After witnessing power grid failures in Texas and California, and because I live in a rural area and on a well, I wanted to design a system to run our basics should we suffer a similar fate. We define the basics (critical loads) as the well, ceiling fans, and refrigerators. In my quest to figure out an optimized system, the plan quickly morphed into asking myself the question, how small of a system could I build that would run my entire house? (or at least the majority of my house)
This is what I came up with ...
Pre-solar I wasn't really paying much attention to our electric consumption nor was I really paying attention to our electric bill that much other than complaining about it to whoever would listen. Since budget was a constraint with regards to building a solar system, I decided to do a deep dive into how we could become as electrically efficient as possible. In a moment I will describe our efficiency plan, but first a little background ...
My family (pre-sloar) consumed between 48kw and 100kw per day based on the season. We live in Central AZ so summer months require heavy amounts of AC, hence the 100kw/day.
The house is 2900-ish sqft and everything is electric including two 3-ton HVAC, 35,000 gallon pool, a hot tub, washer/dryer, range/oven, well pump, booster pump. In addition we have a chest freezer, two upright fridge/freezer units, and a wine cooler fridge. One saving grace is that the two hot water heaters are propane tankless on-demand units. All of the lights in the house are LED, which helps, but the rooms are big and there are several lights on one switch ... for example the great room has nine LED's needed to illuminate it.
My thinking was that for the 3/4's of the year where our consumption is the lowest, theoretically the above set up should get us by and be cost efficient.
This is what my math looked like...
So, here is what we did (results in a moment)
The plan from here is to add about another 10K worth of panels and another 35Kw worth of batteries, but we are waiting for the prices to come down on them even more! Truthfully, at this point, any upgrades would just be a game that we would be playing on how to eliminate the last 20% of our grid usage. I call it a game as it will cost at least as much as we have invested in our entire system that currently provides as much as 80% of our needs. It really wouldn't be cost efficient. The good news is that our system can easily handle the critical loads we set out to cover! So, if prices on panels and batteries drop, then we will likely work to go fully off-grid. If they don't drop, we will just be happy with our lowered utility prices and keep adjusting our consumption paterns to maximize our system!
This is what I came up with ...
- 6000 watts of PV
- 15kw Solark Inverter
- 25,600 watts of EG4 Batteries
Pre-solar I wasn't really paying much attention to our electric consumption nor was I really paying attention to our electric bill that much other than complaining about it to whoever would listen. Since budget was a constraint with regards to building a solar system, I decided to do a deep dive into how we could become as electrically efficient as possible. In a moment I will describe our efficiency plan, but first a little background ...
My family (pre-sloar) consumed between 48kw and 100kw per day based on the season. We live in Central AZ so summer months require heavy amounts of AC, hence the 100kw/day.
The house is 2900-ish sqft and everything is electric including two 3-ton HVAC, 35,000 gallon pool, a hot tub, washer/dryer, range/oven, well pump, booster pump. In addition we have a chest freezer, two upright fridge/freezer units, and a wine cooler fridge. One saving grace is that the two hot water heaters are propane tankless on-demand units. All of the lights in the house are LED, which helps, but the rooms are big and there are several lights on one switch ... for example the great room has nine LED's needed to illuminate it.
- In the Fall, Winter, and Spring we have about 6 hours of peak sunlight per day.
- In the summer we have around 7.5 peak sunlight hours
- In central AZ, the weather is mild for about 7 to 8 months of the year. It is only June, July, August, September, and sometimes October that are hot.
My thinking was that for the 3/4's of the year where our consumption is the lowest, theoretically the above set up should get us by and be cost efficient.
This is what my math looked like...
- 48kw per day divided by 24 hours = 2kw/h
- 2kw/h x 6 peak sunlight hours = 12 kwh of consumption
- 6kw PV array times 6 hours of peak sunlight hours = 36kw worth of production
- 25,600 watt battery bank set to min SOC of 20% = 20,480 usable battery capacity.
