Number crunching

Yeah, real-world performance is likely to have multiple factors affecting the power output, not just temperature coefficient spec of the panels. Nonetheless, it would be very nice to be able to tell the loss (or gain) of power generation is due to temperature or something else. My panel has 25 years efficiency loss warranty, but I am a bit skeptical any manufacturer actually honer such claims ever. I will have to ask for warranty documents on my system to read the small prints, but how can an owner demonstrate such loss of efficiency over years?

 

"how can an owner demonstrate such loss of efficiency over years?" With the handheld photon counter discussed here earlier would be one way.

 

Certainly I will keep record of Daily Light Integral (DLI) and total kWh generated from the system for that day and hand calculate the production efficiency. But I wonder what percentage of owners would have such device and keep the record over the span of warranty period? I wish efficiency of the panel is displayed somewhere in the built-in data logging capability. I have not found such functionality on my PV system.

And even if I can demonstrate generation efficiency loss by comparing kWh/DLI, it does not take into account for temperature difference. So that means, I would also need to keep record of daily temperature.

There maybe more factors that affect power generation. So, it would be easy for a manufacturer to deny even a legit warranty claims, I would think.

 

IMO, you can only keep track of your monthly and yearly production and file a claim if you have a drastic failure of some kind.
Because weather variations and how clean the panels are completely mask a few percentage difference of any kind

Mike

 

I agree. It would be up to the manufacturer and the installer to horner warranty claims. I wonder if there is any data on success rate on such warranty claims. In any case, it seems such a uphill battle if solar panel owner wants to make any claims. On top of it, I am very skeptical of my solar installer and manufacturer will be around 25 years later. I'm glad I didn't go with SunPower, though the panels are still being sold under spin off company Maxeon.

 

A full month of operation from our PV system produced 653kWh of electricity. That's about 60% of our monthly consumption. And at today's rate roughly $180 offset on our electric bill.

I am quite impressed with the number. The installer estimated 500kWh production in month of January. Considering the second shortest daylight month of the year and many days of snow cover, it was very respectable number. I have not heard from our utility about NetBilling set up. So I am not sure if we get a full credit. Right now, I'm just waiting for the 30% tax credit, so I can use the money to install whole house heat pump next.

 

Very interesting , so as I understand it , the PV project will create a whole house heat pump project. ......i'm curious to know how you will address your heatpump project

 

I had heat pump installers give us quote several years ago. At that time, just after Ukraine war started, the oil price got high enough (above $6/gal) such that heating with electricity got cheaper than oil relatively speaking. But that lasted just one winter. Since then, the oil price came down. At current price in our region, at $3 per gal oil and $0.30 per kWh electricity, oil heating is cheaper than heat pump. It made no sense to install heat pump unless I first mitigate the high electricity cost.

Switching to whole house heat pump will likely to increase our winter electricity consumption substantially such that current solar will not be enough to generate net zero electricity. But electric bill is likely less than we pay now. And we will not have to buy as much oil. Should result in net savings.

Unfortunately, even if I install a whole house heat pump, I still have to burn oil for hot water. We determined, without major remodeling, we can not convert the hot water system currently off oil boiler to electric. So after heat pump or it maybe before heat pump heating, I have a plan to go with remodeling out utility room in basement to accommodate heat pump water heater. When done, we should be able to cut off the oil boiler permanently.

Another switch from fossil fuel will be switching from portable gas engine backup generator to battery storage backup solar generator. At today's high price tag on large capacity battery storage, this is likely to be the least bang for a buck conversion. So I am less enthusiastic on this.

 

1,000 Gallons of earl????
Probably one of the better use-cases for solar!!!!!

I remember growing up in my beloved home state of Indiana we had a buried 500 gallon oil tank (now filled with sand.)
My dad borrowed money to get a NatGas boiler/baseboard system that we (he) DIY'd during a %$&#@! union strike and.....the system paid for itself in a few years.

AND....
No oily chimney smoke.
I still have a faint scar on my wrist from back-hauling the old furnace and driving it to a metal recycler for about enough money to pay for the gas that it took to get it there.......

 

One of biggest concern I have in full conversion to heat pump is the longevity of the system and running cost of maintenance/operation. While it is probably still improving, it is generally accepted fact that electrical heat pump are not as durable as well built boiler. Our oil boiler is approaching ~30 years and still maintaining above 80% efficiency with minimal maintenance/repair cost (average less than $100/year). And also while heat pump does work in extreme cold, its efficiency drops at lower temp. Meaning at our low winter temperature when we need most heat, like today at temp -9F, how effective are they going to be both functionally and economically?

At optimal temperature range for current heat pumps when it is at the highest efficiency, heat pumps still cost more to heat than using oil in our region. Even with solar panels on top of our roof, if our total electric consumption doubles, I will be ending up paying more electric bills than we are currently paying for oil because our solar panels production will fall far short on our consumption.

