Want to solar-charge an EV (electric vehicle) but don’t have a solar system or an EV yet?
You might want to consider buying the EV first, then installing your solar system.
As we recently discovered, some utilities, including Xcel Energy, the utility for
- Oversize your solar system so that the system will cover 100-percent of your home electric use and 100-percent of the annual miles you log on an EV that you have not yet purchased or driven;
We signed a contract with REC Solar in July 2009 for a 5.5 kW system which, on our near perfect, south-facing roof in sunny
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Our current annual household electric use falls somewhere between 5,000 and 6,000 kWh, mostly depending on how much, or how little, we use our air conditioning in the summer.
Colorado Public Utility Commision’s ‘120-percent’ roadblock rule
Unfortunately, the Colorado Public Utility Commission (PUC) – and I suspect quite a few other state utility commissions – have erected a roadblock for people like us who want to go solar first, then get an electric vehicle, and build a solar system large enough to cover both the home electric use and 100-percent of the yearly miles driven in a future EV.
It’s called the 120-percent rule.
Basically, according to this rule, utilities in Colorado won’t give customers a rebate for a solar system that threatens to produce more than 120-percent of the customer’s total annual home electric use.
When we submitted our annual kWh to REC Solar in July 2009, we submitted our June 2008 to June 2009 usage, which totalled 6,200 kWh.
This did put our proposed solar system at 129-percent of our total usage, or a little bit above the so-called 120-percent rule – essentially an attempt on the part of utility companies to maintain as much of a stranglehold as possible on power production.
However, REC Solar assured us that Xcel hadn’t ever “pushed back” before on the 120-percent rule.
Ultimately, Xcel used different annual kWh figures than we did when it refused to provide a rebate for a 5.5 kW, 8,000 kWh-output system for our
That’s because our application sat on Xcel’s desk for more than two months. Unfortunately for us, Xcel then used Sept. 2008 to Sept. 2009 kWh figures for our home. Our power use was 5,100 kWh for that period, or 1,100 fewer kWh – primarily because we did not need to turn our central AC on a single time this past summer.
Forced into a smaller solar system
With Xcel’s push-back, we had little choice other than to re-submit another plan for a smaller solar system.
Unfortunately, the Colorado Public Utility Commission (PUC) – and I suspect quite a few other PUCs – have erected a roadblock for people like us who want to go solar first, then get an electric vehicle, and build a solar system large enough to cover both the home electric use and 100-percent of the yearly miles driven in a future EV. It’s called the 120-percent rule.
Thanks to the complexities of solar system sizing – which hinge on:
a) the solar inverter size and capacity, which converts DC energy to AC;
b) so-called ‘stringing’ issues, which basically mean that because of electronic current issues a very particular number of solar panels must be “strung” together, our system became quite complex.
These complexities ultimately forced us to, at least temporarily, sign on for a 2.7 kW system. This system will produce about 4,000 kWh annually, or just half of the 8,000 kWh annual output of the 5.5 kW system.
Lucky for us, when we signed the original contract with REC Solar in July 2009 for the 5.5 kW system, we decided to wait until June 2010 to have the system installed – basically, to give us more time to save money for the system.
Turns out our decision might allow us to get back into our 5.5 kW system.
Crank up the (electric) heat
Ironically, by using more electricity – a lot more – between now and the end of May 2010.
Xcel has indicated it will allow us to use our June 2009 – June 2010 kWh figures as the baseline in calculating whether our system puts us over the 120-percent rule.
So, we’re trying to move as much of our home heating from gas to electric for this winter as possible.
All of this to:
- ensure we receive the $3.50 per watt rebate Xcel is now offering, but which it will soon be dropping to $3.00 per watt;
- ensure we can install a solar system at the current Xcel rebate levels large enough to power both our home electric use and a future EV.
If your state’s public utility commission has established a 120-percent rule (or something similar to it), and if you’re a couple years out from buying an EV, but want to go solar earlier, consider boosting your home electric use for several months before you sign on with a solar company.
Yes, we could have:
- opted to install the system without the $3.50 per watt Xcel rebate – wait, no, we couldn’t have done this, because we could not afford the system without the rebate;
- opted for a smaller system and then added on to it so that it would be large enough to power our home electric use and our EV – but, wait, that would be exorbitantly expensive for us as it would involve replacing the solar inverter, which typically costs around $3,000 to $4,000, and it would require adding on panels at a lower per watt Xcel rebate level;
- waited until we got the EV to install the whole system — but, wait, the Xcel rebate would be substantially lower then and in the meantime we would be forking money over to Xcel to power our electricity use with, you got it, mostly Dirty Coal.
Tips for prospective solar-charged drivers
In sum, for those of you currently without a home solar system and an EV but who are raring to cover as close as possible to 100-percent of your home electric use and future EV miles with electricity generated by a home solar system a couple of suggestions based on our own still unfolding experience:
- Look into whether your state’s public utility comisison has a similar 120-percent rule, according to which a utility can refuse to give a customer a rebate on a solar system which produces more than 120-percent of a home’s annual electric use.
- If your state has such a PUC rule, you might want to consider waiting to install your solar system until after you’ve purchased an EV and have driven it for, say, 6 to 12 months.
- You might want to consider gradually building up your solar system using micro-inverters. These allow you to build out a system, one panel at a time, if necessary, without incurring the high cost replacing a central inverter. Of course, micro-inverters currently cost more than central inverters. However, if you calculate the cost of replacing a central inverter at 12 to 15 years – the time after which all currently built inverters will blow – micro-inverters, which last 20 to 25 years, might actually be cheaper than a system with a central inverter, and they allow you a lot more flexibility in terms of building out a system than a central inverter.
- Finally, if your state PUC has a 120-percent rule, and if you’re a couple years out from buying an EV, but want to go solar earlier, consider boosting your home electric use for a six- to 12-month period before you sign on with a solar company.
I know the final suggestion seems absurd. However, it’s only absurd because rules such as the Colarado Public Utility Commissions’s 120-percent rule actually discourage, rather than encourage, energy conservation — at least for those of us who want to solar-charge our home and our EV, but who don’t yet have either one.