There is much to like about Electric Vehicles (EVs). There is much to like about Solar Photovoltaic power collection (PV) too. But when you put the two together, something extra happens… You can now think of your solar system as being paid off, not by offsetting the cost of the electricity that runs your house, but by offsetting the cost of the gas you’re not buying.
Below, I am going to list the real-world drive data from our two company cars, a Nissan Leaf EV and a Prius Prime PHEV (Plug-in Hybrid Electric Vehicle). Sorry hybrids, you don’t get to play this game. Then I’ll list our real-world solar array data and calculate the value of the electricity we have harvested from our PV array. And answers some important questions; How much PV do I need to offset driving an EV or PHEV?
3.24 kW PV array:
Number of panels: 12
Power per panel: 344 watts
Annual production: 4,128 kWh
Cost after rebates: $5,796
The calculations will vary, of course, from place to place and car to car and driver to driver. These cars live in Carbondale, Colorado. The climate is pretty good for EVs; not too hot, not too cold. Typically highway driving punctuated by small towns. The road is never level, up valley, down valley, up the hill, down the hill. We run Blizzak winter tires for about five months, and Michelin Energy-savers the rest of the year. I’m no engineer; there is much rounding and estimating used in these calculations. For projections I will use these fuel values:
Street value of a kWh: $.11 (summer 2019)
Street value of a gallon of gas: $2.60 (summer 2019)
Total annual value of electricity produced by PV based on utility cost of kWh:
2013 Nissan Leaf EV, 24.0 kWh battery
Miles driven annually: 13,000
Miles/kWh: (average) 4.4 miles/kWh
Total kWh consumed: 3,022
Percentage of public charging: 10%
kWh provided by PV: 2,720
Leaf consumes: 66% of our production
Leaf consumes: 8.0 panels
Miles per panel: 1,463
2018 Prius Prime PHEV, 8.8 kWh battery
Miles driven annually: 19,000
Hybrid ratio: 50% EV : 50% ICE (Internal Combustion Engine)
Gallons of gas: 118
Cost of gas: $307
Miles/kWh: 5.4 miles/kWh
Total kWh consumed: 1,713
Percentage of public charging: 10%
kWh provided by PV: 1,542
Prius consumes: 37% of our production
Prius consumes: 4.5 panels
Miles per panel: 2,111
Total annual value of electricity produced by PV based on gasoline offset:
If 22,500 miles were driven in a gas drive vehicle (e.g. 2005 Subaru Outback, 32 MPG)
Gas offset EV portion of Prius: $772
Gas offset Leaf: $1,056
Total value of gas offset: $1,828 (703 gallons)
Every solar PV panel you put on your roof will push your EV 1,500-2,000 miles.
So, the bottom line is that our PV system makes us $520 worth of electricity annually, not bad. It would pay itself off in about 11 years at that rate. But when we put that electricity into an EV, it saves us from buying $1,828 worth of gas over our old ICE car, which translates to a 3.2 year payback!
Confluence is excited to announce that Prince Creek Home (outside of Carbondale Colorado) is framing. This home is a modern reinterpretation on an existing ranch home foundation. It will be net zero! To achieve net zero the home uses SIPS, good foundation insulation, heat pump heating system, proper window location and shading and PV.
Eagle County, Climate Zone 6, is currently (June 2019) on the 2015 IRC (International Residential Code) and the 2015 IECC (International Energy Conservation Code). The ECO-build checklist is gone. Link to Eagle County…
Eagle County has an exterior energy usage mitigation program. Exterior energy uses listed below shall offset 50% of energy use through onsite renewable energy resources or pay fee-in-lieu option accordingly:
- Snowmelt 34,425 BTU/sf $16.00 per sf (first 200 sf exempt)
- Spa/Hot Tub 430,000 BTU/sf $176.00 per sf (first 64 sf exempt)
- Exterior Pool 83,000 BTU/sf $136.00 per sf
A couple of extra mandatory provisions have been adopted; fenestration U-factor of 0.30 maximum value required, and the main heat source to be a minimum of 92% efficient AFUE.
