwall system is slick bc the backup is fully automatic switchover. But ofc most people that want this backup function still just get an automatic backup generator, which is still cheaper than the powerwall, and can run a long time on a nat gas line or a large propane tank.

The EV is a separate system from the above, and could run off the grid, or be charged by the 'island/solar' in an emergency. The latter doesn't seem very useful to me, bc the EV is likely to have a somewhat larger battery than the powerwall. And for a short outage (days) would not need to be recharged (240 miles/30 miles per day is 8 days). Anyway, the EV is also a commodity, readily available, and non-Tesla BEVs have total cost of ownership (TCO) comparable or lower than ICEV. Current exception use cases (for cheap BEVs) are heavy towing, vehicles with more than 5 seats and ability to road trip 1000s of miles with very fast DCFC (like 150 kW+, or 100 miles in 10 minutes). All of those latter things are currently available (sometimes in limited availability), but at a higher price point.

So, it sounds like you would be happy with a ground mount solar array with grid-tie, a Tesla power wall, a Bolt EUV and a backup ICEV. Anywhere in the mountain west you would have great solar.

Here is a solar+powerwall video:


More exotic things like V2G (vehicle to grid) would allow your EV to use its battery like a Tesla powerwall (and the utility would pay you)... seems rare. You can also use your EV battery as backup power for your house with a suitable inverter. The commercial solutions for this are also rare at low cost. The F150 lightning has a big inverter built in that I suppose would be trivial to backfeed in an outage.
 
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brenndatomu

Minister of Fire
Aug 21, 2013
7,513
NE Ohio
If one is really trying to be self-sufficient, then run a propane generator on cleaned-up methane from an anaerobic digester system
How is the average person going to access digester gas? Most digester owners utilize their own gas.
And it tends to be a wet and dirty gas, requiring a scrubber system to clean it up enough that it doesn't quickly destroy the equipment that is using it...scrubbers are $$$.
My employer owns/operates an anaerobic digester and all of the gas is used to heat the primary digester in the winter...in the summer there is excess that gets flared off...we looked at installing a micro turbine to use that excess gas, but once the cost of the scrubber system was factored in, the ROI was ~23 years...dead project.
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,312
South Puget Sound, WA
How is the average person going to access digester gas? Most digester owners utilize their own gas.
Yes, we have a local anaerobic digester and you are correct about the drier. Gas storage is also needed. Still, if living off-grid, one can start by building a digester when the house is being built. There often are ample resources including human poop. Rural areas in India and China still use simple digesters for fuel.
There are even off-the-shelf units available, but I have no direct experience with them.
The value is minimal for a grid-tied home, but for an off-the-grid remote home, everything should be viewed as a resource.
 

GrumpyDad

Minister of Fire
Feb 23, 2022
553
Champion, PA
Just asking. The wife and I are looking to retire to someplace warmer (but not too warm) in the next few years. Like just far enough south we can grow tomato, but not so far south we have to deal with humidity or poisonous snakes.

In the lower 48, electricity rates are uniformly lower than the 25 cents per kwh I am paying right now.

1. What kind of resale value do EVs have? Is this going to get better? Right now I am driving a 2015 Tacoma, SR5 trim, 90k miles, I paid $33-34k for it and I could probably get $30k for it tomorrow. I can't get a new Tacoma to replace it at all, the local dealer is selling whatever the factory has committed to produce 2-3 months before the vehicle arrives on the lot. A similar replacement truck would probably set my back $42-45k if the factory committed to making one without the expensive decals on it and I happened to stop by the dealership on the correct day to sign on the dotted for a truck that hasn't been built yet. I can easily get another ten years out of the one I have, I can see selling it on 2035 with 300k miles on it for probably $10k in 2022 dollars.

2. When does it make financial sense to put up a solar array and a battery pack on the wall to charge up during the day, and then transfer from the wall battery into the vehicle battery at night? I don't know of anyone doing this, so it probably doesn't make financial sense for most people, but I see lots and lots of folks selling their solar output to the utility for cheap and then paying dear for the kwh they take from the grid.

3. What is really the expected service life on current and future expected batteries? It seems to me if I was starting with bare studs wiring whole house lighting to run on 12 volts dc with LED bulbs would be easy with solar/ battery that would almost never have to hit the grid for lighting, especially down in climate zone 5 or 6.

4. What about 220 vac? My wood working hobby is at the point where I really 'need' a 3-5 horsepower dust collector to go with my electric shop donkeys. I could make do with a 3 horse, only using one of the lathe or planer or jointer at a time, but that is still 18 amps at 220vac just for the dust collector while the (110 volt) lathe or planer or jointer is running. Those machines will run for less than one hour per day average, but really once every week or so the machines will be running all day making racket, and then I can go back to wood working with hand tools in peace and quiet for six days.

