Solar Technology: What’s The State of the Art?

Solar Technology: What’s The State of the Art?

Posted on 06. Nov, 2009 by in Technical

Renewable energy companies must be doing well these days. Between green stimulus dollars, soaring energy costs, recession-weary homeowners, and increasing public demand for clean energy, it seems like homeowners would be queueing up for the next Net Zero Energy conversion. And those who can afford the initial outlay probably are. But what about the rest of us who don’t have $35,000 just lying around?

We spoke with Kent Halliburton of RealGoods Solar about the state of the art in solar technologies, focusing on products that are available today. “Here’s a stat for you,” he said. “At a recent solar symposium, it was said that 92% of customers want solar energy but 88% don’t know how to get it.”

Hmm… well, if I wanted a new furnace, I’d look in the papers for contractors who installed the type of system I wanted. So what’s stopping these people from typing “solar installers” into their favorite online search engine?

Maybe what he meant was they don’t know how to PAY for it. And until now, there weren’t good financing agreements that allowed people to pay as you go. “People talk about solar price points as if it were a deterrent,” Kent said. “People aren’t as upset about the price point for vehicles like a Toyota or a Chevy, because car dealers sell in terms of monthly payments, not total system cost.”

Solar as a Service

“We have a new financial product offering solar as a service,” he explained. Instead of having to purchase their own solar system, the homeowner contracts to have the system installed and maintained by a third party – in this case, Sun Run, our financial partner. The equipment is actually owned by Sun Run and is sized to meet about 80% of the home’s total projected energy needs. The other 20% is purchased as conventional power.”

In the arrangement described by Halliburton, a homeowner signs an agreement through Sun Run to purchase from Sun Run all the power generated by the solar system, locking in a fixed rate for the next 18 years. The homeowner also pays a certain amount down, anywhere from $0 to around $2,000. This pricing is a little different from the more familiar metered pay-for-what-you-use model, since the homeowner commits to purchasing ALL power generated by their solar system system, whether or not they use it. (Unused power is usually fed back into the power grid.)

System output is somewhat variable depending on the weather, and is usually estimated over a year’s time to average out seasonal ups and downs. The systems come with site-specific production guarantees. In any given month, the homeowner might under-produce and end up using a small amount of conventional power – but in the following month, a span of sunny days might generate a solar surplus that would then act to reduce the amount of kWh billed by PG&E at the end of the year.

A More Efficient Home Needs a Smaller Solar Array

Since the homeowners are already committed to paying for the output, the thinking is to size the system a little on the small side so they use up what they’ve already paid for. A conservatively sized system also encourages homeowner to reduce energy consumption. “For every dollar you save on energy efficiency, you can save $3-$5 on your solar system.”

Additionally, PG&E’s tiered rating structure means it’s cheaper to buy power from them at the lowest tiers – but not at the upper ones. And if the system produces more than they need, they’ve already paid for that portion of the power and it’s still overall cheaper than PG&E rates.

“But don’t wait to energy-proof your home first and then get a solar system, because it’ll take you months and during that time you’ll still be paying for conventional power. We encourage people to do everything possible to their home while installing the solar system.”

Latest Solar Technologies

So what’s the state of the art in solar technology? According to Halliburton, there remain two main technologies: silicon-based panels, and thin film panels. The tradeoffs are cost and efficiency – thin film is cheaper but less efficient, so you need more of it, and more roof space, to generate the same amount of power. So, what’s the best money can buy as of today?

  • Silicon-based panels currently cost around $2.25/watt and are around 16% efficiency. That means that 16% of the sun’s rays that actually fall on that panel are converted to usable electric power.
  • Thin-film panels are around $1.50/watt and around 8% efficiency.

[Note: These prices quoted by Halliburton are for the panels, not total installed system cost. On Sun Run’s site the price is listed as closer to $8/watt.]

Large commercial applications can afford the space for huge arrays, but thin-film solar products can be flexible and more adaptable to portable off-grid field shelters.

Large commercial applications can afford the space for huge arrays, but thin-film solar products can be flexible and more adaptable to portable off-grid field shelters.

What’s the most efficient, top-of-the-line system that’s available today? “SunPower and Sanyo both make products that are around $1 per watt more expensive than average. They’re around 17.5% or 18% efficient. You have to watch it though, because some manufacturers use a measure that is per cell, not panel efficiency. By contrast a so-called middle-tier ‘average’ system might be more like 14.5% to 15% efficient.” Today’s thin-film solar products top out around 9% efficiency.

“Silicon-based panels are better for residential and small commercial applications,” said Halliburton. Larger commercial applications have the real estate to install larger arrays of thin-film panels, but smaller buildings might need a smaller footprint and thus a more compact and efficient system is better, even if the initial costs are higher. “The most common choice is definitely the middle tier.”

