Has anybody on this forum used Sense, solar photovoltaics, air source heat pumps, geothermal heat pumps, induction stoves, electric vehicles, battery storage, or other technologies to get their house down to net zero greenhouse gas emissions?
I just installed solar panels on my roof, but I have a lot of devices and appliances that still use fossil fuels and emit greenhouse gas:
Gas oven
Gas stove
Gas water heater
Gas furnace
Gasoline-electric hybrid automobile
Replacing everything would all at once would be very expensive, so I am trying to consider the most cost effective way to reduce my emissions.
How far have you gone in reducing your emissions? What is your experience with owning and operating zero emissions electric replacements for the devices listed above?
Depending upon how much you drive (how many EVs you have, or will) and where you live, the most effective carbon-reduction path (imho) is, in some kind of order:
Get solar [DONE!]
Gasoline-electric hybrid automobile ==> drive in electric-only mode possible?; migrate to EV if you drive a lot; donate/sell car to gas-only driver
Do I need more solar now?
Gas furnace ==> Heat pumps … or a pellet furnace + thermal storage system if you are in a very cold place with trees.
Do I need more solar now?
Gas water heater ==> integrated heat-pump and HW system OR consider a solar collector (not PV) water heater … potentially more efficient and gives you some redundancy if done in an integrated way. Then again, direct PV-to-DC-to-water heating is pretty appealing.
Do I need more solar now?
Gas oven/stove ==> induction
All along the way of course there is the carbon debt of the whole energy cycle for the gear replacement to consider. Not straightforward, especially when the world is moving toward this kind of thing.
One of my many energy peeves (hinted at it the prior post) is the lack of desuperheaters for mini-splits and, for that matter, simple retrofits for air-source heat pumps.
Has anybody successfully managed to take the waste heat from a mini-split (summer-mode cooling) and get it into their hot water supply? And for that matter, you could use it in winter for the added efficiency of a heat-pump vs. resistive heated water tank.
In my mind this could potentially be achieved with a custom lineset heat exchanger that wouldn’t require the addition of refrigerant to a pre-charged mini-split install.
If you’ve done the same with your fridge/freezer you get serious bonus points!
We have an all-electric home; rural farmhouse so the only other option would have been propane, which we didn’t want. Ground-source water-water-air heat pump (Hydron Module), all-LED lights, dryer is a line outside. Just expanded from 6kW to 13.7kW solar, and expect to be net-zero or better over a year. Still have a hybrid car, plus lawn mower and brush hog, but getting closer to carbon-neutral. Sense makes a good cheerleader!
If you’re looking to REALLY become net-zero, a simple 1:1 to/from the grid on cogeneration (solar, wind, hamster wheels) is overestimating your electricity offset. So much energy on the electric grid is wasted. Take a look at the analysis done by Lawrence Livermore National Labs on energy usage in the US. The most recent data is nationwide for 2018: https://flowcharts.llnl.gov/commodities/energy . You can see that, of the energy that goes into electricity generation, only about 1/3 of it is used, so to hit net-zero, you should consider any kWh you pull from the grid to be offset by 3 kWh sent to the grid.
This is one of the great (and sadly underappreciated) things about the new solar screen in the Sense app that shows the percentage of your home powered by solar. For many net metering plans (like mine in Iowa), customers are billed on amount drawn from the grid minus the amount sent to the grid, so it doesn’t matter if all of my consumption is during the day or during the night. From a sustainability (and, in my opinion, net-zero) standpoint, it does matter: if all (or substantially all) of my electricity use came from my panels, that is energy that I can guarantee is completely used (rather than only using 1/3 of it). The higher that “powered by solar” percentage is, the closer you are to net-zero (assuming all of your energy consumption flows through Sense, i.e. not natural gas).