Let us imagine gasoline is going to stay at $5-7 per gallon for several years, and electric rates are going to be what they are in July 2022, once the fuel surcharges catch up, for several years as well. We'll plan on one high quality vehicle like maybe a Rav4 or Camry or similar for the wife, and a half ton truck for me to haul my boat around and bring lumber home. One ICE, one EV. FWIW I am very unlikely to ever have a boat/trailer combination over 1000#, but I can't think of a boat launch I use up here that isn't either mud or sand. Just driving around with an empty bed and no trailer I am averaging about 20 mpg in the Tacoma.

What makes sense as far as size of solar array, house battery capacity, and vehicle choices? What are the variables that have the biggest influence on the teeter-totter? It seems to me the big three variables are the price of oil/gasoline, the price of electricity, and the service life expectancy of large battery arrays.

I saw somewhere on this site one of y'all paid $70 for 18 MBTU of natural gas. That is a cord of green spruce to me, dropped in the driveway as 16" splits that still needs to seasoned, and then carried upstairs to the woodstove one canvas tote at a time, $350 dumped in my driveway. Also, how many square feet is that solar array you are advocating? I am over drilling unnecessary holes in my roof, the solar array is going on posts in the lawn.

Thanks in advance.
you should consider PA. Or WV. PA If you want some stuff to do and want to live near some semblance of civilization, the ridges of WV if you want to feel like you are in Alaska but aren't. PA electric, try 11cents per kilo :). Winters aren't too bad, nor are the summers. Winter months drag on sometimes forever, and summers last just long enough that when you are so sick of cutting grass every 2 weeks before you know it the cold sets it into dormancy and you put away the mower for 7 months. :)
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,312
South Puget Sound, WA
Stay on the west coast if you want to avoid summer humidity (and most snow). We grow tomatoes every year and no poisonous snakes here, just garter snakes.
 

GrumpyDad

Minister of Fire
Feb 23, 2022
553
Champion, PA
Stay on the west coast if you want to avoid summer humidity (and most snow). We grow tomatoes every year and no poisonous snakes here, just garter snakes.
And taxes. And backward utopia destructive politics.
 

DBoon

Minister of Fire
Jan 14, 2009
1,295
Central NY
Winter months drag on sometimes forever
I have to laugh (tongue in cheek), the original poster currently lives in Alaska - his version of "winter months drag on sometimes forever" is probably a lot different than for those of us in the lower 48.
 

Poindexter

Minister of Fire
Jun 28, 2014
2,815
Fairbanks, Alaska
Long summer here. I am currently looking at staying up here until Jesus calls me home. But I need AC to survive the summers.

I visited my local purveyor of the solar panels, they are not well known for competing on price and we didn't talk about price. My copy of Solar Power for Dummies was due yesterday but was not yet in my mailbox when I got home today.

Local/current we are paying 30 cents per kwh for electricity delivered, and the local utility is currently paying 18 cents / kwh for solar delivered to the grid from a grid tied system. These are fairly attractive numbers for what I have seen here and around the internet. The salesman didn't know of any pending foolishness to change that deal around in current discussion at the legislative level and passed my screening for basic nonverbal honesty when making the claim.

It looks like I can skip a battery array, at least short term. One saving grace is the feeder road to my subdivision has some heavy hitters on the other side of the feeder road. In 11 years, my longest power outage was about 10 hours. When 'our' power goes out my across the feeder road neighbor calls the governor of Alaska, "Mike, this is Mary ___. My power is out. Handle it." Then Mary hangs up the phone and Mike (Dunleavy) gets on the phone to get my power turned back on along with Mary's.

It seems like average a biphasial (?) 440 watt panel is good for about half a megawatt hour per year up here. 11 panels will fit on my roof easily, 22 could be done. The guy at the solar place pulled up my lot on google earth or similar and asked about that "L shaped thing" in my back yard- 8 cords in passive solar kilns.

So if I install 22 panels I should be pumping 'about' 10.5 megawatt hours / year into the grid. Without AC in the year ending 07-06-22 the wife and I bought 7034 kwh. 7034 kwh = 7.03 megawatt hours, yes?

The salesman (red flag) felt that with a 22 panel system I should be able to run a rocking and rolling AC system in the hot months for 1200sqft (upstairs) and still be earing credits from the utility in the summer months. His premise was I should, most likely, have 'free' AC and still earn enough credits from the utility to only pay for electricity delivered in Jan-Feb-Mar with April more or less a wash, then pile up credit with the utility company in May-June-Jul-Aug with Sep a wash, and then burn credits in Oct-Nov-Dec.

I get that the efficiency of my heat pumps for AC is a huge unknown in the equation, as is how cold I want my indoor air to be. As is my air sealing and insulation.

