I’m designing and building a solar energy system for our home! I hope to use this blog to document the journey, my goals, and the lessons learned along the way. Hopefully this keeps me motivated, and even better if I can help someone else who shares this interest.
My goals for the project include:
- DIY as much as possible
- Reduce energy costs
- Increase independence and emergency backup
Why DIY?
I went to college for electrical engineering. Although power electronics were not my focus, it’s been a dream of mine to design and build a solar energy system for some time. I love to learn about infrastructure and the things we depend on in our daily lives, and few things are as impactful and pertinent as electricity. Solar energy is one of the most plentiful resources and there have been a number of advancements in technology in the last few years that make a DIY project very approachable.
Energy Costs and Calculations
The first step in any solar project is to understand your electricity usage and energy costs. There are a lot of knobs to tweak when designing a system and the biggest knob is the size of the PV (photovoltaic, i.e. solar) array. This should be sized to
We moved to our new home only a few months ago, so unfortunately we don’t have much data from the utility to estimate future energy usage. I contacted the utility and they offered to share historical data if we had a signed release from the previous owner. I figured this was not worth the effort, for a few other reasons.
Lighting
When we moved in, most of the bulbs in the house were halogen. They’ve all been replaced with LEDs. In the upstairs and downstairs ceilings there were 21 BR30 bulbs, each 100W. In the winter it’s typical for us to have 15 of those bulbs on for an average of 5 hours, so 1500W x 5 = 7500Wh with halogens. With LED replacements (12W) we have 180W * 5 = 900Wh, an 88% reduction.
Appliances
Currently most of the appliances are gas (propane), which include:
- Oven/range
- Water heater (40 gal)
- Furnace (80,000 BTU)
- Heater in workshop (? BTU)
We plan to switch all of these appliances to electric over the next year or so. Propane is rather expensive, and it’s also a major hindrance to indoor air quality.
In order to correctly size the solar installation now, I need to get a reasonable estimation of the future energy needs.
Furnace
I think the furnace is quite oversized, see Technology Connections great video on the subject.
I have a Z-Wave smart thermostat so I can track when the HVAC is heating using Home-Assistant. I have data from February:
The vertical axis is the time (hours) spent heating each day, and you can see that there is no day since early February that we went past about 8 hours heating. Unfortunately I did not have the thermostat in place for the coldest part of the winter in January, but I don’t think that it would be a very significant departure from this data.
I think our furnace is at least 2x oversized so a 40,000 BTU unit would suffice. We plan to go with an dual-fuel air-source heat pump with a gas backup, so we would have plenty of wiggle room for heat pump sizing. By my estimations a typical heat pump in this range would consume about 8-10 KW maximum.
Water Heater
We plan to get a heat pump water heater. Some models plug in to 120V and don’t require more than 15 amps (~1800 W). An alternative is to run a new 240V circuit to the water heater and install one which supports the heat pump for efficient heating in addition to resistive heating for high demand situations. I know Kristen likes excruciatingly hot showers, so there may be a strong bias towards the latter, which would consume about 4000 W.
Oven / Range
We’re looking to get an induction stove to replace our gas model. Typically these consume 12,0000 W maximum, but this is not a critical load like the furnace.
Summary
Critical loads:
- Well ( ??? W )
- Furnace ( ??? W )
Non-critical loads:
- Water Heater (4000 W)
- Stove (12000 W)
Design
Here is a diagram of the electrical connections on the property and the rough measurement between them:
This can be visualized on a satellite view of the house:
A one-line schematic of the system:
Selecting Components
Panels
Bloomberg published a report of the “Tier-1” PV panel manufacturers in 2023.
Inverter
I am choosing between the Sol-Ark 5k and the EG4 18kPV. Since the inverter and batteries will be in our basement, and that basement is not acoustically isolated from the rest of our house, sound level is very important. The Sol-Ark claims a max noise level of 30 dB, while the EG4 claims 68 dB.
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