I am going solar

Savvy decision

 

^^ Yeahh,
A heat pump run on PV is great.
If home insulation is decent, it likely makes sense to run the pump during the day when the sun is shining and the ambient air temp is highest. The idea would be to heat up the house a little more than desired, and let it bleed off during the night.

 

Speaking of insulation...
Any of you gents who've had a roof mostly covered with panels for at least one summer seen reductions in attic temps due to the blocking nature of the panels?

 

Hello, hello... I'm one of those....
To tell you the truth, my attic space it is NOT a living space so I can't gauge any drastic change in temperature.; during summer time it is hot inside of it. I have no rafters insulation and this can be part of the equation.
Theoretically, the PV panels will filter the Sun's heat radiation to the actual roof.

 

A remote thermometer in my attic has shown a sharp temperature reduction, more than 20F. However, the PV installation was (almost) simultaneous with re-roofing, which included adding a ridge vent to an attic that previously had ventilation below modern codes. Thus, I cannot separate the impact of the two projects.

 

^ thanks guys...
One day last summer it hit 115f in my attic (and that's with the exhaust fan on). I'm hoping that a nice spread of PV panels will help lowering those sweltering attic temps.

 

Huh? 115F in the attic is sweltering?

My attic used to hit mid-150s during the hottest Seattle-area summer days. Now it tops out around 130F. Dark roof, no exhaust fan.

It does cool off very rapidly once the afternoon tree shadows (neighbor's trees, not mine) sweep across.

Late last fall I upgraded the attic insulation from nominally R30 to R60, along with fixing several known deficiencies and packed down areas from prior work up there. While the bulk of that upgrade shouldn't be noticeable (in summer) down here, I did find and fix nearly 100 square feet of ceiling at R0, down low by the eaves beyond view of normal inspection. Those areas should make a difference this summer.

Winter heating load is at a record low, but because of this warmest winter since installing a heat pump and sealing many air leaks, I don't really know the how much to attribute to the new attic insulation.

 

The house's energy is all-electric, and billed every other month, but I do have a sub-meter on the heat pump and track usage fairly close.

Month --- HeatPump kWh
Nov ------ 181 kWh
Dec ------ 213
Jan ------ 216
Feb24 --- 126

The price is two-tiered, approximately $0.06/kwh first tier and $0.12/kWh second tier. For the December-January bill, the heat pump straddled the tier boundary. Oct-Nov was all first tier, as is February so far. That puts the primary heat bill at $11 (Nov), $19 (Dec), $19 (Jan), and $7.56 (Feb 1-24). Remember, this coast is having a warm winter.

There is some supplemental heat from direct electric resistance, in the main bathroom daily, and in some other rooms during the brief but serious cold snaps of November and December. But those are not yet separately monitored. Someday I hope to do so.

Heat cost far more back before solar, before heat pumps, before attic and floor insulation upgrades, and before air leak sealing.

BTW, the heating costs above are 'virtual'. Due to solar net metering and solar production incentives, including additional credits from my contribution to a Community Solar Project, my house currently has no actual energy bill. Nada. The last bi-monthly energy bill was $0.60 back in June, before summer overproduction and credits caught up. And I shouldn't have any energy bill until the incentives expire in 2020, or the Legislature slashes them to cover its budget emergencies, or local solar installations overrun the incentive cap, whichever comes first.

AC cost of this house is nil, not counting one ceiling fan and one night-time window fan. I didn't even have AC until the heat pump was installed six years ago, and used in only five days that first year during a heat wave that broke Seattle's all-time high. It has been used only a few days since, not every summer. The eaves are nearly ideally configured to keep summer heat from striking the windows, while letting plenty of winter sun enter.

 

My bet is...... geothermal but I may be wrong.

 

Air-source Fujitsu mini-split, single zone in the main kitchen / dining / rec area. Plenty of heat spills through two doors into the living room. With inside doors left open all the time, sufficient heat flows down the hall to the bedrooms to displace most of their electric heat in normal winters, and almost all of it this warmer winter. (The newly boosted attic insulation probably helps here too.) The master bedroom is running about 5-6F cooler than the main room, we sleep better that way.

This heat pump is rated HSPF = 10, SEER = 20. The latest version of the same capacity appears to be rated HSPF = 13, SEER = 25, while the lower capacity versions have slightly better numbers.

 

talk about confidence, back in 2008 we went with a company called revco, and they've been around since 1976. Can you imagine how inefficient panels were that far back?

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Inferno, I think I understand whats going on. If you only have one meter reporting two different numbers it is likely showing you the following:

1) Net Import: Whenever you are using more electricity than you are generating, this number will go up. It will never go down.
2) Net Export: Whenever you are generating more electricity than you are using, this number will go up. It will never go down.

Essentially its just separately counting kWhs when the meter is "spinning forward" vs. when its "spinning backward". The difference between the two is your Net Usage, which seems to be how your utility is calculating it.
Net Import - Net Export = (usage during excess usage - generation during excess usage) - (generation during excess generation - usage during excess generation) = (usage during excess usage + usage during excess generation) - (generation during excess usage + generation during excess generation) = total usage - total generation = Net Usage

Unfortunately there is no way to calculate total usage or total generation from this one meter's data, so there is really no way to gauge the accuracy of your inverter's reported total generation or compare it to what the utility is crediting you for. To do that you would need a second utility grade production only meter, but its a pretty safe bet your inverter is accurate to within a few percent. There is no fixed relation between net export and total generation, its totally a function of your specific usage and generation throughout the day. The ratio can be anything between 0% (no excess generation) and 100% (no usage) and still be accurate and normal.

As a sanity check you could try comparing your "post-solar" total monthly usage (calculated as utility reported net usage + inverter reported generation) to your "pre-solar" montly usage (as reported by utility) for the same calendar month over the years to see if it all makes some kind of sense, but there can be a fair amount of variation year to year so it will be a little tricky to say. The more years you can average pre and post solar months over the better it might agree, assuming you haven't made any big usage changes.

Rob

 

In general yes, but I wonder about 8 months.

 

.... I'm thinking you mean 2500kWh's?

and "10kWh system" .... vs 10kW's .... the latter referring to a peak rating (mid day summer) while X kWh's relates to hours/time frame.


.

 

What I don't get is I have a 5.3 Kw system. On a slightly cloudy day I've seen my energy production spike to 6 k? I wonder if the clouds are directing all the energy to my panels? It's not sustained but I do see 5.3+ frequently :O