My question is does this sound remotely reasonable, or is someone trying to smoke me?

FWIW the salesman is accustomed to working in dollars. I look at kwh, those cost more every year. He was looking at a 22 panel array producing about '$ 30' worth of electricity in December and about '$360" worth of electricity in June and July. Our current budget is about $130 per month for electricity (annual average) and that savings account runs about square/ straight.

Thanks
 

peakbagger

Minister of Fire
Jul 11, 2008
7,685
Northern NH
Wait for the book read it and then ask questions. Hol off on solar until the new incentives are finalized.
 
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woodgeek

Minister of Fire
Jan 27, 2008
4,776
SE PA
I think you are overestimating the amount of juice required for AC. I have a 2400 sq ft place down here in tropical Philadelphia, with dewpoints over 60°F, low temps over 70°F and high temps over 85°F for months on end. And I think I use ~1000-1500 kWh for AC in the summer. True, I DO have a lot of shade trees.

I assume your attic is well insulated and airsealed (for winter). If so, then the amount of AC energy to keep the place cool is likely less than mine. I run in AC mode from before Memorial Day until after Labor day, never opening a window.

Folks spending lots on AC have inefficient central systems from the 90s, inefficient window units of a similar vintage, and/or poor attic insulation/airsealing bc they live in a warm climate.

Obv 1000 kWh for you would be $300 w/o solar. I'd take the bet that you summer AC bill would be under that.

You could put in AC, and see what you use in a season, and worry about solar later.

--------

As for the solar, yeah, take array kW * H(hours/year) to get kWh/year. H depends on location, you are probably 1100 or 1200 hours/year. Your local installer will know.

The thing with your numbers is that you are not selling all the solar power to the utility for 18 cents. You are offsetting some of your usage (at 30 cents) and selling the surplus back. So you will save more that way. The devil is in the details of how the credit gets carried forward month to month.
 
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EbS-P

Minister of Fire
Jan 19, 2019
3,530
SE North Carolina
My dilemma is, im not sure if I’m going to keep the house long enough to break even. I have a big tree that provides lots of shade an entering it’s fastest rate of growth. Site location matter for solar im just good enough that they would sell it to me but in 5 years the trees would really be impacting my output.

I think a valid question is what else would you do with the money. 0 panels of money, 11 panels worth, 22 panels worth? That’s kinda where I’m at. A small (2-3kw) off grid install with used panels can cover a lot of my cooling and provide emergency power. I feel good about my carbon off sets and have, don’t need to worry about rate structures, and can spend the money I save vs a new large install on other things, retirement, vacations, cars ect.

I’m going to dig deeper into the solar mini splits. I’ve had my copy of solar for dummies for over a year now. Haven’t read it. I decided I need to wait on my HVAC work. Prices are crazy now. Tax credit rules and what qualifies are not available, same with solar. My system is still working no rush. Same goes for EVs. That full federal tax credit is substantial.

I’ll sum everything below this paragraph if you don’t want to keep reading. You can really get into the weeks of HVAC and solar installs. I’m not sure even the professionals really completely understand all the details. Or you can just throw your hands up fork over the money and be done with it. I don’t know which is better. Continue to the weeds.

I’m trying to learn HVAC basics. (Probably solar too) ANSI standard says a load calc should be done when installing any new equipment. No one does. If you have an average house for the area installers guesses are decent but really operate on the premise if customers don’t complain I did a great job. That’s a pretty low bar. With variable speed compressors installers just have to get in the county (and up size 1/2 a ton.

Down here we are in the Hot and humid zone. Where a significant portion of cooling load is latent heat. How much?? I don’t know. You can’t even pay someone to do a a load calc down here. I do know kids and an in and out all the time dog increases REALLY increases that latent load. Neglecting annual maintenance has real implications. Mini split evap coils need cleaned.

I’m really considering seasonal sun shades a 10x20 cost me 40$. My thoughts are to shade the whole side of the house. Probably don’t even need 10’
 

DBoon

Minister of Fire
Jan 14, 2009
1,295
Central NY
Your house sounds small enough to benefit a lot from just one mini split, if it is an open enough floor plan. The nice thing about mini splits is that they do a good job of throttling down efficiently even if oversized, so there is less risk to getting something too large.

I think the installer is probably not taking into account the sell vs. buy price difference in the system sizing. Your system might offset your kWh usage perfectly, but not offset your expenses due to the sell price vs. buy price. Frankly, if you are getting older and want to stay in your house, I would make sure that whatever I installed to cool the house could also warm the house, and run the mini split during fall and spring during daylight hours (so you don't have to sell power at 18 cents/kWh) and run the wood stove after daylight. This might significantly reduce your wood consumption as well - not a bad thing as you get older.

