Both solar panels and batteries have gotten cheaper and better over the last few years. That’s why many homeowners are wondering if now is the time to go off-grid with solar.
Batteries to store solar power have been big topics recently. For example, just in the last few days, we learned that Germany converted a coal mine into a giant battery to store extra solar and wind power while Tesla’s Elon Musk offered batteries to solve South Australia’s electricity crisis in 100 days.
Tesla has been busy on the battery front. In the fall of 2016, the company unveiled its Powerwall 2 battery pack for homes and small businesses. Tesla claims that one unit, which they say will cost about $6,000 installed, can run lights, sockets, and a refrigerator for an average size house all day. To add to its appeal, the new version is even thinner and sleeker than the original.
It certainly does look great. But does it make sense for homeowners going solar? As Angie’s List explains, “Tesla batteries are not a new technology.”
Battery storage has been on the market for some time now, but few homeowners have opted to add that to the cost of their solar PV (photovoltaic) system because it hasn’t been cost-effective. Even with Tesla’s improvements, adding battery backup to a solar PV system is still too expensive for most homeowners. This definitely will change, but cost-effective battery backup isn’t really here yet.
The article goes on to explain that homeowners should not wait for batteries to come down in price to get solar. With a grid-tied system using today’s solar technology, the average homeowner can save 50% to 100% on their electricity bill.
If You’re Already on the Grid, Don’t Leave Yet
Because of cost, we don’t recommend that a homeowner who is already hooked up to utility power disconnect and go off-grid. There are many reasons, but some key ones are:
- Grid-tie systems are less expensive than off-grid because they require no storage batteries.
- Off-grid solar has some unique design limitations, which means most people will need to adjust their power use habits and may need to replace some appliances (such as an electric furnace or electric oven) to make an off-grid system practical.
- While solar panels are basically plug-and-play, most batteries require regular maintenance.
- Batteries also have a shorter life expectancy than most other solar system components, which means that they not only add to the upfront cost of a system, but they add to the costs over time because batteries need to be replaced more frequently.
If you’re already on the grid, on-the-grid solar systems offer you the best of both worlds. You can have your system sized so that your 12-month average electric bill comes in at next to nothing, but you still have the flexibility to at any time draw more than your solar array is producing from the electric grid without having to do a thing.
And when a grid-tie solar electric system generates more power than you are using in your home, the excess electricity is sent out into the utility grid. Since Virginia offers solar “net metering,” it means power going into the grid spins your meter backwards, allowing your neighbors to use it and and essentially giving you a credit on your utility bill. In that case, you’re using the grid as your battery — all while contributing substantial benefits to the grid by offering your extra energy as clean, low-cost power when your neighbors need it.
Grid-Tie System with Battery Backup
If you experience regular blackouts or if you have a critical need to restore power quickly when utility power does go out, then it might be worthwhile at today’s costs to get battery backup even while staying on the grid.
A hybrid system that’s still on the grid but adds battery storage takes advantage of the high efficiency of energy production of the on-grid system, but has a limited battery storage bank to supply power to critical appliances in the home like certain lights or a refrigerator.
Hybrid systems are designed to supply critical loads without the benefit of a solar charge cycle period, referred to as the “days of autonomy” (3 days is typical). The autonomy period is based on the load demand of the appliances to be operated and the length of time those appliances are to be in operation.
Of course the system can be built large enough to power any device as long as cost is not a consideration. If a generator is available to provide recharging of the battery bank, then the days of autonomy can be shortened, as the generator would be called on to offset the loss of access to the sun’s power during extended cloudy periods.
In general, these systems are best for applications in which backup power must be instantly available without interruption (for example, to power computers). Hybrid systems are also good for areas where power outages are a frequent occurrence, or an area where blackouts and brownouts are relatively common, such as after a hurricane.
Hybrid systems typically require a larger up-front investment than grid-tie systems. Batteries make a solar system more complicated and expensive because they:
- Require maintenance
- Need to be replaced after 5-10 years
- Decrease a solar system’s efficiency
Honestly, Sometimes a Gas or Propane Generator is Good Enough
Since we’re in the clean energy business, we love the idea of backing up solar panels with batteries for a zero-emission solution. But we’d rather help make our customers happy than make more money selling batteries that don’t yet make financial sense.
So, our honest advice about storage is that if you need backup power, a more traditional solution may still be the best way to go.
Many of our customers opt for a grid-tie system and purchase a standby gasoline or propane generator with a properly installed manual transfer switch. Such generators are usually the least expensive option for backup power production. Generators provide the most reliable and cost-effective source of extended backup power, eliminate the additional expenses related to batteries, and have backup power available for as long as they have fuel.
Generators usually cost between $3,000 and $7,000, with manual-start gasoline generators at the lower end and auto-start propane/natural gas generators at the higher end. A more durable diesel-powered generator, such as a 10,000-watt auto-start unit, can be purchased for about $10,000. This type of generator has higher quality power output, requires less maintenance, and has a much longer life.
Propane or natural gas generators are also good solutions for remote backup systems. With these higher price range generators you can install an automatic transfer switch and auto-start capabilities so that the generator automatically begins to supply your electrical needs in the event of a power outage. That will get your juice back up more quickly than a traditional manual-start generator.
In the future, the cost of batteries will continue to come down. At some point, battery storage will be worthwhile for more homeowners. And that day could come sooner rather than later if the cost of grid electricity rises more sharply.
In the meantime, homeowners should not wait for batteries to get solar. The longer you wait on solar, the more money you’ll be wasting on utility bills. And the good news is that once you install solar panels, you can always add batteries later on. That keeps your options open for the future.
This article is adapted from our ebook, “Top 10 Questions & Answers on Home Solar in Virginia.” Download your copy for free now and start getting smarter about solar power.
— Andrew Brenner, Main Street Solar
