About

Credit: mark sebastian
Here is the journey I went through to make my Solar PV installation more cost effective, and I hope help others do the same. I hope that by making Solar PV more cost effective there will be some effect, even if small, in increasing the adoption of home Solar PV systems. There are many options to help ensure that we preserve the Earth for future generations. I believe that technological improvements are by far the most palatable option for reducing humankind's environmental impact and improving sustainability, they are far more appealing than forced rationing or taxation. Environmentally beneficial technological improvements tend to be adopted quickly as they typically provide a cost or functional benefit. In 2016 I starting looked at getting a Solar PV system installed on our home. I have an electric vehicle, a Tesla Model S, and it was appealing to generate part of the energy used for driving from our own solar system. Part of deciding to install a solar system involves looking at system sizing, financing, and how long it might take to pay for itself, both through potential clean energy credits and through generated electricity. During my solar research I discovered that there are a range of generation rates and net metering policies depending on your power company.

Net metering and generation credits

Net metering allows you to bank generated energy that is exported to the grid during the day and then consume energy later, like at night, drawing from that banked energy. Net metering is typically the best case for people who want a Solar PV system due to this banking. Other power companies will charge one rate for energy you consume and credit at a lower rate for energy you feed back into the grid. My town's municipal power company provides a credit of approximately 1/3 of the purchase cost for each kilowatt hour (kWh) of energy generated. The net metering or generation credit rates have a direct effect on how long it will take you to break even on a Solar PV system. Power companies are adjusting their rates to account for the actual cost of providing power connections to customers with Solar PV. This isn't to take advantage of customers with solar, it's a result of fixed costs for maintenance and the reality that energy you generate may or may not be valuable depending on the load on the grid at any given time.
"... utilities want rate structures that address cross-subsidies and help recover fixed costs." From https://enerknol.com/wp-content/uploads/2018/01/EKR-PU-Visual-Primer-Power-Industry-Trends-1-9-2018.pdf
The growth rate of Solar PV is amazing:
"In the last decade, solar has experienced an average annual growth rate of 59%." From: Solar Industry Research Data | SEIA https://www.seia.org/solar-industry-research-data
As solar continues to grow there is more pressure for power companies to provide solar generation credit rates that don't result in a net loss in providing a power connection to solar customers. Solar PV growth is driven by a favorable ROI. Given the trend away from net metering and a reduction in credits for exported solar energy, how can Solar PV ROI be improved?

Improving Solar ROI

Tariff schemes pay for generated kWh based on its value to the power company. It costs them X to deliver a kWh to you in terms of maintenance, generation etc, so its not unexpected that they would credit you some amount less than X for a kWh you generated. Today, without real-time energy markets that individual customers can participate in, this payback amount is typically fixed. One way to improve your Solar ROI is to make use of the energy you are generating, rather than selling it and buying it back later at a higher price. In my case I was looking for something that was commonly available and relatively low cost. Battery storage systems are moving in this direction but are still quite costly. The Tesla Powerwall for example is $6,600 (not including ~$1,000-$3,000 for installation), and stores 13.4 kWh.
powerwall_2_XL_721_420_80_s_c1
Tesla Powerwall 2 battery storage unit.

Water as an energy storage medium

There are hundreds of thousands of homes in the US with electric hot water heaters. Water is an amazing energy storage medium with a very high specific heat. Rather than installing expensive batteries, why not use the water in existing electric hot water heaters as storage? Heating hot water with excess solar energy can reduce or eliminate the energy that has to be purchased from the grid.

The SolarOp Energy Management system

First step, a prototype

I went looking for a product that would let me control the energy going into my hot water heater. While there are some mechanical relay based devices, these would allow for the hot water heater to be on and drawing say 4400 watts, or off, drawing zero, there were none that provided variable load control at a reasonable price. Variable load control allows for increasing or decreasing the consumption of the device as the Solar PV output changes throughout the day. Here is an example of how you could use variable load control to consume only as much energy as was produced:
Neurio graph showing the use of SolarPV energy redirected to a hot water heater
You can see from this graph that as solar output increased so did consumption, until it topped out and then stopped as the water in the hot water heater reached its target temperature.

The SolarOp System

We've developed an integrated system including a energy monitoring, control, and cloud integration.
I've been at this nights and weekends for a while now and I'm happy to be able to finally have something that is working well enough to share. Thank you for reading and let me know if you have any thoughts, comments, or questions!
Chris Morgan <cmorgan@op.solar>
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