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Re: Solar wholesale recommendations

Posted: Wed Mar 31, 2021 1:27 pm
by danrjones
ripple4 wrote:
Wed Mar 31, 2021 8:49 am
danrjones wrote:
Wed Mar 31, 2021 7:13 am

Right now my heating is being done by an old NG furnace. It is going to need to be replaced soon, but I haven't quite made up my mind on whether I do a newer more efficient furnace or a go ahead and get a Heat pump. Right now all my AC is done by a evaporative cooler. My evap cooler has a low and high setting, and on high its pulls 1 HP plus a water pump, so ~ 750 watts plus the pump, lets say 50 watts. So 800 watts. From June through end of Aug that mostly runs on high non stop, so about 19.2 kWh per day. Obviously if I got a heat pump I could also run that as an AC, and my wife would love that, and turn off the swampy. I would need a 5 ton unit for Heat pump/AC. I tried to do some estimating before I put in my solar so that I could cover that if needed. I believe a 5 ton AC uses about 6 to 6.5 kW sustained, but obviously it wouldn't run the entire day like my swamp cooler.
In the planning phase it might helpful to not look at the real power, which is the nameplate values on motors etc, but instead the apparent power of your appliances. as you may know, apparent power is 'real' power plus 'reactive' power, or real power divided by the power factor. with grid-tie you may have been living in a real power dreamland, where motors start easily without dimming the lights, and all motors are created equal perhaps (PSC, ECM, induction) etc. also those large condenser units you are looking at with PSC motors will have a starting current that is going to be impossible to meet with an inverter. my 3-ton condenser unit compressor has an LRA of 155amps, you'll need an ECM (inverter drive) compressor for off grid. In an off-grid situation the inverters supplies apparent power, so when summing all your loads you need to divide the nameplate value by the power factor, or better yet measure it with an amp clamp meter. Recently, I just power factor corrected some of my often used appliances so that my inverter had to work less hard, my gas dryer motor had a power factor of .45, so it was drawing '670va' of current while doing 300w of work. with a 75uf run capacitor I got it to .90PF which dropped the AC current draw by 3 amps. here is the website i use to calculate what capacitor to use. ... lator.html

One item i'm keeping my eye on is this product. if it works out like they advertise it will be a big deal, since it will create reactive power and make everything better.
I'm not an EE, but I am at least familiar with power factor. Normally I wouldn't concern myself with it unless I was looking at big three phase motors, i wouldn't have thought about things like my Dishwasher or Dryer. I was aware the startup amps on a compressor are high, but honestly I was going to worry about that later. Seems like something a capacitor kit for your outside unit can solve.

I would imagine, though could be totally wrong, that my 1 HP Swampy motor is the biggest sinner at the moment. Its 240v but single phase.

Still have no idea what direction I will go anyway. I really don't want a heat 15 kW heat strip. A new furnace with a heat pump could work but it adds cost for a furnace I might never use, given today's efficient heat pumps. The heating issue (replacing the old furnace) is really my driving factor, as my swamp cooler itself works just fine, other than increasing water prices and comfort issues.

Re: Solar wholesale recommendations

Posted: Thu Apr 01, 2021 6:24 am
by ripple4
That's right, factories have to pay for reactive power, so they try to add PFC to keep their bill down. residential users get reactive power for *almost* free, however off grid, I need to make it myself. adding capacitors inside of each appliance (switched with the load) is OK, but they don't have the fault current abilities of old-fashioned rotating mass, which is why that evergrid, or something like it is going to be awesome.

For the heating conundrum, I can offer what i have looked at. I've also got a older 80%AFUE NG furnace and it might translate to your situation. So the analysis i did was look at how many BTUs I get per dollar and compare the furnace to the Daizuki 1-ton inverter mini-split that i'm looking to buy at on amazon for $650. I also calculated your resistance heater for reference. Now where I live we have 'hell week' in the middle of February, where depending on the polar vortex its either cold, or deadly cold, so I plan on 0F or -20F for that week. And so a heat pump, even a defrosting one, will not work for that time period for me. but it will work the other 4.5 months i'm adding some heat. here is the cost breakdown.

