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Comment by fred_is_fred | Hacker News Reader

What the NPV and pay-off time of your system? I've been unable to get one bid here that's less than 10 years because electricity is fairly cheap here.

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I have built a system that cost just under $2k and should pay off in about 3-4 years (depending on battery lifetime). 2.4 Kw (8 panels) of used panels @ $.32/Watt, Charge controller, 3Kw inverter, transfer switch and 320ah@48v used Golf Cart Batteries. System is offgrid and supplies all my convenience outlets, kitchen and 240v circuits are on still on the grid. Panels are on top of free standing structures and being off grid permits are not required and only the transfer switch installation needed to be done by an electrician. Bonus is being offgrid it acts as a big UPS in a power failure.

This is a great plan. PG&E here in California forces solar customers onto a more expensive plan. If you can avoid that switch and use solar to dramatically reduce (but not eliminate) your total kwh load then you'll definitely come out way ahead, because you'll be on their cheapest tier.

Yes, most of the electricity I have generated has been what would have been tier 2 @ $.26 kWh, with the climate stuff going thru Sacramento atm I expect the price to go even higher soon.

California will be changing dramatically how it charges for electricity in the next few years[1]. I was talking to a person Tesla today about putting solar on our house and he mentioned in passing that Time-Of-Use Rates will be the default for everyone in California in 2019 by law (AB 327 in passed in 2013). For your net metering you will get credit/pay for power to/from the grid at the rate for the time it happens. A good up-sell for the powerwall. If the rates get way out of wack due to high solar input, one could do well charging your powerwall during the peak solar production hours (see duck curve [2]) and putting them back on the grid a 3-6 hours later.

[1] https://cleantechnica.com/2015/06/08/california-rolls-out-de... [2] http://instituteforenergyresearch.org/solar-energys-duck-cur...

I've wondered about the 'used panel' market for a while. Do you know why your seller didn't just increase the price of the property or move the panels? Does the second-hand price of panels decrease linearly with the amount of lifetime left, and how can you verify?

I got mine from a recycler, he said they failed inspection after installation for scuffs and scratches. Mine produce very close to spec. I have read that most panels degrade at about 1% per year, the ones I got were 3 years old. I checked them all to see that the open voltage was close to the specs when I got them, worked out great.

In the uk most solar installations get a generous subsidy for power produced. The fixed subsidy was set 5 or more years ago at e.g. 44p/kWh for a specific installed capacity.

The high price per kWh means it is economic for these places to upgrade their panels to newer ones that get closer to their rated output (e.g. in low light conditions etc). Hence the market for used panels.

Source: looking at the explanations on used panel shop's website - I think it is reliable.

Yes it's 10 years for me as well. Most of that is because we have a 30% efficiency hit because we didn't want to cut down a tree in our backyard that shades it for 2 hours a day during about 6 months of the year. Our system is also larger than our current usage, because we plan to use more (electric car, more kids, etc).

Another benefit to think about is you've effectively locked in your electricity rate. With some companies that might not be a big thing, but here in CA PG&E has been relentless with their rising kwh costs.

I pay on average about 10.3 cents per kwh and have a newer home that's very efficient at holding cool air (and live in a state where we heat more than we cool). For those reaons it's a tough sell for me. If rates continue to rise and solar continues to fall, we'll have a cross over that works for me probably in a few years.

It's not cost competitive for you at 10 cents. Why bother? I'd kill for that kind of price in electricity. Our total cost with solar is around 13c per kwh over 20 years.

I also have the same (10.7 cents over the past year). We have a community solar project in town, but it is ~13 cents over 20 years as well.

That's also what SolarCity told me...

Any chance some of your energy comes from nuclear?

Coal and wind. I live in Colorado.

You're in a good place. I live in a neighborhood with older homes similar climate. Lots of people are doing solar because it's cool, but ignoring windows and insulation.

We ran the numbers on our house with an energy audit and found that the return on insulation, an attic fan and window replacement was literally like 2-3x solar.

The other thing to look at is solar hot water. It's not sexy, but that has been high ROI since the 80s.

I'm assuming a 10 year payback equates to an annualized return of ~7%. Would you be paying cash for the panels or using financing? If the former, do you have other investments paying that much? If the latter, at what interest rate?

Right now it's a 20 year loan at 5%, $106 a month, but we're going to pay 50% of it cash and 50% HELOC for tax deduction purposes.

There's a 30% tax deduction one time for the total cost. My loan payment is less than my precious monthly power costs including taxes and fees ($15 a month to be hooked up to PG&E).

Remember to look at other below the line costs too... particularly with leasing there are cases where the homebuyers credit situation can make selling your home difficult.

One friend had to take a hit in the selling price as a concession to buyout part of the lease.

The pay off time for our system here in Hawaii was, if I recall, about 6 years, even though the price of installations is really high. The price of electricity is too, though.

What do you pay per kwh?

The internet tells me it's 30c/KWH.

Hawaii's primary source of electricity is oil.

For the one I'm about to install it is little over 5 years.

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