Off-Grid Vs. Grid-Tied Solar

Many people say they want to get "off the grid," when in reality what they mean is they want to reduce their energy use and offset what they do use with sustainable sources.

Grid-tied solar contains no moving parts and will last 40+ years with no maintenance. True "off-grid" systems require batteries, which unfortunately are messy and not environmentally friendly. Typically used are lead acid batteries (similar to what are used in forklifts) which require diligent maintenance, and only last around 5-7 years.

For remote camps, islands, or boats, off-grid may be the right choice. However, it is not the right way to go for nearly all conventional residences. ReVision Energy does not install or service off-grid systems and strongly encourages you to consider the advantages of a grid-tied system if you are in fact evaluating solar for a home. If you want to learn more about off-grid solar, check out New England Solar or the Alt-E Store.

Here are articles we've written on the topic of grid-tied vs. off-grid solar:


Solar When the Grid Goes Out: The Case Against Batteries

December 20th, 2011

Solar During Power OutagesNo one’s happy when the grid goes out. Power outages are at the minimum inconvenient, and, if a home is poorly suited to be without power, problematic or even dangerous. So it would seem obvious, why not install a grid-tied solar electric system and power your home using sunshine during an outage?

While technically this is possible, it is not so simple. Grid-tied photovoltaic systems are designed to provide decades of trouble-free electricity generated by the sun. They are simple, economical, reliable, and, as their name implies, tied to the grid. When the grid goes down, the system goes down, too.

This is by design: by shutting down, the grid-tied solar electric inverter (the component that converts direct-current power from the solar panels into grid-compliant 120V AC power used in your home or business) prevents power from backfeeding to the grid and injuring nearby line workers.

The only way to circumvent this is to add batteries, which provide a backup source of power when the power goes out. Unfortunately, batteries are almost the antithesis of a grid-tied system: they are bulky, inefficient, ecologically unfriendly, unreliable and expensive.

Grid-Tied with Battery Backup Vs. Off-Grid

Sunny Island Off Grid SolarA grid tied battery backup system uses the same principles as an off-grid solar electric system when the grid goes down. Instead of shutting off completely, the system switches to an alternate inverter, which is designed to interact with a battery bank, letting you run household loads off the battery bank and charge them with your solar panels.

The equipment to do this is quite sophisticated (in the situations where ReVision goes this route we install SMA’s Sunny Island product), and is derived from R&D for very remote locations where grid access is not feasible. While they can work smoothly, they come at a great cost, especially once you consider the cost of short-lived lead acid batteries (using similar technology as is in your car battery).

An average home with an electric bill of $100/month, for instance, consumes ~625kWh of power a month (assuming a grid price of .16c/kWh). That averages around 20kWh/day of power. Enough good-quality batteries to carry that load for just two days would cost around $25,000. Realistically, a battery-backup system is only designed to support emergency loads for short periods of time (water pump, refrigerator and maybe a freezer), but even so, the cost reaches approximately $20,000 of additional cost for a short-term grid-tied battery backup solution.

Further limitations of this system is the battery life – approximately 5-7 years – as well as the battery potential. While this system can provide backup power for a few days, for true energy security you need an option for charging the batteries should a long-term outage occur during bad solar weather (which tends to be when we lose power in Northern New England). So, even with a large battery investment you still require a generator to be totally secure.

Getting To Your Goals: Why Are You Going PV?

Most people look at a solar energy investment as a way to reduce their fossil fuel energy consumption while locking in their electric rate below the grid average for a duration of 25+ years. Cost pressure on solar panels and generous state and federal rebates make grid-tied PV an excellent investment right now, with a ‘simple’ payback of around 10 years in Maine or New Hampshire.

Adding battery backup changes this equation completely. Dollars that could be invested in more renewable energy production are invested in short-lived, ecologically unfriendly battery components. Realistically, with the grid down as infrequently as it is, a battery-backup system means you are paying a stiff premium for a system you do not need 99% of the time.

With that caveat, there are times when solar with battery backup meets specific goals, mostly in situations where no grid downtime is tolerable. For example, keeping critical loads like life support equipment online, or simply ensuring failsafe electricity for homes where one spouse travels frequently in the winter and doesn’t want their partner home alone in a power outage!

So What Am I To Do During Power Outages?

Though we are loathe to recommend the installation of a fossil-fuel burning appliance, the reality is that for the average numbers of days a typical home is without power (1-2 days a year or less), and given the cost and complexity of installing a grid-tied system with batteries, a generator is often a better investment.

Even an extremely robust home standby generator is roughly 1/4 of the price of enough batteries and equipment to maintain a home for a few days without power. While a battery bank will struggle to keep up with heavy energy hogs like a refrigerator or well pump, a properly sized generator will carry these without missing a beat.