- So 36kw worth of production minus 12kw worth of consumption = 24kw worth of "excess" capacity to recharge the batteries
So, here is what we did (results in a moment)
- Hot tub went on a timer. I set the temp to 106 degrees (two degrees above it's normal maximum but there is a bypass method to set it that hot). It already had a super thick insulated lid. The hot tub only kicks on during sunlight hours and what I noticed is that it runs for maybe 10 minutes two or three times per day. We use it regularly and even if we hop in at 10pm, it is still nice and hot!
- Swimming pool has a variable speed pump. I set it at the lowest speed that would still circulate the entire 35,000 gallons and run the cleaner during the hours of 10am to 3pm. It pulls about 1600 watts when running.
- While the AC's units don't have WiFi thermostats, they do have programmable ones. The house has a bedroom side HVAC and a living area HVAC unit. I set the time and temp on the two thermostats to come on at opposite times. They rarely ever come on at the same time, and the bedrooms don't run during the day and the living area doesn't run at night. Both HVAC's have a MicroAir easy start and they pull about 2500 watts when running (more or less).
- The beds all have extra thick blankets and the heater setting in the bedrooms at 9pm drops to 59 degrees and rarely comes on until the setting changes to 66 degrees at 5:30am (30 minutes before we get up)
- I installed a 500 gallon water tank, and so generally speaking only the well pump or the booster pump runs at a time, although on occasion they do run at the same time, which is a pretty big draw, but they don't tend to run for more than 30 minutes at a time.
- I purchased a low cost induction hot plate, a toaster over, and hot water kettle. These all have significantly smaller power needs than firing up the stove or the oven. Seventy percent of the time we were only turning on the stove to cook an egg or make a pot of hot water for coffee or tea, so using these small efficient counter top devices save a ton of energy (relatively speaking). I.e The smallest burner on the stove takes about 2kwh of power and takes 5 to 7 minutes to heat up a stainless steel kettle of water versus the counter top kettle takes about three minutes and consumes 1kwh of power. We also cook a lot outside on either charcoal or the propane grill.
- The dryer has an eco-mode which consumes about half the power of the regular setting. Also, we find that we can run it on "quick dry" and it only runs for 30 minutes. We "try" and avoid running the washer, dryer, and dishwasher at the same time, but it isn't always possible.
- The dishwasher also has an eco-mode (air dry) and saves a lot of power.
- We only run the "discretionary" heavy loads during the cheapest electric time which is between 10am and 3pm. That means we have to plan laundry and dishwashing a bit, but my spouse and I work from home so it is pretty easy to manage this with us both being available to turn things on/off as needed.
- We also packed out the freezers and set them to their lowest possible setting that still keeps things rock solid frozen.
- At night if we aren't working or reading, in the cooler months we get a fire going in the fireplace to keep things warm and watch a little tv by firelight.
- Bathroom fans are on spring loaded wall timers. That way, they shut off on their own and aren't wasting power when not needed.
- The family is well trained to shut off lights they aren't using.
- We cut consumption from 48kwh/day down to about 39kwh/day. (We haven't been through a summer yet with this plan).
- Most days, our system provides as much as 90% of our needs.
- We have had several days where we pull only 1 to 3 kw from the grid for the entire day.
- On extremely cloudy and rainy days we have had to pull as much as 23kwh from the grid.
- Our electric bills are down significantly. They have been cut by as much as 80% (so far).
- We can get things down even further, but I have the inverter set to re-charge the batteries up to 75% from the grid during the hours of 10am to 3pm when the cost of KWH is under $.04. I could adjust this to essentially pulling nothing from the grid, but the cost from the grid is so low, I just never wanted to risk my array not being able to keep up and wind up having to buy power at a higher rate!
The plan from here is to add about another 10K worth of panels and another 35Kw worth of batteries, but we are waiting for the prices to come down on them even more! Truthfully, at this point, any upgrades would just be a game that we would be playing on how to eliminate the last 20% of our grid usage. I call it a game as it will cost at least as much as we have invested in our entire system that currently provides as much as 80% of our needs. It really wouldn't be cost efficient. The good news is that our system can easily handle the critical loads we set out to cover! So, if prices on panels and batteries drop, then we will likely work to go fully off-grid. If they don't drop, we will just be happy with our lowered utility prices and keep adjusting our consumption paterns to maximize our system!
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