 

The house I'm currently in had a Heat Pump (badly) installed in 2011.
The previous owners died and their kids moved out to the PNW and they hired some people from 30 states away to make some "upgrades" to the house before I bought it.
Even if they're competently installed, heat pumps may seem like a good idea in the inhospitable regions of the planet north of US I-20, but in the deep south but you might want to do a deep dive into the wonders of heat pump ownership before getting one yourself.
I had to make three repairs to the system before we moved in - one drain, one thermostat faux-pas, and a blown fuse on the motherboard.
I should be eternally grateful, because we bought our house at the bottom of the local market and I think that the infamous 'gym-sock' heat pump thing probably knocked $50,000 off of the move-in price!!!

In the 11 years that I fought that beastie with bi-annual pro HVAC maintenance and my own due diligence AND several steep repair visits we finally ripped out the unit AND the ducting and replaced it with a conventional HVAC system.
I do not know what made me cry the most.....
being rid of the %^$#@! heat pump or the $11,500 upgrade cost.

So far?
My electric bill is about the same.

MY mileage.
Yours might vary.

 

In you location, assuming Deep South, I don't understand why you would even want heat pump. All you are going to use is for cooling isn't it? Or did you ever use it for heating?

I have the same dilemma about heat pump. All I need it is for heating. Historically we don't need air conditioner for cooling... although last few years, we have had hot enough stretch of days in summer that we used window AC for a few days. For those few days, having heat pump that works as AC will come handy. But if we get so accustomed to having AC on during summer, we may become more dependent and thus keep AC on all the time... This will also lead to more electricity consumption than current usage. Thus overall, heat pumps will not save me any money.

Although I am 100% sure that I will install whole house heat pump system this year, I may regret it by this time next year.

 

The farther north you are, the more a ground source heat pump will make sense. They'll work at air temps the air source ones don't, along with being more efficient for heating in general. Install costs more as it requires drilling or lots of digging.

 

We use our A/C 12 months out of the year.
I used it yesterday and (looking at ASOS.....) It's 77 degrees outside now and (looking at HVAC) it's in 'cool' mode at the time.

Theoretically, I guess you can use the HP during the 2-3 weeks out of the year that it's cold enough outside to run a heater but so far (9 months) I've seen no cost increase in getting rid of the heat pump and installing an old-school HVAC unit. I think in this part of the world people were pimping heat pumps just to get folks off of Gas and Propane.
My intentions are to get a propane tank and install a pre-heat/backup water heater, gas fireplace, and a ventless gas heater.
This will give me backups for the occasional ice storms that DO occur in the South as well as hot water and a more robust fuel supply for my backup generator during hurricane season.
Our neighborhood was annexed by the city some years back, which is why the local prices in this neighborhood plummeted(schools) and we've never been connected to NatGas - but this is a feature - NOT a bug.
I actually prefer propane for an emergency backup because it's PAYGO.

 

I have not found any installer who would retrofit ground source heat pump in my area. I am sure if I really look further, I can find some contractor willing to do it with big $$$ bill, but it makes absolutely no sense (economically) to go that route. If it is a new construction, ground-up from location selection and designing, then yes, I would consider it. But, in that case, I would try with passive solar with heat sink. No fuel, no electricity needed.

 

I would keep an alternate heating supplementing the cold weather heatpump system . Today where I live we have a heavy blizzard snow storm for at least 12 hours . Usually the heatpump does the job .....but the unit is defrosting every 25 minutes because it is sucking snow . this reduces the heat output . Usually under non blizzard condition defrost happens every 2 hours + and last 5 to 10 minutes.
Granted this condition happens once every 3 years . My unit is off until the blizzard stops .......it could be in 10 hours The outside temp is
actual temp is 14 deg F , wind chill is -19 deg F and acummulation is 2 inches per hour

 

Yes, I don't plan to remove existing oil boiler and baseboard hot water central heating system, even if I install whole house heat pump. That is unless the boiler gets too old and too costly to repair.

My ultimate goal is to become energy independent and cut loose from the fossil fuel reliance. But, it has to make economic sense. Right now where I live (region and house), all electric from roof top solar only and no gas or oil just is not doable.

I cut out our gasoline consumption to less than half of what it was a few years ago by switching to a single PHEV for our mode of transportation. Installing solar will make driving our PHEV on EV mode cheaper than driving on HV mode for the first time since I first bought Prius Prime in 2017. Though we now drive Ford Escape PHEV.

If I can eliminate buying oil for heating (currently about 1000gal per year) that would be great. But if that means double the cost of heating (because we have to buy expensive electricity from the grid), then it is just not doable. Will have to see how much we can shave off the oil consumption without spending more on electricity after installing heat pump. That is the question remaining to be answered.

 

Don't let perfect be the enemy of good.

 

Yesterday's ice storm knocked down our solar panel communication system. I think no physical damages but IDK. Enphase app says it maybe due to bad weather which may resolve on its own once the weather clears up. The panels have been generating over 40kWh/day on sunny day lately, but yesterday generation was only 0.4kWh. 99% reduction. And the all panels are now covered with thick ice/snow with forecast of temperature remaining well below freezing next 10 days. I am not expecting much generation from the panels for a while. Sigh...