General cost of various solar systems

Welcome to the forum Jeff,

There are no really good "generic answers" to your question. Energy usage by a home is a set of highly personal choices and local weather conditions, etc. And for solar the costs (local cost of panel, wiring, labor, etc.) and the amount of energy that the array can generate--Depends on local weather, seasons, type of system, and any local shading (from standpipes, power lines, nearby buildings/land spacing, etc.).

It has been a few years (and lots of inflation/supply chain disruptions)--A "good price" for installing Grid Tied solar system on a home was (very roughly) around $5 per Watt (i.e, 3,000 Watt system, ~$15,000).

I will give you some rough numbers and calculations to show you the basics.

First, how much energy does a home use? The national average is around 500 to 1,000 kWH per month. A very efficient home (natural gas for heating, hot water, cooking) can be 300 or less kWH per month. An all electric home in Texas with full A/C could be 3,000 kWH per month.. My recent bills are around $0.20 to $0.40 per kWH (PG&E, off peak to summer peak evening usage).

There are two basic types of solar power systems. There is the "Grid Tie" or Utility Interactive which is a solar array => GT Inverter => main power panel. There are two major types of GT inverters--The Central Inverter (one or several multi-KWatt inverters, or Micro Inverters (each inverter around 200 Watts or one per panel, all wired to 240 AC lines on the roof). There are advantages and disadvantages to both. The power from the solar array is sent to the main breaker panel and either shares the AC loads and slows the Utility Meter down, or in the middle of the day, will actually turn the meter backwards (for all the world, a GT inverter is like a car generator powering the radio, lights, ignition and the utility looks like a "giant AC battery bank").

The second major type are Off Grid / Hybrid systems. More or less, the basic setup is Solar array => Solar charge controller => battery bank => hybrid inverter (off grid and GT capable if connected to Utility Power). The system acts like a GT inverter and UPS (uninterruptible Power Supply). Solar Panels + Utility Power act like GT Solar sharing the loads and can turn the utility meter "backwards". And if the utility fails, the hybrid inverter will supply local battery power to the home's AC wiring (a few important circuits, or the whole home, depending on what the customer wants/needs). The battery may supply a few hours of power up to 2-3 days for larger systems.

To size a system's capability, here is some quick math. First, need to figure out energy usage and system type. GT Solar (inexpensive, no or little "backup" AC power if power failure) and Hybrid/Off Grid system.

For a full off grid system, conservation is critical to keep system costs down (batteries are expensive and may last around 5-10 years). For OG system, around 3.3 kWH (3,300) Watt*Hours per day (or 100 kWH per month) is about the minimum size for a near normal power existence (LED lighting, solar friendly well pump, clothes washer, LED TV, Laptop computer, cell phone charging). As a first guess, around $2.00 per kWH all in costs, including battery and equipment maintenance and replacement for 20 year system life);

For a GT system, no (or little) backup power, but cheap(er) costs... GT Inverters around 10+ year life, solar panels around 20+ year life. Can get down towards $0.05 to $0.10 per kWH cost. Note that utility rate plans can dramatically affect payback. For example, my Time of Use plan 10 years ago used to have peak costs around noon-6pm--When the sun was shining. Now something like 5pm - 9pm (no sun at night) for peak costs.

Some quick calculations for a GT System. Say Stockton California, array facing south, on 52 degree from vertical tilt (or 38 degree from horizontal). Using a simple solar harvest calculator:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Stockton
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 52° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.48	4.32	5.68	6.29	6.61	6.87
Jul	Aug	Sep	Oct	Nov	Dec
6.92	6.92	6.60	5.80	4.18	3.36

Lets pick February for a typical month (break even) for a 500 kWH per month customer.

