A top quality solar PV array for the least amount of money and the highest rate of return with a focus on the southeast of the USA with Georgia in particular. The savings and the return on investment (ROI) on the solar PV array could be further enhanced by converting all the natural gas appliances to electric and using heat pumps for cooling, heating and hot water. Replacing a traditional AC unit and a natural gas heater with a heat pump will further enhance the rate of return. Replacing all gas appliances like the water heater with a heat pump water heater (also called a hybrid water heater) will allow the homeowner to discontinue Gas service and avoid around $360 in recurring service charges each year. Local EMC (Electric Member Cooperative) utilities provide savings and rebates to help pay for the heat pump and the hybrid water heater ( rebates of up to $750 for a heat pump and $250 for a heat pump water heater are available from Georgia Power https://www.georgiapower.com/residential/save-money-and-energy/rebates-and-discounts.html and many EMCs https://www.jacksonemc.com/rebates ), other options exist such as adding a heat pump to an existing electric or gas water heater as shown here https://www.youtube.com/watch?v=u4hQVr5qYZo .
The proposed DIY solar array is a 5 Kw system with smart micro-inverters from Enphase and solar panels from Hanwha Q CELLS one of the best solar panel manufacturers, the balance of system components are provided as an estimate as they vary depending on the installation. The ROI (return on investment) of the system is more 20% and is further enhanced if the home or business owner can take advantage of the ITC tax credit.
DIY Solar PV Project Steps
The project proceed as follows:
- 1 — Design the system and obtain a permit from the county. This process varies from county to county. Most counties in Georgia do not have a process specific to solar PV projects, the only two exceptions are DeKalb (which leads the state in solar installations with three solarize campaigns so far) and the city of Atlanta. DeKalb process is nice and simple. The city of Atlanta’s process is slightly more complicated. With other countries the permit process for solar PV uses the permit process for a house addition, the requirements in this case will be a subset of what DeKalb would require so submitting the DeKalb forms will be more than enough. The DeKalb process is based on solar PV permitting best practices promoted by a national body. A permit might not be even necessary in some counties, the solar PV system is not more costly or complicated that a re-roofing project of the installation of a new HVAC system. This system costs less $5000 with ITC credits and requires 22 attachment points on the roof. An average HVAC system costs $3815. Many homeowners will face the need to change aging HVAC system installed prior to 2010 with the phase out of R-22 refrigerant.
An estimate of energy consumption is a good starting point for sizing the solar array. The homeowner should first consider electricity usage and later natural gas usage. A gas furnace and a gas water heater could be replaced by heat pump and a heat pump water heater. In this case the size of the recommended solar PV array might be increased to accommodate the additional electricity needs as this will result in more savings and a better ROI.
- 2 — Obtaining financing. Many banks in the state are now familiar with financing solar projects after the Solarize campaigns in Tybee (68 participants in 2015), Savannah, Athens (701 participants), DeKalb/Decatur (850), Dunwoody (282), and the city of Atlanta (1085), and soon Roswell. The rates of the Solarize campaigns is relatively high compared to what is achievable by the DIY approach described here. Solarize Atlanta achieved a rate of $2.55/watt vs $0.95/watt after ITC for the DIY option. The ROI achievable by the Solarize Atlanta project is around 12% vs 23% for the DIY option.
- 3 — Acquire and install the solar panels and micro-inverters. Installing the system is a relatively straightforward. The panels will generally be installed on the roof but could also be ground mounted. In the case of roof mounted system the companies that sell roof mounting hardware provide tools to help determine the mounting locations where the owner needs to attach the flash mount that will support the mounting structure. In this approach we favor micro inverters from Enphase for many reasons:
- With a micro inverter the installer has to deal only with AC (Alternating Current ) voltage, AC is easier to deal with that high voltage DC. The choice here is between micro-inverters and a string inverter like SolarEdge. In the case of a string inverter the output of the solar panels is combined on the roof and fed through a cable to a string inverter in the garage or on the side of the house. The electricity is fed as DC current with a voltage that could reach up a 600 volts (1000 or 15000 volts for commercial installations) depending on the number of panels in the string. In the case of micro inverters, each solar panel is attached to a micro-inverter, the output of the micro-inverter is a 240 volts AC current similar to what is already available in the house for many appliances like HVAC units, washer/dryers and many woodworking tools.
