지붕 위 태양광 패널, 설치만 하면 끝? 기대 수익 실현 가능할까

You’ve put solar on the roof – but will you get the returns you expect?

지붕 위 태양광 패널, 설치만 하면 끝? 기대 수익 실현 가능할까

최근 태양광 패널 가격의 하락과 지속적인 전기 요금 인상으로 인해 뉴질랜드 내 일반 가정의 태양광 설비 도입 결정이 한결 수월해졌다. 하지만 막대한 비용을 들여 시스템을 구축한 후, 과연 기대했던 만큼의 수익을 회수할 수 있을지에 대해서는 꼼꼼한 따져보기가 필요하다. 전문가들은 태양광 설치 전후로 반드시 고려해야 할 몇 가지 핵심 요소를 제시하고 있다.

설비 비용과 회수 기간은 어느 정도인가?

뉴질랜드 에너지 효율 및 보존청(EECA: Energy Efficiency and Conservation Authority)에 따르면, 적정 조건 하에서 태양광 시스템은 약 7년에서 9년 사이에 설치 비용을 회수할 수 있으며, 이후 약 20년 동안 지속적인 전력 생산이 가능하다.

일반적인 5kW급 시스템의 설치 비용은 약 12,000달러 내외로 추산되며, 배터리를 추가할 경우 비용은 더 늘어난다. 보수적으로 잡았을 때, 태양광 설치 가구는 연간 약 1,000달러의 전기료를 절감할 수 있다. EECA는 시스템 수명 주기 전체를 놓고 볼 때 태양광 전력이 전력망(Grid) 공급 전력보다 약 75%가량 저렴할 수 있다고 분석했다.

EECA의 수석 기술 고문인 제임스 르 페이지(James Le Page)는 지역에 따라 수익성이 달라질 수 있다고 조언한다. “웰링턴은 전력망 인근에 위치해 전기료가 상대적으로 낮지만, 노스랜드(Northland) 같은 지역은 전기료가 매우 비싸다. 또한 일조량 차이도 크다”며, “넬슨, 말보로, 타라나키, 호크스 베이와 같은 지역은 웰링턴이나 사우스랜드에 비해 연간 수익률이 훨씬 높게 나타날 것”이라고 설명했다.

우리 집은 태양광 설치에 적합할까?

태양광 효율을 극대화하기 위해서는 북서향에서 북동향 사이의 방향으로 30도 이상의 경사를 가진 충분한 지붕 면적이 확보되어야 한다. 또한 일조량이 풍부하고 주변에 그늘이 없어야 하며, 무엇보다 낮 시간대에 전력 수요를 집중시킬 수 있는 가구여야 한다. 북향 패널이 가장 높은 효율을 내지만, 북서향 패널도 잠재 출력의 약 90% 수준을 유지할 수 있다.

르 페이지 고문은 사용자가 전력 소비 패턴을 최적화할 때만 기대 수익을 얻을 수 있다고 강조했다. “과거와 똑같은 생활 방식을 고수하면서 지붕에 패널만 얹어 놓는다면 기대하는 만큼의 수익은 보기 힘들 것”이라며, “태양광 설치를 고려한다면 시스템 도입 후 한두 가지 생활 습관을 바꿀 준비가 되어 있어야 한다”고 덧붙였다.

가장 중요한 것은 ‘전력 사용 시간대’의 변경이다. 낮 시간대에 집을 비우는 현대인의 라이프스타일에서는 전력이 생산되는 시간과 소비되는 시간의 불일치가 발생하기 쉽다. 따라서 가전제품 예약 기능을 통해 낮에 세탁기나 건조기를 돌리거나, 전기차(EV)가 있다면 낮 동안 충전하는 방식으로 ‘전력 생산 피크’를 최대한 활용해야 한다.

소매업체 전력 요금제 확인은 필수

현재 이용 중인 전력 요금제에 대한 점검도 필요하다. 르 페이지 고문은 “기존 업체에만 머물러 있다 보면 전력 구매 단가는 너무 높고, 남는 전력을 되파는 ‘태양광 매입 가격(Buyback rates)’은 너무 낮은 요금제를 쓰고 있을 수도 있다”고 경착했다.

가격 비교 사이트를 통해 최적의 요금제를 선택하는 것이 설비 투자 회수 기간을 단축하는 비결이다. 특히 시간대별 요금제(TOU)보다는 단일 요금제가 유리할 수도 있다. 낮 시간대 전력망 사용 요금이 저렴한 요금제의 경우, 직접 전기를 생산하는 태양광 가구 입장에서는 정작 전기를 사야 하는 저녁 피크 시간대에 할증된 비싼 요금을 지불해야 할 수도 있기 때문이다.

유지보수와 배터리 활용법

태양광 시스템은 관리가 까다롭지는 않지만 완전히 방치해서는 안 된다. 해안 지역의 염분, 먼지, 새 배설물 등이 패널에 쌓이면 발전 효율이 떨어지므로 연 1회 정도는 청소가 권장된다. 또한 모니터링 앱을 통해 실제 출력이 예상치에 부합하는지 주기적으로 확인하고, 주변 수목의 성장이 패널에 그늘을 만들지 않는지 체크해야 한다.

배터리는 낮에 생산한 전력을 저녁에 사용할 수 있게 해주지만, 설치 비용이 5,000달러에서 15,000달러 사이로 다소 높아 투자 회수 기간을 늦추는 요인이 된다. 하지만 전력 요금 구조가 시간대별로 세분화될수록 배터리의 경제적 가치는 더욱 높아질 전망이다.