Not so sure of your supposition. The Lawerence Livermore model seems to be looking at lost heat energy at generation time, as well as perhaps transmission/distribution losses. Transmission losses typically only range from 5% to 15%. And utilities are working hard, but a bit challenged to align new incoming renewables with demand, but they don’t convert energy they can’t use to heat - excess supply is sold off, sometimes at near-zero, or even negative rates. And places like CA with a fast-growing cogen supply are putting all the new supply and associated demand on TOU for that very reason.
Any zero carbon energy you buy through the grid or put out on the grid is a good thing, reducing that highly inefficient generation.
Added to the equation is that Utility-scale transmission losses over long distances (now often DC) have been dramatically reduced over time … significantly less than 5% … so the question of local vs. grid generation still holds.
One of the reasons to carefully calibrate your generation and usage is because (some) crazy thoughts can happen when energy seems “free” and no-doubt some get implemented …
I’m not saying that energy put back on the grid from a solar array isn’t a benefit, but it may not have quite the impact that everyone expects. Utilities don’t control how much I put into the grid (or, for that matter, how much I consume), so they still have to plan for my consumption spiking right as a heavy cloud passes over and covers my array. Over time, things may average lower, but I don’t think it’s fair to say that every kWh I put into the grid equals a kWh that doesn’t get generated by the utility in a coal or gas plant somewhere.
@qrnef,
I’m guessing that every kWh of energy you put back on the grid may have 5-10% losses as it get’s shipped someplace else, but not the 3x factor. And parts of the grid that are seeing upsurges in local renewable/low carbon are finding ways of valuing the energy you put back on the grid based on the immediate market and demand, which incents home producers to either do home demand shifting or battery storage. Sure, the grid operators have to have surplus capacity to handle weather related variations, but over the long run, solar and the renewables are statistically predictable, so the over-capacity doesn’t have to be 100% of the renewables.
I will concede the point about LLNL’s flowchart accounting for efficiencies in electrical generation, and that has a significant effect on the percentage of energy that is consumed vs. rejected. For natural gas plants, many sit in the 40-60% efficiency range, so that accounts for much of the wasted energy.
I feel like this speaks to my original point as well. If a kWh were equal in all forms (plus or minus transmission losses, which I hadn’t been considering at all), this wouldn’t be necessary. Taken to the extreme, if I didn’t use any electricity for 9 months out of the year, exporting everything to the grid, but from 5PM-8PM every day from July through September (in the northern hemisphere), I pulled 30-ish times my average production back from the grid, at the end of the year, my overall kWh production vs. consumption would be equal (ignore the fact that I would have blown my mains breakers or burnt my house down). Should that be considered net zero? I don’t think so. My production, in large part, likely offset power generated by higher-efficiency load following plants, but my consumption probably came from lower-efficiency peaking plants.
Currently, all the renewable energy we can put on the grid to offset carbon-produced energy is a win. In the near future, this will get more complicated. For now, a) if this topic is dear to you and b) you want to make the most of self-generated renewable energy and c) you have multiple EVs, then an EVSE capable of load shifting will make your day. Attached is a thing of beauty.
This load shift is primarily achieved by having one EV charging on extreme solar days. This doesn’t apply to everyone but more and more homes have three EVs with at least one parked at home for a better part of the solar day. You only need one EV to do this, it just needs to be plugged in during solar hours. The EVSE slows down when the dryer or stove is on as well as when clouds pass by. With more and more EVs using 60+ kWh batteries it is not critical to charge them everyday. If you really need the more miles one day and/or the sun hasn’t been out for a while then use your power the old fashioned way. Potable hot water and EVs are currently some of the easiest ways to store sunshine on your side of the meter. Some clever programming of your electric heat pump is yet another. One day soon @kevin1 will write a routine to boost the fridge, freezer, hot water, and HVAC around solar events.
Impressive @markhovis73 ! I have the EVs to do it, and with PG&E shifting the TOU schedule to mitigate the energy “duck curve” (Off Peak runs from midnight to 3PM !), I’m more willing to move to peak solar charging.
