Solar Electric Assist--- NOT working

[meierlde]

Interestingly there is a document on heat pumps from the government of the Yukon (not a well known hot spot) that discusses them working even there. It turns out that there are now heat pumps designed to work to below zero f having mulitple compressors and a more complex cycle. Here is a link to work at Oak ridge:
High Efficiency Cold Climate Heat Pump

energy.gov/sites/prod/files/2014/10/f18/emt47_shen..

Note that mini-split systems otherwise known as ductless systems do better in cold weather than traditional ducted heatpumps. The tech in the link appears capable of providing 75% of the heat at 13f that it can at 49f. But this kind of tech is just hitting the market so it is expensive. However it will come down in costs. The fact that Canada is working on heatpumps indicates this as traditional heat pumps really only work in Vancouver and Victoria Bc, at best. One trick is to oversize the system relative to that needed for cooling as well. So over time the heating in the northern us could change. Note that minisplit systems work well in houses without ducts and enable the removal of window ac units also.

One company has achieved a cop of 3 i.e. 3 times the heat comes out compared to electric energy in at -13 f. If this commercializes well then a major change in systems in the north could occur. (as well as reducing energy demand overall in the north)

 

[samclem]

Note that mini-split systems otherwise known as ductless systems do better in cold weather than traditional ducted heatpumps.

I noted that Unico (a major manufacturer of mini-split systems) was a major sponsor of the Oak Ridge research. There was nothing in the linked slides that indicated if/why a mini-split system would be preferable to a traditional ducted system (assuming, of course, that the ducts are within the conditioned spaces). Do you know a reason that would be so?

 

[meierlde]

I noted that Unico (a major manufacturer of mini-split systems) was a major sponsor of the Oak Ridge research. There was nothing in the linked slides that indicated if/why a mini-split system would be preferable to a traditional ducted system (assuming, of course, that the ducts are within the conditioned spaces). Do you know a reason that would be so?

The minisplit systems use a variable speed compressor compared to a maybe 2 speed in the typical split system. (the compressor is electrically communtated so that multiple speeds are available, just like modern blowers in HVAC now can go at different speeds depending on the state of demand) Here is a link to an article about inverter compressors: https://en.wikipedia.org/wiki/Power_inverter#In_refrigeration_compressors
go down to the electric motor speed control and in refrigeration applications sections for details.

 

[jonat]

I always thought panels should have heaters to melt the snow. My neighbors system stays clear up to about 2 inches once the sun comes out.

I have seen some such, but they are rarely needed. Once a bit of the panel gets exposed, the rest often melts/slides off when the sun comes out. At least that has been my experience. Even without sun, the panels don't accumulate a lot of snow as much of it slides off on its own. I do sometimes help things along with a plastic-bladed roof rake.

 

[NW-Bound]

Interestingly there is a document on heat pumps from the government of the Yukon (not a well known hot spot) that discusses them working even there. It turns out that there are now heat pumps designed to work to below zero f having mulitple compressors and a more complex cycle. Here is a link to work at Oak ridge:
High Efficiency Cold Climate Heat Pump

One company has achieved a cop of 3 i.e. 3 times the heat comes out compared to electric energy in at -13 f. If this commercializes well then a major change in systems in the north could occur. (as well as reducing energy demand overall in the north)

Impressive. I looked at the link, but do not understand the thermodynamics reason for its higher efficiency. Wonder how they solve the problem of the heat exchanger icing up.

Regarding the AC compressor using the new variable-speed motor, all new pool pumps use them now. From what I gather, this motor type is nearly universally used in split systems abroad because of the efficiency. The lack of surge current during startup helps a lot too. The US is often last in using modern equipment. I wonder if that is a byproduct of our cheaper electric power.

 

[JoeWras]

Wonder how they solve the problem of the heat exchanger icing up.

Run it with an environmental dew point of -40F/C. Remember, this is a demo.

 

[jazz4cash]

If you have a smart meter, then you can get near-realtime energy usage with a Rainforest Energy Monitor;

https://www.amazon.com/gp/product/B00AII248U/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

Smart meters telemetry their information via a radio link using a protocol called Zigbee. Every smart meter has a second Zigbee radio channel. You can activate the channel from your utility logon page on their website. Once you activate this second radio channel, you are pair it up with the Rainforest device. It is a gateway that uses ethernet though your router to the Rainforest cloud where you can log on and view your energy use with a slight lag of maybe 15 seconds or so.
The first step is to be sure your utility company gives you the ability to activate the 2nd RF channel on your meter. Then buy the Rainforest. Then create an account with Rainforest. (It's free with the purchase). Then power on and set up the Rainforest. Then activate the 2nd RF channel on the meter. Then pair it up.

If you want to archive your data, there are other sites, also free, but you get more info if you pay them $10 a year, such as pvoutput.org

Thanks Skipro, great info. I'm probably too cheap to pay 99 bucks but the 3rd party suppliers are waving $100 gift cards for switching so I could go that route. More significantly I doubt if my utility will support this effort if I can even find anyone there that knows anything.

