The adventures of installing rooftop solar panels on an existing home
There is much to learn! Like “Time of Use Rates.”
Since I posted “Part One” I have had my roof inspected by the solar provider. One cracked tile was found, which they will replace, and they report “the felt is good.” They took photos of all aspects of the roof. I suppose I should get a copy of those.
They say they will be providing a 25-year warranty on my roof. That protects against leaks from the points at which they attach their panels to my roof.
Meanwhile I’ve been refining the numbers on my spreadsheet. Savings each month will vary according to how much solar is used and how much is taken from the grid. It is not simply the total generated minus the total used, because I only get a credit of 75% retail from the utility. So the more I use solar instead of the grid, the less I pay. I can calculate a maximum savings (all solar used, none sent to the grid) and a minimum (no solar used, all sent to the grid). For projections, I’ll use a figure midway between those two points.
Time of Use Rates
My research led me to something called “Time of Use Rates“. This is a plan that might provide savings to almost anyone, but especially for those with solar panels and a bit of discipline. Or it might be a total loser for those who’d rather not think about how they use energy. I’m going to give it a try, and I’m told I can cancel after 12 months and get a refund for any overage. All I had to do was notify NV Energy that I’d like to try those rates.
Basically they charge more (4 times as much) for energy from the grid 1pm-7pm during summer weekdays. At all other times (evenings, weekends, wintertime) I pay about half the going rate. Sounds like if I’m willing to sweat a little during the summer afternoons, I can cool things off at night while saving money.
I don’t know if or how this affects the credit I get for kWh sent back to the grid. Most likely my credit fluctuates with time of use. Either way I’m bound to be using solar during those summer daylight hours and unlikely to ever pay the pumped-up peak price. As I learn more I’ll update this post.
Solar is not a substitute for conservation
I may shift dinnertime from 6pm to 7:30 to avoid using cooking appliances during peak. No dishwasher, washer, dryer etc. I pre-cool the house down to 75° from 11:45am to 1pm during summer weeks, then turn the thermostat up to 81° until 7pm. Today it was 106°. From 1pm to 4pm the inside temperature drifted up from 75 to 81 and the aircon kicked back on. It didn’t take much to keep it below 81 from 4 to 7. At this time it looks like TOU rates might cut $30-60 off my monthly bill, but will be even more beneficial once I switch on the solar.
My solar rep never mentioned “Time of Use”, probably because it might reduce my existing electric bills, thus reducing the cost-effectiveness of installing solar panels. When I asked him about it, he replied, “I think that is a great idea for everyone who has a solar system on their roof.”
In California, solar users who employ “net metering” to sell power to the grid must also adhere to “Time of Use” rates. There’s an article at Energy Sage but I can’t vouch for its accuracy, nor the comments.
Rough Draft of my spreadsheet. Click “Assumptions” tab after opening.