At the same time, I’m willing to exploit the grid as well, via Community Choice Aggregation, that allows be to buy (near) 100% renewable energy via the grid as well, for a little bit of a premium.
The only downside I have heard is that renewable-focused CCAs have put a premium on hydro for evening and nighttime. The flip side is that hydro is given more relief during the day via solar.
My local CCA just put this new “bad boy” into operation.
Well our local co-op is waaay behind. Community Choice Aggregation? Man, that is the future! Not only do we not have TOU, we don’t have ANY form of net metering. People who have net metering take it for granted. There are plenty of us who still want to do our part and change the world even if we don’t have the outside tools. I think that is the most difficult thing about global forums. We have no appreciation of just how different the energy sector operates.
At the same time, I’m willing to exploit the grid as well, via Community Choice Aggregation, that allows me to buy (near) 100% renewable energy via the grid as well, for a little bit of a premium.
For the record exploiting the grid is better. Community Choice Aggregation IS the future. HOWEVER, if you can’t force your utility to step up to the times, as an engineer you can outsmart them.
My EVSE is a MyEnergi Zappi. The interface is elegant in its simplicity. You press one button to toggle through three choices, Fast, Eco+, and Eco++. Fast is available in 7kW or 22kW (3 phase), Eco+ drops to minimum charge and lets your house have priority, and Eco++ which charges 100% on sunshine.
A Tesla Model 3 LR is my primary big battery EV for the moment. I have an order in for a Tesla Cybertruck. I know, it’s hideous, but as an engineer, I really only care about function. I really don’t like driving a truck but require one for certain activities. I am hoping that its standard 220v outlet capability and new battery chemistry will allow V2H usage for those of us who don’t have proper aggregation like @kevin1.
Our two zone HVAC system (gas furnances, AC units) were 20 years old as was our gas water heater. I knew we were on borrowed time for all of them. Also also calculated the carbon output of my gas therm usage and discovered my annual carbon output was the same a passenger vehicle for a year.
So when interest rates dropped last summer (they are just as low now) we did a fixed rate cash out refi at 3% for a complete HVAC retrofit to a ground loop geothermal system. One 4 ton WaterFurnace 7 Series and a 3 ton WaterFurnace 5 Series. The 7 Series also has the desuperheater that feeds a Rheem Marathon super insulated buffer tank that in turn feeds a Rheem hybrid heat pump. Also the “heavy up” to a 400amp service. Even though we will probably never need the capabilities of the heavy up (all component are super efficient), it has to be there to meet the max demands of the equipment to meet code.
We already had a 10kw Sunpower array installed 5 years ago and I wanted to use that solar power to make some heat. Back of the napkin math says we’ll be net zero for the year assuming that the geothermal is as efficient in the summer as I’m expecting.
I’ll say this, geothermal is SUPER EXPENSIVE if you only look at the raw price. But there is still a 26% fed rebate (was 30% last year, will drop to 22% next year) that pretty much offsets all the drilling costs. If you are really into efficiency, you compare the cost of the hardware to the most efficient air source heat pumps/AC system, and it’s a relatively small increase in cost while greatly exceeding the most efficient air source systems. For example, some of the most efficient AC systems have a EER of up to around 15 or 16 depending on run speed (if you see a SEER rating, it’s a different way to test and rate a system and it’s always higher). My 7 Series has an EER of up to 41. The 5 Series has an EER of 27.
So again, really expensive in total dollars. But because my systems were so old, I would have spent the money one way or another. These systems were destined to die soon, probably on the hottest day of the year or coldest night or when the water heater started to leak and I would have had to just pick a drop in replacement for one component at a time and probably not the most efficient. And then another. And then another. So, in my opinion, a big chunk of the cost of the geothermal was already “spent”, money out of my pocket to replace the old stuff. Then it came down to the difference in cost between an efficient air source system and the geothermal, and that cost isn’t that much, especially if you spread it over a 15 year low interest refi. If efficiency works out the way I’m expecting it to, the money we save by not using natural gas will cover the increased mortgage costs for going with a more efficient system. The gas saving doesn’t cover the entire cost by a long shot, but again, I’m only considering the upgrade costs because my hardware was old and needed to be replaced. I also have not paid an electricity bill in years, but I’m expecting that the additional energy saving in the summer will produce more than enough credits on my bill to offset increased electrical winter usage.