1) Resistance heat at $.142/kWh will give 24,500btu/$. (at $.62/kWh its only 5503btu/$)
2) Natural gas at my contracted rate of $.303/CCF (and 80% eff) is 250,000 BTUs/$. (6x more heat/$ than resistance)
3) The (19seer/9.5 HPSR) heat pump heat at my contracted electric utility cost of $.142/kWh I get 73,500 BTU/$ (3x better than resistance heat but 2x the price of natural gas.)
4) but the best is for last, the same heat pump heat at my marginal cost of solar of $.02/kWh (lifetime) I get 550,000 BTU/$!

So adding solar panels in the way I previously described, optimizing winter collection and balancing morning evening collection can heat for less than half the price of natural gas. The inverter heat pump runs continuously as well, so even if its only 12kbtu running flat out will add about the same amount of heat per hour as a 80kbtu furnace cycling on 7 minutes twice per hour, which is typical for outdoor temps in the 20-30F range for me. even if you had to use gas or resistance heat to get through a few days of a cold snap, your going to be saving so much more in the mild weather heating that it may not even be important.

Re: Solar wholesale recommendations

Posted: Tue Apr 06, 2021 4:11 pm
by danrjones
Some good info up there.

I found a website to run a manual J or load calc for my house, so I'm playing with that right now. I'm also going to look to see how much natural gas and hence heating I did last winter, to figure out ~ how many BTUs I would REALLY need. Looking at the load calcs my biggest issue is my old windows.

1) So my morning power until 8am is 0.15 per kWh. After that my solar kicks in, though not sure if it could cover the full load of a 5 ton unit. I have some numbers I found for a unit I'm eying ,showing the BTU output at specific outside temps, and the kWh consumption. I'll put that data below. So my cost per kWh would be much lower unless I'm running from 2 pm to 8pm and have run out of power to trade via "net" metering. Assuming I'm still using net metering.

2) Your gas seems really cheap? I had to look up my gas cost. PGE is "Tiered" meaning the more you use the more you pay. For January I paid 155.93 for 87 therms. Technically they charge $1.59 per therm for tier 1 and $2.03 per therm for tier 2 (price seems to fluctuate though by month), so I'm rolling everything on my bill into the final number. $1.792 per therm I used, or ~ 55800 BTU per $ delivered to my furnace, or 44,640 BTU / $ heating my house if my old furnace is 80%. I do use some for my water heater and our gas stove and our drier, but those amount to $15-$20 a month or so during the summer.

3) Here are the numbers for the unit I was looking at:

Outdoor Temp / BTU Produced / kW Used (Heating Mode)
5f 44000 7.160
17f 49000 7.100
32f 54000 6.600

We rarely get much below 20, and it quickly warms up once the sun is up. We can easily be 25f and 60f in the same day.

Outdoor Temp / BTU Removed / kW Used (Cooling Mode)
95f 55000 5.410
105f 54000 6.650
115f 46000 5.700

Conversely, during the summer we are above 100f during the day for long stretches and occasionally hit 114f or higher. But its a dry heat.

Now I just need to map out my solar production to see how much at what time I'm getting for offset. I have net metering, so its by period right now. 10pm to 8am Rate1, 8am to 2pm and 8pm to 10pm Rate2, and 2pm to 8pm Rate 3. It is "net" for those periods. I have a good daily and monthly estimate of what my new system produces, but need to see how that all lines up in the time periods.

Re: Solar wholesale recommendations

Posted: Wed Apr 07, 2021 8:54 am
by goldbrick
danrjones wrote:
Tue Apr 06, 2021 4:11 pm
I found a website to run a manual J or load calc for my house
Could you share a link? Thanks.

Re: Solar wholesale recommendations

Posted: Wed Apr 07, 2021 2:10 pm
by danrjones
Sure can.

Start here, put it in the closest city to you (you can adjust the temps later anyway).
Then fill out your structure types. I only used side 1. I am not sure what the second column (right side) is for, maybe a second floor? N/A for me. After you choose your structure, insultation, window type, and walls, the next page has you put in your square feet and linear feet for each wall, door, window, etc. Calculate Load. Then you can click "Size Equipment" where you put in your prospective HVAC numbers and it tells you if it is sufficient. Other tabs there as well.

Re: Solar wholesale recommendations

Posted: Wed Apr 14, 2021 1:18 pm
by danrjones
I'm going to split off the HVAC discussion to a new thread.