- The second reason to favor micro-inverters from Enphase is that Enphase micro inverters are building blocks for a micro-grid. The Enphase micro inverter can work as grid connected inverters and grid independent inverters at the same time (The Enphase IQ8 will have many additional features https://runonsun.com/~runons5/blogs/blog1.php/residential-solar/what-i-saw-at-enphase-mind-blown ). They can like many new inverters (e.g. SolarEdge) be connected to batteries. Enphase already sells a solar AC battery so one can use it to maximize self consumption, a heat pump or heat pump water heater could also be considered analogous to a battery in the summer we can cool the house with the excess solar energy instead of sending it to the grid, if the house is well insulated the house can remain cool even after the sun sets. The solar panels can be installed to maximize solar production during periods of highest consumption, in some cases the best orientation could be facing West so that maximum solar production occurs in the evening during summer months where the AC units need to be turned on. In the Georgia cooling accounts for the highest portion of electricity consumption. The same could be also accomplished for heating as has been done by many pioneers like Electrodacus ( https://electrodacus.com/ ) and the Ice Energy company ( https://www.ice-energy.com/ ). The average household in Georgia consumes 89.5 million BTUs, with energy expenditures of $2,067 per year and $1600 on electricity. 30% of the energy is used for space heating and 11% for air conditioning ( https://www.eia.gov/consumption/residential/reports/2009/state_briefs/pdf/GA.pdf ).
- Micro-inverters are required for areas with heavy shade which lekely to be the case for most houses in Georgia. Optimizers can also be used but the price of a system using a string inverter with optimizers on each panel generally exceeds a system with only micro-inverters and has more components.
System Components and ROI
Production estimate for the solar PV array
Is selling excess electricity to the Utility worthwhile?
Georgia Power buys excess production at less than 4.4 cents/KwH (avoided cost which can decrease in future years) and sells it at 15 cents /KwH, even if the published rate is lower. The higher cost is due to all the extra charges GP adds to the cost of electricity like Environmental compliance, Nuclear Construction, Municipal Franchise fee, sales tax.
Although Georgia Power has several buyback programs, right now the only one that is currently open is the RNR tariff Program. Under this program, a customer uses the solar-produced energy for the building use. At any given moment, if the solar production is greater than what the building needs, then the excess electricity flows back on Georgia Power lines. The customer will receive credits on their next bill for that excess power. If the homeowner chooses to participate in the RNR program, the monthly charge is an additional $7.32 per month and Georgia Power will pay avoided cost for the energy put back on the grid. Avoided cost for 2018 is 4.4¢ per kWh (according to Energy Save). This cost per kWh changes annually and has decreased over the past several years. This means the solar PV system would have to generate 166 kWh (2.82+4.50/4.4¢) every month in excess (over the amount the building consumes) in order to recover the costs from the metering charges.
The homeowner can choose not to enroll in the RNR Program and simply offset the home’s energy usage, and save that way. Self-generation and offsetting energy will avoid energy purchased from Georgia Power and will reduce electricity bills. The homeowner may use solar to offset onsite energy consumption without participating in any Georgia Power program, but still needs to notify Georgia Power of the installation to program the Smart Meter accordingly to prevent back feed and unsafe working conditions for Georgia Power employees.
In the proposed system produces 5.18 KwH / day, 155.4 KwH/month so it’s not worth it to sell electricity back to Georgia Power.
The additional charges imposed by Georgia Power make the option of installing batteries more appealing. The Enphase system can be set-up to not export any production to the grid so all the production can be used for self consumption. In this case the cooling system, the heating system and the AC battery could be used to store the excess energy produced during the day. The homeowner will avoid the $7 to $16/month charges imposed by the utility in addition to the delays, and the testing charges. LG Chem sells a 9.8 KwH battery for $7000, Tesla sells only 2 Powerwalls at a cost of $14500 for 36 KwH that’s more than is required and would not provide a positive ROI. Enphase provides batteries in 1 KwH increments at a cost of $1500. The batteries are eligible for the ITC. One Enphase battery produces return of investment of 13.58%, with two batteries the ROI is 9.40%. For users seeking larger systems an interesting option will be to install smart HVAC system that store energy as ICE, Ice Energy sells a AC system that can store the energy as ICE and then use later in the day to cool the house.
The case for installing a heat pump water heater
Homeowners who install a heat pump water heater can except a good ROI ( https://smud-heatpumph2o.org/calc.php ).
ROI for a Heat Pump and Heat Pump Water Heater
Electricity estimates are based on the information in the energy star guides ( https://www.energystar.gov/products/heating_cooling/heat_pumps_air_source ). The water heater used is A.O. Smith Signature Premier 50-Gallon Tall 10-year Limited 4500-Watt Double Element Electric Water Heater with Hybrid Heat Pump from Lowes ( https://www.lowes.com/pd/A-O-Smith-Signature-Premier-50-Gallon-Tall-10-year-Limited-4500-Watt-Double-Element-Electric-Water-Heater-with-Hybrid-Heat-Pump ), the water heater retails for $1,299.00. The heat pump is the Goodman 3 Ton 14 Seer Heat Pump System with Multi Position Air Handler ( https://www.amazon.com/dp/B00VH6RU3Q/ref=psdc_13397451_t1_B00WZ7M7I4 ).