Does a geothermal system make sense for everyone? Maybe, maybe not. It depends on the age of your current HVAC and how you think about financing. If it’s old, it might make sense to do a “big bang” and replace all components in lockstep to work as a complete, efficient system and roll it into a long term, low interest loan. I will also say, natural gas is CHEAP. So if you are looking for big heating costs saving with geothermal versus natural gas you might not find it. It’s something you might be doing to decrease your carbon footprint, not so much your bill.
And how does Sense work into all of this, I do love looking at my Sense meter on a cold day when the sun is shining and seeing my geothermal use in the 2000-3000watt range while the solar is kicking out 8000 watts and I’m heating (or in the summer, cooling) the house with pure sunlight. I tend to kick the heat up during the day when the system is completely solar powered and let it drift down as the sun goes down. We put the geothermal system installed in December. It’s been the first time ever that my wife has said "OK, it’s hot in this house (75 degrees), can we turn the heat off? We are not a 75 degree family .
I have a similar geothermal ground loop setup. My standard programming has a pellet stove come on around 5:00 AM. It runs until 9:00 AM when the sun is producing enough to support the geothermal loop. It runs like that until 4:00 PM, then the pellet stove is programmed to come back on until around 11:00 PM.
How does Sense fit into all of this? I am currently controlling both of my heating devices by time and temperature. I currently use Sense to determine if I have enough solar energy when I am away from home to determine the best heating choice. My Nest thermostat will let me control them remotely. I am considering using IFTTT to control by solar events but a quick cloud cover makes it tricky. The rules just need to be refined and then it can be coded.
As to the carbon footprint, I buy my pellets from a furniture manufacturer, so currently I consider them somewhat carbon neutral, or at least less than natural gas and cheaper. They do take more attention than natural gas but there is that primal instinct to watch a fire burn too.
Running geothermal from solar energy is hard to beat. Believe it or not I installed my geothermal for under $7,000. I did the work myself including free use of a friends backhoe. If you have the ability to dig your own trenches that is the real expense.
I think this is my best way to net zero until my utility cleans up their power or untill I continue to shave hours via battery storage. Wait till I get my Tesla Cybertruck with 220v outlet and maybe I tweak the equation a bit.
Yes! Friends with a (cold, in shade) pool were about to get a heat pump pool heater. Instead, use free waste heat from central A/C to heat pool for free & no maintenance with this Heat Recovery Pool Heater | Compare To Solar Pool Heater | HotSpot Energy LLC
I’m looking at their DC/AC minisplits to replace our 30yr old nat gas boiler & shut off the gas meter. Using Residential Heat Recovery Water Heaters | Free Hot Water | HotSpot Energy LLC + preheat tank for free domestic hot water. If not hot enough, solar powered heat pump water heater adds heat (AO Smith from Lowe’s has been great).
ixu - look at the interface they use & maybe tap into the temp data
Commercial (ie grocery’s freezer, fridge, etc) almost always recapture waste heat for heating air, water elsewhere. Every penny counts for them!
I had to convince our solar installer to size the array for as much as you can fit on the roof & as efficient as we can afford. Not 80% of historical use but size for “electrify everything” scenario inside & outside:
41kW EV
16kW PHEV
E-bike. Add trailer to replace car trips or cargo e-bike.
mower
chainsaw, wood spliter
battery operated stuff
Can’t give up wood stove, propane BBQ.
We’re at 35% solar/use according to Sense for 2020 but I know that’s wrong. Once https://dcbel.ossiaco.com/ becomes available, we could use the 41kW EV for V2H & sell emergency gas generator.
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