 

[jazz4cash]

I have seen some such, but they are rarely needed. Once a bit of the panel gets exposed, the rest often melts/slides off when the sun comes out. At least that has been my experience. Even without sun, the panels don't accumulate a lot of snow as much of it slides off on its own. I do sometimes help things along with a plastic-bladed roof rake.

I think it depends on how the panels are oriented. My neighbors panels do fine up to 2 in or so but if more accumulates before the exposure peaks around 2pm, it sticks around for days. It just seems so intuitive to incorporate a heating element but when I inquired at a seminar held by a local contractor I became "that guy" and they ignored me for the rest of the seminar.

 

[NW-Bound]

... Every smart meter has a second Zigbee radio channel. You can activate the channel from your utility logon page on their website...

I did not know this. But my utility page does not have anything on this either.

Their hour-by-hour display of my usage lags by only a day. They are showing the 24 hours of yesterday as I look. It's good enough, and I log in to check once every few months.

I guess if I had a solar system I would be inclined to monitor more closely to see the variation of power production.

 

[ERD50]

Run it with an environmental dew point of -40F/C. Remember, this is a demo.

I saw what you did there!

-ERD50

 

[Zathras]

I think it depends on how the panels are oriented. My neighbors panels do fine up to 2 in or so but if more accumulates before the exposure peaks around 2pm, it sticks around for days. It just seems so intuitive to incorporate a heating element but when I inquired at a seminar held by a local contractor I became "that guy" and they ignored me for the rest of the seminar.

Heating systems are hardly ever helpful.
Once one little corner of the black surface gets exposed, the rest melts pretty quickly under most circumstances.

On our system, it snowed overnight on Monday. Three inches Tuesday morning, panels were 100% clear by noon. I kind of wished I had checked hourly.
If it is a heavy snow, it sloughs off pretty quick.

The only time a heater would help would be a very cold, fine powder which freezes and with a good amount of sustained wind.
At the energy required is just rather silly compared to the energy gained.

As for the OP, the problem wasn't the fresh snow covering the panels, it was, as everyone else has noted, the really poorly matched heating solution for PA.

 

[ERD50]

Heating systems are hardly ever helpful.
Once one little corner of the black surface gets exposed, the rest melts pretty quickly under most circumstances.

On our system, it snowed overnight on Monday. Three inches Tuesday morning, panels were 100% clear by noon. I kind of wished I had checked hourly.
If it is a heavy snow, it sloughs off pretty quick. ...

What angle are your panels at? The ones on the big installation here are at ~ 20 degrees to optimize the summer sun collection.

The power goes near zero for a week after it snows. There isn't much sloughing off at 20 degree angle.

-ERD50

 

[Chuckanut]

FWIW, in my area we had about 5 days were the high temperature was just a few degrees above zero at best. I saw numerous heat-pumps with ice frozen to the outside of the unit on or near what appeared to be vents. It's hard to imagine that they were working very well under those conditions.

What would have happened if we had experienced sustained sub freezing weather is not a pleasant thought.

 

[gerntz]

These systems solve a non-existent problem: natural gas is cheap & works at night & with snow on the roof. What's so hard?

 

[meierlde]

These systems solve a non-existent problem: natural gas is cheap & works at night & with snow on the roof. What's so hard?

Not if you live in the country or where for one reason or another natural gas is not available where you live. Then your choice really is heat pumps or the significantly more expensive propane.
If you look at efficiency, assume a 90% efficient gas furnace and a 57% efficient electrical environment (generator to your house using a combined cycle plant Then once you get above a heat output to electricity input of about 2 you overall use less energy. (In 50-60 degree weather a heatpump can get a ratio of up to 5)

 

[ERD50]

These systems solve a non-existent problem: natural gas is cheap & works at night & with snow on the roof. What's so hard?

I know the two are getting mixed together in this thread (and the original article I think - I didn't read it), but it's really two separate issues.

Their electric bills are high, looks like they weren't using the heat pumps properly, they may not have been spec'd right, or maybe not appropriate for this area.

Then the solar panel issue - regardless whether you have electric heat or gas heat, the grid is likely to be able to absorb the amount of power those panels produce. I doubt they have a super-large installation of panels, so at most they would offset a part of their bill, under the best of conditions. If they have snow on them, they won't be producing power.

But a moderate set of panels won't produce a lot of power in winter anyhow, they probably would not eliminate their electric bill, even if they had gas furnaces. Add in using electric heat pumps ineffectively so a big bill and little solar offset, and the news has a story that conflates the two.

Not if you live in the country or where for one reason or another natural gas is not available where you live. Then your choice really is heat pumps or the significantly more expensive propane.
If you look at efficiency, assume a 90% efficient gas furnace and a 57% efficient electrical environment (generator to your house using a combined cycle plant Then once you get above a heat output to electricity input of about 2 you overall use less energy. (In 50-60 degree weather a heatpump can get a ratio of up to 5)

True, but those 57% combined cycle plants are not that common, so the average grid eff% is much lower, closer to 30% IIRC. So you need more like a COP of 3 on the heat pump for roughly equivalent energy consumption.

-ERD50

 

[Zathras]

What angle are your panels at? The ones on the big installation here are at ~ 20 degrees to optimize the summer sun collection.

