“rent without tenants”Americans can make thousands from the subsidies paid to people generating renewable energy. But other countries receive far less.  And in Germany you get nothing unless you are connected to the Grid.

When Monica Ball and her husband, Bill, decided to hitch a 9,900-watt solar-panel system to their 4,000-square-foot home three years ago, they had some reservations. Even though the Sergeantsville, N.J., couple got a generous 70% subsidy from the state, they had to borrow $19,000 from their retirement savings to pay the balance.

In retrospect, however, “it was the best decision I ever made,” says Ms. Ball, 43. Not only does the power from the panels help lower the family’s utility bills, which Ms. Ball estimates used to total about $500 each month, the Balls also earn between $6,000 and $7,000 annually from the panels, according to the Wall Street Journal.

In the UK owners of home micro-power only get a few hundred pounds a year for their Renewable Energy Obligation Certificates, ROCS for short. And even then they have to fill in complex forms, or get an agent to do it for them. “We lose money on it,” said Dale Vince, boss of Ecotricity in the UK. His company pays off-gridders 12 pence per unit, but only gets 9 pence back. “For each Kilowatt of PV they might generate a megawatt hour per year about 120 pounds, “ said Vince.

Here’s how it works:

Each year, the state of New Jersey provides the Balls with Solar Renewable Energy Certificates, which represent the cost of offsetting pollution-generating energy. The Balls then sell the certificates for between $5000 to $7000, but normally nearer the top end of that range, on the open market to brokers or electricity suppliers who are required to invest in solar energy under New Jersey’s Renewable Portfolio Standards.

Having this added income is especially helpful as the Balls’ home, which is situated on seven-acre lot, costs a whopping $13,000 a year in property taxes, Ms. Ball says.

“To me, that $19,000 investment on the roof is the equivalent of having a rental property, except you don’t have a tenant,” Ms. Ball says.