The second post in this series, Gaming the Electric Grid – PV Solar will cover my experiences with residential grid-tied PV solar systems as a homeowner over the past fourteen years. Over that time, I’ve had two solar PV systems installed in two different houses, and I think I have learned quite a bit about how they actually work in real life.
One thing you should do before you even think about getting a residential grid-tied PV solar system is to have an energy audit done on your house. Many utility companies offer free or subsidized energy audits that will give you a list of changes or improvements that will give you the best ROI. It is very likely that you can make some improvements to your house and the electric items inside that will significantly reduce your overall electric usage. Many of these are free or very low cost, but some are more expensive.
This may let you get away with a smaller solar PV system and it will save you money on your electric bill whether you have a solar PV system or not.
You might be interested in the first post of this series, Gaming the Electric Grid – Basics
First PV Solar System – Parker, CO
Back in 1999, we bought a new build house in a pretty typical suburban subdivision in Parker, CO. This house was about 2200 square feet on a 1/5 acre lot in a cul-de-sac. As was common (and still is) in the United States, it was a two-story “stick-built” house with wood 2×4 framing and minimal fiberglass batt insulation in the walls and roof.
Residential solar power was the last thing on my mind as we chose the various available upgrades and options from the home builder. We also didn’t think about solar when we chose the lot for the house, but we sort of got lucky by accident. One thing we did do was to pay extra for a high efficiency 14 SEER air conditioner and a 90% efficient gas furnace. Both of these items were much more energy efficient than the standard 10 SEER AC and 80% efficient gas furnace of that era would have been.
In 2009, I decided to have a 3 kW grid-tied solar PV system installed on the roof. Because of the house lot we chose and the design of the roof, we had enough roof space that was facing in a somewhat favorable direction to accomodate the solar panels. I say “somewhat favorable”, because the panels were facing south-southwest rather than due south.
In the northern hemisphere, you want your solar PV panels to face due south to help maximize their production in most cases. You also want them to be tilted between 15 and 40 degrees if possible. The ideal direction and angle will vary based on exactly where you live. If you are building a new house (or buying an existing house) you want to keep this in mind.
I had done a lot of research beforehand, so I specified that I wanted 300W SunPower panels and a SunPower SPR-3000M inverter when I got bids for the system. SunPower has been the “gold standard” for panels and inverters for quite a while.
Luckily, I chose Namaste Solar to install the system which went very smoothly. If you are in the Denver metro area, I highly recommend Namaste Solar. So far, I have had two friends use Namaste Solar for their solar PV systems and they have both been very happy.
These images from May 9, 2012 show some views from my SunPower SPR-3000M inverter. The first picture shows it putting out 2277 watts. It could produce right at 3000 watts during mid-day on a clear sunny day during the summer.
The second picture shows that it had produced 18.38 kWh that day. It could produce about 20-23 kWh on a good day during June and July.
The final picture shows that the system had produced a lifetime total of 10.21 megawatt hours in less than three years. Our electricity cost about 12 cents/kWh at the time.
Just to be clear, this was a typical net-metered, grid-tied, roof-mounted solar-PV system with no battery storage. It reduced our electric bill by about $50-$60 dollars most months. There was a 30% Federal tax credit, but there were no local or utility company credits or rebates. Given the cost of a solar PV system in 2009, the cold, hard ROI was not that great. But that was not my primary motivation. I remember that this was the only solar PV system in the entire subdivision for several years, so I was definitely an early adopter!
We ended up selling the house in Parker in 2015, and I know from the buyer that having a solar PV system made the house much more attractive to him and his family. Having an owned solar PV system (rather than a leased one) also helped with the appraisal value of the house.
Second PV Solar System – Elizabeth, CO
In 2014, we decided to build a custom house out in Elizabeth, CO. This gave me much more flexibility to optimize the house placement and design for better solar production and better energy efficiency.
I took advantage of this by ensuring that the back of the house faced due south and that the south facing roof was large enough to fit the amount of solar panels that we needed. Another important investment was adding a LOT of extra insulation to the foundation, walls and ceiling that was far above what was customary for our climate zone. We have roughly R-60 in the ceilings and R-30 in the walls, with R-5 or R-10 sheathing outside of the 2×6 wood framing under the exterior siding.
