Steren's essays

Our home now runs on the solar energy that it produces almost all the time. Here is our journey and how you can do it too.

The recipe fits in two steps:

1. Solar energy production: panels and batteries
2. Electrify consumption: electric car and heat pumps

Over the last year, our home was 96% self powered. This means that the energy used for heating, cooling, water heating, running appliances, and 30% of car charging (we also charge at work and on the road) is directly produced by ourselves almost all the time, instead of coming from the grid.
To be clear: we are not talking about comparing our yearly energy production to our yearly energy consumption, we are talking about constantly powering our home (night and day) with our own energy.

Our primary goal was to reduce carbon emissions coming from our residential energy consumption, our secondary goal was to save money in the long run.

Our journey in 3 charts

Here are three charts that tell the whole story the journey:

1. We replaced our gas furnate in March 2023: gas consumption goes down, electricity goes up.
2. We installed panels and batteries in summer 2023 and got permission to export a month later: electricity import goes to 0, then negative (exports)
3. We switched to a heat pump water heater in March 2024: we are now at ~0 gas usage.
4. We only import from the grid during rainy winter days.

Solar

We happen to live in a place where it's sunny most days of the year. This means abundant solar power available for everyone to harvest for free.

We installed a solar system of 16kW solar power and 27kWh of battery storage (40 panels and 2 Powerwalls).

Because the sun doesn’t shine at night, batteries were essential to achieve our goal. But even if you only consider the economics, today’s net metering energy contracts (e.g. NEM 3) are designed to incentivise installing batteries. The plus of batteries is that also you won't notice grid power outages anymore (and you'll be the only house in the neighborhood with lights when they happen)

We had to size our system taking into consideration the future electrification of our home. We sized it by estimating power and energy:

1. Peak power production should be able to cover peak power consumption: sum the power (kW) of everything that will be running at peak in your home.
2. Yearly energy production should cover yearly energy consumption: sum the yearly energy consumption (kWh) of everything in your home.

We went with Tesla solar. We recommend them because of their low price and vertical integration. The downside is that you should be ready for minimal customer support and potentially a lot of back and forth in the design phase (it was our case because we wanted to size the system for our future electricity usage and were ready to make modifications to maximize solar production, like cutting one tree).

Electrify

We switched to an electric vehicle four years ago. What was left was our residential energy use, which was mainly gas.

The solution to home electrification is in two words: Heat Pumps.

Why Heat pumps? Of course because they run on electricity, but also because they have an efficiency of 300%. Which means that for each unit of energy that they use, they “produce” 3 units of energy. How is this possible? They move heat, instead of generating it.

We progressively replaced all gas appliances with electric heat pumps, by impact order:

1. Heating, Ventilation, and Air Conditioning (HVAC): We started by replacing our gas furnace with an electric heat pump. We went with a 4T and 24 SEER heat pump system from Bryant. One thing I never understood is why so many US households are equipped with elecric air conditioning but not heating? The machine is the same! I'd bet most AC units could be retrofitted to run in reverse and be used for heating.
2. Water heating: After switching heating and cooling, we were still measuring meaningful daily gas consumption (1 therm a day), just because of water heating. So we installed a hybrid heat pump water heater (Rheem Proterra 50 gallons). The water heater is most efficient in “energy saver” mode, but takes time to heat in that case. So we automatically switch it to "High demand" starting mid afternoon (when our batteries are full but when we're still producing a lot from solar) until late evening, to ensure hot water is ready for evening showers. In a sense, our water tank also becomes a battery that we can fill when the sun is shining and use whenever we want.
3. Dryer: Finally, we replaced our old dryer with a ventless heat pump dryer. This especially matters if you have a gas dryer. In our case, it was already electric, so we replaced it to increase efficiency and to "flatten the curve", as a heat pump dryer uses much less peak power but runs for a bit longer, it is ideal to avoid spikes and match solar production. A bonus is that this removes the need for a dryer vent and its associated maintenance

Adapt usage (optional)

If you’ve done the above, the rest can be considered minor optimizations. You can adapt your usage, potentially automatically, in order to maximize power consumption when the electricity is produced by the solar panels and minimize consumption when you run on battery. This means one simple thing: shift as much as possible when you run on solar.

In our case this meant, sorted by impact:

• Charge the car when the sun is shining (automated via Tesla vertical integration)
• Only run the pool pumps when the sun is shining (automated via custom code)
• Cool during the day in summer, heat less at night in winter (schedulable)
• Run the dryer during the day (schedulable)

Anything else, like lighting or small appliances, is insignificant in terms of impact compared to the above (we have automation for outdoor lights).

How much to adapt your usage is up to you. If you don’t use automation, consider the downsides of micro managing your home for the realized gains. It might not be worth the daily effort.

20x lower carbon footprint

Before electrification and solar installation, in a winter month, our home monthly carbon emissions were 840 kgCO₂ / month. Just by switching to electric heat pumps, our emissions would have been 370 kgCO₂ / month. So, in California, by switching to electric heat pump heating, you cut your emissions in 2.
Of course, in our case, the electricity is not coming from the grid but from our own solar production, which brings down our emissions to 45 kgCO₂ / month, a 20x reduction. (This is without counting the switch to an electric vehicle)

Break even in 8 years

While saving money wasn’t the primary goal, it’s still interesting to see when this investment breaks even.

This was a big investment:

For us it was important, but even after the 30% tax credit on solar panels and batteries, or after the local credits on heating and cooling, it’s far more than what most people are able to afford. Of course, we could have invested this money elsewhere and have much bigger returns, but again, making money wasn’t the primary goal.

Our average monthly electricity bill used to be $632, it’s now $0. On top of that, we make $150 every year from the excess exported electricity and $700 from Tesla virtual power plant. Which means we break even the initial investment in 8 to 9 years.

To recap

After becoming homeowners, it was important for us to make this extra investment. We have now become almost entirely self-powered and almost negated carbon emissions from residential energy use.

The recipe is simple: electrify your home and harvest electricity from the sun!