Eagle County is enforcing separate infiltration tests for ADUs, infiltration limit of 3.0 ACH50 and duct testing when outside the envelope.
Confluence Architecture & Sustainability can provide third-party inspections, all the documentation, modeling, testing and certification required to demonstrate compliance with all provisions of this code.
Please contact us if we can help you comply with the energy code, wherever you project is located.
The Town of Basalt, Climate Zone 6, is currently (June 2019) on the 2015 IRC (International Residential Code) and the 2015 IECC (International Energy Conservation Code). Basalt is enforcing separate infiltration tests for ADUs, infiltration limit of 3.0 ACH50 and duct testing when outside the envelope.
REMP (Renewable Energy Mitigation Program)
Basalt has a REMP (Renewable Energy Mitigation Program) that engages anytime exterior uses of energy are used like; snowmelt, pools spas and garages. REMP fees are offset by renewable energy production, fee-in-lieu, or a combination of the two.
SBR (Sustainable Building Regulations)
Residential Type I (single-family)
Points are determined under one of four compliance paths; prescriptive, performance, Net Zero Energy Ready or LEED for Homes.
Commercial Type II (multi-family and commercial)
Most likely will require at least a COMcheck report for permit application submittal.
We do that…
Please give us a call and we can help navigate the process in the most cost-effective way. And optimize your construction for performance.
I review quite a few residential IECC (International Energy Conservation Code) submittals, and I would estimate that three-quarters of them are submitted as a straight-up prescriptive submittal. That’s when the table below is followed, without deviation. There is nothing wrong with this approach, but if a little flexibility is required, then leave the R-values behind and look at assemblies as U-factors, that can be morphed and traded around.
The U-factor alternative (2015 IECC R402.1.4) is a very powerful and useful method, but I don’t see it get used much.
I think it can be useful to use a chart like the one below to see building assembly alternatives by U-factor. PDF link… U-factor alternative assemblies
For instance; can I substitute OVE (Optimum Value Engineering) or Efficient Framing for CI (Continuous Insulation) in zones 6 & 7. The Prescriptive compliance alternative would have at least R5 CI installed on the exterior of the above grade walls. The U-factor alternative says; use any wall with a U-factor of .045 or better. So, at a glance, from the list, I see that I could substitute R3.6 CI (i.e. 1.5” ZIP insulated sheathing) for the R5 CI and bump up the cavity insulation number to R23 and build the wall with efficient framing techniques. Don’t like CI at all? Then substitute an efficient framed wall with the cavities foamed solid to R36. Don’t like CI or efficient framing? Then you could use a 6” SIP, ICF or straw bale. Check the total U-factor of your specific assembly, it could vary from the U-factors on the list by a couple of thousands. Here is a super-good online wall calculator for R-values and U-factors including checks for moisture control.
If you still don’t like the choices that the U-factor alternatives gives, then it is time to move up to the Total UA Alternative, AKA RESchecks (2015 IECC R402.1.5). Often, projects get bumped out of the prescriptive path alternative because the insulation can’t easily be provided in a particular location. Then the Total UA Alternative could be used, because it can trade-off different assemblies. For instance, slab edge insulation, often hard to do at a door threshold, patio or deck attachment or behind stone veneer. The uninsulated slab edge can be “traded” for surplus U-factors on completely different assemblies anywhere in the project.
If you still don’t like the choices that the Total UA Alternative gives, or still having trouble reaching the code threshold, then it is time to go fully custom with the Simulated Performance Alternative (2015 IECC R405) or the Energy Rating Index (ERI) Compliance Alternative (2015 IECC R406). Both alternatives can checked by the software at the same time, but the ERI Alternative is more powerful, because it take into consideration low infiltration rates, high efficacy lighting, appliances and renewable energy sources. The only certified ERI program currently is the HERS Rating.
Please contact us if we can help you comply with the energy code in the smartest possible way.
Carbondale is currently (June 2019) on the 2009 IRC (International Residential Code), the 2012 IgCC (International Green Construction Code) and the 2015 IECC (International Energy Conservation Code).
Carbondale has adopted the 2015 IECC and has a REBP (Residential Efficient Building Program). The chart below is the crux of understanding the energy code compliance.