The power goes near zero for a week after it snows. There isn't much sloughing off at 20 degree angle.

-ERD50

20 degrees is a huge part of the issue. Is this in Il?
Ours are at 44 degrees. We loose a bit of efficiency in the summer. However we also use very little power in the summer, and a lot more in the winter.
Add that to snow falling off rather easily and it seemed an easy choice.

 

[meierlde]

20 degrees is a huge part of the issue. Is this in Il?
Ours are at 44 degrees. We loose a bit of efficiency in the summer. However we also use very little power in the summer, and a lot more in the winter.
Add that to snow falling off rather easily and it seemed an easy choice.

It depends on the latitude you are at for example at the equator the panels should be flat to the ground. if you subtract 23.5 from your latitude you see the angle for doing best on June 21, if a summer peaking system you likely want around 10 degrees more tilt because aug is hotter than june in general.

 

[Zathras]

It depends on the latitude you are at for example at the equator the panels should be flat to the ground. if you subtract 23.5 from your latitude you see the angle for doing best on June 21, if a summer peaking system you likely want around 10 degrees more tilt because aug is hotter than june in general.

Absolutely!
ERD's location shows as Northern Ill though. I'm guessing that is about 40 degrees?
So sure, their peak efficiency is sumetime between early June an Mid July.
That would make no sense, why would you want your peak then?
I'm hoping the location is somewhere other than his listed location.

 

[ERD50]

20 degrees is a huge part of the issue. Is this in Il?
Ours are at 44 degrees. We loose a bit of efficiency in the summer. However we also use very little power in the summer, and a lot more in the winter.
Add that to snow falling off rather easily and it seemed an easy choice.

-------------------------------------------------------------------

Absolutely!
ERD's location shows as Northern Ill though. I'm guessing that is about 40 degrees?
So sure, their peak efficiency is sumetime between early June an Mid July.
That would make no sense, why would you want your peak then?
I'm hoping the location is somewhere other than his listed location.

It is nearby in Northern IL, and it makes perfect sense, and any reputable source on solar power will show you the same thing (try it!). The goal is to maximize your annual output. With a fixed panel, you maximize for summer, because the solar days are longer.

This is offsetting power, and getting paid for what you produce. I'm not sure of the net metering details on this large facility, but based on some other numbers they've stated, I'm assuming it is the same rate whether it is a kWh saved, or a kWh produced/sold, their usage makes no difference.

This is 2 large schools. 448kW each.

https://www.solrenview.com/SolrenView/mainFr.php?siteId=3067
https://www.solrenview.com/SolrenView/mainFr.php?siteId=3068

You can get details at the 'site analytics' tab, but it doesn't sum the system, you can choose 2 inverters at a time. I have not looked in a while, but at a glance it looks like inverter #1 has been down all year, and maybe #18,19 longer at Butterfield? Dollars to donuts, if I email them, they will have no idea, but they'll assure me the system is doing a 'wonderful job'.

The last time I reported to them that one of the systems wasn't reporting for a month, they did not know, and I got that response.

The 20 degree # was from memory, but I think it's right or withing 5 degrees. There is a video on the school site, they sure look near flat.

-ERD50

 

[marko]

It might be me but looking at the photo the shadows indicate that the sun will only hit the panels at an angle; not full-on.

 

[Zathras]

ERD, it depends upon your goal as well as environment.
For annual maximum, you should maximize the effectiveness in the summer, although I think you would be better off with a double peak before and after peak sun, than a single peak at the sun's peak.

But when you take snowfall into account, you loose more than the efficiency loss due to angle unless you clear those panels.

Our goal is to take less energy from the grid. With this goal, it makes much more sense to have as much production in the winter, even if it means a 5-10% lower maximum in the summer.
Add to that the lack of needing to clear the panels as often, and it is an easy choice.

_-------------------

It looks like, at the weather and latitude of Libertyville, 33 degrees is more efficient on an annual basis.

This accounts for weather, however, I am not sure if the PVWatts calculator takes into account snow cover or not.
pvwatts.nrel.gov

 

[HFWR]

I don't have solar, but given my electric consumption in Oct-May is 300-600 kWh, and in Jun-Sep is 900-1200, I'd get more bang for the buck by maximizing for July or August.

 

[Zathras]

I don't have solar, but given my electric consumption in Oct-May is 300-600 kWh, and in Jun-Sep is 900-1200, I'd get more bang for the buck by maximizing for July or August.

Exactly, as you use more energy in summer, that makes perfect sense on either level.
In northern Il, and MN where I am, more energy is used in winter.
Maximizing efficiency for the system over a year makes sense financially.
Maximizing efficiency when you use the most energy (typically January) makes more sense if you want to use local energy.

The difference isn't all that huge until you get way out there.
But when you have snow as well as a less than optimal shallow angle, you are just shooting yourself in the foot.

 

[NW-Bound]

Even when maximizing for the whole year, one can maximize for the kWh, or for the $. My utility charges more for the kWh during the summer than in the winter.

So, for me I would maximize the kWh for the summer, which also means max $.