Having said all that - so what if your system doesn't cover 100% of your needs? You'll still save a lot of money, and the ROI will probably be faster if it didn't cover 100% of your needs. At 18 cents/kWh (excess sold at price) and 30 cents/kWh (avoided purchased), I would imagine your ROI would be pretty good - 4-5 year time frame if the system price comes in at $3.50 to $4.00 /watt (before incentives). And incentives just got better (though I don't know the details on when the better incentive rate starts).

And if you don't already have electric (heat pump) hot water and stove/range, why not switch to that and up your solar PV system a bit more to cover that usage? That will be cheaper than burning oil or gas up in Alaska, from what I've read about local fossil fuel prices in Alaska.
 

woodgeek

Minister of Fire
Jan 27, 2008
4,776
SE PA
I’m trying to learn HVAC basics. (Probably solar too) ANSI standard says a load calc should be done when installing any new equipment. No one does. If you have an average house for the area installers guesses are decent but really operate on the premise if customers don’t complain I did a great job. That’s a pretty low bar. With variable speed compressors installers just have to get in the county (and up size 1/2 a ton.

Down here we are in the Hot and humid zone. Where a significant portion of cooling load is latent heat. How much?? I don’t know. You can’t even pay someone to do a a load calc down here. I do know kids and an in and out all the time dog increases REALLY increases that latent load. Neglecting annual maintenance has real implications. Mini split evap coils need cleaned.

I’m really considering seasonal sun shades a 10x20 cost me 40$. My thoughts are to shade the whole side of the house. Probably don’t even need 10’

I know I'm a bit of a broken record, but I used to think the same way you do, and now I don't. Bottom line: Airsealing is the best bang for the buck.

Regarding load calcs... I looked at those worksheets years ago, and how they work. They are useful, but there are a lot of assumptions build into them. While the standard says to do load calc (with the intention of not installing oversized equipment), a bad load calc is basically useless. I am not mourning the lack of load calcs anymore.

You can estimate your usage by putting a meter on your AC equipment (and using the rated SEER to convert to BTU/h) or a timer on your furnace (and using the rated BTU/h output). Or even just looking at your monthly summer elec bills and cooling degree days. And that is waaaay more accurate than ANY load calc.

We've already discussed (mostly attic) airsealing for your winter load. It will also save you a bundle on AC, bc it will reduce BOTH heat intrusion AND latent load.

We tend to try to use our senses to guess where the load is coming from... that draft from the window, that sun beating on the outside... and that doesn't really work. Until your house is airsealed to a modern standard, your built in leaks are a huge part of your HVAC load, winter and summer.

Don't believe me... get a blower door test done. That is quick and cheap and they can then estimate the hit you are taking on winter and summer loads just from that.

Quicker version... if your upper story gets hot fast when the attic heats up, and you've got a pile of insulation up there, then you have a big air leak. A sealed R-30 attic lets only a miniscule amount of heat through, even if the attic is blazing at 150°F.

As in Delta T/ Rvalue per square foot. That is (150-70)/30 = 2.7 BTU/h per square foot. With 1000 sqft of attic floor, that is 2,700 BTUs per hour, less than half what a small window unit can handle, or 0.27 'tons'.
 
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begreen

Mooderator
Staff member
Nov 18, 2005
96,312
South Puget Sound, WA
My dilemma is, im not sure if I’m going to keep the house long enough to break even. I have a big tree that provides lots of shade an entering it’s fastest rate of growth. Site location matter for solar im just good enough that they would sell it to me but in 5 years the trees would really be impacting my output.
If the tree is deciduous then it may not be a liability all the time. Have you had a solar analysis done on the property? They can scope out solar gain for the summer and winter.

PS: Let me know if you come across a good installer. My sister is in your area and will be looking to install solar next year.
 

RustyShackleford

Minister of Fire
Jan 6, 2009
1,137
NC
I’m trying to learn HVAC basics. (Probably solar too) ANSI standard says a load calc should be done when installing any new equipment. No one does.
I did, for the minisplit I'm installing at our mountain place. It's not that tough, though I'm an engineer and more comfortable with such stuff. I actually used two tools, and they agreed remarkably closely, which gave me great confidence: https://hvac.betterbuiltnw.com/ and https://www.loadcalc.net/ .

If you have an average house for the area installers guesses are decent but really operate on the premise if customers don’t complain I did a great job. That’s a pretty low bar. With variable speed compressors installers just have to get in the county (and up size 1/2 a ton.
Yeah, and they tend to grossly oversize, because the last thing in the world they want is for the customer to say "the system that you put in does not keep me cool (or warm) enough". We were at a beach rental where the A/C cycled every 10 minutes or so; and when it came on, it was deafening (way too much airflow too).