Solar Inverters: The Hidden Factor

But even more important than the panels themselves are the inverters, and that’s something most people never think about. An inverter is necessary in order to convert the DC power produced by the solar panel into the AC power that’s used in a home. In the past few years, advances in inverter technologies and configurations have further improved the potential yield from an otherwise average solar array.

Halliburton described how inverters function. “The emergence of micro-inverters has done more to change the solar landscape even than the incremental gains in efficiency that we’ve seen over the years. In the older systems, there was one inverter for all the panels, but with a micro-inverter, you can have one inverter for each panel.”

To get an idea of why this is so important, consider a 4 x 4 solar array of 16 panels on a roof that is partially shaded at certain times of day. If even one of those panels is shaded, then its output is reduced – and the inverter can only gather the output from all the panels at the lowest common denominator. “With a single inverter, the weakest link brings down production for the entire array.”

With a single inverter, the two shaded panels will bring down the performance of the entire array during the time that they do not receive full sun.

With a single inverter, the two shaded panels will bring down the performance of the entire array during the time that they do not receive full sun.

By contrast, an array with micro-inverters is less sensitive to partial shading. I observed that this sort of thing must be a no-brainer for an engineer who already knew how the inverters worked with solar arrays.

With separate inverters, each panel is always producing the maximum possible based on the available light that reaches its surface.

With separate inverters, each panel is always producing the maximum possible based on the available light that reaches its surface.

Looking Ahead

What’s the state of the art now as compared to 5 years back? “Gains are incremental year by year,” said Halliburton. “For example, 5 years ago we had a 168-watt product from Sharp. That same product today is 198 watts. We try to avoid the ‘Apple syndrome’ where users hold off on buying a new computer because they’re always waiting for next year’s model.”

Halliburton stressed that homeowners didn’t need to wait to install a solar system, even if they were also planning other home improvements to increase building efficiency. Although they might think that a more efficient building with all the latest energy-scrimping appliances will need a smaller solar array, the systems are already sized with this possibility in mind, and in the meantime, why should the homeowner continue to throw away money on the electric bill for all the months it’ll take to complete their energy remodel?

Where do you see solar technologies 5 years from now? “It’ll become more ubiquitous, and continue to make incremental gains. I don’t see any silver bullets, meaning a brand new technology that’s disruptive in the market. In fact, I think the real change is going to be in education. People judge energy consumption based on the number of switches that they flip. They don’t understand what they can’t see. Customers will need to educate themselves and become more conscious of their consumption habits.”

What About Renters?

What’s really stopping people from buying solar systems? Well, not owning your own home is one barrier, although an arrangement called Virtual Net Metering can allow someone who lives and rents in one area but owns property in another town to install a solar system on the property that they own, and have the power it produces be counted towards the energy bills for their rental unit elsewhere. 

The Solar Homeowner Experience

What’s the solar homeowner experience? Do they notice any difference, or do they need to do different sorts of maintenance? Do they ever run short of power? Does the homeowner get an energy bill every month like the rest of us? 

“Other than washing the dust off the panels every so often to improve their performance, not much. They still get monthly statements. There’s online monitoring and automatic billing. The inverters might need to be replaced sometime between years 12 and 17; the panels themselves are guaranteed to produce up to 80% of their original efficiency even after 25 years.”

Visibility into System Stats

How much visibility do homeowners have into how well their system is doing? “The inverters tell them how much power their system is producing, and with online monitoring, they can see all the stats easily.” 

What about whether their panels are really operating at maximum efficiency? “Most customer don’t care about that level of detail, but one could install sensors to measure solar irradiance levels if someone really wanted to know that.”  What they typically get is a quote on what their system will produce on a monthly basis. 

The early adopters were more likely to be gearheads and DIY types with the engineering skills to really prove and verify their own systems. As solar power gains wider acceptance, people are more willing to trust it the way they would with a new conventional furnace unit.

Financing the Future

The impression I had after speaking with Halliburton, especially about the Solar as a Service arrangement, is that innovations in pricing structures and financial incentives will be as challenging – and as necessary – as any engineering improvements to the products themselves. RealGoods has been around for 31 years, in fact RealGoods sold the first solar panel in the U.S. back in 1978. They’ve installed over 5,000 systems to date, with around 200 customers signed up for the Solar as a Service plan that was introduced only a year or two ago.

It’ll be interesting to see where things are, even two years from now.

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2 Responses to “Solar Technology: What’s The State of the Art?”


    06. Nov, 2009

    Nice article. WE have lots of portable solar power sytems that are available on our website. I wonder if we could help our buyers get government rebates or grants like they are giving to home system buyers.

  2. Ryan

    29. Nov, 2011

    Yes the Goverment Rebates sure do help make the solar power systems and install more affordable.

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