If you just can’t stand the thought of a generator, here are some other power outage tips from our renewable energy experts:

  • Wood is good – Cord wood stoves are a tradition in New England and a wonderful appliance to have when the power goes out. They can be good for cooking and eating.
  • Stockpile water – Most people’s top complaint about power outages is running out of water. Fill up your tubs and empty milk jugs with water so you can cook dinner, wash hands and flush toilets during outages. And if you’re on city water and have a solar hot water system, you can continue to use your solar hot water even without power!
  • Keep alternative lights handy – With the sun firmly set by 5pm nowadays, a power outage can make for a long dark night. Luckily, LED flashlights are lightyears more efficient than their incadescent predecessors. LL Bean has a nice selection.
  • Make it fun – A power outage need only be as much an ordeal as you make it. Kids especially can be encouraged to make it an opportunity for adventure and find it fun to cook on the woodstove or propane grill. A bit of flexibility and patience go a long way.

Stay warm out there!



Why Grid-Tied Solar Power is Better than Off Grid for Most Homes

March 15th, 2010

Woolwich, Maine - Solar Power
A grid-tied solar electric system recently installed on a barn in Woolwich, Maine

There is a common misconception than being “off the grid” is the ultimate goal is sustainability and that off-grid homes are, by their nature, greener and more energy efficient than conventional “on the grid” homes.

Many people say they want to get “off the grid,” when really what they mean is that they want to reduce their energy usage and switch to renewable forms of energy.

The good news – you don’t have to be “off the grid” to enjoy the benefits of renewable energy!

In fact, your conventional home is only a few smart steps away from dramatically shrinking its carbon footprint. We’ll talk about this in a moment – first, let’s demystify “off the grid” versus “grid tied.”

What Does Off-Grid Really Mean?

“Off grid” just means a home that is not connected to the utility grid. While these homes are often designed to be more energy-efficient and sustainable than conventional homes, there is no requirement in the term “off grid” that makes them so.

In fact, a home that is “off grid” can be just as much of a power hog as a regular home, and use a gasoline-powered generator for all of their electric needs. Hardly green OR renewable!

The reality is that power generated off the grid is significantly more expensive, KW/hr to KW/hr, as power generated while tied to the grid. The grid has numerous efficiencies of scale – from generation to transmission – that isn’t achieved in an off-grid set-up.

Because electricity generated off the grid is so expensive, it only makes sense that these homes should use less power. It’s pure economics!

So Why Would Anyone Go Off-Grid in the First Place?

When people think of “off grid,” they probably think of images from the early days of solar power, when people were moving far out in the country to get back to the land and live a more sustainable existence.

Of course, moving far away from civilization brings its own share of challenges and environmental implications. Unless you’re planning to become a hermit, you still are going to need roads to get to your off-grid home, and won’t you want some sort of electricity?

Creating power lines is expensive and destructive. It can cost tens of thousands of dollars per mile to run power lines to a distant homestead.

In these situations, where connecting to the utility grid will easily outweigh the costs of a clean, renewable energy system, being off the grid can make economic and environmental sense.

Most People Don’t Live Far From Power Lines

Most people live near other people, which means that most people don’t need the hassles and expense of an off-grid renewable energy system.

Instead, we can install a solar power electrical system that interacts with the grid – offsetting our home’s energy use and providing surplus power to our neighbors. In effect, we are becoming our own miniature power plant!

This kind of system is called grid-tied solar power.

What Makes Grid-Tied Different than Off-grid?

Grid-tied solar electricity is a much simpler set-up than off grid. In both cases, you have photovoltaic (PV) panels which generate clean, renewable energy when exposed to sunshine.

However, in a grid-tied set-up this power goes straight to your utility meter while in an off-grid set-up there are a few more steps.

With a grid-tied system, any excess power generated from the solar panels goes back into the grid – helping your neighbors reduce their carbon footprint!

In essence, you are treating the grid as if it was one big battery, charging it when you have excess power, and taking energy when you need more.

If an off-grid setup, you also need somewhere to store your solar energy.  Without the grid nearby, you need to buy a large set of batteries.

Unfortunately, battery technology is not as clean and renewable as the electricity generated by the solar panels.

The batteries used in most off-grid installations are lead acid batteries – similar to what starts your car and powers forklifts. As you probably know from the explosion warning stickers on your car battery, the inside of these types of batteries are extremely toxic, and their production is an energy intensive and environmentally harmful process.

While those in an off-grid set-up are stuck using this non green technology, if we have access to the energy grid we can avoid this messy problem and appreciate more reliable service with a grid-tied set-up.

Not to mention – batteries are expensive!  The battery bank significantly adds to the cost of an off-grid solar system. In terms of cost per installed watt, off-grid usually ranges 3-4x the cost of grid-tied solar.

Fossil Fuels are Bad, Not the Grid Itself

While it may seem romantic to be “off grid” and not beholden to the utility companies, the reality is that most homes are connected to the grid already, and the efficiencies of the grid generally outweigh the independence of an off grid system.

The grid itself is not inherently bad – what is bad are the forms of electricity that powers most of the grid.

The way to make real, tangible improvement in the way we consume energy is not to distance ourselves from the grid, but to ensure that the power we consume is generated by clean, renewable solar electricity at home and at our place of work.

Contact us if you’re interested in solar for your Maine or New Hampshire home or business.



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Topsham, Maine - Solar Hot Water

Janet and I have been really pleased with the new system and with Revision Energy's service. You folks do an excellent job.

We tell all of our friends about how great it is to go solar and about how nice it is to work with the people at ReVision.

Damon Gannon
Topsham, Maine

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