배터리 대신 온수 실린더(Hot water cylinder)를 활용하는 방법도 있다. 타이머나 태양광 다이버터를 설치해 낮 동안 남는 전력으로 온수를 미리 데워두면, 이를 일종의 ‘저렴한 배터리’처럼 활용할 수 있어 전력망으로 전기를 헐값에 되파는 손실을 방지할 수 있다.

You’ve put solar on the roof – but will you get the returns you expect?

Falling solar panel prices and the rising cost of power have helped make the decision to put solar on the roof easier for many households.

But once you’ve invested in a system, how can you make sure you get the returns you’re hoping for?

Experts say there are a few things to think about.

First, how much does it cost?

The Energy Efficiency and Conservation Authority (EECA) says under the right conditions, a system would pay itself off for seven to nine years and could be expected to continue generating power for another 20 years.

It said a typical 5kW system would cost about $12,000 installed. Adding batteries would add to the price.

At a conservative estimate, a household with solar would save about $1000 a year on electricity bills. Power from solar could work out about 75 percent cheaper than grid electricity over the life of the system, EECA said.

EECA lead technical adviser James Le Page, the return would vary around the country, partly due to the number of sunshine hours areas had and also the network pricing.

“I’m in Wellington, and the power prices here are quite low … we’re quite near the main trunk line, whereas up in Northland it’s quite expensive. So that does factor into it, but certainly sunshine hours makes a big difference.

“So Nelson, Marlborough, Taranaki and the Hawke’s Bay, those sort of areas, you will be seeing probably better annual returns than say Wellington or Southland, which is down at the lower end there.”

What makes a household a good fit for solar?

EECA said solar would work best when houses had a roof with enough area oriented between Northwest and Northeast with a tilt of 30 degrees or more, where there was good sunlight and minimal shade, the household used a reasonable amount of electricity and when it could shift demand to daylight hours.

North-facing panels produce the highest output, but northwest-facing panels can still have 90 percent of the potential output.

Households with larger electricity bills generally stand to gain the most financially.

Le Page said people would only get the returns they were expecting if they optimised their usage.

“If you just pay for panels and have them installed on your roof and go about your life as before, you’re probably not going to see the returns you’re expecting.

“So it is really important to have that in mind when you’re considering solar, to go, ‘Hey, when this gets on the roof, we’re probably going to just change one or two things around here to really get the most out of it’.”

He said the most important thing was changing the time a household used power.

“For some households, it’s easier said than done. In the modern lifestyle, we’re out all day, come home at night, and at this time of year, the sun’s gone.

“So when the sun is hitting your roof and the panels, you’re going to be generating electricity, and that’s when you want to use it so you can get the best bang for your buck from your system.”

He said people might be able to schedule appliances to come on during the day, which could help.

“You might have an EV plugged in if you’re lucky enough to have an EV and can have that charging during the day as well to take advantage of it.”

Check your power plan

Le Page said people should also check the sort of plan they were on.

“You might find that if you stick with the same retailer forever, which some of us do, your electricity import rates might be too high, and also your solar buyback or export rates might be too low.

“You really want to be investigating with power comparison websites to make sure you’re on the best deal, and then you want to change the economics of how long your payback is going to be on the system and the sort of savings you should expect from it as well.”

He said sometimes having a flat pricing structure, rather than a time-of-use plan, would be a better option for people with solar.

“The reason I say that is because on a time-of-use plan, you would expect that the prices you pay for electricity should be at its lowest during the off-peak times, and that’s kind of during the middle of the day, when you should be generating electricity yourself.

“Now, it depends on your usage… but generally speaking, if you are getting a cheap rate when you’re generating your own electricity, and then when you come home from work, you’re paying premium prices at a time when you’re not generating electricity, you need to buy it back from the grid, then it ends up being more expensive. ”

Maintenance matters

Le Page said solar did not require a lot of maintenance, but it could not be completely forgotten about.

“We live in a coastal environment, we live in a windy, dusty environment…bird poo, all sorts of things can build up on your panels over time, and that just impacts their ability to generate as much electricity as possible. So often, you might only need to clean them once a year, but it might be more frequently.

“Often with systems, you’ve got an app … So the day that it gets installed, you can work out how much power it should be able to generate at any given time, given the amount of sun on it. Now, this does go up and down over the year, because in the middle of winter, there’s not as much sun.

“But you should be able to work out from there, hey, something might be wrong here. It’s in full sun, and I’ve got a five-kilowatt system, and it’s putting out three kilowatts. What’s going on here? Is there a problem with one of the panels? Or are they really dirty? Do I need to get them cleaned? And so you can work out, you can troubleshoot from there.”

He said people might also need to keep an eye on shade.

“Solar works this year, but in five years’ time, that horticulture that you haven’t really looked at is now shading half your panels. So you need to keep an eye on that side of things as well, because it will have a huge, huge impact on the amount of generation you can get from the panels.”

Batteries and storage

Batteries allow households to store solar energy generated during the day for evening and early morning periods, which are peak use periods.

EECA said the cost of installing a battery would vary depending on the type and capacity, but was usually between $5000 and $15,000, including GST.

“While there are benefits from installing batteries, they extend payback times on investments for the majority of NZ households. As electricity pricing becomes more time-sensitive and peak pricing increases, batteries will become increasingly valuable.”

Le Page said using a hot water cylinder with a solar diverter or timer could be another way to store excess energy generated during the day. People could choose to heat up their water at times when they might not be using the power being generated.

“If you’ve got an electric hot water cylinder at home, you can think of that as kind of a budget battery in a sense because it stores energy in it, and if you can keep that up during the day, then you’ve got that.

“You don’t have to pay to do it overnight or later on, and you can actually buy diverters when you get a system installed that will make sure that you’re not feeding electricity back to the grid at a low price.”