• 500 kWH per month / 30 day per month = 16.7 kWH per day
• 16.7 kWH per day = 16,700 WH per day
• 16,700 WH per day * 1/0.77 off grid system deratings * 1/4.32 hours of sun per day (Feb) = 5,020 Watt array (Feb "break even")
• 5,020 Watt array * $5 per Watt system cost = $25,100 estimated GT system cost 

Or looking at California's $9,500 required solar expenditure for new homes (I live here, and was not even aware of this new requirement for 2022):

• $9,500 California Mandate / $5 per Watt = 1,900 Watt array
• 1,900 Watt array * 0.77 GT system deratings * 4.32 Hours of sun per day (Feb) = 6,320 WH per day = 6.32 kWH per day
• 6.32 kWH per day ( 30 days per month) = 189.6 kWH per month

Of course, solar being variable--Will generate more energy in summer and less in winter. The original California solar requirements were to "break even" on power used vs power generated during a 1 year period. Today, that math is a bit more complex with Time of Use and now being paid (somewhat) for excess power generation and some other issues.

If you want to see more details, this website has a solar calculator that will give you that information:

https://pvwatts.nrel.gov/pvwatts.php

Some other random issues:

• New building codes (NEC, etc.) have roof setbacks for firefighters to allow areas free of panels to work fires/disconnect/etc.
• New Codes have solar array shutdown requirements (central inverters more roof top hardware vs micro inverters which usually don't require extra shutdown hardware)
• Shading "kills" Solar Electric output. Shade from a vent pipe, shadows from utilty power lines, etc. can pretty easily kill upwards of an array's output when shading is present (weakness of central inverter systems. Micro inverters limit "loss of power" to actual panel(s) being shaded).
• Roof Leaks. Need good practices for flashing of array mounts. Solar panels on roof can decrease heat inside the home (shading). Solar panels can reflect light into neighbors' homes.
• Lightning. If you have lightning strikes in area--Roof Top solar needs good grounding, surge suppressors, etc. to protect Solar System, home and appliances.
• Electronics (and panels) can fail. Central inverters are "easier" to service/replace from ground. Micro Inverters need to access the array on roof to replace failed units.
• If there is land available, ground mounted arrays are cheaper to install/maintain and "safer" than roof top arrays.
• Everything has a life. Inverters something like 10+ Year life. Solar panels 20+ year.
• Install Central Inverters in a shaded/cool location with good air circulation for best service life, not on south facing wall with full sun. An engineering model is for every 10C/18F increase in temperature, the electronics will last 1/2 as long (i.e, if 77F is "standard temperature", running at 95F electronics will last 1/2 as long.
• Electronics continue to evolve. Around 5 year product life cycle. And 10 Year warranty required by California on solar system hardware. In 5 years, may have difficulties finding replacement parts/solar panels that match OEM parts.

Anyway--A quick run-through for solar power. If I was a contractor--I would seriously look at sub-contracting work to a solar installer. You may be able to save some labor costs by doing basic framing, rough wiring, and roof+flashing yourself--But look at the exposure to you of the solar system itself. A lot of solar companies have disappeared over the years. Not always profitable, and long term liability exposure too. Some examples:

https://forum.solar-electric.com/discussion/3375/panel-fire-question/p1 (gray market solar panels)
https://www.theverge.com/2019/11/5/20949661/walmart-tesla-lawsuit-settlement-solar-panel-fires-solarcity
https://www.app.com/story/news/local/emergencies/2021/03/27/solar-panels-holmdel-hobby-lobby-roof-fire-second-time/7028908002/

Note that DC power is "different" vs AC power/current. DC power makes for a great arc welder (vs AC). Any loose DC power connections, corrosion, animals chewing on exposed insulation, etc... Example:

 https://www.youtube.com/watch?v=Zez2r1RPpWY

Not trying to stop you from getting into the details of solar power for your business... Just be aware that this is not just rough electrical and installing lights/appliances.

-Bill

The contractor that put a roof on my home a decade or so ago... He was thinking of getting into the solar business--Because a fair of his business was fixing leaks from all of the solar contractors calling him.

For him, the electrical part looked pretty simple to him once he flashed and racked the panels...

-Bill