Adding insulation and sealing air leaks in a house (new or existing) usually is the best thing you can do to reduce your cooling and heating costs. A well insulated and sealed house lets you have a smaller, less expensive furnace and air conditioner (or heat pump) and lets them run less often. It also makes the house much more comfortable and reduces ambient noise from outside.
If you are building a new house, you should try to go 100% electric if at all possible. This means making concious choices like picking an induction cooktop, electric oven and a heat pump water heater, furnace and dryer.
Our electric provider is CORE (formerly IREA), and they limit residential solar PV systems to 10 kW if you want to have net metering. CORE has historically been very hostile to renewable energy, and they have never offered any incentives or rebates for energy efficiency improvements, solar PV systems or energy storage systems. In case you can’t tell, I am not a fan of CORE.
I had Namaste Solar install a 9.72 kW roof-mounted grid-tied solar PV system soon after we moved into the house. For tax credit reasons, I did not have the builder do it and roll the cost into the mortgage. This system consisted of 29 SunPower SPR-X21-335 335 watt panels and two SMA SB 5000TL 5000 watt SPS string inverters.
Secure Power Supply (SPS) inverters have a separate dedicated outlet connected to the inverter that lets you pull up to 2000 watts from each inverter (using only that dedicated SPS outlet) when the public grid is down. Regular solar inverters shut off when the public grid is down (to protect utility workers from injury from the grid being back-filled) so you don’t get any solar power even when the sun is shining. With an SPS inverter, you simply flip a switch and wait a couple of minutes for the inverter to restart, and then you can pull up to 2000 watts from the SPS circuit (spread across two outlets) while the sun is shining.
This is a clever feature that works as advertised. Having an SPS inverter lets you run some critical loads (and charge some batteries) from your solar PV system while the grid is is down as long as the sun is shining. It gives you some additional options compared to a standalone grid-tied solar PV system with no permanent battery storage. Unfortunately this feature never became very popular, and I don’t think SMA makes inverters with SPS any more.
Namaste Solar estimated that this 9.72 kW system would produce 15,829 kWh of electricity annually. My system has produced 144,311 kWh in 9.3 years (which is 15,517 kWh annually). That is pretty close to the estimate. One of my inverters had an issue where it was offline for a few weeks several years ago. This was fixed with a firmware update, but that outage explains much of the shortfall.
Gaming the Electric Grid – PV Solar
With this 2015-vintage 9.72kW net-metered grid-tied solar PV system, I have produced more electricity than I used from the public grid most months of the year. When you have net-metering, your electric meter actually runs backwards when your solar PV system is producing more energy than your home is using. If your home is using more electricity than your solar production, the meter runs in the normal direction.
Your utility company keeps track of your net usage and any surplus that you accumulated during the month. This monthly balancing is on a one-to-one basis. My electric company, (CORE) does an annual “true-up” at the end of April (which is the worst possible time for the consumer). This is because you are very likely to have burned through the net-metering credits during the winter that you accumulated during the spring, summer and fall.
To add insult to injury, CORE also only pays you the “avoided cost” of your annual surplus net metering credits. That avoided cost is currently only about 50% of the retail cost per kWh that CORE charges residential customers. Whatever money CORE owes you shows up as a credit on a future bill.
CORE charges $13.50 per month as a basic service charge (for being connected to the grid). This is fair. In addition to that, CORE charges a “demand charge” where they monitor your highest kW electric demand from the grid between 4PM and 8PM during any day each month. Whatever that peak usage is (for example 10 kW) is multiplied by $2.00/kW to calculate your demand charge.
What this all means is that I typically have a $30-40 electric bill even though my house produced more electricity during the month than I used. Despite this, my solar PV system has paid for itself already.
There is not too much I can do about this with a standalone net-metered grid-tied solar PV system, besides doing what I can to reduce usage between 4PM and 8PM. But, if I add local battery storage, enhanced with a smart electric panel, I can do quite a bit about the situation!
In the next part of this series, I will talk about what I have done recently to enhance my solar PV system, reduce my energy usage and reduce my dependence on the public grid. This includes adding local battery storage and a smart electrical panel, so I can power my entire house when the public grid is down, whether the sun is shining or not.
This also gives me the ability to greatly reduce the monthly peak demand charge that CORE uses to try to reduce overall grid demand between 4PM and 8PM.
If you have any questions about this post, please ask me here in the comments or on Twitter. I am pretty active on Twitter as GlennAlanBerry. Thanks for reading!