Solar no telhado: como os proprietários devem fazer as contas sobre o investimento na mudança climática

Quando Josh Hurwitz decidiu colocar energia solar em sua casa em Connecticut, ele tinha três grandes motivos: reduzir sua pegada de carbono, eventualmente armazenar eletricidade em uma bateria movida a energia solar em caso de apagões e – crucialmente – economizar dinheiro.

Now he's on track to pay for his system in six years, then save tens of thousands of dollars in the 15 years after that, while giving himself a hedge against utility-rate inflation. It's working so well, he's preparing to add a Tesla-made battery to let him store the power he makes. Central to the deal: Tax credits and other benefits from both the state of Connecticut and from Washington, D.C., he says.

"You have to make the money work,'' Hurwitz said. "You can have the best of intentions, but if the numbers don't work it doesn't make sense to do it." 

Hurwitz's experience points up one benefit of the Inflation Reduction Act that passed in August: Its extension and expansion of tax credits to promote the spread of home-based solar power systems. Adoption is expected to grow 26 percent faster because of the law, which extends tax credits that had been set to expire by 2024 through 2035, says a report by Wood Mackenzie and the Solar Energy Industries Association. 

Those credits will cover 30 percent of the cost of the system – and, for the first time, there's a 30 percent credit for batteries that can store newly-produced power for use when it's needed.

"The main thing the law does is give the industry, and consumers, assurance that the tax credits will be there today, tomorrow and for the next 10 years," said Warren Leon, executive director of the Clean Energy States Alliance, a bipartisan coalition of state government energy agencies. "Rooftop solar is still expensive enough to require some subsidies.''

California's solar energy net metering decision

Certainty has been the thing that's hard to come by in solar, where frequent policy changes make the market a "solar coaster," as one industry executive put it. Just as the expanded federal tax credits were taking effect, California on Dec. 15 cortou outro grande incentivo permitindo que os proprietários vendam o excesso de energia solar gerada por seus sistemas de volta à rede a preços atraentes, embaralhando a matemática novamente no maior estado dos EUA e seu maior mercado de energia solar - embora as mudanças não entrem em vigor até abril próximo.

Junte as mudanças estaduais e federais, e Wood Mackenzie acredita que o mercado de energia solar da Califórnia encolherá drasticamente em 2024, em até 39%. Antes que os incentivos da Lei de Redução da Inflação fossem considerados, a empresa de consultoria previu uma queda de 50% com a mudança de política da Califórnia. A energia solar residencial está saindo de um trimestre histórico, com 1.57 GW instalados, um aumento de 43% ano a ano, e a Califórnia um pouco mais de um terço do total, de acordo com Wood Mackenzie.

Para potenciais migrantes, os créditos fiscais podem recuperar rapidamente parte do custo inicial de se tornar verde. Hurwitz pegou o crédito fiscal federal para seu sistema quando o instalou em 2020 e está se preparando para adicionar uma bateria agora que também vem com créditos fiscais. Alguns empreiteiros oferecem acordos em que absorvem o custo inicial – e reivindicam o crédito – em troca de acordos para alugar o sistema de volta. 

Combined with savings on power homeowners don't  buy from utilities, the tax credits can make rooftop solar systems pay for themselves within as little as five years – and save $25,000 or more, after recovering the initial investment, within two decades.  

"Will this growth have legs? Absolutely," said Veronica Zhang, portfolio manager of the Van Eck Environmental Sustainability Fund, a green fund not exclusively focused on solar. "With utility rates going up, it's a good time to move if you were thinking about it in the first place."

Como calcular os custos e benefícios da instalação

Aqui está como os números funcionam.

Nacionalmente, o custo da energia solar em 2022 varia de US$ 16,870 a US$ 23,170, após o crédito fiscal, para um sistema de 10 quilowatts, o tamanho para o qual as cotações são procuradas com mais frequência no EnergySage, um site de comparação de cotações com sede em Boston para painéis solares e baterias. A maioria das residências pode usar um sistema de seis ou sete quilowatts, disse o porta-voz da EnergySage, Nick Liberati. Uma bateria de 10 a 12 quilowatts custa cerca de US$ 13,000 a mais, acrescentou.

There's a significant variation in those numbers by region, and by the size and other factors specific to the house, EnergySage CEO Vikram Aggarwal said. In New Jersey, por exemplo, um sistema de 7 quilowatts custa em média US$ 20,510 antes do crédito e US$ 15,177 depois dele. Em Houston, it's about $1,000 less. In Chicago, that system is close to $2,000 more than in New Jersey. A more robust 10-kilowatt system costs more than $31,000 before the credit around Chicago, mas US$ 26,500 em Tampa, Flórida. Todos esses preços médios são cotados pela EnergySage. 

The effectiveness of the system may also vary because of things specific to the house, including the placement of trees on or near the property, as we found out when we asked EnergySage's online bid-solicitation system to look at specific homes.

Os lances para uma casa no subúrbio de Chicago variaram de US$ 19,096 após o crédito federal a US$ 30,676.

Compensando esses custos estão a economia de eletricidade e os incentivos fiscais estaduais que recuperam o custo do sistema em menos de 4.5 anos, de acordo com as licitações. Os empreiteiros alegaram que a economia de energia e os incentivos do estado poderiam economizar até US$ 27,625 em 20 anos, além do custo de capital.

Alternatively, consumers can finance the system but still own it themselves – we were quoted interest rates of 2.99 to 8.99 percent. That eliminates consumers' up-front cost, but cuts into the savings as some of the avoided utility costs go to pay off interest, Aggarwal said. 

A chave para maximizar a economia é conhecer os regulamentos específicos em seu estado - e obter ajuda para entender contratos frequentemente complexos, disse Hurwitz, que é médico.

Armazenamento de energia e excesso de energia

Some states have more generous subsidies than others, and more pro-consumer rules mandating that utilities pay higher prices for excess power that home solar systems create during peak production hours, or even extract from homeowners' batteries.

A Califórnia tinha uma das regras mais generosas de todas até esta semana. Mas os reguladores estaduais das concessionárias concordaram em permitir que as concessionárias paguem muito menos pelo excesso de energia que são obrigadas a comprar, depois que as empresas de energia argumentaram que as tarifas eram muito altas e aumentaram os preços da energia para outros clientes.

Wood Mackenzie said the details of California's decision made it look less onerous than the firm had expected. EnergySage says the payback period for California systems without a battery will be 10 years instead of six after the new rules take effect in April. Savings in the years afterward will be about 60 percent less, the company estimates. Systems with a battery, which pay for themselves after 10 years, will be little affected because their owners keep most of their excess power instead of selling it to the utility, according to EnergySage. 

"The new [California rules] certainly elongate current payback periods for solar and solar-plus-storage, but not by as much as the previous proposal," Wood Mackenzie said in the Dec. 16 report. "By 2024, the real impacts of the IRA will begin to come to fruition."

The more expensive power is from a local utility, the more sense home solar will make. And some contractors will back claims about power savings with agreements to pay part of your utility bill if the systems don't produce as much energy as promised. 

"You have to do your homework before you sign," Hurwitz said. "But energy costs always go up. That's another hidden incentive."

Correção: uma versão anterior desta história distorceu o nome da Solar Energy Industries Association.