The required points refer to the REBP checklist. Points are earned by including features in the house like; efficient framing, water conservation, chemical reduction, etc. Refer to the guidelines to understand how to fill out the checklist. Extra points are awarded for above code HERS (Home Energy Rating Score), infiltration rates and solar.
Currently (June 2019) the Town enforces the HERS maximum on the chart in lieu of the ERI (Energy Rating Index) path compliance limits as listed in the 2015 IECC. Which is quite a bit easier to obtain than the 2015 ERI limit for zone 6; which is 54 for any sized dwelling. But ERI 54 will never become the limit, because the Town adopted the ERI number from the 2018 IECC, ERI 61. Currently, the Town is not considering ADUs (Accessory Dwelling Units) as their own unit, that needs its own; REBP submittal, HERS rating and blower door infiltration test.
HERS ratings are not mandatory, but it would be unlikely to show 20% better than code with only a Total UA calculation (REScheck). Getting to a HERS of 60 or 70 is pretty easy, even without renewables. If a project is small enough to get through under the Prescriptive path or Total UA Alternative, the project will still need an infiltration test report showing 3 ACH50 (Air Changes per Hour at 50 Pascal) or better. And duct leakage testing if any ductwork leaves the thermal envelope.
Other random amendments;
- Carbondale has amended their Climate Zone to 6.
- Maximum infiltration rate changed to 5.0 ACH50.
- Alternate maximum infiltration rate adopted: .24 CFM50 per square feet of thermal envelope area.
- 1.2 CFM/watt minimum efficacy for HRV/ERVs (Heat Recovery Ventilators or Energy Recovery Ventilators) fan motors.
- ERI compliance level is modified to 61.
Confluence can perform these tests and produce these compliance reports. Please call us early in the process so we can help you optimize the insulation and comply with the energy code in the most cost-effective way.
Carbondale is on the 2009 IBC (International Building Code), but they have also adopted the 2012 IgCC (International Energy Conservation Code).
Navigating the IgCC is a deep subject, but expect it touch every phase of your project. The code requires above IECC insulation and infiltration mitigation, construction waste tracking and structured plumbing. The code requires third-party inspections and testing for the envelope. Confluence has been the code compliance and envelope consultant for six IgCC projects now. The Town of Snowmass Village has also adopted this code. Please calls us early in the process if you are planning a commercial project in The Town of Carbondale or The Town of Snowmass Village.
Take the blue pill, go build somewhere else, the story ends, you wake up in your bed and believe whatever you want to believe. Or, you take the red pill, you stay in Wonderland, and we dive down the rabbit-hole…
Pitkin County, Climate Zone 7, has added a residential energy conservation addendum for new construction and remodels, on top of the 2015 IECC requirements. Why? Basically, it is to bring construction in line with the Climate Action Plan. PitCo sponsored some fascinating research. One study says that about 70% of GHG (Green House Gas) emissions in Pitkin County are from the built environment. Another study predicts that more houses will be built in Pitkin County. Yet another study tracked the energy consumption of 900 houses for four years then, consumption was compared to house size. One might expect a 10,000 square foot house to have ten times the consumption of a 1,000 square foot house, but the study shows that the consumption of an average 10,000 square foot house was closer to thirty times the consumption of the 1,000 square foot house! How is this possible? It is because as the houses get bigger, they tend to get more luxurious. This means the house is more likely to be packed with energy-consuming amenities like; high percentages of glazing, large interior volumes, snowmelt, pools, hot tubs, saunas, conditioned wine cellars, conditioned garages, audio-visual-security systems, humidity control, air conditioning, multiple redundant appliances, steam showers, multiple redundant shower heads, heated toilet seats and towel bars and a plethora of other electric-powered gizmos.
The addendum has been come to be know as “The Matrix” because of the table format that outlays the requirements. There are two tiers of compliance; one for houses under 5,750 square feet and one for those over. The Matrix also makes a differentiation between houses that have more and less than 15% glazing. There are special requirements when working with existing construction, including; an energy assessment of the existing structure, air sealing improvements and occupant, crawlspace and attic ventilation compliant with current code.
What does this mean for the Architect?
- Significant mandatory requirements; 50%-75% engineered lumber, insulated headers, 24” stud spacing, insulated corners or alternate construction, glazing U-factor of .28, ENERGY STAR appliances, mechanical commissioning of complex systems, sealed ductwork, garage exhaust fans, rough-in for PV and thermal solar and EV charging outlets.
- Any house with more than 15% of its walls glazed will be required to use the 2015 IECC UA trade-off (REScheck) or ERI compliance (HERS Rating) alternatives; no prescriptive submittals.
- Any house larger than 5,750 square feet will be required to use the 2015 IECC ERI compliance alternative; no UA trade-off or prescriptive submittals.
- Get in the habit of retaining an Energy Rater; early in the process.
What does this mean for the builder?
- Learn to work with efficient framing, SIPS and/or continuous insulation.
- Get in the habit of working with an Energy Rater; through the whole process.
Confluence Architecture & Sustainability can provide all the documentation, modeling, testing and certification required to navigate the Matrix.
Aspen’s energy code amendments could not be more different from Pitkin County’s Matrix. Click here to read about those.
Spoiler Alert! The City of Aspen has customized their energy code. This blog is about the residential code, I’ll tackle the commercial modifications later.
See the amendments text adoption here…Ordinance 40-2016
What are the significant changes?
- The first change to the code drops the prescriptive allowable fenestration U-factor to .28.
- If submitting under the total UA trade-off compliance option, you will be required to go 2% beyond the passing line, in order to compensate for the fenestration glazing U-factor change.
- The option for exhaust-only occupant ventilation and air-cycler systems have been taken away, as balanced heat recovery systems are made mandatory. The HRV or ERV must have an efficiency of at least 65% and its fan powered by an EMC motor. All fans are required to meet a higher standard of efficacy; CFM/watt.
- Air sealing is still required, but infiltration (blower door) testing is not required.
- Mechanical sizing (ACCA Manual J calculations) is not required.
Here’s the interesting part, the City of Aspen, Climate Zone 7, has sought to simplify the code by deleting the IECC ERI compliance alternative and replacing it with their own version. It’s called the Simplified Equivalent Compliance Alternative. Dwellings must meet the following criteria to comply with this alternative.
- Equivalent space cooling energy. The ratio of the air conditioning capacity to conditioned space is less than or equal to 12,000 Btu/hour per 1,000 square feet.
- Equivalent space heating energy. The ratio of the space heating system capacity to floor area of conditioned space is less than or equal to 32,000 Btu/hour per 1,000 square feet.
- Equivalent hot water. The distance from the hot water supply outlet to hot water pipe to the hot water entry to a room where hot water is used shall be no more than 10 feet. This shall apply to the kitchens, bathrooms with showers or tub, and rooms with a clothes washer.
- Equivalent lighting. Lamps over 15 watts shall be CFL, LED, or have an efficacy not less than 90 lumens per watt. Or, at least 90% of the lamps or fixtures shall have an efficacy not less than 75 lumens per watt.
This code change deletes equipment sizing, infiltration testing and energy modeling; the very tenets of the energy rating paradigm. I like the simplicity, but I fear it is too simple. I guess time will tell how Aspen fairs under this code.
Confluence Architecture & Sustainability can provide third-party insulation and air barrier inspections, and certification of compliance with the other provisions of this code.
Pitkin County’s “Matrix” could not be more different from Aspen’s energy code amendments. See link below…
Confluence already uses an electric car for site visits in the valley; 2013 Nissan Leaf.
But it won’t make it to our HERS Rating inspections and blower door tests in Telluride, Mountain Village, Steamboat, Vail Valley and Summit County.
So we have added a PHEV (Plug-in Hybrid Electric Vehicle) to the “fleet”.
A 2018 Toyota Prius Prime…
- Hybrid Synergy Drive with Electronically controlled Continuously Variable Transmission
- 55 city/53 highway MPG
- 133 MPGe
- 640-mile EPA-estimated total driving range
- 25-mile EPA-estimated EV Mode driving range